AUGMENTED HEAT-TRANSFER IN A RECOVERY PASSAGE DOWNSTREAM FROM A GROOVED SECTION - AN EXAMPLE OF UNCOUPLED HEAT MOMENTUM TRANSPORT/

Earlier experiments have shown that cutting transverse grooves into on e Surface of a rectangular cross-sectional passage stimulates flow ins tabilities that greatly enhance heat transfer/pumping power performanc e of airflows in the Reynolds number range 1000 < Re < 5000. In the cu rrent work, heat transfer, pressure, and velocity measurements in a fl at passage downstream from a grooved region are used to study how the flow recovers once it is disturbed. The time-averaged and unsteady vel ocity profiles, as well as the heat transfer coefficient, are dramatic ally affected for up to 20 hydraulic diameters past the end of the gro oved section. The recovery lengths for shear stress and pressure gradi ent are significantly shorter and decrease rapidly for Reynolds number s greater than Re = 3000. As a result, a 5.4-hydraulic-diameter-long r ecovery region requires 44 percent less pumping power for a given heat transfer level than if grooving continued.