Natural convection heat transfer on an inclined unglazed solar absorber-plate: Experimental investigation

Natural convection along an inclined plate under the influence of constant solar radiation was investigated experimentally. The present work aims to assess the natural convection flow and temperature distribution on a bare, non-porous, inclined absorber-plate. An understanding of the details of the temperature distribution and the natural convective flow on a tilted absorber-plate was achieved as a function of thermal boundary layers, plate distance, solar intensity, and tilt angle. In general, the convection heat transfer coefficient of the entire plate as well as the thermal efficiency increased when the inclination angle increased from 30° to 75° due to the decrease in the thermal layers thickness and the change in buoyancy force. The results showed that the highest value of thermal efficiency varies from a value of 28.93 for a tilt angle of 30° to a value of 44.74 for an inclination angle of 75°. The relationships governing the thermo-hydrodynamic behavior of natural convection flow, solar radiation, and buoyancy over an inclined solar absorber-plate within the solar irradiance range from 200 W/m2 to 700 W/m2 and Rayleigh number from 2 × 107 to 108 were determined.