A Small Electric Power Generation System for a Thermal Spring

Abstract

This report is concerned with the performance characteristics of an evaporator, a condenser and a screw expander devised for a small binary cycle system for use in a hot spring. Our evaporator system effectively utilizes hot spring steam which is normally exhausted. It is possible to eliminate the hot water pump and oil pump from our design. Our condenser system consists of an adapted shell and tube heat exchanger. The working medium gas from the expander is absorbed into the working medium liquid in the tube chamber. This absorbed gas is efficiently condensed by direct contact heat exchange. Our system used a small screw expander, and the high temperature working medium which as a high oil content, is supplied as a lubricant. For that reason, the working medium must be wet at that point. In order to provide an estimate of the wet expansion in the expander, we introduced the concept of "actual adiabatic expansion" based on the thermophysical data on the actual working medium.