The instability characteristics of a dielectric fluid layer heated from below under the influence of a uniform vertical alternating current (AC) electric field is analyzed for different types of electric potential (constant electric potential/ electric current), velocity (rigid/free) and temperature boundary conditions (constant temperature/heat flux or a mixed condition at the upper boundary). The resulting eigenvalue problem is solved numerically using the shooting method for various boundary conditions and the solution is also found in a simple closed form when the perturbation heat flux is zero at the boundaries. The possibility of a more precise control of electrothermal convection (ETC) through various boundary conditions is emphasized. The effect of increasing AC electric Rayleigh number is to hasten while that of Biot number is to delay the onset of ETC. The system is more stable for rigid-rigid boundaries when compared to rigid-free and least stable for free-free boundaries. The change of electric potential boundary condition at the upper boundary from constant electric potential to constant electric current is found to instill more stability on the system. Besides, increase in the AC electric Rayleigh number and the Biot number is to reduce the size of convection cells.
Analytical relations, describing the electrical fields of cylindrical piezoceramic radiators with circular polarization as a member of the cylindrical systems with the baffle in the inner cavity, using the related fields method in multiply connected regions were obtained. Comparative analysis of the results of numerical experiments performed on the frequency characteristics of the electric field of the radiating systems for different modes of radiation allow to establish a number of subtle effects of the formation of the electric field of radiators.
In this work, an electrically tunable long-period fiber grating (LPFG) coated with liquid crystal layer (LC) is presented. As a LC layer, a prototype low-birefringence 1550A LC mixture was chosen. As a LPFG host, two types of gratings were studied: the LPFGs based on a standard telecommunication fiber, produced by an electric arc technique with a period of 222 μm, and the LPFGs based on a boron co-doped fiber written by a UV technique with a period of 226.8 μm. The relatively short period of these gratings allowed exploiting unique sensing properties of the attenuation bands associated with modes close to the turn-around point. Experiments carried out showed that for the UV-induced LPFG with a LC layer, on the powered state the attenuation band could be offset from the attenuation band measured in the unpowered state by almost 130 nm. When the arc-induced LPFG was coated with the LC, the depth of the attenuation band could be efficiently controlled by applying an external E-field. Additionally, all experimental results obtained in this work were supported by the theoretical analysis based on a model developed with Optigrating v.4.2 software.
Due to rapid development of wireless systems and future implementation of the 5G system, it is necessary to increase number of the stations and/or number of radio emissions in current and new mobile service frequency bands. For each of the new or modified radio installation in Poland the Electromagnetic Field (EMF) strength levels has to be evaluated and measured/validated in accordance with allowable limits. In the paper the model of estimation of total EMF levels coming from mobile base stations radio emissions to be used for estimation of the whole country territory EMF levels is proposed. Results of preliminary analysis were also shown on practical examples. The model presented in the paper can be used for initial finding of possible places where exist the risk of exceedance of the maximum exposure limits and for analysis of potential radio network development taking into account current regulatory limits. The model will be used in computerized system SI2PEM which is developing in Poland for EMF levels controlling and validation purposes.
A comparative analysis of filtration performance of tangential and axial
inlet reverse-flow cyclone separators and vortex tube separators is
presented. The study showed that vortex tube separators are
characterized by a quality factor q several time higher
than tangential inlet reverse-flow cyclone separators. The cyclone
separators yield low separation efficiency and low filtration
performance at low air flow rates at low air volumes aspired by the
engine at low speed. One of the well-known and not commonly used methods
to improve separation efficiency is to apply electric field. An original
design of a vortex tube separator with insulators generating electric
field in the area of aerosol flow is presented. High voltage was applied
to the cyclone separator housing and its swirl vane. A special method
and test conditions were developed for cyclone separators with electric
field. Separation efficiency, filtration performance and pressure drop
across the cyclone separator in two different variants were determined.
The tests were carried out at five inlet velocity of cyclones υ0
= 1.75; 3.5; 7.0; 10.5; 14 m/s at an extraction rate of m0
= 10%, and at an average dust concentration in the inlet air of
s
= 1 g/m3. Using the electric field in the area of
a swirling aerosol stream resulted in an increase (over 12% – φc
= 96.3%) in separation efficiency at inlet velocity of cyclone ranging
from 1.75 to 3.5 m/s. An increase in separation efficiency at other
inlet velocity of cyclone is minor and does not exceed 3‒4%.