Study On Thermodynamic Parameters And Cooling Effect Of Cold Wall Cooling System

Cold wall cooling refers to the absorption of heat in the roadway by covering the heat absorption system in the wall of the roadway to achieve the purpose of cooling.This paper briefly introduces the layout of the cold wall cooling system in the roadway and builds the experimental platform.Through the six groups of cold wall cooling experiments,the relationship between the flow velocity and the temperature difference between the inlet and outlet of the heat exchanger is（35）T（28）0.88-0.81v（0.3m/s≤v≤0.8m/s）,calculated the convective heat transfer coefficient between the outer surface of the heat exchanger and the air in the roadway is 2.1W/（m²×K）,the average heat absorption of the single-piece heat exchanger is 71.8W,and the accuracy of the experiment was verified by numerical simulation.The thermodynamic parameters of the cold wall cooling system are analyzed:flow velocity（0.01m/s≤v≤0.2m/s）,tube spacing（75mm≤D≤150mm）,roadway wall temperature（35°C≤T_w≤50°C）and inlet water temperature(2°C≤T_in≤22°C),the analysis results show that the flow velocity is inversely proportional to the temperature difference between the inlet and outlet of the heat exchanger,and proportional to the heat absorption;the tube spacing is inversely proportional to the temperature difference between the inlet and outlet of the heat exchanger and the heat absorption,and proportional to the average temperature of the outer surface of the heat exchanger;the inlet water temperature is inversely proportional to the temperature difference between inlet and outlet of heat exchanger and the heat absorption,and proportional to the average temperature of the outer surface of the heat exchanger;the flow velocity is large,the tube spacing is small,and the inlet water temperature is low,which will all increase the cooling effect.The relationship between the flow velocity,the tube spacing,the inlet water temperature and the average temperature of the outer surface as well as heat absorption of the heat exchanger are obtained,and the influence of each parameter on the heat absorption is acquired.The suitable thermodynamic parameters should be selected according to the needs.In the study of the cooling effect of the cold wall cooling system on the ventilation tunnel,the application process of the cold wall cooling technology is introduced,and a 500m roadway is taken as an example to verify the effect of the cold wall cooling system.The curve of the roadway wind temperature when the cold wall cooling technology is not used is calculated,and the airflow reaches 30.17°C at 500m.Then calculate the wind temperature curve after the cold wall is applied on both sides of the roadway.The airflow drops to 27.54°C at 500m to meet the cooling requirements.Then calculate the wind temperature curve of the roadway under different coverage area ratio and the ventilation distance of reaching 28°C.The results show that with the increase of the coverage area of the cold wall,the temperature of the airflow at the same position gradually decreases,and the cooling effect is more significant.And the effect of cold wall cooling system would be better when applying at the lower wind temperature.When the existing heat exchanger parameters cannot meet the cooling demand,reducing the inlet water temperature of the heat exchanger and reducing the tube spacing can effectively extend the ventilation distance of the roadway.In the application of the cold wall cooling system,in order to ensure the pressure difference across the pipeline is stable,the flow direction of the inlet pipe should be the same as the outlet pipe.The flow resistance of the single-piece heat exchanger is353.3Pa.In the 500m roadway,the flow resistance of the single-side cold wall is2478.9Pa;the water demand of the cold-wall cooling system is 4.43L/s.