Cap tube for R23

[lana]

Hi there,

Does anyone know a reference for cap tube sizing for R23? This is required for a cascade system down to -75°C evaporating temperature with 2.2kW capacity.

Appreciate any help.

Cheers

[icecube51]

download " Dancap" , a free program from Danfoss.

works fine.

Ice

[Peter_1]

Ice, Dancap doesn't work with R23

[Chef]

Lana - post as many details as you have especially the mass flow rates and I will run it for you.

Chef

[icecube51]

Ice, Dancap doesn't work with R23

oeps, forgot to check that one.
thnx Peter.

you see, we are learning every day something new here.

Ice

[lana]

Thanks everyone,

I had checked the Dancap before and it does not work with R23.

[Chef]

Lana - I have a program that runs R23 and can run a scenario for you if you wish. I will need the pressures and Temps at the condenser and evap plus the mass flow rate. Although I can estimate the mass flow from the cooling load it would be better to have a precise figure. Any SC info would help and also if the condenser is oversized.

Chef

[Chef]

Based on these conditions
R23, te=-75°C tc=-20°C capacity 2.12 kW suction superheat 20°K.
The following results are shown for your system.

You may be trying to push the duty a little too hard as a tube of 2mm is already 5m and it has gone sonic at the exit which is not advisable, however a smaller tube is shorter and the exit is even more of a problem and a bigger tube gets very long.
A 2.3mm tube is 11m long!!!!!
Setting Tc = -25C helps the duty to be manageble but that of course depends on your first stage?

Hope it helps

Chef

[mad fridgie]

Hi Chef, the programs looks good.
just a question about this application, would installing 2 (or more) caps give better results. (or is just the nature of the application giving you the concerns)
cheers
Mad

[Chef]

Hi Chef, the programs looks good.
just a question about this application, would installing 2 (or more) caps give better results. (or is just the nature of the application giving you the concerns)
cheers
Mad

Hi Mad
Very good point indeed and your absolutely right.
These are the results for multiple tubes

3 off 1.2mm by 3.5 m exit velocity is 151m/s
2 off 1.5mm by 4.1 m exit velocity is 158m/s
1 off 2mm by 5.7 m exit velocty is 171m/s

So using multiple tubes can keep the velocity below sonic and give shorter tubes in the installation.

4 off 1mm has the same exit as 1 off 2mm but 7 off 0.8mm is fine and tube drops to 2.2m.

Interesting set of choices?

Chef

[lana]

Many thanks for your reply.

I am little bit confused. Can you clarify about the cap tube ID and length?
Is it 2mm ID and 5.7m length?

Thanks again.


Is it

[Chef]

Lana - if you open up the little attachment I posted it does show the tube ID as mm and the length as m - both SI units. All other references to the tube are ID and length.

Its too difficult to use OD of the tube as wall thicknesses vary from one to another manufacturer so the ID would be impossible to gauge.

Chef

[lana]

Thanks a lot.
Cheers