Experimental Study On Heat Transfer Enhancement Of Flat Heat Pipe For Cooling

Based on the previous study of authors' group, a new kind of flat heat pipe structure was brought forward by improving the structure of the prior heat pipe. To improve the capacity of cooling, integrated fin was fitted on the wall of condenser pipe. Al2O3 nanofluids with 0.5% mass concentration were selected as the working medium. Besides, different preparation method porous copper foam was used as the wicks of the flat heat pipe. Heat transfer performance test on series of flat heat pipe was carried out by setting up a test beach and designing the test plan. The effect of preparation methods and porosity of porous copper foam, base fluid, connected hole, filling ratio, heat source distribution, inclination and cooling intensity on heat transfer performance was studied, results was compared with the performance of the previous structure of flat heat pipe. At last, the effect of nanoparticle deposition was investigated.1) It could be inferred from the heat transfer enhancement mechanism of the interaction of Al2O3 nanofluids in porous copper wick heat pipe, the difference of the microstructure, surface features and pore density caused by different preparation methods may also have a significant effect on the heat transfer performance of the heat pipe. Under the condition of test, with the decrease in porosity, electrochemical deposition porous copper foam could strengthen heat transfer performance of flat heat pipe, while powder composite method exhibited different trend. In the same thickness and porosity, electrochemical deposition porous copper foam heat pipe performed better, compared to powder composite method.2) Connected hole of flat heat pipe not only improved isothermal characteristic, but decreased thermal resistance, improving the heat transfer performance.3) Under the same conditions, the maximum transmission power of the flat heat pipe increased by more than 10% compared with the previous authors' group.4) Too low and too high filling ratio could decrease heat transfer performance. Compared with 42% and 62% filling ratio, the best filling ratio was 50%.5) Compared with ethanol and acetone base fluid, because water had a higher latent heat of vaporization and greater surface tension, as working medium base fluid flat heat pipe had lower heat transfer performance.6) Compared with partial middle and partial side, the flat heat pipe in overall middle heating method had lower thermal resistance. The heating method could change the position of the highest temperature with little influence on the overall heat transfer performance.7) Results showed that heat transfer performance of flat heat pipe decreased with the increase of the inclined angle of the heat pipe. In the small angle range, the thermal resistance of the heat pipe increased relatively slowly, when the angle increased to a certain degree, the thermal resistance began to increase rapidly.8) Under the same conditions, the increase of the cooling wind speed could improve the heat transfer performance of the heat pipe to a certain extent. With the increase of wind speed, the thermal resistance of the heat pipe was reduced, when the wind speed increased to a certain extent, the variation was very small.9) After a period of placing the flat heat pipe due to the deposition of nanoparticles not only made the isothermal characteristic worse, but decreased the heat transfer performance., With the increase of heating power, part of particles levitated, making the decrease more moderate.