Preliminary Study on Evaporative Cooling and Cooling Refrigerant in Electrical Equipment

Preliminary Research on Evaporative Cooling and Cooling Refrigerant in Electrical Equipment Ma Zhigang, Yu Yuqin, Cao Huiling, Deng Bo (Department of Thermal Energy Engineering, Hebei University of Technology, Tianjin 300130, China) The reaction conditions, structural characteristics and physical properties of the material, and the Out of its superiority in the use of electrical equipment. Finally through the transformer.

The chromatogram of perfluorotriethylamine (FTEA) shows that the chromatogram curve consists of four peaks. Each peak represents a substance. The first peak, ie, the main peak, is analyzed by mass spectrometry and analyzed against a mass spectrometry library. It is known that the fragment ions corresponding to the molecular weights 50, 69, 119, 164, and 302 are CF2, CF3, CF2-CF3, and N-(CF2)2. These fragments are combined and their molecular formula is N-(CF2-CF3)3. It is the perfluorotriethylamine FTEA. Similarly, the other three peaks are analyzed. They are polyfluorine products that are not completely fluorinated. The molecular formula is CF3CF2-N(CHFCF3)2, CF3CH2-N(CF2CF3). 2. CF3CFH-N (CF2CF3) 2. According to the area of ​​each peak of the chromatogram, relative correction factor and normalization method were used to determine the percentage of each material in the product was 60.75% in sequence, and 2 medium properties passed through the molecular structure. It was found that the structural characteristics of the perfluorotriethylamine molecule are that three strong electron-withdrawing groups make the lone pair electrons on the amine atom constrained, thereby losing the basicity of the general organic amine and making the whole molecule have low polarity. And weak intermolecular attraction. So its boiling point and freezing point are much lower compared to non-fluorinated congeners. Table 1 lists the physical properties of FTEA compared to several other commonly used transformer cooling media.

From this table, it can be seen that the cooling performance of perfluorotriethylamine is much better than that of transformer oil. Experiments have confirmed that perfluorotriethylamine is non-toxic, has small viscosity, small flow resistance, large latent heat of vaporization, high breakdown resistance, and suitable boiling point. In particular, it does not damage the ozone layer and is in full compliance with the "Montreal Treaty" so it is an ideal refrigerant for cooling electrical equipment.

In addition, due to the deviation of the actual gas from the ideal gas's state equation, the reason is that there are gravitational and repulsive forces between the actual gas molecules. Therefore, when making a rough estimate of its gas state, due to the thermodynamic complexity of the PVT of matter, it is very difficult to establish a general practical gas state equation that contains gas and liquid in the entire state area with sufficient accuracy, so it can only be roughly Estimate its gas status. Through analysis, it is found that the universal compression factor map is closer to the perfluorotriethylamine gas. Therefore, in the absence of experimental studies and heat transfer equations for perfluorotriethylamine, a general compression factor map is recommended to estimate the gas state.

Table 1 Some cooling media at atmospheric pressure Thermal and electrical characteristics Table Transformer oil SF. Gas breakdown strength (kV/mm) Dielectric constant e Boiling point (°C) Density (liquid) (g/cm3) Kinematic viscosity (mm:/ s) Vaporization latent heat (kcal/kg) 7C sub-saturation S0.01 Evaporative cooling transformer is a cooling medium that is vaporized on the heating surface, and absorbs heat on the heating surface to cool it. Due to the high cooling efficiency and the large amount of heat taken away, the volume of the transformer with the same load can be reduced and the weight can be reduced. This is a promising product, and research in the United States, the former Soviet Union, and Japan has been leading the way. From the aspects of design, manufacture, maintenance, cooling effect and other aspects, impregnation is more appropriate. It has a simple structure, uniform cooling, a wide range of power applications, and is conducive to popularization. Therefore, this paper uses an immersed transformer model to perform experiments through the use of submerged transformer models. Experiments were conducted to determine the relationship between the heat flux density 9 and the wall superheat A7fe (natural logarithmic scale) at atmospheric pressure for perfluorotriethylamine. It can be seen that in the initial stage, the heat flux g increases slowly with the increase of the wall superheat ATe, mainly because the FTEA is overheated, but the vapor bubbles on the heating surface are formed only in the individual vaporization cores, and the frequency of the detachment is low. Relying on the density difference caused by the temperature difference to induce the free movement of the cooling medium; with the increase of the wall superheat A7, the number of vaporization cores increases, the bubbles continue to separate, the convection heat transfer becomes the main body, and the heat flux density increases with the increase of the wall superheat A7fe rapid.

The large-scale saturated boiling heat transfer curve of FTEA under atmospheric pressure is related to the boiling heat transfer coefficient and the surface condition, the type of liquid, the saturation pressure and the heat transfer temperature difference. According to Muxeeb's recommended large-space heat exchange formula of water, as well as other large substances The spatial heat transfer formula and the experimentally obtained graphs can be used to approximate the general form of the large space heat transfer formula of FTEA through the similarity principle: According to the equation (1), the experimental data can be sorted. When the system pressure P is a fixed value, ,, and (: to merge as one, so equation (1) is transformed to: Take the natural logarithm to the left and right of the equation: For the above equation, determine the equations as follows: According to the least squares method, the following equations are obtained: The value is taken into the equation: Therefore, the empirical formula is as follows: 3 Conclusion Electrolytic fluorination is the most effective method for the preparation of perfluorotriethylamine, the reaction voltage, the mass concentration of the amine, the temperature of the electrolysis reaction, and the temperature of the condensation recovery volatile gas. The preparation of perfluorotriethylamine FTEA has a great influence, and the appropriate range must be determined during the experiment. The best ranges determined by experiments are: 410V; 5%~15%; -5~+5. (: Perfluorotriethylamine is an excellent evaporative cooling medium.After simulating evaporative cooling transformers, the relationship between the heat flux of the nucleate boiling heat transfer part 7 of the FTEA large container and the surface superheat A/ is obtained: =6664Af141W/m2 °C. It can be seen from this article that the new evaporative cooling medium, perfluorotriethylamine, will inevitably cause social recognition and attention. In addition, the phenomenon of cracking and reconstitution in the electrolytic fluorination process is very serious, causing perfluorotriethylamine. The yield is not high, generally less than 40%, and the high cost of use has hindered its wide application.At present, the author is looking for the best way to increase the yield, because of the percentage of partial fluoride in the product. Big, so we must seriously consider their comprehensive utilization.