Pressure drop along a channel with modified short pin-fins

Abstract

Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.

Short pin-fin arrays are used to enhance the heat transfer in cooling channels of gas turbine airfoils, combustor liners, electronic chips, bearing housings etc. Numerous experimental and numerical past studies ascertain the optimal spacing and length to height ratios within arrays of round short pin-fins for optimal heat transfer. However, the heat transfer enhancement in pin-finned channels is achieved at the expense of a significant pressure drop across the channel. Augmentation of pin-fins to improve the flow and heat transfer characteristics through the channel, may however lead to further improvements. This paper presents measured pressure drop characteristics in a channel with a staggered array of round short pin-fins where each pin has two through slots. The two slots located at the two ends of each pin have an identical slot-depth to pin-diameter ratio and slot-width to pin-diameter ratio which is 0.48. The slots are oriented parallel to the mean flow direction in the pin-fin array. The pin-height to diameter ratio used is 1.28 and pitch to diameter ratio in both streamwise and pitchwise direction of the pin-fin array is 2. The array consists of 13 staggered rows of pin-fins. Pressure drop in the channel is also measured with conventional solid round pin-fins. The same array spacing, pin-diameter and pin-height was used as with the slotted pin-fin array for comparison. The Reynolds number based on the mass averaged velocity and pin hydraulic diameter ranges between 3,300 and 32,800 covering different cooling applications. The objectives of the measurements are to investigate the effect of the pin-slots on the pressure drop over the array of pin-fins and recirculation region downstream of the slotted pin in the channel. The recirculation regions are responsible for low heat transfer coefficients on the end wall in the immediate vicinity downstream of the pin-fins. In general, the normalized pressure drop over the slotted pin-fin array decreases as Reynolds number decreases. The pressure drop over the slotted pin-fin array was also lower than the predicted pressure drop over an array of solid pin fins without slots. The normalized pressure distribution around the slotted pin circumference at mid-height shows a stagnation region over the frontal section of the slotted pin. The normalized pressure distribution changes little between 90° and 180° over the Reynolds number range that was used; this indicates a region of local flow separation. A short pin-fin array with slotted pins as described in this paper reduces the pressure drop over an array when compared to an unslotted array with the same geometrical arrangement. Slotting of pin fins may enhance the performance of an array of short pin-fins by reducing the pressure drop across the array.