Numerical Simulation Study On Flow And Heat Transfer Characteristics Of Supercritical LNG In Printed Circuit Heat Exchanger

A promising plate heat exchanger,namely a printed circuit heat exchanger(PCHE),which has the advantages of high compactness,large heat exchange area,high pressure and low temperature bearing capacity,and is suitable for the limited volume during vaporization at high-pressure conditions as a vaporizer.The channel type of PCHE generally includes the straight channel,zigzag channel,wave channel,and the discontinuous channel with non-continuous S-shaped fins and airfoil fins.The zigzag channel is one of the most widely used channel shapes due to its relatively simple manufacturing process and low manufacturing and maintenance costs.However,the heat transfer enhancement of the zigzag channel is at the expense of increased pressure drop compared to the straight channel.Therefore,it makes sense to further investigate zigzag channels to improve the heat transfer performance while increasing the pressure drop less.In this study,the flow and heat transfer characteristics of supercritical LNG in straight channel and zigzag channel of PCHE were studied by using SSTκ-ωturbulence model in Fluent software.The thermal properties of supercritical LNG in the range of 6.5-10 MPa were fitted into the piecewise-polynomial function of temperature.Then the effect of the channel bending angle of PCHE(0-45°),the inlet mass flux varied from 207.2 kg/(m~2·K)to 621.6kg/(m~2·K)and the operating pressure of 6.5 to 10 MPa on convective heat transfer coefficient and pressure drop of supercritical LNG are analyzed and discussed.The dimensionless parameters Nusselt number(Nu)and Euler number(Eu)and Fanning Friction coefficient(f)were used to evaluate the heat transfer performance and pressure drop performance of supercritical LNG.Nu/Eu and a performance evaluation criterion(PEC)are proposed to evaluate the comprehensive heat transfer performance by considering the heat transfer and pressure drop characteristics to find better bending angle and operating conditions.The supercritical LNG has a better heat transfer performance when bend angle is less than 15°with the mass flux ranging from 207.2 kg/(m~2·s)to 621.6 kg/(m~2·s),which improves at bend angle of 10°and lower compared to 15°at mass flux above 414.4 kg/(m~2·s).The heat transfer performance is better at larger mass flux and lower operating pressures.In order to improve the heat transfer performance and reduce the pressure drop of the zigzag channel,the new channel shapes of PCHE,i.e.,a zigzag with the inserted straight channel and zigzag channel with radian,are proposed and numerically investigated.The local and total pressure drop and heat transfer performance of supercritical LNG in a zigzag channel,zigzag with 1-5 mm inserted straight channel,and zigzag channel with radian are analyzed varying the mass flux from 207.2 to 621.6 kg/(m~2·s).Nu/Eu and PEC were applied to compare the overall heat transfer performance of zigzag with 1-5 mm inserted straight channel and a zigzag channel with radian to the zigzag channel of PCHE.In terms of heat transfer and pressure drop performance,the heat transfer performance of zigzag with the inserted straight channel and zigzag channel with radian is better than that of the zigzag channel,and it is higher at lower mass flux.The zigzag with 3-5 mm inserted straight channel has the greater heat transfer performance.