The thermodynamic analysis of a gear press is shown in Figure 1. It is a schematic diagram of a single-stage gear compressor.
The housing is symmetrical and the nozzle is also symmetrical. PO is the suction pressure, PH is the exhaust pressure, and the pressure is the high pressure oil at the nozzle. When the crests of two adjacent teeth are closed by the inner wall of the casing, the closed slots are called compression chambers. With the operation of the gear compressor, the intermeshing gears are driven in the opposite direction by the motor, and the slots continuously carry away the gas in the suction chamber. When the slots pass through the nozzle, the high pressure fluid enters the compression through the nozzle. The cavity reduces the volume of the gas, thereby realizing the compression of the gas. The compressed gas is sent to the exhaust chamber through the gear rotation. The cogging and the nozzle as a whole are studied. It is assumed that the gas in the tooth groove is an ideal gas. The initial state parameters of the gas in the tank are: P0T0 skillful foot, po, which is the cogging volume; the state parameter of the high pressure oil entering the nozzle is: where several turns, the predetermined pressure is PH after compression by high pressure oil injection.
According to the ideal gas state equation PVç¥ mRT, it is assumed that the compression process is an adiabatic process, which satisfies the state equation: PV=constant assumes that the gas in the cogging is uniformly mixed after the high-pressure oil injection is completed, and the following relationship can be obtained according to the law of conservation of energy: moc0TO å…€ = (residual c0 å¼ å¼ T (1) The actual compression process is a multi-variable process, according to the above formula, the compression of the multi-variable index according to the same endpoint method, the process of cutting the leading edge and trailing edge of the tooth tip through the nozzle exit In an instant, the time required for the cogging to pass the nozzle is: a few is the diameter of the tip circle, so is the thickness of the tooth tip, z is the number of teeth. The high pressure oil flows in the nozzle with a small cross-sectional area of ​​the outlet of the viscous nozzle. The velocity gradient of the fluid inside the tube is very large. The structure diagram of the nozzle is as shown. The viscous effect caused by the viscous shear stress of the fluid cannot be ignored. Therefore, it is necessary to consider the Bernoulli equations of the viscous total flow. For the nozzle inlet and outlet oil speed, the second use uI.
Corresponding to the oil inlet and outlet pressure, respectively, Hl field is the height position of the nozzle inlet and outlet in the system reference coordinate system, aI, a2 is the kinetic energy correction coefficient, generally take 1,Z heart for the hole resistance loss, mainly The energy loss caused by the effect of the initial stage of the inlet shrinkage loss laminar flow and the velocity uI of the inlet oil loss along the path of the coanda flow are small and negligible. The Bernoulli equation is simplified because this formula is integral and cannot be accumulated. It can be expanded by Taylor series. The cogwheel of the integrand function gear rotates with the gear. The current tooth tip just turns to the nozzle outlet, and the nozzle Under the action of the side pressure difference, the liquid is sprayed until the tooth tip rotates past the nozzle outlet or the pressure difference between the two sides disappears. It is assumed that the oil injected from the start of the spray from the start of the spray has reduced the volume of the liquid in the plant. The mass of the liquid injected by the nozzle is Pd犷, and the mass of the oil sprayed from the nozzle during the hit time is w. r, according to the law of mass balance, the increased liquid mass in the tooth gap is equal to the mass of the liquid ejected through the nozzle, assuming that the gas in the cogging is compressed to the exhaust state.
2 Analysis of variable working conditions 2.1 Analysis of working conditions at different speeds is shown in 3. When the rotation speed of the compressor is less than the full, the time for the nozzle to sweep over the tooth groove increases. When the gas pressure in the tooth tip is equal to the nozzle outlet pressure, the injection is stopped; when the rotation speed is greater than æž·, the time when the nozzle passes over the tooth groove becomes shorter. When the gas pressure in the toothing does not reach the set pressure, the nozzle has been swept through the tooth picking, and finally the gas pressure in the tooth space is smaller than the set pressure. 2.2 Different nozzle outlet area conditions are as shown, oil source pressure At certain time, when the nozzle outlet area A2>month, the oil injected into the dentate increases, and the gas pressure in the tooth tip increases rapidly. When the time rH is not reached, the gas pressure is equal to the nozzle outlet pressure, and the injection is stopped. The gas pressure in the tip remains unchanged; when the pressure on the cross side increases slowly, the time rH.
3 Conclusion Through thermodynamic analysis, the influence of relevant factors on compressor performance under variable working conditions is discussed. Obtained: (1) Considering the viscosity of the oil and introducing a correction coefficient, the formula of the minimum exit area of ​​the nozzle is improved; (2) When the gear speed is greater than the predetermined speed, the oil injection time is short, and the exhaust pressure does not reach the predetermined pressure: (3) The nozzle outlet area is too small, and the exhaust pressure does not reach the preset pressure: (4) When the nozzle outlet area is constant, the oil source pressure is small, and the exhaust pressure does not reach the preset pressure. Therefore, the pressure of the compressor oil source is strictly controlled. Very important
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