20th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics・LISBON | PORTUGAL ・JULY 11 – 14, 2022 Calculation of the Nusselt Number from Temperature and Velocity Data Obtained from Enhanced 3D Two-Colour LIF and 3D PTV in a Rayleigh-Benard Convection Cell Sina Kashanj, Yeganeh Saffar, Reza Sabbagh, and David S Nobes* Dept. of Mechanical Engineering, University of Alberta, Canada * Correspondent author: dnobes@ualberta.ca Keywords: 3D Two-colour LIF, 3D Scanning PTV, Nusselt number, Rayleigh-Benard convection ABSTRACT Experimental study of Rayleigh-Benard convection (RBC) requires 3D measurement of the velocity and temperature due to the complexity of the physics of this system. Using a scanning system, the application of the 3D particle image velocimetry (PTV) and 3D time-resolved two-colour laser-induced fluorescence (LIF) is investigated on a slender RBC cell. Calculation of the out-of-plane velocity component by using the planar velocity components and applying the continuity law is discussed. From these observations that calculation of the dimensionless heat transfer coefficient, the Nusselt number from the 3D reconstructed temperature field close to the boundary of the fluid domain is investigated. 1. Introduction Rayleigh-Benard convection (RBC), a buoyancy-driven flow in an enclosure heated from below and cooled from above, is an idealized flow system to study the flow and heat transfer of a wide spectrum of phenomena and applications from engineering to geophysical subject matter (Adrian, 2013). To characterize and quantify the heat transport of this thermo-fluid system at the asymptotic state, two different theories have been proposed and investigated since 1954 (Lohse & Xia, 2010). The classical theory claims that the dime.nsionless heat transfer coefficient, the Nusselt number, , of this system is related only to the Rayleigh number as ~ 13 ⁄ (Doering, 2019). However, the ultimate theory declares that heat transport of this system is also a function of the Prandtl number as ~ 1/2  12 ⁄ (Doering, 2019). Other than the investigation of these two theories, understanding the velocity and temperature fields of RBC has led to new insights to this system. From numerical simulations, based on the 2D and 3D time-resolved data of RBC it has been found that the temporal evolution of the vortical flow structures is correlated to the evolution of heat and momentum transport (Zwirner, Tilgner, & Shishkina, 2020), (Kashanj & Nobes, 2021b). In another work, the knowledge of the temperature distribution of RBC has led to design of a new DNA