Fluid friction minimizing

The heart is located in the center of the thoracic cavity. It sits directly above the muscles of the diaphragm, which separates the thorax from the abdomen, and lies beneath the sternum between the two lungs. The heart is enclosed and anchored in place by a double-walled fibrous sac referred to as the pericardium. The membranes of the pericardium produce a small amount of pericardial fluid that minimizes friction produced by the movement of the heart when it beats. To function mechanically as a pump, the heart must have ... 

Lubricity is a term used to describe the ability of a fluid to minimize friction between, and damage to, surfaces in relative motion under load. Fuel helps to lubricate and prevent wear of high-pressure fuel injection pump components, especially under boundary lubrication conditions. Boundary lubrication is defined as a condition whereby friction and wear between two surfaces in relative motion are determined by the properties of the surfaces and the bulk properties of the contacting fluid. The bulk viscosity of the fuel or oil is not a critical factor under boundary lubrication conditions. 

In fluid friction, there is no contact between two surfaces. It is obvious that wear and tear is minimal in this type of friction. However, there is still very high need for lubricants for fluid friction, even though it is economically unjustifiable to use this type of friction in big industrial devices. The most popular types of friction in industrial devices are mixed and film friction. Mixed friction is present as a combination of fluid friction and hard surface friction. The tear by mixed friction is obviously higher than by fluid friction, because there is contact between surfaces at some points. The optimal for the industry is the so-called film friction. In this kind of friction, a thin film of surface-active substance is formed. This film protects the surfaces from direct contact and high wear and tear. 

Hydraulic Calculations. Fluid friction and turbulence within a heat exchanger cause the exit pressure of each fluid to be lower than its entrance pressure. It is desirable to minimize this pressure drop. If a fluid is made to flow by a pump, increased pressure drop will require more pumping power. As with convection resistance, pressure drop depends on many factors and is difficult to predict accurately. Empirical methods are again used. Generally, design changes that reduce the convection resistance will increase the pressure drop, so engineers must reach a compromise between these issues. 

A bursa, a sac filled with fluid located around a principal joint, is lined with a synovial membrane and contains synovial fluid. This fluid minimizes friction between the tendon and the bone, or between tendon and ligament. Repeated small stresses and ovemse can cause the bursa in the shoulder, hip, knee, or ankle to swell. This swelling and irritation is referred to as bursitis. Some patients experience bursitis in association with tendonitis. Bursitis can usually be reheved by rest and in some cases by using antiinflammatory medications. Some orthopedic surgeons also inject the bursa with additional medication to reduce the inflammation. 

While designers of fluid power equipment do what they can to minimize turbulence, it cannot be avoided. For example, in a 4-inch pipe at 68°F, flow becomes turbulent at velocities over approximately 6 inches per second (ips) or about 3 ips in a 6-inch pipe. These velocities are far below those commonly encountered in fluid power systems, where velocities of 5 feet per second (fps) and above are common. In laminar flow, losses due to friction increase directly with velocity. With turbulent flow, these losses increase much more rapidly. 

If the effects of friction are to be minimized, a lubricant film must be maintained continuously between the moving surfaces. Two types of motion are encountered in engines, rotary and linear. A full fluid-film between moving parts is the ideal form of lubrication, but in practice, even with rotary motion, this is not always achievable. At low engine speeds, for instance, bearing lubrication can be under boundary conditions. 

Emulsions. Emulsion fluids and foams came into routine use in competition with crosslinked fluids during 1970-80. Simple, barely stable emulsions had been used early in fracturing. These were mainly emulsified acids that "broke" when the acid spent on the formation surfaces. In the late 1960 s Kiel became a proponent of very high viscosity oil fluids as a method to place exceptional (at the time) amounts of proppant(337,338). To avoid the frictional resistance typical of gelled oils he advanced the concept of preparing a very viscous oil-external emulsion with one part fresh water, 0.1% sodium tallate surfactant, and two parts oil. The viscous emulsion had to be pumped simultaneously with a water stream to minimize frictional pressure. This process was clumsy and still... 

Suppose you want to design a hydrocarbon piping system in a plant between two points with no change in elevation and want to select the optimum pipe diameter that minimizes the combination of pipe capital costs and pump operating costs. Prepare a model that can be used to carry out the optimization. Identify the independent and dependent variables that affect the optimum operating conditions. Assume the fluid properties (/i, p) are known and constant, and the value of the pipe length (L) and mass flowrate (m) are specified. In your analysis use the following process variables pipe diameter (D), fluid velocity (v), pressure drop (A/ ), friction factor (/). 

For non-Newtonian fluids in slow flow, friction loss across a square-woven or full-twill-woven screen can be estimated by considering the screen as a set of parallel tubes, each of diameter equal to the average minimal opening between adjacent wires, and length twice the diameter, without entrance effects (Carley and Smith, Polym. Eng. Set, 18, 408-415 [1978]). For screen stacks, the losses of individual screens should be summed. 

Because they are not produced constantly, as are natural tears, tear substitutes should have properties to enhance their retention time in the tear film. The addition of various types of polymers to artificial tears not only improves retention of added fluid but also increases corneal surface wettability, decreases blink friction, and minimizes surfece tension. Natural tears contain glycoproteins and other surfectant macromolecules to decrease surface tension. Although polymers may enhance tear film stability without enhancing viscosity, there appears to be no correlation between retention time and viscosity. Polysaccharides, including mucilages, dextrans, and... 

Modern lubricants are formulated from a range of base fluids and chemical additives. The base fluid has several functions but it is primarily the lubricant which provides the fluid layer to separate moving surfaces. It also removes heat and wear particles whilst minimizing friction. Many properties of the lubricant are enhanced or created by the addition of special chemical additives to the base fluid, as described in later chapters. For example, stability to oxidation and degradation in an engine oil is improved by the addition of antioxidants whilst extreme pressure, EP, anti-wear properties needed in gear lubrication are created by the addition of special additives. The base fluid acts as the carrier for these additives and therefore must be able to maintain them in solution under all normal working conditions. 

The objectives of a drilling hydraulics programme are to ensure good hole cleaning, to minimize frictional losses in the flow in the drill pipe and annulus and to minimize the erosion of open hole formations by the shear stress exerted on the borehole wall. Several texts have described drilling fluid (or non-Newtonian fluid) hydraulics in some detail (82-85). The bulk flow properties of the drilling fluid are calculated from the models r = f(y) used to fit the experimental rheological data. 

---