Heat Transfer During Condensation of a Low-GWP Refrigerant on an Enhanced Cylindrical Surface

2017 ◽  
Author(s):  
Tailian Chen
Keyword(s):  
Heat Transfer ◽  
Smooth Surface ◽  
Cooling Water ◽  
Saturation Temperature ◽  
Condensation Heat Transfer ◽  
Condensation Process ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Cylindrical Tubes ◽  
Enhanced Tube

In this work, heat transfer coefficients during condensation of an environment-friendly refrigerant R-1233zd(e) on the outside surface of two cylindrical tubes are individually measured. The cooling water flows inside the tubes and provides cooling to the vapor refrigerant. One tube is a plain smooth tube (smooth both inside and outside) while the other tube is an enhanced tube, with the inside surface having 2D helical ridges and the outside surface having 3D extruded fins. The tests were conducted at the saturation temperature 36.1 °C, a typical temperature in chiller condensers. The results show the overall heat transfer coefficients of the enhanced tube are approximately 8.4 times higher as a result of the heat transfer enhancement on both sides. The condensation heat transfer degrades with an increase in the degree of subcooling, and the trend of degradation is the nearly the same for both the smooth and the enhanced tube, both is smaller than that in the Nusselt correlation. Compared with condensation on the smooth surface, the condensation heat transfer from the enhanced surface is enhanced approximately 10.8 times higher than that on the smooth surface. In addition to enlarged heat transfer area of the extruded fins, the enhancement in the condensation heat transfer is partly attributed to a better condensate draining mechanism of the 3D-structured fins where surface tension plays an important role. Further analysis reveals that heat transfer during the condensation process on the 3D low-fin surface follows the Nusselt correlation with a multiplier that accounts for the enhancement in heat transfer, which is desirably simple approach to modeling condensation heat transfer on the complex 3D enhanced surfaces. This work can lead to more insights into the physical mechanisms during the complex condensation process.

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.

Condensation Heat Transfer and Pressure Drop of R-134a Flowing in Annular Helical Pipes at Different Orientations

2003 ◽  
Author(s):  
B. Yu ◽  
C. X. Lin ◽  
M. A. Ebadian ◽  
R. C. Prattipati
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Cooling Water ◽  
Saturation Temperature ◽  
Condensation Heat Transfer ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Cooling Water Temperature ◽  
Helical Pipe ◽  
R 134A

This paper presents an experimental investigation of condensation heat transfer and pressure drop characteristics of refrigerant R-134a flowing through an annular helicoidal passage with the hydraulic diameter of 8.5 mm. The angles of helix axis are oriented at 0, 45, 90 degrees to gravity. The overall and refrigerant-side heat transfer coefficients and pressure drops are experimentally determined at saturation temperature 35°C, refrigerant mass flux 35–180 kg/s·m2, and cooling water temperature 27°C. The results show that orientation has significant influence on the thermal and hydraulic behaviors of the helical pipe. The results can be employed for reference in the effective design of annular helicoidal heat exchangers with R-134a as the working fluid.

External condensation heat transfer coefficients of R22 alternative refrigerants on enhanced tubes at three saturation temperatures

2008 ◽  
Vol 222 (6) ◽  
pp. 987-994 ◽  
Author(s):  
K-J Park ◽  
D Jung
Keyword(s):  
Heat Transfer ◽  
Saturation Temperature ◽  
Prediction Equation ◽  
Condensation Heat Transfer ◽  
Alternative Refrigerants ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Azeotropic Mixtures ◽  
Plain Tube ◽  
Fin Tube

In this study, external condensation heat transfer coefficients (HTCs) of R22, R410A, R407C, and R134a are measured on a 1024 fins per meter (26 fins per inch) low fin tube and Turbo-C tube at saturation temperatures of 30, 39, and 50 °C with wall subcooling of 3–8 °C. Test results show that condensation HTCs of all refrigerants decrease as the saturation temperature increases from 30 to 50 °C. This trend is due to the degradation of thermophysical properties of the liquid phase with an increase in saturation temperature. For the low fin tube data, Beatty and Katz's prediction equation showed a reasonably good agreement for all fluids with less than 20 per cent deviation. The performance of Turbo-C tube is better than that of the low fin tube for R22, R410A, and R134a due to the efficient removal of the condensate. For Turbo-C tube, HTCs of R407C were much lower than those of the other three fluids due to a unique condensation phenomenon associated with non-azeotropic mixtures at vapour—liquid interface. The average heat transfer enhancement ratios for the low fin tube and Turbo-C tube against the plain tube are 4.0–5.5 and 3.0–8.1, respectively, for all refrigerants tested.

Effect of Polymer Coating on Vapor Condensation Heat Transfer

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Mete Budakli ◽  
Thamer Khalif Salem ◽  
Mehmet Arik ◽  
Barca Donmez ◽  
Yusuf Menceloglu
Keyword(s):  
Heat Transfer ◽  
Saturation Pressure ◽  
Copper Substrate ◽  
Copper Surface ◽  
Vapor Condensation ◽  
Condensation Heat Transfer ◽  
Condensation Process ◽  
Limiting Factor ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Abstract Condensation heat transfer coefficients (HTCs) are rather low compared to thin film evaporation. Therefore, it can be a limiting factor for designing heat transfer equipment. In this work, heat transfer characteristics of water vapor condensation phenomena were experimentally studied on a vertically aligned smooth copper substrate for a range of pressures and temperatures for two different liquid wettability conditions. The heat transfer performance is dominated by the phase change process at the solid–vapor interface along with the liquid formation mechanism. Compared to heat transfer results measured at an untreated copper surface, heat transport is augmented with a thin layer of perfluoro-silane coating over the same substrate. In this work, the effect of saturation pressure on the condensation process at both surfaces has been investigated by analyzing heat transfer coefficients. The results obtained experimentally show an increase in contact angle (CA) with the surface coating. A heat transfer augmentation of about 26% over uncoated surfaces was obtained and surfaces did not show any degradation after 40 h of operation. Finally, current results are compared with heat transfer values reported in open literature.

Water-Heated Pool Boiling of Different Refrigerants on the Outside Surface of a Horizontal Smooth Tube

2011 ◽  
Vol 134 (2) ◽  
Author(s):  
Tailian Chen
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Saturation Temperature ◽  
The Other ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Water Flows ◽  
Constant Multiplier ◽  
Cylindrical Tubes

Pool boiling heat transfer has been extensively studied over decades, but the effect of boundary heating conditions on boiling received little attention. In this work, heat transfer coefficients during pool boiling of five different refrigerants (R123, R245fa, R236fa, R134a, and R22) on the outside surface of a smooth copper tube were measured at the saturation temperature of 6.7 °C; water flows inside the tube and provides heat to the refrigerants to boil (thus, water-heated boiling). Measurements showed that the refrigerant of a higher vapor pressure has a higher heat transfer coefficient, with the exception that R22 performs nearly the same as R134a. A correlation previously developed for electrically-heated pool boiling on cylindrical tubes underpredicts by 30%–46% the heat transfer coefficients during water-heated boiling of the five refrigerants. Among the pool boiling correlations reviewed in this work, the Cooper correlation (for pool boiling on cylindrical tubes) predicts the boiling heat transfer coefficients of R22 and R245fa reasonably well (within ±8.5%), but not as well those of the other three refrigerants (underpredicts by nearly 30% for R134a and R236fa and overpredicts by nearly 40% for R123). It is found that the predicted boiling heat transfer coefficients of the five refrigerants by the modified Gorenflo correlation (simply adding a constant multiplier of 1.47 to the Gorenflo correlation) are in excellent agreement with their respective measurements.

Experimental Investigation of Condensation Heat Transfer in Annular Helicoidal Pipes at Different Orientations

Volume 3 ◽  
2004 ◽  
Author(s):  
H. L. Mo ◽  
R. Prattipati ◽  
C. X. Lin ◽  
M. A. Ebadian
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Cooling Water ◽  
Saturation Temperature ◽  
Experimental Investigations ◽  
Percentage Increase ◽  
Transfer Coefficients ◽  
Cooling Water Temperature ◽  
Heat Transfer Coefficients ◽  
Mass Flow Rates

Experimental investigations were conducted on condensation of R134a in annular helicoidal pipes with three orientations, 0°, 45° and 90°. The experimental results indicated that the refrigerant heat transfer coefficients increased with the increase of cooling water temperature, mass flow rates of refrigerant and cooling water, and decreased with the increase of saturation temperature of R134a. When the orientation increased from 0° to 90°, the refrigerant Nusselt number increased around 11% at refrigerant Reynolds number of 80, and around 16% at 200, the percentage increase of refrigerant Nusselt number from 0° to 45° accounted for more than two times of that from 45° to 90°. The performance of annular helicoidal pipe was evaluated by comparing with equivalent smooth straight pipe and identical helicoidal pipe.

Water-Heating Pool Boiling of Different Refrigerants on the Outside Surface of a Horizontal Smooth Tube

2011 ◽  
Author(s):  
Tailian Chen
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Saturation Temperature ◽  
Electric Heating ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Water Flows ◽  
Constant Multiplier ◽  
Cylindrical Tubes

Heat transfer coefficients during pool boiling of five different refrigerants (R123, R245fa, R236fa, R134a, and R22) on the outside surface of a smooth copper tube were measured at the saturation temperature 6.7°C. Water flows inside the tube and provides heat to the refrigerants to boil. Measurements showed that the refrigerant of a higher vapor pressure has a higher heat transfer coefficient with the exception that R22 performs nearly the same as R134a. Compared with the predictions by the correlation developed from the data of electric-heating pool boiling on cylindrical tubes, the boiling heat transfer coefficients of the five refrigerants measured in this work are 30–46% higher. Among the pool boiling correlations reviewed in this work, the Cooper correlation (for pool boiling on cylindrical tubes) predicts the boiling heat transfer coefficients of R22 and R245fa reasonably well (within ±8.5%), but not as well for the other three refrigerants (R123, R236fa, and R134a). It is found that the predicted boiling heat transfer coefficients of the five refrigerants by the modified Gorenflo correlation (simply adding a constant multiplier of 1.47 to the correlation) are in excellent agreement with their respective measurements.

Experimental Apparatus for the Determination of Condensation Heat Transfer Coefficient for R134a and R600a Flowing Inside Vertical and Horizontal Tubes Respectively

2009 ◽  
Author(s):  
Ahmet Selim Dalkilic¸ ◽  
O¨zden Ag˘ra
Keyword(s):  
Heat Transfer ◽  
Test Section ◽  
Cooling Water ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Mass Fluxes ◽  
Experimental Apparatus ◽  
Vertical Test

Determination of condensation heat transfer coefficients for HFC-134a in a 7 mm i.d. vertical smooth copper tube and R600a in a 4 mm i.d. horizontal smooth copper tube are experimentally investigated. The test sections are 1 m long horizontal and 0.5 m long vertical counter flow tube-in-tube heat exchangers with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The experiments are performed at average qualities ranging between 0.1–0.99 for the horizontal test section and 0.67–0.99 for the vertical test section. The mass fluxes are ranging between 50–120 kg m−2s−1 and saturation temperatures are between 30–43 °C for the horizontal test section, the mass fluxes are around 29 kg m−2s−1 and saturation temperatures are between 30–36 °C for the vertical test section. The experimental apparatus are designed to capable of changing the different operating parameters such as mass flow rate and condensation temperature of refrigerant, cooling water temperature, and mass flow rate of cooling water etc and investigate their effect on heat transfer coefficients and pressure drops. The ex-proof diaphragm pump for R600a and the gear pump for R134a are used to circulate the refrigerant in these systems. The detailed description of design and development of the test apparatus, control devices, instrumentation, and the experimental procedure are reported and the study of experimental setups from the available literature survey with the existing ones are compared in this paper. The condensation heat transfer coefficients are obtained for two different test sections with various experimental conditions and compared with some well-known correlations in the literature.

Measurement and Modeling of Condensation Heat Transfer Coefficients in Circular Microchannels

2006 ◽  
Vol 128 (10) ◽  
pp. 1050-1059 ◽  
Author(s):  
Todd M. Bandhauer ◽  
Akhil Agarwal ◽  
Srinivas Garimella
Keyword(s):  
Heat Transfer ◽  
Flow Rate ◽  
Heat Transfer Model ◽  
Condensation Heat Transfer ◽  
Low Flow ◽  
Transfer Model ◽  
Shear Stresses ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Circular Microchannels

A model for predicting heat transfer during condensation of refrigerant R134a in horizontal microchannels is presented. The thermal amplification technique is used to measure condensation heat transfer coefficients accurately over small increments of refrigerant quality across the vapor-liquid dome (0<x<1). A combination of a high flow rate closed loop primary coolant and a low flow rate open loop secondary coolant ensures the accurate measurement of the small heat duties in these microchannels and the deduction of condensation heat transfer coefficients from measured UA values. Measurements were conducted for three circular microchannels (0.506<Dh<1.524mm) over the mass flux range 150<G<750kg∕m2s. Results from previous work by the authors on condensation flow mechanisms in microchannel geometries were used to interpret the results based on the applicable flow regimes. The heat transfer model is based on the approach originally developed by Traviss, D. P., Rohsenow, W. M., and Baron, A. B., 1973, “Forced-Convection Condensation Inside Tubes: A Heat Transfer Equation For Condenser Design,” ASHRAE Trans., 79(1), pp. 157–165 and Moser, K. W., Webb, R. L., and Na, B., 1998, “A New Equivalent Reynolds Number Model for Condensation in Smooth Tubes,” ASME, J. Heat Transfer, 120(2), pp. 410–417. The multiple-flow-regime model of Garimella, S., Agarwal, A., and Killion, J. D., 2005, “Condensation Pressure Drop in Circular Microchannels,” Heat Transfer Eng., 26(3), pp. 1–8 for predicting condensation pressure drops in microchannels is used to predict the pertinent interfacial shear stresses required in this heat transfer model. The resulting heat transfer model predicts 86% of the data within ±20%.

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