Thermodynamic process involved in filling pressure vessel 1

[FEAinfotech]

HI,

What is the thermodynamics process involved while filling the gas vessel to a high pressure from an infinite source at high pressure?

It is adiabatic process but I am not sure if the process is isenthalpic or isentropic.

We currently take 15 min. to fill 50 in^3 vessel upto 8000 psig. we would like to increase the rate of filling, the question was how much would the bottle temperature be raised? if it was high the burst disc fails.

Please help me solve this problem.

Thanks and Regards

Surendhar

 

[sailoday28]

If no heat transfer occurs from the gas to the vessel during filling--- the process is adiabatic.
Using a lumped mode model with a mass and energy balance

Delta U change in internal energy of the gas in the tank
ho stagnation enthalpy of source gas
delta m change in mass in the tank
m = mass
u specific internal energy
i refers to initial conditions in tank

Delta U= ho (delta m)
mu -mi*ui =h0(m-mi)
Further neglecting initial mass in tank
u = ho
For perfect gas const spec heats
Cv spec ht const vol
Cp spec ht const press
T absolute temp
CvT=CpTo
gamma Cp/Cv

T=gamma*To

 

[israelkk]

Knowing the gas type, vessel volume and final pressure (at room temperature) you can calculate the gas weight. If you can weigh the vessel while you are filling it you can get an accurate filling.

To solve your problem of temperature raise you need to solve the filling thermodynamic process coupled with the heat transfer from inside of the vessel to the atmosphere.

To get the relevant heat transfer coefficient write a model for the whole process including heat transfer. Then test at few filling rates and compare the test results of temperature raise and pressure raise at the same time to the model results. Now adjust the heat transfer constant in the model to match the test results.

Use the new model to predict a different filling rate process and check for a match. If there is a good match than this will be your process model which can be used to check what will happen at different filling rates.

To my best knowledge the actual filling process is not an adiabatic process but more likely a poly-tropic process. However, at each filling rate the powers in the poly-tropic equation will change for filling rate. For a very long rate it will have a Kapa=1 (isothermal process) up to Kapa=1.4 for an adiabatic process for a gas such as Nitrogen or Air or Kapa=1.67 for a gas such as Helium or Argon.

 

[FEAinfotech]

Hi,

We are planning to increase the time to fill (time tending to zero), so I was expecting the process to be adibatic.

I had been using adibatic isentropic process for the the discharge process, and my pressure vs time curve was matching with the test data. The drop in temperature results were way off assuming same isentropic process.

If I were to introduce the transient phenomenon, i should see the temperature drop during the fill process and as the gas gets compressed close to stagination source pressure the temperature increases. Could any of you suggest some theroy or equations related to the above phenomenon I will be thankfull to them.

Regards

 

[FEAinfotech]

Hi sailoday28,

If

T = Gamma * To

Do you mean to say that the temperature is independent of the source pressure or the final tank pressure?

 

[vzeos]

The attached paper, Experiments to Study the Gaseous Discharge and Filling of Vessels, may be of some help to you.

http://www.ijee.dit.ie/articles/999982/experime.htm

 

[sailoday28]

FEAinfotech (Aerospace) The resulting gas temp in the filled tank is based upon the filled tank mass is much greater than the initial mass in that tank.
NO heat transfer
perfect gas, and const specific heats
An infinite source--Source pressure and temp remain constant.
As a result the temp of the gas is independent of the tank pressure.
If the process is very slow, you can take into account heat transfer to the fill tank metal and perhaps heat trans from the metal to the surrounding environment.

If one considers real gas properties, temperature in the tank will most probably depend on tank pressure.
NOTE HOWEVER THAT THE BELOW ORIGINAL STATED EQUATIONS ARE STILL VALID

Delta U= ho (delta m)
mu -mi*ui =h0(m-mi)


RGasEng (Mechanical) I believe the paper that you have referenced has a source which is finite in volume--not an infinite source.

 

[vzeos]

sailoday28 (Mechanical), You are correct. In the filling analysis, the atmosphere is used as the source.