Cross Flow Heat Exchanger Modeling of Transient Temperature Input Conditions

The effectiveness of heat exchangers strongly influences the thermal performance of data center cooling systems. Rear door heat exchangers, in-row and overhead coolers, and fully contained water cooled cabinets are some examples of liquid and hybrid cooling systems used in data centers. Modeling the dynamic behavior of heat exchangers is important for the design of control strategies to improve energy efficiency. In this paper, an existing 2-D model of the transient temperature response of an unmixed-unmixed cross flow heat exchanger, of the type that is widely used in data center cooling equipment, is solved numerically. A detailed analysis of the transient response to a step, ramp, or exponential change in the hot fluid inlet temperature is conducted. The heat capacity rate ratio (E), thermal resistance (R), capacitance ratio (V), and number of transfer units are varied over a wide range to determine their influence on the heat exchanger dynamic thermal performance under different transient input conditions. In addition, the thermal response to the magnitude and time period of the transient input functions are evaluated. The modeling results are used to analyze specific data center cooling scenarios, and provide a means for predicting the transient behavior of heat exchangers used in data center cooling equipment.