Thermal convection at high aspect ratio: The local distribution and the dynamics of dissipative processes
Final Report Abstract
Phenomenological concept, which are based on a one-dimensional model without a lateral confinement are frequently used to describe the convective heat transport from a solid wall to a surrounding fluid. Dissipation, the transformation of kinetic energy into heat, plays a crucial role in some of these models. However, this quantity is very hardly to measure, and thus, a direct verification of such models is still missing. We report measurements of the heat transport and the thermal dissipation rate done in a large-scale convection experiment, which is called called the Barrel-of-Ilmenau. To this aim, we used specific heat flux plates as well as a homemade Multithermistorprobe. The probe is made of four very tiny thermistors, and it allows to measure the local temperature gradient and the thermal dissipation rate, respectively. The measurements undertaken in the framework of the research project show that the wall heat flux and the thermal dissipation rate strongly fluctuate in turbulent convection flow, and that relatively large excursions appear. Consequently, Gaussian statistics cannot properly describe the frequency distribution of the fluctuations of both quantities. For the local wall heat flux, this is the heat flux measured right at the surface of the wall, the measurement results rather imply the application of the Generalized Extreme Value Theory. In contrast, the fluctuations of the thermal dissipation rate are reflected, at least beyond a certain distance from the wall, by a log-normal distribution. We could also demonstrate in this project that the fluctuations of the wall heat flux normalized by its mean decrease with increasing Rayleigh number.
Publications
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Local and Time-Resolved Wall Heat Flux in Turbulent Rayleigh-Bénard Convection. ERCOFTAC Classic Collection Database, Case 094, 2021.
R. du Puits & A. Hertlein
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Measurements of thermal dissipation rate in turbulent Rayleigh-Bénard convection. 14th European Fluid Mechanics Conference, Athens, Greece, 13. – 16. September 2022.
R. du Puits, A. Hertlein & C. Kaestner
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Time-resolved measurements of the local wall heat flux in turbulent Rayleigh–Bénard convection. International Journal of Heat and Mass Transfer, 188, 122649.
du Puits Ronald
