Transient response of a meso heat exchanger with temperature step variation

Abstract

Heat exchangers are common components of many industrial, residential, and automotive systems. In automotive, heat exchangers are employed in engine cooling and air conditioning to transfer the undesired heat from the engine or the passenger compartment as a condenser, evaporator, inter-cooler, heater core, radiator, and oil cooler. Since, the thermal performance of heat exchangers influences the underhood automotive thermal management system, it is essential to characterize their dynamic response in general and specifically, when a sudden change to their operating parameters occur. Experimental measurements provide the scope for in depth understanding of the dynamic behavior of heat exchangers with respect to various parameters. This study investigates a liquid to gas cross flow meso heat exchanger subjected to transient conditions. Step variations in the hot fluid inlet temperature in the absence of mass flow rate disturbances was considered for 5 different levels ranging from 1.5 to 3.0, while other operating parameters are kept constant. The effect of step change on the thermal performance of a heat exchanger is demonstrated by both fluids outlet temperatures, heat transfer rate, effectiveness, and heat balance error. Results obtained show a faster response of the cold fluid outlet temperature compared to the hot fluid, however, an adverse effect is noticed for the heat transfer rate. Higher step changes in temperature lead to higher heat transfer rate, as expected; though, the hot side exhibited more heat transfer and higher effectiveness than the cold side. The hot fluid heat transfer rate and effectiveness display a non-linear increase reaching a peak, after which, it drops down at a slower rate compared to the cold fluid steady increase. A significant effect on normalized exit temperatures, heat transfer, and effectiveness at low step changes while it diminishes at higher step changes. The key element of this work is the use of meso heat exchanger to examine the transient conditions effect on its performance. This work covers a wide range of temperature step changes and aims to enrich the limited experimental database of dynamic response of heat exchangers. The outcome of this work is of interest to designers for thermal testing, characterization, and performance enhancement of compact heat exchangers.