Study on Channel Heat-Transfer Enhancement Technique for Data Center Air-Handling Unit

A numerical simulation method is used to investigate the flow and heat-transfer enhancement characteristics of a dimple-enhanced data center air-handling unit heat exchanger with Reynolds numbers ranging from 5 728 to 11 176. Traditional spherical dimples and three novel dimple types （ellipsoid， rounded stick， and rounded trapezoid） are studied. The results indicate that the traditional spherical dimple has poor heat-transfer enhancement performance， as its highest performance-evaluation criterion （PEC） is 1.067 （spherical dimple R15h2 with Re = 8 383）. Compared with the spherical-dimple channel， the high-velocity regions are all closer to the wall for the three novel dimple channels， which creates a thinner boundary layer that enhances heat transfer. Among the three novel dimple channels， the heat-transfer ability of the rounded-stick dimple channel is better than that of the ellipsoid dimple channel because of the larger high-velocity area near the upper wall of the channel and the fluid-impingement effect. The more complex second-flow vortexes result in a higher heat-transfer ability for the rounded trapezoid dimple channel compared with the rounded stick dimple. Under the same pumping power， the rounded trapezoid dimple channel can enhance the heat transfer by up to 33% compared with a flat-plate channel when Re = 5 728. In addition， the PEC of the rounded trapezoid dimple channel is larger than 1.27 in the tested Re region.