Fluid's boiling point dependence as function of pressure

In summary, the boiling point of a fluid is dependent on the pressure it is under. In pressurized water reactors, the core inlet temperature is kept lower than the saturation temperature to prevent boiling. However, as the coolant travels through the core, there may be instances of subcooled nucleate boiling due to pressure drops. The saturation temperature increases with pressure, and there are empirical correlations for this relationship. The Jens-Lottes correlation is one such correlation for subcooled nucleate boiling.
  • #1
Stephan_doc
34
2
Greetings to all,
I need some help for i understand how to demonstrate fluids boiling point dependence as function of pressure (i.e for main cool agents). Which are the basic equations for to write a general formula? I know that in PHWR type reactor water is at hight pressure to prevent boilling phenomena.
Thanks a lot
 
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  • #2
I don't know about a general formula, but if you consult the saturation line in any handy steam tables, you can discern a relationship between boiling point and pressure.
 
  • #3
Generally, pressurized water reactors have a core inlet temperature which is subcooled, i.e., Tcoolant < Tsat. By the time the coolant about 70% of the way through the, it is possible that sub-coolant nucleate boiling occurs, i.e., the cladding surface reaches or slightly exceeds the saturation temperature. One also must bear in mind that there is a pressure drop of about 25 psid across a PWR core.

As pressure increases, the saturation temperature increases, and there are empirical correlations for that, just as there are empirical correlations for heat transfer coefficients and fluid properties. Material properties are generally not defined ab initio.


Here are some notes on the Jens-Lottes correlation for subcooled nucleate boiling.
http://www4.ncsu.edu/~doster/NE400/Text/HeatConvection/Boiling.PDF
 

What is the definition of boiling point?

Boiling point is the temperature at which a liquid changes into a gas or vapor at a given pressure.

How does pressure affect the boiling point of a fluid?

As pressure increases, the boiling point of a fluid also increases. This is because the higher pressure prevents molecules from escaping, making it more difficult for the liquid to vaporize. On the other hand, decreasing pressure lowers the boiling point as molecules are able to escape more easily.

What is the relationship between boiling point and vapor pressure?

Boiling point and vapor pressure have an inverse relationship. As the boiling point increases, vapor pressure decreases and vice versa. This is because at higher temperatures, more molecules are able to escape and contribute to the vapor pressure.

How do intermolecular forces affect boiling point?

Intermolecular forces, such as hydrogen bonding and Van der Waals forces, play a significant role in determining the boiling point of a fluid. Stronger intermolecular forces require more energy to break, resulting in a higher boiling point. For example, water has a higher boiling point than ethanol due to its stronger hydrogen bonding.

Is the boiling point of a fluid constant?

No, the boiling point of a fluid is not constant and can vary depending on the surrounding conditions. In addition to pressure and intermolecular forces, factors such as impurities, altitude, and container material can also affect the boiling point of a fluid.

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