Study On Shell-side Heat Transfer Enhancement Of Graded Flow For Shell-and-tube Heat Exchanger

Research on enhancement of heat transfer process and exploitation of high-efficient heat transfer equipment is one of indispensable approach for saving energy of engineering and lessening consumption.Shell-and-tube heat exchanger is one of the most widely used heat transfer equipment in engineering field,studies on heat transfer reinforcement of tube side and shell-side are always arresting extensive attention of the researchers.As a necessary component of shell-and-tube heat exchanger,structure support of tube bundle could direct the fluid in the shell side to move in an expected flow pattern,and a fine structure support would also play an important role in enhancing heat transfer;during the period of further researches into structures support mainly employed in nuclear engineering and chemical industry,the major research work and conclusions are summarized as follows.(1)An anomalous shaped shutter baffle is put forward and the influence of two different kinds of shutter baffle on the performance of shell side thermal-hydraulic characteristics is studied.The results elucidate: the curved surfaces of anomalous shaped shutter baffle increase the fluid turbulent intensity,weaken the thermal boundary layer in the vicinity of heat exchange tube,and make the temperature field and velocity field coordinate better;the validation and feasibility of the simplification for whole model into periodic model was also analyzed.Through the establishment of periodic model and employment of numerical simulation,the effects of different structure values(A)of anomalous shaped shutter baffle,baffle spacing and arrangement for baffles on the temperature and velocity etc were investigated.The results indicate: there is a positive correlation between the change of Nu number and structure parameter value(A).when the value of A increases,the number of Nu also becomes large;the Nu number reaches the highest with parallel arrangement of baffles.Both the correlative equations of the heat transfer coefficient and pressure drop in the shell-side of anomalous shaped shutter baffled heat exchanger are deduced on the theory of dimensionless analysis method.(2)As a variation of longitudinal heat exchanger,the fluid in the shell side of perforated plate mostly flows parallelly to axis direction and goes through the holes in circular plate to exchange mass and heat transfer;by improving the average velocity of main stream,the enhancement of heat transfer can be achieved.Since the velocity of jet flow generated and affected area are directly decided by the dimension of opening,the analysis about the influence of height of opening on shell-side flow and heat transfer of heat exchanger with quatrefoil-hole baffles,trefoil-hole baffles and big-hole baffles was carried out through establishment of periodic model.The results show: the effects of opening height upon the heat transfer and flow resistance are not in the same way,but for trefoil perforated plate,quatrefoil perforated plate and big-hole baffle heat exchanger,the trend of comprehensive performance agrees with the variation of opening height.Enlargement of opening height brings out decrement of heat transfer coefficient and pressure drop;while with decrease of opening height,heat transfer coefficient rises slightly with a tremendous pressure loss,so the comprehensive performance of heat exchanger goes down.According to the results obtained from numerical simulation,the correlation of pressure drop and heat transfer of shell side of quatrefoil-hole and trefoil-hole baffled heat exchanger are deduced with multiple linear fitting method,which could provide reference and guide for popularization and application for perforated plate heat exchanger.(3)According to flow analysis method,with the concern about bypass flow appeared between the inner shell and tube bundle,thermo-hydraulic characteristics of sextant helically baffled heat exchanger under different baffle inclination angle were investigated,and effect of sealing strips was also done.Results indicate that when bypass flow exists,heat transfer will be reinforced with decreasing baffle inclination angle;as to the circumstances with sealing strips,the enhancement becomes obvious while baffle inclination angle turns large.(4)Under the same working condition,the influence of four kinds of structures support of tube bundle selected including segmental baffles,helical baffles,anomalous shaped shutter baffles and rod baffles on the performance of shell side flow and heat transfer was researched to discuss the relatively favorable working range of each kind of heat exchanger and preliminary definition for each level of graded flow.(5)The experimental platform for cold model of fluid flow was set up by employment of LDV optical measurement system and hydraulic system heat exchanger and the comparison between measuring data obtained and simulation results was also conduct.The results state: the deviation between simulation results and measuring values is less than 15.6%,so simulation results can be considered in good agreement with experimental measured data,which gives credit for the correctness and reliability of calculation method.