On the design of a hydrogen micro-rectangular combustor for portable thermoelectric generators

Abstract

Micro-combustion based thermoelectric generators have been proposed to power micro-electromechanical units. The present study aimed to optimize the thermal design of micro-combustor to best suit the requirement of thermoelectric generators. An equivalent heat transfer coefficient was used to consider the arranged thermoelectric generators and its effect was elucidated. Increasing the coefficient enhances combustor wall heat loss, reducing flame stability and uniformity index of temperature. It is thus impossible to constrain combustor outer wall temperature below the maximum allowable temperature of commercial thermoelectric generators (623K) simply through increasing equivalent heat transfer coefficient. To address this issue, three simple strategies of combustor channel modification, adding copper layer and using flue gas heat recirculation were developed. A notable improvement in uniformity index of temperature over 6.5% is achieved for the latter two strategies. Nevertheless, none of these three strategies can ensure outer wall temperature below 623K. Motivated by the different mechanisms to improve temperature uniformity and reduce wall temperature for the two simple strategies of adding copper layer and using flue gas heat recirculation, a hybrid strategy combining them was proposed. The hybrid strategy can maintain flame stability, improve uniformity index of temperature approach to 100% and control combustor outer wall temperature below 623K, making it a qualified strategy for designing high-performance micro-combustors.