We agreed that there were problems ages ago but that there were to small to be worried about.
To measure second law effects you have to take into acoount all 4 temps which is a bugger for testing especially as they are only useful in scaling calcs not overall performance.
TEMA is invlaid use xflow results. There are actually many types of crossflow as well, in our case counterflow might be valid as well.
Actual conditons can play a bit part. Attaching a rad to a warm case full of warm air is obviously going to cause an effect for examplem thats there is obviously no point focusing on.
Another way of including UA is given below. Eq 2 and 3 show relations for eq 1. NTU is a commonly used perfromance indicator for rads. Cmin is whatever masslfow * cp is lower. This is why on other areas i say that either fan or water flow rate is important not both. The effect is easily seen in bills graphs where performance bottoms out at a set point.
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