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  • 1
    Electronic Resource
    Electronic Resource
    Charge synchronization for a piezoelectric droplet generator (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 2334-2339 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Improvements to an existing piezoelectric droplet generator are reported. This instrument produces monosize droplets from the periodic breakup of a liquid jet. Droplets tend to be closely spaced because of the method of generation, so increased separation is obtained by selectively charging and deflecting some of the droplets from the main stream to a drain. A phase-shifting circuit is used to synchronize the charging signal with droplet formation so that droplets are properly charged or discharged, as required. Originally, charge synchronization was obtained by controlling the amplitude of the piezoelectric transducer voltage and thus, altering the breakup length of the jet which was observed to lead to the production of satellite droplets or loss of control at large amplitudes. The present circuit avoids these problems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143930
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    A piezoelectric droplet generator for use in wind tunnels (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 3037-3046 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: This article describes a compact piezoelectric droplet generator. A unique feature of this instrument is the small size of its nozzle assembly which includes a cylindrical piezoelectric ceramic transducer, an interchangeable orifice, a charging ring, and deflection plates. The nozzle assembly is housed in an acrylic tube, 19 mm in outside diameter and 150 mm in length, which can be placed inside a wind tunnel without causing a significant blockage. The main mechanical components consist of a pressurized system which discharges liquid through the orifice to create a free liquid jet in the nozzle assembly. The transducer causes this jet to break up into uniform droplets by exciting the instability mechanism of symmetric varicose deformations. Droplets tend to be closely spaced because of this method of generation so increased separation is obtained by selectively charging and deflecting some of the droplets from the main stream to a drain. One droplet out of 1–9999 droplets can be selected to exit from the nozzle assembly. The electronic circuitry consists of a transducer driver, and circuits for charging and deflecting the droplets. Power metal-oxide-semiconductor field-effect transistors are used in an H bridge and a push-pull configuration to provide rapid operation of the transducer-driver and droplet-charging circuitry. A transient analysis is performed to obtain the gain factor between the applied voltage and the corresponding flow modulation of the liquid jet. This analysis provides operating characteristics of the transducer and may be used to calculate the breakup length of the jet for a typical applied voltage. Uniform droplets can be produced reliably with this instrument over a large range of size and speed. For the current research application, involving droplet drag in turbulent flows, droplets with diameters from 150 to 1000 μm are required at speeds from 3 to 20 m/s. For other studies, the range of size can be changed by using different orifices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142150
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Drag coefficients of spherical liquid droplets Part 1: Quiescent gaseous fields (1995)
    Springer
    Experiments in fluids 18 (1995), S. 258-264 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The drag coefficient of non-evaporating, spherical, liquid droplets in quiescent gaseous fields is measured using a novel experimental methodology at Reynolds numbers from 20 to 120. The experimental uncertainties are typically less than 8 percent, and the results are on average within 6 percent of the drag coefficient of liquid and rigid spheres, based on an accepted relationship. The methodology described in this article is therefore validated so it can be extended with confidence to measurements in turbulent gaseous fields.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195096
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Drag coefficients of spherical liquid droplets Part 2: Turbulent gaseous fields (1995)
    Springer
    Experiments in fluids 18 (1995), S. 265-276 
    Details
    ISSN: 1432-1114
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The drag of non-evaporating, spherical, liquid droplets was measured in turbulent flow fields at parametric ranges relevant to spray combustion, characterized by the droplet Reynolds number, and the intensity and spatial scales of turbulence. The experimental apparatus comprised a wind-tunnel and a piezo-electric droplet generator. The procedure was to inject water droplets of uniform size co-currently and continuously with vertical turbulent air flows while droplet velocity was measured at different elevations using laser-Doppler velocimetry. Turbulence was characterized using hot-wire anemometry prior to droplet injection. Drag coefficients were calculated using these main measurements and the law of conservation of mechanical energy. Reynolds numbers were investigated in the range 10–100, in terms of the equivalent spherical diameter of a droplet, and the mean relative speed between the ambient gaseous field and the droplets. Weber numbers were much less than unity so droplets were effectively spherical. Relative intensities of turbulence were investigated in the range 20–65 percent, in terms of the mean relative speed. Spatial scales of turbulence were large in comparison to the droplets; the ratio between the spatial integral scale and the droplet diameter was in the range 11–38, and the Kolmogorov scale was comparable in size or smaller than the droplet diameter. Experimental data showed that the drag in turbulent fields under these conditions is not significantly different than that of solid spheres in a quiescent field at the same Reynolds number.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00195097
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Transient deformation of freely-suspended liquid droplets in electrostatic fields (1991)
    Hoboken, NJ : Wiley-Blackwell
    AIChE Journal 37 (1991), S. 1305-1317 
    Details
    ISSN: 0001-1541
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The problem of freely-suspended liquid droplets deforming due to an applied electrostatic field is examined. Developed is a numerical model capable of predicting the complete transient histories of droplets in systems with a wide range of dispersedand continuous-phase densities, viscosities, relative permittivities, and electric field strengths. For liquid/gas systems, the predictions of the numerical model demonstrated that the critical field strength and critical permittivity ratio during actual transient breakup are not necessarily the same as those predicted by steady-state theories. An approximate analytical model of transient droplet deformation is also developed, which is able to predict the deformation time histories for large Ohnesorge number, small-deformation liquid/liquid systems. The approximate analytical model agreed well with the results of the complete numerical model.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/aic.690370904
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    Paper (German National Licenses)
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