Spindle Jets

Spindle regulated jets are usually not acceptable except for thermocompressors. A discussion of their application is given in Chapter 18. For critical vacuum pumps, regulating spindles are an ineffective means of control and can lead to unstable jet operation. 

The purchase price of vacuum systems depends upon the operating parameters and type of system. Single-stage jets and rotary blowers are among the least costly. The following equations can be used for making reasonable preliminary estimates of total installed costs. The equations are limited and should never be used as substitutes for detailed engineering. 

Wg = steam consumption based on 100 psig motive steam, Ib/hr 

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The two principal elements of evaporator control are evaporation rate a.ndproduct concentration. Evaporation rate in single- and multiple-effect evaporators is usually achieved by steam-flow control. Conventional-control instrumentation is used (see Sec. 22), with the added precaution that pressure drop across meter and control valve, which reduces temperature difference available for heat transfer, not be excessive when maximum capacity is desired. Capacity control of thermocompression evaporators depends on the type of compressor positive-displacement compressors can utilize speed control or variations in operating pressure level. Centrifugal machines normally utihze adjustable inlet-guide vanes. Steam jets may have an adjustable spindle in the high-pressure orifice or be arranged as multiple jets that can individually be cut out of the system. 

A long, hollow, cylindrical bowl is suspended by a flexible spindle and driven from the top as shown in Figure 13. Axial ribs in the bowl ensure full acceleration of the liquid during its short time in the bowl. Feed is jetted into the bottom of the bowl and clarified liquid overflows at the top, leaving deposited solids as compacted cake on the bowl wall. The clarifying performance of the bowl is reduced as the deposited cake decreases the effective outer radius of the bowl in accordance with equation 11. Consequently, cake capacity of the industrial model is limited to 0.1—10 L. For liquid—liquid separation, the interface position (eq. 26) is determined by selection of ring-dam diameter or by the length of a hollow nozzle-type screw dam. 

There are two basic methods for controlling vacuum pumps suction throttling and using a load gas. Mechanical pumps may also use variable speed drive single stage jets may also use a regulating spindle. 

Installed hose reels are wall mounted and comprise a length of hose wound on a drum. The feed pipe to fhe reel should be charged at all times. In some installahons a valve is incorporated into the spindle of the reel drum that automatically opens when the reel is pulled out. The flow of water is controlled by a valve at the free end which allows adjustment from a water jet to a fine spray. The sifing of the installations and the length of the hoses should be such that no part of the area to be protected is more than 6 m from any nozzle. Hose reels should be checked regularly for leaks and fully run out once a year so the condition of the full length of the hose can be checked. 

In the headbox nozzle, the suspension is accelerated to approximately machine speed. The thickness of the jet and, therefore, the amount of suspension is usually adjusted by swinging the upper wall of the nozzle. The shce at the nozzle outlet is often limited by a bar, which can be adjusted to an accuracy of ca. 1/1000 mm by means of spindles. This bar can be adjusted locally across the width this has been used or is still used in older headboxes to compensate for deviations in the cross machine weight profile of the web. The direction of the jet in the machine direction can be influenced by horizontally shifting the upper wall of the nozzle. In this way, the point and angle of impingement of the jet on the wire can be adjusted (Fig. 6.30). 

Fig. 12.13. Photographs of nanoelectrospray plumes as effected by different spray voltages. The modes observed starting from the upper left are dripping (D), spindle (S), cone-jet (C), pulsed cone-jet (P), and multi-jet (M). Only pure cone-jet mode will deliver stable electrospray for analytical work. Reproduced from Ref. [87] with permission. Elsevier, 2004.

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