Study On The Effect Of Particle Characteristic Parameters And Packing Characteristic Parameters On The Random Packing Performance And Heat Transfer Performance Of Particle Pile

In order to reduce carbon emissions and achieve global climate management,China has proposed a"dual carbon"target.One of the important approaches to reduce emissions,decrease carbon and achieve the goal of"double carbon"is the utilization of renewable and clean energy sources such as solar and wind power to generate electricity.Energy storage system is an important solution to develop continuous and controllable renewable energy supply technology,and the particle thermal storage system is a common thermal storage system in the energy storage system.Particle heat storage tank is a common heat storage device in energy storage system,the heat storage particle pile is the energy storage part of the particle heat storage tank,and many problems of its random packing characteristics and heat transfer characteristics urgently require solution.In this paper,heat storage particles were studied as the object.The corresponding coupled model of random packing and heat transfer of the particle pile in the particle heat storage tank was established.The reliability of the model was also verified by using experimental data of the previous researcher.The effects of particle characteristics parameters(particle size and particle size distribution,particle static friction coefficient)and particle packing characteristics parameters(particle feeding flow rate and vibration parameters)on the random packing performance and heat transfer performance of the particle pile in the particle heat storage tank were investigated by numerical simulation.The main conclusions are as follows:(1)Studying on simulation of packing and heat transfer of isometric particle piles,with the increase of particle size,the particle packing rate decreases linearly,the depth of wall effect increases,the contact number per unit area(specific contact number)decreases,and the average coordination number decreases gradually.As the particle size increased from 10 mm to 30 mm,the packing ratio decreased from 0.585 to 0.553,the specific contact number decreased from 5901 to 640,and the average coordination number decreased from 4.25 to 4.09.As the particle size increased,the temperature uniformity of the particle pile gradually deteriorated.In the initial moment of heat transfer,the heat flux of the particle pile decreased from 2762.9 W/m~2 to 2047.5 W/m~2,and the heat transfer performance of the particle pile hardly changed with the increase of particle size in the stable heat yield period,and the heat flux was 410 W/m~2.In the binary mixed particle size pile,when the mixing ratio of the number of particles in the binary mixed particle size pile(the ratio of the number of small particles to the number of large particles,referred to as the mixing ratio)is 3:1,the highest particle packing rate is 0.602,and when the mixing ratio is 2:1,the average particle coordination number is the largest,which is 4.36.When the mixing ratio increases from 1:3 to 3:1,the local packing rate increases from 0.437 to0.494,and the coordination number The peak value was between 3 and 4 with a probability of about 0.4.When the mixing ratio exceeded 1:1,the mixed particle size pile packing rate was greater than the single particle size pile packing rate.The larger the mixing ratio,the better the temperature uniformity of the particle pile.In the initial moment of heat transfer,the heat flux of the particle pile gradually increased with the increase of mixing ratio,and the heat flux decreased from 2762.9 W/m~2 to 2265.3 W/m~2 when the mixing ratio increased from 0:1 to 1:0.In the heat transfer stabilization period,the heat storage particle pile with the mixing ratio of 3:1 had the best heat transfer performance,and its heat flux was 441.9 W/m~2.In the polydisperse mixed particle size pile,the standard deviation of particle size has a small effect on the random packing performance and heat transfer performance of the particle pile.(2)With the increase of static friction coefficient,the particle packing ratio,the specific contact number and the average coordination number of particles gradually decreased,and the decrease rate gradually became slower,and the distribution curve form of particle coordination number gradually changed from normal distribution to positive skewed distribution,and the distribution of coordination number became more and more concentrated.When the static friction coefficient increased from 0.01 to 0.7,the particle packing ratio decreased from 0.619 to 0.563,the specific contact number decreased from2026 to 1393,the average coordination number decreased from 5.6 to 4.1,and the decrease of specific contact number and average coordination number were 31.2%and 26.8%respectively.The smaller the static friction coefficient,the greater the local packing rate in the near-wall region of particle pile,with the maximum local packing rate of 0.498 and the minimum of 0.425.With the increase of the static friction coefficient,the tilting phenomenon of the isothermal layer of the heat storage particle pile gradually improved,and the temperature uniformity of the particle pile with low static friction coefficient was better.In the two heat transfer periods,with the increase of the static friction coefficient,the heat flux of the heat storage particle pile decreased,and the heat flux density decreased from 3408 W/m~2 to 2133.4 W/m~2 and from 549.3 W/m~2 to 400 W/m~2,respectively,with a decrease of 37.4%and 27.2%respectively.With the increase of feeding flow rate,the particle packing rate linearly decreases,the local packing rate slightly decreases in the area near the heat exchange wall,the average particle coordination number gradually decreases,the heat flux of the heat storage particle pile decreases slightly,and the temperature uniformity of the particle pile with low feeding flow rate is better.(3)Vibration will greatly improve the packing of particles in the near heat exchange wall area,reduce the influence of wall effect on the packing,improve the overall packing density of the particle pile,and make the particle pile change from disorderly to orderly.Compared with the non-vibrated particle pile,the vibrated particle pile had higher packing ratio and higher specific contact number,greater local packing ratio in the near heat transfer wall area,more concentrated particle coordination number and larger average coordination number.The vibration also improves the heat transfer performance of the particle pile.Compared with the non-vibrated particle pile,the vibrated particle pile had higher initial heat storage,lower apparent thermal resistance,and higher heat flux at the moment of initial heat transfer and at the moment of heat transfer stabilization.The optimum amplitude and frequency of vibration were 0.25d and 5Hz respectively.5s was the critical vibration time in this paper,and the random packing performance and heat transfer performance of heat storage particles were almost the same when the vibration time was greater than the critical vibration time.When the vibration time is 3s,the specific contact number of the particle pile was the highest,but the particle packing rate was smaller than that of the particle pile after the vibration critical time.In the initial moment of heat transfer,the heat transfer performance of the pile of heat storage particles with 3s vibration was the best,and the heat flux was the highest,with 2380.6 W/m~2.In the stabilization period of heat transfer,the heat transfer performance of the particle pile with vibration time greater than the critical vibration time was the best,and the heat flux was the highest,with 410.7 W/m~2.