Study On The Heat Exchangers Constructed With Lash Baffles And Courrugated Tubes

Large and small hole or LASH baffle is a new type of baffle developed by Beijing University of Chemical Technology.It could be a whole round baffle or a segmental baffle.Corrugated tube is a kind of special tube with high heat transfer efficiency.Compared with ordinary shell-and-tube heat exchangers,the heat exchangers constructed with LASH baffles and corrugated tubes have good comprehensive properties is worthy of deeply research and development.In this thesis,numerical simulations were performed to study the heat transfer and flow resistance of the special heat exchangers.The main contents and research results are as follows:(1)Numerical simulations were performed to investigate the effects of the diameter of the large holes and the baffle pitch on the heat transfer and flow resistance in the heat exchangers constructed with the whole round baffles and corrugated tubes.With increasing the diameter of the large holes,the pressure drop on the shell-side drops significantly,but the heat transfer coefficients and Nu also decreased in some extent.The baffle pitch,however,has little effects on the pressure drop,heat transfer coefficients and Nu on the shell side.(2)For the heat exchangers constructed with the segmental baffles and corrugated tubes,numerical simulations were performed to investigate the effects of parameters especially the height of the window.Results show that similar to the whole round baffles,increasing the window height of the baffle,pressure drop,heat transfer coefficients and Nu number on the shell-side decrease.Increasing the large holes diameter of the segmental baffle heat exchangers,pressure drop,heat transfer coefficients and Nu number on the shell-side decrease and the baffle pitch has no obvious effects on the shell-side fluid flow and heat transfer.In addition,it is found that the pressure drop and the heat transfer coefficients of the heat exchangers constructed with the segmental baffles and corrugated tubes are lower than those of the heat exchangers constructed with the whole round baffles and corrugated tubes,but the comprehensive heat transfer properties of the former are better than those of the later.(3)The fluid flow and heat transfer models of the whole round baffles and segmental baffles heat exchangers with different structural parameters are established based on orthogonal design L9(34).According to the simulation results,most important structural parameters for heat exchanger performance are determined.By analyzing extreme differences,it is found that not only the whole round baffles but also the segmental baffles heat exchangers,the diameter of the large holes is the most influential factor to the pressure drop and heat transfer coefficient,followed by the window height of the baffle,and the minimum influential factor is the baffle pitch.(4)By changing the structural parameters,different heat exchangers were simulated,and the formulas for Nu associated with heat transfer coefficients were fitted based on sufficient the numerical simulation results.The formulas were numerically verified.(5)Compared the two studied heat exchangers,it is found that the comprehensive heat transfer coefficient of heat exchanger constructed with the segmental baffles and corrugated tubes is higher than that of the heat exchanger constructed with the whole round baffles and corrugated tubes.