Condensing Heat Transfer Coefficients for R134a at Different Saturation Temperatures in Inclined Tubes

2013 ◽  
Author(s):  
Adekunle O. Adelaja ◽  
Jaco Dirker ◽  
Josua P. Meyer
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Inclination Angle ◽  
Saturation Temperature ◽  
Flow Distribution ◽  
Transfer Coefficients ◽  
Mass Fluxes ◽  
Inclination Angles ◽  
Condensing Heat Transfer

This paper presents the effects of saturation temperature and inclination angle on convective heat transfer during condensation of R134a in an inclined smooth copper tube of inner diameter of 8.38 mm. Experiments were conducted for inclination angles ranging from −90° (vertical downward) to +90° (vertical upward) for mass fluxes between 100 kg/m2s and 400 kg/m2s and vapour qualities between 0.1 and 0.9 for saturation temperatures ranging between 30 °C and 50 °C. The results show that saturation temperature and inclination angles strongly influence the heat transfer coefficient. With respect to saturation temperature, an increase in saturation temperature generally leads to a decrease in heat transfer coefficient irrespective of the inclination angle. The effect of inclination angle was found to be more pronounced at mass fluxes of 100 kg/m2s and 200 kg/m2s for the range of vapour qualities considered. Within the region of influence of inclination there is an optimum angle which is between 15° and −30° (downward flow). The inclination effect corresponds to the predominance of the effect of gravity on the flow distribution.

Experimental Investigation of Condensation Heat Transfer and Adiabatic Pressure Drop Characteristics Inside a Microfin and Smooth Tube

2017 ◽  
Vol 25 (03) ◽  
pp. 1750027 ◽  
Author(s):  
M. Mostaqur Rahman ◽  
Keishi Kariya ◽  
Akio Miyara
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Saturation Temperature ◽  
Condensation Heat Transfer ◽  
Vapor Quality ◽  
Transfer Coefficients ◽  
Frictional Pressure Drop

Experiments on condensation heat transfer and adiabatic pressure drop characteristics of R134a were performed inside smooth and microfin horizontal tubes. The tests were conducted in the mass flux range of 50[Formula: see text]kg/m2s to 200[Formula: see text]kg/m2s, vapor quality range of 0 to 1 and saturation temperature range of 20[Formula: see text]C to 35[Formula: see text]C. The effects of mass velocity, vapor quality, saturation temperature, and microfin on the condensation heat transfer and frictional pressure drop were analyzed. It was discovered that the local heat transfer coefficients and frictional pressure drop increases with increasing mass flux and vapor quality and decreasing with increasing saturation temperature. Higher heat transfer coefficient and frictional pressure drop in microfin tube were observed. The present experimental data were compared with the existing well-known condensation heat transfer and frictional pressure drop models available in the open literature. The condensation heat transfer coefficient and frictional pressure drop of R134a in horizontal microfin tube was predicted within an acceptable range by the existing correlation.

An Experimental Investigation of Condensation Heat Transfer Coefficient of R-410A in Horizontal Circular Tubes

2016 ◽  
Vol 819 ◽  
pp. 94-100
Author(s):  
Pham Quang Vu ◽  
Nguyen Ba Chien ◽  
Oh Jong Taek
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Saturation Temperature ◽  
Condensation Heat Transfer ◽  
Good Prediction ◽  
Two Phase ◽  
Circular Tubes ◽  
Mass Fluxes ◽  
Inner Diameter

Condensation heat transfer has been evaluated experimentally on the tube side of three different circular tubes with inner diameter of 6.2, 7.5 and 9.2mm, respectively. Two-phase fluid flow conditions include mass fluxes from 200 to 320kg/m2s, qualities between 0.1 to 0.9, and heat flus range of 5 to 20kW/m2 at a fixed saturation temperature of 48°C. Results showed that the average heat transfer coefficient increased with the increase of vapor quality, mass flux and heat flux, but decreased with inner diameter. The experiment results are compared with the existing heat transfer coefficient correlations, and a new correlation is developed with good prediction.

Visualization Study of Steam Condensation in Rectangular Channel of Multichannel Cylinder Dryer

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Yan Yan ◽  
Dong Jixian ◽  
Tang Wei ◽  
Feng Shiyu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Regime ◽  
Mass Flux ◽  
Rectangular Channel ◽  
Steam Condensation ◽  
Transfer Coefficients ◽  
Steam Quality ◽  
Condensing Heat Transfer

The phenomenon of steam condensation occurring on one surface in a rectangular horizontal channel was experimentally studied. The experiment was conducted using a visualization method with a steam quality of 0.1–0.9 and mass flux of 20–50 kg/m2 s. Four flow patterns (annular, wave, slug, and plug) were observed, and the effects of quality and mass flux on the condensing heat transfer were analyzed. The mass flux and steam quality primarily affect the condensing heat transfer coefficient in the shear-dominated flow regime. The condensing heat transfer coefficients are nearly constant only in a certain range of steam quality. This result is disparate from what has been reported in previous literatures. It was also observed that the condensing heat transfer coefficient rises with an increase in the quality. Two flow regime maps were employed to predict the flow regimes observed in this study. The result reveals that the Tandon flow regime map agrees quite well with the experimental results.

Heat Transfer of Impacting Water Mist on High Temperature Metal Surfaces

2003 ◽  
Vol 125 (1) ◽  
pp. 70-74 ◽  
Author(s):  
N. Sozbir ◽  
Y. W. Chang ◽  
S. C. Yao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Flux ◽  
Water Mist ◽  
Transfer Coefficients ◽  
Air Velocity ◽  
Liquid Mass ◽  
Air Jet ◽  
Mass Fluxes

Experimental studies were conducted to reveal the heat transfer mechanism of impacting water mist on high temperature metal surfaces. Local heat transfer coefficients were measured in the film-boiling regime at various air velocities and liquid mass fluxes. The test conditions of water mist cover the variations of air velocity from 0 to 50.3 m/s, liquid mass flux from 0 to 7.67 kg/m2s, and surface temperature of stainless steel between 525°C and 500°C. Radial heat transfer distributions were measured at different liquid mass fluxes. The tests revealed that the radial variation of heat transfer coefficients of water mist has a similar trend to the air jet cooling. At the stagnation point, heat transfer coefficient increases with both the air velocity and the liquid mass flux. The convective air heat transfer is consistent with the published correlation in the literature. The heat transfer contribution due to the presence of water increases almost linearly with the liquid mass flux. The total heat transfer coefficient can be established as two separable effects, which is the summation of the heat transfer coefficient of air and of liquid mass flux, respectively. This study shows that with a small amount of water added in the impacting air jet, the heat transfer is dramatically increased. The Leidenfrost temperature under water mist cooling was also measured. The Leidenfrost temperature increased with both the air velocity and the liquid mass flux.

Condensation of Different Refrigerants on the Outside Surface of Smooth Cylindrical Tubes

2017 ◽  
Author(s):  
Tailian Chen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Saturation Temperature ◽  
Cylindrical Tube ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Cylindrical Tubes ◽  
Condensation Heat Transfer Coefficient

The Nusselt model of condensation provides the fundamental theory in predicting the heat transfer during the condensation process. Widely verified, its significance lies in the fact that it has been used as the baseline in evaluating the heat transfer enhancement of the condensation and often used as the basis of validating the test rig for multiphase heat transfer. The aim of this work is to re-examine the correlation for condensation on smooth cylindrical tubes. The heat transfer coefficients during condensation of four different refrigerants R123, R245fa, R134a, and R22 on the outside surface of a smooth cylindrical tube were individually measured at large degrees of subcooling, up to 25 K. The experiments were conducted at a fixed saturation temperature of 36.1 °C. Measurements showed that, for each refrigerant, the condensation heat transfer coefficient decreases with increasing degree of subcooling. At a given degree of subcooling, a higher-pressure refrigerant corresponds to a higher condensation heat transfer coefficient, with the exception that the condensation heat transfer coefficients of R134a and R245fa are nearly the same in spite of much higher pressure of the former. The predictions from the Nusselt theory for condensation heat transfer over cylinder tubes match very well with the measurements, where the predictions are 3–9% lower than the measurements for all refrigerants within the range of degree of subcooling considered in this work. A modified constant in the Nusselt number provides more accurate prediction of condensation on smooth cylindrical tubes.

Forced Convective Boiling of Nonazeotropic Refrigerant Mixtures Inside Tubes

1993 ◽  
Vol 115 (3) ◽  
pp. 680-689 ◽  
Author(s):  
K. Murata ◽  
K. Hashizume
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Vapor Phase ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Transfer Coefficients ◽  
Convective Boiling ◽  
Transfer Resistance ◽  
The Heat Transfer Coefficient

Forced convective boiling of nonazeotropic mixtures inside horizontal tubes was investigated experimentally. The heat transfer coefficient and pressure drop of pure refrigerant R123 and a mixture of R123 and R134a were measured in both a smooth tube and a spirally grooved tube. The heat transfer coefficient for the mixture was found to be lower than that for an equivalent pure refrigerant with the same phsycial properties, not only in the boiling-dominant region but also in the convection-dominant region. On the basis of this experiment, correlations were proposed for heat transfer coefficients in smooth and grooved tubes; the reduction in heat transfer coefficient for the mixture is attributed to the mixture effects on nucleate boiling and to the heat transfer resistance in the vapor phase. This heat transfer resistance is caused by the sensible heating of the vapor phase accompanying the rise in saturation temperature. These correlations are able to predict the heat transfer data within ± 20 percent

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.

Heat Transfer Coefficient and Pressure Drop of R410A During Evaporation Inside Aluminum Multiport Minichannels

2015 ◽  
Author(s):  
Chien Nguyen ◽  
Vu Pham ◽  
Choi Kwang-Il ◽  
Oh Jong-Taek
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
High Efficiency ◽  
Saturation Temperature ◽  
Heat Fluxes ◽  
Good Prediction ◽  
Two Phase ◽  
Mass Fluxes

Micro and minichannel are progressively used in heat exchangers nowadays. The application of these heat exchanger types in refrigeration and air conditioning fields show various advantages such as high efficiency, low air side pressure, reducing refrigerant charge and the compactness size. The aim of this study is to investigate the two phase flow heat transfer coefficient and pressure drop of R410A during evaporation. The experimental data were observed in aluminum channel with the hydraulic diameters of 1.14 and 1.16 mm, mass fluxes of 50–150 kW/m2s heat fluxes of 3–6 kW/m2, saturation temperature of 6°C and vapor quality from 0.1 to 0.9. The effect of mass flux, heat flux, and hydraulic diameter on heat transfer coefficient and pressure drop were analyzed. The database was compared with numerous well-known heat transfer coefficient and pressure drop correlations. Finally, a modify heat transfer coefficient correlation was developed that showed a good prediction against the database.

scholarly journals COMPARATIVE ANALYSES OF THE THERMAL PERFORMANCE OF REFRIGERANTS R134A, R245fa, R407C AND R600a DURING FLOW BOILING IN A MICROCHANNELS HEAT SINK

2018 ◽  
Vol 17 (2) ◽  
pp. 57
Author(s):  
H. L. S. L. Leão ◽  
D. B. Marchetto ◽  
G. Ribatski
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

A comparative study of the performance of of refrigerants R134a, R407C, R245fa and R600a during flow boiling was performed for a 123x494 µm2 heat sink composed of 50 parallel rectangular microchannels. Heat transfer experimental results for heat fluxes up to 310 kW/m2, mass velocities from 300 to 800 kg/(m2 s), liquid subcoolings of 5 and 10 °C and saturation temperature close to 30 ºC were obtained. Global heat transfer coefficients (footprint) up to 10 kW/(m2 °C) were found. The liquid superheating necessary for the onset of nucleate boiling (ONB) was also characterized, and the fluids R245fa and R407C presented the highest and lowest, respectively, superheating to trigger the boiling process. Moreover, for a fixed averaged vapor quality, the average effective heat transfer coefficient increases with increasing mass velocity and liquid subcooling. The refrigerants R600a and R407C presented the highest and the lowest heat transfer coefficients, respectively. Five heat transfer predictive methods from literature provided accurate predictions of the data for R134a, R245fa and R600a, capturing most of the data trends. No one method provided accurate predictions of the heat transfer coefficient data of R407C.

Streamline Modeling of Manifold Microchannels in Thin Film Evaporation

2013 ◽  
Author(s):  
Raphael Mandel ◽  
Amir Shooshtari ◽  
Serguei Dessiatoun ◽  
Michael Ohadi
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Wall Heat Transfer ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Mass Fluxes ◽  
Flow Length

Manifold microchannels utilize a system of manifolds to divide long microchannels into an array of parallel ones, resulting in reduced flow length and more localized liquid feeding. Reducing flow length is desirable because it enables the simultaneous enhancement of heat transfer rate and reduction of pressure drop. Furthermore, localized feeding reduces potential for localized dryout, increasing the operational heat flux. Because of the failure of the available conventional heat transfer correlations to predict the thermal performance of manifold microchannels operating in two phase mode, a “streamline” model was created. The heat transfer surface area was divided into parallel, non-interacting streamlines, and the quality, void fraction, film thickness, heat transfer coefficient, heat flux, and pressure drop was calculated sequentially along the streamline. The mass flow rate through each streamline was adjusted in order to obtain the specified pressure drop, and the value of this pressure drop was adjusted in order to obtain the desired microchannel mass flux. Finally, the average wall heat transfer coefficient was calculated, and temperature profile in the fin was adjusted to correspond with the analytical 1-D temperature distribution of a thin fin with an average wall heat transfer coefficient and specified base superheat. The average wall heat transfer coefficients predicted by the model was then compared to the available experimental data with sufficiently good agreement with a wide variety of geometries and working fluids at low mass fluxes.

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