Exploration of a transient method for measurements of airtightness

Paper in proceeding, 2006

By measuring the pressure decline in a pressurised air volume from which air is leaking it is possible to determine the air leakage rate as a function of the pressure difference. The leakage rate is proportional to the time derivative of the pressure. The constants of proportionality turns out to depend on the size of the pressurised volume, the ambient pressure, the change in temperature in the bulk volume of the pressurised air and the stiffness of the structure enclosing the pressurised volume. The studies and analyses leading to a final equation relating air leakage to pressure drop is described. It is shown that the very small temperature drop in the bulk air volume has to be accounted for. Initial tests of the method have been performed. The final, quite handy, equation shows good agreement with air leakage rates obtained with theoretical as well as with standard methods.