Study On Thermal Mixing Law And Valve Flow Resistance Performance Of Three-cylinder Pressure Exchange Device

The temperature of underground working face is too high due to heat damage in the mine,so it is necessary to use ground concentrated mine cooling system and use mechanical refrigeration to transport cold water to underground working face for cooling.Since the existence of gravitational potential energy makes the cold water carry high pressure,the pressure exchange device is used to depressurize the high pressure cold water,and at the same time,the primary high pressure circuit is formed to transport the hot water that completes the cooling function to the ground,so as to achieve the purpose of energy saving and consumption reduction.The pressure exchange device completes the pressure energy exchange in the way of direct contact between hot and cold water in cylinder.The cold water is transported to the air cooler at the end of the secondary low pressure circuit to cool the working face.The mixing of hot and cold water will lead to the increase of the temperature at the outlet of cold water,thus increase the heat load of the terminal air cooler,finally affect the cooling efficiency.At the same time,the flow resistance performance of check valve,a key component of pressure exchange device,is directly related to the overall resistance loss and operating efficiency of the device,so the thermal mixing problem and the flow resistance performance of check valve are the focus of this paper.Aiming at the thermal mixing problem,a three-dimensional numerical model for the mixing of hot and cold water in a three-cylinder pressure exchange device（TC-ERD）was established.Based on the basic parameters of the temperature of hot and cold water at 3℃and 18℃respectively,and the handling capacity of the device at 30 m³/h,the formation and evolution rules of the temperature mixing section in the secondary low pressure circuit were investigated with the instantaneous temperature rise at the cold water outlet less than 1℃as the optimization premise and the volume utilization ratio of the hydraulic cylinder not less than 90%as the optimization objective.The effects of inlet flow、temperature difference between hot and cold water、the length and diameter of cylinder on outlet temperature rise were analyzed,so the design parameters were optimized.Combined with the radial velocity distribution,the velocity field and thermal mixing field in the cylinder show the characteristics of synergistic development with time,and the inlet effect can result in the rapid development of the initial stage of thermal mixing.When the outlet temperature rise is determined,the increase of hot water inlet flow and the decrease of the temperature difference between hot and cold water will both increase the volume utilization ratio of the cylinder.When the handling capacity of the device is 30 m³/h,increasing the length of the cylinder not only improves the volume utilization ratio,but also reduces the switching frequency of the electromagnetic valve.Under conditions of the length of the cylinder reaching 18m and the outlet temperature rising to 1℃,the volume utilization ratio can reach 93.88%,and the switching frequency of the electromagnetic valve is only 1.5 min^-1.Volume utilization rate can reach above 90%when diameter in the range of 100～150 mm.The effect of different check valve structure characteristics on the resistance loss of the device was investigated by comparing the performance of full opening resistance and the dynamic characteristics of disc closing process of the wafer-lift and axial flow check valves.When the wafer-lift and axial flow check valve are fully open,the pressure on the front water side of the disc is larger,the pressure on the back water side is smaller,and from the front end to the back end of the valve,the pressure has an obvious step-type decline,and there are vortex flow and other non-ideal flow in the valve.The average flow resistance coefficient of the wafer-lift and axial flow check valve is 11.09 and 3.25 respectively.By comprehensive comparison of the drag reduction and energy saving performance of the two kinds of valves,the axial flow check valve’s structure design is more reasonable.Using dynamic grid technique to simulate the closing process of two kinds of valve disc,with the change of disc opening,the pressure distribution of axial flow check valve is more stable,the value of inlet and outlet pressure drop is relatively lower,and the pressure field has better adaptability to the dynamic change of disc opening.