Performance of annular heat pipe and optimization of heat recovery unit with heat pipes

Abstract

This study is concerned with performance of annular heat pipe and optimal design of heat recovery unit utilizing heat pipes. The annular heat pipe transports maximum heat which is turned out to be a cubic polynomial function of thickness of annulus. But when the annulus is large, maximum heat transfer rate is limited by a boiling criterion. This limit decreases inversely proportional to the thickness of annulus. Theoretical formula for thermal resistance of annular heat pipe is proposed. Comparison of the annular heat pipe with a wrapped screen heat pipe shows that annular heat pipe can transport more heat at large temperature differences. Experimental results on maximum heat transfer rate agree well with theory. Measured thermal resistance is lower than predicted results when the thickness of annulus is large. Optimization of heat pipes applied to heat recovery unit is studied. Linearized cost function is proposed, and Kuhn-Tucker``s necessary condition is applied. Optimal number of heat pipes, fin areas and outlet temperature are obtained. The optimization procedure proposed in this study may be extended to a more general case of heat exchangers.