A Shell and tube heat exchanger consists of a tube(carrying a fluid to be heated or cooled) surrounded by another fluid at a different temperature.Consider a chemically reacting flow in such a tube with a velocity of 0.1 m/s. The chemical reaction is exothermic and causes the flow to heat up at some axial position x1 at 15 C/min. Simutaneously, the coolant carries the heat away from the flow such that the temperature inside the tube decreases in the axial direction at 4 C/m. What is the Eulerian derivative DT/Dt at x1?