Coil design?

[The MG Pony]

Ok I'm making a coil for a home made 1/2Ton chiller.

Coil:
Size 3/8th Inch ( 6.985mm)
Length 9 Inch ( 228.6mm)
Inside Diameter of coil 3 Inch ( 76.2mm)
Loops 22
Loop spacing 1/4 Inch ( 6.35mm)

Shell:
Inside Diameter 5 Inches ( 127mm)
Length 11 Inches ( 279.4mm)
Liquid In/Out ports 1/2 Inch ( 12.7mm)

How would I go about calculating the wattage or BTU/H of this coil, Now just guesstimating I thing it will be more then able to handle 6,000BTU/h ( 1.758Kw/h)


What do you all thing? good design for a really simple Shell and tube exchanger thats well matched?

[nevgee]

Well iits not like its never been done before .. very ineficient but if you have the time to be assembling it for nothing then go for it.
As for duty, why not build it establish a balanced operating condition and then measure the flow and TD of your secondary medium, that will give you your emperical data to calculate the operating duty.
Big question is what do you need to use it for? If you have a required duty then you should design to acheive that duty. Or have you just realised that you can form a convenient length of tubing into a coil?
When you build be careful not to evaporated too low (sst > -3C) or you'll cause an ice build up on your coil suface and risk busting the shell, unless you use antifreeze, but then you'll reduce the efficiency again.
try to ensure you get contra flow for max heat exchange.
You'll need a good deal of turbulent flow around the coil.
Have you considered whether you should DX or flood the coil ...how will you control the superheat, should you consider hot gas injection?

Personally I would consider using a brazed plate exchanger, Alfa Laval or SWEP as they are probably the best for eficiency economically, thermodynamically and space savers to boot. Along with the fact that someone else has worked out all the thermal characteristics and coefficients.

[The MG Pony]

this is just a random project with absaluetly no bounds other then what parts I happen to have. it will be used with a TXV.

Brazed plate assumes I actualy have money, that should deal with that idea.

[nevgee]

we used to build a coil in open tank for water chilling . The tubing used was 3/4" od with a fine spiral finning to the outer surface. length of tube was 3M (10') coiled into a spiral with supporting copper tubing brazed to it to give support. We got between 6 and 8 kW at sst 5C sdt 38/40 C using R134A chilling water with 25% glycol to 6C.

If you use a valve type that allows you to change orifice sizes you'll be able to tweak the gas regulation to help maintain your superheat to a safe value.

[The MG Pony]

Ah K, like I said I'll be using either a 1/4Ton or a 1/2Ton TXV with it.

As for what it will be used for: The system its self is a small condensing unit that will be attached to the shell and tube exchanger with an MCP655 12 Pump, that will circulate water in a large 5 or so gallon reservoir, that in turn will be fed through a cooling system for a computer and air or what ever, the tank is being used like a thermal capacitor ie to smooth out the heat fluxes within the system.