The fully developed laminar mixed convection flow in a vertical tube of constant surface temperature is investigated assuming that (i) the effect of viscous dissipation is significant, (ii) the Boussinesq approximation holds, and (iii) the average flow velocity Um (as an experimentally accessible quantity) is prescribed. It is shown that under such conditions both upward (Um> 0) and downward (Um< 0) laminar flow solutions may exist. Whereas the downward flow solutions exist for any prescribed Um< 0, upward flows only exist below a maximum value Um,max of Um. Moreover, a nontrivial flow configuration is possible also for Um= 0. A remarkable feature of the problem is that for Um< Um,max, even two solution branches (dual solutions) exist, which merge when Um approaches its maximum value Um,max. The mechanical and thermal characteristics of the flow configurations associated with the dual solutions are discussed in the paper in detail.
Uni- and bidirectional mixed convection flow regimes described by dual solutions in a vertical duct
Lazzari, S.;
2007-01-01
Abstract
The fully developed laminar mixed convection flow in a vertical tube of constant surface temperature is investigated assuming that (i) the effect of viscous dissipation is significant, (ii) the Boussinesq approximation holds, and (iii) the average flow velocity Um (as an experimentally accessible quantity) is prescribed. It is shown that under such conditions both upward (Um> 0) and downward (Um< 0) laminar flow solutions may exist. Whereas the downward flow solutions exist for any prescribed Um< 0, upward flows only exist below a maximum value Um,max of Um. Moreover, a nontrivial flow configuration is possible also for Um= 0. A remarkable feature of the problem is that for Um< Um,max, even two solution branches (dual solutions) exist, which merge when Um approaches its maximum value Um,max. The mechanical and thermal characteristics of the flow configurations associated with the dual solutions are discussed in the paper in detail.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.