Time taken for pressure equalization between two tanks

  • Thread starter Thread starter Raghav Seetharamu
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Homework Help Overview

The discussion revolves around calculating the time taken for pressure equalization between two tanks filled with air. The original poster seeks a rough approximation and has proposed using equations related to pressure and volume, as well as exponential functions to model the pressure changes over time.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • The original poster attempts to use the total pressure equation and exponential functions to model the pressure equalization process. Some participants question the assumption that the exponential constant B is the same for both tanks. Others suggest that additional information is needed regarding the transport of air between the tanks, particularly the characteristics of the connecting pipes.

Discussion Status

The discussion is ongoing, with participants exploring different aspects of the problem, including the need for more information about the transport conditions and the effects of pressure differences on flow rates. There is no explicit consensus yet, but guidance has been offered regarding the need to consider the physical setup of the system.

Contextual Notes

Participants note that the tanks are connected through relatively large and short pipes, which may influence the rate of pressure equalization. There is also mention of the need to account for the density of air, which varies with pressure, and the assumption of adiabatic processes in the calculations.

Raghav Seetharamu
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Homework Statement


How to calculate time taken (rough approximation) for pressure equalization between two tanks.
Both the tanks have same fluid (Air).

Homework Equations


Rough equilibrium pressure can be achieved by using equations Ptot = (P1V1+P2V2)/Vtot.
Thought of using exponential equation P=Ae^(Bt) for calculating time required for pressure equalization.
A and B are constants.
P=A1e^(-Bt) for tank with decreasing pressure;
P=A2e^(Bt) for tank with increasing pressure;

Exponential constant B, is assumed to be same for the tanks. Am I correct with this assumption?

The Attempt at a Solution


P1 = 1000mbar; P2 = 0.1mbar, V1=6m3, V2 = 1m3,
Ptot = 860 mbar

P=1000*e^(-Bt) for tank with decreasing pressure ;
P=0.1*e^(Bt) for tank with increasing pressure;

How to obtain the exponential constant and hence the time taken for pressure equalization using these equations?
 
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Hello Rahghav, ##\qquad##:welcome: ##\qquad## !

To settle this somewhat, you need more information: a certain amount of material has to be transported from one vessel to the other. The rate depends on the pressure difference and on the resistance in that transport: is it a thin and very long tube or a big short pipe ?
 
BvU said:
Hello Rahghav, ##\qquad##:welcome: ##\qquad## !

To settle this somewhat, you need more information: a certain amount of material has to be transported from one vessel to the other. The rate depends on the pressure difference and on the resistance in that transport: is it a thin and very long tube or a big short pipe ?
Thanks for reverting:)
They are connected through relatively big and short pipes.
 
Suppose the pressures at time t are P1(t), Ppipe(t), P2(t). A= cross-sectional area of pipe, L=length.
Mass velocity in pipe = v(t).
Can you write some equations for how the pressure differences result in acceleration of air into, through and out of the pipe, and for how the rate of flow affects P1 and P2?
Bear in mind that density depends on pressure. You should probably assume adiabatic compression/decompression.
 

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