# How to calculate outlet dia for required pressure drop in case of compressible fluid?

1. Jan 9, 2009

### johnmane

hii ,
i know the inlet conditions i.e. dia 2mm , pressure = 100 bar, density= 0.001176 m3/kg, mass flow rate remains constant= 0.09017 m/s , for same mass flow rate for pressure drop 80 bar(i.e. pressure at outlet is 20 bar) for COMPRESSIBLE FLUID what will be the outlet dia???? take fluid carbon dioxide........

Last edited: Jan 9, 2009
2. Jan 16, 2009

### Thaakisfox

Re: how to calculate outlet dia for required pressure drop in case of compressible fl

Use the Bernoulli equation, and continuity equation ;)

3. Jan 22, 2009

### ravijha

Re: how to calculate outlet dia for required pressure drop in case of compressible fl

no u cant use bernouli equation for a compressible fluid.....use steady flow energy equations

4. Jan 22, 2009

### stewartcs

Re: how to calculate outlet dia for required pressure drop in case of compressible fl

Depends on what level of accuracy you want. The general rule of thumb is that if the pressure drop is less than 10% of the inlet pressure, then reasonable result can be obtained.

CS

5. Jan 22, 2009

### Topher925

Re: how to calculate outlet dia for required pressure drop in case of compressible fl

Yes you can.

Is this for a real application, or is this a text book problem? It this is for a real application, geometry matters. Is this a nozzle, piping system, what?

6. Jan 23, 2009

### Thaakisfox

Re: how to calculate outlet dia for required pressure drop in case of compressible fl

Of course you can use the Bernoulli equation..., the Bernoulli equation says:

$$\frac{v^2}{2}+w+U=constant$$

Over one streamline if the flow is "general" (well, almost, fluid is barotropic, outer force field is conservative etc), and everywhere if the flow is irrotational.

Here w is the specific enthalpy, and U is the potential of the force field.
This can be applied to "any" fluid, compressible and incompressible alike...

7. Jan 27, 2009

### johnmane

Re: how to calculate outlet dia for required pressure drop in case of compressible fl

hiiiii thanks for ur help and sorry for late response,
Topher925 u may be right........this is real problem........
but i know only inlet conditions ........don't know the outlet conditions........then how to apply this equation???? if assumed outlet dia, then i am able to calculate velocity at outlet......but again one parameter misssing that is specific volume........actually this real problem came while analysing the expansion valve for carbon dioxide...............