An investigation into the use of a wind shield to reduce the convective heat flux to a nocturnal radiative cooling surface

The effect of a wind shield on the convective heat flux from an ambient air stream blowing over a horizontal surface intended for nocturnal radiative cooling has been studied by computational fluid dynamical calculations and by wind tunnel experiments under conditions appropriate for the climate of Thailand. The test unit was a rectangular plate 312mm×250mm, with vertical metal strips for the wind shield having heights up to 100mm along the edges of the plate. It was found that a wind shield of height 25mm slightly increased the convective heat transfer due to increased turbulence over the surface, but wind shields of height 50mm and 100mm reduced the convection due to a separation of the main airflow from the surface. Radiative cooling was reduced by the wind shields. The net cooling of the surface was best with no wind shield at wind velocities less than about 1ms–1, and with the wind shield of height 100mm at wind velocities greater than about 2ms–1.