Leakage for Different Fluids.

[siddesh]

Consider a system with  fluid 'A'  of sp.gravity 's1' is  having certain leakage 'Q1' into the surrounding through geometrical imperfections(pores).

Now if the fluid is replaced with another fluid 'B' of sp.gravity 's2' ,considering all the other system parameters like pressure,temperature etc remain the same,how will the new leakage change  through the same geometrical imperfections(pores)

[Enthalpy]

Hi siddesh, welcome!

In some cases, there is a relationship with the density, in other cases not.

When the viscosity of the liquid has no influence, typically when the "pores" are big holes, then all the pressure serves to accelerate the liquid. In such a situation, the pressure drop equals the liquid's density multiplied by the half of the squared speed attained by the liquid. Then, the liquid's speed (which tends to be uniform then) varies as the reciprocal of the pressure square root.

The other extreme case is when the liquid's viscosity determines what speed it attains. You word "pores" suggests rather this situation. Then, the liquid's density has not direct effect at all. Only the viscosity has, and it does not relate with the density. Mercury for instance is dense and runny. The leakage throughput varies as the reciprocal of the viscosity.

Sometimes both the density and the viscosity matter. Then no simple scaling is possible. When the exact shape of the flow is known and simple, which is rarely the case in a leak, some semi-experimental computations are possible, with Reynolds number and so on. If the shape is known but not very simple, software can try predictions using finite elements.

[siddesh]

Hello Enthalpy.

Thank you so much for a clear and elaborate explaination.

Now as an extension of the question,  Consider a micro level simple cylindrical pore of dia 'D' and length 'L' . 

The system has stationary fluid under some pressure 'P'. Are there any equation/laws that can be used to establish the relationship between the leakage,system properties (pressure,temperature,pore geometry) and fluid properties(viscosity,density etc)

Edited December 17, 2019 by siddesh

[studiot]

2 hours ago, siddesh said:

Hello Enthalpy.

Thank you so much for a clear and elaborate explaination.

Now as an extension of the question,  Consider a micro level simple cylindrical pore of dia 'D' and length 'L' . 

The system has stationary fluid under some pressure 'P'. Are there any equation/laws that can be used to establish the relationship between the leakage,system properties (pressure,temperature,pore geometry) and fluid properties(viscosity,density etc)

Of course, but there is much you have not said.

In particular there is a capilliary relationship between specific fluids and pore sizes.

There is also a (different) relationship between pores and different fluids due to electrostatic forces.
This is particularly important in situations such as flow through clay minerals.

 

So are we talking Civil Engineering (eg soil mechanics), or Chemical Engineering (eg flow through fluidised beds) or what?

 

Good sources are

Transport Phenomena

by Bird,  Stewart and Lightfoot

Dynamics of Fluids in Porous Media

by Jacob Bear

 

[siddesh]

thank you for the update.

I will definetly go through the books u suggested.

we are looking at a mechanical system where in the fluid rests in metal container under some pressure.

what change in leakage can be expected if the fluid inside the container is changed ,i.e  how various factors  will effect this new leakage is what I am looking for.

 

[studiot]

2 hours ago, siddesh said:

thank you for the update.

I will definetly go through the books u suggested.

we are looking at a mechanical system where in the fluid rests in metal container under some pressure.

what change in leakage can be expected if the fluid inside the container is changed ,i.e  how various factors  will effect this new leakage is what I am looking for.

 

 

Well fluids that leak out of properly fabricated metal containers are likely to be light gases such as hydrogen or helium, and that is yet a different situation.

Why don't you properly describe the situation ?

 

Edited December 18, 2019 by studiot

[Enthalpy]

Yes, please describe the situation.

If leakage results from micro-cracks, I tend to answer "replace or repair the vessel, rather than modelling the problem". But sometimes (vessel for a nuclear reactor) it's impossible. At such micro-cracks, the first factor I think of is the fluid's viscosity, not the density - though Studiot brought a good point with capillary action and surface tension.

If the fluid diffuses through the metal, it's essentially an experimental value. Each fluid through each metal has a measured diffusion coefficient. The volume throughput is proportional to this coefficient and can be scaled accordingly between different fluids if everything else is the same. The difference of partial pressures uses to act proportionally within reasonable limits and once an equilibrium exists. The temperature tends to influence over some activation energy.

[siddesh]

Hello both,

Sorry for this late reply as I was inactive for a long period.

Unfortunately I cannot explain the situation in detail as it is confidential but I can give you a compact system detail.

I have a fluid channel with pressure P. This channel has one flow control device (valve) which at complete position should ideally allow zero flow but  in practical applications there is a leakage present of average value='L1'( Determined Experimentally).

Now all I would like to know is what would be the new leakage if the system of channel+valve is used for a different fluid and all other parameters remaining same.

Reason for this is I would like to get the intuition if this change of fluid will affect my system leakage in such a way that I have to consider redesigning it or is it ok to go with same system design without actually able to perform the experimental analysis. I understand that this depends how much leakage am I looking at but all I can say is that this leakage at complete is one of the important criteria for my design.