Natural convection in a vertical channel: I. Interacting convection and radiation. II. The vertical plate with and without shrouding

Numerical finite-difference solutions enabled the determination of heat transfer rates for pure natural convection and for Interacting natural convection and radiation in a vertical parallel plate channel of finite height. Attention was focused on the effect of the thermal boundary conditions and on the role of radiation as an enhancement mechanism. The results also enabled comparisons of the heat transfer from a single isothermal vertical plate with that for a plate that is shrouded by an adiabatic wall situated parallel to the plate. For pure convection and at intermediate and large Grashof numbers, the rate of heat transfer for a channel with two Isothermal equt-temperature walls exceeds by more than a factor of 2 that for a channel with one isothermal wall and one adiabatic wall (note that the ratio of active heat transfer areas for the two cases Is equal to 2). At lower Grashof numbers, the heat transfer rates differ only slightly. Radiation effects were explored for the case of a channel having one isothermal wall and one adiabatic wall. The radiative transport between the walls increases the convective heat transfer by 50-75% in the range of intermediate and large Grashof numbers. The direct radiation from the channel walls to the surroundings via the inlet and exit cross sections is about 10% of the radiation-enhanced convection. In the absence of radiation, shrouding of an isothermal vertical plate with an adiabatic wall is not an effective means of decreasing the heat transfer from the plate. However, when there is a significant radiation contribution, shrouding reduces the total rate of heat transfer.