What could be done to the initial experimental setup?
In actual use there are at least two common things that are done to improve heat transfer. One is to add fins to the pipes to increase the surface area. The other is to add a spiral device inside the tube to increase turbulence and therefore the heat transfer coefficient.
the surface area of the 2 pipes has to match that of the densities ie. water and irs, air side needs about 1000 times the surface area than water side look at automobile radiator second if it is made with cross flow, that is input 1 is at the same end as output 2 there is more exchange here are a few examples images.google.ca/images?hl=frsou... Anita
