NUMERICAL-ANALYSIS OF FREE CONVECTIVE HEAT-TRANSFER IN VERTICAL DUCT WITH LAMINAR UPFLOW

To elucidate the heat transfer phenomena for a package in a refrigerat ing room with upflow, we considered a vertical-duct model in which one wall was isothermally heated and gas flowed upward through the duct i n the laminar-flow range. The velocity profiles, temperature distribut ions and the local and average heat transfer coefficient were calculat ed numerically by fundamental equations.The main fluid flow is drawn t oward the heated wall in the range of low Re and becomes parallel to t he axial coordinate with increasing Re. The higher on the heated wall, the smaller is the local Nusselt number. However, the average Nusselt number does not undergo much change with increasing Re and Gr.A corre lated equation for heat transfer was obtained under the operating cond itions of this calculation. To check these calculated results, the tem perature distributions and heat transfer coefficient were measured exp erimentally under the same operating conditions as those of the theore tical analysis. The calculated temperature distributions agreed closel y with the measured ones. To compare the heat transfer coefficient of the downflow and the upflow, we found that the latter is about twice t hat of the former.