Numerical Simulation And Exergy Analysis For The Shell-side Flow Within Shell-and-tube Water-heat Exchangers

CFD simulation has been widely used in shell-and-tube heat exchangers over last 30 years.In this article,Thermo-hydraulic performances of shell-and-tube heat exchangers with different baffle types will be studied using CFD methods.First,an attempt has been made to study hydraulic-thermal performances in the shell side of a segmental baffled shell-and-tube heat exchanger(SB-STHE)Furthermore,the second law of thermodynamics and the exergy theory are adopted on the simulation results to give a quantitative analysis of exergy utilizing efficiency.The results reveal that the exergy analysis is a more scientific means to analyze the utilization of energy compared with energy analysis.Increasing the mass flow rate of shell side water can increase the recovered quality and heat transfer coefficient,but decrease the utilization degree of hot water.Lastly,STHEs with different height of baffle cuts are studied,with the increase of the height of baffle cut,both the heat transfer coefficient and pressure drop decreases,but the performance ratio ?/P increases prominently.Then,double-tube-pass shell-and-tube heat exchanger(DTP-STHE)is proposed to improve the recovered heat quality from the point of the exergy theory.To prove this point,single-tube-pass shell-and-tube heat exchanger(STP-STHE)and DTP-STHE with segmental baffles are compared under the same conditions.The conclusion is surely made that the recovered heat quality in DTP-STHE is almost twice as that in STP-STHE.Furthermore,the heat transfer rate in both heat exchangers are nearly the same.In all heat exchangers,increasing the mass flow rate of water in shell side can increase the cold water quality and heat transfer rate,but decrease the utilization degree of hot water y.In order to investigate thermo-hydraulic performances of different DTP-STHEs,three kinds of DTP-STHEs with segmental,helical and flower baffles respectively are compared under same conditions.The results show that flower baffles produce the lowest pressure drop and lowest heat transfer coefficient.In order to better evaluate the economy of these three kinds of heat exchangers,heat transfer rate per effective pumping power QH/Po is introduced.The simulated results show that QH/Po of the flower baffle is the highest and QH/Po of the segmental baffle is the lowest.Therefore,heat exchangers with flower baffles balance the heat transfer rate and effective pumping power,thus it is the most economical.