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Lubricant Contribution to Energy Efficiency
Published in Don M. Pirro, Martin Webster, Ekkehard Daschner, Lubrication Fundamentals, 2017
Don M. Pirro, Martin Webster, Ekkehard Daschner
The Stribeck curve provides an example of how a lubricated contact can transition between different regimes of lubrication. At high speed, low load, and higher viscosity, the lubricant film will be relatively thick and can fully separate the two surfaces. In this regime, located on the right-hand side of Figure 19.3, the viscous forces provide the main contribution to the friction loss in a hydrodynamic bearing. As viscosity increases, the viscous friction losses also increase. If speed or viscosity is reduced, or load is increased, the lubricant film gets thinner as we move to the left on the Stribeck curve. At some point, the highest points on each of the surfaces begin to make contact with one another. At each one of these small contacts, a tiny amount of localized friction force is generated as the surfaces slide past each other. Within the contact, there may be many of these contacts depending on the relative roughness of the two surfaces and the thickness of the lubricant film. The total friction generated in the contact is thus a combination of the viscous forces and the friction generated at the asperity contacts. Because both hydrodynamic and surface effects govern behavior, this is referred to as the mixed lubrication regime. If the speed or viscosity is reduced or load is increased, the lubricant film generated by hydrodynamic effects is reduced even further. This results in a greater number of asperity contacts. In this regime, surface friction effects dominate, and the term “boundary lubrication” is used. As the friction generated at surface contacts is generally larger than the friction generated by shearing the lubricant, the total friction increases, which results in the upturn seen in the left-hand side of the Stribeck curve.
The design of water transport and distribution systems
Published in Nemanja Trifunović, Introduction to Urban Water Distribution, 2020
After the inventory of the present situation has been made, design goals have become clear and design parameters have been adopted, the next dilemma is in the choice of the distribution scheme and possible layout of the network. The following should be born in mind while thinking about the first alternatives: Water flows to any discharge point choosing the easiest path: either the shortest one or the one with the lowest resistance.Optimal design from the hydraulic perspective results in a system that demands the least energy input for water conveyance. Translated into practical guidelines, this means: maximum utilisation of the existing topography (gravity),use of pipe diameters that generate low friction losses,as little pumping as necessary to guarantee the design pressures, andvalve operation reduced to a minimum.Yet, the hydraulic logic has its limitations. It should not be forgotten that the most effective way of reducing friction losses, by enlarging pipe diameters, consequently yields smaller velocities. Hence, it may appear difficult to optimise both pressures and velocities in the system. Furthermore, in systems where reliable and cheap energy is available, the cost calculations may show that the lower investment in pipes and reservoirs justifies the increased operational costs of pumping.
Hydraulics
Published in David Butler, Christopher Digman, Christos Makropoulos, John W. Davies, Urban Drainage, 2018
David Butler, Christopher Digman, Christos Makropoulos, John W. Davies
The head or energy losses in flow in a pipe are made up of friction losses and local losses. Friction losses are caused by forces between the liquid and the solid boundary (distributed along the length of the pipe), and local losses are caused by disruptions to the flow at local features like bends and changes in cross section. Total head loss hL is the sum of the two components.
Improvement in head loss characteristics of fine particulate coal-water suspension with addition of coarser particulate
Published in International Journal of Coal Preparation and Utilization, 2022
Mani Kanwar Singh, Satish Kumar, Dwarikanath Ratha, Harkirat Sandhu
It is also found from Figure 2 that there is an increase in the pressure drop during the flow of coal-water slurry with increase in solid concentration. It is observed that the pressure drop is increased by 6.75, 7.32, and 7.84% with the increase in solid concentration from 29 to 41, 41 to 51, and 51 to 61% (by weight), respectively, during the flow of coal-water slurry at a velocity of 5 m/s. When the viscosity of a fluid increases, more friction loss occurs during the flow of that fluid. Since the viscosity of coal-water slurry increases due to the increase in the solid concentration, the increase in the pressure drop is also observed by increasing the solid concentration. Similar trend in pressure drop is also observed by the various investigators (Chandel, Seshadri, and Singh 2009; Kumar et al. 2017; Seshadri et al. 2008; Verma, Singh, and Seshadri 2006).
On friction factor of fluid channels fabricated using selective laser melting
Published in Virtual and Physical Prototyping, 2020
Yi Zhu, Lei Zhou, Shuai Wang, Chao Zhang, Cong Zhao, Lei Zhang, Huayong Yang
Schmelzle et al. (2015) proposed non-circular channels (e.g. diamond, teardrop shapes) in an SLM fabricated hydraulic manifold, which significantly reduces the overhang regions. However, compared to a circular channel, non-circular channels inevitably have stress concentration. As a result, wall thickness needs to be increased to compensate, which adds extra weights. On the other hand, fluid flow in a channel also depends on the channel surface roughness. Friction loss is the pressure loss due to the effect of the fluid’s viscosity when viscous fluid flows through a pipe. It is related to the flow rate, viscosity, properties of the fluid and the pipe, etc. Similar to the coefficient of friction, friction factor describes the value of the friction loss under a given condition. Based on the classical theory (Darcy 1857; Fanning 1877; Moody 1944), the friction factor is proportional to the Reynolds number in the laminar flow. While in the turbulent flow, the relation between the friction factor and Reynolds number becomes complex. The pipe roughness starts to affect when a large Reynolds number appears (further detailed in the discussion part). A horizontal fluid channel (without supports) has poor dimensional accuracy and extremely high surface roughness (particularly on the top). How do those characteristics affect friction loss remains unknown, which is crucial in designing complex fluid channels.
Computational fluid dynamics for sub-atmospheric pressure analysis in pipe drainage By Mohsen Besharat, Oscar Enrique Coronado-Hernández, Vicente Samuel Fuertes-Miquel, Maria Teresa Viseu and Helena Margarida Ramos, J. Hydraulic Res. 58(4), 2020, 553–565, 10.1080/00221686.2019.1625819
Published in Journal of Hydraulic Research, 2021
Arman Rokhzadi, Musandji Fuamba
Figure 1 illustrates the air pressure distribution during the emptying process for two different valve opening ratios, and two different initial air lengths. As can be seen, the solutions of the PMSV model are competitive with the solutions presented in the original paper. Note that the discharge coefficient is calculated as and 0.089 for % and , respectively. It is known that the discharge coefficient depends on different parameters including the pipe diameter, and Reynolds number. Therefore, as can be seen in Fig. 1, the deviations between the solutions of the PMSV model and the solutions of the original paper could be linked to the discharge coefficient, which needs to be calibrated for this drainage system. Another influential parameter is the friction loss, which is calculated by the Darcy–Weisbach formula. For this example, the friction loss is mainly caused by the elbow and the partially opened valve at the downstream. Since the PMSV is a one-dimensional model, it cannot take into account the effect of the elbow. In addition, there is no specific rule to calculate the friction loss of the valve. Therefore, for this Discussion, an iteration was performed manually to find the most appropriate friction factor , which is and for the solution in the left and right graphs of Fig. 1, respectively. As anticipated, for , the friction factor is larger, which implies more friction loss caused by the smaller valve opening ratios. Therefore, the deviation between the original results and the one calculated by the PMSV model could be also linked to the friction factor, which needs to be calibrated experimentally for this drainage system.