Numerical Investigations Of Flow And Heat Transfer Characteristics Of Supercritical Hydrocarbon Media In Semicircle Microchannels

After the strategic goal of‘carbon peak’and‘carbon neutrality’is put forward,it has become an inevitable trend to gradually reduce coal consumption,and to vigorously develop new clean energy such as hydrogen and natural gas.Natural gas has the advantages of high calorific value and clean.In China’s 14th five modern energy system planning,it pointed out that enhancing oil and gas supply capacity,and increasing domestic oil and gas exploration are the main direction of China’s energy industry development.To extract natural gas from offshore natural gas more efficiently,floating production storage and offloading unit（FPSO）emerges at the times require.It requires the heat exchanger with small volume and high safety.PCHE is the ideal heat exchanger for offshore natural gas exploration vessels as its incomparable compact structure and high efficiency.In this paper,under the supercritical and pseudo critical condition,the flow and heat transfer characteristics of supercritical methane and supercritical methane-ethane mixture in Zigzag-channel and wavy-channel PCHE was investigated numerically.The structure optimization of Zigzag PCHE was conducted.And the flow and heat transfer correlations for Nu and f was developed.First of all,the structure optimization of the double-channel Zigzag PCHE was conducted through the multi objective optimization method.Based on the double-channel model,the flow and heat transfer process was simulated numerically.The influence of inlet mass flux,inlet temperature and outlet pressure was summarized with supercritical methane-ethane mixture as flow media numerically.And the influential mechanism was analyzed from the perspective of the secondary flow intensity,regularize helicity,vortex distribution and entropy generation.The results show that with the increase of mass flux and inlet temperature,and the decrease of outlet pressure,the frictional pressure drop will increase.This is because that the secondary flow,and the intensity and range of vortex will increase.The convective heat transfer coefficient will increase as the rising inlet temperature,outlet pressure and inlet mass flux.But the increase of inlet mass flux and inlet temperature will also lead to increasing heat transfer entropy generation.And the increase of outlet pressure will lead to the opposite effect.Finally,according to the above simulation results,the correlation of flow and heat transfer is fitted.Secondly,the flow and heat transfer characteristics of supercritical methane flow were simulated in the wavy channeled PCHE.The flow and heat transfer performance of zigzag and wavy channels were compared and analyzed.The convection heat transfer coefficient under the same pressure drop was considered,and the heat transfer coefficient at constant pressure drop in the wavy channel was enhanced by about 20%.The effect of operating parameters on flow and heat transfer characteristics of supercritical methane was investigated.The influence law of these operating parameters is consistent with that in Zigzag channel.When the applicability of the existing correlations was analyzed,it is found that the correlations with S-CO₂as flow media is not accurate to predict the flow and heat transfer performance of supercritical methane,even though the channel structure is the same.This is because the difference of the thermal properties of these two fluids.Therefore,the correlation of supercritical methane flow for Nu and f in wavy microchannel is proposed,with high reliability.Finally,based on single-channel model,flow and heat transfer characteristics of supercritical methane was investigated under pseudo-critical condition.Comparison of single-phase model and two-phase model is conducted.It is found that the two-phase model can simulate the pseudo-critical flow and heat transfer performance of supercritical methane more accurately.This is because that the interaction between the gas and liquid phases are taken into consider in two-phase model.The effect of mass flux is simulated by two-phase model and found to be the same as that under the supercritical condition.But when the wall temperature is approximate to the critical temperature,the local heat transfer coefficient decreases dramatically.