Air Cooler -40°C

[rohit_k]

I want to generate a cool air of temperature -40°C continuously at a rate of 1000L/min. Please suggest me the system to use for this purpose.

[mbc]

use R -507 a

Boiling point: -47.1

[Brian_UK]

Some more information would be useful.

What is the entering air temperature, for example.

[rohit_k]

I'm from India. So the entering air temperature will be a room temperature from 25°C to 40°C.

[Brian_UK]

What are you trying to cool?

If it is a space/room, can the air not be recirculated to save energy?

[rohit_k]

Actually I want to cool a laser head of a machine. So the air cannot be recirculated. Can you suggest me how to generate the cool air & what will be the setup?

[sanjaysondhi]

I want to generate a cool air of temperature -40°C continuously at a rate of 1000L/min. Please suggest me the system to use for this purpose.
Kindly inform about the load factor. Air to be recirculated and inlet temp of air.

[mad fridgie]

load is approx 3Kw
You need a very deep evap coil.

[NoNickName]

I'm afraid a 80K cooling in one pass is some sort of a challenge.
dry air has got a specific heat of 1 kJ/Kg K.
Density varies considerably across the temperature range, from 1.1 to 1.5 Kg/m3, with an average of 1.3Kg/m3 or 1.3x10E-3Kg/l

80k x 16.6 l/s x 1.3x10E-3 = 1.7 kJ/s that is 1.7kW, which is away from the 3kW you say, if my calculation is right.

The point is that in India air is very moisty and you would end up with a frosted coil in minutes or seconds.

I would suggest to buy liquid nitrogen and evaporate it on your laser.

[mad fridgie]

I'm afraid a 80K cooling in one pass is some sort of a challenge.
dry air has got a specific heat of 1 kJ/Kg K.
Density varies considerably across the temperature range, from 1.1 to 1.5 Kg/m3, with an average of 1.3Kg/m3 or 1.3x10E-3Kg/l

80k x 16.6 l/s x 1.3x10E-3 = 1.7 kJ/s that is 1.7kW, which is away from the 3kW you say, if my calculation is right.

The point is that in India air is very moisty and you would end up with a frosted coil in minutes or seconds.

I would suggest to buy liquid nitrogen and evaporate it on your laser.
80C single pass is not an issue1
Yes your calculation is right, apart from the air is not dry, you must include humidity, water and ice then load is approx 3KW (of course depends upon original RH, for this calc 40Cdb 70%RH)
If the coil was at one low temp then you would have a frost loading of aprox 2.1Kg/hr.
With one pass air systems with big TD you should have at least two coils , 1st stage SST just above 0C and low face velocity (no water carry over) this reduces frost loading
Second stage needs to be around -48C (care has to be taken on evap(refrigeration) pressure drop.
The arrangement needs to be reapeated twice to allow for defrosting along with appropriate air dampers

[rohit_k]

Can you guide me about the system setup?
Which compressor & refrigerant to use?
Compressor capacity?

[mad fridgie]

Can you guide me about the system setup?
Which compressor & refrigerant to use?
Compressor capacity?
May I suggest you employ an expert in refrigeration, this type of project even though is small, still needs a high level of knowledge.

[NoNickName]

Definitely. Multipass refrigeration is quite a challenge for anyone, let alone rookies.