Waste heat recovery from a biomass heat engine for thermoelectric power generation using two-phase thermosyphons

Abstract

In this study, we propose a thermoelectric generator (TEG) based power generation system operated through waste heat of a biomass engine. Power generated by TEGs is utilized for recharging a 12 V uninterruptible power source (UPS) battery. Experiments are done to study the variation of power output, current and conversion efficiency with average flue gas temperature, output voltages, thermosyphon filling ratio (TFR) along with source and sink temperatures. Gasifier operation is optimized to identify the appropriate equivalence ratio (ER). The optimized ER for the present system is evaluated as 0.305 yielding a maximum flue gas temperature of 283 C. Thereafter, experiments are conducted to study various performance parameters when 48 TEGs are provided on the two-phase octagonal-shaped thermosyphons. Experimental results indicate that the maximum open circuit voltage of the present system is 31.52 V (17.12 V at DTmax.,1 ¼39 C and 14.40 V at DTmax.,2¼ 31 C) at an optimum TFR of 0.496. A thermal resistance based model is finally developed from which the maximum temperature gradient across the TEG for two thermosyphons is found as 40.12 C with a maximum relative error of 14.91% between model and experimental values. The total power generated from the system is found as 1.033W, whereas, the maximum conversion efficiency is calculated as 2.218%.