Experimental Studies On The Performance Of Separate Heat Pipe Heat Exchanger Of Mine Return Air

As a common challenge facing all mankind,climate change cannot be ignored by any country.Therefore,China is actively adjusting and optimizing the energy consumption structure.Coal mine is one of the industrial objects of national key reform,and there is still huge room for improvement in energy conservation and emission reduction.At present,the mine return air low temperature waste heat resource,which is an important derived heat energy of mine,has been recognized by the industry.The efficient recovery of the waste heat can replace coal to preheat fresh air and prevent freezing in the shaft,which will promote the formation of a clean and sustainable energy supply system for mines,and guarantee the achievement of the carbon peak and neutrality targets in China.Nowadays,waste heat recovery technology of mine return air is becoming more and more mature.In addition to the advantages of traditional heat exchange technology,the separate heat pipe heat exchange technology also has the characteristics of long-distance transmission,flexible layout,no additional configuration of other machinery and equipment,and low investment.Through the engineering test of an actual separated heat pipe heat exchange system in Shanxi Province,it is found that the project has the problems that the actual operation effect and the theoretical design are greatly different,and the unreasonable height difference and rising pipe diameter cause the increase of civil construction cost.In view of the above problems,this thesis mainly discusses the heat transfer characteristics and resistance characteristics of the separated heat pipe heat exchange system applied to the mine return air waste heat recovery project from the theoretical analysis and experimental studies,and provides reasonable structure parameters and working conditions parameters.The main contents and conclusions are as followings:1)The heat transfer characteristics of the separated heat pipe are summarized,and based on the heat and humidity characteristics of the mine return air,guided by the similarity theory,a similar model experimental system is built according to the prototype design,which mainly includes structural design,heat transfer calculation,resistance calculation and work safety check.After confirming that the experimental working fluid is R22,the evaporation section is planned to be fully filled,that is,the liquid filling rate for the evaporation section is 100%,and the liquid filling rate is 37% based on system consideration,with a total of 132 Kg working medium.2)The separated heat pipe heat exchanger system is tested to analyze the influence of height difference on the heat transfer characteristics of the system,and the influence of air volume and riser pipe diameter on the heat transfer characteristics and resistance characteristics of the system.The experimental results show that when the height difference is less than or equal to 3.845 m,the heat exchange and efficiency increase with the increase of the height difference,and when the height difference continues to increase,the heat exchange and efficiency tend to be stable;the height difference of 3.845 m is more reasonable;with the increase of air volume,the heat transfer in the evaporation section and the condensing section increases first and then decreases;the heat transfer coefficient increases with the increase of air volume;compared with the ascending tube diameters of 20 mm,25 mm and 20 mm,the heat transfer performance of 20 mm diameter is the best,25 mm diameter takes the second place,and 20 mm is not dominant;determining the air volume is the main factor affecting the pressure drop of the heat exchanger;air volume of evaporation section 140 m~3/min,air volume of condensation section 225 m~3/min,the rising pipe diameter of 20+25mm are more reasonable.3)After sorting out the experimental data of the working conditions with a height difference of 3.845 m and a riser pipe diameter of 20+25 mm,it is found that the existing empirical formulas of heat transfer and resistance cannot accurately describe the heat transfer of the separated heat pipe heat exchanger under the background of mine return air waste heat recovery.Therefore,the experimental correlations of heat transfer and resistance characteristics suitable for this condition were proposed.In conclusion,this thesis provides a reference for the optimization,design and application of the separated heat pipe heat exchange system in other mine return air waste heat recovery projects.