Effects of number of air holes on flame and heat transfer characteristics in a multihole baffled combustor combined with micro-thermophotovoltaic and micro-thermoelectric systems

Abstract

• A multihole baffled micro combustor combined with micro-thermoelectric generators is proposed as a micro power generator. • The optimal number of air holes related to the combustion efficiency and the preheating effect is obtained. • The good features for micro-thermophotovoltaic(TPV) and micro-thermoelectric(TEG) systems is linked to wavy and lobed flames. • The emitter efficiency for TPV applications is comparable to the swirling flow combustor. • A high conversion efficiency of 3.58% is obtained for the multihole baffled micro combustor. Currently, micro power generators have been widely drawing attention for various applications. In this study, the H 2 –air micro combustor (MC) with a multihole baffle plate was combined with two power generators based on micro-thermophotovoltaic and micro-thermoelectric systems. The reacting flow and conjugate heat transfer including the MC wall were analyzed by the detailed reaction mechanism and the outer wall condition of convection and radiation. From the resulting thermal fields, the characteristics of heat emission and electrical potential were examined. Eight baffles with different numbers of air holes (N a ) and three global equivalence ratios were selected, and a baffle with N a = ∞ was adopted to compare the multihole and annular air flows. The combustion characteristics depending on N a were explored by analyzing the changes in the reaction zone, the flammable range, reaction rate, and wall heat transfer rate. The N a effect on wall and center recirculation zones was comparable to the variation due to other geometrical variables of the baffle plate. As N a increased, the combustion efficiency increased to 20% of the N a = ∞ case. The combustion efficiency equivalent to the swirl MC was obtained for N a = 5–8, having enhanced preheating effects and large center recirculation zones. Compared to N a = ∞, the mean temperature of the multihole baffled MC increased by 6.4%–19.2% depending on N a . The emitter efficiency related a TPV system was comparable to the swirling flow MC. For a thermoelectric generator, the conversion efficiency of N a = ∞ was similar to that of a Swiss-roll MC, and the multihole baffled MC showed a high conversion efficiency of 1.55%–3.58% depending on N a and the global equivalence ratio.