Wheel speed

Silicate. Once important, siUcate-bonded wheels have faded almost to obhvion increasing wheel speeds have made this inherently weak bond obsolete. Some wheels are produced, however, for old grinding equipment still in existence. 

The wisest fan choice is frequently not the cheapest fan. A small fan operates well on its curve but may not have adequate capacity for maximum flow control, future needs, or process upset conditions. It may be so lightly constmcted that it is operating near its peak speed with no provision for speed increases in the future, if needed. As fan size is increased, efficiency generally improves and wheel speed is lower. These factors decrease operating cost and provide reserve capacity for the future. However, it is also possible to oversize a fan and impair its performance. 

Low Density Gases. A fan may have to operate on low density gas because of temperature, altitude, gas composition (high water vapor content of the gas can be a cause of low density), reduced process pressure, or a combination of such causes. To develop a required pressure, the fan has to operate at a considerably higher speed than it would at atmospheric pressure, and hence it must operate much closer to top wheel speed. Bearing life is shorter, and the fan tends to vibrate more or can be overstressed more easily by a slight wheel unbalance. Abrasion of the blades from dust particles is more severe. Therefore, a sturdier fan is needed for low density gas service. 

An impulse-type turbine experiences its entire enthalphy drop in the nozzle, thus naving a very high velocity entering the rotor. The velocity entering the rotor is about twice the velocity of the wheel. The reaction type turbine divides the enthalphy drop in the nozzle and in the rotor. Thus, for example, a 50 percent reaction turbine has a velocity leaving the nozzle equal to the wheel speed and produces about V2 the work of a similar size impulse turbine at about 2-3 percentage points higher efficiency than the impulse turbine (0 percent reaction turbine). The effect on the efficiency and ratio of the wheel speed to inlet velocity is shown in Fig. 29-27 for an impiilse turbine and 50 percent reaction turbine. 

For a stage with a heat drop of about 35 Btu, the steam velocity through the nozzle of the turbine will be about 1,300 ft/sec. For an efficient stage, with a wheel speed of about 600 ft/sec, the nozzle will be between 3,500 and 4,000 rpm. 

Residual velocity, not utilized in buckets, causing a loss which is reduced when wheel speeds are high or several stages are used. 

Two compressors are similar when they have the same compressor constant. In similar compressors all impeller and discharge-vane linear dimensions are in the same ratio as their impeller diameters, while their impeller and discharge vane angles are respectively equal. For the same revolutions per minute the quantities delivered by sinailar compressors will vary as the cubes of their diameters the pressures will vary as the squares of their diameters, and the shaft powers will vary as the fifth powers of their diameters. For the same wheel speed the quantity and the power will vary as the square of the diameter, while the pressure will remain constant. 

Solution.—The compressor is rated for an initial pressure of 14.7 lb. per square inch.. Since the pressure ratio depends only on the wheel speed, the hydraulic eflSiciency and the initial temperature, all of which are supposed to remain the same, the initial suction pressure is (14.7/16.7) X 14.7 = 12.94 lb. per sauare inch absolute, and the suction obtained is 14.70 — 12.94 = 1.76 lb. per square inch. 

Therefore, the remaining material (38 rpm 4 kg) was Jet milled at a classifier wheel speed of 3700, collected in an 85 1 polyethylene container and homogenized for 2 hr using a Turbula mixer. 

As indicated above, the atomizer wheel speed is the important parameter influencing the spray droplet size ancfthus the particle size of the final product. The atomizer machine will normally have the capability to operate the wheel at the required speed. More important for the atomization process is the selection of a wheel capable of handling a specific liquid feed with characteristic properties such as abrasiveness, high viscosity, nonnewtonian behavior, or tendency to coagulate. 

The F800 atomizer is the largest rotary atomizer offered to industry today. It has the capability of handling up to 200 t/h in one single atomizer. The capacity limit of an atomizer is normally its maximum power rating. As indicated above, the atomizer wheel speed is the important parameter influencing the spray droplet size. The wheel speed also determines the power consumption of the atomizer. It can be shown that the atomizer power consumption exclusive mechanical losses amount to... 

One high-volume application is the wheel speed detection for anti-lock braking (ABS) systems. Wheel speed information is also needed in modern vehicle dynamics control (VDC) and navigation systems. Both require, in addition to the wheel speed, the steering angle as an input value, which is also often provided by magnetic sensors. A classic field of application is the power train, in which magnetic sensors deliver information about the cam and crank shaft positions as well as the transmission speed. 

Navigation systems record the position of a vehicle using satellite-based location systems (GPS) and match the determined position with the navigation system s digital street map. Yaw-rate sensors, in combination with wheel-speed sensors, permit interpolation in situations where no satellite reception is possible, such as when driving through tunnels or if the GPS signals cannot be clearly interpreted due to multiple reception as a result of reflections from houses in urban situations, for example. 

This system improves driving safety by preventing lateral instability of the vehicle. Besides sensors for wheel speed, steering-wheel movement, and yaw rate, a high-pressure sensor is needed to detect the brake pressure. 

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