Study On Flow And Heat Transfer Characteristics Of Mixed Nanofluids In Concave Microchannels

With the development and progress of technology,electronic equipment and industrial facilities are tending towards miniaturization and integration,which requires heat exchange systems to have higher heat exchange and heat dissipation capabilities.This article selects a mixed nanofluid as the heat transfer working medium and a concave microchannel as the heat transfer device to enhance the flow and heat transfer effect,and completes the enhanced heat transfer analysis of the flow and heat transfer experiment.The main research content of this article is as follows:（1）Preparation,stability,and thermal conductivity of mixed nanofluids.This article selects Ag,TiO₂ nanoparticles and different types of surfactants to prepare Ag-TiO₂/DW mixed nanofluids using a"two-step method"and analyzes the stability and thermal conductivity of different factors.Through experimental analysis,it was ultimately determined that PEG4000with a ratio of 0.8 was the optimal surfactant,with an optimal ultrasound duration of 1.5 hours and an optimal Ag to TiO₂ nanoparticle ratio of 2:3.（2）Design,processing,and experimental setup of concave microchannels.Based on the rectangular straight microchannel,a concave structure is added inside the channel to complete the size design of the concave microchannel.The rectangular straight microchannel,the concave microchannel plate detector and the fixture used are fabricated by using the micromachining technology.We evaluated the flow and heat transfer characteristics of microchannels and completed the experimental setup based on the experimental schematic diagram.（3）Experimental study on flow and heat transfer of mixed nanofluids in concave microchannels.Through the flow and heat transfer experiments of mixed nanofluids in microchannels with different mass fraction,inlet flow rate,temperature and microchannel shape,the enhanced heat transfer mechanism of mixed nanofluids applied in concave microchannels was comprehensively analyzed from the perspectives of inlet and outlet pressure drop,friction Drag coefficient,working medium outlet temperature,Nusselt number,Microchannel plate detector bottom temperature,and enhanced heat transfer factors.The results show that the friction Drag coefficient of Ag-TiO₂/DW mixed nanofluid with 2%mass fraction in the concave microchannel decreases by 74.6%when the inlet flow rate is 20-60 ml/min and it decreases by72.78%in the rectangular straight microchannel,indicating that the concave microchannel is more conducive to the drag reduction effect.The Nusselt number of the Ag-TiO₂/DW mixed nanofluids with 2%mass fraction in the concave microchannel increased by 272.94%when the inlet flow rate was 10-60 ml/min,and the Nusselt number in the rectangular straight microchannel increased by 248.06%,indicating that the concave microchannel structure is more conducive to heat transfer.The enhanced heat transfer factors of Ag-TiO₂/DW mixed nanofluids with different mass fractions in both microchannels are greater than 1,and the study found that at an inlet flow rate of 60 ml/min,the number of enhanced heat transfer factors of 2%Ag-TiO₂/DW mixed nanofluids in concave microchannels increased by 45.31%compared to rectangular straight microchannels.This indicates that the combination of high-quality mixed nanofluids and concave microchannels can improve the heat transfer capacity of the entire heat transfer system.Therefore,this experimental system has an enhancing effect on enhancing heat transfer.