Mechanism efficient

Fans Axial-flow fans are large-volume, low-pressure devices. Fan diameters are selected to give velocity pressures of approximately 2.5 mm (0.1 in) of water. Total fan efficiency (fan, driver, and transmission device) is about 75 percent, and fan drives usually have a minimum of 95 percent mechanical efficiency. 

The mechanical output of the motor for crimes iind hoists in lifting the hook load is the useful work done by it. The losses produced in the crane or hoist mechanism are taken into account by the mechanical efficiency of the hoisting mechanism. 

Most ethylene plants operate continuously with the expanders operating at or near design conditions. If necessary, due to their unique design characteristics, radial inflow turboexpanders can accommodate a wide range of process conditions without significant losses in thermal or mechanical efficiency. Expanders may be loaded with booster compressors, gear-coupled generators, dynamometers, or other in-plant mechanical equipment such as pumps. In ethylene plants, turboexpanders are typically used in eitlier post-boost or pre-boost applications. 

Figure 1. Bhp per million curve mechanical efficiency—95% gas velocity through valve—3,000ft/min (API equation).

For any process converting heat energy to mechanical efficiency, the Carnot efficiency is the theoretical maximum. It is calculated as... 

To assist the engineer in making estimates, the curve in Figure 3-6 gives values of efficiency plotted against pressure ratios. The values on the curve include a 95% mechanical efficiency and a valve velocity of 3,000 feet per minute. Table 3-1 and Table 3-2 are included to permit a correction to be made to the compressor horsepower for specific gravity and low inlet pressure. They are included to help illustrate the influence of these factors to the power required. The application of these factors to... 

Figure 3-6. Reciprocating compressor efficiencies plotted against pressure ratio with a valve velocity of 3,(M)0 fpm and a mechanical efficiency of 95%.

A proportion of the shaft power is used to overcome the bearing friction. This is allowed by using the mechanical efficiency. Thus, the required axial power is... 

Friction in bearings, gasket, and impeller side walls. These losses are taken into consideration by the mechanical efficiency rj... 

Mechanical efficiency The actual work possible by a machine, related to the work put into that machine. 

Vehicle fuel economy is normally measured in miles per gallon. At any given instant, it depends on the energy content of a gallon of fuel (Qf), the vehicle velocity (V.,) and power required (P,-5q), the thermal efficiency with which the engine converts fuel energy into useful output work (rj,.), and the mechanical efficiency with which the driveline delivers that work to the vehicle wheels (r j). Specifically,... 

Its internal mechanical efficiency can be nearly perfect—a 1999 test at Johns Hopkins University... 

The light weight and mechanical efficiency not only allow the bicycle to be powered by a nonathlet-ic human, but it can be walked over extreme terrain, or laden ivith heavy cargo, or picked up and carried. These options make the bicycle more versatile than any other vehicle, and allow a bicycle user door-to-door, on-dcinand transport. 

The bicycle s advantages as the world s most mechanically efficient means of transportation are clouded by the limitations of the human engine. To put it in power output terms, the human body can produce sustained power only at modest levels. For most people, 100 watts would be too much, and for an elite athlete, 400 watts is the approximate ceiling. (The athlete may manage a brief burst of 1.1 kilowatts.)... 

The human engine cannot match this power output, yet the mechanical efficiency of the bicycle helps tremendously because a vei y small amount of horsepower can generate great speed. For example, 0.4 horsepower (298 watts) of output can result in 25 niph (40 kph) speeds or better. One set of calculations shows that if a cyclist rode on level ground, with no rolling resistance, and aided by a 25 mph tailwind, it would require only around 0.2 horsepower (150 watts) to sustain a 25 mph pace. 

As a general guide, speed is reduced 25-35 percent below rating for each tenfold increase in viscosity above 1000 SSU. Also, generally, the mechanical efficiency of the pump is decreased 10 percent for each ten fold increase in viscosity above 1000 SSU, and referenced to a maximum efficiency of 55 percent at this point. [1]... 

Mechanical efficiencies of steam pumps vary with the types of pump, stroke and the pressure differential. Some representative values are 55 to 80 percent for piston pumps with strokes of 3 inches and 24 inches respeedvely, and pressure differential up to 300 psi. For the same strokes a plunger design varies from 50 to 78 percent, and at over 300 psi differendal the efficiencies are 41 to 67 percent [9]. Steam required is approximately 120 Ibs/hour per BHP. 

Note 1 A function of the mechanical efficiency of these combined exhauster and dust collectors. 

System efficiency is influenced by the air plenum chamber and fan housing. Industrial axial flow fans in proper system design will have efficiencies of approximately 75% based on total pressure. Poor designs can run 40%. Speed reducers are about 75% mechanically efficient. 

Mechanical efficiency is the ratio of compressor cylinder indicated horsepower to the brake horsepower. Efficiency values range from 90-93% for direct-driven cylinders to 87-90% for steam engine units. The efficiency of the driver is not included. 

Note that this is horsepower available to the cylinders. It includes a 95% mechanical efficiency incorporated into the bhp/MMCFD curves. The rating of a gas engine must be such that its delivered horsepower is at least 420 hp, or if an electric motor drive is used, the mechanical losses of the intermediate frame (about 5%) must be added to arrive at the required motor shaft horsepower. 

This is the horsepower consumed by the cylinders and does not contain any losses in transmitting the power from the driver to the point of use, such as belts or gears. It does contain 95% mechanical efficiency for the cylinder itself. 

Figure 12-25 represents combined compression and mechanical efficiency of a compression unit. Therefore, for approximation... 

Figure 12-25. Combined compression and mechanical efficiency of reciprocating compressors. (Used by permission Campbell, J. M. Oil and Gas Journal and Ridgway, R. S. California Natural Gasoline Association Meeting, 1945. All rights reserved.)...

Adiabatic Efficiency. The ratio of theoretical adiabatic horsepower to actual brake horsepower required at the compressor shaft is adiabatic efficiency. It is equal to compression efficiency X mechanical efficiency. ... 

The mechanical efficiency of a fan is the ratio of the horsepower output to the horsepower input at the fan shaft. The input horsepower to drive the fan consists of the air horsepower, the energy losses in the fan, fluid dynamic losses, shock losses, leakage, disk friction, and bearing losses (all as horsepower), The fan oudet velocity pressure loss has been included in the fluid dynamic losses. 

Mechanical efficiency e (which usually refers to the efficiency of the prime mover to supply power to the pump) is... 

The mechanical efficiency e of a power pump at full load of pressure and speed is 0.90 to 0.95. When the pump has a single built in gear as part of the power frame, the mechanical efficiency is 0.80 to 0.95. Table 3-25 shows the typical effects of speed and pressure on the mechanical efficiency of a power pump [17]. 

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