5. Energy aspects of vacuum bagging

In a positive-displacement vacuum pump (compression by volume reduction), a thermodynamic cycle is described, and compression can only be achieved by expending mechanical energy.

Putting things at their best and assuming that compression is isothermal, the power P required to compress, from suction pressure p _a to discharge pressure p _r a gas flow of volume flow S is given by the formula : $P=p_{\text{a}}S\text{ln}\frac{p_{\text{r}}}{p_{\text{a}}}$