Study On The Flow Boiling Characteristics Of Nano-refrigerant In Mini-channels Under The Synergy Of Ultrasound And Electric Field

Due to the characteristics of small size and high heat transfer efficiency,the mini-channels can transfer the heat of the high heat flux in the integrated element to the surrounding medium in time,which has a broad application prospect.The two active strengthening technologies of ultrasound field and electric field,combined with the passive strengthening technology of nanofluid,are used to study the flow boiling characteristics of nano-refrigerant in mini-channels under the action of ultrasound field and electric field.The main research contents include:(1)Research on the flow boiling heat transfer of nano-refrigerant in mini-channels under the action of ultrasound field.The mini-channel test section where the ultrasonic transducer can be placed was built,and the ultrasound field power and frequency range are 0?60W and0?40kHz,respectively.Three kinds of nano-refrigerants,TiO₂/R141b,Al₂O₃/R141b and SiO₂/R141b with nanoparticle mass fraction of 0.01%?0.2%were prepared by ultrasonic oscillation method.The flow boiling test was carried out in a rectangular mini-channel with section width of 2mm,and the mechanism was analyzed by combining with the visual image.The results show that the ultrasound field can significantly enhance the heat transfer,and the optimal concentration of the nano-refrigerant is different under different ultrasound field conditions,when the ultrasound field power and frequency are 60W and 23kHz,the TiO₂/R141b nano-refrigerant with a mass fraction of 0.1%has the best heat transfer effect.The ultrasound field power and frequency are 40W and 40kHz,and the best mass fraction is 0.05%.(2)Research on the flow boiling heat transfer of nano-refrigerant in mini-channels under the synergistic effect of ultrasound field and electric field.A linear electrode is arranged in the middle of each channel to generate a non-uniform electric field in the channel,and the voltage range of the electric field is 0?800V.The TiO₂/R141b nano-refrigerant with a mass fraction of0.01%?0.2%was used as the working fluid,and the flow boiling test was carried out under different ultrasound field and electric field conditions.When the ultrasound field power and frequency are 60W and 23kHz,the single ultrasound field can effectively enhance the heat transfer heat flux density in the range of 10.2?18.6 kW/m²,and the ultrasound field and the800V electric field can effectively enhance the heat transfer heat flux density in the range of10.2?25.2 kW/m².The optimal concentration of nano-refrigerant is different under different ultrasound field and electric field conditions.(3)Research on the pressure drop characteristics of nano-refrigerant flow boiling under the synergistic effect of ultrasound field and electric field.Experiments have studied the boiling pressure drop characteristics of the TiO₂/R141b nano-refrigerant flowing in the channel under the effect of a single ultrasound field and the synergistic effect of ultrasound field and electric field.The two-phase frictional pressure drop per unit length of nano-refrigerant under ultrasound field is 11.4%higher than that without ultrasound field.When the ultrasound field is coordinated with the 400V,600V,800V electric field,the pressure drop increases with the increase of the voltage.The comprehensive performance evaluation of different enhanced heat transfer methods is carried out.At low heat flux density,the enhanced heat transfer method of nanofluid/sound field/electric field has the best performance.