Thermal instability and heat transfer by natural convection in an inclined rectangular water layer at low Rayleigh number have been studied using an interferometer. At different angles of inclination to the horizontal (θ) different preferred flow modes are observed. For 0° < θ < 57.5°, the preferred mode is longitudinal rolls superimposed on the base flow. For 57.5° </ θ ≤ 90° a single two-dimensional roll is observed. Measured local and average Nusselt numbers are compared to numerical solutions carried out assuming a two-dimensional transverse roll.
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Acknowledgements-.-This study was supported by a grant from the Heat Transfer Program of the National Science Foundation, Division of Mechanical Engineering and Applied Mechanics. H. D. Chiangcontributed significantly to the final preparation of the manuscript.
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