| Hydrate cold storage technology is a new and efficient energy storage technology,which can solve the problems of low density of traditional material storage,low system efficiency and easy aging of equipment,etc.,showing great application potential in air conditioning system,data center cooling,regional cooling and other fields.However,the development and application of hydrate cold storage technology are restricted by the unclear stability of cycle formation,strong randomness of nucleation,slow growth process,long period of cold storage and lack of pilot-scale system development and research.Based on this,this paper focuses on the method of hydrate strengthening generation,the stability of cycle generation and the performance analysis of hydrate pilot system.Specific research contents are as follows:(1)In view of the unclear mechanism of hydrate cycle formation,the phase transition growth characteristics and cycle formation stability of TBAB hydrate were studied in this paper.The nucleation characteristics of hydrate in the first generation system,the cycle generation system and the cycle generation plus gas disturbance system were analyzed.The experimental results show that there are A and B types of hydrate in the TBAB hydrate samples.When the concentration is 35wt%,ΔHSCH reaches a maximum value of 208.04 J·g-l,which is the best cooling storage concentration condition.In addition,the driving force of hydrate nucleation can be significantly reduced during the formation of TBAB hydrate cycle.The maximum reduction rate of supercooling degree is 28.3%,and the induction period is reduced by 41.5%~55.7%.On the basis of cyclic formation,gas disturbance can further promote the rapid and uniform nucleation of hydrate.The transition temperature of hydrate increases from 3 to 8.5℃ ℃,and the maximum reduction rate of supercooling is 60.1%.The reduction rate of induction period was above 60.5%.Finally,the cyclic formation stability analysis shows that TBAB hydrate with 35wt% concentration has stable cyclic formation ability.(2)In order to solve the problems of slow nucleation growth and long cold storage period in the process of hydrate cold storage.A method of rapid nucleation growth of hydrate induced by decompression was proposed.The decompression inducement method is based on the phase transition boiling process of refrigerant R134 a in solution.The gas-liquid boiling phase transition increases the degree of undercooling of solution and greatly shorens the completion period of hydrate.Experiments show that the hydrate formation rate can reach0.0217 mol/min under decompression,which is 868 times higher than that of pure water system.In addition,the combined agitation induced by decompression can further refine the boiling bubble size and improve the gas conversion rate.Under the combined agitation,the gas conversion rate of R134 a increased by 8.6%.In addition,the optimal operating conditions of decompression induction were obtained by comparing hydrate production and gas conversion at different temperatures.Finally,an improved gas cycle method with higher hydrate production efficiency is proposed.It provides theoretical basis for promoting the rapid and high density cold storage application of hydrate.(3)The mechanism of hydrate growth in large space is not clear,and there is a lack of pilot-scale system development and performance analysis for hydrate cold storage.In this paper,the first pilot-scale phase change storage system of hydrate(4 m3)was developed,and the influence mechanism of phase change growth characteristics of TBAB hydrate and heat transfer properties of the pilot-scale system was studied.It is found that the probability of hydrate nucleation increases in large scale space,and the hydrate can rapidly and uniformly nucleate in the volume phase space.When the phase equilibrium condition is reached,TBAB hydrate can immediately nucleate at a low undercooling degree of 1.35℃,and TBAB hydrate can be stably produced in large quantities at about 10℃.In the pilot system,TBAB hydrate has stable cycle generation ability,and the hydrate generation rate is stable at about 120kg/(m3·h)during the cycle generation process.In the process of hydrate cycle,due to the accumulation of hydrate deposition at the bottom,the solution after hydrate decomposition has a concentration difference and presents stratification.The regularity of hydrate growth and occurrence is different.The stratification disappeared when the concentration of the solution increased by 37%.Through the analysis of heat transfer characteristics,the heat transfer coefficient of hydrate decreases by 56% during the process from nucleation to stable growth,resulting in a decrease of cold storage rate by 73%.Therefore,the optimal design of heat transfer is the key to realize the application of hydrate efficient cold storage technology.The properties of hydrate and ice storage system(COP)were compared and analyzed,and the system of hydrate as a cold storage medium has greater development potential. |
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