INFRARED DEHYDRATION OF BLANCHED QUINCE SLICES: STUDY ON PROCESS AND MASS TRANSFER CHARACTERISTICS

In the present work, moisture removal characteristics of quince slices in a convective tray dryer were studied. The blanched slices (with thicknesses of 3, 5 and 7 mm) were dried at drying temperatures of 50, 60 and 70 °C and air flow rates of 1, 1.5 and 2 m/s. The analytical model proposed by Dincer and Dost was used to determine the mass transfer parameters. The obtained Biot numbers (0.108‒0.293) revealed that both the internal and external resistance control the moisture diffusion within the samples. The moisture diffusivity and convective mass transfer coefficient were found to be in the ranges of 1.578×10-7‒7.331×10-7 m2/s and 2.040×10-5‒3.507×10-5 m/s, respectively. The activation energies for moisture diffusion and surface mass evaporation were determined to be in the ranges of 17.607 to 48.019 kJ/mol and 5.270 to 27.430 kJ/mol, respectively.

Transition region adaptive conduction (TRAC) in multidimensional magnetohydrodynamic simulations

Context. In solar physics, a severe numerical challenge for modern simulations is properly representing a transition region between the million-degree hot corona and a much cooler plasma of about 10 000 K (e.g., the upper chromosphere or a prominence). In previous 1D hydrodynamic simulations, the transition region adaptive conduction (TRAC) method has been proven to capture aspects better that are related to mass evaporation and energy exchange. Aims. We aim to extend this method to fully multidimensional magnetohydrodynamic (MHD) settings, as required for any realistic application in the solar atmosphere. Because modern MHD simulation tools efficiently exploit parallel supercomputers and can handle automated grid refinement, we design strategies for any-dimensional block grid-adaptive MHD simulations. Methods. We propose two different strategies and demonstrate their working with our open-source MPI-AMRVAC code. We benchmark both strategies on 2D prominence formation based on the evaporation–condensation scenario, where chromospheric plasma is evaporated through the transition region and then is collected and ultimately condenses in the corona. Results. A field-line-based TRACL method and a block-based TRACB method are introduced and compared in block grid-adaptive 2D MHD simulations. Both methods yield similar results and are shown to satisfactorily correct the underestimated chromospheric evaporation, which comes from a poor spatial resolution in the transition region. Conclusions. Because fully resolving the transition region in multidimensional MHD settings is virtually impossible, TRACB or TRACL methods will be needed in any 2D or 3D simulations involving transition region physics.

Влияние концентрации капель воды в аэрозольном облаке на скорости их испарения

The results of experimental studies of the integral characteristics of the water droplets evaporation in aerosol cloud are presented. Variable parameters: initial radius of droplets 0.1–0.25 mm, temperature of combustion products 573–873 K, concentration of water droplets 0.03–0.1 l /m3. The ranges of variation of the water mass evaporation rate are determined depending on the concentration of droplets in the aerosol cloud and their initial sizes. Approximation expressions for the established dependencies are obtained. For the first time, an approach was proposed to determine the evaporation rate of aerosol droplets taking into account the known/calculated values of the evaporation rate of a single drop.

Effect of mass evaporation on measurement of liquid density of Ni-based superalloys using ground and space levitation techniques

Loss of mass due to evaporation during molten metal levitation processing significantly influences the evaluation of density, viscosity and surface tension during thermophysical property measurement. Since there is no direct way to track the evaporation rate during the process, this paper describes a mathematical approach to track mass loss and quantify any changes in alloy composition as a function of time and temperature. The Ni-based super alloy CMSX-4 Plus (SLS) was investigated and a model was developed to predict the dynamic loss of mass with time and track the potential for composition shifts throughout each thermal cycle based on the Langmuir’s equation for ideal solution behavior. Results were verified by post-test chemical analysis of key elemental constituents including Al, Cr, Ti, and Co where the error in composition for each element was less than 1% when the activity of aluminum in solution was fixed at zero – effectively eliminating evaporation of aluminum for ground-based electrostatic levitation (ESL) testing in vacuum. This model predicts the mass evaporation for Al and Co within ±6 % errors for CMSX-4 plus samples processed in ESL. Application of this technique to the space tests using the ESA ISS-EML facility shows that by conducting experiments in an inert shielding-gas environment, composition shifts due to differential relative evaporation become negligible and the composition is maintained within the desired limits. By tracking overall mass loss during testing the influence of evaporation on density measurements is discussed.

MATHEMATICAL MODELING OF A NEW METHOD OF THERMAL PROTECTION BASED ON THE INJECTION OF SPECIAL COOLANTS

A closed mathematical model of heat and mass transfer under the non-isothermal filtration through the organized pores of coolants with a strong dependence of dynamic viscosity on temperature with further injection into a viscous gas-dynamic flotation with the formation of liquid film and evaporation under the influence of aerodynamic heat flows has been developed. The aim of the paper is to develop the physical and mathematical basis of thermal protection with the automatic supply of coolant having a strong dependence of dynamic viscosity on temperature (by 3–5 orders of magnitude when the temperature changes by 200–2500°C). Such thermal protection system allows for operating without the mass removal that preserves the geometry of the structural elements at the intensive heating, which is very relevant. To achieve this goal, a mathematical model of the automatic coolant supply with filtration through the organized pores, injection into a high-temperature gasdynamic boundary layer with the formation of the protective liquid film and evaporation is formulated. The results with respect to the mass flow rate of the coolant, the mass evaporation rate of the formed liquid film and the temperatures of the structure which in all cases remain below the evaporation temperature of the cooler have been obtained.

Thermal protection of aircraft units using film cooling with regard to unsteady heat conductivity

A simplified physical and mathematical model of combined thermal conductivity and filtering of a cooler with a strong dependence of dynamic viscosity on temperature during film cooling of bodies was developed. The model takes into account the inflow of the cooler into the gas-dynamic boundary layer and the evaporation of the resulting protective film of the cooler. Analytical solutions are obtained for the mass evaporation rate, the rate of non-isothermal filtration, and the temperature distribution in the body, taking into account filtration. The resulting relationships are calculated by iterative methods. Analytical solution of the problem permitted us to clearly establish the functional relationship of all the defining characteristics of the system for automatic cooling of bodies.

Mathematical modeling of processes of heat and mass transfer during drying of wood biomass

For the first time, a mathematical model for the drying of woody biomass during conductive heating with localization of the evaporation front has been formulated. The processes of moisture removal during the filtration of steam through the porous structure of the material at an ambient temperature of Te = 373 K were considered. Humidity was varied (in the range from 6% to 40%) and dimensions of wood blanks (Rd = 0.0035 - 0.035 m). Based on the results of numerical simulation, the conditions and characteristics (evaporation rate Wisp, drying time τ dry) of the process of moisture removal from wood biomass are determined. The mathematical model allows to calculate the drying time, as well as the mass evaporation rate for different sizes of wood sample, humidity and temperature conditions.

Revealing the Location of the Mixing Layer in a Hot Bubble

The fast stellar winds can blow bubbles in the circumstellar material ejected from previous phases of stellar evolution. These are found at different scales, from planetary nebulae (PNe) around stars evolving to the white dwarf stage, to Wolf-Rayet (WR) bubbles and up to large-scale bubbles around massive star clusters. In all cases, the fast stellar wind is shock-heated and a hot bubble is produced. Processes of mass evaporation and mixing of nebular material and heat conduction occurring at the mixing layer between the hot bubble and the optical nebula are key to determine the thermal structure of these bubbles and their evolution. In this contribution we review our current understanding of the X-ray observations of hot bubbles in PNe and present the first spatially-resolved study of a mixing layer in a PN.