Numerical Simulation Research On Heat Storage And Release Characteristics Of Triplex Tube Phase Change Heat Storage Unit

Efficient utilization of energy has become an important factor in our country’s social and economic development.Industrial waste heat has the characteristics of dispersion,indirectness and instability,which make it difficult to recycle,resulting in a lot of waste.Phase change heat storage technology can break the constraints of time and space,solvinge the problem of unbalanced heat supply and demand,and ensuringe stable output and storage of heat.It has broad application prospects and practical significance in the field of industrial waste heat recovery.Due to the generally low thermal conductivity of phase change materials,the energy storage efficiency of phase change heat accumulators is low,which seriously hinders the development of phase change heat storage technology.Therefore,optimizing the structure of the phase change regenerator and improving the energy storage efficiency of the phase change regenerator have become the research focus.This paper takes the horizontally placed three-tube phase change regenerator as the research object,and establishes a two-dimensional phase change model through reasonable simplification.Considering the gravity and the natural convection,the heat storage/release process of the two-tube and three-tube phase change heat storage units in the circular channel was simulated first,and the heat storage/release time and average heat storage time were compared and analyzed.The effects of different phase change materials and different wall temperatures on the heat storage process of the three-tube phase change heat storage unit were simulated.Secondly,a three-tube phase change heat storage model with built-in straight fins was established,and the effects of different fin lengths and numbers on the melting/solidification process of the three-tube phase change heat storage unit were compared.Finally,the built-in straight fin three-tube phase change thermal storage unit is optimized,and the built-in Y-fin three-tube phase change thermal storage unit is designed.The simulation results of the heat storage/release process of the Y-fin and straight-fin phase change heat storage unit are compared and analyzed.In addition,the melting/solidification process of the phase change heat storage unit with different opening and closing angles of the Y-fins is simulated.The main contents of this paper are as follows:(1)The physical model of the three-tube phase change heat accumulator is established,which is reasonably simplified into a two-dimensional three-tube phase change heat storage unit.Based on the enthalpy method model,after verifying the independence of grid number and time step,the experimental data in the literature is simulated and verified,and a reasonable and feasible calculation model is obtained.(2)The melting/solidification process of the two-tube and three-tube phase change heat storage units in the circular channel is simulated.The results show that compared with the two-tube phase change heat storage unit,the three-tube type reduces the storage/release time by 95% and70%,respectively.(3)In the three-tube phase change heat storage unit,the effects of different phase change wall temperatures and different phase change materials on its melting process were simulated.The results show that when the temperature difference is 10°C and20°C,the melting time is reduced by 46% and 63%,respectively;under the same boundary conditions,the melting time of PCM2 and PCM3 is reduced by 49% and 136% compared with PCM1.(4)On the basis of the three-tube phase change thermal storage unit,a three-tube phase change thermal storage unit with built-in straight fins is established.The effects of different fin lengths and fin numbers on the heat storage/release process were studied.The results show that,taking the rib length L=11.15 mm as the standard,the melting time of the rib length L=22.30 mm,L=33.45 mm and L=44.60 mm is shortened by 11.6%,26% and 9%,and the solidification time is shortened by17%,24% and 25%;taking the number of fins N=0 phase change heat storage units as the standard,the number of fins N=4,N=6 and N=8 phase change heat storage units reduces the melting time37%,44% and 47%,and the setting time was shortened by 38%,53% and 66%.(5)The structure of the built-in straight fin three-tube phase change heat storage unit,was optimized,and a Y-finned phase change heat storage unit was designed.The heat storage/release process of the phase change material in the Y-fin three-tube phase change thermal storage unit is simulated,and the comparison with the straight fin three-tube phase change thermal storage unit with N=8 fins is carried out.The results show that the Y-shaped fins increase the contact area with the phase change material,and improve the local overheating problem caused by the heat flow path in the phase change heat storage unit and the excessive temperature difference between the upper and lower areas.Compared with the straight fin phase change heat storage unit,the storage/release time of Y-fins is reduced by 37% and 33%;the average heat storage/release power is increased by48% and 50%.(6)The influence of different opening and closing angles of the Y-shaped fins on the heat storage/release process of the phase change heat storage unit is simulated.The study found that the opening and closing angle θ=60°,θ=90°and θ=120°shortened the heat storage time by 9%,18%and 21% respectively compared with θ=30°,and the heat release time reducde 14%,24% and 47%respectively.Through the comprehensive analysis of the built-in fin phase change heat storage unit,it is concluded that the phase change heat storage unit when the opening and closing angle isθ=120° is the best three-tube phase change heat storage unit.