Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
669379 | International Journal of Thermal Sciences | 2014 | 19 Pages |
Abstract
This study investigates the effect of channel height-to-width ratio (Aspect Ratio, AR) on heat-transfer rates, pressure-drop coefficients (f) and thermal performances of air-water flows through horizontal and vertical U-bend rectangular channels at intermittent slug and slug-annular flow conditions. Interfacial two-phase flow structures, local and area-averaged Nusselt numbers (Nu), f coefficients, channel-wise averaged void fractions (α) and thermal performance factors (TPF) for three sets of horizontal and vertical U-bend channels of AR = 1, 0.83 and 0.33 are measured with liquid Reynolds numbers (ReL) and air-to-water mass flow ratios (AW) in the range of 1500 â¤Â Re â¤Â 10000 and 0 â¤Â AWâ¤0.024. Early transitions from slug flow to slug-annual flow along with the shortened air slug and the extended period of the trailing-edge bubbly flow over each intermittent cycle are promoted by decreasing AR to elevate both heat transfer rates and pressure drops for the U-bend channels with small AR. A set of selective Nu, f and TPF data illustrates the interdependency between Nu, f, TPF and the air-water flow structures in present test channels with different AR. The area averaged endwall Nu for each U-bend test channel (Nu¯) and the corresponding f and TPF are cross-examined to generate a set of heat-transfer and pressure-drop correlations, which permit the evaluations of isolated and interdependent ReL, AW and AR effects on Nu¯ and f, to assist various design applications.
Keywords
Related Topics
Physical Sciences and Engineering
Chemical Engineering
Fluid Flow and Transfer Processes
Authors
Shyy Woei Chang, Kuei Feng Chiang, Ching Yuan Lin,