Study Of Enhanced Heat Transfer And Photothermal Thermoelectric Power Generation Applications Based On Bionic Structures And Nanofluids

The thermoelectric power generation device based on Seebeck effect has the characteristics of compact structure,small occupation area,no noise during operation,and environment-friendly,which makes it have broad application prospects in the field of new energy.According to Seebeck effect,increasing the temperature difference between the two ends of the thermal power plant is a direct means to increase its output power.Due to the excellent performance of biomimetic structures in the field of enhanced heat transfer,carbon nanotubes have strong light capture and photothermal conversion capabilities,and coupling the two to a photothermal thermoelectric power device is innovative and feasible.Therefore,in this thesis,the flow and heat transfer characteristics of the heat transfer system based on the bionic structure of ocean waves under the excitation of nanofluids and magnetic field were studied experimentally.Carbon nanotube composite nanoparticles（FCNTs）loaded with Fe₃O₄ were prepared by chemical coprecipitate method.FCNTs nanofluids were prepared by a two-step method and used on the hot end of a photothermal thermoelectric power plant.The temperature rise characteristics of FCNTs in a thermoelectric power plant were studied.Finally,the photothermal power generation characteristics of the thermal power generation system coupled by the two were studied experimentally.The specific research contents of this thesis are as follows:（1）Fe₃O₄-H₂O nanofluids with gum acacia（GA）as dispersant were prepared by a two-step method.The stability of the nanofluids was verified by observation sedimentation method.Composite magnetic nanoparticles（FCNTs）were prepared by chemical coprecipitation by modifying Fe₃O₄ onto carbon nanotubes,and their morphology and elemental characterization were performed.The photothermal temperature of FCNTs nanofluids with different concentrations at different light intensity and cold end Reynolds number was experimentally studied when they were used as the hot end of the thermoelectric power plant.（2）A heat dissipation system model based on the bionic structure of ocean waves and magnetic nanofluids was established,and a related experimental platform was built to experimentally study the effects of different Reynolds numbers（Re=600-1300）,the concentration of nanofluids（w=0,0.1%,0.3%,0.5%）,and the depths（H=2 mm,3 mm,4 mm）and angles（α=55°,65°,75°）of the bionic structure of ocean waves on the flow and heat transfer characteristics.Overall evaluation index and exergy efficiency evaluation model were established to analyze the thermal hydraulic performance of thermal dissipation system from the quantity and quality of energy.The results showed that there is a critical mass fraction of 0.3%in the heat transfer system,and the nanofluids exhibit the best heat transfer performance at this concentration.At the same time,there is an optimal bionic structure angle of 65°and depth of 4 mm,which can maximize the heat transfer performance of the heat dissipation system.It can be seen from exergy efficiency evaluation diagram of the system that most working conditions are located in the first and second parts,which shows that the heat dissipation system based on ocean wave bionic structure has good heat transfer characteristics from the energy mass analysis.（3）The heat transfer system model of the bionic structure cavity under magnetic field excitation was established,and the relevant experimental platform was built.The flow and heat transfer characteristics under different magnetic field intensity（20 m T,30 m T,40 m T）,nanofluids concentrations（w=0,0.1%,0.3%,0.5%）and bionic structure angles（α=55°,65°,75°）were investigated experimentally.Overall performance evaluation index and exergy efficiency evaluation model were applied to analyze the comprehensive heat transfer performance of the system under magnetic field excitation.The results showed that the addition of magnetic field can effectively enhance the heat transfer effect of the heat transfer system.The heat transfer effect increases with the increase of magnetic field intensity.When the wave structure angle is 65°,compared with deionized water,the Nusselt number of the heat exchange system can be increased by 54.43%at 40 m T.At the same time,the Nusselt number of the heat exchange system under the condition of 40 m T magnetic field intensity can be increased by 16.19%at maximum,compared with the nanofluids as working medium under the condition of no magnetic field intensity.Exergy efficiency evaluation showed that the introduction of magnetic field increases the exergy efficiency of heat exchange system,and exergy efficiency increases with the increase of magnetic field intensity.When the magnetic field intensity is 40 m T,the bionic structure angle is 65°,and the mass fraction of nanofluids is 0.3%,the thermal hydraulic performance of the heat exchange system is the best.（4）The new wave bionic structure was used in the cold end of the photothermal thermoelectric power generation system to strengthen heat transfer,and the FCNTs nanofluids were used in the hot end of the photothermal thermoelectric power generation system to absorb solar energy and improve the temperature of the hot end,so as to improve the output performance of the system by increasing the temperature difference between the two ends of the thermoelectric power generation.An experimental platform for thermoelectric power generation with coupled heat dissipation,photothermal and power generation modules was set up,and the effects of different nanofluid concentrations（50 ppm,100 ppm,150 ppm）,light intensity（2 sun,3 sun,4 sun）and cold end Reynolds number（Re=600,800,100,1200）on the temperature difference between hot and cold ends of the system and open-circuit voltage of the system were studied.The results showed that increasing the Reynolds number at the cold end and increasing the illumination intensity can both increase the open-circuit voltage of the thermoelectric power generation system.For the temperature at the hot end,the open-circuit voltage of the system reaches the maximum when the nanofluids concentration is 100 ppm.Through the analysis of the experimental data,it was found that the new bionic structure of ocean waves has a good ability to enhance heat transfer,and FCNTs nanofluids have excellent temperature rise ability under different light intensity.The coupling of the two can make the thermoelectric generation system have higher open circuit voltage and maximum output power,which has a certain guiding role for the design of the thermoelectric generation system.In this thesis,there are 10 tables,58 figures and 115 references.