In order to solve the problem of heat dissipation of permanent magnet synchronous motors, a technology using the principle of nanofluid electrochemistry is proposed. The main content of this technology is based on the characteristics and applications of nanofluids; according to the experimental system, the preparation and experimental parameters of nanofluids were determined; finally, by studying the influence of ultrasonic oscillation time and dispersant on the stability of nanofluids, it was concluded that the improvement of the thermal conductivity of nanofluids contributed to the improvement of the heat transfer rate of nanofluids. Experimental results show that when the volume fraction is 0.5, the increase rate of thermal conductivity is 1.51, the increase rate of convective heat transfer coefficient is 20.33, and the increase rate of convective heat transfer coefficient is greater than that of thermal conductivity, which shows that nanofluids have very good heat dissipation ability. It is proved that the technical research of nanofluid can meet the heat dissipation requirements of a permanent magnet synchronous motor.

This research establishes 5 mm three-dimensional (3-d) flow and heat transfer microfin tube theoretical models with three different geometric structures. Using these models, the thermal-hydraulic performances of supercritical CO2/R32 in microfin tubes with different structures at various working conditions were investigated. The influences of each of three factors (pressure, mass flow, and microfin tube structures) on the thermal-hydraulic performance of CO2/R32 were evaluated respectively. Furthermore, orthogonal tests were undertaken to obtain the optimized combination of overall thermal-hydraulic performance. Results indicate that: the more the temperature of working media approximates to the critical temperature, the bigger the local convective heat transfer coefficient. Compared to non-critical temperatures, the convective heat transfer coefficient at critical temperature shows an eight-fold increase. The closer the pressure of the mixed working media is to the critical pressure, the greater the maximum convective heat transfer coefficient (CHTC) and the lower the temperature corresponding to the peak point, among which, the maximum CHTC under 7.5 MPa is three times as large as that at 8.5 MPa; the CHTC increases with increasing mass velocity, generally showing a linear relationship; through calculating the most optimal combination of thermal-hydraulic performance evaluation using orthogonal tests, the maximum CHTC is determined to be 96 kW/(m2?K).

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