Capillary Simulator?

[mad fridgie]

There seems to be a few of these cap. sims. around, so i thought i would have ago my self.

Firstly i have had alook at others (no I do not know code)

I can not find a reference on any to the coiled diameter of the capillary. Surely when you reduce the coiled diameter (like we all do) the physical shape of the round pipe much change. This must effect any simulation program.
Also no allowance for effect of ambient

Then i had a look at the transport properties of the refrigerant (liquid and vapour), these do change slightly acoss the temp and pressure range. (Can sort of handle this one)

Then I came to to phase change in the cap. WOW.
Where i got stumped is not so much the end, but handling this first bubble of vapour. this bubble if I dare call this, varies in its properties, and is dependent upon the down stream, which dependent upon the up stream.

I have given up. i wonder how many of the simulators actally allow for the varing transport properties of the this mixed state. or do they use a expansion constant to give required pressure drop at varing mass flows.

So the question is to what level of accuracy should we be working to +/- ?%

[desA]

http://www.nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Ref%20and%20Air%20Cond/pdf/R&AC%20Lecture%2024.pdf

You will find this link very useful. Download it.

[mad fridgie]

Thanks Des, interesting, most above my head "lol".
What can be taken from the report is that the simulators are estimators! As certain constants are presumed.
The main point for the practical application, is start with a longer cap than estimated for mass production (testing required) and shorter for one off applications.
If I go back to when I charged by "feel", I used block the condensor (to give 55C cond pressure) bring the fridge down to temp, see what the suction pressure was, (if close to design OK) then i would use the frost line principle (frost back to the comp), let a little refrigerant out, until frost moves up the suction line.
Always worked, not scientific, no doubt illegal today vent refrigerant off to atmosphere.

[desA]

Thanks Des, interesting, most above my head "lol".


The credit goes to our Happy, Smiling Cook - Chef. :rolleyes:

He posted a link in one of the earlier threads. Download the whole series - it's very interesting.

[nike123]

Download the whole series - it's very interesting.

Did you mean this:
http://www.nptel.iitm.ac.in/courses/Webcourse-contents/IIT%20Kharagpur/Ref%20and%20Air%20Cond/New_index1.html
?

[desA]

^ Yes, that's the one. It's excellent. :)

[nike123]

:off topic:
Here (http://www.youtube.com/user/nptelhrd#grid/user/E2DA184A2E479885) are videos of all lectures.

[jcook1982]

All those formulas.. UGHHH driving me nuts...