EFFECTS OF HEIGHT-TO-DIAMETER RATIO OF PIN ELEMENT ON HEAT TRANSFER FROM STAGGERED PIN-FIN ARRAYS

A pin-fin array is a compact heat exchanger and widely used for cooling of turbine airfoils. This study is to experimentally examine the effects of pin height or height-to-diameter ratio (H/D) on the heat transfer from a pin-fin array. The test models are designed to facilitate three different H/D ratios, from 2 to 4, with a staggered pin-fin array of inter-pin spacing 2.5 times the pin diameter (S/D=X/D=2.5) in both longitudinal and transverse directions. The Reynolds number ranges from 10,000 to 30,000. The experiment uses a hybrid technique based on the transient liquid-crystal imaging to obtain detailed local heat transfer coefficients over both the pin-fin surface and endwalls. Overall array-averaged heat transfer increases with the HID value or pin height. Most of the heat transfer contribution for H/D>2 comes from the pins rather than the endwall. However, higher HID leads to a greater pressure loss. As a measure of heat transfer enhancement per pressure loss, H/D=2 leads to the highest performance index and H/D=4 is the lowest.