Is Water a Good Refrigerant
Let’s remind ourselves of these two basic rules:
- There will only be a heat transfer between two bodies if those two bodies are at different temperatures.
- Heat always flows from the hotter body to the colder body.
In our fridge, if we wish to keep the temperature of the feed at 4°C, then the temperature of the ‘cold’ heat exchanger must be less than 4°C.
We have seen that it is possible to lower the temperature of evaporation of water by reducing the pressure, for example, by increasing altitude. So why couldn’t we make water evaporate at 0°C in our fridge’s freezer?
The pressure must be very low to make water boil at 0°C. Therefore, unless we can take our fridge into outer space or use very sophisticated (and therefore very expensive) vacuum pumps, we will have to find a fluid other than water for our fridge.
You are aware that all liquids don’t have the same boiling temperature. So then, why not use, say, an oil? For example, cooking oil boils at approximately 300°C. Unfortunately, although this temperature is perfect for making potato chips, it would be too high for our fridge.
What about using ether? Ether evaporates at 35°C (at atmospheric pressure, of course). So it is already better than oil. However, with a freezer at 35°C, you couldn’t reduce the temperature in the fridge to less than 35°C. So this wouldn’t be particularly good for keeping your drinks cold!
So to make ice cubes in our refrigerator, we must find a substance whose boiling point is less than 0°C.
Question: why can’t we use ether? Suppose we reduce the pressure so that it’s below atmospheric pressure. In that case, the external forces will decrease, and just like water at high altitudes, the evaporation temperature of ether will also fall. Can’t we get to temperatures below 0°C like this? Can we?
In theory, the reasoning is correct and should work like this.
However, in practice, several problems mean that ether is of little interest as a refrigerant. You won’t find any commercial refrigerators that run using ether, especially since refrigeration engineers have much more exciting refrigerant fluids available to us.
So what are these exciting refrigerant fluids?
Back to Basic!
Related
Read more: Fan wall
Read more: How to verify the percentage of outside air in an enclosure
Read more: BCA Part J5 Air-conditioning system control
Read more: Microbial Induced Corrosion (MIC) in Pipes
Read more: Is your kitchen exhaust system a fire hazard
