Flow and heat transfer characteristics of a rectangular-cross- section duct constructed with perforated or slitted staggered ribs mounted on two opposite walls

1.1 The Problem and Its ImportanceNumerous problems are encountered dealing with flow channels whereheat transfer to or from fluid is an important element in theirperformance. One of the problems encountered here is the influence ofsurface roughness on the flow and heat transfer characteristics of suchchannels. The surface roughness here may be either natural or artificial.Artificial roughness may take various forms . Sand grains of differentsizes have been used as an early technique of artificial roughness onsurfaces where heat transfer augmentation is required. Later, other moreeffective artificial roughness techniques have been introduced. To namesome such techniques we have: dimpled surface, ribbed surface,corrugated surface, etc. Mounting ribs on channel walls is the artificialroughness technique that will be the subject matter of the present work.The importance of the problem of using ribs on flow channel walls as aheat transfer augmenting technique stems from the need in many cases tocool ( no heat) the surfaces in many engineering systems and devices.Cooling of turbine blades by ribs, electronics devices, machine tools,.... etc, are some known applications. It should be noted here thatalthough the main target is to augment the heat transfer rate, a side effectthat is undesirable, is the rise in pressure DROP ( flow resistance) as aninevitable result of the presence of ribs ( and roughness elements ingeneral) . Here, again the heat transfer side should be weighed against theincrease in power requirement to account for the increased resistance .Some kind of break even must be reached here for economicaloptimization . However, in some applications, the Increase in heat