Study On The Effect Of Single Vacancy On Heat Transfer Of Particle Pile Under Regular Arrangement

In China's industrial field,high temperature solid particles contain huge waste heat.If these energy can be effectively utilized,it will play a positive role in reducing energy consumption and improving energy utilization.In the process of waste heat recovery of high temperature solid particles,due to the irregular shape,rough surface and poor fluidity of solid particles,the friction and extrusion collision between particles will lead to vacancy.The vacancies increase the heat transfer resistance of particle pile and reduce the efficiency of waste heat recovery.At the same time,due to the irregular movement of particles,the number of vacancies is uncertain,the location is random and the shape is irregular,which makes it more difficult to study the heat transfer of high-temperature solid particles.Based on the waste heat recovery method of one-time heat transfer,the heat transfer characteristics of particle pile with vacancy were simulated by using Fluent software.In this paper,a heat transfer model of particle pile with single vacancy in regular arrangement was established,and the independent verification of the heat transfer model was carried out.At the same time,the usability of the heat transfer model was verified by the self-built heat transfer experimental platform of particle pile.The influence mechanism of single vacancy on the heat transfer in the surrounding granular layer was calculated and analyzed.The effects of particle characteristic parameters(thermal conductivity,particle size)and particle pile characteristic parameters(temperature gradient and contact area coefficient between particles)on the heat transfer characteristics of the particle pile with vacancy were systematically studied.The main results were as follows:(1)By calculating and analyzing the basic working conditions,it is found that the existence of vacancy reduces the heat transfer performance of particle pile,and the closer to the vacancy,the more obvious the effect of vacanc y on temperature distribution and heat transfer.The heat transfer modes around vacan cy mainly include solid heat conduction along X direction(vertical to the direction of main heat flow),solid heat conduction along Y direction(parallel to the direction of main heat flow),heat conduction and radiation between particles and gas,in which the solid heat conduction along the Y direction is the dominant heat transfer mode;when there are vacancies,the total heat transfer throw the hot wall decreases by 0.63%,the contribution of solid heat transfer on the hot wall increases by 0.0006%,and the apparent thermal resistance of the particle pile increases by 0.71%;In the X direction,the heat transfer affected zones of the vacancy on the left and right sides of the particle pile are equal,both of which are 1.79 times of the particle size.In the Y direction,the upstream heat transfer affected zones of vacancy is 4.03 times of the particle size,and the downstream heat transfer affected zones of vacancy is 3.81 times of the particle size.(2)With the location of vacancy moving from the cold wall to the hot wall,the heat transfer affected zone of vacancy moves along with the vacancy;the total heat transfer between the particle pile and the hot wall decreases first,then remains unchanged and finally increases,the contribution of solid heat transfer on the hot wall remains unchanged,and the apparent thermal resistance of the parti cle pile increases first,then remains unchanged and finally decreases.Within the range of 2.81 times the diameter of the cold wall from the center of vacancy,the existence of vacancy will affect the heat transfer between the particle pile and the cold wall.Within the range of 2.94 times the diameter of the hot wall from the center of vacancy,the existence of vacancy will affect the heat transfer between the particle pile and the hot wall.(3)With the increase of thermal conductivity of solid particles from 0.5 W/(m·K)to 50 W/(m·K),the total heat transfer between the particle pile and the hot wall increased from 0.43 W to 36.95 W,the contribution of solid heat transfer on the hot wall increased from 72.24% to 99.53%,and the apparent thermal resistance of the particle pile decreased from 863.58?/W to 10.15?/W.In the X direction,the heat transfer affected zone of vacancy on particle pile increased from 0.61 times of particle size to 1.82 times of particle size,In the Y direction,the upstream heat transfer affected zones of vacancy increased from 1.61 times of particle size to 3.91 times of particle size,and the downstream heat transfer affected zones of vacancy increased from 1.69 times of particle size to 3.93 times of particle size.(4)With the increase of particle size from 5.36 mm to 23.04 mm,the total heat transfer between the particle pile and the hot wall increased from 11 W to 47.37 W,the contribution of solid heat transfer on the hot wall decreased from 99.41% to 99.37%,and the apparent thermal resistance of the particle pile decreased from 34.08?/W to 7.92?/W.In the X direction,the heat transfer affected zone of vacancy on particle pile decreased from 1.81 times of particle size to 1.79 times of particle size.In the Y direction,the upstream heat transfer affected zones of vacancy decreased from 4.06 times of particle size to 4.01 times of particle size,and the downstream heat transfer affected zones of vacancy decreased from 3.84 times of particle size to 3.79 times of particle size.(5)With the increase of the temperature gradient from 175? to 975?,the total heat transfer between the particle pile and the hot wall increased from 16.28 W to 70.78 W,the contribution of solid heat transfer on the hot wall decreased from 99.63% to 97.91%,and the apparent thermal resistance of the particle pile increased from 10.75?/W to 13.78?/W.In the X direction,the heat transfer affected zone of vacancy on particle pile decreased from 1.83 times of particle size to 1.71 times of particle size.In the Y direction,the upstream heat transfer affected zones of vacancy increased from 3.94 times of particle size to 4.16 times of particle size,and the downstream heat transfer affected zones of vacancy decreased from 3.94 times of particle size to 3.48 times of particle size.(6)With the increase of the contact area coefficient between particles from 0.062 to 0.234,the total heat transfer between the particle pile and the hot wall increased from 27.76 W to 39.83 W,the contribution of solid heat transfer on the hot wall increased from 98.94% to 99.69%,and the apparent thermal resistance of the particle pile decreased from 13.51?/W to 9.41?/W.In the X direction,the heat transfer affected zone of vacancy on particle pile decreased from 1.81 times of particle size to 1.75 times of particle size.In the Y direction,the upstream heat transfer affected zones of vacancy decreased from 4.09 times of particle size to 3.95 times of particle size,and the downstream heat transfer affected zones of vacancy decreased from 3.86 times of particle size to 3.67 times of particle size.