RAYLEIGH-BÉNARD-MARANGONI INSTABILITIES DURING EVAPORATION OF AQUEOUS ALCOHOL SOLUTIONS, DETECTED BY PYROELECTRIC SENSORS

A simple pyroelectric sensor is presented for on-line monitoring of Rayleigh-Benard -Marangoni convective instabilities in methanol, ethanol and isopropanol aqueous solutions, caused by alcohol evaporation from the free surface of the liquid. The signals measured at the liquid-substrate interface represent thermal fluctuations of the order of 10−2 K, having a frequency spectrum between 0.08 Hz and 0.4 Hz. The numerical estimation of the Rayleigh and Marangoni numbers leads to the conclusion that the latter is dominant in the conditions of the experiment. The amplitude and duration of the thermal noise are investigated as a function of alcohol concentration. An attempt is made to determine characteristic invariant quantities.