Why can we assume the temperature of a fluid is T_sat?

In summary, the conversation discusses finding the temperature and total enthalpy of a container with 10-kg of R134a at 100kPa. The specific volume is used to determine if the sample is a compressed liquid or superheated vapor, and it is found to be between the specific volume of saturated liquid and vapor. The conversation also touches on using the equation v=v_f + x(v_fg) and what it means if the resulting quality is greater than one.
  • #1
zachdr1
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0
For example, in this question..

A 11 L rigid container contains 10-kg of R134a at 100kPa. Determine the temperature and total enthalpy in the container.

Why can we just assume that the temperature we're looking for is T_sat, how do we know this isn't a compressed liquid? How do we know it isn't a superheated vapor?

The answer (-26.37) is found by looking it up in the saturated R134a table.
 
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  • #2
The specific volume of your sample is 1.1 L/kg = 0.0011 m^3/kg. Look in your tables and see if you find any compressed liquid or superheated vapor with this specific volume at 100 kPa. But it does lie between the specific volume of saturated liquid and the specific volume of saturated vapor at 100 kPa.
 
  • #3
Chestermiller said:
The specific volume of your sample is 1.1 L/kg = 0.0011 m^3/kg. Look in your tables and see if you find any compressed liquid or superheated vapor with this specific volume at 100 kPa. But it does lie between the specific volume of saturated liquid and the specific volume of saturated vapor at 100 kPa.
Ohhh okay that makes sense. Thank you.

This doesn't relate the the original problem I posted, but what happens if when using the equation v=v_f + x(v_fg) with the values from the saturated tables, I get a quality that is greater than one? Does that mean that the substance is actually a vapor or what?
 
  • #4
zachdr1 said:
Ohhh okay that makes sense. Thank you.

This doesn't relate the the original problem I posted, but what happens if when using the equation v=v_f + x(v_fg) with the values from the saturated tables, I get a quality that is greater than one? Does that mean that the substance is actually a vapor or what?
Sure. In fact you should be able to see that from the superheated tables.
 

1. Why do we assume the temperature of a fluid is at its saturation point?

The saturation point of a fluid is the temperature at which it transitions from a liquid to a gas state. This point is important because it represents the maximum amount of vapor that can exist in equilibrium with the liquid. By assuming the fluid is at its saturation point, we can accurately analyze and predict its behavior in various systems and processes.

2. How is the saturation temperature determined for a fluid?

The saturation temperature for a fluid can be determined through experimental measurements or by using thermodynamic equations. It is typically dependent on factors such as pressure, composition, and temperature. In some cases, the saturation temperature may also be given by a phase diagram for a specific substance.

3. Can we assume the temperature of a fluid is always at its saturation point?

No, the temperature of a fluid can vary from its saturation point depending on the external conditions. For example, if the pressure of a closed system is increased, the temperature may increase as well, causing the fluid to exist above its saturation point. In such cases, the fluid is considered superheated and may exhibit different behavior than when it is at its saturation point.

4. Why is the concept of saturation important in thermodynamics?

The concept of saturation is important in thermodynamics because it helps us understand the relationship between a fluid's temperature, pressure, and phase. By analyzing the saturation behavior of a fluid, we can predict its behavior in various thermodynamic processes, such as phase transitions, heat transfer, and power generation.

5. How does the saturation temperature affect the properties of a fluid?

The saturation temperature of a fluid can significantly impact its properties, such as density, viscosity, and specific heat capacity. As the temperature of a fluid approaches its saturation point, these properties may change rapidly, leading to unique behaviors, such as phase changes and boiling. Understanding these changes is crucial in the design and operation of various industrial processes and systems.

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