Effect of evaporation on a drying thermometer

We studied the temporal evolution of the temperature in the sensor of a digital thermometer of the skewer type in which tap water or 70° alcohol (ethanol) evaporates. We present a theoretical model based on the principle of conservation of energy, in which the difference in temperature of the sensor in relation to the environment has two exponential components, one being proportional to the heat lost due to the evaporation of the liquid that wets the thermometer rod and the other exponential proportional to the heat received from the ambient air, when the sensor rod is colder than the ambient. We quantitatively analyze the phenomenon by fitting the theoretical equation to the experimental data. To confirm the exponential behavior related to evaporation, we measured the mass change during evaporation. The proposed model works very well for ethanol evaporation. The minimum experimental material needed for the proposed quantitative study is a digital thermometer on a skewer, a bottle with alcohol and a stopwatch and/or a digital camera that can be taken from a smartphone. A qualitative demonstration can be made by comparing the minimum temperature reached for the two liquids used.

Keywords:
Evaporation; Temperature; Exponential Function