Strange Behaviour
This little puzzle began with watching the response of a shell and tube heat exchanger in an experimental rig. We let the rig run for a while. Then we increased the cooling by dropping the shell side feed temperature quickly... we were looking for dynamic responses...but instead of the tube side exit temperature dropping, it went up.

Explanation
The exit temperature had been falling, so the pipe beyond the heat exchanger had a temperature profile in it which was rising away from the exit. When we increased the cooling, the material inside the tube of the exhanger shrank very rapidly because of the very big temperature coefficient of expansion of this super-critical fluid. As a result, some fluid which had already passed through the exchanger was drawn back in so the exit temperature indicated an increase.

What next
The result was that we had to rethink the way we modelled the heat-exchanger. Thinking in terms of a passing stream of fluid within it was not enough. It became necessary to track the state of the fluid and at all times, recognise its volume and hence the position of each elemental region beyond the heat-exchanger exit. It became in effect a problem in space as well as time, a distributed parameter system. This work was published: with H.S.Wade.

Your Problem?
Maybe you have a problem that involves the behaviour of strange materials with unusual properties. I can probably find a way to quantify its behaviour and give you a basis for rational design. Call any time or email to discuss the ideas, in confidence, of course. There's no charge for finding out if I can help. As it subsequently happened, my brother, Dr A.D.McCann, did his doctoral work on Supercritical Boilers at the University of Cambridge, England.