Comparison and Analysis of Heat Transfer and Inflow Rate for Supercritical Carbon Dioxide Based on Different Tubes

This paper is twofold.First,the effect of non-linear thermophysical property variation was presented using supercritical carbon dioxide(SCO_(2))around the thermodynamic pivotal point.The second part exhibits an experimental examination of the heat transfer(HT)behaviour of SCO_(2) in a helical tube with a hydraulic diameter of 2 mm at different mass fluxes(MF),heat fluxes(HF),and pressures(P).The experiments were carried out based on various pressures,mass fluxes,and heat fluxes for both scenarios.CO_(2) was cooled in a 2 mm diameter serpentine tube made of copper material.The experimental results showed that HT degradation could happen under the circumstances of a change in HF and MF and have significant effects on fluid inflow and HT performance.Also,buoyancy plays an essential and influential role in the HT factors.By increasing the pressure value,the HT parameters decrease when the pressure reaches 8 MPa,and the flotation value is more significant,which means a decrease in the HT factor.Finally,under the system circumstances,the HT value decreases with the increase in heat flux and pressure and increases with the increment in MF.

Thermal Performance of Mini Cooling Channels for High-Power Servo Motor with Non-Uniform Heat Dissipation

High-power servo motor is widely employed as a necessary actuator in flight vehicles.The urgent problem to be solved restraining the working performance of servo motor is no longer the torque and power,but the heat dissipation capability under high-power working conditions,which may cause the overheat,even burn down of motor or other potential safety hazards.Therefore,a structure of mini cooling channels with appropriate channel density is designed in accordance with the non-uniform heat flux of servo motor in this paper.Combined with the regenerative cooling method,the cryogenic fuel supercritical methane is served as the coolant,which is easy to be obtained from the propulsion system,and the heat from the servo motor can be transported to the combustion for reusing.According to the actual working cases of servo motor,a numerical model is built to predict the thermal performance of cooling channels.In order to better represent the secondary flow of coolant in the cooling channels,especially the turbulent mixed flow in the manifold,the k-εRNG model with enhanced wall treatment is employed resulting from its precise capacity to simulate the secondary and wall shear flow.On this basis,the heat transfer mechanism and thermal performance of cooling channels,as well as the influence of various heat flux ratios are investigated,which can offer an in-depth understanding of restraining excessive temperature rise and non-uniformity distribution of the servo motor.By the calculation results,it can be concluded that under the adjustment of the channel density according to the corresponding heat flux,the positive role of the appropriate channel density and the manifolds on heat transfer is manifested.Moreover,the maximum temperature difference of heating wall can be kept within an acceptable range of the servo motor.The heat transfer coefficient in the manifold is nearly 2–4 times higher compared with that in the straight cooling channels.The effect of buoyancy force cannot be neglected even in the manifold with turbulent mixed flow,and the pattern of heat transfer is mixed convection one in all the flow regions.The thermal resistance R and overall Nusselt number Nu are affected remarkably by all the operation parameters studied in the paper,except the pressure,while the overall thermal performance coefficientηdemonstrates differently.The strong impact of heat flux ratio is implied on thermal performance of the cooling channels.Higher heat flux ratio results in the stronger non-uniform temperature distribution.Meanwhile,only tiny temperature differences of the fluid and inner wall in manifolds among various heat flux ratios are demonstrated,resulting from the positive effect of mixture flow on heat transfer.