Tuesday, March 05, 2013

PV=nRT or: How I learned to stop worrying and love cooking under pressure

I'll try to be as brief as possible here. Just going to talk about the physics behind Pressure Coking and why it's so cool (and hipster). Hey, it saves fuel and hence damages the environment to a much lesser much lesser extent than does normal cooking.

From How Does A Pressure Cooker Work?: "Simply put, water boils at 212°F (100°C). At this point, no matter how long you continue to boil, it always stays the same temperature. As the water evaporates and becomes steam it is also the same temperature, 212°F.

The only way to make the steam hotter (and/or to boil the water at a higher temperature) is to put the system under pressure. This is what a pressure cooker does. If we fit an absolutely tight cover to the pan so no steam can escape while we continue to add heat, both the pressure and temperature inside the vessel will rise. The steam and water will both increase in temperature and pressure, and each fluid will be at the same temperature and pressure as the other. "

To explain the last paragraph above, let's turn to physics and the Ideal Gas Law, which states that PV=nRT where,
and we don't really care about what the other symbols mean.

This means that Pressure and Temperature vary directly with each other, and if you raise the pressure of a fluid, then the temperature at which it changes state will also increase!!

No comments: