Particle traps

The development of the electrodynamic balance and other particle traps has made it possible to perform precise measurements of the properties of small particles by focusing on the single particle. The variety of processes and phenomena that can be investigated with particle traps is quite extensive and includes gas/liquid and gas/solid chemical reactions, chemical spectroscopies, heat and mass transfer processes, interfacial phenomena, thermodynamic properties, phoretic forces, and other topics of interest to chemical engineers. 

It is the purpose of this survey to review the principles of electrical and optical traps, to explore the numerous applications of the devices that have been examined in recent years, and to indicate the use of the instruments for chemical engineering research. 

The classical electrostatic balance is the Millikan condenser, which was first used to measure the charge on the electron in the famous Millikan oil-drop experiment. In principle, the device can be used to levitate a small charged mass by using the electrical field generated by two flat plates to 

Wyatt and Phillips (1972) commercialized an electrostatic balance with electro-optic feedback control and light-scattering capabilities the device is shown in Fig. 2. The dc field was generated by a lower electrode and an electrified pin mounted in the upper plate. The particle was illuminated by a laser beam, and light scattered from the particle hit the edge of an adjustable 

The Wyatt and Phillips instrument has the features of primary importance for subsequent electrical levitators—specifically, feedback control for vertical positioning and scattered light detection. However, the restoring forces exerted on the particle were not adequate for a number of applications. Slight convective currents in the chamber would cause the particle to be lost, so it was not possible to provide flow through the device. The electrodynamic balance does not have this difficulty. 

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Ashkin A and Gordon J P 1983 Stability of radiation-pressure particle traps an optical Earnshaw theorem Opt. Lett. 8 511-13... 

Whiskey stills are usually fitted with entrainment removal sections that consist of a plate above the top stripping plate to remove particles trapped in the vapor. 

By number count the great majority of particles in the outside air are likely to be less than 1 pm. By weight, these small particles will account for a very small proportion of the sample. A filter with a high efficiency measured by weight of particles trapped may be almost transparent to the small ones. Very high counts can be found in rural areas from pollen or agricultural activities. 

The determination of the velocity of individual panicles can be carried out in a number of ways. First, the particles in a given section of pipe can be isolated using two rapidly acting shutters or valves, and the quantity of particles trapped measured by removing the intervening section of pipe. This method was used by Segler 71, Clark ei aL and Miti.in It is. however, cumbersome, very time-consuming, and dependent upon... 

We shall illustrate the concept with an example (a particle trapped in a hox), which though simple, reveals a number of important consequences of his approach. At the end of this section we shall he ready to move on to the hydrogen atom and see how the concepts apply to it and answer the remaining questions about its spectrum. 

Type Examples Minimum size particle trapped (/dll)... 

The main result of the particles trapping is a fooling effect for the porous medium that leads to a reduction of the material permeability. As shown on Figure 7.7, this fooling... 

Figure 7.8. DPF operating mode with alternation of soot particles trapping sequence and DPF regeneration step.

Fig. 4.11. Proposed RNA life. The membrane was made by the production of oils. The monomers were made from basic available forms of elements, H20, C02, NH3 and HP042. The source of energy was, for example, an energised Fe/S particle trapped on the membrane. The system reproduces when the duplex polymer, say [ATJ ATJ]2, is released as two single strands only for each to be trapped in a new synthesising vesicle. The improbability of such a scheme emerging is very high, yet some such event happened. Note that it is not necessary to have a simple [ATJ]n unit and a variety of units of any ordering A and U is reproducible with fidelity on second copying.

Fig. 18.15 Advanced methods for single particle analysis in LC ARROW chips, (a) Nanopore added to reservoir for single particle entry into LC ARROW (b) Optical dual beam particle trap based on balancing the scattering force due to counter propagating beams...

Fig. 1.2 Motions of balls in attiitor mills the dotted vertical line represents the axis of rotation of a vertical shaft on which a number of horizontal shafts (arms) are mounted, which strike balls and agitate their motion in a very energetic manner powder particles trapped between the balls are subjected to high-rate deformation processes...

Particle trapping is also a substantial economic issue, as in many countries the sUtation time scale is relatively short (about 100 yr on a global scale). In alpine reservoirs this time scale is much longer, and measures to mitigate siltation had low priority. However, in the future, sediment management, including removal, will be unavoidable. An occasionally used method is to divert the early arrival of a turbid flash flood past the reservoir, so that most of the sediment is delivered to the downstream river. Also, sediment removal and downstream re-deposition is periodically applied, especially when the downstream river suffers from erosion. 

In remote reservoirs not affected by anthropogenic pollution, particle trapping can reduce the available nutrients. In the Canadian Rocky Mountains, fertihzer has been added to lakes and rivers in the form of liquid ammonium polyphosphate with the goal to stabihze nutrient concentration at historical levels [5]. 

Figure 9. Elemental maps obtained using a scanning auger microscope—soot (C) particle trapped in a copper grid...

FIGURE 6.8 TH power generated from a 200-nm-diameter polystyrene particle trapped by a CW laser beam as a fnnction of the incident power of the trapping beam. Dashed line shows a third-power dependence on the incident power. 

Figure 4. Qualitative fluorescence analysis of a 5 n fly ash particle trapped on the first stage of the Cassella cascade impactor used to sample the precipitator inlet...

The initial and steady state wear rates of the siloxane-modified epoxy pins on the steel disks correlated with the inverse of the KIC values which agrees with previous abrasive wear tests 47>. The steady state wear rates on the smooth glass disks were comparable to those on the steel disks. Thus in both cases the wear mechanism is abrasive wear by the wear particles trapped in the interface between the pin end and the disk. 

The XPS measurements were performed on a Leybold-Hereaus EA-11 spectrometer using Mg K- (1253.6 eV) radiation at 15 kV and 20 mA. Figure 27.4 shows an XPS spectrum for LP-produced Mo2CAOv prepared from a Mo(CO)6 precursor. The particles were passivated by controlled surface oxidation in 5% oxygen/95% helium prior to its removal from the particle trap (see Figure 27.1(a)). 

P. Mela, A. van der Berg, Y. Fintschenko, E.B. Cummings, B.A. Simmons and B. J. Kirby, The zeta potential of cyclo-olefin polymer microchannels and its effects on insulative (electrodeless) dielectrophoresis particle trapping devices, Electrophoresis, 26 (2005) 1792-1799. 

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