Convective instability of air flows in the exhaust shaft above a four-row finned beam

Abstract

Herein, multidirectional quasiperiodic air flows in an exhaust shaft above a four-order horizontal bundle consisting of bimetallic finned tubes used to remove heat in heat exchangers are considered. Modeling of the air movement is carried out on the basis of equations for thermogravitational convection in the Boussinesq approximation. It takes into account the viscosity of the air and the dependence of the air density on the temperature. An interpretation of quasiperiodic airstreams is proposed on the basis of Rayleigh – Bénard convection, as a result of which regular structures, called Rayleigh – Bénard cells, are formed in a liquid or gas. Rayleigh – Bénard cells are an analytical solution to the problem of the stability of hydrodynamics flows in the linear approximation. The appearance of two-dimensional (convective rolls) and threedimensional (rectangular cells) is possible. To estimate the number of emerging structures, the critical Rayleigh numbers were calculated, which characterizes the transition from an unstable mode of the convective fluid flow to a stable mode. For two experiments, the experimental Rayleigh numbers are compared with their critical values. The differences between the experimental conditions and the ideal boundary conditions used in the calculations and the partial destruction of quasiperiodic structures as a result of this are also discussed.