with constant holdup (ection 2.4.1) but we relax the assumption that energy is transferred instrantaneously from the heating element to the content of the tank.
Suppose that the metal heating element has a significant thermal capacitance and that the electrical heating rate Q directly affects the temperature of the element rather than the liquid contents.
For simplicity, we neglect the temperature gradients in the heating element that result from heat conduction and assume that the element has a uniform temperature