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Thread: analysis of expansion valve
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28-01-2009, 05:46 PM #1
analysis of expansion valve
hiiiii ,
i am student, my project is related with expansion device. i want to know more @ expansion valves.
how to fix the inlet dia, outlet dia(i.e. orifice size)for particular pressure.
for example for carbon dioxide (compressible fluid)inlet pressure is 100 bar and required pressure at outlet is 20 bar. how to fix diameters???? which formulae have to use??? if we assumed dia, then how to calculate pressure drop(coz compressible fluid) corresponding to dia assumed dia.pls help me.
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28-01-2009, 08:26 PM #2
Re: analysis of expansion valve
For most of us we will size an expansion valve by reference to a manufacturers' data book available from most reputable manufacturers.
I see that you did not have much success with this question on the Physics Forum either, even when asking about R22.Brian - Newton Abbot, Devon, UK
Retired March 2015
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16-04-2009, 05:38 AM #3
Re: analysis of expansion valve
100 bar inlet represents a transcritical system....the component you are referencing is the gas cooler control valve. For such a high pressure device of considerable size, that would be responsive to thermal conditions, would almost have to come out of the utility steam or nuclear industries.
The sizing equations those people will employ are published by the Flow Controls Institute and deal with characteristics of the valve as well as of the fluid. They deal with a condition called "Expansion Factor" in terms of the body geometry; but if this is to be a sharp-edged orifice centred in a larger pipe, the ASME characterizations for sharp-edged orifices under critical compressible fluid flow will give you an area as a starting point.
This is simply Q=CdAP/sqrt(GT)
where G is gas specific gravity; A is Area; T is absolute temp and P is absolute press. The CdA term is Coefficient of Discharge times Area and is in some manuals is combined into a single number: the point being, the Cd terms is constant for a given size of orifice and upstream pipe and under conditions where the orifice diameter is less than a tenth of the upstream pipe, the whole thing converges on Cd=0.6. This can be found in a number of web references on safety relief valves and on instrumentation.
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