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-   -   Can Flow-3D solve the Joule-Thomson effect? (http://www.cfd-online.com/Forums/flow-3d/75721-can-flow-3d-solve-joule-thomson-effect.html)

 seasoul May 3, 2010 23:39

Can Flow-3D solve the Joule-Thomson effect?

I am doing some projects about VOF. So I want to buy a Flow-3D license. But my supervisor askd me if Flow-3D can solve Joule-Thomson effect. I think he is thinking to use it for another project under him, which is about gas leaking. I told him Flow-3D is good at VOF, but not so powerful to deal with other processes. My quesiton is if Flow-3D can solve Joule-Thomson effect? If can, is there any example I can use to show my professor?

Joule Thomson effect describes the temperature change of a gas or liquid when it is forced through a valve or porous plug while kept insulated so that no heat is exchanged with the environment

 JBurnham May 4, 2010 10:35

FLOW-3D & Joule Thomson Effect

2 Attachment(s)
The answer is yes: FLOW-3D can model compressible gases (simultaneously with incompressible fluids, if necessary), and has full heat transfer calculations available. I've modeled steam through an orifice to show the Joule Thomson (throttling) effect: as you can see the jet temperature is much lower than the upstream temperature. The steam jet is at an angle because it's 'swinging' back and forth (oscillating). Two images are attached. Let me know if you have any other questions.
[IMG]file:///C:/Users/Jeff/AppData/Local/Temp/moz-screenshot.png[/IMG]

 seasoul May 4, 2010 12:13

Quote:
 Originally Posted by JBurnham (Post 257529) The answer is yes: FLOW-3D can model compressible gases (simultaneously with incompressible fluids, if necessary), and has full heat transfer calculations available. I've modeled steam through an orifice to show the Joule Thomson (throttling) effect: as you can see the jet temperature is much lower than the upstream temperature. The steam jet is at an angle because it's 'swinging' back and forth (oscillating). Two images are attached. Let me know if you have any other questions. [IMG]file:///C:/Users/Jeff/AppData/Local/Temp/moz-screenshot.png[/IMG]

 seasoul May 4, 2010 22:34

JBurnham, sorry to bother you. My supervisor, asked me how to define joule-thomason coefficient in flow 3D. Oh my god, I even do not have flow 3D. So i came here again to ask, is there a direct way to define j-t coefficient, or there is a indirect way to define it.

 JBurnham May 5, 2010 11:00

Joule Thomson Coefficient

Seasoul - the Joule Thomson coefficient is usually defined as

Kjt = V/Cp (aT-1),

where V is the gas volume, Cp is the constant-pressure heat capacity, a is the coefficient of thermal expansion, and T is the absolute temperature.

I assume you're looking at gas or vapor for this problem, not liquid. In FLOW-3D, activating the fully-compressible 2-fluid model 'turns on' the heat transfer and density evaluation physics packages. Then, for Fluid #2 (the fully compressible fluid), you can define the constant-volume heat capacity Cv. Temperature T and volume V are dynamically computed. The coefficient of thermal expansion is an available input in FLOW-3D, but it controls density evaluation as a function of temperature only. For compressible fluids, only the specific gas constant R needs to be defined (specific to the fluid - not the universal gas constant). Then the constant-pressure heat capacity will be dynamically computed as a function of Cv and R.

For example, in the steam problem I showed, Cv (cv2) is about 9128 ft^2/s^2/R, R (rf2) is 2760 ft^2/s^2/R, and compressibility coefficient a is not specified because the steam is compressible and the density is determined from the equation of state (rho = p/RT). FLOW-3D can use other unit systems as well, this problem just happened to be in ft-slug-Rankine units. A heat transfer coefficient for internal heat transfer is also specified for the fluid, but that's not explicitly related to the Joule-Thomson effect.

So, in short, you don't actually need the JT coefficient, but you can calculate it from R if necessary, and you don't need Cp, but again, you can calculate from Cv (which you do need): cp - cv = R. The specific gas constant is an intrinsic property of the fluid you're working with. FLOW-3D assumes that the ideal gas law applies for evaluating the relation between T, p, and rho. If the problem involves a non-ideal gas (Cv varies significantly with pressure and/or temperature), then you might be looking at a code-customization. However, I'll point out that the ideal gas assumption is OK for most problems and most gases and gas mixtures, and as shown in the example I sent earlier, the pressure drop does correlate with a temperature change (small departures from the ideal gas rules that occur due to molecular internal work won't be modeled).

Hope that helps.

 seasoul May 11, 2010 04:48

Thanks.
After I get the software, I will try this case as soon as possible.

 JBurnham May 11, 2010 13:45

Sounds good. Once you get it installed, let me know if you'd like the test case that generated the images I sent earlier: I can provide the case with some commentary on the setup to help you get started.

 seasoul May 12, 2010 00:50

JBurnham,
Can you send me the case file (or the input text file) now? My supervisor has started the purchasing, and I want to start learning from now on. I am learning flow 3d by reading the early tech notes in the flow-3d official website. But the cases in the quite early days seem to be obsolete, I think now flow-3d is different and more powerful than at that time.