Gravity-assisted air mixing in data centers and how it affects the rack cooling effectiveness

As power and heat densities continue to increase, the behavior of the data-center environment grows in importance, especially when developing new in-room cooling technologies. As a result, there has been a continued interest in understanding the behavior of various technologies in data centers. One issue is whether gravity plays a role in air cooled high density environments with an open architecture. A previous paper (Herlin, 2005) suggests that technologies working with gravity perform better. This poses the question: Does gravity indeed play a key role in forced convection environments such as data centers? The purpose of the present paper is to try to answer this question by further analyzing what we call "gravity-assisted" air mixing. Computational fluid dynamics (CFD) modeling in conjunction with the rack cooling index (RCI) are used to demonstrate that such mixing is central to creating an adequate and "forgiving" thermal equipment environment. The paper also describes why this is an important finding for designing new high-performance cooling systems.