Characterization of wall temperature and radiation power through cylindrical dump micro-combustors

The micro-combustor (emitter) is a key component of the micro-thermophotovoltaic (TPV) system. An experimental study on the wall temperature and radiation power through the wall of a series of cylindrical dump micro-combustors was carried out. The effects of combustor diameter (d), combustor length (L), step height (s), flow velocity (u0) and fuel–air equivalence ratio (Φ) on the wall temperature distribution were investigated. ‘Emitter efficiency’ was defined and quantified based on the measured wall temperature. It was demonstrated that for this particular configuration, that is, a cylindrical micro-combustor with a backward-facing step, the two dimensionless ratios – L/d and s/d, are sufficient to determine the emitter efficiency, provided the flow velocity (Ue) and Φ are known. Based on this result, the effects of the dimensionless step height (s/d) on the emitter efficiency were examined. It was shown that such a sudden flow expansion in the dump combustors does not favor the radiation through the outer wall. Finally, the position of the highest wall temperature and its variation with the flow Reynolds number were discussed. It was noted that the Reynolds number and the relative flow expansion (s/d) alone are inadequate to determine the relative position of the highest wall temperature.