Heat Transfer Characteristics in Narrow Vertical Rectangular Channels Heated from Both Sides

Abstract

The effects of gap size on heat transfer characteristics were investigated experimentally for a vertical rectangular flow channel with gaps of 2.5mm, 6mm and 18mm. As a result, the following was revealed. The flow shows a nature of forced convective heat transfer when Gr_x/Re^(21)/18_xPr^1/2 is less than 2.5×10^-4, and a free-convective heat transfer when Gr_x/Re^(21)/18_xPr^1/2 is higher than 1.8×10^-3, for all three gap sizes of the flow channel. As for the data for a gap of 2.5mm in the transition region between forced convection and free convection, it was confirmed that the heat transfer coefficient higher than that predicted by the heat transfer correlation for turbulent forced convection along a flat plate was due to the acceleration of the main flow through the development of the boundary layer, not to buoyancy force.