HEAT TRANSFER FROM THE COLD WALL OF A SQUARE CAVITY TO THE HOT ONE BY OSCILLATORY NATURAL CONVECTION

ABSTRACT

The periodic natural convection in an inclined square enclosure is studied numerically. One of the cavity sides is maintained at a constant temperature, and the temperature of the opposite wall is varied by the sine law. The mean value of this temperature in a period was lower than the given constant temperature. The other two walls of the enclosure were adiabatic. The system of Navier–Stokes Equations in Boussinesq approximation is solved numerically by the control-volume method with the SIMPLER algorithm. Solutions are obtained for Grashof number equal to 5 × 10⁵ and Prandtl number equal to unity in a wide range of oscillation frequency variation. The heat transfer dependency on oscillation frequency is studied for different values of inclination angle. It is found that there is a possibility of heat transferring from the colder wall to the hotter one in the whole range of problem parameters. The possible causes of such a phenomenon are analyzed.     

Specific Features of the Electrochemical Capacitance–Voltage Profiling of GaAs LED and pHEMT Structures with Quantum-Confined Regions

GaAs light-emitting (LED) and HEMT structures with δ-doped regions, InGaAs/GaAs quantum wells, and surface layers of InAs/GaAs quantum dots were studied by means of the electrochemical capacitance- voltage profiling technique. The concentration depth profiles of free charge carriers were obtained. Charges accumulated in quantum wells and quantum dots, as well as the doping levels of the emitter and δ layers were determined. The band structure and free carrier density distribution over the depth of the samples with different quantum well geometry were simulated. The specific features of electrochemical capacitance- voltage profiling in different heterostructure types are analyzed. A method of integration of capacitance- voltage curves at each etching stage was suggested. This method provides the efficient separation of responses from closely located layers, particularly the quantum well and δ layer.     

Formation of nitromethane under γ-Ray irradiation of nitrate-acetate aqueous solutions

Radiation-chemical transformations of nitrate-acetate aqueous solutions simulating LRW that are disposed of in underground reservoir beds were studied. It was found that the degradation of acetic and nitric acids and their salts is accompanied by formation of nitromethane. The dependences of nitromethane and nitrite accumulation and of nitrate decomposition on the absorbed dose were determined.     

Radiolysis Products of Nitrate-Acetate Aqueous Solutions and Their Influence on pH of the Solutions

The influence of the components of nitrate-acetate aqueous solution and products of their radiolysis on pH of the solutions was experimentally studied in a wide dose range. The results can be used to estimate the speciation and migration conditions of radionuclides in a reservoir bed of underground disposed sites of liquid radioactive waste.     

Hybrid neural network for the adjustment of fuzzy systems when simulating tests of internal combustion engines

The use of a hybrid neural network for automatic formulation of fuzzy control rules is considered, in the testing of internal combustion engines. The topology of this network is determined. On the basis of the resulting fuzzy rules, the quality of combustion-engine control is assessed.     

Nondestructive diagnostics of nanoheterostructures with InGaN/GaN multiple quantum wells by thermal admittance spectroscopy

On the basis of the designed complex of low-temperature admittance spectroscopy, the electron spectrum of semiconductor light emitting diode (LED) heterostructures with InGaN/GaN multiple quantum wells was investigated. The features of the construction of the measuring complex, as well as the technique of measurements of semiconductor nanoheterostructures and processing of admittance spectra, are presented.     

Application of density functional method to problem of creating hydrogen adsorption fuel cell

Local density profiles of molecular hydrogen adsorbed at 20.3 K in a plane-parallel pore of graphite adsorbent have been calculated using the method of density functional. It is shown that the optimum hydrogen storage is ensured by porous graphite structures with the pore width corresponding to five to six removed graphene layers.