Quote Originally Posted by desA View Post
For these tests, they are quasi-static, in the sense that a small amount of water is passed through the system, in order to slow down the heatup rate - in order to allow data capture (manual), without temps moving off too far.

So, in this sense, the tank is not a static mass of water - it is being adjusted as the incoming water feeds in from the bottom. So, at worst, you could estimate the 'average' water temp in the tank to be (Tw,in + T,top)/2.

So, given that scenario, at the hottest reading Tw,av ~ (28+60)/2 = 44'C... So, yes this is remotely possible.
Replacing warm water at the top with cold water at the bottom increases the dT between top and bottom, lowering the average temp. Average temp of 44C is not a remote possibility. It is a strong probability.