Temperature characteristics along the centreline in quasi-two-dimensional Rayleigh-Bénard convection filled with liquid metal

In the present study, we observe interesting profiles and fluctuations in a quasi-two-dimensional thermal convection system filled with low-Prandtl-number liquid metal. A high-precision thermistor, which can be precisely controlled to move up and down, is used to measure the temperature distribution along the centreline of a convection cell. As the thermistor probes move away from the heated wall surface, the measured temperatures initially decrease to values below the central temperature of the cell, then recover to the central temperature, indicating an inverse temperature gradient. Furthermore, by analysing the root-mean-square temperature along the centreline, we find a second peak away from the wall location, which has never been reported before, in addition to the first peak associated with the thermal boundary thickness. This phenomenon is also confirmed by the results of third- and fourth-order moments of temperature. Experimental results, together with insights from previous studies, suggest that in liquid metal, the distinct flow organisation arising from the large thermal diffusivity plays an important role in shaping the observed temperature distribution.