| Printed Circuit Heat Exchanger(PCHE)is a compact plate heat exchanger that etches microchannels on heat exchange plates by chemical etching method and exploits bonding force between the atoms to achieve diffusion bonding,and it has promising application prospects in the fields of floating natural gas,offshore oil and gas processing,solar thermal power and high-temperature reactor intercoolers.Currently,investigations on flow and heat transfer characteristics in PCHE are limited to the study of structural and operating parameters with supercritical carbon dioxide and helium as working fluids on flow and heat transfer evaluation indexes,viz.fanning factor and Nusselt number,and investigations about the mechanism of flow and heat transfer are not deep enough.Meanwhile,the fundamental problems of flow and heat transfer with methane and methane/ethane mixtures as working media as well as the exploitation of relevant correlations are still in their infancy.Therefore,herein,methane and methane/ethane mixtures are as working fluids in this paper to explore the mechanism about the influence of structural and operating parameters on flow and heat transfer characteristics and develop relevant flow and heat transfer correlations in semi-circular section Zigzag type PCHE.Firstly,three-dimensional turbulent steady state numerical simulation method was determined and verified through the SST k-ω turbulence model in FLUENT platform,and mechanism of the influence of structural parameters on flow and heat transfer characteristics from the perspective of heat transport capability of fluids,viscous dissipation rate,degree of vortex occurrence and fluid boundary layer.The results indicated that worse flow and better heat transfer performances exhibited under smaller channel diameter,pitch,and bigger bending angle conditions;meanwhile,optimization analysis was also conducted though the coupling consideration of its flow and heat transfer performances,and draw the conclusion that the optimum channel diameter,channel pitch,and bending angle is 1.51 mm,20.0mm,and 15° in scope of this paper,respectively.Secondly,the mechanism of flow and heat transfer characteristics in semi-circular section Zigzag channel influenced by operating parameters with methane and methane/ ethane mixtures as the working media from the perspective of high-speed components of the turbulent core region,degree of flow separation,energy transport and dissipation rate based on the optimum Zigzag channel structure.The results indicated that worse flow and better heat transfer performances exhibited under higher mass flux and inlet temperature conditions,whereas higher outlet pressure conditions exhibited better flow and heat transfer performances,moreover,numerical simulation database under distinctive parameter conditions was constructed.Finally,applicability of current flow and heat transfer correlations based on semi-circular section Zigzag type PCHE in existing literatures were analyzed whether can be used to predict the flow and heat transfer characteristics with methane and methane/ethane mixtures as the working media preciously.Moreover,the applicability analysis results showed that existing correlations in literatures were not applicable to methane and methane/ethane mixtures,therefore generic correlations for methane and methane/ethane mixtures were developed based above numerical simulation database.The maximum relative errors of nusselt number and fanning factor between the numerical simulation results and results predicted by correlations are controlled within ±2%,which are of high prediction accuracy. |
