Natural convective flow and heat transfer on unconfined isothermal zigzag-shaped ribbed vertical surfaces

Natural convective heat transfer is commonly used as heat transfer mechanism in applications with low heat flux due to its reliability and cost effectiveness. In this study, we introduce zigzag-shaped ribs to vertical, isothermal, heated surfaces with the purpose of increasing natural convective heat transfer. The ribs are characterised by a rib height h, rib length p and vertical pitch distance L. We perform numerical simulations using the Boussinesq approximation by prescribing a linear density-temperature relation and investigate how changes in rib length p/L, rib height h/L affect heat transfer at GrL = 10^5 and GrL = 10^6 at Pr = 0.71.
The results show how geometric variations affect heat transfer locally. Generally, local heat transfer increases along each outward-facing section and peaks at the tip of each rib. In the limiting case when surface approaches a forward facing step (e.g. p/L = 1), a significant decrease in heat transfer is observed on the horizontal section.
A peak in heat transfer is observed for geometries with high rib lengths p/L = 0.9, where the surface-averaged Nusselt number is increased by 4.43% compared to the flat surface. This increases to 11.60% when correcting for the increase in surface area.