Sizing a Compressing Unit

Hi there,

my knowledge on the topic of refrigeration units is basic to say the least - however I have been given the task to size a compressing unit for an experiment that will be under taken.

The system is basic, where a copper coil (1/4" Outer diameter) will be wrapped around a 2" O.D. and 4 foot long hollow steel pipe - insulation will be placed around the system. We hope to pass the refrigerant through the copper coil to cool what will be inside hollow steel pipe (down to as low as -20 degrees Celsius).

Of what I was told from several individuals, only a condensing unit and an expansion valve would be required - however it seems as if the sizing of the condensing unit is the most difficult task at this point in time.

Any help or direction you may be able to provide me would be of enormous help,

thank you for your time!!
Mitch

Yes, you need to calculate how much cooling you require to whatever is going to be inside your steel tube.

From that answer will come the sizing of the condensing unit.

Brian_UK is telling you that the first thing you have to do is to calculate what you need or want from the system.

But there's another issue if you manufactured the heat exchanger, you will also need to know how efficient is the heat exchanger in getting what you need.

The question is at what temperature your refrigerant needs to be to exchange from your fluid what you want.

If you manufactured the heat exchanger you will have to run some tests.

If the heat exchanger is manufactured you will have to get the data at what temperature differential you can get what you want.

With this information you only have to look up for condensing unit’s capacity tables.

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Hi Mitch the others have answered this quite well....

You need to know what the duty is over the evaporator.
If you make one you may have to experiment practicaly to find out what it can do.

As has been explained the pressure that the evap works at will dictate the
type of compressor and the load on the evap will dictate the size of the
condensing unit.

This can be done mathamaticaly or you can put the bits together and
run a system until you find the info you require.

A good start point is knowing what you are cooling in the evap.

If it was a tube full of water then find the specific heat content of
water and weigh how much you have. For every 1 degree you cool the
water you will have to remove an amount of heat.

The numbers and figures can easily be found on the net, calculate how
much heat is to be removed and that will give you some sort of base line to start
working from.

Water for example needs 4.19 kJ/Kg of heat removing per degree C of cooling
So 1 Kg of water cooled by 100 degC would require 419 kJ of heat to be removed

From that you can size the rest of the system..........

All the best

taz

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Thank you everyone, hopefully this head start will get me somewhere this time around.

Cheers!
Mitch