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The conventional refractive index-based optical techniques show limitations in measuring the thermal field inside refractive surfaces due to the curvature effects. The present work reports on the application of lensless Fourier transform digital holographic interferometry for mapping heat transfer phenomena inside highly refracting axisymmetric enclosures. Experiments have been performed to characterize the buoyancy-driven natural convection heat transfer around a vertically oriented heated cylinder placed concentrically inside a relatively large cylindrical enclosure filled with de-ionized water. The experiments were performed under various heating conditions, and the corresponding holograms were analyzed in real-time to show the transients of the temperature field. Quantitative results were obtained in the form of a two-dimensional temperature distribution field and local heat transfer coefficients along the heated surface. Experimental results were validated by comparing the values of the surface temperatures obtained from the analysis with that obtained from the thermocouple data. The work presented highlights the ability of the lensless Fourier transform digital holographic technique to map the real-time temperature field inside a highly refracting enclosure. [ABSTRACT FROM AUTHOR]

In view of this, an ensemble average of the single-phase (bulk liquid under subcooled conditions) velocity field has been estimated and the corresponding convective time scales at different stages of the bubble growth process have been quantified by measuring the absolute fluid velocity at a height that corresponds to the diameter of the vapour bubble (apex of the vapour bubble). Thus, the initial growth of the vapour bubble, for I t i Graph $\lesssim$ 0.3 ms, is predominantly governed by the pressure difference (inertia-driven) and evaporation of the superheated liquid layer enveloping the nucleating vapour bubble (diffusion-controlled growth). During this time period, the liquid layer entrapped pushes the vapour bubble upwards and enables the vapour bubble to hover over the heated substrate, as observed after the detachment of the vapour bubble in figure 11( I b i ). Keywords: boiling; bubble dynamics EN boiling bubble dynamics 1 36 36 12/29/21 20220125 NES 220125 1. [Extracted from the article]