Properties of Refrigerant Blends

EPA 608 Core Chapter 24 (Take full course for free)

In this module, we will discuss various properties of refrigerant blends. Skip to quiz!

1. Temperature Glide

With zeotropic blends, we have to consider temperature glide. Temperature glide is the difference between the dew point and the bubble point.

The dew point is the temperature at which the first refrigerant in a blend turns from vapor to liquid. The dew point is specific to refrigerant blends. This is the same as the temperature of condensation in single refrigerants.

For example, in R-407c, the first refrigerant condenses at 21.94°F. So the dew point of R-407c is 21.94°F.

And the bubble point is the temperature at which the first refrigerant in a blend starts to turn from liquid to vapor. Like the dew point, the bubble point is specific to refrigerant blends. It’s the same as a boiling point in single refrigerants.

For example, in the blend R-407c, the first refrigerant starts to boil at 10.44°F. So the bubble point of R-407c is 10.44°F.

As we said, temperature glide is the difference between these two points.

Since the dew point is 21.94°F and the bubble point is 10.44°F, the temperature glide is the difference. 21.94°F - 10.44°F = 11.5°F So the temperature glide of R-407c would be 11.5°F.

2. Fractionation

Recall that charging is when you add refrigerant into a system. It’s less like charging your phone and more like filling up your gas tank.

Blended refrigerants need to be charged as a liquid. This is because there are different refrigerants in the blend that may be spread out unevenly.

We call this separation fractionation. It occurs when the refrigerant is a vapor. Fractionation is when the different refrigerants in a blend settle into layers.

Think of a glass containing oil, water, and sand. If you leave the mixture, it will settle into three layers. If you then pour out some of the mixture, it will be mostly the oil that is poured out.

The same thing is happening with this blended refrigerant in vapor form. If you charge this separated refrigerant blend, you will not get the full blend. You will get what is on top of the mixture. That is why we charge blends as a liquid.

Fractionation is a problem particularly with the refrigerant blend R-407c. This is because R-407c is a zeotropic blend. As we discussed, this means that the refrigerants in this blend will boil separately.

3. Leaks

When a system that contains refrigerant blends is leaking, the refrigerant will leak at different

rates. This is because of the different vapor pressures of the refrigerants present in the blend.

4. Charging Blends

Refrigerant blends need to be charged as a liquid to get the full blend. Since refrigerant blends can experience fractionation, charging as a liquid ensures that we get the correct ratio of all the components.

You can think of this fractionation as orange juice with pulp. The pulp settles down to the bottom of the container when you leave it in the fridge. If you want the pulp to be evenly distributed, you would shake the container.

We don’t want to shake the container of refrigerant, because it is pressurized after all. But we do want to charge it as a liquid so we get the full blend of different refrigerants.

5. Conclusion

In this module, we discussed the properties of different refrigerant blends.

Question #1: Temperature glide is:

1. The difference between the bubble and dew point

2. The difference between the boiling point of R-22 and the replacement

3. When temperature changes in a refrigerant

4. None of these

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The difference between the bubble and dew point

Question #2: The bubble point is

1. The temperature that the first refrigerant in a blend turns to liquid

2. The temperature that the first refrigerant in a blend turns to vapor

3. The temperature that the last refrigerant in a blend turns to vapor

4. The same as the boiling point

Scroll down for the answer...

The bubble point is the temperature that the first refrigerant in a blend turns to vapor. It is not the same as the boiling point. The boiling point is used for single substances. The bubble point is specific for blends of substances.

Question #3: The dew point is

1. The temperature that the last refrigerant in a blend turns to liquid

2. The temperature that the first refrigerant in a blend turns to liquid

3. The temperature that the last refrigerant in a blend turns to liquid

4. The same as the condensation point

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The dew point is the temperature that the first refrigerant in a blend turns to liquid. It is not the same as the condensation point which is used for single refrigerants, not blends.

Question #4: Fractionation (select all that apply):

1. Is when refrigerants settle into layers

2. Happens in vapor phase

3. Happens in liquid phase

4. Happens in solid phase

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Is when refrigerants settle into layers and happens in vapor phase

Question #5: Refrigerant blends need to be charged as a liquid.

1. True

2. False

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True! This is correct. Refrigerant blends need to be charged as a liquid because of fractionation. Charging as a liquid ensures an even sample of the blend.