Effect of Fluid Expansion on Pressure vessel/chamber

In summary: Therefore, in summary, the initial pressure and volume of the vessel/chamber filled with 25% silicon fluid and 75% nitrogen gas can be used to predict the final pressure after an increase in temperature, assuming that the silicon fluid does not evaporate and is incompressible. However, the expansion of the container also needs to be considered for a more accurate calculation.
  • #1
Tripoly
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Hi,
I have a vessel/chamber filled partially (25%) with silicon fluid (coefficient of thermal expansion is 0.00096 cm^3/cm^3/ °C) and the rest is filled with nitrogen gas at a certain pressure (P1) and temperature (T1).
my question is, how to predict the final pressure (P2) If I increased the temperature to a certain value (T2) ? because I will be having the effect of pressure increase from the gas due to temperature increase and the effect of pressure increase due to vessel/chamber volume reduction occurred by the silicon expansion
 
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  • #2
OK, assuming that a negligible amount of the silicon fluid evaporates, and that the silicon oil is incompressible, we can just use the perfect gas law.

Initial : ##P_1V_1=n_1RT_1##
Intial quantity of Nitrogen ##n_1=\frac{P_1V_1}{RT_1}##
Nitrogen is conserved, so ##n_2=n_1##
Volume is conserved so ##V_2=V_1##
Final: ##P_2V_2=n_2RT_2##

The last step, solving for ##P_2##, I leave for you.
 
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  • #3
That silicone oil has significant thermal expansion. A 100 deg C temperature change will change the volume of oil by 0.00096 X 100 = 0.096 = 9.6%. Since the oil fills 25% of the volume, the gas space volume change will be about 25% of that, or 0.25 X 9.6% = 2.4% for a 100 deg C temperature change. The pressure change due to volume change is smaller than the pressure change due to gas temperature change, but is still large enough that it needs to be included in the calculation.

I say about 25% because the percent fill changes as the volume of the silicone oil changes.
 
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  • #4
anorlunda said:
OK, assuming that a negligible amount of the silicon fluid evaporates, and that the silicon oil is incompressible, we can just use the perfect gas law.

Initial : ##P_1V_1=n_1RT_1##
Intial quantity of Nitrogen ##n_1=\frac{P_1V_1}{RT_1}##
Nitrogen is conserved, so ##n_2=n_1##
Volume is conserved so ##V_2=V_1##
Final: ##P_2V_2=n_2RT_2##

The last step, solving for ##P_2##, I leave for you.
anorlunda said:
OK, assuming that a negligible amount of the silicon fluid evaporates, and that the silicon oil is incompressible, we can just use the perfect gas law.

Initial : ##P_1V_1=n_1RT_1##
Intial quantity of Nitrogen ##n_1=\frac{P_1V_1}{RT_1}##
Nitrogen is conserved, so ##n_2=n_1##
Volume is conserved so ##V_2=V_1##
Final: ##P_2V_2=n_2RT_2##

The last step, solving for ##P_2##, I leave for you.
I tried that method to compare it with my experiment. this method is under estimating the results (huge difference) do you think that the Z factor is the reason or what else may affect the results ?
 
  • #5
Might there be moisture in the oil that evaporates to make steam?

I'm not sure what you mean by Z factor.

I'm going to ping an expert @Chestermiller , maybe he can give better help.
 
  • #6
anorlunda said:
Might there be moisture in the oil that evaporates to make steam?

I'm not sure what you mean by Z factor.

I'm going to ping an expert @Chestermiller , maybe he can give better help.
The Z factor is the "compressibility factor" which represents deviation from ideal gas behavior. I would guess that the pressures in this system are not high enough for significant deviation from ideal gas behavior. What is the value of P1?

There is another factor that needs to be considered. What is the equilibrium vapor pressure of the oil at the 100 C higher temperature? This will add to the ideal gas pressure of the nitrogen.
 
  • #7
@Chestermiller
experimental results as follows:
initial pressure at 60F is 1,479 psig
finial pressure at 150F is 1,972 psig
Total volume of silicon (occupying 75% of chamber) 240.2 cc
Total volume of the chamber is 320.3 cc
thermal expansion is 0.00096 cm^3/cm^3/ °C
I do not know about the equilibrium vapor pressure but this is the silicon details that I am using
https://krayden.com/technical-data-sheet/dow_510_tds/
 
Last edited:
  • #8
The absolute pressure ratio is 1.33. The absolute temperature ratio is 1.163. For a 90 F temperature increase, the increase in silicon oil volume is (0.00096)(90)/1.8=0.048 of the initial volume. So, the change in volume of the silicon oil is (240.2)(0.048)=11.5 cc. The initial volume of air is (320.3-240.2)=80.1 cc. So, the volume of air at the higher temperature has decreased to 80.1 - 11.5 = 68.6. So the volume ratio is 0.856. So, assuming Z = 1, the predicted pressure ratio would be 1.163/0.856 = 1.36. This is pretty close to the observed 1.33. What has been neglected here is the increase in volume of the container as a result of thermal expansion.
 
  • #9
Chestermiller said:
The absolute pressure ratio is 1.33. The absolute temperature ratio is 1.163. For a 90 F temperature increase, the increase in silicon oil volume is (0.00096)(90)/1.8=0.048 of the initial volume. So, the change in volume of the silicon oil is (240.2)(0.048)=11.5 cc. The initial volume of air is (320.3-240.2)=80.1 cc. So, the volume of air at the higher temperature has decreased to 80.1 - 11.5 = 68.6. So the volume ratio is 0.856. So, assuming Z = 1, the predicted pressure ratio would be 1.163/0.856 = 1.36. This is pretty close to the observed 1.33. What has been neglected here is the increase in volume of the container as a result of thermal expansion.
Great! many thanks
 

Related to Effect of Fluid Expansion on Pressure vessel/chamber

1. How does fluid expansion affect pressure in a vessel/chamber?

When a fluid is heated, its molecules gain energy and move around more, causing the fluid to expand. This expansion leads to an increase in pressure within a closed vessel or chamber. Conversely, when a fluid is cooled, its molecules lose energy and move around less, resulting in a decrease in pressure within the vessel/chamber.

2. What factors can influence the amount of fluid expansion in a pressure vessel/chamber?

The amount of fluid expansion depends on several factors, including the type of fluid, the volume of the vessel/chamber, the temperature change, and the material of the vessel/chamber walls. Different fluids have different coefficients of expansion, meaning they expand at different rates when heated. Additionally, larger volumes and higher temperature changes will result in greater expansion, and the material of the vessel/chamber walls can affect the rate of expansion.

3. Is there a limit to how much pressure can increase due to fluid expansion?

Yes, there is a limit to how much pressure can increase in a vessel/chamber due to fluid expansion. This limit is known as the burst pressure, which is the maximum pressure that a vessel/chamber can withstand before it ruptures. It is crucial to consider and design for the burst pressure when working with pressure vessels/chambers.

4. How can fluid expansion be controlled in a pressure vessel/chamber?

Fluid expansion can be controlled in a pressure vessel/chamber through various methods. One approach is to use a pressure relief valve, which opens when the pressure reaches a certain level to release excess fluid and prevent a buildup of pressure. Other methods include using flexible materials for the vessel/chamber walls, allowing for expansion, or using a heat exchanger to regulate the temperature of the fluid.

5. What are the potential dangers of fluid expansion in a pressure vessel/chamber?

If not adequately controlled, fluid expansion in a pressure vessel/chamber can lead to increased pressure, which can result in the vessel/chamber rupturing or exploding. This can cause significant damage and pose a safety hazard to anyone nearby. It is crucial to consider and properly manage fluid expansion when working with pressure vessels/chambers to ensure the safety and integrity of the system.

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