Throttling process (Joule Thomson coefficient)

In summary, the conversation discusses a graph obtained during the throttling process and the nature of isenthalpic curves for a real gas. The sudden change in temperature at the inversion point is attributed to the deviation of a real gas from an ideal gas. The graph for an ideal gas would have horizontal lines of constant enthalpy, but for a real gas, the isenthalpic lines are not horizontal due to the Joule Thompson coefficient. In some cases, the isenthalpic curves may touch the ordinate axis, but this does not mean a complete absence of pressure and temperature.
  • #1
theo dsouza
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14.4.gif

This is a graph obtained during throttling process by keeping pressure and temperature at the inlet of the valve fixed and varying them at the outlet to get different isenthalpic curves for different inlet pressures and temperatures.

Is it true that the sudden change in temperature of this isenthalpic graph at the inversion point is due to the deviated nature of a real gas from the ideal gas? Will the graph for an ideal gas be lines parallel to the abscissa?
 
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  • #2
theo dsouza said:
View attachment 79412
This is a graph obtained during throttling process by keeping pressure and temperature at the inlet of the valve fixed and varying them at the outlet to get different isenthalpic curves for different inlet pressures and temperatures.

Is it true that the sudden change in temperature of this isenthalpic graph at the inversion point is due to the deviated nature of a real gas from the ideal gas?
I don't see any sudden changes at the inversion point.
Will the graph for an ideal gas be lines parallel to the abscissa?
Yes. The lines of constant enthalpy for an ideal gas undergoing a throttling process are horizontal on the graph. Note that, even in the low pressure region (where we usually expect ideal gas behavior), the isenthalpic lines are not horizontal. This is because the Joule Thompson coefficient is the result of deviation from ideal gas behavior.

Chet
 
  • #3
In some graphs of the Isenthalpic curves (not the one above) I've seen that the isenthalpic curves touch the ordinate axis to give a positive temperature value and a zero pressure value on the exit side of the throttle valve. Is this possible?
 
  • #4
theo dsouza said:
In some graphs of the Isenthalpic curves (not the one above) I've seen that the isenthalpic curves touch the ordinate axis to give a positive temperature value and a zero pressure value on the exit side of the throttle valve. Is this possible?
The zero pressure value doesn't really mean zero pressure; it just means "at low pressures," where deviations from ideal gas behavior are negligible. Obviously, if you go all the way to zero pressure, the gas is not longer present, and its temperature is meaningless.

Chet
 

Related to Throttling process (Joule Thomson coefficient)

1. What is the Joule Thomson coefficient?

The Joule Thomson coefficient, also known as the Joule-Kelvin coefficient, is a measure of how the temperature of a gas changes when it is subjected to a throttling process. It is defined as the rate of change of temperature with respect to pressure at constant enthalpy.

2. What is the purpose of throttling in a gas system?

Throttling is used in gas systems to reduce the pressure of a gas without changing its enthalpy. This process is commonly used in refrigeration and air conditioning systems to cool gases, but it can also be used for other purposes such as gas separation and control of gas flow rates.

3. How does the Joule Thomson coefficient affect the temperature of a gas?

The Joule Thomson coefficient determines whether the temperature of a gas will increase or decrease during a throttling process. If the coefficient is positive, the gas will cool down as it expands, while a negative coefficient will result in the gas heating up.

4. What factors affect the value of the Joule Thomson coefficient?

The value of the Joule Thomson coefficient depends on the properties of the gas, such as its specific heat capacity, molecular weight, and critical temperature. It also varies with temperature and pressure, and can be influenced by the type of throttling device used.

5. How is the Joule Thomson coefficient calculated?

The Joule Thomson coefficient can be calculated by taking the partial derivative of temperature with respect to pressure at constant enthalpy. It can also be determined experimentally by measuring the temperature change of a gas as it undergoes a throttling process at different pressures.

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