EFFECT OF SURFACE GEOMETRY AND ORIENTATION ON LAMINAR NATURAL-CONVECTION HEAT-TRANSFER FROM A VERTICAL FLAT-PLATE WITH TRANSVERSE ROUGHNESS ELEMENTS

An interferometric technique was used to determine local heat transfer coefficients for surfaces with repeated ribs and steps. The effects of parameters such as protuberance height-to-spacing ratio, conductivity of ribs, and angle of inclination were studied. It was found that heat transfer enhancement, relative to a plain vertical surface of equal projected area, was possible in laminar natural convection using transverse roughness elements of proper size and shape. In general, the stepped surfaces helped improve the heat transfer. The maximum increase in average heat transfer coefficient was 23.2% with a step pitchto-height ratio of 16. The study indicated the presence of an optimum step pitch-to-height ratio. All of the ribbed surfaces resulted in degraded heat transfer performance. © 1990.