Two-Phase Flow Patterns and Evaporation Heat Transfer of R134a in a Vertical Narrow Rectangular Channel

2018 ◽  
Vol 26 (01) ◽  
pp. 1850007
Author(s):  
Hoheum Cho ◽  
Daisuke Jige ◽  
Hiromasa Miyata ◽  
Norihiro Inoue
Keyword(s):  
Heat Transfer ◽  
Void Fraction ◽  
Mass Velocity ◽  
Thin Liquid Film ◽  
Rectangular Channel ◽  
Saturation Temperature ◽  
Flow Patterns ◽  
Two Phase ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer

This study experimentally investigated the flow pattern, void fraction, and evaporation heat transfer characteristic of R134a upward flow in a vertical narrow rectangular channel having a hydraulic diameter of 0.99[Formula: see text]mm, resembling a plate heat exchanger. Experiments were performed with mass velocities and vapor quality ranging between 30–200[Formula: see text]kgm[Formula: see text]s[Formula: see text] and 0.05–0.9, respectively, at a saturation temperature of 15[Formula: see text]C. Flow patterns were classified into bubble, slug, churn, and annular flows. The void fraction increased with increasing quality, and decreased with decreasing mass velocity in the low-quality region. Further, the influence of flow inlet/outlet positions remarkably appeared when the superficial gas velocity was low. The observed flow patterns and the measured void fraction were compared to that in previous studies. The effects of mass velocity and heat flux on the evaporation heat transfer coefficient were small, and the heat transfer through the thin liquid film was dominant.

Predicting Heat Transfer in Long R-134a Filled Thermosyphons

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
M. H. M. Grooten ◽  
C. W. M. van der Geld
Keyword(s):  
Heat Transfer ◽  
Saturation Temperature ◽  
Good Alternative ◽  
Condensation Heat Transfer ◽  
Air Cooling ◽  
Transfer Coefficients ◽  
Reduced Pressure ◽  
Evaporation Heat ◽  
Evaporation Heat Transfer ◽  
R 134A

When traditional air-to-air cooling is too voluminous, heat exchangers with long thermosyphons offer a good alternative. Experiments with a single thermosyphon with a large length-to-diameter ratio (188) and filled with R-134a are presented and analyzed. Saturation temperatures, filling ratios, and angles of inclination have been varied in wide ranges. A higher sensitivity of evaporation heat transfer coefficients on reduced pressure than in previous work has been found. Measurements revealed the effect of pressure or the saturation temperature on condensation heat transfer. The condensate film Reynolds number that marks a transition from one condensation heat transfer regime to another is found to depend on pressure. This effect was not accounted for by correlations from the literature. New correlations are presented to predict condensation and evaporation heat transfer rates.

Visualization of the Heat Transfer Enhancement During Condensation in a Microfin Tube

2006 ◽  
Author(s):  
Alberto Cavallini ◽  
Davide Del Col ◽  
Luca Doretti ◽  
Simone Mancin ◽  
Luisa Rossetto ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Saturation Temperature ◽  
Flow Patterns ◽  
Operating Conditions ◽  
Vapor Quality ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Plain Tube ◽  
The Heat Transfer Coefficient

Microfins tubes are largely used in refrigeration industry for in-tube refrigerant condensation, because of the heat transfer enhancement when compared to equivalent smooth tubes under the same operating conditions. But not much evidence about the effect of microfins on the condensation flow patterns is available in the open literature. There is agreement in the open literature that the mechanisms of heat transfer are intimately linked with the prevailing two-phase flow regime. The present authors have recently measured the heat transfer coefficient during condensation of R410A in a microfin tube. The heat transfer enhancement in this tube can be experimentally evaluated by comparing those coefficients to the ones measured by Cavallini et al. (2001) in a plain tube, at the same operating conditions. The same operative conditions (saturation temperature, vapor quality and mass flux), occurring during the heat transfer measurements, were reproduced in a different section for visualization of flow patterns during condensation of R410A. The flow visualization has been carried out both in the plain tube and in the microfin tube. The objective of the present paper is to present the heat transfer enhancement during condensation of R410A and to show the flow visualized at the same operating condition for both the smooth and the microfin tube, aiming to link the heat transfer enhancement to the flow pattern variation.

Condensation and Evaporation Heat Transfer Characteristics of Low Mass Fluxes in Horizontal Smooth Tube and Three-Dimensional Enhanced Tubes

2019 ◽  
Vol 12 (2) ◽  
Author(s):  
Xiang Ma ◽  
Wei Li ◽  
Chuan-cai Zhang ◽  
Zhi-chuan Sun ◽  
David J. Kukulka ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Mass Flux ◽  
Three Dimensional ◽  
Saturation Temperature ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Evaporation Heat ◽  
Enhanced Tubes ◽  
Evaporation Heat Transfer ◽  
Enhanced Surface

Abstract An experimental investigation of condensation and evaporation heat transfer characteristics was performed in 15.88-mm-OD and 12.7-mm-OD smooth and three-dimensional enhanced tubes (1EHT, 3EHT) using R134A and R410A as the working fluid. The enhanced surface of the 1EHT tube is made up of dimples and a series of petal arrays; while the 3EHT tube is made up of rectangular cavities. Evaluations are performed at a saturation temperature of 45 °C, over the quality range of 0.8–0.2 for condensation; while for evaporation the saturation temperature was 6 °C and the quality ranged from 0.2 to 0.8. For condensation, the enhancement ratio (enhanced tube/smooth tube) of the heat transfer coefficients was 1.42–1.95 for the mass flux ranging from 80 to 200 kg/m2s; while for evaporation, the heat transfer enhancement ratio is 1.05–1.42 for values of mass flux that range from 50 to 180 kg/m2s. Furthermore, the 1EHT tube provides the best condensation and evaporation heat transfer performance, for both working fluids at the mass flux considered. This performance is due to the dimples in the enhanced surface that produce interface turbulence; additionally, the increased surface roughness causes additional disturbances and secondary flows near the boundary, producing higher heat fluxes. The main objective of this study was to evaluate the heat transfer enhancement of two enhanced tubes when using R134A and R410A as a function of mass flux, saturation temperature, and tube diameter. As a result of this study, it was determined that the heat transfer coefficient decreases with an increase in saturation temperature and tube diameter.

Sign in / Sign up

Export Citation Format

Share Document