Laminar Natural Convection in a Square Enclosure with... 83 Laminar Natural Convection in a Square Enclosure with Discrete Heating of Vertical Walls

ABSTRACT. Natural convection heat transfer in a square air-filled enclo-sure with one discrete flush heater is examined numerically. The enclo-sure is vertical with isothermal heating strip on one wall, the remainder of the wall and the opposing one are isothermally maintained at a lower temperature. The top and bottom sides are adiabatic. The two dimen-sional differential conservation equations of mass, momentum and en-ergy are solved by a finite difference method for Rayleigh number var-ying from 102 to 106. The changes in temperature and flow fields (stream functions) with increase in Rayleigh number are investigated for different heater locations. The isothermal cold sections adjacent to the heater assist the development of secondary circulation cells, that de-pend upon both Rayleigh number and the position. With discrete heat-ing and cooling sections on one wall, the flow is characterized by boun-dary layers lining these sections with separate circulation cells. The variation of the local Nusselt number is influenced by this flow pattern and the average Nusselt number is higher than that of a discrete heating strip mounted on an adiabatic wall. The optimum location over the range of Rayleigh number is for the heater mounted at the center of the wall, s/L = 0.5 a result confirmed by previous experiments. 1