Шостак Ю.А., Никулин Н.К.
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Аннотация
Представлена математическая модель течения газа в торцовом зазоре дискового вакуумного насоса в молекулярном режиме течения газа. Расчет основан на использовании метода Монте Карло (методе пробной частицы). Математические зависимости позволяют проследить траекторию молекулы от момента старта с поверхности входа до выхода из зазора и вычислить вероятности прямого и обратного перехода молекул газа через торцовый зазор между вращающимся и неподвижным диском. Взаимодействие молекул газа с поверхностью дисков описывается диффузным законом отражения при коэффициенте аккомодации равном единице, распределение молекул по скоростям теплового движения описывается законом Максвелла. Представленная модель позволяет определить проводимость зазора, величину
потока перетеканий через зазор и максимальный перепад давлений на уплотнении при нулевом потоке перетеканий. В результате расчётов установлено влияние геометрических параметров зазора и скорости вращения дисков на проводимость зазора
Simulating of the gasflow in the flowing part of a hybrid turbomolecular pump with a disk stage
Shostak J.A., Nikulin N.K.
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Abstract
In all high-vacuum mechanical pumps, namely molecular and turbo-molecular there is a need in sealing of inputs of the movement. A dynamic seals type is widely applied in modern industry. Protective properties and optimization of the dynamic seals at the stage of design become a relevant topic to be researched. The aim of the work is to develop a mathematical model of gas flow in the face gap between two rotating disks. In building this model, the following assumptions are introduced: molecular gas flow, full exchange of momentum in collisions of molecules with disk surface, reflection of particles from the wall submits to the law of diffuse reflection, distribution of gas molecules according to the thermal motion speeds described by Maxwell`s law. The calculation is based on the use of the Monte Carlo method (method of test particle), which consists in the statistical modeling of processes. The article describes an algorithm to construct a mathematical model step by step. The trajectory of each molecule movement is traced from the moment of its moving in till its moving out of the system. The article defines both a probability for gas molecules to pass through the face gap of disk vacuum pump in forward and backward direction and a conductivity of
the gap. A numerical experiment based on the developed program has been conducted with considering the movement of the required number of molecules to provide a sufficient accuracy of calculation. Gas flow in the face gap of disk vacuum pump is studied. As a result of the experiment it was found that geometrical parameters of the gap and speed of disk rotation have an impact on the conductivity.
With raising speed of disk rotation the probability for particles to pass in forward direction increases, accordingly increasing the conductivity, and for particles to pass in backward direction it decreases thereby improving the vacuum properties of the pump. The work carries out a process adequacy test based on the equality of the conductivity of the forward and reverse passages with disks being stationary. The accuracy does not exceed a tolerance. Results and, accordingly, recommendations, given in the article, can be used in designing a flow passage
