Transient experimental investigation of airside heat transfer in a crossflow heat exchanger

Abstract

• Experimental analysis is performed to study the dynamic response of a heat exchanger. • Residence time is found to have a significant effect on the response time. • Transient air heat transfer coefficient is obtained by energy balance on the wall. • An empirical correlation of airside Nusselt number is developed. • The response time of both fluids was not instantaneous to the step imposed. The increase in energy consumption and the demand for effective thermal management systems necessitate the search for enhanced heat exchangers with high thermal performance, lower weight, and compact size. Crossflow heat exchangers are a key component in the thermal management system of many industries such as HVAC, automotive, etc. Transient analysis helps predict the behavior of heat exchangers when they experience variations in their operational conditions in terms of flow rate or temperature. This work experimentally studies the dynamic response of a cross flow heat exchanger to overcome the data scarcity in transient airside and presents the results for various cases of step changes in air mass flow rate. The effect of the step change on heat transfer is investigated and presented by airside Nu, fluids dimensionless temperature, airside Re, heat transfer rates, and Colburn j factor. Results show that the two fluids do not respond instantaneously to the step imposed. The magnitude of the step change has a dissimilar effect on the response time of each fluid. The response time increases with the increase in the step change. A generalized empirical correlation is obtained to predict the airside Nu. This study advances the control of heat exchangers by exploring their transient response due to step changes in one of the fluids inlet condition.