A review of drag reduction and heat transfer enhancement by riblet surfaces in closed and open channel flow

Turbulence and heat transfer are two critical factors in the chain of world energy consumption. Hence, development of more efficient energy transfer techniques in engineering applications through control and optimization of the thermal turbulent boundary layer and turbulence continues to be a subject of intense interest. This is why reviewing a passive flow control technique with a focus on unique characteristics of heat transfer in devices called riblets is beneficial as technology pushes to revolutionize design and manufacturing of heat exchanger equipment. Riblet surfaces are considered beneficial to many commercial applications as they reduce forces between surface and fluid, and in some cases can enhance heat transfer in the turbulent flow regime. As there is no literature study that focuses on heat transfer and riblets, the current study reports experimental and numerical investigations reviewing both drag reduction and heat transfer using riblets in closed and open channels. Drag reduction studies are limited to water and oil flow studies, and heat transfer studies are expanded to air flow studies as there are none on water or oil flow. In addition, physical mechanisms of fluid drag and convective heat transfer are discussed. This paper outlines the challenges of fabricating riblets and provides a design summary for optimal drag reduction and heat transfer. This review also looks at applied numerical methods and their accuracy in evaluating drag reduction and heat transfer over riblet surfaces. The important findings and a possible future optimization approach on riblet surfaces are highlighted as well.