Server-Rack Air Flow and Heat Transfer Interactions in Data Centers

The current study focuses on modeling the server-rack airflow and heat transfer interaction in a data center. In a typical computing facility, the computing requirements are often gradually built-up. For example, in this instance, two servers are placed in a rack designed for a six-server stack. Each server will be separately modeled to the required specifications, and also so that their numbers and placement can be changed. The mass flow rate through the server is determined by examining how pressure profiles develop at the inlet and outlet. This mass flow rate then becomes the input into the rack model. The air inflow temperatures at the front and rear grills were obtained from experiments. The pressure profile into and out of the servers were extracted from the rack model and substituted back into the server model. Iteration continues till an acceptable level of convergence is obtained. To validate the models, experiments were carried out using thermocouples arranged in a 3 × 3 grid on a vertical plane between the exit of the server and the rear cabinet wall of the rack. The results showed that the modeling had captured the essence of the flow and heat transfer interaction. The temperature and pressure profile at the rack inlet and outlet, although in a segmented form, have performed adequately to obtain a good approximation of the flow and temperature distribution within the server/rack. The methodology of passing parameters at the server-rack level using a segmented pressure profile has been established. A similar rack-room level interaction will subsequently be developed. In essence, the methodology is equivalent to replacing the server in the rack and the rack in the room with combined flow network - thermal models. But because of the coupled nature of these two different length scale systems, the models are obtained through an iterative process. The approach enables various combinations of servers and racks to be studied quickly for any undesirable effects of off-design data center operation or layout.© 2007 ASME