Publications Repository - Gdańsk University of Technology

The study describes natural convection through a vertical channel, open on four sides and bound by two isothermal walls. Both balancing and infrared experimental investigations were performed in air (Pr = 0.71) to estimate the impact of channel width s and wall-to-ambient temperature difference (tw - t∞) on natural convective heat transfer, the formation of air flow patterns and the rate of flow pattern formation. The study was conducted on two parallel vertical plates of height H = 0.5 m and width B = 0.25 m, with the heated surfaces facing each other, thus creating peripherally open channels of different widths s = 0.045, 0.08, 0.180 and ∞ m. The surface temperature tw, identical for both heating plates, was changed every 10 K and set at tw = 40, 50, 60, 70 and 80 °C, while the ambient temperature was maintained within the 18–25 °C range. In the balance method, heat fluxes were determined based on measurements of voltage and electric current supplying the heaters placed inside the walls. In the gradient method, the heat fluxes were calculated from the temperature distribution in air, within a plane perpendicular to the heating plate surfaces. Temperature fields were visualized using a plastic detecting mesh and a thermal imaging camera. The distribution of temperature tx,y, and its gradient at the walls dt/dx|x=0,y were obtained at different heights y along the channels. The gradient values obtained and the results, presented as dependencies of the Nusselt number on the Rayleigh number, indicate that the channel width has a significant impact on heat transfer. Compared to the vertical plate s = ∞, the following levels of convective heat transfer enhancement were observed: 29.5% (s = 0.045 m), 38.8% (s = 0.085 m) and 61.6% (s = 0.180 m).

Authors

• prof. dr hab. inż. Witold Lewandowski link open in new tab ,
• dr hab. inż. Michał Ryms link open in new tab ,
• Hubert Denda link open in new tab