Transient characterization of data center racks

Abstract

The increased computational and storage demand has increased the heat dissipation of servers in data centers. The flow inside the data center is highly dynamic due to various parameters such as server workload, server fan speed, tile porosity, Computer Room Air Conditioning (CRAC) air flowrates, CRAC supply & return air temperatures and data center cold & hot aisle arrangements. Data center facility level transient CFD analysis was reported in recent literature which needs weeks to accomplish the computation. Hence, such facility level simulations are difficult to achieve with good accuracy. The main contributions of this paper are transient experiments, transient CFD model & transient effects on thermal and flow field due to variation in server load of server rack inside the raised floor plenum data center.

In the current study we have developed a transient CFD model of three racks in a raised floor plenum data center room with cold and hot aisle containment based on experiments. The middle 42U (1U = 4.45 cm) rack houses four server simulators each having height of 10U. The flow tiles supply the cold air as inlet with average velocity of 1.53 m/s at 17°C. All the rack servers were modelled with 75% porosity and estimated thermal mass Each server simulator was assigned a total heat dissipation of 2500 W, with a total heat load of 10 kW per rack. The effect on rack inlet and outlet air temperatures were monitored by providing server heat loads as step & ramp inputs to the middle simulator rack. The results show that the rack level transient effects are significant and cannot be ignored.