The reduction of pressure losses in thermally modulated vertical channels

Abstract

The role played by patterned heating in reducing pressure losses within vertical conduits is investigated. The heating generates flow separation structures which reduce the direct contact between the stream and the sidewalls, thereby limiting the frictional resistance. This also modifies the temperature field thereby inducing a net buoyancy force which may either assist or oppose the pressure gradient required to maintain a fixed flow rate. If the flow Reynolds number is increased sufficiently, the separation structures may be washed away, which means that the pressure-gradient-reducing mechanism is eliminated. The details of the system response are a function of the form of spatial heating distribution, its intensity, the flow Reynolds number and the fluid Prandtl number. Carefully chosen heating of the two walls can induce a pattern interaction effect and a judicious choice of the two patterns can have as much as an order of magnitude effect on the system response.