David B. Rasche
Bio: David B. Rasche is an academic researcher from University of Paderborn. The author has contributed to research in topic(s): Particle & Speed of sound. The author has an hindex of 1, co-authored 2 publication(s) receiving 16 citation(s).
Topics: Particle, Speed of sound, Scanning mobility particle sizer, Particle-size distribution, Sound pressure
TL;DR: The fundamental design considerations for a hot wall reactor system able to produce oxide nanoparticles and it is found that applying electrical charges to the aerosol particles (in opposite polarity) can significantly foster aggregation.
Abstract: For gas phase nanoparticle production, hot wall reactors are widely used. In this article, we will describe the fundamental design considerations for a hot wall reactor system able to produce oxide nanoparticles. The system is outstanding in its ability to produce mostly spherical nanoparticles at particle sizes of up to 100 nm and even larger at mass outputs in the order of grams per hour by being able to rapidly quench the aerosol. While high production rates or larger particle sizes are already easily obtained with hot wall reactors, it is very challenging to produce these spherical particles at high mass rates. We will show in this research that the temperature and the particle number concentration are the major aspects influencing the particle morphology at the end of the process. Investigation on the performance of the setup shows good control over the temperature and the particle production stability. A representative particle characterization using SEM and scanning mobility particle sizer showed that particles are mostly spherical, while the particle size distribution had a geometric standard deviation close to 1.5. In addition to the aspects mentioned above, a possibility to manipulate the aggregation downstream of the reactor is to be presented as well. We found that applying electrical charges to the aerosol particles (in opposite polarity) can significantly foster aggregation.
TL;DR: An apparatus for the measurement of the speed of sound based on the pulse-echo technique is presented andspeed of sound data are presented with an uncertainty between 0.02% and 0.1%.
Abstract: An apparatus for the measurement of the speed of sound based on the pulse-echo technique is presented. It operates up to a temperature of 480 K and a pressure of 125 MPa. After referencing and validating the apparatus with water, it is applied to liquid ammonia between 230 and 410 K up to a pressure of 124 MPa. Speed of sound data are presented with an uncertainty between 0.02% and 0.1%.
Abstract: A measurement procedure using a modified two-chamber pulse-echo experimental setup is presented, enabling acoustic absorption and bulk viscosity (volume viscosity) measurements in liquids up to high temperature and pressure. Acoustic absorption measurements are particularly challenging, since other dissipative effects, such as diffraction at the acoustic source and at acoustic reflectors, are typically superimposed to the measurement effect. Acoustic field simulations are performed, allowing to investigate acoustic wave propagation qualitatively. The absorption coefficient is determined by evaluating the signal spectrum’s raw moments and applying a method to identify and correct systematic measurement deviations. Measurement uncertainties are estimated by a Monte Carlo method. In order to validate the present measurement procedure, the acoustic absorption in liquid methanol, n-hexane, n-octane, and n-decane is determined experimentally and compared to literature data. The measurement results for methanol are additionally validated by comparison to bulk viscosity data sampled with molecular dynamics simulation.
Abstract: A recent study published by the authors, where correlation methods are proposed to reproduce the density, vapour pressure, and viscosity of glycerol over wide ranges of temperature and pressure, here we present a similar methodology that was applied to the speed of sound in liquid glycerol. The speed of sound in liquid glycerol was calculated from the propagation time measured by using two 5 MHz ultrasonic transducers in through transmission mode, up to 20 MPa and at temperatures ranging from (303.15 to 373.15) K. The density, isothermal compressibility, and isobaric heat capacity were evaluated in the temperature range (298.15 to 348.15) K and pressures up to 100 MPa, from the measured speed of sound starting from the density and specific heat capacity data at 0.1 MPa available in literature, and using a computational method originally developed by Davis and Gordon. The derived density and speed of sound data made the molar compressibility calculation possible, from which a new method was developed for the speed of sound estimation for pressures up to 100 MPa. The proposed method provided speed of sound with high accuracy (AARD% = 0.2%).
01 Jan 2020
Abstract: Motivation One major issue in the realization of acoustic absorption measurement systems is the fact that the absorption caused by dissipative effects in the fluid, such as viscosity, is superimposed by other losses resulting from the sound propagation in the respective measurement system. Examples for these effects are the spreading of the acoustic signal caused by diffraction and unwanted transmission at acoustic reflectors or waveguide boundaries. Unwanted reflected signals from planar surfaces included in the measurement system for constructive reasons may also interfere with the measurement. In this contribution, we describe several measures, which aim to reduce systematic measurement deviation by decreasing or compensating the aforementioned effects.
••03 Oct 2019
Abstract: Of all fluid and solid properties, quantities that describe losses are among the most challenging to quantify. In part, this is due to superimposed dissipative mechanisms, such as diffraction effects from spatially limited sources. Inherent to all these phenomena, however, is a specific frequency dependence. The nature of the frequency dependence varies, resulting from the respective absorption mechanism. Pure fluids, for example, exhibit absorption of acoustic waves with quadratic frequency dependence. In solids, there are several absorption models that can be applied, each having different characteristics with respect to frequency. Other dissipative effects, such as diffraction, also show frequency dependence. In an approach using the raw moments of the signals from acoustic transmission measurements, a method to quantify absorption and dissipation phenomena with arbitrary frequency dependence is presented. The described method is applied to different absorption measurement problems. To verify that accurate results can be achieved under ideal conditions, the method is applied to signals generated using acoustic field simulation with different absorption models. To show its numerical stability, it is used qualitatively to evaluate the absorption of a fluid at different thermodynamic states.
Author's H-index: 1