Drop ejector

A schematic cross-section diagram of a drop ejector fabricated in the PolyMUMPS process is shown in Figure 6.10. The actuator is a clamped circular diaphragm similar to the M-Test structure CD discussed in Chapter 2, Section 2.8. The membrane diaphragm is defined in the Polyl layer (2 pm) and is pulled down by application of a voltage to a... 

Figure 6.10 Electrostatic membrane drop ejector, (a) The membrane has been pulled down by the application of a voltage applied to the counterelectrode. (b) The voltage is removed and the membrane relaxes back to its initial position, ejecting a drop of ink through the orifice in the nozzle plate, as shown in (c). The membrane is fabricated in Polyl and the counterelectrode is fabricated in PolyO. The nozzle plate with the orifice can be fabricated in Poly2 or in a separate thick polymer layer such as SU-8 (Xerox MEMSJet). See color plate section.

Figure 6.12 Drop ejection from a MEMSJet drop ejector (Xerox MEMSJet).

A second type of inkjet with an electrostatic actuator has been fabricated in the Sandia SUMMiT V process [3], [4]. In this design, the ink fills in the gap in the electrostatic actuator, increasing the dielectric constant and thus the pressure that is generated. Since the ink is exposed to the drive voltages, a high-frequency RF drive signal is used to avoid problems with electrolysis of the ink. A schematic cross section of the drop ejector is shown in Figure 6.13 [5]. 

A scanning electron microscope (SEM) image of a piston drop ejector with part of the front face removed to show the actuators is included in Figure 6.14. 

Figure 6.13 Electrostatic piston drop ejector. (Reprinted with permission from A Surface Micromachined Electrostatic Drop Ejector, P. Galambos, K. Zavadil, R. Givler, F. Peter, A. Gooray, G. Roller, and J. Crowley, 1967 IEEE.)...

Design a MEMS inkjet drop ejector in the PolyMUMPS process, as shown in the cross section in Figure 6.10. You do not need to worry about the fluid reservoir shown above the actuator that is formed as a circular diaphragm in Polyl (red). 

E.P. Furlani, Analysis of an electrostatic MEMS squeeze-film drop ejector, Sensors Transducers J. 7, Special Issue, October, pp. 78-87 (2009). 

J. Crowley, A Surface MicromachinedElectrostatic Drop Ejector, Transducers Ol, June 2001. 

Steam pressure. The main boosters can operate on steam pressures from as low as 0,15 bar up to 7 bar gauge. The quantity of steam required increases rapidly as the steam pressure drops (Fig, 11-106), The best steam rates are obtained with about 7 bar. Above this pressure the change in quantity of steam required is prac tically negligible. Ejectors must be designed for the highest available steam pressure, to take advantage of the lower steam consumption for various steam-inlet pressures. 

In liquid ejectors or aspirators, the hquid is the motive fluid, so the gas pressure drop is low. Flow of slurries in the nozzle may be erosive. Otherwise, the design is as simple as that of the Venturi. 

If the material ejector in the pipe is accelerated from a velocity of zero to c then the corresponding pressure drop is... 

A distillation column is operating at 27.5 inches mercury vacuum, referenced to a 30-inch barometer. This is the pressure at the inlet to the ejector. Due to pressure drop through a vapor condenser and trays of a distillation column, the column bottoms pressure is 23 inches vacu-... 

The air bleed is u.sed to maintain a constant condition. However, a control valve may be used instead. Control or hand valves in the lower pressure vapor lines to an ejector are not recommended, as they must be paid for in system pressure drop and ejector udlity requirements. 

Calculate pressure drop from this point to the process location of the suction flange of the first stage ejector. 

Figure 6-31 illustrates control schemes for the single stage unit which allow greater stability in performance. As the load changes for a fixed suction pressure, the process fluid is replaced by an artificial load (usually air Figure 6-31, item 1) to maintain constant ejector operation. An artificial pressure drop can be imposed by valve (2), although this is not a preferred scheme. Wlten the addi-... 

This assumes dry air with no condensables and negligible pressure drop through the system to the ejector. Also, the jet air handling capacity is assumed approximately twice the design capacity, and air inleakage during evacuation is negligible. 

Once the polymer has cooled to its solid state, the molding is ejected. This is accomplished with the aid of ejector pins that protrude from the mold walls as it opens. Small items typically drop directly into a catch pan or onto a conveyor belt below the mold. Larger items are removed manually. 

The vapors leaving the primary barometric condenser proceed to a steam ejector that is followed by another barometric. Pressures at the tops of the towers are maintained at 50mmHg absolute. Pressure drop is 2mmHg per tray. Bottom temperatures of the three towers are 450, 500, and 540°F, respectively. Tower overhead temperatures are 200°F. Pitch and roan go to storage at 350°F and the other products at 125°F. The steam generated in the pitch and rosin coolers is at 20 psig. Process steam is at 150 psig. 

The test results with the ultrasonic nozzle were obtained with an estimated steam to copper (S/Cu) ratio of 23 and the humidified Ar was injected co-currently with the CuCl2 solution. Several variables remain to be investigated, i.e. lower S/Cu ratios, counter-current instead of co-current operation, and subatmospheric pressures. LeChatelier s Principle predicts that reducing the pressure in the hydrolysis reactor should reduce the S/Cu ratio. The effect of a reduced pressure was quantified by the results of a sensitivity study using Aspen. Aspen predicts that a S/Cu ratio of 17 is needed for essentially complete conversion at 375°C and atmospheric pressure while a S/Cu ratio of 13 is required at 0.5 bar. The conceptual process design specifies that the hydrolysis reactor be run at 0.25 bar. The pressure drop in the reactor is achieved by adding a low temperature steam ejector after the condenser at the exit of the hydrolysis reactor in the conceptual design. 

Vaporization controls depend on the operating pressure. If vacuum is required to vaporize the process fluid and if steam jets are used to create that vacuum, it is recommended that a pressure controller be installed on the steam inlet to maintain the optimum pressure required by the ejector. For processes in which load variations are expected, the operating costs can be lowered by installing a larger and a smaller ejector and automatically switching to the small unit when the load drops off, thereby reducing steam demand. 

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