Dual Solutions in Mixed Convection Flow Along Non-Isothermal Inclined Cylinder Containing Gyrotactic Microorganism

The purpose of this research is to present dual solution for combined free and forced convection flow towards a non-isothermal permeable inclined cylinder containing gyrotactic microorganism. Though several researches were done on dual solutions for mixed convection and also along the vertical cylinder for the numerous engineering applications but very few works have done on dual solutions for mixed convection with gyrotactic microorganisms. Two steps are performed here to carry out numerical calculations. Firstly, the governing partial differential equations are simplified into set of coupled non-linear ordinary differential equations using similarity transformations and then solved numerically using bvp4c function from MATLAB. Dual solutions are observed for heat, mass and density of motile microorganism transfer rate and also for velocity, temperature, concentration, and microorganism profile beyond a critical point. The research is reached to excellent argument by comparison in few cases between the results obtained from MATLAB and Maple algorithm. The heat, mass and motile microorganism transfer rate decreases from free to mixed convection regime and then increases to forced convection regime with the influence of different flow control parameters. The results also indicate that dual solutions for different flow profiles exist only in free convection dominated regime.

Thermal regime of the local working zone in the industrial premises under radiant heating conditions

The results of experimental studies on recording temperatures and heat fluxes for the local working zone in industrial premises under radiant heating conditions and supply and exhaust ventilation operation are presented. The characteristics are measured on the surface of the horizontal remote panel directly under the radiator and along the wall with the ventilation inlet. Experimental results show that mixed convection caused by the operation of air exchange systems leads to mixing of air masses and more intensive cooling of the horizontal panel surface, as well as air, compared to the natural convection regime.

A map of regimes of evaporation and boiling in the horizontal liquid layer on the modified surface

The paper presents the results of the study of the evaporation and boiling regimes in thin horizontal layers of liquid on a modified surface in a wide range of changes in the pressure and height of the liquid layer. Depending on the heat flux, pressure, and height of the liquid layer, the formation of various structures was observed. In this paper, maps of the evaporation and boiling regimes are obtained, which show the heat fluxes from the natural convection regime up to the boiling crisis, depending on the height of the liquid layer. The results are compared with the calculation dependencies.

ABOUT SPECIFIC FEATURES OF CONVECTION IN COMPRESSED GAS

Stability characteristics of static Rayleigh - Benard convection regime in a compressible, viscous and heat-conducting gas are investigated by means of numerical simulation. It is shown that, depending on the height of convection region and the magnitude of temperature gradient, various convection modes are realized - isobaric, adiabatic, and superadiabatic. The conditions under which convection develops at stable stratification are determined. A diagram of convection modes is plotted depending on the height of the region and the magnitude of temperature gradient.

ОБ УПРАВЛЕНИИ ИНТЕНСИВНОСТЬЮ КОНВЕКЦИИ ХИМИЧЕСКИ РЕАГИРУЮЩЕГО ГАЗА

A linear analysis of the stability of Rayleigh-Benard static regime convection is performed in a chemically reacting equilibrium hydrogen-oxygen gas mixture with added chemically inert microparticles of aluminum oxide. It is shown in the Boussinesq approach that a suitable choice of temperature can intensify convection and adding chemically inert microparticles can suppress convective motion. It is established that the isobaric convection regime is realized when the height of the region is less than the critical value, and when the height of the region exceeds this critical value, the convection regime is superadiabatic. During convection in the superadiabatic regime, its adiabatic suppression is observed. Within the framework of the isobaric convection regime, the limits of applicability of the Boussinesq approach are determined.

Convection of magnetic fluid in a closed hydrodynamic loop

Thermal convection of ferrofluid in a closed side-heated hydrodynamic loop is investigated experimentally when a nonuniform magnetic field is applied to the tube section near the electric heater. The nonuniform magnetic field with a strength of up to 24 kA/m is created by a permanent magnet of the “neodymium-iron-boron” type, equipped with ferrite pole pieces. For temperature measurements, miniature copper-constantan thermocouples are used. The temperature distribution along the circuit and temperature differences on both sides of the heater is measured. The tubes of the loop are cooled by a stream of thermostatic air which ensures a constant heat transfer coefficient at the outer surface of the tubes and an exponential temperature distribution along the circuit. The exponent determined in the experiments is used to provide information about the integral axial heat flux (Nusselt number). The experiments were performed with undecane in the ordinary gravitational convection regime and with medium concentrated magnetic fluid in the combined (gravitational and thermomagnetic) convection regime in the range of Rayleigh numbers 103–104. The estimation of the characteristic magnetic Rayleigh numbers was carried out taking into account the demagnetizing fields. For all modes, the dependence of the Nusselt number normalized to the heat transfer coefficient on the thermal Rayleigh number is plotted. It is shown that thermomagnetic convection increases the intensity of heat exchange by 4–6 times.

ESTIMATION OF THE CHANGE FROME HEIGHT OF THE VERTICAL AIR FLOW IN THE SURFACE LAYER OF THE ATMOSPHERE FOR A REGIME CLOSE TO THE ‘PURE CONVECTION’ REGIME

The purpose of this work is to analyze and concretize the asymptotic form of writing the continuity equation [3] for modeling thermo-physical processes in the surface layer of the atmosphere. In this case, the solution of the system of spatially one-dimensional equations of conservation laws for vertical dependences of air temperature and mass fraction of water vapor can be obtained in the future by using the calculated empirical dependences for the coefficient of turbulent exchange, based on the Monin-Obukhov “universal functions” approach.

Mixed Bioconvective Flow Over a Wedge in Porous Media Drenched with a Nanofluid

A mathematical model is accentuated the mixed bioconvective flow on a vertical wedge in a Darcy porous medium filled with a nanofluid containing both nanoparticles and gyrotactic microorganisms. Thermophoresis and Brownian motion impacts are addressed to consolidate energy and concentration equations with passivelycontrolled boundary conditions. A mixed convective parameter for the whole regime of the mixed convective is appointed. The system of governing partial differential equations is converted into a non-similar set, which are then solved by an implicit finite difference method. By taking the impacts of the varying pertinent parameters, namely, the bioconvection nanofluids and wedge angle parameters in the entire mixed convection regime, the numerical results are analyzed graphically for the dimensionless the velocity, temperature, nanoparticle volume fraction and the density motile microorganisms profiles as well as the local Nusselt and motile microorganism numbers.