TOPIC: EFFECT OF HEAT SOURCE TEMPERATURE ON THE ELECTRICAL ENERGY OUTPUT AND THERMAL EFFICIENCY OF A SMALL-SCALE STEAM-DRIVEN GENERATOR: A BENCHTOP MODEL OF GEOTHERMAL POWER CONVERSION

Abstract

Geothermal Plant (Small Scale, bench top): Small-scale analogues of the various stages within a geothermal plant give access to tests of whether laws of classroom thermodynamics – the 2nd, Faraday’s induction, and numerical integration – work within the lab. We explored the effects on (i) the total electrical energy delivered by a steam-powered mini DC generator – measured via integration of P(t)=V(t)I(t) using trapezoids with a 120s window of data, and (ii) the Carnot efficiency of the equivalent heat engine, as we varied the temperature of a resistively-heated water reservoir from 60 °C up to 100 °C, in 10 °C increments. Average power Output Energy across three replicates, as a function of the operating water temperature, ranged from 22.4  1.8 J (60 °C) up to 198.3  6.2 J (100 °C – an increase of a factor of 8.9) while Carnot efficiency of the equivalent ideal device increases more gradually and almost linearly from 10.5% to 20.1% with progressively lesser increase every 10 °C increments of water temperature. In actual efficiency (Thermal->Electric efficiency), the theoretical maximum efficiency, or the Carnot efficiency, never came close.