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ABSTRACT: A water-based functionalized nanofluid was made by surface functionalizing the ordinary silica nanoparticles. The functionalized nanofluid can keep long-term stability. and no sedimentation was observed. The functionalized nanofluid as the working fluid is applied in a thermosyphon to understand the effect of this special nanofluid on the...
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... maximum mass concentrations of functionalized nanofluid and tra- ditional nanofluid were both 2.5 wt.% in the present study. Figure 3 shows the transmission electron microscope (TEM) pictures of functionalized nanofluid and tradi- tional nanofluid. As is shown, functionalized nanoparti- cles have no aggregation and can disperse well. ...Citations
... Yang and Liu [92] evaluated two types of SiO 2 /water nanofluid in THP. The first type was a conventional nanofluid (prepared with nanoparticles without functionalization). ...
... A decrease of heat transfer coefficient up to 11% was obtained using traditional nanofluids, depending on the process temperature. Yang and Liu [92] argued that the deposition layer on the evaporator surface was the cause of this deterioration. ...
Application of nanofluids as a working fluid can increase the thermal efficiency of heat pipes. The objective of this comprehensive review is to study the previous works to understand the dominant mechanisms of heat transfer when nanofluids are used in thermosyphon heat pipe (THP). The influence of heat input, type and concentration of nanoparticles on the thermal behavior of THPs are investigated. In general, nanofluids significantly improve the thermal characteristics of THP by decreasing the thermal resistance and increase the thermal efficiency of THP. The thermal performance of THP strongly depends on operating variables, especially the type of nanoparticles, their concentration and addition of surfactant and heat inputs. Further, the thermal performance of THP at various heat input is remarkably related to the type of nanofluid. This study also presents a review of the applications of the nanofluid-based heat pipes in energy systems. Finally, some challenges are identified and suggestions are made to fertilize the future investigations.
... Many studies show that nanofluids may improve heat transfer capabilities of the thermosyphon [7,9,14,[16][17][18][19]. Literature agrees that the effect of nanofluids on the condenser section is negligible [9,[20][21][22], and thus focus should be put on the evaporator section and the boiling process. Results suggest that the main improvement in heat transfer capabilities of the thermosyphon comes from the interplay between nanoparticles, evaporator surface, and bubble release during boiling. ...
Thermosyphons are heat transfer devices characterized by high efficiency due to simultaneous phase changes occurring in the evaporation-condensation cycle of working fluid. One of the most promising solutions to enhance their heat transfer capacity of the device is the use of nanofluids – suspensions of particles with at least one dimension below 100 nm. It was determined that nanofluid does not influence the work of thermosyphons condenser section and the focus should be put on the boiling process in the evaporator section. During boiling, nanoparticles tend to deposit on the heater’s surface, what alters characteristics of this surface and near surface hydrodynamics. This changes the appearance of nanofluid, but the precise effect on how the deposition of particles affects the properties of nanofluid is unknown. Changes in surface tension and wettability affect boiling regimes (e.g. reduced surface tension reduces the size of departing bubbles and inhibits geysering), and efficiency of heat transfer through the device. Understanding of those parameters is crucial for the development of appropriate models describing heat transfer in thermosyphon working with nanofluids. The main goal of this study is to determine surface tension and contact angle of nanofluids based on silica nanoparticles and nano-sized graphene oxide flakes before and after the experimental boiling cycle in the thermosyphon. Results show that, in comparison with water, silica nanofluid (2 vol.%) is characterized by lower surface tension and contact angles on both analysed surfaces. After-use silica nanofluid exhibited noticeably higher averaged surface tension and smaller contact angles in comparison to the fresh working medium. The change was most likely due to the decreased concentration caused by the deposition of nanoparticles during the thermosyphon operation. Still, the differences between before-use and after-use samples were smaller than the measurement uncertainties. Before-use graphene oxide nanofluid already showed surface tension and contact angle similar to water due to low concentration of graphene flakes (0.1 g/L). Consequently, the properties of after-use graphene oxide fluid were also not much different from water. Additional measurements of surface tension for graphene oxide nanofluid with and without addition of sodium dodecyl sulfate surfactant allowed to differentiate the effects caused by graphene flakes and surfactant. The surfactant reduced the surface tension of the nanofluid, but the change was smaller than in case of surfactant addition to pure water.
... 47,48 However, in many cases, the effect of nanoparticle concentrations cannot be described by this simple equation as the heat transfer in nanofluids may be the result of nanostructures formed ( Fig. 1) involving multiple heat-transfer mechanisms: Brownian motion (still controversial since it is too slow in comparison with heat diffusion; however, it could have an important indirect role in particle clustering), liquid layering at a liquid-particle interface, heat transport in nanoparticles (ballistic conduction), or nanoparticle clustering. [49][50][51] Sometimes the dispersed nanoparticles act as thermal insulators; for example, even metallic powders can be as insulating as ceramic powders. 52 Also, aerogels are considered one of the most promising insulation materials. ...
In recent years, the demand for more efficient cooling circuits has resulted in active studies of nanofluids, two-component liquids consisting of a base fluid, and dispersed nanoparticles with high thermal conductivity. From the viewpoint of both physics and chemistry, nanofluids are systems that require the characterization of many interconnected thermal and chemical properties. This perspective article sums up the state of the art and recent trends in the development and applications of nanofluids and especially carbon nanofluids. A focus of the paper is the possibilities of photothermal and photoacoustic methods—as techniques combining molecular spectroscopy and thermal characterization—for the assessment of thermal conductivity and thermal diffusivity of nanofluids. The possibilities of photothermal spectroscopy for wider characterization of nanofluids and related materials are discussed and compared with other techniques. As nanofluids are one of the examples of complex objects dedicated to photothermal spectroscopy, more general outlooks of phototermics are also discussed.
... The results showed that the payback period of the system was 4.5 years when it was operated with electrical backup. In a similar study, the technical and environmental performance of a FPSWH system was investigated by Koroneos and Nanaki [19]. Around 4280 € can be saved in Greece by implementing the solar system over its lifetime. ...
... Around 4280 € can be saved in Greece by implementing the solar system over its lifetime. Similar studies regarding the energy, economic, and environmental aspects of FPSWH systems can be found in [18][19][20][21][22][23]. ...
... This type of solar systems has higher thermal efficiency compared to the FPSWH systems even in cold environments with low solar radiation [17]. However, the possibility of overheating, vacuum loss, material problems [18], high initial costs [19], and fragile structure [18] have remained as their major drawbacks. ...
This study presents a detailed methodology for evaluating the energy, environmental, and economic contributions of heat pipe solar water heating (HPSWH) systems in various households. The hot water consumption patterns of Perth residents in Australia in one, two, and four-occupant houses are extracted in hourly basis throughout a year. The annual performance of the system is evaluated based on parameters such as saved energy, solar fraction, avoided CO2 emission, saved money, and payback period. Moreover, an experimental rig is designed, manufactured, and tested. The results show that the contribution of the solar system in meeting the hot water demand is around 99% in summer, while this contribution drops to 36–51% in winter. Almost 387–1146.8 kg of CO2 emissions can be avoided annually in Perth if HPSWH systems are integrated with the conventional heating systems. In addition, it is shown that the HPSWH system has its most economic justification in households with higher number of occupants. Moreover, the payback period is much lower for houses with conventional electric water heating systems compared to houses with LPG systems.
... . همچنین لوله از نوع این اولیه هزینه ها نیز باال ً نسبتا است [18] . [14] . ...
Solar energy is the most accessible of environmentally friendly energy source and renewable to meet the growing demand for energy in the world. In order to increase the efficiency of the solar thermal systems, applying suitable absorber tube is very important due to the initial cost, radiation conditions, weather conditions and heat transfer. This paper investigations and analyzes different types of solar collector tubes. The applications of solar collector tubes in water heating, air conditioning, pool heating, solar stoves, steam generation, solar dryers, greenhouse heat supply and for residential and industrial sectors are summarized and presented. The most efficient and the best solar collector tubes are evacuated tubes that have higher efficiency, pressure tolerance and heat tolerance than flat collector common tubes. In using solar absorbent tubes, the type of desired application, the desired maximum temperature and the cost required are the utmost importance in order to select the best tube. Hence, considering the advantages and disadvantages of each, it also will be has an acceptable efficiency for the user.
... Parametthanuwat et al. [23] experimentally examined the rate of heat transfer in a THP using silver/water nanofluid and oleic acid as surfactant. They also investigated the effects of operating temperature (60, 70, and 80 C), the filling ratio (30, 50, and 80%), the concentration of oleic acid surfactant in nanofluid (0, 0.5, 1.0, and 1.5), and the [24] performed an experimental study on the thermal performance of a THP using functionalized silica nanofluid with nanoparticles concentrations of 0.5, 1.0, 1.5, and 2.0 wt% with 3-glycidoxylproyl surfactant and operating temperatures of 40, 55, and 70 C. They reported that the evaporating heat transfer coefficient of functionalized nanofluid increased by 17% at the operating temperature of 40 C. Surfactants are added to disperse the nanoparticles in the base fluid more effectively. ...
... Parametthanuwat et al. [23] experimentally examined the rate of heat transfer in a THP using silver/water nanofluid and oleic acid as surfactant. They also investigated the effects of operating temperature (60, 70, and 80 C), the filling ratio (30, 50, and 80%), the concentration of oleic acid surfactant in nanofluid (0, 0.5, 1.0, and 1.5), and the [24] performed an experimental study on the thermal performance of a THP using functionalized silica nanofluid with nanoparticles concentrations of 0.5, 1.0, 1.5, and 2.0 wt% with 3-glycidoxylproyl surfactant and operating temperatures of 40, 55, and 70 C. They reported that the evaporating heat transfer coefficient of functionalized nanofluid increased by 17% at the operating temperature of 40 C. Surfactants are added to disperse the nanoparticles in the base fluid more effectively. ...
An experimental analysis is done to investigate the thermal performance of a thermosyphon heat pipe (THP) using three working fluids, namely, distilled water, nanofluid, and a mixture of nanofluid and surfactant. The working nanofluid is titanium dioxide and THP is made of copper tube with the outer diameter of 15 mm and length of 1000 mm. The effects of the input power and inclination angle on the THP performance are investigated. The experimental results indicated that with increasing the concentration of nanofluid, thermal efficiency increases and thermal resistance of the thermosyphon decreases. According to the results, mixing the nanofluid with the surfactant will decrease the evaporator wall temperature and the thermal resistance, while it increases the thermal efficiency of THP. Comparison between two nanofluids and a conventional fluid in a THP shows that the best pipe inclination angles are 60° for water and 90° for nanofluids. Adding the proper amount of surfactant increases THP’s thermal efficiency by 20%. The best thermal performance of THP achieved at the input power of 200 W for all the working fluids. The average deviation of 1% was observed between the experimental results of this study and those available in the open literature.
... Yang and Liu [111] have compared the functionalized silica nanofluid in the thermosyphon heat pipe with conventional silica nanofluid. Sedimentation has not been observed in the functionalized nanofluid for 12 months. ...
... TEM images of nanofluids a conventional nanofluid b functionalized nanofluid[111] ...
The nanofluid is a colloidal solid–liquid mixture obtained by the dispersing nanoparticles with a high heat transfer coefficient in the base fluid. In general, metal, metal oxide, ceramic and magnetic nanoparticles are used in nanofluids. The nanoparticles suspended in the base fluid of heat pipes effectively increased the heat transfer rate and thermal conductivity properties of the base fluid. The nanofluids have been found to be acting much better for some problems such as sedimentation, erosion, clogging and pressure drop compared to common slurries. The energy transfer is carried out by two-phase heat transfer mechanism in heat pipes. There are many parameters and factors that have an effect in the boiling heat transfer coefficient. It is not easy to understand the positive and negative changes caused by nanofluids in this complex heat transfer mechanism. The surface geometry is a significant indicator on the boiling heat transfer mechanism. Investigation into nanofluid effects besides the surface geometry is very important in the experimental studies. In addition, it is known that nanofluids change the properties of the heater surface, apart from the thermophysical properties. The synthesis methods of nanofluids are presented in this article. Then, the physical and chemical mechanisms determining the long-term stability of nanofluids are explained in detail. Finally, some useful information about the use of nanofluids in heat pipes and pool boiling of nanofluids is given. The presented study also describes the pool boiling mechanism of nanofluids to understand the positive effects of nanofluids on the heat pipes heat transfer mechanism.
... There is no difference either we use nanofluids to enhance heat transfer or to use nanofluids coated surface [26]. In contrast to the above works highly stable nanofluids were used by [27] and there surface functionalized nanofluids developed earlier by [28]. These novel nanofluids have minimal surface deposition on the boiling surface. ...
Nanofluids are suspensions of nanoparticles with small concentration spread in base fluids such as water, oil and ethylene glycol. Nanofluid boiling is an important research area which provides many chances to explore new frontiers but also poses great challenges. Over the last decade, various studies have been carried out on pool boiling of nanofluids for the enhancement of critical heat flux which is otherwise limited by the use of base fluids. Several efforts have been made in the literature on nanofluid boiling, however, data on the boiling heat transfer coefficient and the critical heat flux have been unpredictable. Current study is a review of the status of research work on effects of nanofluids on heat transfer coefficient and critical heat flux. An emphasis is put in a review form on the recent progresses in nanofluid heat transfer coefficient and critical heat flux of pool boiling. This study also focuses on advancements in nanofluids, their properties and various parameters affecting boiling critical heat flux and heat transfer coefficient. At the end correlations used by different researchers to find out the critical heat flux and heat transfer coefficient are listed.
... For the time being, the focus is mainly on the phase-changing heat transfer of nanofluids, while previously they were analyzed for thermal conductivity [4][5][6] and single-phase flow heat transfer [7,8]. Of ever growing popularity is the application of nanofluids for the phase-changing heat transfer in heat pipes , specifically grooved heat pipes [11,12], wicked heat pipes [13,14], sintered heat pipes [15,16], loop heat pipes [17], oscillating heat pipes [18,19] and thermosyphons [20][21][22][23][24][25][26][27][28][29][30]. ...
... Yang and Liu experimentally investigated the thermal performance of a thermosyphon using water, a functionalized nanofluid, and a traditional nanofluid (unfunctionalized nanoparticles) under steady operating pressures [29]. The authors showed that functionalized nanoparticles maintained adequate nanofluid dispersion after a long storage period, and no sedimentation was observed. ...
