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26. Vibration characteristics of a 75 kW turbo machine with air foil bearings

Author

Kim, Kyeong-Su and Lee, In

Subjects
Vibration -- Evaluation, Turbomachines -- Design and construction, Aerofoils -- Equipment and supplies, Engineering and manufacturing industries, Science and technology
Abstract

Air foil bearings are very attractive bearing systems for turbomachinery because they have several advantages over conventional bearings in terms of oil-free environment, low power loss, long life, and no maintenance. However, most of the developed machines using airfoil bearings are limited to small and high-speed rotors of 60,000-120,000 rpm, since the increase in power of turbomachinery requires lower rotor speed and greater loading in bearings, which makes it difficult to use airfoil bearings for large machines. In this paper, a 75 kW turboblower using airfoil bearings is introduced, and the vibration characteristics of the machine have been investigated experimentally under a wide range of operating conditions, including compressor surge in the performance test. The machine is designed to be fully air lubricated and air cooled, and its operating speed is 20,000-26,000 rpm with maximum pressure ratio of 1.8. The results show that the airfoil bearings offer adequate damping to ensure dynamically stable operation in the whole range. [DOI: 10.1115/1.2718220] Keywords: airfoil bearings, turbo blower, environment-friendly system

Published
2007

28. On the role of carboxylated polythiophene in defect passivation of CsPbI2Br surface for efficient and stable all‐inorganic perovskite solar cells.

Author

Chung, Yoseob, Kim, Kyeong Su, and Jung, Jae Woong

Subjects
*METHYLAMMONIUM, *SOLAR cells, *POLYTHIOPHENES, *PEROVSKITE, *SURFACE passivation, *ELECTRIC power production, *CONJUGATED polymers, *LIGHT sources
Abstract

Summary: Improved film surface is a prerequisite to achieve high photovoltaic performance of inorganic perovskite solar cells because defective (under‐coordinated) lead ions derived from imperfect lattice structure of the film surface or grain boundaries the principal nonradiative recombination centers in the inorganic perovskite absorber. In this study, we suggest poly[3‐(4‐carboxybutyl)thiophene‐2,5‐diyl] (P3CT), a carboxylated p‐type conjugated polymer, as a passivating agent of the CsPbI2Br layer to tailor electronic properties of a perovskite absorber. With the P3CT passivation, the defective sites of the perovskite film surface were improved and stabilized, which can suppress nonradiative recombination to promote charge transport of CsPbI2Br‐based all‐inorganic perovskite solar cells. Consequently, the P3CT passivation delivers a power conversion efficiency (PCE) of 12.25% and decent long‐term stability of CsPbI2Br perovskite solar cells, which surpasses the pristine device without the passivation. The electricity generation capability under indoor light source of the passivated device is also studied, demonstrating a promising PCE of 27.47%. This work unveils the role of P3CT as a passivating agent to passivate the defective sites of CsPbI2Br perovskite film surface and grain boundaries, which facilitates charge transport and reduced carrier recombination of CsPbI2Br absorber in solar cell devices. [ABSTRACT FROM AUTHOR]

Published
2022
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33. Viscoelastic model of finitely deforming rubber and its finite element analysis

Author

Kim, Seung Jo, Kim, Kyeong Su, and Cho, Jin Yeong

Subjects
Viscoelasticity -- Models, Finite element method -- Usage, Deformations (Mechanics) -- Research, Science and technology
Abstract

Principles of continuum mechanics were utilized to create a viscoelastic model of finitely deforming rubber. This model was subjected to finite element analysis using numerical simulation and nonlinear finite element approximation. The validity of the model was verified by simulating uniaxial stretch tests at varying stretch rates. Experimental results confirmed the model's validity.

Published
1997

36. Reduced energy loss in SnO2/ZnO bilayer electron transport layer-based perovskite solar cells for achieving high efficiencies in outdoor/indoor environments.

Author

Noh, Young Wook, Jin, In Su, Kim, Kyeong Su, Park, Sang Hyun, and Jung, Jae Woong

Abstract

The energy loss in perovskite solar cells (PSCs) is a key factor that limits the full potential of photovoltaic performance to values below the Shockley–Queisser limit. Herein, we report a bilayer structure of the electron transport layer (ETL) for reducing energy loss in methylammonium lead triiodide (MAPbI3)-based planar heterojunction PSCs. The controlled electronic structure of the bilayer ETL affords suitable energy band matching at the interface of the MAPbI3 layer for electron transport/hole blocking, which effectively suppresses trap-assisted recombination at the interface of PSCs. As a result, the optimized bilayer ETL reduces charge recombination at the interfaces of the perovskite layer, boosting the power conversion efficiency (PCE) of the MAPbI3-based PSCs up to 20.43% with an open circuit voltage (VOC) as high as 1.20 V under 1 sun conditions. In addition, the bilayer ETL-based devices retained a high VOC of 0.98 V under illumination from a white light emitting diode (1000 lux), realizing PCEs of up to 37.2% under indoor conditions with good ambient stability for >800 h. These findings suggest the importance and potential of the bilayer ETL for reduced energy loss to generate high power outputs in outdoor/indoor environments of PSCs. [ABSTRACT FROM AUTHOR]

Published
2020
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