Numerical Investigation And Experimental Verification Of Flow And Heat Transfer Characteristics In Printed Circuit Heat Exchanger

The gasifier of the regasification module of the Floating Storage and Re-gasification Unit(FSRU)is the core equipment of the entire gasification system.The traditional heat exchanger is in terms of equipment volume,heat exchange efficiency and equipment stability and other aspects are gradually unable to meet the demand for offshore LNG gasification.As a new type of microchannel heat exchanger,Printed Circuit Heat Exchanger is considered as the first choice of LNG gasifier for FSRU platform.Therefore,using LNG as the working medium to carry out the research on the mechanism and characteristics of different flow heat exchange forms in PCHE is of great significance for realizing the efficient operation of the FSRU vaporizer.In this paper,the numerical models of single-phase flow and heat transfer,supercritical flow and heat transfer,and condensing flow and heat transfer in PCHE channels are established respectively,and the simulation results are verified with experimental results to ensure the accuracy of the numerical model.The conclusions of this paper are as followsFor the single-phase propane flow,the velocity and temperature of the fluid will stabilize after the third cycle of the Z-type PCHE channel;When the turning angle θ is 5°,there is no reverse flow phenomenon at the turning point,but for channels with θ greater than 15°,there will be reverse flow phenomenon at the turning point;For PCHE channels with different turning angles,different pitches and different diameters,the correlation equations under laminar flow conditions and transitional flow conditions have been developed.The average errors of the Fanning factor correlations under laminar flow conditions and transitional flow conditiongs are 4.6%and 5.1%,respectively;The average errors of the developed Nu correlation are 4.0% and 4.6% respectively;The channel with a turning angle of 15°has the best comprehensive performance.For the supercritical methane flow,the pressure drop rises sharply near the pseudocritical point;When the fluid temperature is higher than the pseudocritical temperature,the pressure drop increases with the increase of heat flux,and decreases with the increase of working pressure;The heat transfer coefficient first increases and then decreases with the fluid temperature,and reaches a maximum value near the pseudocritical temperature;When the fluid temperature is near the pseudocritical temperature,increasing the heat flux at a low mass flux will significantly worsen the heat transfer;The heat transfer coefficients at different working pressures all reach peaks near the pseudocritical temperature corresponding to each pressure,and are consistent with the change trend of specific heat capacity at each pressure;The pressure drop correlation developed for single-phase flow is also applicable to supercritical flow;The average errors of the pressure drop and heat transfer correlation developed by supercritical methane in the Z-type PCHE channel are 5.7%and 5.1%,respectively.For the propane condensation flow,annular flow,annular wave flow and plug flow are observed in the Z-type PCHE channel;As the mass flux increases,the quality of the transition from annular flow to intermittent flow gradually reduce;The newly developed flow pattern boundary model can distinguish the flow pattern of the Z-type PCHE channel well;The condensation pressure drop first increases and then decreases with the quality,and reaches the maximum when the dryness degree reaches around0.78;The influence of heat flux on the pressure drop can be ignored;The pressure drop decreases with the increase of the saturation temperature;The heat transfer coefficient first increases and then decreases with the quality,and reaches a peak around 0.78;Under the medium quality condition,increasing the heat flux can slightly enhance the heat transfer in the channel;Affected by physical properties,when the quality is less than0.6,the heat transfer coefficient decreases with the increase of the saturation temperature,and when the quality is greater than 0.6,the heat transfer coefficient slightly increases with the increase of the saturation temperature.The average errors of the condensing pressure drop and heat exchange correlations developed for the Z-type PCHE channel are 6.6%and 6.5%,respectively.