Simulation of a Wet-Surface Bare Rod Heat Exchanger

Abstract

In this paper, a CFD analysis is carried out in ANSYS Fluent to investigate the enhancement of heat transfer and vapor condensation rate in a novel air-to-solid micro bare rod heat exchanger. Literature indicates that the enhancement of heat transfer occurs at the cost of increasing pressure drop across the heat exchanger; due to proximity of the rods. The heat exchanger is first modeled in Engineering Equation Solver (EES) to perform under Abu Dhabi’s hot and humid climate conditions. The heat exchanger is modelled to operate at low Reynolds number to increase the air residue time and allow condensation to occur. In the model, copper rods of diameter 1 mm are evenly spaced out between 2 plates to form the heat exchanger. Fixing the space occupied by the heat exchanger, i.e. volume occupied, the diameter of the copper rods is varied from 0.5 to 5 mm. The effect of the copper rods’ diameter and the spacing between the rods on the rate of vapor condensation, heat transfer, and pressure drop are investigated. Correlations for a micro bare rod heat exchanger exposed to a humid air stream are not available in the literature. Thus, using CFD modeling, the j (dry and wet side) and f factor correlations are determined for this novel heat exchanger operating at low Reynolds numbers. Lastly, the performance of the novel heat exchanger is compared to a fin-tube heat exchanger occupying the same volumetric space operating at the same conditions.