Channel Height Effect on Heat Transfer and Friction in a Dimpled Passage

Abstract

The heat transfer enhancement in cooling passages with dimpled (concavity imprinted) surface can be effective for use in heat exchangers and various hot section components (nozzle, blade, combustor liner, etc.), as it provides comparable heat transfer coefficients with considerably less pressure loss relative to protruding ribs. Heat transfer coefficients and friction factors were experimentally investigated in rectangular channels which had concavities (dimples) on one wall. The heat transfer coefficients were measured using a transient thermochromic liquid crystal technique. Relative channel heights (H/d) of 0.37, 0.74, 1.11 and 1.49 were investigated in a Reynolds number range from 12000 to 60000. The heat transfer enhancement (NuHD) on the dimpled wall was approximately constant at a value of 2.1 times that (Nusm) of a smooth channel over 0.37≤H/d≤1.49 in the thermally developed region. The heat transfer enhancement ratio Nu¯HD/Nusm was invariant with Reynolds number. The friction factors (f) in the aerodynamically fully developed region were consistently measured to be around 0.0412 (only 1.6 to 2.0 times that of a smooth channel). The aerodynamic entry length was comparable to that of a typical turbulent flow (Xo/Dh = 20), unlike the thermal entry length on dimpled surface which was much shorter (xo /Dh<9.8). The thermal performance Nu¯HD/Nusm/f/fsm1/3≅1.75 of dimpled surface was superior to that 1.16<Nu¯HD/Nusm/f/fsm1/3<1.60 of continuous ribs, demonstrating that the heat transfer enhancement with concavities can be achieved with a relatively low-pressure penalty. Neither the heat transfer coefficient distribution nor the friction factor exhibited a detectable effect of the channel height within the studied relative height range (0.37≤H/d≤1.49).

Heat Transfer and Pressure Loss Characteristics of Zig-Zag Channel With Rib-Turbulators

“…Depending on the geometry, the heat transfer enhancement exhibited by hemispherical dimples could reach up to 2.5 times compared to smooth channel. Such findings are reported by Mahmood et al [17], Chyu et al [18] and Moon et al [19] based on their research studies in confined channels using hemispherical dimples with Re up to 60,000.…”

Investigation to Compare Heat Augmentation From Plane, Dimpled and Perforated Dimple Rectangular Fins Using Ansys

“…They conclude use of dimples on surface which results in heat transfer augmentationwith lesser pressure drop and also heat transfer enhancement is more effective in staggered arrangement as compare to in line arrangement. Moon [10] investigated the channel height effect on heat transfer over the dimpled…”

Heat Transfer Enhancement for Turbine Blade Internal Cooling

“…The benefit of dimples was quickly realized with such significant reduction in pressure losses and moderate heat transfer enhancement; the use of dimples was also viewed favorably as the level of heat transfer enhancement was shown to be independent of Reynolds number (for ribs as the Reynolds number increases, the Nusselt number ratios decrease) [44]. Moon et al [45] confirmed the Reynolds number independency, and from their study of detailed heat transfer coefficient distributions, they determined the majority of heat transfer enhancement occurs outside the dimples (with a reduction of heat transfer inside the concavities).…”