Sufficient conditions for existence of free convection flow in vertical  narrow channels


It is proved that the existence of free convection flow (FCF) in a vertical slit with asymmetric heating is sufficient to satisfy the condition:0 < n< nex, where nex — the polytropic index in the FCF, nex - polytropic index corresponding to the equilibrium state of the gas column. In particular, if the equilibrium state corresponds to the condition of no supply of heat, then: 0 < n< k, k— ratio of specific heats. For the existence of the gap in the maximum mass flow rate it is necessary that: n=gL/RT0, where L— the height of the slit, T0 - temperature at ground level. Polytropic index n is related to the intensity of heat transfer from hot wall to the flow: with increasing intensity of heat transfer n →+0.