I have an application where I need to calculate the vacuum (pressure change below atmospheric) generated from a cooling liquid in a semi-rigid container. If the container is filled near full (e.g. 2 litres) with a liquid at e.g. 70C, sealed and left to cool to ambient (e.g. 20C) there is a pressure differential to atmospheric generated from the volume change of the cooling liquid that equalises when the seal is broken. How do I calculate what that pressure differential (vacuum effect) is? How much will it vary depending on the size of the container?