ABSTRACT

Waste heat utilization heat exchanger in waste heat utilization system of ship engine can improve fuel utilization efficiency and reduce greenhouse gas emissions. An efficient heat exchangers help protect the ecosystem of ocean and the earth. This study aims to optimize the structure of fins to enhance heat transfer coefficient of the spiral finned tube which is widely used in waste heat recovery. In this paper, the mathematical model of the heat transfer coupling the fluid and solid substances of spiral finned tubes is established, and the flow field is experimentally verified by particle image velocimetry. In order to improve the heat transfer over air side, triangular winglets are built on the surface of fins. The heat and flow characteristics are numerically computed the same as the experimental model by using large eddy simulation, and compared these optimized fins with ordinary spiral fin tube at the Reynolds number ranging from 500 to 9,000. The heat transfer and resistance are calculated for sixteen different optimized spiral finned tubes by orthogonal experimental design method, and the correlations of Nusselt number and fanning friction coefficient of the optimized model are presented. The results show that the spiral finned tubes with triangular winglets have significant performance compared with ordinary spiral fin tube. The heat transfer coefficient is also improved as the number of triangular winglets increases. The optimized model shows good accuracy above 95% in terms of the correlation of heat transfer and resistance.

INTRODUCTION

Energy plays an important role in economic and social development. A large amount of fossil fuel has been used for economic development these years, which bring up the problem of energy shortage and global warming. The greenhouse effect causes polar glaciers to melt, raises sea levels and other series problems. Therefore, it is very important to improve fuel utilization efficiency. For a waste heat utilization system of ship engine, the mean of a high-performance waste heat utilization heat exchanger is much more than that, it also can help a ships sail greater distances.

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