Air Conditioners Move Heat
All scenes › Chapter 5 Expansion valve: cold again
A tiny opening
The pressure is very different on each side of a tiny opening
View in 3DThrough a tiny opening
Liquid refrigerant at about 40 °C passes through a very tiny opening in the expansion valve. The opening is so narrow that the refrigerant cannot rush through all at once, so the pressure in front of it is high, about 28 atm, and the pressure behind it is low, about 10 atm. Coming out of the opening, the refrigerant suddenly meets low pressure.
Why?On one side, the compressor pushes refrigerant in hard; on the other, the tiny opening lets it out only a little at a time. That keeps the pressure different on the two sides.
Learn moreMany air conditioners today use valves whose opening is adjusted electronically, changing how much refrigerant flows to match the weather and the room temperature.
- Pressure before and after the valve (atm)
- 28 → 10
calculated from R-32 property tables (CoolProp) · example: room 27 °C, outdoors 35 °C
View this scene in 3D →Read more
Wikipedia: Thermal expansion valve
More in the series
Temperatures, pressures and amounts of heat are calculated from property tables for the refrigerant R-32 (CoolProp). The example is a home air conditioner removing 2.5 kW of heat, with the room at 27 °C and the outdoors at 35 °C. In the 3D view, the refrigerant moves far slower than in real life, and the inside of the compressor and the expansion valve are shown as enlarged, simplified models.