Effect on natural convection of the distance between an inclined discretely heated plate and a parallel shroud below

An experimental study on air natural convection on an inclined discretely heated plate with a parallel shroud below it-as carried out. Three heated strips were located in different positions 017 the upper wall. The distance between the walls, b, was changed in the range 7.0-40.0 mm and two values of the heat flux dissipated by the heater's were taken into account. Several inclination angles between the vertical and the horizontal were tested. The wall temperature distribution as a function of the channel spacing and the inclination angle, the source heat flux, the number and the arrangement of the heat sources are presented. The analysis shows that, for angles not greater than 85 deg, increasing the distance between walls does not reduce the wall temperatures, whereas at greater tilting angles (>85 deg) there is an opposite tendency. This is confirmed by flow visualization at angles equal to 85 deg and 90 deg and b = 20.0 and 32.3 mm. Dimensionless maximum wall temperatures are correlated to the process parameters in the ranges 1.2.10(4) less than or equal to Ra(l)cos theta less than or equal to 8.6-10(5); 0 deg less than or equal to theta less than or equal to 88 deg; 0.48 less than or equal to l/b less than or equal to 1.6 and 10 less than or equal to L/b less than or equal to 32.6 with 1.0 less than or equal to d/l less than or equal to 3.0; the agreement with experimental data is good. The spacing which yields the hest thermal performance of the channel is given. Local Nusselt numbers are evaluated and correlated to the local Rayleigh numbers and the tilting angles if? the ranges 20 less than or equal to Ra-x' less than or equal to 8.0.10(5) and 0 deg less than or equal to theta less than or equal to 88 deg. The exponent of monomial correlations between local Nusselt and Rayleigh numbers are in the 0.23-0.26 range. Comparisons with data from the literature, in terms of Nusselt number; exhibited minor discrepancies.