An experimental investigation into the operation of a direct contact heat exchanger for solar exploitation

The use of a direct contact heat exchanger (DCHX), if properly applied, will allow several benefits. Primarily these include the elimination of the cost of a closed heat exchanger and the ability to operate with much lower temperature differences. This paper examines the operation of a liquid-liquid type DCHX in harressing the solar energy. Heat is delivered to the working fluid (heat transfer fluid) in the collection loop composed of solar collectors and a circulation pump. Two different kinds of working fluid were tested for their thermal characteristics that are immiscible with water. Texatherm 46 and diethyl phthalate (C6H4(CO2C2H5)(2)) and those that are experimented in the present analysis. Different schemes were used to introduce these fluids into the DCHX as they are either lighter (Texatherm 46) or heavier (diethyl phthalate) than water. A series of outdoor tests were conducted to determine the overall performance of DCHX as well as transient behaviors as the sun's energy is exploited. It is worthwhile to note that no thermal stratification was observed throughout the DCHX when in operation regardless of the working fluid. Stability and thermal performance, however, appear to improve when the working fluid is dispersed from the top of a DCHX. A difference of 8% is measured in the heat exchanger effectiveness, which gives a measure of the heat exchanger's overall ability in heat transfer. (c) 2004 Elsevier Ltd. All rights reserved.