Preliminary Study on Evaporative Cooling and Cooling Refrigerant for Electrical Equipment

Preliminary study on evaporative cooling and cooling refrigerant for electrical equipment Ma Zhigang, Yu Yuqin, Cao Huiling, Deng Bo (Department of Thermal Power Engineering, Hebei University of Technology, Tianjin 300130, China) Out of its superiority in the use of electrical equipment. Finally through the transformer.

The chromatogram of perfluorotriethylamine (FTEA) shows that the chromatogram consists of four peaks, each of which represents a substance. The first peak, the main peak, is analyzed by mass spectrometry and analyzed by mass spectrometry. It is understood that the fragment ions corresponding to the molecular weights of 50, 69, 119, 164, and 302 are CF2, CF3, CF2-CF3, and N-(CF2)2, respectively, and these fragments are combined, and the molecular formula is N-(CF2 -CF3)3. It is the perfluorotriethylamine FTEA, which analyzes the substances represented by the other three peaks. They are polyfluorinated products that are not fully 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, using the relative correction factor and the normalization method, the percentage of each substance in the product is 60.75%, and the dielectric properties pass through the molecular structure. It is found that the structural characteristics of perfluorotriethylamine molecules are that three strong electron-withdrawing groups restrict the lone pair electrons on the amine atom, thereby losing the basicity of the general organic amine and making the whole molecule have low polarity. And weak intermolecular gravity. So its boiling point and freezing point are much lower than those of unfluorinated congeners. Table 1 lists the physical properties of the FTEA compared to several other commonly used transformer cooling media.

It can be seen from the table that the cooling performance of perfluorotriethylamine is much better than that of transformer oil. The experiment confirmed that perfluorotriethylamine is non-toxic, has small viscosity, small flow resistance, large latent heat of vaporization, high puncture resistance and suitable boiling point. In particular, it does not destroy the ozone layer and is fully compliant with the Montreal Treaty, so it is an ideal refrigerant for cooling electrical equipment.

In addition, since the actual gas is deviated from the equation of state of the ideal gas, the reason is that there are gravitational and repulsive forces between the actual gas molecules. Therefore, when the gas state is roughly estimated, due to the complexity of the material PVT thermodynamics, it is very difficult to establish a general practical gas state equation containing the entire state region of gas and liquid with sufficient accuracy, so it can only be roughly Estimate its gas state. Through analysis, it is found that the general compression factor map is closer to perfluorotriethylamine gas. Therefore, in the absence of experimental research and heat exchange equation for perfluorotriethylamine, it is recommended to use a general compression factor map to estimate the gas state.

Table 1 Some cooling medium heat and electric characteristics under normal pressure Table transformer oil SF. Gas breakdown strength (kV/mm) Dielectric constant e Boiling point (°c) Density (liquid) (g/cm3) Kinematic viscosity (mm: / s) latent heat of vaporization (kcal/kg) 7C partial saturation S0.01 Evaporative cooling transformer is a cooling medium that is vaporized on the heating surface to absorb heat on the heating surface to cool it. Because of the high cooling efficiency and the high heat taken away, the transformer of the same load can be reduced in size and weight, which is a promising product. The United States, the former Soviet Union and Japan have been leading this research. From the aspects of design, manufacture, maintenance, cooling effect, etc., the impregnation type is more suitable. It has simple structure, uniform cooling, wide power application range, and is conducive to popularization. Therefore, this paper adopts the dip-type transformer model to conduct experiments and adopts the impregnated transformer model. Experiments were carried out to determine the relationship between the heat flux density 9 and the wall superheat A7fe (natural logarithmic coordinates) of perfluorotriethylamine under normal pressure. It can be seen that in the initial stage, the heat flux density g increases slowly with the increase of the wall surface superheat degree ATe, mainly because the FTEA is overheated, but the steam bubbles on the heating surface are formed only in the individual vaporization cores, and the detachment frequency is low, and the heat transfer is low. Relying on the density difference caused by the temperature difference, the free movement of the cooling medium is induced; as the wall superheat degree A7 increases, the number of vaporization cores increases, the bubbles continuously detach, and the convective heat transfer becomes the main body, and the heat flux density increases with the increase of the wall surface superheat degree A7fe. rapid.

The large container saturated boiling heat transfer curve of FTEA under normal pressure is related to the surface condition, liquid type, saturation pressure and heat transfer temperature difference. According to Muxeeb, the large space heat transfer formula of water: and other substances are large. The space heat exchange formula and the experimentally obtained curve, through the similarity principle, can be inferred from the general form of the large space heat transfer formula of FTEA: according to equation (1), the experimental data is compiled. In the case where the system pressure P is constant, Let, and (: merge into one, so equation (1) is transformed into: Take the natural logarithm of the above equation: For the above equation, the equations are as follows: According to the least squares method, the following equations are obtained: the experimental measurement will be The value is taken into the above formula: so the empirical formula is as follows: 3 Conclusion Electrolytic fluorination is the most effective method for preparing perfluorotriethylamine. The voltage in the reaction, the mass concentration of the amine, the temperature of the electrolysis reaction, and the temperature at which the volatile gas is condensed and recovered The preparation of perfluorotriethylamine FTEA has great influence. It is necessary to determine the suitable range of the experiment. The best range is determined by experiment: 410V; 5%~15%; -5~+5. Perfluorotriethylamine is an excellent evaporative cooling medium. By simulating the evaporative cooling transformer, the relationship between the heat flux density 7 and the surface superheat degree A/ of the EBEA large vessel nucleate boiling heat transfer part is obtained: =6664Af141W/m2 °C. It can be seen from the paper that the new evaporative cooling medium perfluorotriethylamine will inevitably cause social recognition and attention. In addition, due to the serious cracking and recombination in the electrolytic fluorination process, perfluorotriethylamine is caused. The yield is not high, generally less than 40%, and the cost of use is high, which hinders its wide application. At present, the author is looking for an optimal way to improve the yield, because the percentage of partial fluoride in the product is higher. Large, so we must seriously consider their comprehensive utilization.