| Knudsen pump based on the thermal transpiration effect has many advantages,such as environmental protection,simple structure,no moving parts,no lubrication,and can use low grade energy.Knudsen pump is composed of cold cavity,hot cavity and micro channel,etc.When there is thermal transpiration effect in the micro-channel,the gas will flow from the cold cavity to the hot cavity,so the Knudsen pump has a boost effect.Vortex tube has the characteristics of adjustable cooling capacity,simple structure and no moving parts.Based on the vortex effect in the vortex tube,the flow will be divided into cold and hot streams,so it has the cooling and heating effects.Combining the advantages of the two,a new type of refrigeration system is developed.This new refrigeration system has no moving parts,simple structure,can utilize low grade energy,and can be combined in series and parallel according to the demand of environmental cooling capacity.This provides a new way to save energy,reduce emissions and build an environment-friendly society.In this paper,a new type of refrigeration system composed of Knudsen pump and vortex tube is developed.Secondly,the performance of the important parts of the new refrigeration system,such as the Knudsen pump and the vortex tube,is analyzed and the system is designed experimentally.The influence of micro-channel structure and gas properties on the net mass flow rate and pressure performance of the Knudsen pump was studied,and a COMSOL Multiphysics software was used to simulate the He flow in the Knudsen pump.The results show that the micro-channel structure has a great influence on the net mass:flow rate and pressure of the gas,and the gas property has a relatively small influence on the net mass flow rate and pressure of the gas.The net mass flow rate and the pressure change with the length of the micro-channel should be paid attention to when the gas flows in the micro-chan-nel with different shapes.Based on the simulation results,we have a clearer understanding of the pressure distribution,temperature distribution and velocity distribution in the Knudsen pump,and an intuitive understanding of He flow in the transition flow state in the micro-channel.The influence of He inlet parameters(pressure and temperature)on the performance(refrigeration effect,heating effect,refrigeration efficiency and heating efficiency)of the vortex tube is analyzed.The conclusion shows that when the inlet pressure of the vortex tube He increases,the refrigeration effect increases and the heating effect also increases.When He inlet pressure is between 0.7 and 3MPa,the effect of increasing the inlet temperature on cooling and heating is more obvious.With the increase of He cold flow rate in the vortex tube,the cooling effect first increases and then decreases,and the heating effect has the same change rule.When the cold flow rate is 0.3,the maximum cold effect of vortex tube is obtained.When the cold flow rate is 0.6,the thermal effect of the vortex tube reaches the maximum value.When the He cold flow rate in the vortex tube increases,the changes of its refrigeration efficiency and heating efficiency are consistent with the changes of refrigeration effect and heating effect.When the cold flow rate is 0.5,the heating efficiency of the vortex tube reaches the maximum value,and the refrigeration efficiency also reaches the maximum value.When the flow medium in the vortex tube is a gas medium,the gas with a large adiabatic index and a specific heat capacity at constant pressure is beneficial to the refrigeration effect and the refrigeration efficiency.Finally,based on the whole system,the effects of various factors on the efficiency and energy consumption of the new refrigeration system are studied.The conclusion shows that when the gas pressure ratio increases,the maximum system efficiency in the transition flow state is greater than that in the free molecular flow state.As the exit temperature of the system increases,the efficiency of the system decreases no matter which state the gas is in(transitional flow state,free molecular flow state).With the increase of the cold flow rate of the system,the system efficiency increases no matter what state the gas is in(transition flow state,free molecular flow state).According to the calculation,a 50m2 central control room needs 19,194 kW of cooling capacity in a year.By using the new refrigeration system,it can save 11,132.52 yuan(converted into electricity consumption)in a year. |
