Influence of Wall Sub-Cooling on Local Heat Transfer for Forced Convection Condensation of Steam/Air in a Horizontal Tube

2016 ◽  
Author(s):  
Huiqiang Xu ◽  
Qiunan Sun ◽  
Haifeng Gu ◽  
Xiaofan Hou ◽  
Zhongning Sun
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Mass Fraction ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Condensation Heat Transfer ◽  
Fraction Mixture ◽  
Condensation Heat Transfer Coefficient

For the purpose of analyzing the influence of wall sub-cooling on condensation heat transfer characteristic in the presence of noncondensable gases inside a horizontal tube, experiments for air-cooling and water-cooling at the secondary side outside the condenser tube have been conducted. By comparing the experimental data of different inlet air mass fraction, mixture gases velocity and coolant volume flow rate, the variation of local heat transfer coefficient with wall sub-cooling was obtained. The results show that for annular and wavy flow, the condensation heat transfer coefficient increases with increasing wall sub-cooling but decreases for stratified flow. For annular and wavy flow, the positive influence of wall sub-cooling on condensation heat transfer coefficient is enhanced by the rise of inlet noncondensable gas mass fraction, mixture gases velocity and pressure.

A Study on Gas–Liquid Film Thicknesses and Heat Transfer Characteristics of Vapor–Gas Condensation Outside a Horizontal Tube

2013 ◽  
Vol 136 (2) ◽  
Author(s):  
Huijun Li ◽  
Wenping Peng
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Film ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Horizontal Tube ◽  
Local Heat ◽  
Condensation Heat Transfer ◽  
Gas Condensation ◽  
Noncondensable Gas

Noncondensable gases deteriorate heat transfer in the condensation process. It is therefore necessary to study vapor–gas condensation heat transfer process and analyze main factors influencing the process. Based on the double-film theory and the Prandtl boundary layer theory, this investigation developed a mathematical model of gas–liquid film thicknesses and local heat transfer coefficient for studying laminar film condensation in the presence of noncondensable gas over a horizontal tube. Induced velocity in the gas film, gas–liquid interfacial shear stress, and pressure gradient were considered in the study. Importantly, gas–liquid film separations were analyzed in depth in this paper. It obtained the distributions of gas–liquid film thicknesses, local heat transfer coefficient, condensate mass flux, and gas–liquid interfacial temperature along the tube surface, and analyzed the influences of bulk velocity, total pressure, bulk mass concentration of noncondensable gas and wall temperature on them, providing a theoretical guidance for understanding and enhancing vapor–gas condensation heat transfer. Gas film thickness and gas–liquid film separations have certain effects on vapor–gas condensation heat transfer. The average dimensionless heat transfer coefficients are in agreement with the data from related literatures.

Local Heat Transfer Measurements in Turbulent Flow Around a 180-deg Pipe Bend

1987 ◽  
Vol 109 (1) ◽  
pp. 43-48 ◽  
Author(s):  
J. W. Baughn ◽  
H. Iacovides ◽  
D. C. Jackson ◽  
B. E. Launder
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Turbulent Flow ◽  
Transfer Coefficient ◽  
Secondary Flow ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Pipe Bend ◽  
Streamline Curvature

The paper reports extensive connective heat transfer data for turbulent flow of air around a U-bend with a ratio of bend radius:pipe diameter of 3.375:1. Experiments cover Reynolds numbers from 2 × 104 to 1.1 × 105. Measurements of local heat transfer coefficient are made at six stations and at five circumferential positions at each station. At Re = 6 × 104 a detailed mapping of the temperature field within the air is made at the same stations. The experiment duplicates the flow configuration for which Azzola and Humphrey [3] have recently reported laser-Doppler measurements of the mean and turbulent velocity field. The measurements show a strong augmentation of heat transfer coefficient on the outside of the bend and relatively low levels on the inside associated with the combined effects of secondary flow and the amplification/suppression of turbulent mixing by streamline curvature. The peak level of Nu occurs halfway around the bend at which position the heat transfer coefficient on the outside is about three times that on the inside. Another feature of interest is that a strongly nonuniform Nu persists six diameters downstream of the bend even though secondary flow and streamline curvature are negligible there. At the entry to the bend there are signs of partial laminarization on the inside of the bend, an effect that is more pronounced at lower Reynolds numbers.

An Experimental Study of High Rayleigh Number Mixed Convection in a Rectangular Enclosure With Restricted Inlet and Outlet Openings

1987 ◽  
Vol 109 (2) ◽  
pp. 446-453 ◽  
Author(s):  
L. Neiswanger ◽  
G. A. Johnson ◽  
V. P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Rayleigh Number ◽  
Mixed Convection ◽  
Transfer Coefficient ◽  
Heated Surface ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Test Fluid ◽  
Rectangular Enclosure

Measured local heat transfer data and the results of flow visualization studies are reported for cross-flow mixed convection in a rectangular enclosure with restricted inlet and outlet openings at high Rayleigh number. In this study, experiments using water as the test fluid were conducted in a small-scale test section with uniformly heated vertical side walls and an adiabatic top and bottom. As the flow rate through the enclosure increased, the enhancement of heat transfer, above that for natural convection alone, also increased. The variation of the local heat transfer coefficient over the heated surface was found to be strongly affected by the recirculation of portions of the forced flow within the enclosure. Mean heat transfer coefficients are also presented which were calculated by averaging the measured local values over the heated surface. A correlation for the mean heat transfer coefficient is also proposed which agrees very well with the experimentally determined values. A method of predicting the flow regime in this geometry for specified heating and flow conditions is also discussed.

Local and Average Heat Transfer Characteristics for a Disk Situated Perpendicular to a Uniform Flow

1985 ◽  
Vol 107 (2) ◽  
pp. 321-326 ◽  
Author(s):  
E. M. Sparrow ◽  
G. T. Geiger
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stagnation Point ◽  
Radial Distance ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Average Heat ◽  
Radial Profiles

Wind tunnel experiments were performed to determine both the average heat transfer coefficient and the radial distribution of the local heat transfer coefficient for a circular disk facing a uniform oncoming flow. The experiments covered the range of Reynolds numbers Re from 5000 to 50,000 and were performed using the naphthalene sublimation technique. To complement the experiments, an analysis incorporating both potential flow theory and boundary layer theory was used to predict the stagnation point heat transfer. The measured average Nusselt numbers definitively resolved a deep disparity between information from the literature and yielded the correlation Nu = 1.05 Pr0.36 Re1/2. The radial distributions of the local heat transfer coefficient were found to be congruent when they were normalized by Re1/2. Furthermore, the radial profiles showed that the local coefficient takes on its minimum value at the stagnation point and increases with increasing radial distance from the center of the disk. At the outer edge of the disk, the coefficient is more than twice as large as that at the stagnation point. The theoretical predictions of the stagnation point heat transfer exceeded the experimental values by about 6 percent. This overprediction is similar to that which occurs for cylinders and spheres in crossflow.

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