Research Of Fluctuating Fluid-solid Heat Transfer Characteristics And Refrigeration Enhancement In A Double-Opening Wave Tube

The double-opening gas-wave refrigerator is a new type of expansion refrigeration device.It takes the double opening gas-wave tube as the core component and uses the unsteady wave to exchange energy between the two air streams to realize the separation of cold and hot gas.Due to the advantages of simple structure,low speed and liquid carrying,the device has great advantages in harsh working conditions and has broad application prospects.At present,the isentropic expansion efficiency of this kind of refrigerator is up to 65%,however the refrigerator with small flow rate and large expansion ratio,the refrigeration efficiency decreases seriously.One of the important factors is the fluctuating fluid-solid heat transfer between the unsteady fluid and the tube wall.By intensive studing of the fluctuating fluid-solid heat transfer and refrigeration enhancement of double opening gas-wave tube,it is conducive to improve refrigeration performance,expand refrigerator application,and promote the development of gas-wave refrigeration technology.At present,there is a lack of comprehensive analysis on the fluctuating fluid-solid heat transfer of gas-wave tube.The heat transfer characteristics and its influence on refrigeration performance have not been systematically revealed.Therefore,a pulsating fluid-solid heat transfer calculation method was constructed.And a double-opening gas-wave refrigeration experiment platform with a stationary gas-wave tube bundle and rotating nozzles was built,by which the dynamic pressure and tube wall temperature were measured.In this paper,by combining theoretical calculation and experimental measurement,the fluctuating fluid-solid heat transfer and flow characteristics of double opening gas-wave tube are studied.And a forced cooling gas-wave tube bundle method is proposed to effectively improve the isentropic performance of refrigerator.The main work and research results are as follows:(1)A calculation method of fluctuating fluid-solid heat transfer was built.The heat transfer model of the solid region was simplified and a calculation program for the heat transfer in the solid domain was established.Through the wall heat flux and flow parameters which were obtained by numerical heat transfer calculation of unsteady flow in the fluid domain,the relationship between the gas wave tube and the fluid in the tube is established.The calculation method retains the accuracy of the numerical heat transfer model for unsteady flow,and at the same time,it can realize the fast dynamic calculation of the heat transfer process in the solid domain.It can predict the pulsating liquid-solid heat transfer behavior and the temperature distribution of the gas-wave tube of a double-opening gas-wave refrigerator.The results show that the calculation deviation is less than 3%compared with the experimental measurement results of the wall temperature.(2)The mechanism of fluctuating heat transfer was quantitatively analyzed.The results show that the convection heat transfer has a fast feedback to the unsteady flow,and has the characteristics of large amplitude fluctuation.The heat releasing behavior of high temperature gas is severe,and the heat is absorbed by the low temperature gas mostly,which directly causes the loss of refrigeration efficiency.The increasing of axial heat conduction of the gas-wave tube will increase the intensity of convective heat transfer.The axial temperature distribution of the gas-wave tube is non-uniform and fluctuates with small amplitude due to the fluctuating fluidsolid heat transfer.The calculation results show that when the axial heat conduction increases from 2W to 9W,the total heat involved in convective heat transfer increases by 0.02kw,the ratio of high temperature gas heat release to total heat transfer rises from 91.8%to 97.2%,and the ratio of low temperature gas heat absorption to total heat transfer rises from 77.5%to 85.5%.(3)The influence of pulsating fluid-solid heat transfer on refrigeration performance was revealed.The measured wave diagram were and the relationship between the pressure wave and two end boundaries of the gas-wave tube was obtained,and the effect of pulsating fluidsolid heat transfer on unsteady flow was analyzed.Research shows that under the influence of fluid-solid heat transfer,shock wave and expansion wave are weakened to a certain extent,while the flow rate of high-temperature gas decreases,which makes the optimal speed deviate from the theoretical value.The influence of convective heat transfer on refrigeration performance of the equipment under different structural parameters,physical parameters and operating parameters are studied.The results show that:improving the equipment capacity,reducing the wall thickness of the gas-wave tube and selecting the material with low thermal conductivity are conducive to improving the refrigeration performance of the equipment.The experimental results show that the refrigeration efficiency of the double nozzle device was increased by 1.1%(expansion ratio 1.6),1.8%(expansion ratio 1.8)and 1.7%(expansion ratio 2.0)compared with the single nozzle device;the cooling efficiency increased by 0.55%(1.6 expansion ratio),0.89%(1.8 expansion ratio)and 0.77%(2.0 expansion ratio)when the wall thickness of the tube bundle was reduced from 10 mm to 5 mm.Based on the calculation results,the cooling efficiency of stainless steel gas-wave tube was 3.61%higher than that of aluminum gas-wave tube.The uneven wall temperature distribution of the gas-wave tube will lead to tube thermal deformation.In the traditional gas-wave equipment,the thermal deformation is affected by the constraint position of the gas-wave tube on the axis.The research shows that when the maximum wall temperature of the gas-wave tube is higher than the ambient temperature,avoiding to arranged the constraint position in the middle of the gas-wave tube,which will cause the expansion of the high temperature part of the gas-wave tube and threaten the normal operation of the equipment.(4)A forced cooling gas-wave bundle method was proposed,which can effectively improve the refrigeration performance,especially under the conditions of small flow rate and high pressure ratio.The experimental results show that the performance of the forced cooling method is related to the circulating water flow rate and the forced heat transfer range.When the flow rate is not lower than the critical value,and the heat exchange chamber is forced to cool only the part of tube bundle where temperature is higher than the circulating water,the forced cooling can maximize the performance of the equipment,and its own cooling efficiency is the highest;By adjusting the rotating speed of the equipment,the influence of the decrease of the high temperature gas flow rate on the equipment performance caused by forced cooling can be reduced.The experimental results show that under the conditions of expansion ratio of 1.6,1.8 and 2.0,the refrigeration efficiency was increased by 4.94%,8.42%and 8.81%,and the optimal speed decreases by 27r/min,36r/min and 18r/min respectively.