Search

We propose a new method for calculating the processes of melting and solidification of heat-accumulating materials placed inside small-sized elastic capsules of symmetric form. The specific feature of the method is the simultaneous solution of the heat conduction equation joined for both phases and the equation for the rate of change in the mass fraction of the new phase in the layer between two neighboring nodes of a stationary computational mesh. The method permits using explicit finite-difference schemes for continuous calculations of the nonlinear heat conduction equation without loss of stability at weak and alternating external heat flows, as well as in the presence of several phase transition zones in the capsule. The paper presents the results of a test solution of the two-phase Stefan problem for an unbounded plate and the results of calculations for spherical capsules with n-paraffin in one regenerative convective heat cycle.

Waveguide methods for determining the magnetic properties of magnetic liquids are proposed. The methods are based on the use of the results of measurements of the position and value of the extrema of the experimental dependence of the reflection coefficient of a wave from a layer of the material.

UDC 621.365 The conditions of nonreflective absorption of an electromagnetic wave in its incidence, at an angle, on a plane layer of absorbing magnetic applied to a metal substrate are found. The dependences of these conditions on the angle of incidence of the wave, the thickness of the layer, and the magnetic properties of the coating material are investigated. The possibility of separating a prescribed polarization component of the incident radiation with the use of the phenomenon of nonreflective wave absorption in the magnetic–metal system is considered.

The conditions of nonreflective passage of an electromagnetic wave on its incidence at an angle on a plane layer of an absorbing dielectric applied to an infinitely thick nonabsorbing backing have been found. Their dependences on the coating layer thickness, angle of wave incidence, and on the dielectric properties of the backing and coating materials are investigated.

Conditions for reflectionless quenching of electromagnetic radiation in the layer of absorbing dielectric applied to a nonabsorptive quarter-wave substrate have been found. These conditions as functions of the layer thickness and the dielectric properties of the coating and the substrate are investigated.

The conditions for occurrence of total reflectionless absorption of electromagnetic waves in a layer of magnetic material applied to a metal substrate have been found. Their dependence on the layer thickness and the magnetic properties of the coating has been investigated. The frequency band within which this phenomenon can exist has been determined.

Equations are obtained which give a unique functional relation between the required magnetic properties of a liquid magnetic material and the informative parameters on the position and value of the extrema of the experimental dependence of the reflected signal on the thickness of the layer of material. Various methods and algorithms for solving them are considered, taking the degree of attenuation of the wave in the material into account.

Investigations of dielectric properties of solutions of methyl ethyl ketone and methyl isobutyl ketone in n-heptane in a microwave range established the existence, in these solutions, of a spectrum of concentrations and thicknesses of the solution layer at which resonant reflectionless radiation absorption originates.

A method of measuring the dielectric properties of weakly absorbing liquids in the microwave band is proposed. The method is based on analyzing the standing-wave field for thicknesses of the liquid layers for which the conditions for total nonreflecting absorption of the incident radiation to occur in the layer of material, or conditions close to this, are satisfied.

The authors investigate the dependence of the selective absorption band of electromagnetic radiation in a two-layer dielectric-metal system on the dielectric properties and thickness of a coating near wavelengths at which in the system total absorption of incident radiation develops. The narrowing of the absorption band of this system due to an increase in the thickness of a coating material and in its refraction index is established.

A method is proposed for measuring the dielectric constant e′ and dielectric loss e″ of high-absorption dielectric materials by measuring the reflection of electromagnetic radiation with the aid of an adjustable quarter-wave matching plate of nonabsorbing material close to the dielectric surface.

An investigation is made of the conditions of occurrence of reflectionless absorption of electromagnetic radiation in a layer of polar mixtures deposited onto a reflecting metallic matrix.

Owing to the use of nomograms the above method is universal and rapid. It is independent of the frequency at which the values of e′ and e″ are measured, and it is equally applicable for measuring dielectric parameters of polar liquids which are highly absorbent at ultrahigh frequencies and have one or two clearly expressed minima in the relationship of η tol, and for liquids with low dielectric losses in the uhf range, whose measurement with adequate precision is difficult by other methods. Among the deficiencies of the suggested method one should note the two values obtained for λd and tan Δ/2 from the nomogram readings. However, this deficiency can easlly eliminated either by comparing the two values for λd and tan Δ/2 with those obtained for them from a similar nomogram and the second minimum in the relationship of η tol, or by an approximate evaluation of λd and tan Δ/2 by means of any other less precise measuring method.