Heat transfer and flow characteristics of air-water heat exchanger inserting porous material with high porosity

Abstract

There are several methods for heat transfer enhancement. For example, one can attach various fins on the heat transfer surface, process the surface roughly, insert twisted tape, and so on. These methods increase the heat transfer coefficient or area by manufacturing changes to the heat transfer surface. However it is necessary to consider the problem on account of processing heat transfer area. In this study, we have obtained heat transfer characteristics of an air-water heat exchanger inserting a metal wire as porous material. In addition to that the heat transfer characteristics of the heat exchanger compared with those of a fin type heat exchanger. Experimental apparatus is composed of a heat exchanger, a blower, a heater and a cooling water system. The heat exchanger consists of a horizontal rectangular duct having narrow eight channels. Air was used as working fluid. Air was supplied to the heater from the blower and then supplied to the heat exchanger. In the experiment, water was supplied to the cooling water channel of the heat exchanger from an isothermal bath. The temperature of cooling water was constant at 70°C. A copper wire was inserted into the heat exchanger as a porous material. Experiment was conducted changing the porosity of the flow channel. Heating temperature of air set to the range from 200°C to 450°C with the porosity changing from 0.97 to 0.995. In order to investigate the heat transfer and fluid flow characteristics in the high temperature region, the heating temperature set to the range from 200°C to 800°C with the porosity changing from 0.99 to 0.995. The heat and fluid flow characteristics of the heat exchanger were evaluated by an amount of removed heat and a pressure drop. As a result of the experiment, the amount of removed heat by the heat exchanger having copper wire was slightly decreased as compared with that by the fin type heat exchanger. However, the pressure drop of the heat exchanger was greatly reduced as compared with that of the fin type heat exchanger.