Papers by Keyword: Film Thickness

Abstract: Falling film on horizontal tube evaporators, of both Mechanical Vapor Compression (MVC) and the Multi-Effect Distillation (MED) desalination systems, plays an important role in the heat and mass transfer (evaporation) and accordingly the systems productivity. Falling film thickness is mainly influenced by the intertube space, circumferential angle and the film’s Reynolds number. This paper presents two-dimensional numerical study of falling film thickness around horizontal tube in MVC and MED evaporators. The study is based on computational fluid dynamics (CFD) using volume of fraction (VOF) as a multi-phase technique in ANSYS Fluent. The numerical model is developed in order to study the heat and mass transfer charactristics, the liquid falling film behaviour and thickness distribution around circular horizontal. Four CFD study cases are developed to simulate the falling film behaviour at circumferential angle range from 150 to 1650 with inter-tube spacing of 10 mm, 16 mm, 33 mm and 40 mm and for constant value of flow rate and at the same surrounding conditions. Simulations are conducted using a domain of only two tubes with 20 mm outer diameter.The results from the numerical models are compared with the published experimental correlations, showing a comparatively reasonable agreement. In addition, a parametric study is carried out to illustrate the effect of flow Reyonlds number (Re) and intertube space on the average circumferential film thickness and heat transfer rates.

Abstract: Many machine components work within an elastohydrodynamic lubrication (EHL) regime. Unconfined space is widely used in EHL formulas for to evaluate film thickness, which is related to operating conditions and material properties. In classical theoretical EHL studies, film pressure matches the loading balance and the location of the lubricated components can be adjusted. In the present study, the lubrication performance is analyzed based on a confined space. A thrust ball bearing lubrication simulation system is designed and used to examine the relationship between velocity and film thickness. It was found that the central film thickness and minimum film thickness increased as entrainment velocity increased. Fluctuations in the film thickness curve were observed, which may have arisen from slight gap variations in the ball-plate contact area.

Abstract: The gears of a gear box were modeled and analyzed through Romax, and the effects of pressure angle on their lubrication properties were studied. The studies had shown that as the increase of pressure angle, the safety factor against micropitting had significantly increased. The gears were less prone to micropitting. The minimum film thickness and the maximum film thickness of the gears had also significantly increased, so the gear lubrication performance had been improved. It had important significance to improve the carrying capacity and prolong the service life of the gears.

Abstract: The thickness of the plastic film is an important physical index to the production of plastic. The measurement reslut relates directly to the companies’ economic benefit. This paper mainly introduces the digital signal processing in the detection system of film thickness. Through a perfect processing, the system can improve its SNR and finally get a high precision. Firstly, the principle and scheme was presented. After that, this paper mainly introduces the hardware implementation of the system. It includes analog filter circuit, AD sampling and digital filter. With the experimental verification, the system realizes the measurement of the film thickness on-line which can get the precision of micrometer. At present, the equipment has aready put into use by some companies.

Abstract: The article describes an experimental investigation of scale effect in a starved elastohydrodynamically lubricated contact on lubricant film thickness. Lubricant film thickness and its distribution is one of the most important parameters determining the performance and life of machine parts. Current experimental and numerical studies are mostly connected with oil lubrication. However, greases are used in more than 80 % of all rolling bearings where the starvation phenomenon occurs most frequently. The aim of this work is to compare two approaches to measuring film thickness of different greases. The use of multiple contacts optical test rig based on thin film colorimetric interferometry for film thickness measurement has enables to obtain film thickness of starved contact and the film distribution. The experimental observation of full-scale model of bearing will help to understand better the behavior of real bearing. The evaluation of the experiment was made by chromatic interferometry. This method is used to measure thin lubrication films.

Abstract: Conditions such as the execution of repair works and ambient environment can affect the protective performance of surface coating material for concrete structures, and they are important in terms of exhibiting a long-term repair effect. This paper presents a fundamental study on the influence of film thickness and ambient temperature to the protective performance of surface coating material: oxygen, moisture vapor and chloride ion permeability. It was confirmed that as film thickness and ambient temperature increased, oxygen, moisture vapor and chloride ion permeation rates decreased and increased, respectively. Test results showed a good agreement with the behavior of polymer molecule membrane.

Abstract: The Cu/Ni, Ni/Cu and Cu/Ni/Si film/substrate and film/film/substrate systems were prepared by magnetron sputtering method to investigate the surface segregation. The chemical composition of film was analyzed by Auger Electron Spectroscopy (AES). The microtopographies of the Cu/Ni surface and the cross section of the film were observed by Transmission Electron Microscope (TEM), where the blocky distribution of Ni-rich area on surface of Cu film and columnar grains was observed in the specimen. It is found that the thickness of sputtered film has stronger effect on the composition of segregation layer near the surface than that of the annealing time. The surface segregation could be ascribed to the fast vertical diffusion of the substrate atoms through the columnar grain boundaries and the subsequent lateral surface diffusion.

Abstract: An investigation on the liquid holdup, wave velocity, and wave frequency in horizontal annular flow has been experimentally conducted through the measurement of liquid holdup using constant electric current method (CECM) sensors. To investigate the effect of viscosity, water and glycerin were used as working liquid, using superficial liquid velocity and superficial gas velocity of 0.05 to 0.2 m/s and 12 to 40 m/s, respectively. Liquids with higher viscosity give the higher liquid holdup, lower wave velocity, and lower wave frequency. Correlations for liquid holdup and mean film thickness, wave velocity, and wave frequency have been developed with mean average errors (MAE) of 13.5%, 9.2%, and 8.6%, respectively.

Abstract: In order to study the differences in load-carrying capacity of surface-textured soft materials and stiff materials, a theoretical hydrodynamic model considering elastic deformation is developed for numerical simulation analysis. Minimum oil film thickness at a certain load is computed as an index to evaluate the load-carrying capacity of textured sliding surfaces made of soft materials and stiff materials. The results show that the elastic modulus affects greatly on the load-carrying capacity. In the case of the surface texture with a dimple aspect of 0.05, textured soft materials has a higher load-carrying capacity than that of the stiff materials. In the case of the surface texture with a dimple aspect of 0.01 and only under high loads, textured stiff materials provides a better load-carrying capacity than that of the soft materials.

Abstract: Electrical capacitance has been applied in the past for measuring the lubricant film thickness in rolling element bearings. The main difficulty arises from the fact that the measured capacitance is a combination of the capacitances of many rolling elements, which come in contact with both the inner and outer rings. Besides, the capacitance of the Hertzian contact itself and the surrounding area must also be separated. It results in a complex system which, in order to be solved for the film thickness at a particular location on the bearing many approximations have to be made. In the present study the authors use an experimental rig in which the capacitance of a single ball can be isolated. Moreover the capacitance of the ball – inner ring and ball – outer ring contacts can be measured separately.