Abstract
In this work, fluid flow and heat transfer performance of a radiative coil coating oven is numerically investigated. In the coil coating oven concept under consideration, porous radiant burners provide the required energy to evaporate the volatile species (solvents) from the applied coating and to promote curing reactions. To avoid the mixing between burners flue gas (with a non-negligible oxygen content) and evaporated (combustible) solvents in the oven (which could lead to a catastrophic oven failure), a semi-transparent window in between both atmospheres is applied. To ensure the window thermal stability during the oven operation, window cooling by wall jets is considered. Different turbulence models were compared against available wall jet heat transfer correlations to select the most suitable for three-dimensional (3D) numerical simulations. Convective heat transfer correlations purposefully developed were embedded in a one-dimensional (1D) window energy model for fast performance characterization, analysing the most influencing parameters—window radiative properties, thickness, inlet temperature and velocity of wall jets, and cooling strategy. The 1D window thermal performance is compared with literature and 3D results considering the full coil coating oven, providing satisfactory confidence on the developed strategy. The 1D model is used for an optimisation study to find the minimum energy consumption while ensuring the safety requirements (maximum window temperature and thermal gradient) are met.
Highlights
Received: 4 January 2022The drying/curing process of pre-paint organic coatings applied onto the surfaces of a continuously moving metal sheet is an essential process in the coil coating industry, which aims to provide anti-corrosion protection to bare metal substrates—most commonly, aluminum and steel, enhance its appearance, and improve optical properties for energy saving concerns on final costumer applications [1–3]
The wall jet development consists in three regions, the potential core zone at the jet exit, followed by the intermediate region, and the fully developed region where the mean velocity and turbulent intensity show self-similar characteristics
From the wall to the free stream the turbulent wall jet flow is usually categorized into three different zones
Summary
The drying/curing process of pre-paint organic coatings applied onto the surfaces of a continuously moving metal sheet is an essential process in the coil coating industry, which aims to provide anti-corrosion protection to bare metal substrates—most commonly, aluminum and steel–, enhance its appearance (aesthetics), and improve optical properties for energy saving concerns on final costumer applications [1–3]. (This innovative oven concept allows simultaneously to treat volatile organic compounds and utilize its energetic content for IR radiant energy generation.) In order to separate the atmosphere comprising the evaporated solvents from the burners exhaust gas environment, a thin semi-transparent glass window partition slab is applied. Reported the results of an experimental study to determine the heat transfer coefficient and to select RANS turbulence model for three-dimensional (3D) plane jets. They showed that the width of the slot influences the Nusselt number only in the developing region. The innovative drying and curing (coil coating) oven is presented as well as the different wall jet cooling schemes studied. The mathematical and numerical models exhibit, the principles and equations according to which the full oven and window were modeled, and the last two sections are devoted to the presentation of the main results and ensuing discussion, and conclusions
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