Search

Electromagnetic (EM) heat exchangers (HX) are systems that convert EM energy into heat or mechanical work. One potential design consists of a porous lossy ceramic material heated by EM waves with a compressible gas coolant. EM heating of ceramics is nonlinear, since the loss factor is temperature dependent. Designing such EM HXs requires an understanding of coupling between temperature, the electric field, and gas dynamics at the pore scale. To mimic this microscale phenomenon, a single channel with a high-speed gas coolant in perfect thermal contact with a thin solid ceramic layer is considered, with an applied plane-wave electric field propagating normal to the channel walls. From a thin-domain asymptotic analysis, the conservation laws reduce to a Rayleigh flow in the gas coupled with averaged thermal energy conservation equations at leading order. The model predicts that the kinetic energy of the gas increases up to 12.5 times the inlet value when thermal runaway occurs in the ceramic region for the cases considered, and thermal choking is possible when the coolant reaches the sonic state. Local maxima of efficiency occur on a discrete set of ceramic thicknesses that correspond to Fabry–Bragg resonances of the electric field. [ABSTRACT FROM AUTHOR]

A systematic-study is conducted using an innovative technology for paper drying by applying ultrasound mechanism. The advantages include greater energy efficiency, lower drying time and temperature, improvement of the product quality, and it is considered a green technology. The effects of initial moisture content, thickness, and refining condition are studied for different types of pulps (hardwood and softwood) using 23 factorial design of experiments. Analysis of Variance show that in the range of the studied parameters, thickness has the maximum effect on ultrasonic drying time followed by the initial moisture content. In addition, using a linear regression model, a relationships for the total time of drying is provided. The results confirmed that ultrasonic drying is more efficient at higher moisture content and higher thickness of the sample. These results are related to the structural characteristic of the samples such as porosity, pore distribution, and surface roughness. [ABSTRACT FROM AUTHOR]

Electromagnetic heating is the process where a composite material absorbs applied electromagnetic radiation and converts this energy to internal energy in the material. While homogenization models for electromagnetic heating have been around for decades, these approaches break down when the wavelength of the electromagnetic wave is comparable to the characteristic microscale length. Here we derive from Maxwell's equations and the energy equation effective equations for a binary composite in the case where the characteristic microscale length and wavelength are compa- rable. Under the assumption of small loss factors in the materials, high-frequency homogenization results in a locally temperature dependent elliptic problem for the field amplitude via Floquet--Bloch theory. The length scale for thermal transport is the macroscale, and classical homogenization applies. We characterize the results in terms of a complex wavenumber for propagation, and validate our results for a lamellar structure for which an exact solution exists under isothermal conditions, and characterize field strength needed to achieve thermal runaway in the composite as a function of the resonant frequency and volume fraction of the lossless material. [ABSTRACT FROM AUTHOR]

The compressible flow between a slider and a moving rough surface is examined asymptotically and numerically in the limit of very small gap height. The roughness is assumed to consist of a well-defined periodic pattern of grooves whose amplitude and wavelength are of the order of the gap height. A two-scale homogenization analysis is employed to determine a non-linear elliptic partial differential equation governing the leading order pressure in the gap on the scale of the slider. The equation involves coefficient functions that are determined numerically by averaging Stokes flows on the scale of the patterned roughness. Numerical results are obtained for the cases of transverse and longitudinal roughness for both no-slip and slip-flow boundary conditions, and for the limiting case of large bearing number. Comments and a brief analysis are given on the reduction of the governing equation for pressure in the conventional limit of long wavelength of the surface roughness. [ABSTRACT FROM AUTHOR]

An integrated set of courses, or Integrated Course Block (ICB), developed for incoming first-year students at the Franklin W. Olin College of Engineering, is presented. Bound by a common theme of 'Kinetic Sculptures', the individual courses in this ICB are mathematics (single variable calculus and ordinary differential equations), physics (kinetics and dynamics of linear and rotational motion, thermodynamics and fluids), and an open-ended engineering project. The project part of the ICB allows students to explore the motion through the design of kinetic (moving) sculptures while utilizing the mathematics and physics concepts learned in the accompanying courses. This paper considers the 'Kinetic Sculptures' ICB from the pedagogical and epistemological points of view by presenting its implementation and discussing the results and analysis of three student surveys taken during three semesters, and seven semesters after participating in the ICB. [ABSTRACT FROM AUTHOR]

We present the linear stability of the laminar flow of an immiscible system of a compressible gas and incompressible liquid separated by an interface with large surface tension in a thin inclined channel. The flow is driven by an applied pressure drop and gravity. Following the air–water case, which is found in a variety of engineering systems, the ratio of the characteristic values of the gas and liquid densities and viscosities are assumed to be disparate. Under the lubrication approximation, and assuming ideal gas behaviour and isothermal conditions, this approach leads to a coupled non-linear system of partial differential equations describing the evolution of the interface between the gas and the liquid and the streamwise density distribution of the gas. This system also includes the effects of viscosity stratification, inertia, shear and capillarity. A linear stability analysis that allows for physically relevant non-zero pressure-drop base state is then performed. In contrast to the zero-pressure drop case which is amenable to the classical normal-mode approach, this configuration requires numerically solving a boundary-value problem for the gas density and interfacial deviations from the base state in the streamwise coordinate. We find that the effect of the gas compressibility on the interfacial stability in the limit of vanishingly small wavenumber is destabilizing, even for Stokes flow in the liquid. However, for finite wavenumber disturbances, compressibility may have stabilizing effects. In this regime, sufficient shear is required to destabilize the flow. [ABSTRACT FROM PUBLISHER]

An important class of electrokinetic, microfluidic devices aims to pump and control electrolyte working liquids that have spatial gradients in conductivity. These high-gradient flows can become unstable under the application of a sufficiently strong electric field. In many of these designs, flow channels are thin in the direction orthogonal to the main flow and the conductivity gradient. Viscous stresses due to the presence of these walls introduce a stabilizing force that plays a major role in determining the overall instability. A thin channel model for fluid flow is developed and shown to provide good agreement with a complete three-dimensional model for channel aspect ratios ≲0.1. [ABSTRACT FROM AUTHOR]

Objective: The purpose of the present study is to investigate the inactivation of bioaerosols containing Bovine Coronavirus, BCoV, under repetitively pulsed radio frequency (RF) electromagnetic exposure., Methods: These experiments were performed in a waveguide containing a flowing aerosol stream and were limited to a single RF waveform: ∼2 μs square envelope, 5.6 GHz, 4.8 kHz repetition rate. Aerosol streams were exposed to RF electric field amplitudes in the range of 41.9 +/-6.2 kV/m. Under laminar flow conditions, 75% of the total collected aerosol stream spends 0.85 seconds or less in the RF exposure region., Results: Application of the RF waveform changed mean survival rate of the aerosolized BCoV by -0.58 decades (roughly a 74% reduction) and impacted the variance and standard deviation of the experimental results, with the RF exposure data showing an 800% increase in variance and 196% increase in standard deviation over the control results. Experimental results were compared to those from an analytic electromagnetic-heating inactivation model., Conclusion: The comparison indicated the feasibility that the observed reduction in BCoV survival rate might be due to a combination of thermal effects and non-thermal electric field effects., Significance: Developing better insight into the mechanisms of inactivation is important for understanding the potential limits of efficacy for this method. Additionally, these results contribute an important baseline for the impact of electromagnetic fields on aerosolized pathogens.