Vol 28, No 3 (2019)

The paper presents results of an experimental study of separation efficiency and distribution of flow parameters over the cross section of the distillation columns. The experiments were carried out on the large-scale research setup “Large Freon Column” with diameter of packing of 0.6 m and 0.9 m. The mixture of refrigerants R114 and R21 was used as the working liquid at a pressure of 3 bar in the column. Experimental data were obtained at uniform and nonuniform irrigation of the Mellapak 350.Y and Sulzer 500X structured packings by a controlled liquid distributor. The liquid distributor with independently controlled valves for each drip point was used for controlled packing irrigation. The newmethod for dynamically controlled irrigation of the packing by an operated liquid distributor is suggested. This method is aimed at the destruction of large-scale maldistribution areas (flows) inside the column and the achievement of higher separation efficiency through periodic irrigation of the entire packing or its individual areas under the liquid distributor. The use of dynamically controlled irrigation of the packing allows an increase in efficiency of mixture separation of up to 20%.

In this paper, a detailed investigation on MHD flow over a porous stretching sheet was conducted by taking power-law heat flux and heat source into account. Series solutions are achieved for the reduced nondimensional ordinary differential equations by admitting an analytical technique known as a homotopy analysis method (HAM). A precise way of convergence of series solutions is also furnished. The attained results of the present study are in excellent connection with the previous results. Nature of magnetic parameter, permeability parameter, radiation parameter, Prandtl number, Eckert number, heat generation parameter and suction/injection parameters on velocity, temperature, skin friction coefficient and Nusselt number are presented in tables and graphs.

The general solution to the radiation exchange problem in the zone method is given in the system of surfaces in the presence of nonparticipating medium for the model of specular-diffuse reflection and direct and diffuse transmission. The reflection indicatrix for all surfaces of the considered system of bodies is assumed as a superposition of diffuse and specular components of reflection, and the transmitted radiation for transparent materials—as a superposition of direct and diffuse transmission. The cornerstone of the offered approach is in obtaining the exchange radiation factors by the semi-analytical method by solving a system of linear algebraic equations that include specular exchange factors or diffuse configuration factors of radiation. This allows one to combine exact computational methods of diffuse reflection and diffuse transmission through diffuse configuration factors with methods of direct ray tracing for accounting of specular reflection and direct transmission. Solutions for all possible particular models of reflection and transmission are provided. The solution for diffuse transmission by the semi-analytical method is obtained for the first time. Results of the numerical experiments confirming accuracy and efficiency of the offered approach are given.

The evaporation and crystallization of a droplet and a thin layer of aqueous solutions of LiBr and LiCl salts on a heated wall with a temperature T_w = 86°C were studied experimentally. Crystallization curves were obtained for a wide range of initial salt concentrations. For the first time it was shown that for different C₀₁ values the crystallization rates J_cr were different; the J_cr curve was nonlinear. With C₀₁ decreasing, the supersaturation at the onset of crystallization increased, because of different induction times with respect to the generation of the first active crystallization center. It is known for relatively large crystals that heat transfer influences the rate of crystallization. Processing of the experimental data with due account of the basic thermophysical parameters shows that supersaturation also affects the crystal growth. The crystallization rate in a thin layer is significantly higher than in a droplet. It was found that description of crystallization in a droplet should take into account strong anisotropy of the crystallization.

A numerical modeling of a swirling turbulent jet in a coflowing stream was carried out. The flow description involved two second-order mathematical models. The first one includes the averaged equations of motion and the differential equations for transfer of normal Reynolds stresses and dissipation rate in the thin shear layer approximation. The second model relies on the far wake approximation. The distances from the source of the jet in the calculations reached very large values. At small distances, the calculated profiles of the averaged velocity components agree well with the known experimental data from Lavrent’ev Institute of Hydrodynamics SB RAS. At large distances from the source, the flow becomes close to the self-similar one, with degeneration laws and normalized profiles consistent with the known theoretical concepts of the dynamics of swirling turbulent jets in a coflowing stream. The problem of asymptotic behavior of a nonswirling turbulent jet in a coflowing stream was also considered. A self-similar solution based on numerical experiments was obtained.

Unsteady laminar slip flow along an infinite vertical plate with ramped plate temperature and concentration in the presence of thermal radiation and buoyancy is investigated. Approximated Navier–Stokes equation along with the energy and species equations are solved analytically by adopting the Laplace transform technique. The dependencies of the flow, heat and mass transfer characteristics on time (t), space (y) and nondimensional governing parameters, namely, slip (λ), radiation (R), buoyancy forces ratio (N), Prandtl number (Pr) and Schmidt number (Sc), are explored for both ramped and constant plate temperature and concentration conditions. The results show that radiation effect is appreciable at a lower range of R and found to be greater for the constant than that for the ramped condition. A strong flow near to the plate is generated by radiation and buoyancy effects, and accelerated by slip effect. Finally it is also shown logically and mathematically that in the absence of radiation and presence/absence of slip the flow should be brought to stationary flow when two buoyancies are opposite and equal in magnitude with equal solutal and thermal diffusions.