Their electrical scheme is sketched in Fig. 2b. Each circuit is composed of a 9 V DC generator and a 7.5 MX resistance, and it is connected to the DAQ system. Inside the tank, the circuits are made of copper wires insulated with high temperature silicone. The system senses a discontinuous resistance variation as the tip of the wire gets out of the water. 2.6. Heater The heating source used is a common 600 W electric cooker, whose temperature has been monitored and kept as steady as possible during the experiments