Steady-State and First-Order Transient Thermal Performance of an Axially Finned Heat Pipe Heat Exchanger—AFHPHE in the Evaporator Region

Abstract

This article presents a refined analysis of evaporator region of an axially finned heat pipe heat exchanger (AFHPHE), which is being theoretically evaluated for use in operating room air conditioning systems. The analysis provides an unusually simple first-order transient model for a multi-thermosiphon bundle heat exchanger. The objective is to provide an approximate theoretical prediction of the first-order transient response of a heat exchanger with 49 closed two-phase thermosiphons, with 30 axial fins in each thermosiphon, in the evaporator region. The steady-state solution for the heat exchanger is already well established, with theoretical experimental comparisons performed with other similar heat pipe systems presented in the literature. The transient solution uses steady-state results of the working fluid and the heat exchanger to validate the conclusions. The working fluid is the refrigerant R404a, widely used in similar systems. The transient results presented are the temporal variations in the heat exchange rate, working fluid temperatures, heat pipe wall temperatures, and air outlet temperatures. Variations in the working fluid filling rates are simulated to demonstrate the consistency of the developed model. Although the theoretical model appears logically consistent, its irrefutable validation depends on future experimental results, which represents a significant challenge.