On the thermal hydraulics of Magnox reactor pressure vessel insulation: Part 2. Numerical simulations of laminar forced and mixed convection in an insulation passage

The paper presents a computational study of laminar flow and heat transfer in a layer of the multiple plate insulation used to line the interior surface of ‘Magnox’ reactor pressure vessels. The flow passage consists of a 2 mm deep channel, which is plane on its upper surface and has raised ‘dimples’ on its lower surface. Under forced convection conditions strong flow ‘streaming’ is found in the unobstructed regions of a channel, and Nusselt numbers there rapidly attain full development. Between adjacent dimples heat transfer levels are characterized by single- and double-peaking distributions which are shown to be due to convective influences. The effect of buoyancy is examined in mixed convection flows with the passage oriented at various angles between horizontal and vertical. Complex non-monotonic trends of heat transfer enhancement and impairment are found, and these are also shown to be attributable to changing patterns of convection.