Study Of Heat Transfer Enhancement Of Shell And Tube Oil-cooler In Shell Side

Shell and tube heat exchangers(STHXs),as one of the most indispensable devices,are widely used in many fields such as power generation,metallurgy,chemical industry,automotive industry etc.The development of STHXs is very late.It has been more than half century since the first TEMA shell and tube heat exchanger was made in China in 1963.Though mature the traditional STHXs are,many defects are still available.For many years,Chinese researchers are devoted to study the heat transfer enhancement of STHXs by changing the structures of shell side or tube side.Therefore,three structures are proposed in the present paper based on a certain type of single segmental baffle heat and tube oil cooler.Periodic model and unit model is used to simulate the flow field by using the commercial software FLUENT and HTRI.This paper mainly studies the effect of heat transfer performance according to three different shell side structures.The first structure is adding side baffles.The numerical results showed that the flow velocity near the shell wall of the original design was very fast,whereas the counterpart between the central tube bundles was comparatively slow,which weakened the heat transfer rate between the hot and cold fluids.For the new configuration,the flow near the shell wall slowed down while the velocity in the central region was significantly increased,which led to the heat transfer augmentation between the hot and cold fluids.Trefoil-hole baffles are applied in the second structure instead of traditional single segmental baffles.The effect on heat transfer performance of the trefoil-hole size is discussed.And the result shows that the flow and heat transfer characteristic is periodic.In addition,the effect of the width of the trefoil-hole ? on heat transfer performance is much more than the height of the trefoil-hole H.A small size of ? and a moderate size of H are able to get a preferable heat transfer capacity.The analysis shows that the most intense heat transfer area is near the baffle.And the effect on heat transfer coefficient of the change of ? is larger than that of H.Therefore,? plays a more vital role in trefoil-hole baffle heat exchanger than H.The third structure is based on the second structure.The heat transfer tubes are replaced by trefoil-shape finned tubes.And the effect on heat transfer performance of trefoil-shape finned tubes is studied.The result shows that trefoil-shape finned tubes are much more suitable than bare tubes,if the shell side working medium has a high Pr number such as oil.Moreover,the less the spacing of the fins is the better the heat transfer capacity is.In addition,according to the arrangement model of the fins of adjacent tubes,the heat transfer performance is also different.Based on the core flow heat transfer enhancement theory and field synergy theory,the dislocation arrangement model is better than that of normal arrangement model.