Steve Lusardi wrote:
Jon,
Good info. The cold plates I have bought are used units and they all have
the expansion valves with them. I have assumed they also have integral spray
orifices.
Yes, they should. The orifice size should be able to be looked
up from the part number. Also, thermostatic expansion valves
have to have the same refrigerant in the sensing bulb as is used
in the system.
I suppose I could apply compressed air to determine approximate
flow rates. How else would I test these, as they are not able to be
disassembled? The cold plates are used marine units and I want to use them
for a freezer, not a refrigerator, hence the -40 requirement. I am aware of
the requirement to change the medium in the cold plate itself in order to
reduce the temperature of the state change. The goal is to freeze the plates
down once a day or less when in use. How do I estimate the heat load? The
cold plates are aproximately 24" x 18" x 4".
What are you cooling? Just the plates? A tank of brine?
Making a block of ice?

It gets messy. What is the starting temp of the plates when you
begin to cool them? Will you be cooling only one at a time?
Would you be keeping one or more plates cold while starting the
cool-down process on a warm plate? That's the worst-case
scenario. To calculate the heat load, you need to know the
surface area of the tubing, and the thermal conductivity of the
heat source to the cold plate. If you are hanging the plates in
mid air and cooling the air in a room, the heat flow is very
low. If the cold plates are attached to metal walls or immersed
in circulating brine, the heat flow is maybe 100x higher. You
really aren't telling us enough to give you any help.

Anyway, to get to -40 C (or F) you need an evaporator pressure
(suction, low-side) of 105 kPa absolute, or just barely above
atmospheric pressure. This will cut the performance of the
evaporator, as well as making the compressor work a lot harder.

Jon