Experimental and Computational Evidence of Damped Axial Conduction with Reciprocating Flow

Abstract

Axial conduction is a crucial performance deteriorating factor in miniaturized heat transfer devices, primarily due to the low fluid flow rates, high solid cross-sectional to free-flow area ratio, and use of high thermal conductivity materials. These causative factors, inherent to micro-scale systems, should be such that the axial conduction is minimum. The reciprocating flow of the convective fluid (instead of steady unidirectional flow) is proposed per se as an alternative, which directly alters the solid temperature profile, the root cause of axial conduction. An experimental setup is built as a proof of the concept. In the test rig, a double-acting reciprocating pump generates a fully reversing periodic flow of air through a flow channel carved into a steel block embedded with a heater. The experimental temperature profile in the solid at the cyclic steady state is bell-shaped, indicating a virtual adiabatic plane capable of restricting axial heat transfer. The experimental results are verified taking the help of an independent finite-element-based numerical analysis. Similarly, the non-dimensional interfacial flux ratio (?_0 ), integrally related to axial conduction, for unidirectional and reciprocating flow is significantly different. This ratio in the vicinity of the inlet is ~53% less with the reciprocating compared to the equivalent unidirectional flow. The optimal thermal performance with the reciprocating flow is correlated through a critical Strouhal number expression, Sr ≤ (pDh)/L. In thermal management applications employing reciprocating flow, the limiting relation can be used to determine flow parameters and optimum geometry design.