Experimental Study On Heat Storage Performance Of Open Adsorption Heat Storage System

Heat storage technology,which is a key technology to realize clean energy supply in the building field,can effectively improve utilization efficiency of solar energy and other resources,and can also play the role of peak clipping and valley filling on the energy demand side,while it can alleviate the supply and demand contradiction between the constant output end and the demand side of power resources.Compared with sensible heat storage and latent heat storage,thermochemical adsorption heat storage has higher density of energy storage,which can realize long-term zero-loss heat storage and has a very high development potential.For example,the open adsorption heat storage system with zeolite 13X/water as the adsorption working medium has the advantages of simple system structure,excellent adsorption performance of heat storage materials,which is suitable for clean heating in the building field.However,there are still some issues need to be studied in the open adsorption system,including the influence of desorption time and desorption temperature on the performance of open adsorption heat accumulator;variation law of performance parameters of heat accumulator with geometric size of heat accumulator.The theoretical analysis and experimental study of open adsorption heat storage system are carried out in this paper for those issues.Firstly,based on the similarity principle,the proportional relationship between the physical parameters and the geometric size of the heat accumulator is deduced by using the improved test analysis method.On the basis of the selected momentum equation,energy equation,and mass equation,the simplified equations are obtained after simplifying the energy equation heat source intensity term,fluid-solid composite heat capacity term and mass source intensity term.The proportional relationship of each parameter is brought into the simplified equation to obtain the relationship that makes the prototype and the model meet similar conditions.Under the condition that the ratio of porosity and each physical parameter is set to 1,the proportional relationship between the physical parameters of the heat accumulator and the geometric size is derived,the proportional relationship between the energy density of the heat accumulator and the geometric size and the related expression of the input energy ratio is further obtained.Secondly,an open adsorption heat storage system experiment test bench with replaceable heat accumulators was designed.Two size heat accumulators are designed to realize the analogy of size scaling.Combining the theoretical analysis and the operating parameter range of the experimental bench,an experimental scheme suitable for studying the effect of desorption conditions on the performance of the heat accumulator and a verification experimental scheme for the correlation expression of the ratio of the performance parameters and the geometric size ratio of different heat accumulators are proposed,and error analysis.of the test system is completed.Third,the variation law of the performance parameters of the heat accumulator and the characteristics of heat transfer inside the heat accumulator under different desorption time,desorption temperature,and adsorption humidity conditions is experimental studied.The research results show that the energy storage density of the accumulator increases with the increase of the experimental desorption temperature,the thermal efficiency decreases with the increase of the experimental desorption temperature,and the thermal efficiency of the accumulator decreases with the increase of the experimental desorption time.This variation law is consistent with the law obtained by previous studies.The accumulator energy storage density and average thermal power gradually increase with the increase of the experimental desorption time,but when the experimental desorption time exceeds 1 h,the accumulator energy storage density and average thermal power increase rate slows down.The average thermal power and energy storage density of the accumulator increase with the increase of the adsorption humidity,but the peak time of the adsorption heat release of the accumulator rises and then decreases with the increase of the adsorption humidity.The transfer rate of the"heat wave"inside the heat accumulator increases with the increase of the air humidity at the inlet of the heat accumulator.The experimental desorption time and temperature have little effect on the transfer rate of the"heat wave"inside the heat accumulator during the adsorption process.Under different experimental desorption conditions,the transfer rate of the"heat wave"inside the heat accumulator is about 2×10^-5 m/s.Finally,the correlation expressions between the ratios of performance parameters and the ratios of geometric dimensions of different heat accumulators is verified.In two heat accumulators of different geometric sizes（the geometric size ratio is 0.5）,the zeolite materials of different particle sizes is used,while keeping the other operating parameters of the experimental bench unchanged（desorption temperature,adsorption humidity）;take the porosity and the ratio of the physical parameters as 1.On the basis of keeping the input energy ratio constant during the desorption of the heat accumulator,adjust the flow rate ratio and the time ratio of the heat accumulator,so that the experimental test bench runs under stable conditions and completes the desorption experiment.The adsorption experiment was carried out without changing the adsorption humidity of the heat accumulator,and the results showed that:for a certain adsorption reaction time period（the temperature difference between the inlet and outlet of the two heat accumulators reached 4℃as the calculation start and end point）,the heat accumulator adsorption reaction time ratio is 0.25,the average heat source intensity ratio is 4.0,and the material storage density ratio is 1.0.The difference between these experimental values and the corresponding theoretically derived values is within 2%,3%,and 2%,thus verified the correctness of the correlation expression between the ratios of performance parameters and the ratios of geometric dimensions of different heat accumulators.