Analysis of Pressurized Cylinder: Flashing to Steam or Hot Water?

In summary, the conversation is about calculating the percentage of flash steam when a pressurized cylinder of water at 200*F and 300psig is drained to atmospheric pressure. The equation used is (% flash steam = (100 * (hf1 - hf2)) / hfg2) and the result is approximately 22%. The conversation also includes different units and enthalpy values, with a suggestion for someone else to verify the calculation.
  • #1
NASNAS
2
0
I have a question for you all, say you have a pressurized cylinder with water in it, it is at 200*F and at a pressure of 300psig. Now you open a drain valve on the bottom to the atomosphere.

Will it flash to stream or just come out as hot water or a combo of the two?

What equations and info do tyou use to figure this out?

Thanks!
 
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  • #2
Here is a calculation for flash steam:

% flash steam = (100 * (hf1 - hf2)) / hfg2

where:
hf1 = enthalpy of liquid at pressure p1
hf2 = enthalpy pf liquid at pressure p2
hfg2 = latent heat of vaporization at pressure p2

This calculation is from ASHRAE Systems 2004.

Now if I'm interpretting this correctly, that equals

% flash steam = (100 *(393.84 - 180.07)) / 970.3 =
% flash steam = (100 *(213.7)) / 970.3 =
% flash steam = 21377.00 / 970.3 = 22.03%

So approximately 22% should flash to steam.

Do not try this experiment at home!
 
  • #3
what units are you using? I used 80*F as the ambient temp.

I got hf1=169 BTU/lb, hf2=49 BTU/lb and hfg2 970 BTU/lb.

so I came up with 12% steam.
 
  • #4
Sat. Liquid Enthalpy hf of 393.84 at 300 psi Abs Pressure and 180.07 at atmospheric pressure of 14.696 psi Abs Pressure.

I'm not positive that I am right, but the formula calls for the hf at the given pressure, not the given temperature. Maybe someone else can verify this.
 

1. What is the purpose of analyzing pressurized cylinders?

The purpose of analyzing pressurized cylinders is to understand the behavior of the cylinder when it undergoes a sudden pressure drop, such as flashing to steam or hot water. This analysis can help determine the potential hazards and safety concerns associated with the cylinder and the contents it holds.

2. How is the analysis of pressurized cylinders conducted?

The analysis of pressurized cylinders typically involves using mathematical equations and thermodynamic principles to model the behavior of the cylinder and the fluid inside. This can be done using computer simulations or by hand calculations, depending on the complexity of the system.

3. What factors are important to consider in the analysis of pressurized cylinders?

Some important factors to consider in the analysis of pressurized cylinders include the initial pressure and temperature of the fluid, the type of fluid and its properties, the material and dimensions of the cylinder, and the surrounding environment. These factors can greatly influence the behavior of the cylinder and the potential consequences of a pressure drop.

4. What are some potential hazards associated with flashing to steam or hot water in pressurized cylinders?

Some potential hazards of flashing to steam or hot water in pressurized cylinders include overpressurization, rapid expansion of the fluid, and potential rupture of the cylinder. This can lead to injuries or damage to surrounding equipment and structures.

5. How can the results of the analysis of pressurized cylinders be used?

The results of the analysis of pressurized cylinders can be used to inform safety protocols and procedures for handling and storing pressurized cylinders. It can also be used to design and improve the safety features of pressurized cylinder systems to prevent accidents and mitigate potential hazards.

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