| MQL is a kind of machining method, which can effectively lubricate the mixture of compressed air and a very small amount of lubricating fluid and then spray to the processing area.It is a kind of lubrication technology between dry and wet cutting, which is mainly used in automotive engine manufacturing, high precision electronic device cooling and other fields.However, due to the shortage of the biological and ester lubricating oil in cooling performance,and it will rapidly increase the concentration of oil mist particles in the application process. MQL is difficult to meet the high requirements of the green high efficiency cutting.In view of this, this paper has carried out the research on the cooling mechanism and performance of micro water based nano fluid electrostatic spray, aiming to lay the foundation for the development of a new generation of green cutting technology.And the specific work is as follows:(1) As graphite, molybdenum disulfide, multi walled carbon nanotubes for particles, and use six partial sodium phosphate, Tween 20, polyethylene glycol, Arabic gum as the dispersant prepared water-based nanofluids.The effects of different factors, such as the type of dispersant, the mass fraction of the dispersant and the volume fraction of nanoparticles on the dispersion stability of nano particles were studied by the method of static precipitation and laser particle size analyzer.It was found that the suitable dispersant type, the mass fraction of the dispersing agent and the volume fraction of the nanoparticles were different.And the preparation of multi walled carbon nanotube based nano fluid with good stability, which provides the basis for the subsequent electrostatic atomization cooling heat transfer test.(2) Based on the principle of electrostatic atomization and the basic theory of heat transfer, the electrostatic atomization cooling performance evaluation system was developed for the first time..The device can not only be used to measure the critical heat flux of the transient heat transfer test, but also can be used to measure the heat transfer coefficient in the steady state heat transfer test,and in order to provide a basis for the comprehensive evaluation of the cooling performance of micro water based nano fluid electrostatic spray.(3) The spray cooling experiments were carried out under different injection angles, voltage, electrode distance, flow rate and nano particle volume fraction,and the effect of the above factors on the critical heat flux and heat transfer coefficient was found.Combined with the measurement results of nano fluid thermal properties and the nozzle to the top surface of the copper bars electrostatic field simulation results,and analyzed the effect of various factors on the critical heat flux and heat transfer coefficient in depth,and the transient and steady state heat transfer mechanism of micro water based nano fluid was revealed.It is pointed out that the mechanism of the transient and steady state heat transfer is related to the deposition of nano fluids.In the transient heat transfer test, the spray time is short, and the nano particles are deposited on the boiling surface to form a porous scale layer to increase the number of bubbles, the formation radius decreases and the detachment rate increases, thus the critical heat flux density is enhanced.And In the steady state heat transfer experiment, the injection time is longer, the nano particles form a thick and dense scale layer on the heat exchange surface, and the heat transfer resistance increases, thus weakening the heat transfer coefficient. |
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