Calculate refrigerant temp inside evaporator based on exit temp and pressure

In summary, the person is seeking help with thermodynamic calculations for determining the refrigerant temperature in an evaporator. They mention using a two-phase lumped parameter model and provide equations for calculating the refrigerant temperature in each phase. They also mention having a refrigerant table but not knowing how to use it. They ask for guidance and mention that the enthalpy of the vapor is known and saturated.
  • #1
bobboviking
6
0
Hi guys,

I'm stuck on some thermodynamic calculations and I would really appreciate some help!

I'm trying to calculate the refrigerant temperature inside of an evaporator (two-phase lumped parameter model) based on the exit temperature of the evaporator and the pressure.
I've understood that the refrigerant temperature in phase 1 (fluid) may be expressed as
Tr1 = T(Pe) (temperature as a function of evaporator pressure)

and the refrigerant temperature in phase 2 (vapor) may be expressed as
Tr2 = T(Pe,he2) (temperature as a function of evaporator pressure and enthalpy in the second region)

But I'm not quite getting how to do that after measuring the exit temperature and evaporator pressure (I'm assuming constant pressure in the evaporator). I've got a refrigerant table (see attachment) but I'm not sure how to use it.

I would really appreciate if you could point me in the correct direction!

Thanks in advance,
 

Attachments

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  • #2
If you know the exit temperature and pressure coming out of the valve, then you know the enthalpy. From the 1st law of thermodynamics, there is no change in the enthalpy of the vapor in passing through the valve. So you know the enthalpy of the vapor in the evaporator and you know that it is saturated. So you go to the saturated tables and look up the temperature and pressure of the refrigerant at which this is the enthalpy.
 

1. What is the formula for calculating refrigerant temperature inside an evaporator?

The formula for calculating refrigerant temperature inside an evaporator is:
Refrigerant Temperature = (Exit Temperature / (1 - (Exit Pressure / Evaporator Pressure Ratio)))

2. How do exit temperature and pressure affect the refrigerant temperature inside an evaporator?

Exit temperature and pressure both play a crucial role in determining the refrigerant temperature inside an evaporator. As the exit temperature increases, the refrigerant temperature inside the evaporator also increases. Similarly, as the exit pressure increases, the refrigerant temperature inside the evaporator also increases.

3. Can I use this formula for all types of refrigerants?

This formula can be used for most common refrigerants, but it may not be accurate for all types of refrigerants. Some refrigerants may have unique properties that require a different formula for calculating the refrigerant temperature inside an evaporator. It is always best to consult the manufacturer's specifications for the specific refrigerant being used.

4. What is the significance of the evaporator pressure ratio in this formula?

The evaporator pressure ratio is used to account for the pressure drop that occurs as the refrigerant flows through the evaporator. This pressure drop can affect the refrigerant temperature inside the evaporator, and the evaporator pressure ratio helps to compensate for it in the calculation.

5. Is this formula accurate for all operating conditions?

The formula for calculating refrigerant temperature inside an evaporator is based on ideal conditions and may not be completely accurate in all operating conditions. Factors such as ambient temperature, humidity, and refrigerant flow rate can also affect the refrigerant temperature inside the evaporator. It is best to use this formula as a guide and make adjustments as needed based on real-world conditions.

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