Data center crossflow heat exchanger study under different transient temperature boundary conditions

Heat exchangers are primary components of HVAC systems. The effectiveness of the heat exchangers strongly influences the thermal performance of cooling systems. Rear door heat exchangers, in-row and overhead coolers, and fully contained cabinets, are some examples of liquid and hybrid cooling systems used in data centers. Characterizing the dynamic behavior of heat exchangers is important for thermal management of data centers, especially for the design of control strategies to improve energy efficiency. In this study, a model based on energy conservation of the transient temperature response of an unmixed-unmixed crossflow heat exchanger, of the type that is widely used in data center cooling equipment, is solved numerically. Detailed analysis of the transient temperature boundary conditions such as a step, ramp or exponential change to the inlet temperature of the hot fluid are conducted. Two governing parameters, heat capacity rate ratio (E) and number of transfer units (NTU), are varied in a wide range to determine their influence on the transient performance of heat exchangers under different transient input conditions. Also, the effects of the magnitude and time period of the transient input conditions are evaluated. Some specific data center cooling scenarios are analyzed based on the results from the heat exchanger dynamic performance study. The results obtained provide a means for predicting the transient behavior of heat exchangers used in data center cooling equipment.