The heat transfer characteristics of airflows in serpentine cooling channels in stator vanes of gas turbines and the novel QuTech® Heat Pipe (QTHP) for electronic cooling applications were studied. The cooling channels are modeled as smooth and roughened two-pass trapezoidal channels with a 180° turn over a range of Reynolds numbers between about 10,000 and 60,000. The naphthalene sublimation technique and the heat and mass transfer analogy were applied. The results showed that there was a very large variation of the local heat (mass) transfer distribution in the turn and downstream of the turn. The local heat (mass) transfer was high near the end wall and the downstream outer wall in the turn and was relatively low in two regions near the upstream outer wall and the downstream edge at the tip of the divider wall in the turn. The variation of the local heat (mass) transfer was larger with ribs on two opposite walls than with smooth walls. The regional average heat (mass) transfer was lower in the turn and higher in the entire channel with the flow entering the channel through the larger straight section than when the flow was reversed. The pressure drop across the turn was higher with the flow entering the channel through the larger channel than when the flow was reversed. Thermal performance of the QuTech® Heat Pipe was identified over a range of inclination angles between 90° and -90° and thermal mechanism of the QTHP was studied with GC-MS, ICP-OES, XRD, XPS, and DSC. This study resulted in the following findings: the performance of the QTHP was severely dependent on gravity; the QTHP utilizes water as working fluid; there were inorganic components such as Na, K, P, S, and Cr, etc.; and the vaporization temperature of the working fluid (mostly water) was lower than the boiling temperature of pure water. This was due to the presence of inorganic salt hydrates in the QTHP. It may be concluded that thermal performance of heat pipes increases with additional latent heat of fusion energy and energy required to release water molecules from salt hydrates.

Film cooling is a cooling technique widely used in high-performance gas turbines to protect turbine airfoils from being damaged by hot flue gases. Film injection holes are placed in the body of the airfoil to allow coolant to pass from the internal cavity to the external surface. The ejection of coolant gas results in a layer or “film” of coolant gas flowing along the external surface of the airfoil. In this study, a new cooling scheme, mist/air film cooling is proposed and investigated through experiments. Small amount of tiny water droplets with an average diameter about 7 μm (mist) is injected into the cooling air to enhance the cooling performance. A wind tunnel system and test facilities were build. A Phase Doppler Particle Analyzer (PDPA) system is employed to measure droplet size, velocity and turbulence. Infrared camera and thermocouples are both used for temperature measurements. Mist film cooling performance is evaluated and compared against air-only film cooling in terms of adiabatic film cooling effectiveness and film coverage. Experimental results show that for blowing ratio M=0.6, net enhancement in adiabatic cooling effectiveness can reach 190% locally and 128% overall along the centerline. The general pattern of adiabatic cooling effectiveness distribution of the mist case is similar to that of the air-only case with the peak at about the same location. The concept of Film Decay Length (FDL) is proposed to quantitatively evaluate how well the coolant film covers the blade surface. Application of mist in the M=0.6 condition is apparently superior to the M=1.0 and 1.4 cases due to the higher overall cooling enhancement, the much longer FDL, and wider and longer film cooling coverage area. Based on droplet measurements through PDPA, a profile describing how the airmist coolant jet flow spreads and eventually blends into the hot main flow is proposed. A sketch based on the proposed profile is provided. This profile is found to be well supported by the measurement results of Turbulent Reynolds Stress. The location where a higher magnitude of Turbulent Reynolds Stress exists, which indicates higher strength of turbulent mixing effect, is found to be in the close neighborhood of the edge of the coolant film envelope. Also the separation between the mist droplets layer and the coolant air film is identified through the measurements. In other words, large droplets penetrate through the air coolant film layer and travel further over into the main flow. Based on the proposed air-mist film profile, the heat transfer results are reexamined. It is found that the location of optimum cooling effect is coincident with the starting point where the air-mist coolant starts to bend towards the surface. Thus the data suggests that the “bending back” film pattern is critical in keeping the mist droplets close to the surface which improves the cooling effectiveness for mist cooling.

This thesis introduces a design optimization methodology that is based on minimizing the Cost of Energy (COE) of a Horizontal Axis Wind Turbine (HAWT) that is to be operated at a specific wind site. In the design methodology for the calculation of the Cost of Energy, the Annual Energy Production (AEP) model to calculate the total energy generated by a unit wind turbine throughout a year and the total cost of that turbine are used. The AEP is calculated using the Blade Element Momentum (BEM) theory for wind turbine power and the Weibull distribution for the wind speed characteristics of selected wind sites. For the blade profile sections, either the S809 airfoil profile for all spanwise locations is used or NREL S-series airfoil families, which have different airfoil profiles for different spanwise sections, are used,. Lift and drag coefficients of these airfoils are obtained by performing computational fluid dynamics analyses. In sample design optimization studies, three different wind sites that have different wind speed characteristics are selected. Three scenarios are generated to present the effect of the airfoil shape as well as the turbine power. For each scenario, design optimizations of the reference wind turbines for the selected wind sites are performed the Cost of Energy and Annual Energy Production values are compared.