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Effects of mass flux and vapor quality on frictional pressure drop: (a) smooth tube; and (b) microfin tube.
Source publication
This study was made to investigate the condensation local heat transfer and adiabatic pressure drop of R134a inside a 2.5 mm outside diameter smooth and microfin tube at low mass flux condition. Data were measured for mass fluxes from 50 to 300 kg m −2 s −1 , vapor qualities from 0 to 1 and saturation temperatures from 20 to 30 °C. The effects of m...
Contexts in source publication
Context 1
... effects of mass flux, vapor quality, saturation temperature and tube diameter of the frictional pressure drop were analyzed. Figure 5a,b shows the effects of mass flux and vapor quality on the frictional pressure drop, in smooth and microfin tubes for mass fluxes of 50, 75 and 100 kg m −2 s −1 at a saturation temperature of 20 °C. As shown in Figure 5a,b, the frictional pressure drop increased as the mass flux increased. ...
Context 2
... 5a,b shows the effects of mass flux and vapor quality on the frictional pressure drop, in smooth and microfin tubes for mass fluxes of 50, 75 and 100 kg m −2 s −1 at a saturation temperature of 20 °C. As shown in Figure 5a,b, the frictional pressure drop increased as the mass flux increased. For a given mass flux, the pressure drop increased slightly at the low vapor quality (x < 0.3) region for both tubes. ...
Citations
... Comparison of the data ofBashar et al. (2018) [44] for saturated condensation with various correlations. R-134a in a horizontal tube: D = 2.14 mm; T SAT = 30 • C; G = 50 kg/m 2 s; and We GT = 22. ...
... Comparison of the data ofBashar et al. (2018) [44] for saturated condensation with various correlations. R-134a in a horizontal tube: D = 2.14 mm; T SAT = 30 • C; G = 50 kg/m 2 s; and We GT = 22. ...
Condensation heat transfer is involved in many industrial applications. Therefore, it is important to know the relative accuracy of the available methods for predicting heat transfer. Condensation can occur with saturated as well as superheated vapors. Predictive methods for both conditions were evaluated using a wide range of data. Twelve well-known correlations for the condensation of saturated vapor, including the most recent ones, were compared with data for 51 pure fluids and mixtures from 132 sources in horizontal and vertical channels of many shapes. Channel hydraulic diameters were 0.08–49 mm, the mass flux was 1.1–1400 kg/m2s, and the reduced pressure range was 0.0006–0.949. The fluids included water, CO2, ammonia, hydrocarbons, halocarbon refrigerants, various chemicals, and heat transfer fluids. The best predictive technique was identified. The three most commonly used models for heat transfer during the condensation of superheated vapors were studied. They were first compared with test data using measured saturated condensation and forced convection heat transfer coefficients to select the best model. The selected model was then compared with test data using various correlations for heat transfer coefficients needed in the model. The best correlations to use in the model were identified. The results of this research are presented, as are recommendations for use in design.
... The present model predicts the frictional pressure drop in 85% of databases (68 databases) with a MARD value of less than 5%, in 13.75% of databases (11 databases) with a MARD in the range of 5-10%, and only in 1.25% of databases (1 database) with a MARD in the range of 15-20%. The maximum MARD obtained by the present model with a value of 18.78% belongs to the database of Bashar et al. [22]. A comparison of the performance of the present model with previous models and correlations is provided in Table 6 for a total of 11,411 data points. ...
This study proposes a universal machine learning-based model to predict the adiabatic and condensing frictional pressure drop. For developing the proposed model, 11,411 data points of adiabatic and condensing flow inside micro, mini and macro channels are collected from 80 sources. The database consists of 24 working fluids, hydraulic diameters from 0.07 to 18 mm, mass velocities from 6.3 to 2000 Kg/m ² s, and reduced pressures from 0.001 to 0.95. Using this database, four machine learning regression models, including “artificial neural network”, “support vector regression”, “gradient boosted regression”, and “random forest regression”, are developed and compared with each other. A wide range of dimensionless parameters as features, “two-phase friction factor” and “Chisholm parameter” are each considered separately as targets. Using search methods, the optimal values of important hyperparameters in each model are determined. The results showed that the “gradient boosted regression” model performs better than other models and predicts the frictional pressure drop with a mean absolute relative deviation of 3.24%. Examining the effectiveness of the new model showed that it predicts data with uniform accuracy over a vast range of variations of each flow parameter.
... At a mass flow rate of 100 kg/m 2 s, the HTC of the micro-fin tube is approximately 2-5 times higher than the smooth tube. Bashar et al. [5] investigated the heat transfer characteristics of R1234yf in 2.5 mm diameter smooth and micro-fin tubes. The HTC of the micro-fin tube was 1.21-3.85 ...
Micro-fin tube, 3-D enhanced tube and smooth tube with an inner diameter of 9.52 mm were used as test tubes to study the condensation heat transfer performance with R410A and R32 as the working fluids at different mass flow rates (150–400 kg/m²s) and vapor qualities (0.2–0.8). For R410A and R32, the heat transfer coefficient of the micro-fin tube is 2.0–2.2 times and 1.5–2.0 times that of the smooth tube, and the heat transfer coefficient of the 3-D enhanced tube is 1.4–1.5 times and 1.5–1.6 times that of the smooth tube, respectively. The micro-fin tube is effective in thinning the condensate thickness and reducing the thermal resistance. The 3-D enhanced tube promotes the generation of turbulence and droplet entrainment, which improves heat transfer of enhanced tubes. The heat transfer coefficient of R32 is greater than that of R410A due to its higher thermal conductivity, latent heat and specific heat capacity. The frictional pressure drop increases monotonically with the mass flow rate. Considering the increment in surface area and the additional pressure drop penalty, the performance evaluation factor of the enhanced tubes ranges from 0.9 to 1.4. The study presents flow pattern maps for smooth and enhanced tubes. Enhanced tubes promote the appearance of intermittent and annular flow.
... Bashar et al. [40] measured the condensation HTC and pressure drop of R-134a inside a i D = 2.14 mm smooth and i D = 2.17 mm microfin tube at saturation temperatures from 20 to 30 °C. The microfin tube exhibited a nearly 1.01 to 2.11 times higher pressure drop than that of the smooth tube. ...
In this review, the condensation HTCs (heat transfer coefficients) and pressure drop characteristics of some major low-global-warming-potential (GWP) refrigerants alternative to R-134a such as R-1234ze(E), R-1234ze(Z), R-1234yf, R-513A, and R-450A are reviewed. The thermofluids’ characteristics inside/outside a tube, minichannel, microfin tube, and plate heat exchanger are examined. In addition, several other refrigerants attributed to low GWP are also included in the present review. The experimental/numerical/simulation results’ analysis reveals that condensation HTCs and pressure drop characteristics depend on several parameters such as thermodynamics and transport properties of the working fluid, mass flux of the refrigerants, heat flux, saturation temperature, vapor quality, flow patterns, flow conditions, orientation of the condensing geometry, and condensation geometry (shape, size, and smooth/enhanced).
... Totally, 299 experimental data points were obtained, including 118 from R1234ze(E) and 181 from R134a. Specifically, 63,195, and 41 data points were collected from the vapor quality ranges of 0-0. to larger adiabatic two-phase frictional pressure drop. Actually, its influence is similar to that of mass flux, namely, it is weakened for lower vapor quality and enhanced for higher vapor quality. ...
To protect the environment, a new low-GWP refrigerant R1234ze(E) was created to substitute R134a. However, its flow boiling performances have not received sufficient attention so far, which hinders its popularization to some extent. In view of this, an experimental investigation was carried out in a 1.88 mm horizontal circular minichannel. The saturation pressures were maintained at 0.6 and 0.7 MPa, accompanied by mass flux within 540–870 kg/m2 s and heat flux within 25–65 kW/m2. For nucleate boiling, a larger heat flux brings about a larger heat transfer coefficient (HTC), while for convective boiling, the mass flux and vapor quality appear to take the lead role. The threshold vapor quality of different heat transfer mechanisms is around 0.4. Additionally, larger saturation pressure results in large HTC. As for the frictional pressure drop (FPD), it is positively influenced by mass flux and vapor quality, while negatively affected by saturation pressure, and the influence of heat flux is negligible. Furthermore, with the measured data, several existing correlations are compared. The results indicate that the correlations of Saitoh et al. (2007) and Müller-Steinhagen and Heck (1986) perform best on flow boiling HTC and FPD with mean absolute deviations of 5.4% and 10.9%.
... Totally, 299 experimental data points were obtained, including 118 from R1234ze(E) and 181 from R134a. Specifically, 63,195, and 41 data points were collected from the vapor quality ranges of 0-0. to larger adiabatic two-phase frictional pressure drop. Actually, its influence is similar to that of mass flux, namely, it is weakened for lower vapor quality and enhanced for higher vapor quality. ...
A numerical investigation on the melting process of paraffin wax RT44 under supergravity (5–20 g) was conducted to evaluate the effect of supergravity on the melting heat transfer characteristics. The simulations were conducted in a horizontally placed container with constant heat flux of 5–50 kW/m2 maintained on the bottom wall under both supergravity and the Earth gravity (1g). The numerical data under supergravity are compared with those under the Earth gravity for all circumstances. The results indicate that the melting heat transfer characteristics of the phase change material (PCM) are affected by supergravity significantly (around 30%) within 20 g. With the increase of supergravity, the heating wall temperature decreases, and the liquid fraction as well as the melting rate increase. Meanwhile, the variation amplitudes of these melting characteristics decrease gradually until less than 2% at 20 g. The effect of supergravity can be attributed to the intensification of the natural convection due to buoyancy, yielding vortexes in internal flow and fluctuations of solid-liquid interface and temperature field.
... A condensation heat transfer correlation for smooth tube was developed. Present experimental data and other sources data ( Haraguchi et al., 1994 ;Hossain et al. 2012 ;and Bashar et al. 2018 ) were considered to develop this correlation. Newly developed correlation may applicable to both the small diameter and large diameter tubes, many kinds of refrigerant and wide range of operating conditions. ...
... A test facility is fabricated to precisely investigate the condensation heat transfer coefficients of the refrigerants with horizontal smooth and microfin tubes. The description of the experimental apparatus and data reduction has to a large extent already been published in our previous paper ( Bashar et al. 2020 ;Bashar et al. 2018 ) and is repeated here for the sake of completeness. ...
... In order to predict the heat transfer coefficient, experimental smooth and microfin data are compared with previous correlations and they are listed in Table 3 . Considering this study and our previous study ( Bashar et al., 2018 ), in total 220 smooth and microfin tube data points are predicted with correlations. ...
Condensation heat transfer of R1234yf inside smooth and microfin tube with 2.5 mm outer diameter are studied experimentally. The experiments are carried out at a saturation temperature of 20°C and 30°C, mass velocity ranging from 50 to 200 kg m−2s−1 and vapor quality ranging from 0-1. The effects of mass velocity, vapor quality, and saturation temperature on the condensation heat transfer coefficient are analyzed with R1234yf and R134a. Condensation heat transfer correlation for smooth tube is developed considering present experimental data and other researchers’ data. Correlation is developed using experimental data for 2.5 mm to 10 mm outer diameter tubes and refrigerants are R134a, R1234yf, R123, and R1234ze (E) by including other researchers’ data. Newly developed correlation is successfully predicted experimental data and other sources data within mean deviation of 15 %. Experimental data are also compared with previous correlations proposed for smooth and microfin tube.
... A recent trend in AC and refrigeration industry is to use small diameter microfin tubes instead of the large diameter tubes. Many researchers have already studied and experimentally found high heat transfer performance in the small diameter microfin tubes ( Diani et al., 2017 ;Bashar et al. 2018 ;Hirose et al., 2018 ;Jige and Inoue, 2019 ). On the other hand, decreasing tube diameter obviously leads to higher pressure drop, although this problem can be https://doi.org/10.1016/j.ijrefrig.2020.08.013 0140-7007/© 2020 Elsevier Ltd and IIR. ...
... The description of the experimental apparatus, test section and data reduction has to a large extent already been published in our previous papers ( Bashar et al. 2019 ;Bashar et al. 2018 ; and is repeated here for the sake of completeness. ...
... The present experiment was conducted over the mass velocity range from 50 to 200 kg m −2 s −1 , vapor quality ranges from 0.1 to 0.9 and saturation temperature range of 20 and 30 °C as shown in Table 3 . The ther- The data of R134a were taken from Bashar et al. (2018) . mophysical properties of R134a and R1234yf were obtained from NIST REFPROP 9.1 ( Lemmon et al., 2013 ). ...
This study investigated the pressure drop of adiabatic vapor-liquid two-phase flow inside horizontal smooth and microfin tubes with 2.5 mm outside diameter. R134a and R1234yf were used as working fluid and the experiments were carried out at saturation temperatures of 20 and 30°C, mass velocities ranging from 50-200 kg m−2s−1 and vapor qualities ranging from 0.1-0.9. The effects of mass velocity, vapor quality, refrigerant properties and tube diameter on the pressure drop were analyzed. Some typical previous pressure drop correlations were used to predict the experimental data. A new two-phase pressure drop correlation for small diameter tubes was proposed based on the experimental data. The new correlation agrees with the available other researchers’ data and it can be broadly applied to the small diameter smooth and microfin tubes, wide range of mass velocity and many kinds of refrigerants.
... A lot of researchers [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17] have studied enhanced tube surfaces effects on flow patterns, pressure differences and heat transfer. In those studies, it was found that enhanced tubes generally improved thermal performance but with corresponding pressure drop increase. ...
In this study, experiments were conducted for the flow of R-134a condensing in an enhanced inclined tube at a saturation condensing temperature of 40 °C. The enhanced tube had a helix angle of 14° with a mean internal diameter of 8.71 mm. The mass velocities were varied from 200 to 600 kg m−2 s−1, while the inclination angles were varied from − 90° to + 90°. It was found that the inclination angle had a considerable effect on the flow patterns and the thermal performance. It was also found that the maximum heat transfer coefficients were obtained at tube inclinations of between − 15° and − 5° (downward flows). By using the experimental data and artificial neural networks (ANN), a model was proposed to predict the heat transfer coefficients during condensation inside the enhanced inclined tube. By using four statistical criteria, the performance of the proposed model was examined against experimental data, and it was found that ANN was a useful tool for the prediction of the heat transfer coefficients based on the effective parameters of vapour quality, mass velocity and inclination angle.
... Table 4 provides the sample size, the mean absolute error (MAE) and the percentage of results predicted within 30% and 50% of the experimental results, θ and ζ respectively. The predicted results are obtained using the correlation derived by [40] and [44] for saturated boiling and condensing frictional pressure drop respectively, and the experimental 365 data points are from [53] for boiling flow and [54] for condensing flow. For the saturated two-phase flow heat transfer coefficient, predicted values are obtained using [39] and [43] for boiling and condensing flow, respectively. ...
Small satellites are receiving increased recognition in the space domain due to their reduced associated launch costs and shorter lead time when compared to larger satellites. However, this advantage is often at the expense of mission capabilities, such as available electrical power and propulsion. A possible solution is to shift from the conventional solar photovoltaic and battery configuration to a micro-Organic Rankine Cycle (ORC) and thermal energy storage system that uses the waste energy from a solar thermal propulsion system. However, limited literature is available on micro-ORC systems, which are capable of producing a few hundred Watts of electrical power. This paper describes the proposed system layout and model of the integrated micro-ORC system, for various working fluids such as Toluene, Hexamethyldisiloxane (MM), and Octamethylcyclotetrasiloxane (D4). Toluene has been identified as a promising working fluid candidate resulting in a power generation system volume fraction of 18% for a 215 kg Low Earth Orbit satellite. The micro-ORC system is capable of producing 200 W of electrical power. The design provides high specific energies of at least 500 Wh/kg but, has a low shared specific power of 10 W/kg. A preliminary design of the micro-turbine provides a conservative total-to-static efficiency of 57%.
