If you are thinking : ‘What a simple question, I know the answer to that! It is used to control the temperature on my refrigerator’
You are absolutely right ! In fact most people I have asked this question seem to know thus far. But how does turning a knob control the temperature ?
The refrigeration cycle
The fridge works in a rather simple way:
Refrigerant (liq) takes up heat from the object you want to cool
Changes state from liquid to gas
Compressor pressurizes fluid, heating it up. ( Why ? for better heat exchange )
This hot gas meets the cool gas outside, changing state back to liquid
Further de-pressurizes as it heads back
The thermostat switch
If the temperature inside the fridge goes up, the compressor must be turned on to circulate the refrigerant.
Here’s the crux of the post :
That knob determines when the compressor is to be turned on !
That knob is coupled to a screw type mechanism which lowers or moves up as it is rotated.
A bellow ( like a balloon ) keeps expanding as the temperature inside the fridge increases until it hits the arm and flicks the thermostat;
Compressor : ON ;
Refrigeration cycle : START
That’s the story of that mysterious knob that had baffled me for quite some time.
Have a great day!