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Abstract:
The hydrostatic bearing is the core component of ultra-precision computer numerical control (CNC) machine tools. Because the temperature rise in the oil film of hydrostatic bearings seriously affects the working accuracy of the bearings, it is important to study the flow and heat transfer characteristics of the oil film. Based on the physical model of an incompressible viscous fluid flowing in a flat microfluidic boundary layer, velocity, temperature and heat flux distribution equations of oil film are constructed by theories of heat transfer and hydrodynamics. Then, the effects of several parameters on velocity distribution, temperature distribution and heat flux distribution are analyzed, such as the upper plate velocity, the channel length, and so on. The results show that the dimensionless velocity of the oil film decreases with the increase in the upper plate velocity and the channel length. The oil film temperature distribution can be divided into three zones: the increasing zone, stabilizing zone and decreasing zone. The heat flux decreases linearly with the increase in the plate thickness, and increases linearly with the increase in the temperature difference.

Keywords:
microfluidic boundary layer,hydrostatic oil film,velocity,temperature,heat flux

Abstract:
Hydrophilicity/hydrophobicity is a common physical property of the material. Water droplets roll on lotus leaf, and a lot of dust and dirt on the surface of the lotus leaf will be taken away, playing a certain cleaning role. The hydrophobic surface has drag reduction effect that would produce slip on the hydrophobic wall. There are some studies on hydrophilicity/hydrophobicity in channels, most of which focus on the effect of surface drag reduction and heat transfer on microchannels. However, few people pay attention to the effect of the hydrophilicity/hydrophobicity of the injector inner wall on the atomization performance. In this paper, three groups of the open-end swirl injector with different tangential channels were designed to study the effect of hydrophilicity/hydrophobicity on atomization performance. The hydrophobic coating was prepared and used on the inner wall of the injector, and the atomization experimental system was built. In the experiment, the liquid film thickness was measured using the conductance method. Details of the liquid film breakup and spray development were recorded with a high-speed camera. The average droplet diameter was measured by the Malvern particle size analyzer. The atomization performance of injectors with different tangential channels on the hydrophilicity/hydrophobicity was compared, and the effect of the velocity profile on the jet stability is discussed.