Research On Performances Of Fluid Flow And Heat Transfer Of Pillow Plate Heat Exchanger With Protrusion And Ellipsoid Dimple

Pillow plate heat exchanger,as a new type of plate heat exchanger,is used in several fields because its corrugated flow channels can increase the fluid heat transfer area and enhance the fluid disturbance,thereby improving heat transfer in the channels.At present,most of the researches on pillow plate heat exchanger focus on the changes in weld spot type,longitudinal and transverse spacing,and channel height.There are few studies on the arrangement of protrusions and ellipsoid dimples on the fin surface of pillow plate heat exchanger.When dimples are arranged on the fin surface of the heat transfer channel,longitudinal vortices can be generated in the channel,which can thin the thermal boundary layer,promote the heat exchange between the heat transfer wall and the fluid and the mixture of the cold and hot fluid in the channel.Thereby,the heat transfer of the channel is improved.Protrusion and ellipsoid dimple are arranged on the fin surface of pillow plate heat exchanger,and the flow resistance of the channel is often increased while the heat transfer is improved.To enhance the overall heat transfer performance of the pillow plate heat exchanger,numerical simulation is utilized to analyze the influences of weld spot type,protrusion,and ellipsoid dimple on the flow and heat transfer characteristics of pillow plate heat exchanger in this study.The numerical simulation results are as follows:(1)The study on weld spot types,circular,teardrop,wing,elliptic Ⅰ(Long axis along the flow direction),elliptic Ⅱ(Long axis perpendicular to flow direction)and flat tube,found that heat transfer in the main flow area plays an important role in the heat transfer of the pillow plate channel,and the heat exchange in the recirculation zone behind the weld spot is poor.Compared with circular weld spot,the mainstream velocity of the teardrop,wing,elliptic Ⅰand flat tube weld spot types decreases,resulting in reduced heat transfer in the mainstream area of the channel,but the heat transfer is improved in the recirculation area.The main flow velocity and flow resistance in the channel with the weld spot of elliptical II type are the highest,and the main flow heat transfer is the best.The main flow velocity and flow resistance of the channel with the weld spot type of wing are the smallest,and the main flow heat transfer is poor,but the heat transfer in the recirculation zone behind the wing weld spot is better.The comprehensive performance factor(JF)of the heat transfer channels for teardrop,wing,elliptical I,elliptical II,and flat tube weld spot increases by 1.0%-4.2%,1.3%-8.9%,1.0%-8.1%,1.0%-3.8%,and 1.0%-6.7%,respectively,compared with circular weld spot.(2)After placing the protrusion,the longitudinal vortices generated by the protrusions can scour the upper and lower wall surfaces and thin the thermal boundary layer,which can promote the mixture between the hot and cold fluid and hence the enhancement of heat transfer.The longitudinal vortices generated by the protrusion can enhance the heat exchange between the fluid in the recirculation zone and the mainstream area,reduce the dead zone behind the weld spot and improve the heat transfer in the recirculation zone.The fluid flow resistance increases with the improvement of heat transfer in the protrusion channel.The arc protrusion can improve the heat transfer in the main flow area and the recirculation zone,and the flow resistance in the arc protrusion channel is more greater.Comparing the heat transfer channels with different weld spots and protrusion shapes,the Nu and f of the elliptic Ⅱ weld spot channel with arc-protrusion is the largest,and the Nu and f of the wing weld spot channel with straight-protrusion is the smallest.When using straight protrusion,the elliptic Ⅰ weld spot channel with straight-protrusion has the largest JF,and JF increases by 14.3%-23.4%.When using the arc-protrusion,JF of the wing weld spot channel with arc-protrusion is the largest,and JF is improved by 15.3%-27.8%.Thus,the arc protrusion can better improve the overall performance of channel.(3)After arranging the ellipsoid dimples,the longitudinal vortices generated by ellipsoid dimples can promote the mixing of hot and cold fluids in the channel,and the longitudinal vortices behind the weld spot can promote the heat transfer in the recirculation zone,which decreases the heat transfer dead zone.The values of Nu and f of the elliptic Ⅱ weld spot channel with ellipsoid dimple are the largest,and the values of Nu and f of the wing weld spot channel with ellipsoid dimple are the smallest.Compared with the circular weld spot smooth channel,JF of the dimpled channel with circular,teardrop,wing,elliptic Ⅰ,elliptic Ⅱ and flat tube weld spot increases by 6.8%-16.7%,12%-22%,14.6%-22.4%,14.4%-23.4%,3.6%-10.4%,and 12.3%-22.1%.When Re<6000,JF of the elliptic Ⅰ weld spot channel with ellipsoid dimple is the largest,while the JF of the wing weld spot channel with ellipsoid dimple is the largest when Re>6000.