Guid for choosing the right air-cooled heat exchanger

[MatiZaidman]

Hi Guys,
Could somebody direct me to a clear simple and short E-Guide that will show me how to choose the right size of fan, radiator and flaw rates, given the working temperatures of the refrigerant? A software maybe?
Thanks.

[Xooyoo]

I don't know what you like to do but it sounds to me a little strange. ;-)

That's the area of the manufactures of air cooled heat exchangers. So if you have to choose an air cooled heat exchanger simply buy an fan coil of one of the well know manufacturers.
They also have programs where you can insert your needed temperatures, refrigerants and so on, and you'll get presented the best fitting fan coil.

And btw it is not simple to choose the right fan for an coil, you also have to obtain sound levels, tube geometry probably de-frost, the right capacity...

[MatiZaidman]

Thanks Xooyoo,
What I actually need is the mathematical relations between the relevant parameters, so I can plug them into a refrigeration simulator program. The parameters that I think are relevant are the refrigerant temperatures and enthalpies, radiator UA (or efficiency?) air temperature and flow rate and fan size (both in terms of power needed and geometric size).
Any suggestions?

[Xooyoo]

The mathematical relations between the temperatures are extremly difficult.

For example the pressure loss during evaporation is splitted into pressure drop due:

• friction
• accelearation
• height difference

You need them to calculated the evaporation end temperature.

Then you need the overheating temperature and, and the data around the injection into the evaporator.

Of course you could neglect pressure drop during evaporation, but if you have multiple injection you have to know the pressure drop in the capillary tubes, to ensure a uniform refigerant distribution.

The question is of course how accurate your calculation should be.

I don't know which software you actually have to put your data into, so maybe we're talking a litte bit about different things.

Probably you could do something like this:

Q_air=dot m air * cp * (T_in-Tout)
Qair*eta=Qref
Qref=dot m ref * (h_out-h_in)

h_out, h_in you chosse out of an log p,h diagramm
dot m_ref depends on the compressor
dot m air depends on your fan
cp of air is well kown
T_in you should now
Tout you have to calculate
Q are the capacitys - you should know
eta nobody will tell you. so you have to do an assumption.

This calculation will definitly go wrong but you'll get a basic feeling.

And if you try to do it "right" you'll notice there are only empirical equations for evaporation - and yeah they bring a lot of fun... [/sarcasm off]

[MatiZaidman]

Thanks,
Any guidelines for choosing the efficeincy (eta) for common configurations of air-cooled radiators?