What is the Reference State for Finding Specific Enthalpy on a Mollier Diagram?

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SUMMARY

The discussion centers on determining the specific enthalpy of a saturated vapor mixture with a relative humidity of 80% at a temperature of 30°C using a Mollier diagram. It is clarified that the mixture cannot be considered saturated due to the relative humidity being less than 100%. The reference state for calculating specific enthalpy is typically set at 0°C and 1 atm for pure species, although some tables may use 25°C. The Mollier diagram must specify the reference state for zero enthalpy to accurately perform the calculations.

PREREQUISITES
  • Understanding of Mollier diagrams
  • Knowledge of specific enthalpy calculations
  • Familiarity with relative humidity concepts
  • Basic thermodynamics principles
NEXT STEPS
  • Review the use of Mollier diagrams for enthalpy calculations
  • Study the concept of reference states in thermodynamics
  • Learn to calculate specific enthalpy for various mixtures
  • Explore resources on relative humidity and its effects on vapor mixtures
USEFUL FOR

Students in thermodynamics, engineers working with HVAC systems, and anyone involved in calculating specific enthalpy in vapor mixtures will benefit from this discussion.

Gauss M.D.
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Homework Statement



We have a saturated vapor mixture with relative humidity 80% at a termpature of 30 C. Find the specific enthalpy of the mixture.

Homework Equations





The Attempt at a Solution



I missed a lecture and a session due to illness and have fallen behind. We are allowed to use a Mollier diagram. Been trying various calculations and table lookups for hours now but getting nowhere. Any pointers?
 
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Gauss M.D. said:

Homework Statement



We have a saturated vapor mixture with relative humidity 80% at a termpature of 30 C. Find the specific enthalpy of the mixture.

Homework Equations





The Attempt at a Solution



I missed a lecture and a session due to illness and have fallen behind. We are allowed to use a Mollier diagram. Been trying various calculations and table lookups for hours now but getting nowhere. Any pointers?

There are several ways of doing what you want. The mixture can't be saturated, because the humidity is not equal to 100%. Saturated means 100% RH.

A second thing you should know is that, to find the specific enthalpy of the mixture, you need to know the reference state at which the enthalpy is taken to be zero. This is usually 0 C and 1 atm for the pure species, but, in some tables it is 25C.

Your Mollier diagram should give you what you want. Can you show us the Mollier diagram you are working with. The diagram should specify the reference state for zero enthalpy.

Chet
 

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