elogesh
Mechanical
- May 10, 2002
- 187
Hi,
This is regarding the flow analysis of pneumatic valve of plunger type with 30% valve opening.The objective of the analysis is detemination of pressure drop for specified mass flow rate with 30% valve opening.The fluid medium is air at normal atmospheric pressure and temperature condition.
In this problem, following flow conditions are known.
a)atmospheric pressure at inlet b)total mass flow rate through the system
We use fluent software for the analysis.Inlet, we specified the pressure inlet boundary condition (Static pressure = atmosphric pressure and dynamic pressure for the velocity). Initially,We assumed outlet pressure and carried out the analysis and determined the mass flow rate.Based on the results, we adjusted the outlet pressure by iterations,until we achieved the desired mass flow rate.
By this approach, we determined the pressure drop across the valve.
Since the mach number is less than 0.3, we are solving it as incompressible and also as steady state, turbulent flow (Re>50,000).
Other details:
Inlet and oulet diameter of the valve = 150 mm
Mass flow rate = 0.60 kg/sec
Whether it is possible to do hand calculations for this problem? Even a ball park figure with + or -10% variation is reasonable to start with...
I don't have crane hand book to perform hand calculations accounting the valves.
Hence, I planned to do pressure drop calculation as follows,
1) Pressure loss due to area change (change in shape of the cross-section is not accounted)
= density *gravity *(v^2/(2g)
2) Pressure loss due to obstructions,
Loss due to drag = Cd*0.5*density*v^2/(2g)
Where Cd- drag co-efficient
3) Pressure loss due to direction change (90 deg elbow)
= don't know how to calculate.
4) Pressure loss due to viscous friction
= Possible to calulate using head loss formula
f (L/D) * (v^2/2g)
Where f - friction factor
I would like to have your valuable comments about this approach.
If there are any corrections required in the computation or understanding, kindly let me know.
My intention is to know, whether the software calculated results are reasonable by comparing with the hand calculated results (Ball park figure).
Thanks for your time.
Regards,
Elogesh
This is regarding the flow analysis of pneumatic valve of plunger type with 30% valve opening.The objective of the analysis is detemination of pressure drop for specified mass flow rate with 30% valve opening.The fluid medium is air at normal atmospheric pressure and temperature condition.
In this problem, following flow conditions are known.
a)atmospheric pressure at inlet b)total mass flow rate through the system
We use fluent software for the analysis.Inlet, we specified the pressure inlet boundary condition (Static pressure = atmosphric pressure and dynamic pressure for the velocity). Initially,We assumed outlet pressure and carried out the analysis and determined the mass flow rate.Based on the results, we adjusted the outlet pressure by iterations,until we achieved the desired mass flow rate.
By this approach, we determined the pressure drop across the valve.
Since the mach number is less than 0.3, we are solving it as incompressible and also as steady state, turbulent flow (Re>50,000).
Other details:
Inlet and oulet diameter of the valve = 150 mm
Mass flow rate = 0.60 kg/sec
Whether it is possible to do hand calculations for this problem? Even a ball park figure with + or -10% variation is reasonable to start with...
I don't have crane hand book to perform hand calculations accounting the valves.
Hence, I planned to do pressure drop calculation as follows,
1) Pressure loss due to area change (change in shape of the cross-section is not accounted)
= density *gravity *(v^2/(2g)
2) Pressure loss due to obstructions,
Loss due to drag = Cd*0.5*density*v^2/(2g)
Where Cd- drag co-efficient
3) Pressure loss due to direction change (90 deg elbow)
= don't know how to calculate.
4) Pressure loss due to viscous friction
= Possible to calulate using head loss formula
f (L/D) * (v^2/2g)
Where f - friction factor
I would like to have your valuable comments about this approach.
If there are any corrections required in the computation or understanding, kindly let me know.
My intention is to know, whether the software calculated results are reasonable by comparing with the hand calculated results (Ball park figure).
Thanks for your time.
Regards,
Elogesh
