| Fabricating nickel micro heat exchangers directly on planar or non-planar metal surfaces has been demonstrated using the LIGA micromachining process. These heat exchangers can effectively control the temperature of surfaces in high heat flux applications. Of particular interest is the temperature control of gas turbine engine components. The locations in the gas turbine engine where improved, efficient cooling is required includes gas turbine blades, stator vanes, the turbine disk, and the combustor liner. In this dissertation, the primary application of interest is the use of such heat exchangers to cool airfoils such as turbine blades. In the first part of the study, the manufacturing and testing procedures of a flat configuration parallel plate micro pin fin heat exchanger are described. The pin fin array geometry investigated is staggered, with pin diameters of 500 mum, height to diameter ratios of 1.0 and spacing to diameter ratios of 2.5. Pressure loss and heat transfer experimental results for 4,000 ≤ Re ≤ 20,000 are reported and a Nu-Re correlation is provided. Favorable comparisons with studies on similar pin fin patterns tested at a larger scale are revealed. The flat micro pin fin heat exchanger performance is concluded to always exceed the parallel plate (smooth channel) counterpart by a factor of 1.35 to 1.78 in the Reynolds number range studied. An analytic model based on these experimental results is described and used to make predictions for cooling effectiveness values attaining 0.72 in a gas turbine blade cooling application. In the second part of the study, the feasibility to fabricate a micro pin fin heat exchanger on a simple airfoil, with a leading edge approximated by a cylinder, is demonstrated. The corresponding pin fin array geometry used is in-line, with pin diameters of 200 mum, height to diameter ratios of 2.5 and spacing to diameter ratios of 5. Heat transfer tests performed in a high temperature rig at gas Reynolds numbers near 10,000 are reported. Cooling effectiveness values ranging from 0.70 to 0.88 are obtained for coolant to mainstream gas mass ratios from 1% to 4% and coolant to mainstream gas temperature ratios from 1.62 to 2.26. |
