Research On The Water Energy Storage Device Applied On Combined Cooling Heating And Power System

The combined cooling heating and power(ie.CCHP)system has become an important energy application technology under the background of carbon neutrality due to its safety,cleanliness and high energy utilization efficiency.The natural stratified water energy storage technology has a good application value in the actual CCHP system for it`s advantage that can offset the disadvantage of the CCHP system that the energy efficiency reduction due to load fluctuation on the user side.At present,there are few special studies on the hydro-energy storage devices,that are large-scale,low-water depth,and rectangular-structured,for CCHP systems.Starting from the actual energy storage demand of CCHP system,this paper uses numerical-simulation method to study the optimal setting of hydro-energy storage devices applied to CCHP system.The effects of different height-diameter ratios,different forms of water distributors and external thermal insulation thickness on the cold storage performance of water storage devices were analyzed,in order to provide technical reference for engineering application of distributed energy.First of all,this paper analyzes the influencing factors and evaluation indexes of the performance of the water energy storage device.Introducing Θ as the dimensionless temperature of the thermocline,considering 0.15<Θ<0.85 as the effective thickness of the thermocline layer.The limitations of two commonly used performance evaluation indicators,the mixed number MIX and the performance index FOM,are analyzed,and an evaluation indicator(the cooling efficiency,η)that is more suitable for CCHP engineering applications is proposed.According to the actual engineering characteristics of the water storage tank of the CCHP system,the CFD model of water-cooling device with constant volume and constant flow is established and verified.Then,the influence of the main factor changes on the cold storage performance was compared and analyzed by CFD simulation.Changing the height-diameter ratio of the established water storage tank model,the distribution form of the water distributor and the thickness of the external insulation layer,then analyzes the effect of some factors on the cold storage performance of the water tank:(1)The cold storage efficiency and charging time at the end of cooling were studied under different height-diameter ratios of the cuboid water storage tank.The larger the height-diameter ratio of the cold-water storage tank,the better the cold-storage performance of the water-storage tank,but the optimum height-diameter ratio range of 2～6 is taken into account comprehensively considering the cooling efficiency and cooling time of the water storage tank.(2)The influence of different types of water distributors,that is,the change of Reynolds number at the inlet of the water distributor,on the cold storage performance of the water tank is studied.When the Reynolds number at the inlet of the water distributor of the sink is between 120 and 950,the distribution form of the water distributor is suitable.(3)Under non-adiabatic conditions,in order to achieve the optimal situation under the combined factors of cold storage performance and engineering economy,suitable thickness of the external thermal insulation layer of the water storage tank is 8cm.Finally,optimizing the design of natural layered water storage tank of a CCHP system based on an actual engineering case.Proposing a cold storage scheme of multislot connection type tank,as the double-baffle structure added,the height-diameter ratio of the cell water tank is getting increased.It is verified that the multi-slot connection type water storage scheme can significantly improve the cold-storage performance of the water storage tank,but the double baffle structure will bring flow loss to the multi-slot connection type tank.