•Normalized sensitivity analysis is performed for design and performance cases.•A modified lumped ED model, along with a cost model, is used up to 160,000 ppm.•During operation, controlling salt ...removal rate needs optimal feed concentration.•During operation, better control of energy consumption requires optimal velocity.•More reliable plant sizing is obtained at lower feed concentrations.
Brackish water desalination can be performed efficiently using electrodialysis (ED). The technology can also be used to mitigate hypersalinity (>50,000 parts per million (ppm)). In this study, a simple and modified lumped ED model combined with cost calculations is used to perform a normalized sensitivity analysis up to 160,000 ppm. The model takes care of the effect of Donnan potential as well as boundary layers (films) and water transport through charged membranes. The analysis reveals that the (linear) velocity and feed concentration are generally the most significant factors affecting ED performance. Considering both control and cost issues, for the specific energy consumption per unit of salt removed, an optimal flow velocity should be chosen. For the rate of salt removal, a combination of lower flow velocity and optimal feed concentration is recommended. In the ED design case, the analysis shows that the feed concentration is generally the most significant factor. Considering both control and cost issues, for the total membrane area and rate of salt removal, a lower feed concentration is recommended irrespective of cost considerations.
The article presents the basic principles of three-dimensional mathematical modeling of the operation of a thrust plain bearing with fixed pads of the compressor. The model is based on the periodic ...thermoelastichydrodynamic (PTEHD) theory which allows calculating the temperature at the inlet to the pad and considering the complete thermal pattern. A description of the main provisions of the numerical implementation is given. In the stationary mode of the bearings operation, using the Sm2Px3Tx program, numerical experiments were carried out aimed at studying different boundary conditions to the Reynolds equation, the physics of the hydrodynamic process in the lubricating and boundary films of the bearing and the heat propagation in the body of the pad and thrust collar.
The influence of added naphthalene derivatives on the formation of boundary lubricant films during frictional processes in synthetic dioctyl sebacate oil is considered. The activity of the additive ...is determined by the presence of acidic groups in their molecules and the ability to form complexes with metals.
This study was initiated with the aim to assess the influence of boundary films on the tribologically induced metallurgical transformations and deformations of metals in lubricated contacts and their ...effect on wear. For this, the tribological behavior of a carbon steel contact was studied in two commercially available oils expected to form boundary films of quite different chemistry and structure. Surface analysis by AES and XPS revealed that under the investigated conditions the first oil led to the formation of an iron–zinc oxide surface film while the second to a calcium–carbon–oxygen rich film. The results show that, without influencing the coefficient of friction, the nature of the formed films significantly affected the metallurgical transformations (characterized by electron microscopy of focused ion beam cross sections) occurring in the near surface region of the metal and the corresponding wear response. The effect of boundary films on wear was attributed to their capability to influence the plastic flow of the nano-grained structures generated in the studied tribological contacts.
•Boundary films critically affect the surface metallurgical response to friction.•As a consequence, they can significantly modify wear of oil lubricated steel.•This effect is attributed to the nature and hardness of the boundary film.
The investigations deal with the study of the heat-shielding effect of thin oil films during the passage of heat flux through them, the conditions for its occurrence, and the space-time region of ...propagation through heterogeneous media with account for the reduced thermophysical characteristics. The paper presents theoretical calculations and experimental investigations conducted on a special self-engineered device. Consideration has been given to the influence of the oil film thickness, the amplitude and time of the heat pulse on the velocity of its propagation simultaneously through a lubricated contact and an unlubricated one. The results of observations over the pattern of heat flux propagation has made it possible to draw a conclusion that the heat flux released, for example, as a result of friction on a microscopic contact is characterized by high density and propagates with a significant velocity predominantly in the direction with the least thermal resistance determined by the thermophysical characteristics and the temperature potential of the material. Considering that the processes occur at the microscopic level, such materials include thin boundary films (oil. oxide, spray-applied and other films) with a thickness comparable with the height of microroughnesses.
An analytical method based on statistical mechanics is proposed to predict ultra-thin adsorbed films of physical fluids with molecular diversity formed on smooth surfaces. The model is representative ...of molecular interactions at the smooth summits of surface asperities in the nano-scale. At this physical scale the constraining effect of the solid barriers promotes discretization of the fluid volume into molecular layers. These layers are usually ejected from the contact in a stepwise manner. The integrated effect of intermolecular forces as well as their interactions with the contiguous surfaces is responsible for the discontinuous drainage of the fluid. However, at the same time, the adsorption energy of the molecular species strives to form a molecular monolayer upon the boundary solids. The net result of these complex interactions is an ultra-thin adsorbed film, whose shear characteristics depends on a competition between the repulsive solvation pressure and the energy of molecular adsorption. It is shown that very thin low shear strength films are formed in this manner. This would depend on the molecular concentration and the wall adsorption energy. An important implication is that boundary adherent films should be viewed as a result of surface-fluid combination for which the choice of concentration and fraction content of particular species are crucial.
The paper presents measurements of friction of any ultra-thin film entrained into the contact of a pair of very smooth specimen subjected to entrainment in a converging micro-wedge of a ...special-purpose micro-tribometer. An ultra-thin film is expected to form at the boundary solids through adsorption of boundary active molecules. Fluids with linear and branched molecules are used in the investigation. It is found that the frictional characteristics of these films can be adequately described through use of Eyring thermal activation energy and a potential energy barrier to sustain conjunctional sliding motion. The combined experimental measurement and the simple activation energy approach shows that the thin molecular adsorbed films act like hydro Langmuir–Blodgett layers, the formation and frictional characteristics of which are affected by the competing mechanisms of adsorption, forced molecular re-ordering and discrete-fashion drainage through the contact by the solvation effect. This process is a complex function of the contact sliding velocity as well as a defined Eyring activation density (packing density of the molecules within the conjunction). It is shown that the contribution of solvation to friction is in the form of energy expended to eject layers of lubricant out of the contact, which unlike the case of micro-scale hydrodynamic films, is not a function of the sliding velocity.
Thin film colorimetric interferometry was used to map changes in film thickness in the vicinity of micro-dents of various depths produced on rubbing surfaces. It has been shown in recent studies that ...shallow micro-features within concentrated contact can increase mean film thickness by supplying more lubricant to the contact; however, this beneficial effect can also be accompanied by a local film thickness reduction. Nevertheless, these observations were done with mineral base oils that exhibited no boundary films formation. In this study the behavior of micro-textured surfaces are observed using formulated lubricant containing polyalcylmethacrylate (PAMA), viscosity index improver with boundary film forming properties. Obtained results show that an enlarged film thickness due to the presence of viscous boundary films is formed within the whole contact and these boundary films minimize the local film thickness reduction caused by micro-dents and further increase the efficiency of surface texturing within non-conformal contacts. It can be suggested from the obtained results that joint action of both boundary film formation and surface texturing combines both contributions that can help to increase tribological performances in different stages of machine parts operation by increasing lubrication film thickness.
The mechanism of the appearance of reverse secondary flows in boundary lubricating films in a radial sliding bearing has been proposed. It has been found that the axial load and the velocity of ...sliding determine the sign and magnitude of the pressure gradient in the lubricating films astride the contact. The inter-relation between the aggregate state of the lubricant, as well as the local pressure in it and the force of friction, has been established.
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