Abstract
A numerical study is described to predict, in the non-boiling regime, the heat transfer from a circular flat surface cooled by a full-cone spray of water at atmospheric pressure. Simulations based on coupled Computational Fluid Dynamics and Conjugate Heat Transfer are used to predict the detailed features of the fluid flow and heat transfer for three different spray conditions involving three mass fluxes between 3.5 and 9.43 kg/m2s corresponding to spray Reynolds numbers between 82 and 220, based on a 20 mm diameter target surface. A two-phase Lagrange-Eulerian modelling approach is adopted to resolve the spray-film flow dynamics. Simultaneous evaporation and condensation within the fluid film is modelled by solving the mass conservation equation at the film-continuum interface. Predicted heat transfer coefficients on the cooled surface are compared with published experimental data showing good agreement. The spray mass flux is confirmed to be the dominant factor for heat transfer in spray cooling, where single-phase convection within the thin fluid film on the flat surface is identified as the primary heat transfer mechanism. This enhancement of heat transfer, via single-phase convection, is identified to be the result of the discrete random nature of the droplets disrupting the surface thin film.
Highlights
Spray cooling has been the subject of research focused on several important potential application areas.[1,2,3,4,5,6,7] These applications mainly include cooling in grid power generation systems and power electronics, where in some cases traditional convective cooling methods have reached their physical limitations
The ultimate aim of the current study is an automotive application focusing on robust spray cooling for thermal management of highly boosted combustion engines used in hybrid electric vehicles
The main objective of the current study is to develop and verify Computational fluid dynamics (CFD)–conjugate heat transfer (CHT) simulations for non-boiling spray cooling on a flat circular surface as a precursor to application of spray evaporative cooling simulations to the curved geometries under engine-like operating conditions
Summary
Spray cooling has been the subject of research focused on several important potential application areas.[1,2,3,4,5,6,7] These applications mainly include cooling in grid power generation systems and power electronics, where in some cases traditional convective cooling methods have reached their physical limitations. The ultimate aim of the current study is an automotive application focusing on robust spray cooling for thermal management of highly boosted combustion engines used in hybrid electric vehicles. As a method of thermal management, spray cooling has not yet been industrially applied to any significant degree. The most likely cause for this is a lack of theoretical understanding of the underlying heat transfer mechanisms. These mechanisms inherently occur at small scale involving complex interactions of several phenomena such as droplet break-up, impingement, thin fluid film formation, convection, conduction, nucleation, and phase change. The performance of spray cooling is known to depend on many factors including nozzle type, spray volumetric flux, droplet size, spray angle, orifice-to-surface distance, and the degree of fluid ‘sub-cooling’.8–14
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