How Pressure Cooker works?

To understand it, first you should know about

Boiling Point, it is the point at which molecules of liquid begins to leave the liquid in the form of vapour or gas. The reason is that we supplied energy to molecules by heating.

First we start heating then the temperature of liquid increase this heat is called sensible heating which change the temperature.

If we keep on heating a point come after which temperature doesn't rise further, if still we keep heating then now this heat will used to convert liquid into gas(vapour). So the heat which is used for phase change is called Latent heat, it doesn't change the temperature.

BOILING POINT is an intensive quantity which means it doesn't depends on mass of matter. If you take 1kg or 100kg of water both will boil at the same temperature.

The boiling point of water is 100°C at sea level Pressure 101.325 KPa.

Temperature and Pressure Relationship

At constant Volume as pressure increase temperature also increase and hence boiling point.

There are total five main thermodynamics process out of which Constant volume process is used in Pressure cooker, yet we lost the volume frequently but the approximation is good enough.

In Cosntant Volume Process (CVP), 

V=constant

if we assume air as ideal gas the form ideal gas equation PV=mRT or   P/T= mR/V = constant.

Cooking in open vessel

Now the maximum temperature available for cooking our food is 100°C at sea level, because after that water temperature doesn't increase but it converts into vapour. So cant go beyond 100°C in open vessel at sea level, 

if you keep on heating all the water will vapourised and your food might burn black.

Morever Cooking in open vessel on the mountain where atomspheric presaure is low, boiling point of water also reduced, and hence the maximum temperature available for cooking also decreased. So it takes longer time and energy to cook food on mountains.

To solve those problems we used The Pressures cooker or the closed vessel, In which we increased the presaure artificially by heating in partially sealed vessel, so that boiling point of water increase and hence the maximum available temperature for cooking.

As we increased the pressures in closed vessel so on the mountains it doesn't affect by the low pressure of air. So cooking in Closed vessel is more efficient on mountains than the open vessel.

✓Extra Knowledge

Why liquid changes into gas by heating?

Heat is the form of energy transfer, and by transfering energy the kinetic enery of molecules increase and thus their random motion, Therefore molecules have enough energy to jump out from liquid.

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