Heat Transfer and Pressure Loss Characteristics Of Zig-Zag Channel with Rib-Turbulators

This paper describes a detailed experimental study of rib-turbulators in a novel four-pass channel with 110 degree turns that exhibits a "zig-zag" pattern, and hence the name. The rectangular cross-sectional channel has the cross-section of 63.5 mm by 25.4mm, corresponding to the aspect ratio of 2.5:1. This specific design with several turns will generate additional secondary vortices, while providing longer flow path that allows coolant to remove a greater heat load before being discharged downstream. Heat transfer is further enhanced by the presence of rib-turbulators. Four test cases with different rib-configurations are explored and compared to the baseline case, the smooth zig-zag channel. For the first three cases, the rib pitch-to-height (pie) ratio is 10 and height-to-hydraulic diameter (e/Dh) of 0.044. Larger ribs are used in the fourth case, giving the p/e ratio of 5, and e/Dh of 0.088. The local heat transfer coefficient of the entire zig-zag channel is determined using the transient liquid crystal technique. The Reynolds number is based on the hydraulic diameter of the channel and bulk mean velocity ranges from 15,000 up to 30,000. The heat transfer in the zig-zag channel is enhanced due to the additional vortices and bulk flow mixing induced by the presence of turns and ribs in the entire channel. The highest heat transfer is observed along each rib-turbulator, followed by the region immediately behind the rib-turbulators. However, the heat transfer at the corner of each turn remains low and unaffected by the presence of rib-turbulators. The zig-zag channel with larger rib-turbulators exhibits the highest heat transfer enhancement at approximately 4.0-4.8 times higher than that of the smooth channel, followed by the other test cases with the heat transfer enhancement ranging from 2.5-3.5. In each zig-zag channel test case, although rib-turbulators have profound impact toward the heat transfer enhancement, with rather minimal increment in pressure loss within the tested Reynolds number.