Nozzle needle

Optimum atomization is achieved by fine adjustment of the air cap and atomization air pressure measured at the nozzle. The binder solution is delivered to the nozzle port through a spray lance and tubing. The peristaltic- or positive-displacement pump is commonly used to pump the binder solution. The pneumatically controlled nozzle needle prevents the binder liquid from... 

Much effort has been invested in integrating mass spectrometry with on-chip CE. The flow rates typically used (nL to p,L/min) are very suitable for electrospray ionisation (ESI) prior to MS. However, the buffers used in CE tend not to be compatible with ESI and there is also a need to decouple the two electric fields (one for the electrophoretic separation, one for the electrospray). One method that has been used for interfacing electrospray with chips is to bond electrospray nozzles/needles to the outlet of the microchannel. Electrospray tips can also be incorporated onto the chip as part of the fabrication process. Electrospray detection following separation by CE has worked well for proteins, carbohydrates and many other compounds. 

A nozzle needle can also influence the motive flow rate of a jet compressor. The installation of such a nozzle needle controlled ejector is shown in Figure 4.11. The needle Is adjusted by a pneumatic or electric actuator, as used for standard control valves. When a nozzle needle control is used, the motive pressure is not influenced. In contrast to the throttle control, described above, the motive mass flow is reduced without reducing the motive pressure that is required for the compression. The efficiency of a nozzle needle controlled ejector for partial load is therefore higher than with a throttle control valve. 

Figure 4.11 Assembly of a nozzle needle controlled ejector.

There are several types of nozzle. The simplest is an open nozzle as shown in Fig. 4.34(a). This is used whenever possible because pressure drops can be minimised and there are no hold up points where the melt can stagnate and decompose. However, if the melt viscosity is low then leakage will occur from this type of nozzle particularly if the barrel/nozzle assembly retracts from the mould each cycle. The solution is to use a shut-off nozzle of which there are many types. Fig. 4.34(b) shows a nozzle which is shut off by external means. Fig. 4.34(c) shows a nozzle with a spring loaded needle valve which opens when the melt pressure exceeds a certain value or alternatively when the nozzle is pressed up against the mould. Most of the shut-off nozzles have the disadvantage that they restrict the flow of the material and provide undersirable stagnation sites. For this reason they should not be used with heat sensitive materials such as PVC. 

In electrostatic atomization, an electrical potential is applied between a liquid to be atomized and an electrode placed in the spray at a certain distance from liquid discharge nozzle. As a result of the mutual repulsion of like charges accumulated on the liquid surface, the surface becomes unstable and disrupts when the pressure due to the electrostatic forces exceeds the surface tension forces of the liquid. Droplets will be generated continuously if the electrical potential is maintained above a critical value consistent with liquid flow rate. Both DC and AC systems have been employed to provide high electrical potentials for generating fine droplets. Many configurations of electrode have been developed, such as hypodermic needles, sintered bronze filters, and cones. 

The bubble-forming section consists of a control valve (needle valve type), a chamber, and the liquid column. It is customary to have flat glass plates as two sides of the column, to assist photography and visual observation of the phenomenon. A manometer is also provided to evaluate the pressure difference across the nozzle. 

Fuel-handling systems (diaphragms for fuel pumps, see Figure 5.5, fuel hose or fuel hose liner, inject or nozzle seals, needle valves, filter casing gaskets, fuel shutoff valves, carburetor parts)... 

Sampling Samples of sulfur dioxide may be safely withdrawn from a tank or from transfer lines, either of which should be equipped with a 3/8-in. nozzle and valve. Samples should be placed in sample cylinders constructed of 316 stainless steel, designed to withstand 1000 psig and equipped with 316 stainless-steel needle valves on both ends. 

Fig. 5.3. Apparatus used in the iodometric assay. G inert gas supply PS presaturator P pipettor M magnetic stirrer SD solvent delivery nozzle FR flow regulator D gas distributor CT connecting tube V vial S stopper with capillary opening SV side valve ST screw-top stopper holder N syringe needle. (Gebicki and Guide, 1989.)...

Figure 4.4-1 Basic composition of an apparatus for matrix-isolation experiments a) Rotatable cryostat with gas-handling system, b) Sectional view in the level of the matrix support, (1) matrix support, (2) refrigerator, 4-40 K, (3) radiation shield, 77 K, (4) vacuum shroud, (5) infrared window, X KBr, y PE, z quartz glass, (6) spray-on nozzle, (7) synthetic device, e.g., Knudsen cell, (8) turbomolecular pump, p < 10 mbar, (9) to backing pump, (10) transfer line, quartz or stainless steel capillary, (11) needle valve, (12) inert gas inlet, Ne, Ar, N2,..., (13) bulb for gas mixtures, (14) capacity manometer, (15) sample, (16) to high-vacuum system.

Gravity-fed applicators use the size of the nozzle orifice and the pressure created by gravity to regulate the output of fumigant. Constant speed is necessary to maintain a uniform delivery rate. In most applicators, a constant head gravity flow device keeps the pressure at the orifice(s) constant as the tank or container of fumigant empties. Needle valves, orifice plates or discs, and capillary tubes are used to adjust the flow rate. 

The sample—solvent flow is mixed with a controlled flow of nitrogen or air that generates an aerosol. The aerosol flows through a needle and exits the nozzle. As it exits, it is surrounded by a heated sheath gas, again nitrogen or air, that serves to confine the spray to a 2.5-3-mm spot and provides the necessary energy to evaporate the mobile phase. The resultant dry sample is directed onto a 60-mm-diameter Ge disc that is placed on a rotating platform 5—10 mm below the nozzle. Disc rotation in the system is automatically started after injection of the sample. The main portion of each collection took lO min. 

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