No abstract

Extended surfaces are frequently used in heat exchanging devices for increasing the heat transfer between a primary surface and the surrounding fluid. Heat transfer augmentation by providing an extended surface to air side, increases weight of the system, obstruct air-flow, increases pressure drop and pumping power to keep the fluid stream flowing. These major problems will be minimized with the help of recent developments in the field of nanotechnology that provides an avenue to augment heat transfer by providing a coating of nanometer thickness on the heat exchanger surface. The present work aims to investigate the effect of the nanocoating on the heat exchanger surface with the experiments. The experimental results show that the presence of nanocoating does not have any effect on drag change, where the actual pressure drop of the coil for air velocity of 0.6 m/s, 1.6 m/s is 20 Pa and 60 Pa, respectively. For nanocoated surface, 24.2% improvement in heat transfer rate was observed and transient temperature response of the nanocoated heat exchanger tube is higher than uncoated one for a given experimental conditions.

A B S T R A C TGearbox failure is one of the highest risk events in wind turbines. In most of the wind turbines, planetary gearboxes are preferred over conventional gearboxes due to their significant advantages. But condition monitoring of planetary gearboxes present a huge challenge to the vibration analysts due to complex design and construction of its unit, vibration transducer type and locations, wide frequency range of the vibrations, resolution required to separate frequencies and dynamic range required to observe both low frequency and high frequency components in the spectrum.Due to strong Gear Mesh Frequency (GMF) signals, gear defect vibration characteristics can often be suppressed in the overall vibration signal. So there is a need to develop or utilize various special signal processing techniques in order to identify and monitor the progression of defects in gears more effectively.This paper focuses on one such technique namely Sideband Energy Ratio (SER) for monitoring of gear defect progression in wind turbine gearboxes. Theory behind SER is and its significance in gear defect monitoring is presented in this paper through three case studies. In all the three case studies, SER of 2XGMF were found to be more sensitive than 1XGMF towards gear defect progression.

No abstract