Numerical Study On Flow And Heat Transfer In Shell Side Of Twisted Tube And Shell Heat Exchanger

The shell-and-tube heat exchanger plays a dominant position in heat exchangers because of their strong high temperature and pressure bearing capacity and high reliability.However,flow dead zone exists in the back region of shell baffle,which has a great influence on the heat exchanger.And the shell side fluid flow mode will cause large shell side resistance.Therefore,the research on how to eliminate the flow dead zone and reduce the resistance in the shell side of the shell-and-tube heat exchanger is the key to improve the heat transfer efficiency of the shell-and-tube heat exchanger.Twisted tube is a kind of heat transfer tube which is produced by flattening the round tube on the basis of the round tube and used to replace the smooth round tube by special processing.The twisted structure interferes with the fluid inside and outside the tube,which increases the turbulence of the fluid and benefits the heat transfer.In view of the problems of large flow dead zone and high flow resistance in the shell side of the traditional bow baffle heat exchanger,this paper proposes two new twisted tube heat exchangers: bow baffle twisted tube heat exchanger and opening baffle twisted tube heat exchanger.The heat transfer enhancement mechanism of two twisted tube heat exchangers was studied by numerical simulation,and compared with the traditional bow baffle heat exchanger.Then the change of the comprehensive performance of the two twisted tube heat exchangers with different aspect ratio and baffle spacing is studied.The flow field,temperature field,heat transfer and resistance of the two twisted tube heat exchangers with different parameters are analyzed.The results show that:(1)Under the same conditions,the comprehensive performance of the two twisted tube heat exchangers is stronger than the traditional bow baffle heat exchanger.The heat transfer coefficient and pressure difference are lower than the traditional bow baffle heat exchanger,but there is no flow dead zone in the shell side of the twisted tube heat exchanger.(2)The aspect ratio of twisted tube has a great influence on the comprehensive performance of twisted elliptical tube bow baffle heat exchanger when the inlet velocity is small.When the inlet velocity is 1m/s～2.2m/s,changing the aspect ratio of twisted tube has a great influence on the comprehensive performance of twisted elliptical tube bow baffle heat exchanger.For v=1m/s,the maximum JF of twisted elliptical tube bow baffle heat exchanger is 1.24 when the aspect ratio of twisted tube is 0.4,and the minimum JF is 1.126 when the aspect ratio of twisted tube is 0.7,the difference is 10.1%.When the inlet velocity is2.2m/s～3.4m/s,changing the aspect ratio of twisted tube has little effect on the comprehensive performance of twisted elliptical tube bow baffle heat exchanger.For v=3.4m/s,the difference between maximum and minimum JF is 0.98%.(3)The aspect ratio of twisted tube has a great influence on the comprehensive performance of twisted elliptical tube opening baffle heat exchanger when the inlet velocity is small.When the inlet velocity is 1m/s～2.2m/s,changing the aspect ratio of twisted tube has a great influence on the comprehensive performance of twisted elliptical tube opening baffle heat exchanger.For v=1m/s,the maximum JF of twisted elliptical tube opening baffle heat exchanger is 1.167 when the aspect ratio of twisted tube is 0.4,and the minimum JF is 1.089 when the aspect ratio of twisted tube is 0.7,the difference is 7.2%.When the inlet velocity is2.2m/s～3.4m/s,changing the aspect ratio of twisted tube has little effect on the comprehensive performance of twisted elliptical tube opening baffle heat exchanger.For v=3.4m/s,the difference between maximum and minimum JF is 0.5%.(4)The baffle spacing has a great influence on the comprehensive performance of twisted elliptical tube bow baffle heat exchanger.For v=1m/s,the maximum JF of twisted elliptical tube bow baffle heat exchanger is 1.146 when the baffle spacing is 100 mm,which is 6.5%different from the minimum JF.For v=3.4m/s,the maximum JF of twisted elliptical tube bow baffle heat exchanger is 1.379 when the baffle spacing is 60 mm,the difference between maximum and minimum JF is 4.5%.(5)The baffle spacing has little effect on the twisted elliptical tube opening baffle heat exchanger.For v=1m/s,the maximum JF of the twisted elliptical tube opening baffle heat exchanger is 1.095 when the baffle spacing is 100 mm,which is 4% different from the minimum JF.For v=3.4m/s,the maximum JF of the twisted elliptical tube opening baffle heat exchanger is 1.29 when the baffle spacing is 75 mm,the difference between maximum and minimum JF is 0.5%.