Film Condensation of R-134a on Tube Arrays With Plain and Enhanced Surfaces: Part II—Empirical Prediction of Inundation Effects

2005 ◽  
Vol 128 (1) ◽  
pp. 33-43 ◽  
Author(s):  
D. Gstoehl ◽  
J. R. Thome
Keyword(s):  
Heat Transfer ◽  
Local Heat ◽  
Heat Transfer Process ◽  
Finned Tube ◽  
Film Condensation ◽  
Condensation Temperature ◽  
Asymptotic Model ◽  
Transfer Coefficients ◽  
Empirical Prediction ◽  
R 134A

New predictive methods for R-134a condensing on vertical arrays of horizontal tubes are proposed based on visual observations revealing that condensate is slung off the array of tubes sideways and significantly affects condensate inundation and thus the heat transfer process. For two types of three-dimensional (3D) enhanced tubes, the Turbo-CSL and the Gewa-C, the local heat flux is correlated as a function of condensation temperature difference, the film Reynolds number, the tube spacing, and liquid slinging effect. The measured heat transfer data of the plain tube were well described by an existing asymptotic model based on heat transfer coefficients for the laminar wavy flow and turbulent flow regimes or, alternatively, by a new model proposed here based on liquid slinging. For the 26fpi low finned tube, the effect of inundation was found to be negligible and single-tube methods were found to be adequate.

Film Condensation of R-134a on Tube Arrays With Plain and Enhanced Surfaces: Part I—Experimental Heat Transfer Coefficients

2005 ◽  
Vol 128 (1) ◽  
pp. 21-32 ◽  
Author(s):  
D. Gstoehl ◽  
J. R. Thome
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Finned Tube ◽  
Surface Structures ◽  
Film Condensation ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Tube Arrays ◽  
R 134A ◽  
Enhanced Surface

The aim of the present investigation was to study the effect of condensate inundation on the thermal performance of a vertical array of horizontal tubes with plain and enhanced surfaces. Refrigerant R-134a was condensed at a saturation temperature of 304K on tube arrays with up to ten tubes at pitches of 25.5,28.6,and44.5mm. Notably, local condensing heat transfer coefficients were measured at the midpoint of each tube, as opposed to mean values. Four commercially available copper tubes with a nominal diameter of 19.05mm(0.75in.) were tested: a plain tube, a 26fpi∕1024fpm low finned tube, and two tubes, with three-dimensional (3D) enhanced surface structures. At low liquid inundation rates, the tubes with 3D enhanced surface structures significantly outperformed the low finned tube. Increasing liquid inundation deteriorated the thermal performance of the 3D enhanced tubes, whereas it had nearly no affect on the low finned tube, resulting in a higher heat transfer coefficients for the low finned tube at high liquid film Reynolds numbers. All the tests were performed with minimal vapor shear.

scholarly journals Condensation inside smooth horizontal tubes: Part 1. Survey of the methods of heat-exchange prediction

2015 ◽  
Vol 19 (5) ◽  
pp. 1769-1789 ◽  
Author(s):  
Volodymyr Rifert ◽  
Volodymyr Sereda
Keyword(s):  
Heat Transfer ◽  
Heat Exchange ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Film Condensation ◽  
Experimental Investigations ◽  
Phase Flow ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Horizontal Tubes

Survey of the works on condensation inside smooth horizontal tubes published from 1955 to 2013 has been performed. Theoretical and experimental investigations, as well as more than 25 methods and correlations for heat transfer prediction are considered. It is shown that accuracy of this prediction depends on the accuracy of volumetric vapor content and pressure drop at the interphase. The necessity of new studies concerning both local heat transfer coefficients and film condensation along tube perimeter and length under annular, stratified and intermediate regimes of phase flow was substantiated. These characteristics being defined will allow determining more precisely the boundaries of the flow regimes and the methods of heat transfer prediction.

Stratified Flow Condensation of CO2 in a Tube at Low Temperatures

2015 ◽  
Vol 789-790 ◽  
pp. 184-192
Author(s):  
Pei Hua Li ◽  
Joe Deans ◽  
Stuart Norris
Keyword(s):  
Heat Transfer ◽  
Temperature Difference ◽  
Saturation Temperature ◽  
Horizontal Tube ◽  
Stratified Flow ◽  
Heat Transfer Process ◽  
Film Condensation ◽  
Significant Feature ◽  
Transfer Coefficients ◽  
Flow Condensation

This study presents an experimental investigation of CO2flowing condensation at the saturation temperature of-10°C, mass flux in the range from 40 to 60kgm-2s-1and vapour quality ranging from 0.2 to 0.8, in a 6.52mm inside diameter horizontal tube. Previous research on refrigerant condensation has shown that under these conditions, CO2two phases are expected to develop as a stratified flow. The significant feature of the stratified flow heat transfer is vapour film condensation in the upper region which dominates the overall heat transfer process. Test series in this study confirm that the saturation-to-tube wall temperature difference has a significant influence on the condensing heat transfer coefficient when the temperature difference is within 3K. Comparisons between the experimental results and the predictions by the Dobson, Cavallini and Thome models show that CO2stratified flow condensation heat transfer coefficients are over-predicted by these models with mean deviations of 104%, 81% and 127%, respectively.

scholarly journals A Comparative Study on the Condensation Heat Transfer of R-513A as an Alternative to R-134a

Machines ◽  
2021 ◽  
Vol 9 (6) ◽  
pp. 114
Author(s):  
Andreas Karageorgis ◽  
George Hinopoulos ◽  
Man-Hoe Kim
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Mass Flux ◽  
Condensation Heat Transfer ◽  
Test Facility ◽  
Condensation Temperature ◽  
Transfer Coefficients ◽  
Active Length ◽  
Heat Transfer Coefficients ◽  
R 134A

This paper presents the two-phase condensation heat transfer and pressure drop characteristics of R-513A as an alternative refrigerant to R-134a in a 9.52-mm OD horizontal microfin copper tube. The test facility had a straight, horizontal test section with an active length of 2.0 m and was cooled by cold water circulated in a surrounding annular space. The annular-side heat transfer coefficients were obtained using the Wilson plot method. The average heat transfer coefficient and pressure drop data are presented at the condensation temperature of 35 °C in the range of 100–440 kg·m−2·s−1 mass flux. The test data of R-513A are compared with those of R-134a, R-1234yf, and R-1234ze(E). The average condensation heat transfer coefficients of the R-513A and R-1234ze(E) refrigerants were similar to R-134a at the lower mass flux (100~150 kg·m−2·s−1), while they were up to 10% higher than R-134a as the mass flux increased. The pressure drop of R-513A was similar to R-1234yf and 10% lower than that of R-134a at the higher mass flux. The R-1234ze(E) pressure drops were 20 % higher compared to those of R-134a at the higher mass flux.

Condensing and Evaporating Heat Transfer and Pressure Drop Characteristics of HFC-134a and HCFC-22

1997 ◽  
Vol 119 (1) ◽  
pp. 158-163 ◽  
Author(s):  
X. Liu
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Hfc 134A ◽  
Grooved Tube ◽  
Condensing Heat Transfer ◽  
R 134A

Condensing and evaporating heat transfer and pressure drop characteristics of an ozone friendly refrigerant HFC-134a and a HCFC refrigerant R-22, flowing inside a 9.5 mm (3/8 in) OD axially grooved tube were investigated experimentally to obtain the quasi-local heat transfer data and the correlations. When compared to R-22 at the same refrigerant flow rate, the condensing heat transfer coefficients for R-134a are 8 percent to 18 percent higher, and the pressure drop is 50 percent higher. The evaporating heat transfer coefficient with R-134a is about the same for mass velocity below 270 kg/m2-s and decreases above that velocity, relative to R-22. Performance characteristics are compared with data from literature reports.

Extended surface convective cooling studies of engine components using the transient liquid crystal technique

1997 ◽  
Vol 211 (3) ◽  
pp. 273-287 ◽  
Author(s):  
A J Neely ◽  
P T Ireland ◽  
L R Harper
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Convective Heat Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Finned Tube ◽  
Correct Selection ◽  
Transfer Coefficients ◽  
Cooling Performance ◽  
Convective Cooling

A heat transfer tunnel used for local convective heat transfer coefficient measurements on liquid crystal instrumented models is described. The tunnel uses the new mesh heater device to produce a good approximation to a step change in the test section flow temperature. A simple analytical model of the cooling performance of cylindrical extended surfaces is derived from empirical relations obtained from the literature. Experiments conducted on a smooth cylinder and selected cylindrical finned geometries are discussed. In the configurations investigated, the relative sizes of the fin diameter to the fin array greatly exceed any geometries previously reported. The use of liquid crystal mapping techniques is shown to provide the full distribution of local heat transfer coefficients across the fin surface. This enables a greater understanding of the convective cooling process than could be obtained from the simple average measurements of h previously reported in the literature. Existing finned tube correlations are shown to be unable to predict the measured heat transfer levels. The investigation shows that correct selection of fin geometry can result in a significant increase in overall convective cooling performance.

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