Heat Transfer Coefficient, Pressure Gradient, and Flow Patterns of R1234yf Evaporating in Microchannel Tube

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Houpei Li ◽  
Pega Hrnjak
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Gradient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Flow Boiling ◽  
Saturation Pressure ◽  
Saturation Temperature ◽  
Heat Mass Transf ◽  
The Heat Transfer Coefficient

Abstract This paper presents the heat transfer coefficient, pressure gradient, and flow pattern of R1234yf in a microchannel tube. Both heat transfer coefficient and pressure gradient are presented against real saturation pressure, while flow pattern captures at the exit of data points are presented in the same plot. The experiment was conducted on a 24-port microchannel tube with an average hydraulic diameter of 0.643 mm. The experiment covers mass flux from 100 to 200 kg m−2s−1, heat flux from 0 to 6 kW m−2, vapor quality from 0 to 1, and inlet saturation temperature from 10 to 30 °C. Comparing the correlations to the HTC measurements at very low quality (about 0.1), Gorenflo, D., and Kenning, D. (2010, Pool Boiling, in: VDI Heat Atlas, 2nd ed, Springer, pp. 757–788) agree with the results. As vapor quality increases, pressure gradient increases. The adiabatic pressure gradient is a strong function of mass flux and saturation pressure (temperature). Flow patterns of R1234yf are also affected by mass flux and saturation pressure. The heat transfer coefficient is a strong function of mass flux and heat flux. The saturation temperature has a smaller effect on HTC in the condition range (10 – 30 °C). Under the test range, the accelerating pressure drop is insignificant compared to friction. Comparing to the results, Mishima, K., and Hibiki, T. (1996, “Some Characteristics of Air-Water Two-Phase Flow in Small Diameter Vertical Tubes,” Int. J. Multiph. Flow, 22(4), pp. 703–712) and Muller-Steinhagen, H., and Heck, K. (1986, “A Simple Friction Pressure Drop Correlation for Two-Phase Flow in Pipes,” Accessed March 1, 2018)., 20, pp. 297–308.) have small mean absolute error (MAE) to predict local pressure gradient. For the heat transfer coefficient, Sun, L., and Mishima, K. (2009, “An Evaluation of Prediction Methods for Saturated Flow Boiling Heat Transfer in Mini-Channels,” Int. J. Heat Mass Transf, 52(23–24), pp. 5323–5329) and Gungor, K. E., and Winterton, R. H. S. (1986, “A General Correlation for Flow Boiling in Tubes and Annuli,” Int. J. Heat Mass Transf, 29(3), pp. 351–358) have an MAE less than 30%.

Shell-Side Condensation Characteristics of R410A on Horizontal Enhanced Tubes

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Weiyu Tang ◽  
Wei Li
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Saturation Temperature ◽  
Diffusion Resistance ◽  
Outer Diameter ◽  
Vapor Quality ◽  
Enhanced Tubes ◽  
The Heat Transfer Coefficient

Abstract An experimental investigation into heat transfer characteristics during condensation on two horizontal enhanced tubes (EHTs) was conducted. All the tested EHTs s have similar geometries with an outer diameter of 12.7 mm, and a plain tube was also tested for comparison. Investigated enhanced surfaces consist of dimples, protrusions, and grooves, which may produce more flow turbulence and enhanced the liquid drainage effect. The effects of mass fluxes and vapor quality were compared and analyzed. Test conditions were as follows: saturation temperature fixed at 45 °C, mass flux varying from 100 to 200 kg m−2 s−1, and vapor quality ranging from 0.3 to 0.8. The heat transfer coefficient was presented, and the results show that the proposed enhanced surfaces seem to have worse performance than the conventional tubes when the mass flux is less than 150 kg m−2 s−1, while one of the enhanced tubes (2EHT-1) produce an enhanced ratio of 1.03–1.14 when G = 200 kg m−2 s−1. Besides, it was found that the heat transfer coefficient increases with increasing vapor quality, which can be attributed to the increasing diffusion resistance. Mass flux seems to have little effect on the heat transfer performance of smooth tubes, while that of 1EHT increases obviously with increasing mass flux, especially for high vapor qualities.

Study on Flow Boiling Heat Transfer of Carbon Dioxide With PAG-Type Lubricating Oil in Pre-Dryout Region Inside Horizontal Tube

2010 ◽  
Author(s):  
Chaobin Dang ◽  
Minxia Li ◽  
Eiji Hihara
Keyword(s):  
Heat Transfer ◽  
Carbon Dioxide ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

In this study, the boiling heat transfer coefficients of carbon dioxide with a PAG-type lubricating oil entrained from 0 to 5 wt% in a horizontally placed smooth tube with an inner diameter of 2 mm were experimentally investigated under the following operating conditions: mass fluxes from 170 to 320 kg/m2s, heat fluxes from 4.5 to 36 kW/m2, and a saturation temperature of 15 °C. The results show that for a low oil concentration of approximately 0.5% to 1%, no further deterioration of the heat transfer coefficient was observed at higher oil concentrations in spite of a significant decrement of the heat transfer coefficient compared to that under an oil-free condition. The heat flux still had a positive influence on the heat transfer coefficient in low quality regions. However, no obvious influence was observed in high quality regions, which implies that nucleate boiling dominates in the low quality region whereas it is suppressed in the high quality regions. Unlike the mass flux under an oil-free condition, mass flux has a significant influence on the heat transfer coefficient, with a maximum increase of 50% in the heat transfer. On the basis of our experimental measurements of the flow boiling heat transfer of carbon dioxide under wide experimental conditions, a flow boiling heat transfer model for horizontal tubes has been proposed for a mixture of CO2 and polyalkylene glycol (PAG oil) in the pre-dryout region, with consideration of the thermodynamic properties of the mixture. The surface tension and viscosity of the mixture were particularly taken into account. New factors were introduced into the correlation to reflect the suppressive effects of the mass flux and the oil on both the nucleate boiling. It is shown that the calculated results can depict the influence of the mass flux and the heat flux on both nucleate boiling and convection boiling.

Convective Boiling of R-22 in a Flat Aluminum Multi-Minichannel Tube With Dh = 1.4 mm

2008 ◽  
Author(s):  
Nae-Hyun Kim ◽  
Wang-Kyu Oh ◽  
Jung-Ho Ham ◽  
Do-Young Kim ◽  
Tae-Ryong Shin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Saturation Temperature ◽  
High Mass ◽  
High Heat Flux ◽  
Convective Boiling ◽  
The Heat Transfer Coefficient

Convective boiling heat transfer coefficients of R-22 were obtained in a flat extruded aluminum tube with Dh = 1.41 mm. The test range covered mass flux from 100 to 600 kg/m2 s, heat flux from 5 to 15 kW/m2 and saturation temperature from 5°C to 15°C. The heat transfer coefficient curve shows a decreasing trend after a certain quality (critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique ‘cross-over’ of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kandlikar correlations underpredict the low mass flux and overpredict the high mass flux data.

Flow Boiling Heat Transfer Characteristics of a Minichannel Up to Dryout Condition

2009 ◽  
Author(s):  
Rashid Ali ◽  
Bjo¨rn Palm ◽  
Mohammad H. Maqbool
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

In this paper the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.7mm and a uniformly heated length of 220mm. R134a was used as working fluid and experiments were performed at two different system pressures corresponding to saturation temperatures of 27 °C and 32 °C. Mass flux was varied from 50 kg/m2 s to 600 kg/m2 s and heat flux ranged from 2kW/m2 to 156kW/m2. The test section was heated directly using a DC power supply. The direct heating of the channel ensured uniform heating and heating was continued until dry out was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux while mass flux and vapour quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

Flow Boiling Heat Transfer Characteristics of a Minichannel up to Dryout Condition

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
Rashid Ali ◽  
Björn Palm ◽  
Mohammad H. Maqbool
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Working Fluid ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

In this paper, the experimental flow boiling heat transfer results of a minichannel are presented. A series of experiments was conducted to measure the heat transfer coefficients in a minichannel made of stainless steel (AISI 316) having an internal diameter of 1.70 mm and a uniformly heated length of 220 mm. R134a was used as a working fluid, and experiments were performed at two different system pressures corresponding to saturation temperatures of 27°C and 32°C. Mass flux was varied from 50 kg/m2 s to 600 kg/m2 s, and heat flux ranged from 2 kW/m2 to 156 kW/m2. The test section was heated directly using a dc power supply. The direct heating of the channel ensured uniform heating, which was continued until dryout was reached. The experimental results show that the heat transfer coefficient increases with imposed wall heat flux, while mass flux and vapor quality have no considerable effect. Increasing the system pressure slightly enhances the heat transfer coefficient. The heat transfer coefficient is reduced as dryout is reached. It is observed that the dryout phenomenon is accompanied with fluctuations and a larger standard deviation in outer wall temperatures.

scholarly journals Comparison between R134a and R1234ze(E) during Flow Boiling in Microfin Tubes

Fluids ◽  
2021 ◽  
Vol 6 (11) ◽  
pp. 417
Author(s):  
Andrea Lucchini ◽  
Igor M. Carraretto ◽  
Thanh N. Phan ◽  
Paola G. Pittoni ◽  
Luigi P. M. Colombo
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Fluid Dynamic ◽  
Saturation Temperature ◽  
Operating Conditions ◽  
Two Fluids ◽  
The Heat Transfer Coefficient

Environmental concerns are forcing the replacement of commonly used refrigerants, and finding new fluids is a top priority. Soon the R134a will be banned, and the hydro-fluoro-olefin (HFO) R1234ze(E) has been indicated as an alternative due to its smaller global warming potential (GWP) and shorter atmospheric lifetime. Nevertheless, for an optimal replacement, its thermo-fluid-dynamic characteristics have to be assessed. Flow boiling experiments (saturation temperature Tsat = 5 °C, mass flux G = 65 ÷ 222 kg·m−2·s−1, mean quality xm = 0.15 ÷ 0.95, quality changes ∆x = 0.06 ÷ 0.6) inside a microfin tube were performed to compare the pressure drop per unit length and the heat transfer coefficient provided by the two fluids. The results were benchmarked for some correlations. In commonly adopted operating conditions, the two fluids show a very similar behavior, while benchmark showed that some correlations are available to properly predict the pressure drop for both fluids. However, only one is satisfactory for the heat transfer coefficient. In conclusion, R1234ze(E) proved to be a suitable drop-in replacement for the R134a, whereas further efforts are recommended to refine and adapt the available predictive models.

scholarly journals Flow Boiling in a 1.1 mm Tube With R134A: Experimental Results and Comparison With Model

2007 ◽  
Author(s):  
D. Shiferaw ◽  
T. G. Karayiannis ◽  
D. B. R. Kenning
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Film Thickness ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Flow Boiling ◽  
Experimental Results ◽  
Vapour Quality ◽  
The Heat Transfer Coefficient

A detailed comparison of the three-zone evaporation model, proposed by Thome et al. (2004), with experimental heat transfer results of two stainless steel tubes of internal diameter 4.26 mm and 2.01 mm using R134a fluid was presented by Shiferaw et al. (2006). In the current paper the comparison is extended to flow boiling in a 1.1 mm tube using R134a as the working fluid. Other parameters were varied in the range: mass flux 100–600 kg/m2.s; heat flux 16–150 kW/m2 and pressure 6–12 bar. The experimental results demonstrate that the heat transfer coefficient increases with heat flux and system pressure, but does not change with vapour quality when the quality is less than about 50% for low heat and mass flux values. The effect of mass flux is observed to be insignificant. For vapour quality values greater than 50% and at high heat flux values, the heat transfer coefficient does not depend on heat flux and decreases with vapour quality. This could be caused by partial dryout. The three-zone evaporation model predicts the experimental results fairly well, especially at relatively low pressure. However, the partial dryout region is highly over-predicted by the model. The sensitivity of the performance of the model to the three optimized parameters (confined bubble frequency, initial film thickness and end film thickness) and some preliminary investigation relating the critical film thickness for dryout to measured tube roughness are also discussed.

Convective Boiling of R-22 in a Flat Extruded Aluminum Multi-Port Tube

2004 ◽  
Author(s):  
Nae-Hyun Kim ◽  
Young-Sup Sim ◽  
Chang-Keun Min
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Saturation Temperature ◽  
High Mass ◽  
High Heat Flux ◽  
Convective Boiling ◽  
The Heat Transfer Coefficient

Convective boiling heat transfer coefficients of R-22 were obtained in a flat extruded aluminum tube with Dh = 1.41 mm. The test range covered mass flux from 200 to 600 kg/m2 s, heat flux from 5 to 15 kW/m2 and saturation temperature from 5°C to 15°C. The heat transfer coefficient curve shows a decreasing trend after a certain quality (critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique ‘cross-over’ of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kandlikar correlations underpredict the low mass flux and overpredict the high mass flux data.

scholarly journals Experimental Investigation of Condensation Heat Transfer Characteristics of R-134a Vapor in Horizontal Heat Exchanger

2018 ◽  
Vol 26 (6) ◽  
pp. 16-31
Author(s):  
Ahmed Jasim Hamad ◽  
Rasha Abdulrazzak Jasim
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Saturation Temperature ◽  
Vapor Quality ◽  
Test Conditions ◽  
R 134A ◽  
The Heat Transfer Coefficient

An experimental investigation of refrigerant R-134a two-phase flow condensation heat transfer coefficient and pressure drop in condenser tube section of refrigeration system under different operating conditions is presented. The experimental and theoretical investigations are based on test conditions in range of 10 -17 kW/m2 for heat flux, 42-63 kg/m2s for mass flux, vapor quality 1-0.03 and saturation temperature 44 to 49˚C. The experimental tests are conducted on test rig supplied with a test section to simulate the water cooled double pipe heat exchanger, which is designed and constructed in the present work. “The experimental results have revealed that, the heat flux and mass flux have significant impacts on the heat transfer coefficient. “The heat transfer coefficient was increased with increase in heat flux and mass flux at prescribed test conditions, where the enhancement in heat transfer coefficient was about 47% and 14% for relatively higher heat flux and mass flux, respectively. “The enhancement in the heat transfer coefficient was about 51% for relatively lower saturation temperature 45.97˚C and 43% for higher vapor quality 0.88 compared to other values at constant test conditions. “The pressure drop was higher in the range of 12% and 49% for relatively higher mass flux and heat flux respectively. “The present work results have validated by comparison with predictive models and with similar research work results and the comparison has revealed  an acceptable agreement.

Flow Boiling of Refrigerants Inside a Single Circular Minichannel

2008 ◽  
Author(s):  
Stefano Bortolin ◽  
Alberto Cavallini ◽  
Davide Del Col ◽  
Marko Matkovic ◽  
Luisa Rossetto
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Test Tube ◽  
Inlet Temperature ◽  
Transfer Coefficients ◽  
The Heat Transfer Coefficient

The present paper reports the heat transfer coefficients measured during flow boiling of HFC-32 and HFC-134a in a 0.96 mm diameter single circular channel. The test runs have been performed during vaporization at around 30°C saturation temperature, correspondent to 19.3 bar for R32 and 7.7 bar for R134a. As a peculiar characteristic of the present technique, the heat transfer coefficient is not measured by imposing the heat flux; instead, the boiling process is governed by controlling the inlet temperature of the heating secondary fluid. The quality of the inner surface of the test tube has been measured to check the influence of surface roughness on the heat transfer coefficient. The flow boiling data taken in the present test section is presented and discussed, with particular regard to the effect of heat flux, mass velocity, vapor quality and fluid properties.

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