Optimizing the Non-Inertive-Feedback Thermofluidic Engine for the Conversion of Low-Grade Heat to Pumping Work

Abstract

This paper deals with the dynamic modeling and multiparametric optimization of a thermally powered, reciprocating/oscillator fluid pumping technology known as the Non-Inertive-Feedback Thermofluidic Engine (NIFTE), with the aim of proposing pathways for the improvement of the capabilities of this technology. Analogies are drawn between the physical device and an electric circuit. All system parameters are perturbed simultaneously and independently, and configurations exhibiting the highest efficiencies, highest pumped volumetric flow rates, and lowest feedback gains (corresponding to lowest temperatures or heat inputs necessary for continuous operation) are examined. A sensitivity analysis is also undertaken. Low feedback tube resistances and inductances, low thermal resistances, and also low adiabatic volume capacitances all allow for high efficiencies and flow rates, as do somewhat elevated (relative to a preselected "nominal" design) load resistances and inductances, and displacer cylinder capacitances and inductances. The power cylinder inductance has its optimum near its selected nominal value. Generally, the power and displacer cylinder capacitances do not significantly affect the investigated performance indicators. The heat exchangers, vapor volume, and power cylinder are identified as important components that control the performance of the device. The optimal parameter values can be taken as useful indications toward the design of an improved NIFTE pumping device.