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Design and evaluation of flat plate solar collector equipped with nanofluid, rotary tube, and magnetic field inducer in a cold region
Abstract and Figures
Flat plate solar collectors lose a massive part of heat accumulated near the contact region because of the poor thermal characteristics of the working fluid. A new cost-effective design is numerically studied to cover up such deficiency by equipping the flat plate collector with revolutionary tubes and magnetic field inducer to affect Fe3O4/water working nanofluid in the collector tubes. Results substantiate that each of the applied rotary tubes and magnetic field inducer improves the convection mechanism in the tubes by circulating the flow inside the tubes and saves more of available solar energy. Results reveal that 27.8% and 10.44% of lost energy are restored in the solar collector equipped with the magnetic inducer and rotary tubes, respectively. Manipulating the flat plate collector by both rotary tubes and inducer is more influential in comparison with each individual method, and there is an optimal rotational speed in each magnetic field intensity to achieve the best performance. This hybrid technique increases the energetic performance of the plate solar collector from 44.4% to 61.7% which implies that roughly 300 W of the lost energy can be restored in the collector.
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... The useful energy increases by 1.65% due to adding the nanoparticles and increases to 10.44% due to pipe rotation. They continued their work by adding a magnetic field inducer on the riser pipes of the SC [8]. The results showed that this technique improved the thermal efficiency to 61.7% while the conventional FPSC efficiency was 44.4%. ...
... Fig. 16a and b draw the instantaneous and accumulated energy efficiencies variation with time for the different collectors' tilt angles. The instantaneous efficiency is calculated according to equations (5) to (7), and accumulated efficiency is calculated according to equations (8) and (10) in Section 2.4.1. As expected from the previous results, the PDSC has higher efficiency than the FPSC for the studied tilt angles. ...
... However, these countries could harness their sunshine radiation potential to mitigate the effects of pollutant emission technologies, thereby employing cleaner and sustainable heat and power production solutions and improving air quality. Solar collectors of the flat-plate type are the most common devices to exploit solar radiation energy (Bezaatpour and Rostamzadeh, 2021a). A simple description of a flat-plate solar collector (FPSC) consists of a structure made of a wide glazing plate and tubes containing a circulating fluid to transfer the absorbed heat from the glazing sheet to the outlet where it is used for, e.g., heating water (Alawi et al., 2020). ...
... The heat transfer fluid can be water or some other fluid that does not freeze if the FPSC is used in a cold region. However, these devices have low efficiency due to heat loss, and hence a not so high outlet temperature (Bezaatpour and Rostamzadeh, 2021a). Different methods exist to enhance the heat transfer rate in solar collectors, including using nanofluids (Bezaatpour and Rostamzadeh, 2021b), phase change materials (Aramesh and Shabani, 2020), magnetic field (Bezaatpour et al., 2021), turbulators, and twisted tape (Vengadesan and Senthil, 2020). ...
Flat-plate solar collectors are a cost-effective technology for water heating in residential buildings. Comprehensive sensitivity analysis and multi-objective optimization of five crucial factors in a flat-plate solar collector equipped with twisted tapes are investigated. The studied factors are the Nusselt number (Nu), friction factor (f), solar collector efficiency (η), thermal performance factor (ξ), and the temperature difference of the heat transfer fluid across the device (ΔT). The simulation of functions is carried out by four soft computing methods, such as the linear and cubic form of multivariate adaptive regression splines (MARS), group method of data handling (GMDH), and multivariate polynomial regression (MPR). The linear form of the MARS algorithm shows the highest accuracy in predicting Nu, f, and η by R2 = 0.99986, 0.9984, and 0.98821, respectively. The Reynolds number (Re) is from 4000 to 14,000, and the twisted tape ratio (Y) is between 0 and 15. The simulated annealing optimization is employed to find the global optima. According to the study, Nu, η, ξ, and ΔT reach their maximum when f is minimum, which occurs for Y = 5 and Re in the 13,200 to 13,400 range for different global solar radiation levels. The maximum temperature difference happens at noon, about 6.54 K at the Re = 5362.5 and Y = 5 with the collector surface area by 2 m2. When the appropriate working conditions are met so that these factors are simultaneously optimal, ΔT, hence the efficiency, can be increased.
... In order to increase convection heat transfer and reduce heat losses accumulated near the contact region, a FPSC equipped with a revolutionary tube and magnetic field inducer was designed by Bezaaatpour and Rostamzadeh (2021). They reported that the hybrid system with Fe2O3-water nanofluid enabled an increase in efficiency from 44.4% to 61.7% (Bezaatpour & Rostamzadeh, 2021). The efficiency of FPSC is enhanced by 2.48% and 8.46% by using 0.5% Al2O3 and 0.5% crystal nanocellulose, respectively (Farhana et al., 2021). ...
Flat plate solar collectors (FPSC) are commonly used for a variety of applications and have a very simple design. However, the main drawbacks of the collector are its low outlet temperature and poor thermal performance. In present study, the fluid outlet temperature, heat removal factor, energy efficiency, exergy efficiency, and pressure drop have been evaluated for a rectangular-shaped minichannel FPSC operating with two different nanofluids (Cu-water and TiO2-water). The ranges of volumetric concentration ratio and mass flow rate are 1-5% and 0.01-0.07kg/s, respectively. A mathematical model based on the energy balance has been solved using energy equation solver software. The result revealed that fluid outlet temperature, mean plate temperature, and overall heat loss coefficient (HLC) increase with increasing concentration ratios for both nanofluids. But at the same concentration ratio and MFR, the fluid outlet temperature, mean plate temperature, and overall HLC for Cu-water nanofluid are greater than those of TiO2-water. The outlet temperature and mean plate temperature for the nanofluid TiO2-water of volumetric ratio 1% are 369.4K and 347.9 K, respectively, and these values increase to 395.9K and 351.1K at volumetric ratio 5% for the same MFR of 0.01 kg/s. Efficiency and heat removal factor for the TiO2-water nanofluid are greater than those for the Cu-water nanofluid for the same MFR and concentration ratio. Pressure drop increases with increasing concentration ratios for both fluids, but it is greater for Cu-water as compared to TiO2-water.
... However, installing an agitator in a DASC may not be feasible from a system operation and equipment manufacturing perspective. Rotating the collector tube has been proposed as an alternative [26]. However, this approach incurs extra power consumption and maintenance challenges for the solar system. ...
Improving surface absorption of solar radiation is a critical challenge due to the negative impact of endothermic coating and significant heat loss during energy transfer. In this study, magnetic nanofluids are proposed as the thermal medium in a parabolic trough direct absorption solar collector to overcome the limitations of surface absorption and improve solar energy utilization. Thermal and exergy analyses are performed for the parabolic trough direct absorption solar collector to evaluate the potential of magnetic nanofluids in photothermal conversion under various magnetic fields. The present work experimentally investigates the heat transfer and efficiency of ferrous-ferric oxide–water nanofluids. The nanofluids have nanoparticle concentrations ranging from 0.01 wt% to 0.40 wt% and flow rates from 50 L/h to 100 L/h. The results indicate that the optimal nanoparticle concentration of 0.20 wt% achieves maximum gains in heat transfer, thermal efficiency, and exergy efficiency compared to deionized water. Specifically, a 161.0 % increase in heat production, a 26.1 % increase in thermal efficiency, and a 2.4 % increase in exergy efficiency are observed. Furthermore, when exposed to S[sbnd]S magnetic fields, a 226.0 % increase in heat production, a 40.2 % increase in thermal efficiency, and a 4.0 % increase in exergy efficiency are achieved for the magnetic nanofluid with a ferrous-ferric oxide nanoparticle concentration of 0.20 wt%, also compared to deionized water. The combined application of ferrofluid and magnetic fields shows promise as an effective means for utilizing solar energy efficiently. The results and generalized criteria are of great significance for designing and optimizing direct absorption solar collectors, which will indirectly contribute to reducing carbon dioxide emissions by promoting more efficient solar energy utilization.
... Yousefi et al. [30], in a study, stated that the heat transfer and pressure drop of two-phase flow in a tube rise by about 280% and 82%, respectively, using a non-uniform magnetic field. Other studies on the use of magnetic fields have been performed experimentally and numerically [31][32][33][34][40][41][42]. ...
... The authors discovered that inserting nanopowders and using a magnetic field together resulted in an 86% boost in heat exchange, but introducing only ferroparticles resulted in only a 20% increase in heat exchange. Bezaatpour and Rostamzadeh [22] conducted a numerical study on a solar collector with a flat surface, and they used a hybrid technique to increase its performance. Their results show that by operating the system with ferrofluid, magnetic field, and rotary tube, the performance increased by about 17.3%. ...
The present paper investigates a magnetic source’s thermal and flow impacts on mixed convection conditions in a novel arc-shaped lid-driven cavity problem. The examined cavity consists of a square enclosure of length (L) with two arc-shaped vertical plates, and it is filled with Fe3O4/water ferrofluid. For this purpose, an in-house solver has been developed within the OpenFOAM® libraries based on the finite-volume method to solve the governing equations. In this regard, different parameters were implemented, which include various magnetic numbers (0 ≤ Mn ≤ 100), Richardson numbers (0.04 ≤ Ri ≤ 40), solid volume fractions (0 ≤ ϕ ≤ 0.05), and the dimensionless wide length of the arc (b* = b/L) varies from 0 to 0.15. The outcomes revealed that applying the magnetic source in the vicinity of the heater causes the appearance of a recirculation zone which boosts the diffusion phenomena. At Ri = 0.04, with the actions of the magnetic field, arc-shaped walls, and suspending magnetite nanoparticles, heat transfer enhancement can reach up to 338.35%. However, the heat transfer rate diminishes when the kelvin force is considered at Ri = 40. Finally, these outcomes are followed by developing two new correlations of the NuM versus Ri, ϕ, Mn, and b*.
... Bezaatpour et al. [8] tried to improve the performance of a flat plate solar collector by using four rotary tubes and a magnetic field inducer. As the working fluid inside the collector tube, a ferrofluid composed of Fe 3 O 4 and water was used. ...
In this study, experiments, simulations, and optimization were performed to evaluate heat transfer performance of ferrofluids. Ferrofluids are colloidal suspensions containing magnetic-nano particles with a diameter of 5 to 15 nm in a base fluid such as oil or water. Recently, as many devices are miniaturized, the design of heat dissipation systems are being diversified to consider cost and safety, and it is becoming important to separate an ancillary device for cooling from main unit. In ferrofluids, the behavior and vortex of magnetic-nano particles are actively generated by an external magnetic field, and the cooling system can be designed in a simplified manner by using this characteristic. The main design parameter is the arrangement of permanent magnets, and the output variable is the temperature inside the magnetic nanofluid. The permanent magnet can be moved up and down, and the temperature inside the magnetic nanofluid was measured at various locations. A predictive model was created using a design of experiments (DOE) and response surface method (RSM) using selected design and temperature variables. Based on the generated regression model, an optimization was applied to find a permanent magnet arrangement that maximizes heat transfer performance. Through the optimization technique used in this study, economic efficiency in terms of time and cost was obtained by reducing the number of experiments.
... As it is clear, the capacity of power generation by modules depends on their temperature and decreases when the PV temperature rises. Also, the energy saved by the airflow through the cavity behind the modules is calculated as [40,42]: ...
A remarkable amount of solar energy can be harnessed for generating renewable energy by applying giant photovoltaic/thermal systems to the façades of structures. However, the applicability of these systems is overshadowed by two key parameters of building geometry and complex wind behavior. This study aims to present a clear benchmark for the applicability assessment of these systems by predicting wind complexity and identifying the position of modules with critical temperatures and wind loads prone to jeopardy and destruction. For this purpose, four hundred integrated photovoltaic modules are applied to the façade of a high-rise and a mid-rise tower with the same capacity (12000 m³) and photovoltaic façade area (600 m²), and the temperature, wind load, and thermal/electrical efficiency are studied for one by one of them. The evaluation is conducted for various wind speeds using state-of-the-art computational fluid dynamics models. The results reveal that each module undergoes different wind loads and temperatures relative to its neighboring modules and has an exclusive thermoelectrical performance in the entire system. The temperature difference among the modules exceeds 55 °C, and some modules experience operating temperatures higher than 100 °C. Based on the results, both mid-rise and high-rise structures have almost the same potential for power supply, with a maximum of 70 kW obtained at the highest wind speed, while the high-rise structure is more suitable for heating production, with a maximum of 115 kW obtained at the lowest wind speed. Therefore, more energy is produced in the high-rise tower compared to the mid-rise one. Moreover, the maximum total energy and exergy efficiencies of the system reach 33.28 % and 21.2 % in the mid-rise building and 37.05 % and 20.9 % in the high-rise building, respectively. Overall, the findings of this study give a guideline for future sustainable constructions and optimal designs of façade-based photovoltaic/thermal systems.
... The equation for entropy balance, 62 based on the second law of thermodynamics, can be written in the following form Equation (18): ...
In this study, a numerical investigation has been carried out to analyze thermal and flow behavior with thermodynamic perspectives in a cooling application problem. The configuration under consideration in this analysis consists of a cubic electronic chip placed in an open cavity filled with porous media. The solver's reliability is achieved by comparing our results with experimental studies. In this regard, various parameters were considered, which consist of different nanoparticles (Al2O3, TiO2, Cu, and Ag), porosities (0.85–0.97), and Reynolds numbers under turbulent conditions within the range (5000 ≤ Re ≤ 30,000). Their imprints have been highlighted on temperature distribution, streamlines, local and average Nusselt numbers, pressure drop, global entropy generation, and exergy efficiency. Results reveal that there is an optimal porosity to achieve the highest cooling performance based on the Reynolds number. In addition, using Al2O3–water nanofluid as a working fluid, the highest values of the mean Nusselt numbers were recorded. Furthermore, operating the system with a porous medium and the Al2O3–water nanofluid results in only a minor increase in pressure drop. Finally, the results substantiate that using porous media reduces global entropy production and slightly decreases the exergy efficiency in the system.
... They can transfer heat through working fluid like water, refrigerants, air, etc. For flat plate collector, radiation hits transparent cover with surface of high absorptivity, the plate absorbed portions of the radiation energy which in turn converts into heat then transmit to the transport fluid through tubes for storage or use (Bezaatpour & Rostamzadeh, 2021). Thermal performance is important and for flat plate, it is analyzed in two ways: glazed and unglazed type. ...
Fresh water is one of the basic needs in daily life where the sources are shrinking due to pollution and climate change. Sea water desalination system is one of the potential solutions that can minimize the scarcity of fresh water. Solar energy is one of the promising renewable energies that can be used for water desalination system. The concepts of solar water desalination system, energy conversion from solar irradiation to thermal energy, and different types of solar thermal collectors are the leading technologies. Solar water desalination is also natural, abundant, environment-friendly than the conventional processes. This chapter describes the different types of solar water desalination system, geometrical shapes, modeling of different types of desalination processes, solar thermal processes, thermal collectors, energy conversion, and performance analysis.
... Since its development, the use of ferrofluids in presence of a magnetic field found many applications to enhance heat transfer, e.g., heat exchangers [20,21], mini heat exchangers [22], flat plate solar collectors [23] and latent heat storage systems [24]. However, few studies studied the effect of magnetic fields on ferrofluids as HTF in PTSCs. ...
A novel configuration for heat transfer enhancement in parabolic trough solar collector absorbers by the use of a ferrofluid and an external magnetic field generated by a current-carrying wire is analyzed using numerical simulation. This new configuration consists of a wire which varies its position periodically along the tube. The analysis is focused on the study of the thermal hydraulic characteristics, Nusselt number and friction factor, and the average flow patterns in the turbulent flow regime (15·103⩽Re⩽250·103). In addition, different parameters of the periodic wire are analyzed: wire pitch and position angle. Ferrofluid Fe3O4/Therminol 66 is considered for this application. Firstly, the effect of an increase on the magnetic field intensity is studied. The periodic wire configuration shows a higher increment of the Nusselt number in comparison to the straight wire for the same magnetic field increase. The results reveal that the presence of a non-uniform magnetic field generates a disturbed flow with a high velocity region near the current-carrying wire. The periodic wire configuration leads to a spatially-periodic behavior that increases the average Nusselt number and the friction factor, in comparison to a straight wire. Among the studied cases, the position angle θ=30° and the pitch length l=3D are found to provide the maximum Nusselt number (Nu = 244.25 for Re = 15000).
... To address the deficiency, the concept of tube rotation was introduced by Norouzi et al., [13] to reduce the maximum temperature of the tube and to make its distribution on the tube more uniform. Bezaatpour and Rostamzadeh [14] studied the numerical investigation of innovative and cost-effective design by equipping the flat plate collector with revolutionary tubes and magnetic field inducer. By integrating both rotary tubes and magnetic inducer, their results revealed a 17.3% enhancement from current performance in the optimal condition, which is 31% of the energy loss, could be restored in the FPSC. ...
Solar thermal energy plays a vital role in the industrial sector, especially for water heating applications. Further research to improve the efficiency of flat plate solar collectors by focusing on collector design modification is imperative. This research aimed to carry out an experimental investigation on comparative designs and fabrication approaches that deal with the analysis of flat plate solar collector thermal performance, thermal efficiency, the effect of various mass flow rates, and pressure drop analyses. In this paper, a different design modification of pipe collector with serpentine-shaped was established with different tube diameters (3/4-inch and 3/8-inch), and different pipe spacing (18.5 cm and 27.0 cm). Under the same heat radiation intensity and constant mass flow rate, a pipe collector with a tube diameter of 3/4-inch achieved 3.5% and 9.4% higher thermal performance and collector efficiency respectively compared to the tube diameter of 3/8-inch. Furthermore, the pipe collector with pipe spacing of 18.5 cm exhibited 4.3% and 12.6% higher thermal performance and collector efficiency respectively compared to pipe spacing of 27 cm. The relationship between collector efficiency and temperature difference was also investigated. Moreover, the effect of different mass flow rates was studied upon and it was found that a flow rate of 0.03 kg/s exhibited optimum thermal performance for the pipe collector. Additionally, a pressure drop was observed with the increase in flow rate, while decreases when the fluid temperature increases.
This paper reviews the impacts of employing inserts, nanofluids, and their combinations on the thermal performance of flat plate solar collectors. The present work outlines the new studies on this specific kind of solar collector. In particular, the influential factors upon operation of flat plate solar collectors with nanofluids are investigated. These include the type of nanoparticle, kind of base fluid, volume fraction of nanoparticles, and thermal efficiency. According to the reports, most of the employed nanofluids in the flat plate solar collectors include Al2O3, CuO, and TiO2. Moreover, 62.34%, 16.88%, and 11.26% of the utilized nanofluids have volume fractions between 0 and 0.5%, 0.5 and 1%, and 1 and 2%, respectively. The twisted tape is the most widely employed of various inserts, with a share of about one-third. Furthermore, the highest achieved flat plate solar collectors’ thermal efficiency with turbulator is about 86.5%. The review is closed with a discussion about the recent analyses on the simultaneous use of nanofluids and various inserts in flat plate solar collectors. According to the review of works containing nanofluid and turbulator, it has been determined that the maximum efficiency of about 84.85% can be obtained from a flat plate solar collector. It has also been observed that very few works have been done on the combination of two methods of employing nanofluid and turbulator in the flat plate solar collector, and more detailed work can still be done, using more diverse nanofluids (both single and hybrid types) and turbulators with more efficient geometries.
This is a numerical study that analysis the heat extraction potential of solar collector tubes by assembling a couple of nozzles at the sealed end of the pipe to make swirl flow. Swirl flow intensifies the turbulence rate which augments heat transfer by ruffling the boundary layer. To this end, several decisive factors including nozzle angle (A: 30°, 45°, 60°, 90°), tube diameter (D: 20 mm, 50 mm), nozzle edge size (N: 6.25, 12.5, 25 mm (for D50) and N: 2.5, 5, 10 mm (for D20)), and mass flow rate (M: 0.1, 0.5, 1 kg/s (for D50) and M: 0.04, 0.2, 0.4 kg/s (for D20)) were considered. Results demonstrated that all of the models of class ''A…/D20/N…/M…“ had higher heat extraction potential but lower friction factor compared with ”A…/D50/N…/M…“. Maximum and minimum values of heat flux extractions are 2113390 W/m² and 59239 W/m² that were obtained by ”A60/D20/N2.5/M0.4″ and “A30/D50/N25/M0.1″. The created friction factor by class ”A…/D50/N…/M…“ is higher than class ''A…/D20/N…/M…”. The highest friction factor is 3.51 (''A90/D20/N2.5/M0.04″) and the lowest friction factor is 0.019 (“A30/D20/N2.5/M0.2″). Overall, for all cases, class ”A…/D50/N…/M…“ bear the higher TPF compared with class ”A…/D50/N…/M…“ so that the greatest and lowest values of TPF are 5.09 and 0.49 achieved by ”A30/D50/N6.25/M1″ and “A90/D20/N5/M0.4″, respectively.
Nanofluids have evoked extensive interest from researchers around the globe due to their distinctive thermo-physical properties and numerous potential benefits and applications in important fields such as energy, aerospace, electronics, vehicles and biomedicine. This paper summarizes the latest research about the heat transfer characteristics, fluid characteristics, and its influencing factors, influencing rules, and influencing mechanisms of nanofluids. It summarized the preparation, stability, thermal conductivity, specific heat capacity, light absorption characteristics and photothermal conversion performance of nanofluids based on the categories and influencing factors of nanofluids, and analyzed their laws and mechanisms. The purpose of this paper is to summarizes the latest research findings in the open literature on nanofluids, so that researchers in the field of energy conversion have a more detailed and clear understanding of the energy conversion properties and applications of nanofluids.
The present study investigates the performance of various porous fin materials (copper, aluminum, bronze, and steel) with different porosities in a parabolic rotary trough solar collector driven by magnetic nanofluid. The nanofluid circulates in the rotary pipe and flows into the attached inner porous fin by a centrifugal force. This design enhances the heat transfer while reducing the pressure drop in the parabolic trough solar collector compared to previous configurations. Based on the results, the copper foam has the best performance among the studied materials, and the role of porous material is more salient in the rotational state than in the stationary one. Moreover, the increment of porosity causes more energy storage in the solar collector, while an optimal value is obtained for the rotational speed. The findings show that the heat transfer rate and pressure drop increase 3.7 times and 2.6 times in the optimal state of using copper porous fin with 97 % porosity in the rotary pipe with 0.6 rad/s angular velocity, respectively. Also, the energetic and exergetic performance increases from 71.6 % to 87.2 % and from 24.2 % to 40.5 %, respectively, and more than half of the lost energy is restored in the manipulated system.
The application of compound parabolic concentrator (CPC) in photovoltaic/thermal (PV/T) system increases the thermal and electrical energy gain, and the phase change material (PCM) helps cool down the operating temperature of cells. In this study, an open-air experiment is constructed to compare the overall performance of conventional flat photovoltaic (FPV), concentrating photovoltaic/thermal (PV/T-CPC) and concentrating photovoltaic/thermal phase change (PV/T-CPCM) system. The maximum PV backplane temperature is 69.9 °C in PV/T-CPC, 59.2 °C in PV/T-CPCM and 36.7 °C in FPV system respectively, and the PV temperature distribution non-uniformity in PV/T-CPC is 1.5 times higher than that in PV/T-CPCM system, showing the application of concentrator enhances the useful thermal energy and meanwhile the PCM effectively improves the local overheating and temperature distribution non-uniformity problem. The average thermal energy and efficiency of PV/T-CPCM are over 2462.0 kJ and 9.0% higher than those of PV/T-CPC system respectively. Besides, the electrical power/total exergy of PV/T-CPCM system are over 1.3/4 and 1.6/2 times of FPV and PV/T-CPC system respectively. Results present that the PV/T-CPCM system owns superior thermal, electrical and exergy performance among the three systems, and the application of CPC and PCM has great advantages in improving the overall performance of the PV/T unit.
Solar energy is one of the promising clean and nondepleting renewable energy types which is excessively used all over the world in the form of electrical as well as thermal energy. From domestic to industrial level applications of solar thermal collectors have made them really important to share prominent amount in the worlds energy mix. In this chapter, different solar thermal collectors types are presented together with their basic construction and applications. At the outset, fundamentals of solar thermal collectors are defined and the types of all the thermal collectors are categorized according to their energy collection methods/physics, shape, and size. The optical, thermal, and thermodynamic analysis of each type of thermal collector, e.g., flat plate, compound parabolic, evacuated tube, parabolic trough, Fresnel lens, parabolic dish, and heliostat field collectors is provided along with complete mathematical equations for investigating their efficiency. This chapter provides the latest data on solar thermal collector, which can be used further for research, applications, and latest developments in the field of solar thermal energy.
The unsophisticated configuration of plants with magnetohydrodynamic liquid metal and no dynamic parts has made them cost‐effective and sustainable compared to the turbine‐based types. This paper proposes an innovative liquid metal magnetohydrodynamic‐based system for electricity, cooling, and hydrogen production utilizing a parabolic solar unit and waste exhaust gases as renewable heat sources, a double effect absorption cooling cycle, and a proton exchange membrane electrolyzer. Hence, an environmentally‐friendly system is devised and analyzed thermodynamically towards a lower emission footprint. The results of the thermodynamic analysis reveal that 71.5 kW, 10.26 m3/day, and 834.9 kW, power, hydrogen, and cooling are produced by the designed unit, respectively, with exergy efficiency and energy utilization factor of 45.28% and 40.27%. Also, the overall destruction of the exergy is obtained 527.4 kW, the main cause of which is the receiver due to high heat loss to the environment. The output of the parametric study indicates that the energy efficiency of the present plant improves by reducing the biogas temperature or by increasing the effectiveness of the solution heat exchanger and mass flow rate of the magnetohydrodynamic stream.
The present study investigates the advanced exergy assessment in a solar absorption power cycle to reveal the inefficiency of the system. Unlike simple exergy assessment, which only assesses exergy destruction, advanced exergy evaluates avoidable, unavoidable, exogenous, and endogenous exergy destructions. EES software is employed to model the proposed absorption power cycle, in which the power is generated using a low-temperature heat source driven by solar energy. The novelties of the present study are the use of solar energy in absorption power and applying the advanced exergy assessment. According to the results, the total energy and exergy efficiencies are 6.655% and 7.011% in the real state, 8.517% and 8.973% in the unavoidable state, and 9.433% and 9.938% in the ideal state, respectively. In other words, both efficiencies improve by 41.7% and 10.75% under ideal and unavoidable conditions compared to the real state, respectively. The outcomes reveal that the unavoidable exergy destruction is greater than the avoidable exergy destruction in the constituents, implying that no structural refinement can be effective in the system. Among the components, 73.69 kW exergy destruction occurs in the solar collector, of which 67.47 kW is endogenous destruction. Also, the unavoidable and avoidable exergy destructions equal 73.03 kW and 0.66 kW in the solar collector, respectively. Moreover, the unavoidable endogenous part accounts for the highest proportion of exergy destruction in the solar collector, while the avoidable exogenous destruction is less than zero. It means that by improving the component itself, it is possible to reduce the exergy destruction.
A huge amount of accumulated heat is lost in concentrating solar collectors due to the weak thermal performance of working fluid. High temperature concentration on absorber tube increases the exergy destruction as well as the damage of cover glass in this type of solar collector. A novel and cost-effective method is employed to obviate such deficiencies by furnishing the collector with a revolutionary receiver, microporous metal foam, and magnetic nanofluid. In the new design, the collector is manipulated in such a way that first, a thin metal foam as a porous fin is attached inside the tube to increase the heat transfer area of the absorber tube. Then, while the nanofluid flows through the plain region in the center of the tube, a revolution in the tube circulates the nanofluid and pushes it toward the porous fin by a centrifugal force. For more agitation, a magnetic force is inducted on nanoparticles by a magnetic field inducer as a stimulus in the collector. The hybrid technique improves both convection and conduction mechanisms in the collector. Besides, less pumping power is needed in the present configuration of porous media compared to previous designs since the momentum is prepared by the centrifugal force. Results reveal that 62.7% of lost heat is managed and restored in the collector by applying the new method. Also, the first and second law efficiencies rise by 16.5% and 8.3% in the manipulated system.
A novel and cost-effective method is employed to obviate conventional shortages of plate solar collectors by utilizing revolutionary tubes, microporous metal foam, and nanoparticles. In the new design, a thin metal foam is attached inside the tubes as a porous fin to increase the heat transfer area near the surface. Then, as the nanofluid passes through the tube, the rotation of the tube circulates the nanofluid and pushes it toward the porous fin by centrifugal force. This combined technique improves both convection and conduction mechanisms in the tubes and causes more thermal energy storage. Besides, the proposed method requires less pumping power because centrifugal force supplies part of the momentum for transport in the porous fin. Results reveal that 50.68% of the lost energy is managed and restored using the new method in the collector. In other words, 413 W more energy storage is achieved by the equipped solar collector compared to the simple one. Also, energy and exergy efficiencies rise by 22.8% and 8.5% in the manipulated system. Results confirm that the consuming power for pumping the nanofluid and rotating the tubes can be supplied by the system itself.
Enhancing the thermal efficiency of parabolic solar collectors is still a challenging issue. In this study, two strategies including using nanofluid and a rotary turbulator are applied to ameliorate thermal efficiency. Here, graphene oxide/SiO2 nanofluids are fabricated in different concentrations and their thermophysical properties are measured. Subsequently, a numerical model is carried out to study the influence of applying nanofluid and the rotary turbulator on thermal efficiency. The results indicate that using nanofluid leads to a 9% increase in thermal efficiency and adding the turbulator enhances thermal efficiency by more than 20%. Although hydraulic analysis reveals the Performance Evaluation Criteria remains in an acceptable range, the friction factor and Nusselt number increase by the addition of nanoparticles to the basefluid.
This study presents a thermodynamic evaluation of a flat plate collector (FPC) operating with both mono and hybrid nanofluids. The performance of a collector operating with alumina-water, alumina-iron/water hybrid nanofluids, and water as its heat transfer fluids are evaluated. The two nanofluids were experimentally synthesized at nanoparticle concentrations of 0.05%, 0.1%, and 0.2%, their thermal properties were measured for varying temperature ranges and is used to create a correlation model for the thermal conductivity, specific heat, and viscosity of the nanofluids. A thermal model for the FPC was created on the engineering equation solver for both the first law and second law evaluation of the collector. Then a parametric study and optimization of the system were carried out for varying values of temperature, nanoparticle volumetric fraction and mass flow rate. The results show that the use of alumina-water at a concentration of 0.1% presented a thermal enhancement of 2.16% in the collector, while the hybrid nanofluids reduced the thermal performance of the collector by 1.79% when compared to water. Though the use of the hybrid nanofluids did not provide a better thermal option to water, it provided an exergetic efficiency enhancement of 6.9% as against 5.7% using the alumina-water na-nofluids.
An active vortex generator is proposed for heat transfer enhancement in heat sinks and heat exchangers and removal of highly concentrated heat fluxes. It is based on applying a uniform magnetic field of permanent magnets to a magnetic fluid (ferrofluid) flowing in a heated channel. Numerical simulations are carried out for a 2 Vol% ferrofluid at different Reynolds numbers (150‐210) and magnetic field intensities (0‐1400 G) to investigate the possibility of simultaneous heat transfer enhancement and pressure drop reduction by the proposed method. Comparisons are also made with the other conventional vortex generators. Results indicate that the external magnetic field acts as a vortex generator that changes the velocity distribution, improves the flow mixing, and thereby increases the convective heat transfer. Surprisingly, the heat transfer enhancement is accompanied by a decrease of the friction coefficient due to the flow separation and decrease of the flow contact with the surface. It is also concluded that increasing the magnetic field intensity, decreasing the flow rate, and adding a second identical magnetic vortex generator have favorable effects on both pressure drop and heat transfer. A maximum of 37.8% enhancement of heat transfer with a 29.18% reduction of pressure drop has been achieved at the optimum condition.
The scientific community has focused on the use of nanofluids to enhance solar collectors' thermal efficiency. Solar energy is considered an extensively available energy resource with a weak effect on the environment. The flat-plate solar collector is considered to be the most common collector used, but the efficiency of the collector has limitations, such as the low effectiveness of the absorber in terms of energy absorption and the transmission of that energy to the working fluid. The flat-plate solar collector can be enhanced by replacing the working fluid with a nanofluid. Nanofluids are considered new media that exhibit thermophysical properties superior to those of ordinary working fluids. In this study, the effect of using multi-walled carbon nanotubes in a thermosiphon and forced-circulation flat-plate solar collector was investigated experimentally. A set of different concentrations was tested (0.01 wt%, 0.05 wt% and 0.1 wt%) with distilled water. The experimental results show an enhancement of the system's exergy efficiency and energy efficiency when a nanofluid was used compared with those attained using distilled water in both forced and thermosiphon systems.
Solar liquid collectors are potential candidates for enhanced heat transfer. The enhancement techniques can be applied to thermal solar collectors to produce more compact and efficient energy collection/storage mechanism. Those collectors can be induced for simplest and most direct applications of energy conversion of solar radiation into heat. This work presents a comparative representation of computational simulation and experimental for the processes occurring in liquid flat-plate solar collectors. The working fluid used is propylene glycol and the concentration of propylene glycol (PG) is varied for various mass flow rates. The effect of this variation, on the efficiency of a flat plate solar collector was investigated computationally and experimentally. The experiments were carried out using 4 different mixture concentrations. The designed model is simulated under various flow conditions by varying the mass flow rate and varying the working fluid concentration. In order to verify the designed model and results, an experiment was designed and conducted for several days with variable ambient conditions, flow rates and concentrations. The comparison between the computed and measured results of the fluid temperature at the collector outlet showed a satisfactory convergence. The model is appropriate for the verification of overall efficiency of the system and can be used for any number of working fluids in order to find the outlet temperature.
The effect of an external magnetic field on the forced convection heat transfer and pressure drop of water based Fe3O4 nanofluid (ferrofluid) in a miniature heat sink is studied experimentally. The heat sink with the dimensions of 40 mm (L) × 40 mm (W) × 10 mm (H) consists of an array of five circular channels with diameter and length of 4 and 40 mm, respectively. It is heated from the bottom surface with a constant heat flux while the other surfaces are insulated. The heat sink is also influenced by an external magnetic field generated by an electromagnet. The local convective coefficients are measured at various flow rates (200 < Re < 900), magnetic field intensities (B < 1,400 G), and particle volume fractions (φ = 0.5, 1, 2 and 3 %). Results show that using ferrofluid results in a maximum of 14 % improvement in heat transfer compared to the pure water, in the absence of magnetic field. This value grows up to 38 % when a magnetic field with the strength of 1,200 G is applied to the ferrofluid. On the other hand, it is observed that the significant heat transfer enhancement due to the magnetic field is always accompanied by a pressure drop penalty. The optimum operating condition is obtained based on the maximum heat transfer enhancement per pressure loss.
A considerable amount of energy is lost in the parabolic trough solar collectors due to the poor capability of working fluid in full absorption of the concentrated solar irradiation across the receiver tube. A new hybrid method is recommended here to cover up such deficiency by simultaneously using a rotary absorber tube and magnetic field inducer with nanofluid. Results showed that the combination effects of the receiver rotation and the magnetic field improve the convection mechanism in the absorber and increase both energetic and exergetic performance of the collector. The study reveals that there is an optimal rotational speed in the each magnetic field intensity for different hydrothermal and thermodynamic parameters. That is, in comparison with the case with no magnetic field and rotational tube employment, the total heat loss in the collector can be saved by 37.4% when a magnetic field of 1000 G and a rotary tube with speed of 0.4 rad/s are employed simultaneously. In this comparison, a maximum improvement of 101% and 24% in the performance evaluation criteria (PEC) and exergy efficiency of the system is achieved by employing the proposed hybrid method, respectively. Results also revealed that there is an optimal rotational speed in the each magnetic field intensity, in which employing a magnetic field at this rotational speed does not increase pressure drop for the sake of improving energetic and exergetic efficiencies of the solar collector.
In the present study, the effects of rotary tubes and magnetic-induced nanofluid on heat transfer characteristics of a compact heat exchanger are individually investigated. Two-phase Eulerian model is employed to predict the hydrothermal and entropic characteristics of Fe3O4/water ferrofluid in the heat exchanger. Results indicate that utilizing each rotary tubes and magnetic field method can improve the energy and exergy efficiencies of the compact heat exchanger under specific circumstances by forming different types of secondary flow. It is found that employing each method individually can increase the maximum heat transfer rate by more than 60%. In comparison with methods like passive vortex and swirl generators, subtle pressure drop and entropy generation is observed in the new proposed methods since no additional obstacles were employed. Results also reveal that 12.5% of the possible maximum energy can be regenerated along with a 3.5% increase in the exergy efficiency of the heat exchanger at low Reynolds numbers by employing each method.
A high-efficient method has been considered for simultaneously improving the hydrothermal and entropic efficiencies of heat exchangers. Two-phase Eulerian model is employed in a 3-D numerical study to precisely study the hydrothermal and entropic behaviors of Fe3O4/water nanofluid under the effect of a magnetic field inducer. The findings reveal that employing the magnetic field can improve the energetic and exergetic performance by generating a swirling flow in the heat exchanger. The pressure drop and entropy generation minimization are also achieved by the induced flow in comparison with other passive techniques due to the lack of any additional obstacle in the flow path. Results show that thermal and entropic efficiencies are increased up to 90% and 33% in the presence of the magnetic field, respectively. Regarding that, the proposed method for boosting energy and exergy efficiencies of similar applications like heat exchangers can be highly efficient.
In present study, performance of two nanofluid-based solar stills at the peak of Mount Tochal nearly 4000 m and city of Tehran during four consecutive days in July 2018 for the first time was examined. Silver nanofluid due to prominent advantages such as excellent optical properties, high thermal conductivity, and anti-bacterial characteristics at 0.04% weight of concentration was used. Since the rate of ultra-violet (UV) at the apex of Tochal is ~30% higher than Tehran; the produced water from systems collected in transparent plastic bottle and expose under sunlight during 8 h of experiment to use the advantage of solar water disinfection (SODIS). Results showed that from energetic point of view, utilizing nanofluid has great impact on the systems while from exergetic viewpoint the altitude has the greatest impact on the systems. The highest instantaneous energy and exergy efficiency was obtained by Tochal-located loaded with nanofluid by 55.98% and 9.27% respectively. Also, overall energy and exergy efficiency of Tochal-located system loaded with nanofluid compared to Tehran-located without nanofluid improved by about 106% and 196% respectively. Finally, using silver nanoparticle for double-purposes (anti-bacterial and enhancing heat/mass transfer) and exposure the distilled water under sunlight for SODIS can results to produce healthier water.
The outdoor deployment of solar nanofluids in practical solar photothermal conversion devices for prolonged periods of time has been an ongoing challenge. This is due to their exposure to intense solar radiation, elevated temperatures, thermal and solar cycling, and other rough operation conditions that compromise their dispersion and chemical stability. This work is an attempt to address this challenge in light of state-of-the-art advances in understanding, characterizing, and mitigating issues pertaining to the stability of solar nanofluids. We first defined the concept of nanofluids, along with their types and applications, merits and limitations, and preparation techniques. This was followed by presenting the basic physical principles that govern the interparticle interactions, clustering and deposition kinetics, and theories of colloidal stability for nanoparticles in aqueous environments. Building on a sound understanding of these necessary fundamentals, the destabilization factors and instability effects on solar nanofluids were systematically identified. A critical evaluation of the most recent stability characterization techniques and stabilization strategies for solar nanofluids was then provided. A coverage of selected state-of-the-art works in the literature that target the enhanced stability of solar nanofluids in different photothermal conversion processes based on the direct volumetric absorption of solar radiation was presented and comparatively evaluated. Finally, recommendations were drawn regarding current knowledge gaps and future research directions in order to overcome the stability limitations hindering the deployment of solar nanofluids in practical solar photothermal conversion applications.
Flat plate solar collector is an essential device, which facilitate direct application of solar energy for water heating in household and industrial sector. Existing Flat plate solar collectors (FPSC) suffers from stagnant and comparatively low efficiency. Further research to improve efficiency of FPSC by inculcating innovative design is necessary. To fill the gap, the presented work is an experimental investigation of an innovative design and fabrication approach which deals with analysis of flat plate solar collector efficiency. Design modifications of solar collector always offer an important alternative to achieve significant effect on thermal efficiency. In this work single spiral shaped collector tube as compare to number of riser tubes connected with headers in conventional type flat plate solar collector has been developed. Keeping all other parameters similar to conventional design, it has been observed very encouraging outcomes in efficiencies of solar collector. Under forced mode of testing, enhancement in thermal efficiency achieved is, 21.94% compared to conventional flat plate collector design. Enhancement in exergy efficiency is 6.73%. Overall material saving is about ~30% and cost of manufacturing and maintenance can be significantly reduced at equivalent performance of conventional collector.
In this paper, an innovative method has been proposed that improves the convective heat transfer in heat exchangers and also reduces the pressure drop penalty compared to the other conventional enhancement techniques. The method is based on applying an external magnetic field to generate a swirling flow in the magnetic working fluid. A three dimensional numerical simulation has been carried out to investigate the performance of the presented method in a double pipe mini heat exchanger at different concentrations and flow rates of the magnetic nanofluid, and magnetic field intensities. Results show that application of the external magnetic field augments the heat transfer enhancement up to 320% with only a slight increase of the pressure drop. The induced swirling flow improves the heat transfer rate by disrupting the thermal boundary layer and increasing the flow mixing in the heat exchanger. Moreover, flow resistance and consequently the pressure drop is minimized due to the lack of any additional obstacle in the flow passage. It is concluded that the favorable conditions for the mini heat exchanger operation are low Reynolds numbers, high magnetic field intensities, and high concentrations of the nanofluid.
This paper investigates the accuracy of the magnetic force models which are conventionally used for simulation of ferrofluid flow and heat transfer. Three different correlations provided in finite volume method have been separately used to calculate the forced convective heat transfer of magnetite (Fe3O4) ferrofluid flowing in a miniature heat sink. Simulations have been carried out at different Reynolds numbers, volume fractions and magnetic field intensities. The accuracy of the magnetic force models have been evaluated by comparing the numerical results with the experimental data. Therefore, the reliable working conditions for each magnetic force model have been determined. It is shown that predictions of all the magnetic force models are qualitatively similar. However, the models exhibit noticeable discrepancy due to the different magnetic susceptibility correlations. The accuracy of the all models decreases with increase of the magnetic field intensity while different behavior is observed with volume fraction and Reynolds number.
Nanofluids are getting the utmost preference for heat transfer applications due to their excellent thermal properties over the base fluid. In the present study, the stability of Magnesium oxide/Ethylene Glycol-Distilled water nanofluid and its effect on the thermal performance of flat plate solar collector (FPSC) was experimentally investigated. Cetyltrimethyl ammonium bromide (CTAB) surfactant was added to the mixture and sonicated to stabilize the suspension. The stability was analysed at different nanoparticle concentrations (0.08%–0.4%) as a function of time. The thermal performance of FPSC was investigated at different particle concentrations (0.08%–0.2%) under varying flow rate (0.5–2.5 Lit/min). Nanofluid characterizations; zeta potential & U–V spectroscopy reveal that nanofluids were stable for more than 15 days up to 0.2 vol% concentration. At higher volume fraction (0.4 vol%), as a result of agglomeration, nanofluid become unstable. The highest thermal efficiency of the collector was achieved by 69.1% for 0.2 vol% at 1.5 Lit/min, which was 16.7% more than EG/DW solely. The results depict that the absorbed energy factor increased by 16.74% and heat loss parameter decreased by 52.2% at the identical parametric condition. The results encourage the use of MgO nanofluid in FPSC.
Performance improvement of a flat-plate solar collector is studied numerically using computational fluid dynamics based opensource tool, OpenFOAM. The collector channel is filled with fully saturated porous metal foam, and extended Darcy-Brinkman-Forchheimer model is used to model this porous region. The present code has been tested thoroughly against various numerical and experimental works from the literature, and a reasonable agreement is achieved. The influence of permeability (Darcy number, Da = 10−4 - 10−1), radiation insolation parameter (Rd = 0 - 5), buoyancy parameter (Richardson number, Ri = 0 - 5), and collector channel inclination angle (α = 0° - 45°) on the collector channel outlet temperature i.e., effective heating achieved has been studied. The novelty of the present study lies in the implementation of Rosseland approximation for modelling radiation influence, along with buoyancy consideration by varying channel inclination angles. The computational results suggest that the flow and thermal fields vary when modelling buoyancy and radiation influences combined. The insertion of porous metal foam enhances the thermal performance because of better thermal mixing, along with buoyancy parameter and volumetric radiation parameter. Although the performance does improve with the channel inclination angle, the maximum increment is obtained at intermediate angles, while any further rise in inclination gives a minor performance improvement. A comparison of different boundary conditions along with Rosseland approximation usage is given. A remark on the inclusion of the Forchheimer term in the present flow regime is given. The manuscript provides an impetus for further experimental work on the present case and comments on buoyancy parameter influence on channel performance.
Shadow on the absorber plate of a flat-plate solar collector or a solar cooker box can reduce absorbed energy. The main goal of this research is to investigate the effective factors on the shadow formation inside a solar collector. In addition, the energy gain reduction due to shadow was calculated. The length, width (0.5–2.5) and height (0.01–0.2 m) of a solar collector, tilt angle (0.01–80°) and latitude (0.01–65°) were considered as the effective variables on the shadow formation. The sum of shadow ratio and the percentage of energy gain reduction per year were chosen as the dependent variables, and the effect of each factor was discussed. Results showed that the effective variables (strong to weak) were height, width, tilt angle, latitude and length for the sum of shadow ratio per year, and height, tilt angle, width, latitude and length for the energy gain reduction per year. The minimum and maximum energy gain reduction per year due to shadow for a solar collector with length = width = 1 and height = 0.04 m were obtained 5.23 and 21.64%, respectively. If a solar collector has a rectangular plate, the larger width is more suitable than the larger length for the shadow reduction.
In the present study, in addition to using nanofluid, the flow direction in a flat plate solar collector is changed to increase the convective heat transfer coefficient. To this end, U-shaped, wavy and spiral pipes with identical pipe lengths on a flat plate collector are simulated. Three-dimensional and steady state equations of continuity, momentum, SST k-ω turbulence model, and energy are solved. Al2O3/water and CuO/water nanofluids are used in volume fractions of 1 % and 4%. Results show that using wavy and spiral pipes can significantly increase the heat transfer coefficient and Nusselt number. Also, it is observed that the pressure drop has its highest value for the wavy pipes. In all cases, the heat transfer coefficient increases by using nanofluid instead of water. In all cases except for the CuO 4%, the Nusselt number has decreased due to a remarkable increase in thermal conductivity by adding nanoparticles to water. Results reveal that by using wavy pipes and CuO/water nanofluid with a volume fraction of 4%, the heat transfer coefficient can increase up to 78.25%.
The objective of this paper is to investigate comprehensively energy, exergy and financial parametric analyses of a solar flat plate collector (FPC) using heat pipes. A validated 1-D mathematical model was established and implemented in MATLAB to assess the collector performance. Hourly meteorological variables for one complete year in Fez (Morocco) were fitted and incorporated into the computation tool to describe accurately the thermal behavior of the whole collector. The combined effects of various climatic data, operating and design parameters were analyzed energetically and exergetically based on hourly and monthly performance indexes. Multi-objective optimization using a dimensionless-geometrical index was practiced to find out the best operating scenario achieving the highest energy and exergy outputs at a reduced cost. The best compromise between thermal/exergy performances was obtained at 986.93 W/m ² for the incident solar radiation, 12.18 °C for the ambient temperature and 1.50 m/s for the wind velocity. Also, it was found that the best combination of operating conditions is 45 °C inlet temperature and 0.036 kg/s mass flow rate. Fixing the number of heat pipes to 13 leads to an optimized collector design in terms of energetic, exergetic and financial performances. The obtained results confirm that an appropriate design of the collector should be undertaken carefully depending on the prevailing meteorological conditions to achieve optimum energetic/exergetic and economic performances.
Free convective flow and heat transfer of nanofluid close to the inclined plate immersed in the porous medium under the effects of uniform magnetic field and solar radiation has been studied. Boundary-layer approach, Boussinesq approximation and two-phase nanofluid model have been used for a formulation of the governing equations taking into account convective-radiative heat exchange with an environment. The local similarity method has been adopted for the analysis of the considered phenomenon. The obtained equations have been solved numerically using MATLAB software. The effects of control characteristics on profiles of velocity, temperature and nanoparticles volume fraction as well as Nusselt number have been studied in detail.
The increase of renewable sources in power generation is a global concern. Research and development of renewable energy devices use are leading to changes in the global energy mix. In this scenario, solar energy has a great potential for new applications. Thus, this study analyzes possible improvements in the thermal efficiency of solar flat plate collectors commonly used in domestic water heating systems. The influence of the inclusion of convective barriers inside the air cavity located between the absorber plate and the glass cover is evaluated based on the increase of the thermal efficiency in the solar collector. The use of these barriers limits the space between the absorber plate and the glass cover, which may reduce heat losses in some conditions. The experimental analysis was performed using four solar collectors with one to four convective barriers. The results obtained were compared with a reference solar collector, without any barrier. An instrumented test bench was built to measure the flat plate solar collector thermal efficiency. The results showed that there was no significant variation in solar radiation absorption since the maximum thermal efficiency remains unchanged. However, the barriers inclusion implies in changes in heat loss. The experimental data shown that changes in heat loss are −2,2%, −5,3% and 2,9% for two, three and four barriers, respectively. In this way, the convection barriers are able to reduce the heat loss in two cases, but increase the heat loss in one case. This result indicates that there is an optimal number of convective barriers for each solar collector design.
In cold environments, flat plate solar collectors are of limited value because high heat losses lead to low efficiency. The integration of polymethyl methacrylate (PMMA) sheet into flat plate collector is presented in this paper. The performance of this collector in cold weather was investigated using a three-dimension simulation model. A simplified experiment was conducted to verify the precision of numerical model and the simulation data can agree very well with practical ones. The effects of the thickness and location for PMMA sheet on the performance of collector efficiency following steady state were analyzed. The transmittance of transparent insulation material is the key parameter to achieve high performance for the collector. The optimum thickness of the transparent insulation material is 1 mm in simulated conditions and the best location of PMMA sheet was achieved. The result shows that the increase of the collector efficiency from the conventional collector is 11.3%, when reduced temperature difference is equal to 0.1 m ² °C/W and the ambient temperature is −20 °C.
The present study numerically investigates the effects of a uniform external magnetic field and porous fins on
convective heat transfer and pressure drop of magnetite (Fe3O4/water) nanofluid in a heat sink. Effects of volume
fraction, porosity, Reynolds number, and magnetic field strength on the performance of the heat sink are studied.
Results indicate that heat transfer increases at high volume fractions, fin porosities and magnetic field intensities
and decreases with the Reynolds number. A 13% enhancement of heat transfer is obtained for the heat sink with
solid fins by using ferrofluid compared to the pure water flow. This value grows up to 35% by using porous fins
and imposing magnetic field to the heat sink. Moreover, using porous fins is shown to decrease the pressure drop
while the magnetic field effect is not considerable. Therefore, it is concluded that the proposed methods result in
a remarkable heat transfer enhancement while decreasing the pressure drop
In this study, low-flux direct absorption solar collectors (DASCs) with nanofluid volume absorbers were modeled, analyzed, and optimized. The Rayleigh scattering approximation with size-dependent effects was used in order to determine nanofluid optical properties. Upon validating the mathematical model resulting from numerically solving and coupling the energy conservation equation with the radiative transfer equation, effects of internal bottom-surface optical boundary condition and base-fluid type on nanofluid temperature homogeneity and collector first-and second-law efficiencies were studied for different particle loadings, film thicknesses, and nanoparticle materials. Non-linear multi-variable constrained single-and multi-objective global optimization studies were conducted to find the optimal design vectors with respect to first-and/or second-law objective functions. The type of bottom surface in a DASC was shown to significantly affect its performance, particularly for relatively low particle loadings. Beyond a critical nanoparticle volume fraction value, collector performance was independent of bottom surface type and a DASC operates similar to a surface absorber. It has been also found that regardless of particle loading and bottom surface type, collectors with thinner nanofluid films always had a lower efficiency compared to collectors with thicker films. Water-based nanofluids were shown to offer stronger radiation absorption than therminol®-based ones up to a nanoparticle volume fraction of about 0.005%, at which level, therminol® becomes the stronger solar absorber. However, it was established that a nanofluid exhibiting stronger photo-thermal conversion does not necessarily lead to a higher collector efficiency. Finally, it was shown that optimizing with respect to a normalized combination of energy and exergy efficiencies (as opposed to only energy or exergy efficiencies) results in more reasonable design vectors with a balance between collector power and temperature gains.
The investigation of nanofluids effects on the performance of solar energy devices has converted to an important topic of research in recent years. The present experimental study deals with the effects of using WO3/water nanofluids on the efficiency of a flat plate solar collector which operates under weather conditions of Budapest, Hungary. First, water based nanofluids containing WO3 nanoparticles (with an average size of 90 nm) at three different volume fractions including 0.0167%, 0.0333%, and 0.0666% have been synthesized. The stability of nanofluids has been evaluated through Zeta potential tests which unveiled the prepared suspensions have high stability. In the next step, the thermal performance of the flat plate solar collector using nanofluids is investigated at different mass flux rates including 0.0156, 0.0183, and 0.0195 kg/ s.m². The results showed that adding WO3 nanoparticles to water ameliorates the efficiency of the solar collector. The experiment results reveal that the maximum enhancement in efficiency of the collector at zero value of [(Ti–Ta)/GT] was 13.48% for volume fraction of 0.0666% and mass flux rate of 0.0195 kg/s.m² compared to water, which clearly shows the high potential of WO3 nanoparticles for solar energy applications.
Numerical analysis of natural convection combined with entropy generation in a square open cavity partially filled with a porous medium has been performed for a ferrofluid under the effect of inclined uniform magnetic field. Governing equations with corresponding boundary conditions formulated in dimensionless stream function and vorticity using Brinkman–extended Darcy model for porous layer have been solved numerically using finite difference method. An influence of key parameters on ferrofluid flow and heat transfer has been analyzed. It has been found that an inclusion of spherical ferric oxide nanoparticles can lead to a diminution of entropy generation in the case of similar flow and heat transfer structures.
Solar flat plate collectors are devices used to trap solar thermal energy and use it for heating applications like water heating, room heating and other industrial applications. Flat plate collectors are popular for low and medium heating applications and there are undergoing constant development in terms of size reduction and enhanced efficiency. This paper presents an overview on the different techniques that are employed to enhance the efficiency of flat late collectors. Effect of using nanofluids as heat transfer fluid, effect of altering absorber plate design for better capture of radiation, methods of heat loss reduction, use of polymer, employing mini channels for fluid flow, using PCM (phase changing materials) to provide heat during night without tank and effect of use of enhancement devices like inserts and reflector have been discussed in this paper. A brief insight on various techniques used to analyse the effects and various designs has also been presented with the development methodology. Some analytical studies and CFD models have also been mentioned. This review paper also deals with the suggestions for the research work which can be carried out in the direction of heat transfer from solar flat plate collectors.
The main aim of this study is to compare two- phase and single- phase approaches in simulating forced convective heat transfer of Fe3O4- water nanofluid in both developing and fully developed regions of a tube under constant heat flux. Three different two- phase models, namely, Mixture, Volume of Fluid and Eulerian models have been utilized in the numerical analysis for the simulation of the nanofluids flow. In the single- phase models, four different correlations have been chosen for estimation of conductivity of nanofluid (constant, Maxwell, Brownian, proposed model). In order to validate single and two- phase simulations, an experimental setup is designed and fabricated. The experiments have been performed for nanofluids in volume fraction range of 0.5 to 2% and Reynolds number range of 300 to 1200 in the tube with diameter and length of D=0.0098 m, L=2.375 m, respectively. Results of the two- phase models have been compared with that of the best single- phase model and the collected experimental data. It is concluded that considering the Brownian motion effect in the static Maxwell model significantly improves the accuracy. However, the presented correlations for thermal conductivity and viscosity lead to the closest results to the experimental data.
An experimental research was performed on a solar facility with a nine-year-old, on-campus field with 50 m2 area of flat plate solar collectors. A transient model was developed, adapted to the characteristics of this facility and experimentally validated as described in Part I of this paper.The efficiency normalization curve (ENC) operating conditions for the steady-state test are different from the working conditions. Significant differences between the ENC and the model based predictions were found and quantified.The significance of the transient behavior is compared with the thermal inertia proposed in the EN-12975:2006 standard for the quasi-dynamic test.Using the model capabilities to predict the collector performance under transient working conditions, the influence of the operating conditions on the collector efficiency and on the useful heat produced is studied individually. The relevance of those conditions is ranked as follows: the wind (velocity magnitude and direction) was the most influential, followed by the aging of the collector surfaces, convective heat losses, thermal inertia and the incident angle of irradiance.
Heat and mass transfer: fundamentals and applications
- Y Cengel