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Recently, domestic gas turbines are primarily operated under partial loads. Hence, thermal expansion of components decreases, leading to a discontinuity between the 1st blade and 2nd vane. In this study, the local heat transfer coefficients are derived using the naphthalene sublimation method to analyze thermal characteristics based on step height, and flow characteristics are analyzed using numerical simulation. An extreme heat load of the flat endwall appears around the leading edge of the vane due to the secondary vortex. Under the step conditions, the heat load increases in the upstream region as the main flow near the endwall is reattached to the endwall surface. In addition, two high heat transfer distributions appear due to the recirculation flow, and a step-induced vortex is formed. As the step-induced vortex moves to the suction side within the vane flow path, a high thermal load appears in the corresponding region. Consequently, we found that the occurrence of a step causes severe thermal damage in the upstream region of the vane endwall. The area-averaged heat transfer of the stepped endwall is increased by about 10.6 % and 17.3 % at hs/Cx = 0.05 and 0.1, respectively, as compared to that of the flat endwall. [ABSTRACT FROM AUTHOR]

• Investigation of heat transfer characteristics on the 2nd vane endwall when the misalignment occurs without and with purge flow using Naphthalene sublimation method and CFD. • Significant increase in heat transfer coefficient in the upstream of vane endwall due to misalignment. • With purge flow, the mixing of mainstream and purge flow increases heat transfer in the upstream of vane endwall due to increase the intensity of vortex. • The area-averaged heat transfer of the stepped endwall is increased by about 11.4% and 13.7% without and with purge flow, respectively, as compared to that of the flat endwall. Since the domestic power plants are typically operated at a partial load rather than the design point, the thermal expansion decreases, resulting in misalignment between first stage rotor and second stage stator. In this study, we investigate the heat transfer characteristics of a misalignment under purge flow at the second stage vane endwall through heat/mass transfer experiments using the naphthalene sublimation method and CFD simulations. Experiments are conducted at 4 vanes in a linear cascade with an inlet Reynolds number of 120,000, based on the vane axial chord length. In the absence of purge flow, a high heat transfer occurs in upstream of the vane endwall via horseshoe vortices. When a misalignment occurs, a more severe thermal load is observed as the mainstream attaches to the endwall due to recirculation flow upstream of the leading edge. Additionally, two high heat transfer regions are observed when a step-induced vortex occurs in the vane flow path. In case of the purge flow, the mixing of the mainstream and purge flow increases the intensity of the vortex, which increases heat transfer in the region upstream of the both flat and stepped endwall. In conclusion, we have found that the step difference has a crucial effect on thermal damage upstream of the second stage vane endwall as a little misalignment occurrence. The area-averaged heat transfer of the stepped endwall is increased by about 11.4% and 13.7% without and with purge flow, respectively, as compared to that of the flat endwall. [ABSTRACT FROM AUTHOR]

• Effect of anisotropic wicking plays an important role on subcooled flow boiling. • Significant enhancement in critical heat flux and heat transfer coefficient in presence of anisotropic wicking surfaces. • Wicking characteristic enhancement in the presence of surfaces with bent-polymerized pillar arrays. Anisotropic wicking surfaces have attracted the attention of numerous research groups in recent years. Wicking characteristics can be improved by generating unidirectional flow behavior within surfaces composed of micropillars that are bent in the direction of interest. In the present work, we created surfaces composed of bent polymerized pillar arrays with center-to-center spacings of 250 and 500 µm and experimentally investigated boiling heat transfer under subcooled flow conditions (40 K). The test surfaces were chemically coated with a 200-nm-thick hydrophilic layer to evaluate the effects thereof on subcooled flow boiling. Surface anisotropy and the center-to center spacings between neighboring pillars significantly improved surface wickability and boiling heat transfer, compared to surfaces with vertically polymerized pillars. Enhancements of the critical heat flux (17–34%) and the heat transfer coefficient (8–71%) were evident on polymerized pillar surfaces compared to bare polymerized surfaces. The experimental results were validated by theoretically analyzing the relationship between the liquid pinning forces and the polymerized pillar surfaces' configurations to understand better how boiling heat transfer was enhanced on anisotropic wicking surfaces during subcooled flow boiling. [ABSTRACT FROM AUTHOR]