Low-speed

Heavy fuels are used for two kinds of applications industrial combustion in power plants and furnaces, and fueling large ships having low-speed powerful diesel engines (Clark, 1988). 

The effective saturation depth,, represents the depth of water under which the total pressure (hydrostatic plus atmospheric) would produce a saturation concentration equal to for water ia contact with air at 100% relative humidity. This can be calculated usiag the above equation, based on a spatial average value of T, measured by a clean water test. For design purposes,, can be estimated from clean water test results on similar systems, and it can range from 5 to 50% of tank Hquid depth. Effective depth values for coarse bubble diffused air, fine bubble diffused air, and low speed surface aerators are 26 to 34%, 21 to 44%, and 5 to 7%, of the Hquid depth, respectively. 

Small ultrasonic motors such as the rotary actuator shown in Figure 10 have also been made and can be used for automobile windows, seats, and windshield wipers. Many small industrial motors could make use of the high torque, low speed, and precise stepping character of these actuators. 

Fig. 4. Representative stress—strain curves of spun and drawn PET A, low speed spun-mechanically drawn yam B, 6405 m /min C, 5490 m /min D, 4575...

Mechanical Cake Removal. This method is used in the American version of the dynamic filter described under cross-flow filtration with rotating elements, where turbine-type rotors are used to limit the cake thickness at low speeds. The Exxflow filter, introduced in the United Kingdom, is described in more detail under cross-flow filtration in porous pipes. It uses, among other means, a roUer cleaning system which periodically roUs over a curtain of flexible pipes and dislodges any cake on the inside of the pipes. The cake is then flushed out of the curtain by the internal flow. 

These two test methods and the octane numbers of the fuels measured are ultimately used to evaluate the performance of vehicles. The two methods provide usehil information about how fuels perform in cars. The RON corresponds to light load, low speed conditions, whereas the MON corresponds to heavier loads, and high speed severe driving conditions. 

Fuel economy, typically expressed as distance driven per volume of fuel consumed, ie, ia km/L (mi/gal), is measured over two driving cycles specified by the Federal Test Procedure (63). Oae cycle simulates city driving and consists of relatively low speed (- 32 km/h) driving, and iacludes a portion where the car starts after having equiUbrated at ambient conditions for 16 hours. The second simulates highway driving conditions and iacludes higher speeds and... 

Positive Pumps. Positive pumps employed by the food industry have a rotating cavity between two lobes, two gears that rotate in opposite directions, or a crescent or stationary cavity and a rotor. Rotary positive pumps operate at relatively low speed. Fluid enters the cavity by gravity flow or from a centrifugal pump. The positive pump also may use a reciprocating cavity, and may be a plunger or piston pump. These pumps are not truly positive with respect to displacement, but are used for metering product flow. 

Rotational Molding. Hodow articles and large, complex shapes are made by rotational mol ding, usuady from polyethylene powder of relatively low viscosity (57—59). The resin is in the form of a fine powder. A measured quantity is placed inside an aluminum mold and the mold is heated in an oven and rotated at low speed. The resin sinters and fuses, coating the inside of the mold. The mold is then cooled by water spray and the part solidifies, dupHcating the inside of the mold. 

As only a small proportion of the material is in contact with the roUs and friction on the rollers is low, hard materials can be processed with tittle wear. The high pressure action creates a slab of ultrafine particles which usually requires a low speed impact milting system to disagglomerate. Used in closed circuit with such a disagglomerator and an air classifier, such machines can reduce the energy requirement for fine grinding many minerals. 

Carbon Steels and Low—Medium Alloy Steels. Plain carbon steels, the most common cutting tool materials of the nineteenth century, were replaced by low—medium alloy steels at the turn of that century because of the need for increased machining productivity in many appHcations. Low—medium carbon steels have since then been largely superseded by other tool materials, except for some low speed appHcations. 

Low—medium alloy steels contain elements such as Mo and Cr for hardenabiHty, and W and Mo for wear resistance (Table 4) (7,16,17) (see Steel). These alloy steels, however, lose their hardness rapidly when heated above 150—340°C (see Fig. 3). Furthermore, because of the low volume fraction of hard, refractory carbide phase present in these alloys, their abrasion resistance is limited. Hence, low—medium alloy steels are used in relatively inexpensive tools for certain low speed cutting appHcations where the heat generated is not high enough to reduce their hardness significantly. 

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