| The super open-rack vaporizer with seawater as the heat source is a heat exchange equipment used by most receiving terminals of liquefied natural gas.The core structure of the vaporizer is a heat transfer tube,whose function is to vaporize natural gas by heating the liquefied natural gas in the tube with seawater outside the tube.Currently,the heat transfer of the tube is often calculated by the fixed outer wall temperature simulation method,although the calculation is simple,the calculation results may have errors due to neglecting the heat transfer of the seawater outside the tube and possible ice formation on the outer wall.Therefore,in this thesis,the whole heat transfer simulation method is used to simulate the heat transfer inside and outside the tube,and the results are compared with those of the fixed outer wall temperature simulation method,and the applicable conditions of the two methods are obtained.This study can provide reference for the design and operation of super open-rack vaporizer,and has practical significance.Firstly,based on the heat transfer characteristics of the tubes,heat transfer models of the tubes with the fixed outer wall temperature and the whole heat transfer simulation methods are established.Then,the heat transfer characteristics of the tubes under actual conditions are calculated by these two methods,and compared with the experimental data.Finally,the effects of the sea water temperature outside the tube,the flow rate inside the tube and the pressure inside the tube on the results are analyzed,and the applicable conditions of different methods are obtained.The specific research contents and main results are as follows:(1)Based on the structure and heat transfer mode of the tube,the whole heat transfer process of the tube is analyzed in terms of heat and mass transfer mechanism,including unidirectional heat transfer in preheating and heating section of the tube,phase change heat transfer of liquid boiling in vaporizing section of the tube,phase change heat transfer of seawater outside the tube and heat transfer of the tube wall.According to the above heat transfer characteristics,heat transfer models of the tube with the fixed outer wall temperature and the whole heat transfer simulation methods are established.(2)According to the experimental conditions of Morimoto.N and N.Hisada,the heat transfer of the tubes were calculated by the above two simulation methods.The simulation results were compared with the experimental data.It was found that the error of the whole heat transfer model in calculating the fluid temperature in the tube was within 3K,while that of the fixed outer wall temperature heat transfer model was up to 17K,which indicated that the whole heat transfer model is more accurate in simulating the tubes.In addition,it was found that the freezing rate in the groove on the outer wall of the tube was 17.5%for the complex structure tube and 9.6%for the common tube,combining with the difference of the simulation results,it can be seen that the freezing rate outside the tube was the main factor affecting the accuracy of the two heat transfer simulation methods.(3)By analyzing the influence of the sea water temperature outside the tube,the flow rate inside the tube and the pressure inside the tube on the results,it is found that the difference between the results of different simulation methods is positively correlated with the freezing rate,and the heat transfer characteristics are mainly affected by the temperature outside the tube and the flow rate inside the tube,while the pressure inside the tube has little effect.Therefore,the influence of the temperature(274K-285K)outside the heat transfer tube and the flow rate(0.02kg/s?0.13kg/s)inside the heat transfer tube on the results of the two methods is further analyzed,and the applicable conditions of the two simulation methods are determined:For composite structure tube,When the inlet flow rate is 0.02kg/s?0.05kg/s and the outside temperature is 274K?275K,or the inside flow rate is 0.06kg/s?0.07kg/s and the outside temperature is 274K?279K,or the inside flow rate is 0.08kg/s?0.13kg/s and the outside temperature is 274K?281K,the whole heat transfer method should be selected to calculate,and the other conditions can be calculated by the fixed outer wall temperature method;For ordinary tubes,when the inlet flow rate is 0.02kg/s?0.06kg/s and the temperature outside the tube is 274K,or the inlet flow rate is 0.07kg/s?0.10kg/s and the temperature outside the tube is 274K?277K,or the inlet flow rate in the tube is 0.11kg/s?0.13kg/s and the temperature outside the tube is 274K-278K,the whole heat transfer method should be chosen to calculate,and the other conditions can be calculated by the fixed outer wall temperature method. |
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