| Because the gas hydrate storage cold storage overcomes the weakness of the ice storage cold phase transformation temperature and the refrigeration system mismatch,the water storage cold density is small,and the eutectic salt cold storage can be poorly cycled,it is an ideal new cold storage technology.However,in practical engineering applications of gas hydrate storage,there are problems such as long induction period and slow growth rate.Therefore,it is of great significance to study the mechanism of gas hydrate nucleation,shorten the induction period of nucleation,increase the growth rate of hydrate and increase its hydration rate so as to enhance its cold storage density.In this paper,R141 b refrigerant gas hydrate is taken as the research object,and the process of bulk nucleus,ice crystal nucleus,bulk hydrate historical solution and historical water-crystal growth process is visualized and the macroscopic induction time of nucleation is recorded.Then,the prepared hydrate sample is subjected to Raman and XRD tests.The crystal type of the sample is determined by qualitative analysis of the diffraction pattern.Finally,the gas hydrate crystallization theory is used to combine the visual growth of the prepared sample with the qualitative analysis of the diffraction pattern.The results of the analysis were combined to analyze the mechanism of crystal nucleation of these crystal-promoting modes.Using Fluent software simulation analysis,the role of metal in crystal nucleation nucleation was studied from the perspective of heat transfer,and the relevant influencing factors were analyzed.Finally,the cold storage density and the latent heat of phase change of the ideal condition HCFC-141 b hydrate were measured by the heat balance method,and the hydration rate of the hydrate was calculated according to the hydration rate according to the hydration rate measured by the centrifugal weighing.The results show that ice nucleation is suitable for system temperature not exceeding 4 C,while HCFC-141 b hydrate core should not exceed 6 C.Comparing XRD and Raman spectra,it is found that the bulk nucleus of HCFC-141 b hydrate is sII crystal.Ice has both sI and sII crystals.Ice crystals at 2.2 and 25 degrees have similar peaks with hydrate crystal samples.Therefore,ice crystals have crystallization promotion effect because ice crystals have similar crystal structure to hydrate crystals.The effect of homogeneous nucleation on promoting crystallization and nucleation is more obvious than that of heterogeneous nucleation,and the greater the undercooling is,the more obvious the effect of promoting crystallization is.Whether the reaction heat of hydrate formation can be removed within a period of time under the temperature of hydrate phase transition is one of the important reasons why metals have the effect of promoting crystallization.The latent heat of phase change of HCFC-141 b hydrate is 340.73J/g measured by heat balance method and centrifugal method.The storage density of HCFC-141 b hydrate is 202.37 J/g according to the ideal mass ratio.The phase change of hydrate can be accurately measured only by experimental form.It has general simplicity and accuracy in practical application.The hydration rate of hydrate growth in ice-promoted samples within 4 hours was 84% of that in HCFC-141 b bulk nucleus and HCFC-141 b historical solution,which indicated that homogeneous nucleation was better than heterogeneous nucleation.The excessive ratio of host and guest materials can reduce the hydrate growth rate and reduce the storage density.The sample prepared according to HCFC-141b/water ideal mass ratio of 1:2.62 has the highest hydrate rate,but increasing the ratio of guest materials can shorten the induction period of hydrate growth. |
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