EXPERIMENTAL STUDY OF NATURAL-CONVECTION PLUMES FROM A HEATED HORIZONTAL SQUARE PLATE AND A VERTICAL CYLINDER Irma Welling LOW REYNOLDS NUMBER FORCED CONVECTION IN MICRO WIRE SCREENS AT ATMOSPHERIC PRESSURE AND LOW PRESSURES

This article describes an experimental study of natural convection around a horizontal square plate and a vertical cylinder, and provides data for the velocity and temperature profiles around representative heat sources of high heating capacity. From the measured velocity and temperature distributions, enthalpy fluxes, average convective heat transfer coefficients, and volume flow rates were derived for the plate and cylinder heat sources. New relationships between volume flow rate and distance above the plate and cylinder are presented, Very low Reynolds number forced-convection heat transfer of air flow through microscale wire screens with equivalent channel diameters of 34.34 and 93.75 (mu)m (surface area density 67,400 and 32,300 m^2/m^3) was measured using resistance thermometry, in which the surface temperature was detected through the measurement of electric resistance of the screens. The dependency of the Nusselt number on the Reynolds number, screen porosity, and Knudsen number was investigated at Reynolds numbers ranging from 0.03 to 5.7. The results show that the screen porosity has great influence on the heat convection and the Nusselt number is higher in the case of higher porosity. When the Reynolds number increases from 0.03 to 3, the Nusselt number increases by two orders of magnitude, and the growth rate gradually slows down. In the very low Reynolds number region, the j factor has a maximum value. In the test region, the influence of the Knudsen number on heat convection is small.