Numerical Simulation Of Supercritical Fluid Flow And Heat Transfer Characteristics In A Straight PCHE Channel

In order to achieve a sustainable development strategy and long-term stable supply of natural gas,in recent years,China has gradually transitioned from traditional offshore natural gas exploitation to deep-sea floating LNG mining.Printed circuit heat exchanger(PCHE)has the advantages of compact structure,low temperature resistance and high pressure,high heat transfer efficiency,etc.It is the preferred main heat exchanger for liquefaction equipment in floating LNG liquefaction vessels.In order to obtain the flow and heat transfer characteristics of supercritical natural gas in PCHE,this paper uses supercritical methane and supercritical mixture as the flow medium to study the influence of geometrical dimensions and operating parameters of semi-circular straight channel on its flow and heat transfer characteristics..It provides reference for the analysis of actual flow conditions of natural gas in PCHE.Using Fluent software to simulate the influence of the geometry of the semi-circular straight channel on the flow and heat transfer characteristics of the PCHE,this paper select a total of five different channel diameters of 1.4mm,1.5mm,1.6mm,1.8mm and 2.0mm.When the inlet mass flow rate of supercritical methane is increased,the convective heat transfer coefficient and pressure drop of different diameters of semi-circular channels are increased.Compared with the channel with diameter of 1.4 mm,the convective heat transfer coefficients of the other four diameters are respectively reduced 9.89%,20.47%,31.8%,42.06%,pressure loss decreased by 26.29%,40.08%,67.94%,81.25%,respectively.Although the smaller channel diameter has stronger heat transfer performance,its flow loss increases accordingly.When the influence of operating parameters on the flow and heat transfer characteristics of PCHE is analyzed,the influencing factors are inlet temperature,operating pressure and inlet mass flow rate,respectively,and supercritical methane and supercritical mixture are used as working fluids.When the inlet temperature changes,the convective heat transfer coefficient and pressure drop increase with the increase of inlet temperature;when the operating pressure changes,the heat transfer performance increases with the increase of pressure,and the flow loss gradually decreases;when the inlet mass flow changs,both the convective heat transfer coefficient and the pressure drop increase with the increase of the mass flow rate.Although the variation laws of the two fluids are basically the same,the convective heat transfer coefficient of supercritical methane is 2.41% higher than that of the supercritical mixture due to the difference in physical properties,but the pressure loss is also increased by 9.37%.According to the simulation results,the flow and heat transfer characteristics of supercritical methane and supercritical mixture in straight channel PCHE are summarized and analyzed,and the criterion correlations of Nusselt number and Fanning friction factor are fitted.When fitting the criterion correlations between the flow and heat transfer characteristics of supercritical methane and supercritical mixture,the relative error between the Nusselt number results and the correlation are within ±3%;the relative error between the Fanning friction factor results and the criterion correlation are within ±2%.In addition,when comparing the simulation data of this paper with the existing criterion correlation,the relative error is greater than ±15% due to the difference of the physical properties of the fluid medium and the setting of the boundary conditions during the numerical simulation.Therefore,it can be stated that the criterion correlations of this paper have applicability to supercritical methane and supercritical mixtures.