cap tube hx question

[bazx]

hi need some input

i have a hx coil of 10 inch dia 1/2 with 1/4 inch inside the total hx length is 12 foot

i am using a danfoss SC21 compressor

the cap tube feeding the hx is .031 at 1.7m or 67 inch

now this does cool the hx all the way to the suction return with out load
but fails when loaded

i also have 3 colis of cap tube .028, .031, .042 to use

is my choice of cap tube wrong for this size of compressor?

[jinu117]

Could be too long of slhx. I noticed too big of hx means much more refrigerant needing to be in highside to condense properly (like having huge condenser... really huge).

PS) whoops read wrong. Is it hx for cascade? Whats high side and low side reading when idle and when loaded... (when it collapses, does suction go to vacuum?)

[bazx]

yes it is for cascade

and the gas is 402a

the hx is @ 12 bar/180 psi and at the moment the load was only from the low stage running but with no load on the evap co2/402a

what length of cap would you start with ?

[fatty]

What I was told or suggested was use the same length for both sides dont know if it right or not??
for 200w 93" of 0.0028

[cold_ice]

The captube lenght seems right to me. Maybe a bit short but should work very good.
Whats your lowside pressure? Seems you lack of refrigerant, try to add some more.

[kayl]

i had troble with my 12' hx hard to keep it flooded at load.
Maybe try longer.
i normally use 1.8m to 2.1m 0.031" for first stage of cascade.
You could try as short as 1.5m but any shorter and refrigerant wont condenser as well as it could and get blow by

[bazx]

thanks guys for all your input there is enough info here to keep me busy for a while

baz

[wdrzal]

make sure you have enough condensed refrigerant available first. If problem still exists you need to shorten cap tube or use a larger diameter.If you meter enough refrigerant it will roll down the tube until it all boils off. I have a electronic sight glass which work great for this. you just charge untill you "see" a little liquid exiting the hx.

Other suggestions: use 2 cap tubes of same length but enter the second one half way down the tube on hx.

or just make 2 paralell hx but shorter in length.

[n00b 0f l337]

Did you use a sight glass, if so, is it solid?

[wdrzal]

I use a electronic sight glass, you just clamp it on the tube.There is just a series of lights that flash and a audible tone for indication. You need to understand where in the system vapor is and liquid. I would charge a evap or hx until a few drops of refrigerant pass out occasionly (every couple seconds.) once liquid start exiting the evap or hx ,it's asorbing as much heat as possible..

[fatty]

Can you post a pic of it I haven't seen an electronic one :)

[bazx]

make sure you have enough condensed refrigerant available first. If problem still exists you need to shorten cap tube or use a larger diameter.If you meter enough refrigerant it will roll down the tube until it all boils off. I have a electronic sight glass which work great for this. you just charge untill you "see" a little liquid exiting the hx.

Other suggestions: use 2 cap tubes of same length but enter the second one half way down the tube on hx.

or just make 2 paralell hx but shorter in length.


this interested me so i gave it ago

2x cap @.031/1.8m

and it held a load better than with one



thanks