How Do Refrigerants Actually Work?

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Graham Hendra

(@grahamh)

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Topic starter 18/03/2024 12:17 am

Water boils at 100°C, as everyone knows. Inside the water, there are numerous molecules moving rapidly, similar to ping pong balls in motion. The hotter the water, the faster they move. At the water's surface, air molecules act like a lid, preventing the excited water molecules from escaping. Any overly excited water molecules attempting to escape are forcefully pushed back down by the air molecules, reminiscent of the game whack-a-mole.

As the water heats up, the molecules move faster, constrained by the air above. However, if the water is heated sufficiently, the water molecules will move so quickly that they overpower the air molecules and escape. This point of escape is known as the boiling point, typically 100°C.

At higher altitudes, like the summit of Mount Everest, there is less air, meaning fewer air molecules to contain the water molecules. This makes it easier for the water molecules to escape. While I haven't been there, it's said that at Everest's summit, water boils at 80°C due to the lower pressure, which decreases the containment by air.

To recap, the boiling temperature of water depends on the air pressure above it. We could theoretically adjust the boiling point of water to our liking by altering this pressure. This principle is precisely what we utilize in refrigeration: manipulating pressure to change the boiling point.

Step 2: Instead of water, which is inefficient as a refrigerant, we use propane, or R290. Opening a can of propane causes it to boil vigorously. The propane molecules move so fast that they easily escape the air molecules above, and each escaping molecule carries away a bit of heat, cooling the propane container to -42°C.

However, releasing the propane into the atmosphere is inefficient, so we capture it. We then use a pump to compress it to 300psi and store it in a new container. At this pressure, the propane condenses back into liquid, releasing heat as it transitions from gas to liquid. This process of compression essentially squeezes the heat out of the propane, allowing it to condense at 45°C.

So, in one container, we have propane boiling at -40°C, absorbing heat. In another, we have propane condensing at 45°C, releasing heat, with a compressor between them. We're essentially moving heat from one place to another using a compressor.

Refrigeration engineers now cleverly adjust these pressures to achieve precise temperatures, but it all boils down to pressure manipulation. In your fridge, freezer, or heat pump, this is exactly what's happening. It's not complex or new. It's a beautiful example of science in action.

This topic was modified 2 years ago by Mars

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