Application of 4D two-colour LIF to explore the temperature field of laterally confined turbulent Rayleigh–Bénard convection

Abstract

Recent studies show the significant effect of the third dimension and flow unsteadiness of laterally confined Rayleigh-Bénard convection (RBC). However, there are limited studies investigating 4D flow properties. The application of 4D two-colour laser-induced fluorescence to explore a laterally confined RBC at high Rayleigh number of 𝑅𝑎 = 9.9 × 10 7 and Prandtl number of 𝑃𝑟 = 6.1 is investigated using a scanning laser system. A two-colour, two dyes approach was employed to resolve the laser sheet intensity variations due to refractive index variations caused mainly by the generation of thermal plumes. Two temperature-sensitive fluorescent dyes with opposite sensitivities were used to enhance the overall temperature sensitivity to 7.3 % /℃. Details of the experimental procedure and optical system employed to reach such a high sensitivity is demonstrated. From the whole field temperature distribution, the dimensionless heat transfer coefficient, the Nusselt number, and its evolution was calculated for both hot and cold boundaries.Temperature field and Nusselt number obtained from 3D and 2D fields are reported to compare the results for these two scenarios. Thermal plumes were found to have a conical shape in the laterally confined RBC compared to the conventional mushroom shape. From visualization of the time-resolved 3D temperature field and 2D distribution of the Nusselt number, it was also found that only by volumetric measurement, temporal and spatial variations of the temperature and heat transfer can be evaluated. This shows that to evaluate the classic and ultimate theories, volumetric measurement is required for a coherent understanding of the physics.

Development of a Temperature Distribution Measurement System for Transmission Oil for Transportation Equipment

“…LIF (laser-induced fluorescence) [ 3 , 4 , 5 , 6 , 7 ] is a measurement method that uses laser light to generate the fluorescence of specific molecules and measure scalar quantities such as the concentration, temperature distribution, and physical quantity of specific substances from the intensity of emission at a specific wavelength. The PIV (particle image velocimetry) method is frequently used in conjunction with the LIF method.…”

“…As optical sensors for flow diagnostics with temperature distribution, there are precedents for two-dimensional and three-dimensional temperature distribution measurements using the temperature-sensitive liquid crystal method [ 2 ] and the two-color LIF (laser-induced fluorescence) method [ 3 , 4 , 5 , 6 , 7 ]. The two-color LIF method was applied to clarify the mechanism of the Rayleigh–Bénard convection phenomenon [ 8 , 9 , 10 , 11 , 12 ].…”

Improvement of Temperature Measurement Accuracy of Hot Airflow Using Ultrafine Thermo-Sensitive Fluorescent Wires of Lumisis Phosphor

“…In contrast, various flow visualization methods have been developed for the fluid temperature distribution measurement of liquids. To measure hot water in a water tank, a temperature field measurement method that applies the two-color laser-induced fluorescence (LIF) method [ 3 , 4 , 5 , 6 , 7 ] is known. The authors proposed a method for the simultaneous measurement of temperature and velocity fields using a color camera in combination with two-color LIF and particle image velocimetry by optimizing the type and concentration ratio of fluorescent dyes.…”

Volumetric Lagrangian temperature and velocity measurements with thermochromic liquid crystals

“…They were able to measure the temperature within a hot jet but were limited to low seeding concentrations. Kashjan and Nobes [28] applied a scanning approach to 2D twocolor laser-induced fluorescence. By scanning several parallel planes in rapid succession, they could reconstruct the temperature distribution within a slender RBC cell.…”