Anyone know how to use Dancap?

[Freddie123]

Posting this for a friend. He attempted to register here but has never received an activation e-mail

I need help with Dancap i've been trying to use it but it spits out some strange numbers. I've set refrigerant as R404a, heat load as 200w, evap temp as -35ºC (According to danfoss the NL11F does 200W at -30ºC with 134a so I estimated -35 with r404a), condensing temp as 40ºC (halfway between the top and bottom numbers on the envelopes @ -35ºC in Danfoss RS3) and return gas as 0ºC (didnt know what to set this at)

Its told me to use 26" of 0.028 cap tube, seems slightly off to me :P What have I done wrong? Is Dancap just useless? Help?

If anyone could help him it'd be much appreciated. Also, if anyone could resend the activation e-mail that'd be great too, he set up the acc as Denbob99 here too

[PhilippF]

All the programs I tried now seem not to get any good results:

Tecumseh Capillary Tube (4.1 feet of 0.028 for the given specs)

Technisolve CapTube (7.8 feet of 0.036 for the given specs)

Does anybody have a nice program, that actually works?


regards,

Philipp

[Freddie123]

Seems its best just to use Gary's method

[PhilippF]

Totally, absolutely, definitely positively agreed :up:

[n00b 0f l337]

Wouldnt return gas be quite a bit colder no? What happens if you set the return gas to -30C?

[Freddie123]

25 inches of 0.28

[SoddemFX]

I don't know what it's doing, i dont know where that L/min figure comes from and the pressure drop is unreasonable.

Mass flow for 200W at -35C vapour and 10K superheat is 0.0019Kg/sec, so 0.114Kg/min. Density of r404a condensing at 35C subcooled by 2K is 1004Kg/m^3 so 1.004Kg/litre so volume flow of liquid is 0.114L/min

I don't know where the 15L per min used here comes from unless they're taking the two phase flow in the capillary tube into account...? Maybe it's discharge or suction volume flow but i haven't got time to work out what they are, i don't see how they would be relevant anyway...

Also pressure drop accross the capillary tube seems to be held at a constant 145PSI whatever the conditions, whereas for Tc = +35C and Te = -35C the pressure drop accross the capillary tube is 211PSI

From the 0.031" length it seems to be approx 3x too short, there must be some basis behind the tool but i'm not sure what it is :confused:

Tom

[SoddemFX]

If the pressure drop was actually 145PSI, the tool might be right or at least very close.

Maybe, who knows...

Tom

//Why does the flow rate go down with increased condensing temperature...?!

[Freddie123]

Anyone know a decent program that actually works?

[DetroitAC]

That screen shot of DanCap that tom posted says "15.0 l/min (N2 at delta p 145 psi)"

It's pretty common in refrigeration to rate devices in terms of air or nitrogen flows. TXV manuf. do this also, it's much easier to test a valve on the bench for the proper flow of N2 than to use refrigerant.

DanCap, I would guess is using a correlation between nitrogen flow and the refrigerant. If it were my software, I would not show that information, it just causes confusion.

[Freddie123]

Still it doesn't seem to give accurate cap tube lengths

[Clemmaster]

Select 32° for the Return gas temperature?

The calculation may be based on bigger compressors that indeed work with bigger captube, and we're running with insulated succion line so the return gas temperature may be set higher?

[Clemmaster]

//Why does the flow rate go down with increased condensing temperature...?!

I still don't remember how you call it in english : dead point --> The volume that prevents the piston from hitting the compressor when the stroke is maximal.

Any way this dead zone contains an amount of gas that stay Inside the cylinder during the discharge phase. this amount of gas is at constant volume (the dead point), and its pressure, when the discharge has occured, is a bit higher than the discharge pressure. During the succion phase, the pressure inside the cylinder must be a bit lower than the succion pressure, but as an amount still remains in : there's a phase during witch the pressure decrease but nothing enters the cylinder. When the condensing temperature increase, this phase is longer, so the volume needed for the pressure to be low enough increase --> the displacement decrease, the mass flow too.

Sorry I don't know technical vocabulary so my explaination is hard to understand :/

[[XC] gomeler]

I understand what you are talking about, on an ICE that'd be the volume of the combustion chamber but in this application I don't know what you'd call it.

[DetroitAC]

We call it clearance volume in English.

[Freddie123]

At 32ºC return temp its recommending 34 3/4" of 0.028 cap

[Clemmaster]

We call it clearance volume in English.

Yeah that's it, you already told me but I forgot it :p:

[Freddie123]

So, in short. For our purposes there isn't really a viable program, basically trial and error and the rough calculations of Gary?

[Clemmaster]

I couldn't be precise, it seems to be calculated in conditions closed to those we're running with (NL compressor on the pics :D), maybe it's done for bigger systems and the calculations could be false in this case (0.8mm becomes very restrictiv for the massflow/speed and a very short captube give the same pressure drop than a longer one with the compressors we're running with). We don't know the calculations and their limits :/