3 replies to this topic

[Surirama]

why is throttling using a control valve an isoenthalpic process? how is this different from throttling using an orifice?

[JoeWong]

Surirama,

The term used shall be isenthalpic process instead of "isoenthalpic process"

Throttling through a control valve is a quick process involve change in state but no energy be in the form of work or heat is exchanged with the environment. Those it is commonly accepted as isenthalpic process.

You may view a control valve as a device with changeable orifice. Thus, there is no different between them.

Please also read the following...HERE 1, HERE 2, HERE 3, HERE 4


Other CheJedi, please assist further...

JoeWong

[Surirama]

[quote name='JoeWong' date='Sep 10 2007, 01:41 AM' post='12812']
Surirama,

The term used shall be isenthalpic process instead of "isoenthalpic process"

Throttling through a control valve is a quick process involve change in state but no energy be in the form of work or heat is exchanged with the environment. Those it is commonly accepted as isenthalpic process.

You may view a control valve as a device with changeable orifice. Thus, there is no different between them.

Please also read the following...HERE 1, HERE 2, HERE 3, HERE 4


Other CheJedi, please assist further...

JoeWong
[/quote


Hi Joe,

Much appreciate your reply...However, I did have another question.

Consider a steam turbine. Steam passes from the steam chest to the turbine case via a nozzle where it impinges on the impeller blades. Would the change in flow variables in this case be small and gradual (big steam chest, small nozzle, big impeller casing - the flow area changes drastically) and would this be considered an isentropic process?

Cheers,
Surirama

[JoeWong]

Consider a steam turbine. Steam passes from the steam chest to the turbine case via a nozzle where it impinges on the impeller blades. Would the change in flow variables in this case be small and gradual (big steam chest, small nozzle, big impeller casing - the flow area changes drastically) and would this be considered an isentropic process?

Surirama,
An IDEAL steam turbine will goes through isentropic process. In REAL world, NO one steam turbine is isentropic. Thus isentropic efficiency come in picture to take care the deviation of a REAL from IDEAL steam turbine.

Please read more...STEAM Turbine

JoeWong