| Surface heat transfer is an important form of heat transfer.It is mainly divided into two types of heat transfer methods: convection and radiation.It has practical application requirements in the fields of electronic integrated devices,aerospace,heat exchanger,solar power generation and nuclear power,and the performance of surface heat transfer has been widely concerned.The current research results show that the micro-nano structure has a significant enhancement effect on the surface heat transfer characteristics,and the heat transfer effect and heat transfer mechanism of different structures are different.Based on the surface fabrication technology of femtosecond laser micro-nano structure,we carried out the research on boiling(convection heat transfer)and radiation.The main contents are as follows:In terms of boiling heat transfer,domestic and foreign scholars have obtained a general increase in critical heat flux(CHF)by optimizing surface wettability,structural morphology,porosity and other parameters,however,the lifting effect of heat transfer coefficient(Heat transfer coefficient,HTC)is subtle and even reduced.In view of the insufficiency of CHF and HTC in the current research,this paper creatively puts forward a scheme of splicing micro-nano structure with original surface(changing the proportion of laser scanning).The experimental results show that the surface micro-nano structure accounts for 3/4,the synchronization between CHF and HTC was significantly improved,and the CHF value is increased by 120% compared with the original surface(and the corresponding HTC was 40% higher).The reason is that the splicing surface has a destructive effect on the boiling film formation state,which is beneficial to the rapid detachment of large bubbles,thereby enhancing the heat exchange efficiency.Further simulation to calculate the velocity of the fluid in the process of boiling,we found that the splicing surface can bring more severe fluid disturbance,which has positive feedback on the detachment of the bubble and forced convection in the later stage of boiling.It is a brand-new work to comprehensively enhance the boiling heat transfer on the surface of the spliced micro-nano structure,and the physics based on it provides a new technical development idea for boiling heat transfer enhancement.In terms of radiation heat transfer,micro-nano structures were fabricated on the aluminum surface by femtosecond laser for thermal radiation experiments.The results showed that the thermal radiation power is significantly enhanced with the increase of micro-nano structure scale,and the maximum thermal radiation power increased to 4.5 times compared with the original surface.On the other hand,due to the relationship between surface radiation and absorption characteristics,in view of the research of absorption heat transfer,a power measurement device considering solar radiation and TEG heat dissipation is constructed by imitating the real use environment which based on the application background of solar thermal power generation.The micro-nano composite structure was fabricated on the surface of the aluminum by laser pulse,and it was used as a solar thermal power generator(Thermoelectric generator,TEG)light absorber.The results of power generation experiments showed that the photoelectric conversion efficiency(power generation efficiency)of aluminum surface with micro-nano structure compared with polished aluminum foil or bare power generation sheet can be increased by 43.3 and 10.7 times respectively.The physical mechanism of the photoelectric conversion can be summarized as follows: the surface of the micro-nano structure generates high thermal energy deposition by absorbing sunlight,which leads to the improvement of the carrier mobility of TEG module,thus improving the power generation performance.The fabrication of micro-nano structure surface by femtosecond laser can enhance the spectral absorption characteristics of radiation.This study is of great significance for the research of heat dissipation in the field of aviation and solar temperature difference power generation. |
PDF Full Text Request