Research For Fluid Flow And Thermal Performance In A Three-phase Closed Thermosyphon

A three-phase closed thermosyphon(THPCT)was constructed to study the heat transfer performance,which working medium was the mixture of SiC solids and water.Its heat transfer performance was compared to that of a two-phase closed thermosyphon(TPCT)using pure water.The thermal performance of the THPCT using water/SiC(particle size of 35-mesh,48-mesh,60-mesh)was investigated under the filling ratio of 80%,the solid holdup of 0%-20%,and the heat flux of 8-232 kW m-?.For the the same solid holdup and heat flux,the thermal performance of the THPCT using 60-mesh SiC/water was also investigated in the filling ratio of 40%.The evaporator heat transfer coefficient,the condenser heat transfer coefficient,and the overall thermal resistance were calculated to evaluate the thermal performance.The results show that the evaporator heat transfer coefficient reduces as the heat flux increases in the filling ratio of 80%.At a low heat flux level(less than 182 kW m-?)the THPCT using 60-mesh SiC/water with the solid holdup of 20% acquired the optimal heat transfer performance in the evaporator section.Besides,the condenser heat transfer coefficient improves when increasing the heat flux.Under all the heat flux,the best thermal performance was achieved in the condenser section when the solid holdup of the medium of 48-mesh SiC/water was 15%.The overall thermal resistance decreases generally as the heat flux increases.In terms of the overall thermal resistance,adding SiC solids in the water deteriorates the heat transfer performance,and 48-mesh and 60-mesh SiC solids may improve the thermal performance a little(no more than 7.4%)just at a low heat flux level(less than 182 kW m-?).When the filling ratio is 40%,the evaporator heat transfer coefficient of the THPCT using 60-mesh SiC/water increases 10% at least in contrast to that of the THPCT with the same medium.The 60-mesh SiC enhances heat transfer as the solid holdup is 5% or 10% and the heat flux is less than 122 kW m-?,and the evaporator heat transfer coefficient increases 12.5% at most.The condenser heat transfer coefficient of the THPCT using 60-mesh SiC/water increases 44% at most,compared to that of the THPCT with the same medium.The 60-mesh SiC particle enhances heat transfer as the solid holdup is 5% or 10%,and the condenser heat transfer coefficient increases 10% at least.In terms of the overall thermal performance,the minimum reduction of 8.7% is acquired when the filling ratio changes from 80% to 40%.The 60-mesh SiC enhances heat transfer as the solid holdup is 5% or 10%,and the overall thermal resistance reduces 4.7% at least.In a word,reducing the filling ratio is very beneficial to the improvement of the heat transfer performance of the thermosyphon.In addition,the 35-mesh SiC solids failed in enhancing the heat transfer performance under all the heat flux while 48-mesh and 60-mesh Si C can enchance heat transfer in a low heat flux level.The effect of solid particles on the thermal performance of the thermosyphon is related to their fluidization condition.The fluidization of solids help accelerating the nucleate boiling while their accumulation in the liquid pool hinders the boiling.As a result,the common effect of the two factors determines the final heat transfer performance in the evaporator section.