Condensation heat transfer coefficients for R22 and R407C in gravity driven flow regime within a smooth horizontal tube

2003 ◽  
Vol 26 (4) ◽  
pp. 393-401 ◽  
Author(s):  
C. Aprea ◽  
A. Greco ◽  
G.P. Vanoli
Keyword(s):  
Heat Transfer ◽  
Flow Regime ◽  
Horizontal Tube ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Gravity Driven ◽  
Gravity Driven Flow

Effect of Temperature Difference on In-Tube Condensation Heat Transfer Coefficients

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Malcolm Macdonald ◽  
Srinivas Garimella
Keyword(s):  
Heat Transfer ◽  
Temperature Difference ◽  
Film Theory ◽  
Horizontal Tube ◽  
Condensation Heat Transfer ◽  
Effect Of Temperature ◽  
Test Fluid ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Underlying Mechanisms

The effect of temperature difference (Tsat − Tcoolant) on condensation heat transfer coefficients inside horizontal tubes is investigated in detail. Condensation experiments are conducted on propane inside a 7.75 mm horizontal tube at four temperature differences between the test fluid and coolant at three mass fluxes and four saturation temperatures. The heat transfer coefficient is shown to increase with temperature difference, with this effect diminishing with larger temperature differences, and being most significant at higher saturation temperatures. Heat transfer coefficients at the low-reduced pressures (Pr = 0.25) corresponding to lower saturation temperatures (30 °C) are mostly unaffected by the temperature difference. Subcooling of the condensate is expected to increase heat transfer coefficients at the larger temperature differences. Flow visualization studies are used to explain the inadequacy of the Nusselt film theory for the conditions investigated. The underlying mechanisms are also used to explain why the correlations from the literature do not predict the observed trend, and a new correlation to account for the effect of temperature difference is developed.

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%.

Analysis and Prediction of Condensation Heat Transfer of the Zeotropic Mixture R-125/236ea

2000 ◽  
Author(s):  
Alberto Cavallini ◽  
Giuseppe Censi ◽  
Davide Del Col ◽  
Luca Doretti ◽  
Luisa Rossetto ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Saturation Temperature ◽  
Horizontal Tube ◽  
Transfer Coefficients ◽  
Tube Heat Exchanger ◽  
Heat Transfer Coefficients ◽  
On Line ◽  
Zeotropic Mixture ◽  
Film Method ◽  
Experimental Runs

Abstract The high temperature glide mixture R-125/236ea at three mass compositions (28/72%, 46/54%, 63/37%) is tested during condensation against water in a tube-in-tube heat exchanger. The experimental runs to measure the heat transfer coefficients are carried out at saturation temperature ranging from 40°C to 60°C and mass velocities ranging from 100 to 750 kg/(m2 s). A gas chromatograph is used for on-line concentration measurements. By comparing the heat transfer performances of the three compositions to the condensation coefficients previously measured for the two pure components inside a smooth horizontal tube [Cavallini et al. (2000)], the dependence of the heat transfer performance on composition during condensation for a non-azeotropic mixture is investigated. The film method by Colburn and Drew (1937) is applied to predict the experimental coefficients and it is found to underestimate the heat transfer rate, with more conservative results as compared to the equilibrium method by Silver (1947), Bell and Ghaly (1973).

The Impact of Fin Deformation on Condensation Heat Transfer Coefficients in Internally Grooved Tubes

2013 ◽  
Author(s):  
Sunil Mehendale
Keyword(s):  
Heat Transfer ◽  
Heat Exchangers ◽  
Thermal Contact ◽  
Heat Pumps ◽  
Condensation Heat Transfer ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Condensing Heat Transfer ◽  
The Impact ◽  
Tube Expansion

In HVACR equipment, internally enhanced round tube (microfin) designs such as axial, cross-grooved, helical, and herringbone are commonly used to enhance the boiling and condensing performance of evaporators, condensers, and heat pumps. Typically, such tubes are mechanically expanded by a mandrel into a fin pack to create an interference fit between the tube outside surface and the fin collar to minimize the thermal contact resistance between tube and fin. However, during this expansion process, the internal enhancements undergo varying amounts of deformation, which degrades the in-tube thermal performance. Extensive data on condensing heat transfer coefficients in microfin tubes have been reported in the open literature. However, researchers have seldom used expanded tubes to acquire and report such data. Hence, it is always questionable to use such pristine tube data for designing heat exchangers and HVACR systems. Furthermore, the HVACR industry has been experiencing steeply rising copper costs, and this trend is expected to continue in coming years. So, many equipment manufacturers and suppliers are actively converting tubes from copper to aluminum. However, because of appreciable differences between the material properties of aluminum and copper, as well as other manufacturing variables, such as mandrel dimensions, lubricant used, etc., tube expansion typically deforms aluminum fins more than copper fins. Based on an analysis of the surface area changes arising from tube expansion, and an assessment of the best extant in-tube condensation heat transfer correlations, this work proposes a method of estimating the impact of tube expansion on in-tube condensation heat transfer. The analysis leads to certain interesting and useful findings correlating fin geometry and in-tube condensation thermal resistance. This method can then be applied to more realistically design HVACR heat exchangers and systems.

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