Help with refrigerant selection

[Dpalo022]

Hey,

We're designing a cascade system for a freeze-dryer, I was wondering if anyone had tips for how refrigerant choice effects the compressor. Should we be matching pressure differences or compressor power.

Right now we're usign DUPREX, a program by Dupont to compare refrigerants, and so far are looking at R-404A for the high temperature loop and R-508B for the low temperature loop (-70 C).

Any assistance would be greatly appreciated.

[Tapas K Mitra]

Use R-23 Gas, but be careful. At ambient temp the sat. pr. is extremely high

[CoolAids]

Tapas Is right,Use R-23 Refrigerant....Good matchup....Also be advise that R-23 is Costy $$$$

[The MG Pony]

http://www.xtremesystems.org/forums/...wpost&t=144007

Read this thread, you get to watch one be designed, parted out, assembled and charged.

All open for all to see and explained in detail, amazing auto cascade -141c! made from a 5000btu/h AC

As posted in another topic, after reading the thread several times you'll have a far more indepth understanding of why and how refrigerents need to match up and such!

I to am planning a Vacuum freez drier, I am opting for an auto cascade for obvious reasons of performance Vs power ratio is superior and equipment life will be longer too!

[The MG Pony]

start with evap load, based on evap duty you slect the best refrigerant, then based on evap temp and load you select compressor displacment.

After figuring out the second stage systems total needed condesor duty you select the first stage gas and based on required temps & duty you select the first stage compressor!

ALL WAYS START AT THE EVAP! This seems to be the most over looked basic fact by people trying to design their own kit! And be mind full of local ambient trends!

- Design in a high safety margine
- Use all manual reset safety devices to force the opperators to fix the issue
- Ensure the first stage has plenty of condensor capacity to spare