Pressure drop expansion valves

In summary, expansion valves work by converting kinetic energy into potential energy as the gas passes through a diffuser, increasing its pressure. However, in an expansion valve, the pressure drops as the gas expands, leading to confusion about the process. This is due to the Joule Thompson Effect, where the velocity of the gas increases on the low pressure side, converting potential energy into kinetic energy.
  • #1
chrisbolivia
3
0
I'm having trouble understanding expansion valves.

Gas leaving a diffuser increases its pressure as the cross-section increases (i.e as the gas expands), like in a compressor. We convert kinetic energy in potential energy. That I understand.

But in a expansion valve, pressure drops as the gas expands.

There seems to be a contradiction, please explain to me where I am wrong!

Thanks
 
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  • #2
When gas goes through an expansion valve the velocity on the LP side will be higher then the velocity on the HP side so you are taking PE out of the gas and turning it into KE. This is very much simplified look up Joule Thompson Effect.
 

1. What is a pressure drop expansion valve?

A pressure drop expansion valve is a type of valve used in refrigeration and air conditioning systems to control the flow of refrigerant and maintain the desired pressure and temperature inside the system. It is typically installed at the outlet of the condenser and is responsible for reducing the pressure and temperature of the refrigerant before it enters the evaporator.

2. How does a pressure drop expansion valve work?

A pressure drop expansion valve works by creating a restriction in the flow of refrigerant, causing a drop in pressure and temperature. This is achieved by using a small opening or orifice that the refrigerant must pass through. The valve also has a sensing bulb attached to it, which measures the temperature of the refrigerant leaving the evaporator. Based on this temperature, the valve adjusts the size of the opening to maintain the desired pressure and temperature in the system.

3. What are the main types of pressure drop expansion valves?

The two main types of pressure drop expansion valves are thermostatic expansion valves (TXVs) and electronic expansion valves (EEVs). TXVs use a mechanical sensing bulb and a diaphragm to control the valve opening, while EEVs use electronic signals from a temperature sensor to adjust the valve opening. Within these two main types, there are also different variations based on the type of refrigerant, system size, and application.

4. What are the benefits of using a pressure drop expansion valve?

Pressure drop expansion valves offer several benefits in refrigeration and air conditioning systems. They help to regulate the flow of refrigerant, maintain consistent pressure and temperature, and improve the overall efficiency of the system. They also allow for more precise control and can accommodate different load conditions, making them suitable for a wide range of applications.

5. What are some common issues with pressure drop expansion valves?

Some common issues with pressure drop expansion valves include clogging of the orifice due to debris or contaminants in the refrigerant, malfunctioning of the sensing bulb or temperature sensor, and improper adjustment of the valve. These issues can lead to fluctuations in pressure and temperature, reduced efficiency, and potentially damage to the system. Regular maintenance and proper installation and adjustment can help prevent these issues.

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