Calculation of gas flow velocity
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Suppose I have two tanks of the same size, each with a capacity of 10 m3. One tank is under a pressure of 1.5 MPa, while the other is under a pressure of 1 MPa. Now, I need to transfer the gas from the tank with higher pressure to the tank with lower pressure, until the pressures in both tanks are equal. Ignoring pipeline resistance, how long will it take me to equalize the pressure in both tanks? At the beginning, the flow rate should be the highest, but what exactly is it? How should it be calculated? In which book is this calculation formula? . . . . . . . . . . Also: If I have 10 M3 at 1.5 MPa, how long would it take to vent it completely? What about the changes in flow rate? Those who work on PSA should be involved in the calculations related to this area; I hope they can share the calculation process. . . . . . . . . . . . . . Pipe: 48x5mm, length about 10 meters, with 3 elbows; the gas is 99.5% hydrogen, at a temperature of around 35 degrees. Last edited by lcpinging on 2009-1-7 16:10]
Relationship between gas pressure and flow velocity: The greater the flow velocity of a gas, the lower its pressure. 1 Pressure According to the principles of engineering thermodynamics, the ratio of the critical pressure Pc to the inlet pressure P1 (absolute pressure) is called the critical pressure ratio pβ, that is, β = Pc/P1. It can be seen from this formula that the critical pressure ratio β of a gas depends only on its specific heat ratio n; the specific heat ratio can be regarded as a constant. The values of n for different types of gases are as follows: For monatomic gases, n = 1.67, so β = 0.487, meaning that Pc = 0.487P1 ； For a diatomic gas, taking n=1.40 gives β=0.528, so Pc=0.528P1 ； For multiatomic gases, taking n=1.30 gives β=0.546, so Pc=0.546P1 ； Therefore, for air (a diatomic gas), Pc = 0.528P1, and for gases (polyatomic gases), Pc = 0.546P1. The pressure at the outlet section during gas release is P2, while the external pressure is Po = 0.1 MPa. The release pressures for high and medium pressure conditions are relatively high; in this state, the external pressure is Po
It’s too complicated. Could you show the calculation process using my example? Thank you
Such calculations are integral processes. The initial velocity is relatively high; as the pressure difference decreases, the velocity drops. Refer to the registration materials for chemical engineers, which contain similar calculation examples.
Forgot to mention 2 conditions: diameter DN40, length of about 10M
Not only did they forget the conditions, but they also forgot the storage medium...
I have reedited this question; I hope experts can give me some guidance. I looked at the Bernoulli equation in the principles of chemical engineering and felt it isn’t applicable here
This post was last edited by guobao on 2010-3-22 at 13:52. Is there a detailed method for calculating the answer to the original poster’s question, or can such calculation methods be found in any relevant sources? What was said on the second floor is quite thorough and professional, but it seems unable to truly solve practical problems!