EFFECT OF RADIATION TRANSFER ON THERMAL AND HYDRODYNAMIC CONDITIONS IN SHALLOW, SLOWLY MOVING, LIQUID LAYERS
Abstract
The purpose of this study is to obtain a better understanding of the influence of radiative transfer on thermal and hydrodynamic conditions in slowly moving irradiated liquid layers. To this end, experimental and theoretical studies were conducted. The theoretical studies involve development of a comprehensive model to predict hydrodynamic, thermal, and radiative conditions within the liquid. The model consists of two main components, one involving radiative transfer and the other thermal-hydraulic structure. The radiation model incorporates a discrete ordinate approach which rigorously treats spectral variations in properties, bottom and air-liquid interface reflection, absorption, anisotropic scattering, and directional variations in the incident irradiation. The laminar thermal-hydraulic model considers the effects of buoyancy, energy exchange at a free surface, and internal radiation absorption in a parabolic solution to the 3-dimensional momentum and energy equations. Parametric calculations are undertaken to determine the extent to which scattering, absorption, bottom reflection, and the magnitude of incident irradiation influence the thermal and hydrodynamic structure of the layer. Results show that the onset of thermal instability in shallow layers is hastened by increasing the bottom substrate absorptivity, the irradiation, and the ratio of scattering to absorption. Experimental simulations were conducted in the laboratory by using an overhead array of high intensity tungsten filament lamps to irradiate shallow liquid layers within an open channel. Vertical temperature profiles along the channel centerline were obtained by tranversing copperconstantan thermocouples through the liquid, and different test conditions were prescribed by altering the height of the fluid layer, the irradiation, the inlet velocity, the substrate reflectivity, and/or the optical properties of the liquid. The irradiation, mass flowrate, and liquid optical properties were measured from each experiment and used in the models to predict temperature profiles for comparison with the data. Agreement between the theory and data is extremely good for highly reflecting bottoms but less favorable for highly absorbing substrates.
Degree
Ph.D.
Subject Area
Mechanical engineering
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