The paper is focused on developing a mathematical model capable to describe thermodynamic processes connected with the vacuum technique. The model is based on the laws of energy and mass conservation, the air state behavior, and the principles of airflow, including the critical flow. The problem has been solved numerically by MATLAB. The results of the solution include the pressure evolution for a given pumping speed and the volume to be evacuated. Solutions are obtained for cases of airflow to the vacuum chamber through an inlet opening for three various diameters. The solutions are validated by comparing with experimental data. The presented model agrees with the experiment quite well. One very useful application is the determination of the relation between the diameter of the inlet opening and the pumping speed of the vacuum pump at the pressure steady state condition. This is an important knowledge for a simple and reliable quantitative pressure control in vacuum systems.
The paper is focused on the developing a predictive mathematical model for describing thermodynamic processes connected with the moist air depressurization in vacuum chambers. Equations of the mathematical description are based on principles of the energy and mass conservation, which are complemented by the moist air thermodynamics, the state behavior of water and vapor, including principles of the critical flow. The described problem has been solved using the MATLAB software. In the paper, two cases are applied and discussed: the vacuum drying and the specimen chamber of an environmental scanning electron microscope. The specific requirements are especially important for environmental scanning electron microscopes, where it is possible to observe samples, which contain water, in their natural condition. If the air pressure, temperature and humidity do not have suitable values, observed sample may be dried or damaged.
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