A Combined Numerical and Experimental Study of Heat Transfer in a Roughened Square Channel with45∘Ribs

[摘要] Experimental investigations have shown that theenhancement in heat transfer coefficients for air flow in achannel roughened with low blockage(e/Dh<0.1)angled ribs ison the average higher than that roughened with90∘ribsof the same geometry. Secondary flows generated by the angled ribsare believed to be responsible for these higher heat transfercoefficients. These secondary flows also create a spanwisevariation in the heat transfer coefficient on the roughened wallwith high levels of the heat transfer coefficient at one end ofthe rib and low levels at the other end. In an effort toinvestigate the thermal behavior of the angled ribs at elevatedReynolds numbers, a combined numerical and experimental study wasconducted. In the numerical part, a square channel roughened with45∘ribs of four blockage ratios(e/Dh)of0.10,0.15,0.20, and0.25, each for a fixed pitch-to-height ratio(P/e)of10, was modeled. Sharp as well as round-corner ribs(r/e=0and0.25) in a staggered arrangement were studied.The numerical models contained the smooth entry and exit regionsto simulate exactly the tested geometries. Apressure-correction-based, multiblock, multigrid,unstructured/adaptive commercial software was used in thisinvestigation. Standard high Reynolds numberk−εturbulence model in conjunction with the generalized wallfunction for most parts was used for turbulence closure. Theapplied thermal boundary conditions to the CFD models matched thetest boundary conditions. In the experimental part, a selectednumber of these geometries were built and tested for heattransfer coefficients at elevated Reynolds numbers up to150 000, using a liquid crystal technique. Comparisons betweenthe test and numerically evaluated results showed reasonableagreements between the two for most cases. Test results showedthat (a)45∘angled ribs with high blockage ratios(>0.2)at elevated Reynolds numbers do not exhibit a goodthermal performance, that is, beyond this blockage ratio, theheat transfer coefficient decreases with the rib blockage and (b)CFD could be considered as a viable tool for the prediction ofheat transfer coefficients in a rib-roughened test section.

[学科分类] 力学，机械学