Abstract
Ribs were added into a pin fin array for a uniquely new cooling concept enabled through additive manufacturing. Heat transfer measurements are obtained using the thermochromic liquid crystal technique in a trapezoidal duct with pin fins and rib turbulators. Three pin blockage ratios and four rib heights at Reynolds numbers between 40,000 and 106,000 were tested. The Nusselt number augmentation is generally higher at the longer base of the trapezoidal duct. The same high heat transfer trend is seen at the columns closer to the longer base of the trapezoidal duct than on the shorter base. Through the length of the duct, the flow shifts from the nose region to the larger opening on the opposite wall. Also, it is observed that increasing the blockage ratio as well as increasing the rib height has a positive impact on heat transfer as ribs act as additional extended surfaces and alter the near-wall flow field. The heat transfer augmentation of pins and ribs is found to not be equal to the sum of both: Both heat transfer mechanisms are highly non-linear, thus cannot be superimposed. The observed heat transfer augmentation of the combined cases exceeded over the rib and pin only cases by up to 100%, but the weighted friction factor also doubled. The combination of ribs and pins is an excellent concept to achieve more uniform cooling over an array at higher levels when pressure drop is not of concern.
