htxcc1.m is a matlab program for simple counter current heat exchangers created by Dr. Sam Davis at Rice University.
>>[Qx,TAout,Area]=htxcc1(250,150,80,7200,7000,200,10,20)
Qx =
-720000
TAout =
182.8571
Area =
52.5076
As one can see, counter current flow is an efficient way to operate a heat exchanger because the temperature difference throughout the exchanger remains relatively constant.