Cascade: Refrigerant blending and Oil Management

[sdumper]

Guys, I normally use r-1150 in 2 stage cascades because frankly its usually pointless to use anything else.

That said I have a client that wishes to use r-23 and also would like it to hold on the contact point -80c under loads ranging from 100 watts to 250 watts.

Given the following properties of both I dont think im going to be able to obtain a guaranteed temp of -80c am I correct?

r-23
Appearance: Clear, colourless liquid and vapour.
Physical State: Gas at ambient pressure and temperature.
Chemical Formula: CHF3
Odour: Faint ethereal odour.
pH Neutral
Boiling Point: -82.1oC (-115.7oF)
Freezing Point: -155oC (-247oF)
Vapour Pressure: 42.4 Bar at 21oC (70oF)
Vapour Density (Air =1.0) 2.4


r-1150
APPEARANCE, ODOR AND STATE: Colorless gas at normal temperature and pressure; faint, sweet, musty odor.
MOLECULAR WEIGHT: 28.05
SPECIFIC GRAVITY (air=1) at 32?F (0?C) and 1 atm: 0.978
GAS DENSITY at 32?F (0?C) and 1 atm: 0.0787 lb/ft3 (1.261 kg/m3)
SOLUBILITY IN WATER, vol/vol at 32?F (0?C) and 1 atm: 0.26
BOILING POINT at 1 atm: -154.62?F (-103.68?C)
MELTING POINT at 1 atm: -272.9?F (-169.4?C)
% VOLATILES BY VOLUME: 100