scholarly journals Investigation of R134a Flow Boiling Heat Transfer and Pressure Drop in the Evaporator Test Section of Refrigeration System

2018 ◽  
Vol 25 (1) ◽  
pp. 13-31
Author(s):  
Ahmed J. Hamad ◽  
Zahraa Kareem Yasser
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Operating Conditions ◽  
Refrigeration System ◽  
Test Conditions

This paper presents an experimental and theoretical analysis to investigate the two-phase flow boiling heat transfer coefficient and pressure drop of the refrigerant R-134a in the evaporator test section of the refrigeration system under different operating conditions. The test conditions considered are, for heat flux (13.7-36.6) kW/m2, mass flux (52-105) kg/m2.s, vapor quality (0.2-1) and saturation temperature (-15 to -3.7) ˚C. Experiments were carried out using a test rig for a 310W capacity refrigeration system, which is designed and constructed in the current work. Investigating of the experimental results has revealed that, the enhancement in local heat transfer coefficient for relatively higher heat flux 36.6 kW/m2 was about 38% compared to 13.7 kW/m2 at constant operating conditions. The enhancement in heat transfer coefficient was about 57% when the mass flux increased from 52 kg/m2.s to 105 kg/m2.s at constant test conditions. The enhancement in the heat transfer coefficient was about 64% when the saturation temperature increased from -8 to -3.7 at fixed refrigerant mass velocity and heat flux. The effect of mass velocity on pressure drop was relatively higher by about 27% than that for heat flux at specified test conditions. The comparison between the experimental and theoretical results has shown an acceptable agreement with an average deviation of 21%.  

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.

Experimental and Numerical Analyses of R134a Flow Boiling Heat Transfer Characteristics in an Evaporator Tube of Refrigeration System

2019 ◽  
Vol 27 (03) ◽  
pp. 1950024
Author(s):  
Zahraa Kareem Yasser ◽  
Ahmed J. Hamad
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Refrigeration System ◽  
Heat Transfer Characteristics

The heat transfer characteristics of R134a flow boiling in a horizontal tube of an evaporator section for a refrigeration system of 310-W capacity are investigated experimentally and numerically. The experimental work was conducted using an evaporator tube test section of inner diameter 5.8[Formula: see text]mm and length 600[Formula: see text]mm. The ranges of investigated experimental data for heat flux, mass flux, saturation temperature and vapor quality were 13.8–36.6[Formula: see text]kW/m2, 52–105[Formula: see text]kg/m2[Formula: see text][Formula: see text][Formula: see text]s, [Formula: see text]–[Formula: see text]C and 0.2–1, respectively. Numerical analysis was based on two-phase flow turbulent model and this model was solved using the Ansys-18 code. The results showed that the effects of heat flux, mass velocity and saturation temperature on local heat transfer coefficient and pressure drop were greater compared to that of the refrigerant vapor quality. The enhancements in local heat transfer coefficient due to the increase in heat flux, mass and saturation temperature were 38%, 57% and 64%, respectively, within the prescribed test conditions. The influence of mass flux variation on pressure drop along the evaporator channel was higher in the range of 27% compared to the heat flux effect. The average deviations between experimental and numerical results of heat transfer coefficient and pressure gradient were 14% and 17%, respectively, while the same between the experimental and predicted results were 16% and 33%, respectively.

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.

Novel Arrangement of Rough Tubes for Heat Flux Improvement

2012 ◽  
Vol 326-328 ◽  
pp. 81-86
Author(s):  
Farshad Farahbod ◽  
Sara Farahmand ◽  
Farzaneh Farahbod
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Crude Oil ◽  
Transfer Coefficient ◽  
Three Dimensional ◽  
Operating Conditions ◽  
Set Up ◽  
The Heat Transfer Coefficient

The objective of the research is to represent a novel arrangement of conical three dimensional rough tubes (FS3D) for heat transfer coefficient enhancement. Experiments were performed with 316 stainless steel tubes of FS3D roughness and hot crude oil was circulated in constant heat flux condition in the related set up. The pressure drop is measured in this set up and compared with the pressure drop in a smooth tube with the same operating conditions. The heat transfer coefficient is one of essential parameters for design of heat transfer equipments and in this experimental work this is investigated for an Iranian crude oil in the FS3D rough tube. The heat transfer coefficient in FS3D rough tubes is higher than in other commercial enhanced tubes. FS3D rough tubes improve the performance of heat transfer equipments and also optimize the size of the mentioned devices. Consequently this type, the FS3D rough tube, is advantageous in energy and cost saving.

Heat Transfer and Pressure Drop of CO2 Flow Boiling in Microchannels

2000 ◽  
Author(s):  
Yuan Zhao ◽  
Majid Molki ◽  
Michael M. Ohadi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Flow Boiling ◽  
Dominant Factor ◽  
Vapor Quality ◽  
Co2 Flow

Abstract An experimental investigation was performed to study the flow boiling heat transfer of CO2 in microchannels. Tests were conducted in a horizontal triangular microchannel with the hydraulic diameter of 0.86 mm. Heat to the test section was provided by direct electrical heating. Experiments were conducted with CO2 at saturation temperatures of 273 to 293 K, mass fluxes of 100 to 820 kg/m2s, heat fluxes of 3 to 23 kW/m2, and qualities of 20% to 85%. It was demonstrated that heat flux had an enhancing effect on the heat transfer coefficient, while mass flux had a negligible effect. Nucleate boiling mechanism is found to be the dominant factor for CO2 flow boiling in microchannels. Heat transfer coefficient degraded quickly at high vapor quality region (0.6–0.7), which is possibly due to flow mal-distribution. Pressure drop increases slightly with vapor quality and/or heat flux. Mass flux has a strong increasing effect on pressure drop.

scholarly journals Peripheral Heat Transfer Coefficient during Flow Boiling: Comparison between 2-D and 1-D Data Reduction and Discussion about Their Applicability

Energies ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 4483 ◽  
Author(s):  
Rita Mastrullo ◽  
Alfonso William Mauro
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Data Reduction ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Operating Conditions ◽  
Phase Flow ◽  
Two Phase

This paper presents a critical analysis of possible data reduction procedures for the evaluation of local heat transfer coefficient during flow boiling experiments. The benchmark method using one-dimensional (1-D) heat transfer in a heated tube was compared to a new data reduction method in which both radial and circumferential contributions to the conductive heat transfer inside a metal tube are considered. Using published experimental flow boiling data, the circumferential profiles of the wall superheat, inner wall heat flux, and heat transfer coefficients were independently calculated with the two data reduction procedures. The differences between the two methods were then examined according to the different heat transfer behavior observed (symmetric or asymmetric), which in turn was related to the two-phase flow regimes occurring in a channel during evaporation. A statistical analysis using the mean absolute percentage error (MAPE) index was then performed for a database of 417 collected flow boiling data taken under different operating conditions in terms of working fluid, saturation temperature, mass velocity, vapor quality, and imposed heat flux. Results showed that the maximum deviations between the two methods could reach up to 130% in the case of asymmetric heat transfer. Finally, the possible uses of the two data reduction methods are discussed, pointing out that the two-dimensional (2-D) model is the most reliable method to be employed in the case of high-level modeling of two-phase flow or advanced design of heat exchangers and heat spreader systems.

Flow Boiling Heat Transfer in a Silicon Microchannel Heat Sink Using Liquid Crystal Thermography

2008 ◽  
Author(s):  
Ayman Megahed ◽  
Ibrahim Hassan ◽  
Tariq Ahmad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Microchannel Heat Sink

The present study focuses on the experimental investigation of boiling heat transfer characteristics and pressure drop in a silicon microchannel heat sink. The microchannel heat sink consists of a rectangular silicon chip in which 45 rectangular microchannels were chemically etched with a depth of 295 μm, width of 254 μm, and a length of 16 mm. Un-encapsulated Thermochromic liquid Crystals (TLC) are used in the present work to enable nonintrusive and high spatial resolution temperature measurements. This measuring technique is used to provide accurate full and local surface-temperature and heat transfer coefficient measurements. Experiments are carried out for mass velocities ranging between 290 to 457 kg/m2.s and heat fluxes from 6.04 to 13.06 W/cm2 using FC-72 as the working fluid. Experimental results show that the pressure drop increases as the exit quality and the flow rate increase. High values of heat transfer coefficient can be obtained at low exit quality (xe < 0.2). However, the heat transfer coefficient decreases sharply and remains almost constant as the quality increases for an exit quality higher than 0.2.

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