In-situ measurements of temperature field and Marangoni convection at hydrogen bubbles using schlieren and PTV techniques

This work adapts the schlieren technique for in-situ measurement of temperature fields around gas bubbles growing during water electrolysis. First, the optical setup and the algorithm of data processing are explained. The method is then validated by comparing measurements near a laser-heated spherical thermocouple with numerical simulations. Further validation is obtained by comparing with temperature data measured earlier by a different method near a hydrogen bubble generated at a platinum microelectrode. The schlieren technique is shown to deliver accurate temperature distributions with an uncertainty of less than 15%. The method was then used to investigate the temperature distribution near hydrogen bubbles during growth at different cathodic potentials. Additionally, particle tracking velocimetry was used to visualize the Marangoni flow pattern generated by strong Joule heating near the bubble foot. Combining the information from schlieren and PTV imaging allows to provide a more complete understanding of the fluid dynamics and heat transfer around gas bubbles growing during electrolysis.