From the top of my head, COMSOL provides modules enabling you to simulate all sorts of capillary flow/heat conduction and/or environmental influences in a greenhouse environment.

Might not be the best commercial solution for your specific problem, but since I am not an expert in this field my knowledge about viable alternatives is quite limited. maybe someone else can help you further.

I have modeled a tube-shell heat exchanger. I wrote code on my own

Comsol looks best to serve your purpose, unless you want to write your own code.

Hamid,

It depends on how accurate you want the answers to be, and how much effort you are willing to put in.

You may find that there there are empirically-derived equations for the heat transfer rate of arbitrary capillary heat-exchangers - a good thermodynamics engineering textbook would be my starting point.

Or, if you really want arbitrary geometries, you may find that an FEA package would be better. There are a number of free (few nodes, limited size) FEA packages available:

I've used:

VisualFEA

LISA

And can recommend both.

A list of free-ish packages is available here;

http://www.freebyte.com/cad/fea.htm

I *have* written FEA thermal models in the past - it doesn't really matter what language you use. As long as loops, branches, arrays and floating point numbers are supported :) then you'll be fine.