The Thermodynamic Model for Vacuum Technology

Abstract

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.

Thermodynamics of Moist Air for Vacuum Technology

“…2. The convective heat transfer rate dQ/dτ between the chamber surface area and the air is solved in the authors' previous study (3), applying (4).…”

“…Concurrently, the saturated humidity (φ1 = 100 %) in the specimen chamber must be kept, by the controlled injection of water from a hydration system, so that the sample is not dried. In addition, the specimen chamber must by evacuated very slowly to prevent freezing (crystallization) of the sample at the very beginning of the chamber depressurization, see (3).…”

“…The mass of liquid water in the chamber can be expressed by applying the definition of specific humidity [3] as The sum of enthalpy rates of the moist air incoming and outgoing from the chamber can be expressed by the air mass flow rates and specific enthalpies similarly as in Eq. [8]…”