Heat Transfer Analysis Of Heat Pipe Heat Exchanger Under Dehumidifying Conditions And Variable Conductance Heat Pipe For Mine Air Return

As a low-temperature waste heat resource produced in the normal operation of coal mine,mine return air is very suitable for coal mine preheating and fresh air after recovery to meet the demand of antifreezing of coal mine wellhead.In the engineering practice of heat pipe heat exchanger for recovery of mine return air waste heat,the recovery effect of heat pipe heat exchanger for mine return air is not good.When the outdoor temperature is low,the condensate water will freeze in the heat pipe heat exchanger,causing safety hidden danger.In view of the above problems and the shortcomings of the current research,this paper adopts the method of combining theory and experiment to analyze the heat transfer effect of heat pipe heat exchanger under different outdoor fresh air temperature conditions.Combined with the variable heat conduction tube technology,a scheme of variable heat conduction tube heat exchanger which can effectively solve the above problems is proposed and its application effect is analyzed.The actual operation condition of heat pipe heat exchanger used for recovery of waste heat from mine air was monitored and the actual heat transfer situation was analyzed.During the test,the temperature of fresh air inlet was in the range of-12.3?3.4?,and the temperature of fresh air outlet was in the range of 3.5?10.1?,which could meet the requirements of antifreezing of coal mine wellhead.The total heat transfer of the heat pipe heat exchange system is 2300?5800k W,and the latent heat of the return air is about 45%?50% of the total heat.It can be seen that the latent heat is an important part of the waste heat resources of the mine return air.By Threlkeld method based on enthalpy potential method,the heat transfer coefficient and fin efficiency of the heat pipe heat exchanger under the condition of moisture separation at the return air side of the mine were calculated,and then the moisture separation mode of the heat pipe heat exchanger was established,and the heat transfer effect under different fresh air temperatures was calculated and analyzed.The results show that there is a big difference between the temperature of mine return air and the temperature of condensed water film in heat pipe heat exchanger.The design of gravity heat pipe heat exchanger cannot be limited by the outlet temperature of mine return air > ?.The temperature of water film(that is,the temperature of the outer wall of heat pipe in the evaporation section)should be more than 0?.Because of its constant thermal conductivity,gravity heat pipe can not well meet the mine air return waste heat recovery application with low outdoor temperature.This paper puts forward a design and application scheme of variable conductance heat pipe with fixed gas storage chamber temperature.The analysis model of steady-state heat transfer resistance of a variable conductance heat pipe was established.Combined with the application of waste heat recovery of mine return air,the heat transfer process and temperature control effect of the variable conductance heat pipe under different mine return air temperature,fresh air temperature and new return air temperature difference were analyzed.The results show that the heat flux of the variable conductance heat pipe is determined by the temperature difference between the heat source and the working medium in the tube.When the variable conductance heat pipe is in the control stage,the range of working temperature in the heat pipe is very small,between 0 ?1 ?,and the heat flow of the variable conductance heat pipe is basically determined by the temperature of the mine return air.Finally,the heat transfer effects of gravity heat pipe heat exchanger and variable conductance heat pipe heat exchanger under the same inlet temperature of fresh air are compared and analyzed.The variable conductance heat pipe heat exchanger can be more suitable for the situation of low outdoor ambient temperature and less waste heat resources in mine return air.It is an extension of application scope for the technology of mine return air waste heat recovery by heat pipe heat exchanger.In addition,to meet the demand of wellhead antifreeze for the extreme minimum temperature of-25 ? in winter of the coal mine,18 heat exhaust pipes should be set for the variable conductance heat pipe heat exchanger,which provides some reference for the subsequent design of such engineering.