Deposition studies were conducted using two impingement jet facilities: a 60m/s cold jet (830 - 950K) impinging on a heated Hastelloy-X surface (1033-1255K) and a 215m/s hot jet (1450-1625K) impinging on an uncooled ceramic target or a cooled thermal barrier coated (TBC) surface (1090-1400K). These can be considered analogs for an internal impingement cooling jet flow and an external nozzle guide vane leading edge flow respectively. Airflows were seeded with 0-10μm Arizona Road Dust and deposition accumulated over a period of 5-10 minutes. Select tests were completed with other size distributions. Studies were conducted by varying flow temperature at constant surface temperature, and vice-versa. For both the hot and cold impingement jets, the sensitivity of capture efficiency to fluid (and thus particle) temperature was found to be roughly double the sensitivity to surface temperature. Hot jet tests with three different size distributions of dust (0-5, 0-10, and 5-10μm) allowed particle size sensitivity to be evaluated. For both target types (ceramic and cooled TBC), the 0-10μm test dust produced the highest deposition rate of the three size distributions. Possible explanations for the observed behavior are proposed. Companion CFD studies modeling both impinging jets with particle deposition demonstrate that temperature induced variations in particle trajectories alone are not sufficient to explain observed deposition trends with temperature. Implications for the development of a universal sticking model relevant for gas turbine deposition are discussed.
This paper seeks to unpack synergies that exist between minerals during deposition of the heterogeneous AFRL02 mixture in gas turbine engines and demonstrate that the contributions of each mineral cannot be considered independently. In each experiment, one gram of a mineral dust (0-10μm particle diameter distribution) was injected into an 894K, 57m/s coolant flow impinging normally on a Hastelloy X plate with a surface temperature of 1033K, 1144K, or 1255K. Capture efficiency measurements, deposit morphology analyses, and X-ray diffraction results are reported. Besides AFRL02, single mineral dusts, dual mineral dusts, and AFRL02-like dust blends lacking in one mineral were tested. The results of the experiments elucidate that the deposition behavior of single minerals indeed cannot explain the composite deposition of heterogeneous mixtures. For example, gypsum had the highest capture efficiency of any single mineral in ARFL02; yet removing gypsum from AFRL02 counterintuitively raised the capture efficiency of that blend when compared to AFRL02. Quartz was found to erode albite deposits but stick to and build upon dolomite and halite deposits, even though quartz did not deposit significantly by itself. Quartz also chemically reacted with gypsum and dolomite to form wollastonite and diopside, respectively. Finally, we found that the capture efficiency of each blend increased with plate temperature, but not according to the same trend. Results are interpreted through the lens of CaO-MgO-Al2O3-SiO2 eutectic chemistry, but the chemical pathways by which these eutectics come into existence is found to be of equal importance.
This paper seeks to unpack the synergies that exist between minerals during deposition of the heterogeneous AFRL02 mixture in gas turbine engines and demonstrate that the contributions of each mineral cannot be considered independently of others. In each experiment, one gram of a mineral dust (0–10μm particle diameter distribution) was injected into an 894K, 57m/s coolant flow impinging normally on a Hastelloy X plate with a surface temperature of 1033K, 1144K, or 1255K. Capture efficiency measurements, deposit morphology analyses, and X-ray diffraction results are reported. Besides AFRL02, single mineral dusts, dual mineral dusts, and AFRL02-like dust blends lacking in one mineral were tested. The results of the experiments elucidate that the deposition behavior of single minerals indeed cannot explain the composite deposition of heterogeneous mixtures of minerals. For example, gypsum had the highest capture efficiency of any single mineral in ARFL02, and yet removing gypsum from AFRL02 counterintuitively raised the capture efficiency of that blend when compared to AFRL02. Quartz was found to erode albite deposits but stick to and build upon dolomite and halite deposits, even though quartz did not deposit significantly as a single mineral. Quartz also chemically reacted with gypsum and dolomite to form wollastonite and diopside, respectively. Finally, we found that the capture efficiency of each blend increased with plate temperature, but not according to the same trend. Results are interpreted through the lens of CaO-MgO-Al2O3-SiO2 eutectic chemistry, but the chemical pathways by which these eutectics come into existence is found to be of equal importance.
Deposition studies were conducted using two impingement jet facilities: a 60m/s cold jet (830–950K) impinging on a heated Hastelloy-X surface (1033–1255K) and a 215m/s hot jet (1450–1625K) impinging on an uncooled ceramic target or a cooled thermal barrier coated (TBC) surface (1090–1400K). These can be considered analogs for an internal impingement cooling jet flow and an external nozzle guide vane leading edge flow respectively. Airflows were seeded with 0–10μm Arizona Road Dust and deposition accumulated over a period of 5–10 minutes. Select tests were completed with other size distributions. Studies were conducted by varying flow temperature at constant surface temperature, and vice-versa. For both the hot and cold impingement jets, the sensitivity of capture efficiency to fluid (and thus particle) temperature was found to be roughly double the sensitivity to surface temperature. Hot jet tests with three different size distributions of dust (0–5, 0–10, and 5–10μm) allowed particle size sensitivity to be evaluated. For both target types (ceramic and cooled TBC), the 0–10μm test dust produced the highest deposition rate of the three size distributions. Possible explanations for the observed behavior are proposed. Companion CFD studies modeling both impinging jets with particle deposition demonstrate that temperature induced variations in particle trajectories alone are not sufficient to explain observed deposition trends with temperature. Implications for the development of a universal sticking model relevant for gas turbine deposition are discussed.
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