Journal of Engineering Thermophysics最新文献

Single-phase heat transfer from a vertical titanium plate with area of 140 mm² to a water droplet flow (spray) normal to the surface of the heat exchanger was studied experimentally. Two models of commercial hydraulic full-cone nozzles with different characteristics of flow and spray pattern were used, the average mass flow rate being 2.4 kg/m²s to 6.46 kg/m²s. The maximum heat flux density of the heater was 204 kW/m². The area-averaged heat transfer coefficient was found to be highly dependent on the mass flow rate of the coolant. The average droplet diameter and the outflow velocity from nozzle openings appear to have secondary influence on single-phase heat transfer.

The paper focuses on computational and experimental studies of processing ash residues from an incineration plant (IP). To prevent environmental contamination, it is required to melt IP ash and slag to obtain a useful product with neutral properties. Combined heating of ash and slag is proposed, and the time for melting of dispersed particles of silicon dioxide ((alpha) quartz) under the action of arc plasma and resistive heating is calculated.

The paper presents the results of a study of oxidation of bulk bismuth samples by oxygen, water vapor, and water-oxygen fluid in a reactor heated to 873 K at a rate of 1 K/min with high-density reagents ((rho_{{rm O_{2}}}le0.62) and (rho_{{rm H_{2}O}}le5.24) mol/dm³). The results include temperature dependences of the pressure of the reaction mixtures. The rate of oxygen consumption is found from these dependences through the Redlich–Kwong equation of state. Formation of dense oxide film during the oxidation of bismuth in the O₂ environment was shown. No oxide formation was detected during treatment of bismuth with water vapor. The combined action of O₂ and H₂O molecules enhances the oxidation of bismuth and leads to formation of oxides of different compositions and morphologies. At (T>720) K, the bismuth oxidation rate was observed to increase due to the higher pressure of saturated bismuth vapor.

The paper presents the implementation of a user-defined function (UDF) for the Navier boundary condition in the Fluent software package. The study focuses on a microchannel with a laminar steady flow and a bubble structure on one of the surfaces. The influence of velocity and gradient components on the flow near the boundary is investigated. The numerical solutions obtained in a 2D formulation were verified and compared with experimental data from the literature.

In this study, a mathematical model of the dual suction compressor which can be applied to the household temperature and humidity independent control air conditioning system was established. The parameters of R410A were calculated with the help of REFPROP. The power consumptions of the dual suction compressor at different frequencies were calculated at different evaporation and condensing temperatures. Comparing with the experimental data, relative errors within (pm10)% between the simulated and experimental values of compressor power consumption occurred under various conditions, suggesting that the accuracy of the established energy consumption model met the requirements of engineering application. With the established model, the influence of different evaporation and condensing temperatures on the compressor power consumption and energy efficiency were simulated. The results showed that when keeping the evaporation temperature and condensing temperature of the LT side as a constant, the compressor power consumption decreased by 3.2% with each 1°C increment of the average evaporation temperature of the HT side. On the other hand, when the HT side evaporation temperature and condensing temperature was maintained as a constant, increased by 10% and the compressor power consumption decreased by 1.7% with each 1°C increment of the average LT side evaporation temperature. The verified model can be applied to guide the optimization of evaporation and condensing temperatures in the future practical application of dual suction compressor in temperature and humidity independent control air conditioning system.

An unsteady MHD-free convection heat-mass transfer from a viscous, incompressible fluid flow past an infinite vertical moving plate is studied here. The fluid is considered to be electrically conducting and chemically reacting. We consider three types of plate movements: uniform velocity, uniform acceleration, and periodic acceleration. Ramped as well as constant conditions at the plate for both temperature and concentration are considered. We obtain the exact solutions of the governing equations using the method of the Laplace transform technique. The impact of the type of thermal and concentration boundary condition (constant/ramped) at the plate as well as the kind of plate movement on the flow, heat and mass transfer characteristics, are presented and analyzed here. While doing so, we also consider the variation of our governing parameters: thermal and solutal Grashof numbers, magnetic field intensity, radiation ((R)), chemical reaction ((Kc)), Prandtl number and Schmidt numbers. It is observed that the presence of buoyancy and other forces close to the plate can be almost nullified due to the imposition of a strong transverse magnetic field. The viscous drag at the plate diminishes (and increases) with the increase of the strength of the applied magnetic field (and (R) and (Kc)). The rate of increment of skin friction with respect to time is more for the case of periodic oscillating plate movement. The magnitude of viscous drag is reported as more significant for the constant case compared to the ramped case.

Detailed experimental data on the kinematic characteristics of the flow in a vortex tube along its entire length are presented and analyzed. Experimental data obtained in a vortex tube with square cross-section of the working channel were compared at three values of the cold mass fraction: 0.4, 0.5, and 0.75 with the air expansion ratio in the apparatus of (pi=5). The behavior of standard deviations from the mean values of velocity components is analyzed. The noticeable peaks in the percentage of standard deviation from the longitudinal mean velocity component are observed in the area of the near wall flow temperature growth along the tube.

The flow in the far planar momentumless turbulent wake in a passively stratified medium is investigated with the use of a mathematical model that includes, along with the averaged equation for transfer of the longitudinal component of velocity, the differential equations for balance of the turbulence energy (e), transfer of its dissipation rate (varepsilon), fluid density defect (langlerho_{1}rangle), shear turbulent stress (langle{u}'{v}'rangle), and vertical component of the mass flux vector (langle v'rho'rangle) in the far wake approximation. Algebraic truncation of the last two equations leads to the known gradient relations for the shear turbulent stress and the vertical component of the mass flux vector. It has been established that with a certain limitation on the values of the empirical constants of the mathematical model and with a time scale growth law consistent with the mathematical model, these relations are joint differential constraints of the model. It has been found that the local equilibrium approximation for the shear turbulent stress is equivalent to the equality to zero of the Poisson bracket for dimensionless values of the turbulent viscosity coefficient and the defect of the longitudinal velocity component. It has been obtained that the local equilibrium approximation for the vertical component of the mass flux vector is equivalent to the equality to zero of the Poisson bracket for dimensionless values of the turbulent diffusion coefficient and mean density. Results of numerical experiments illustrating the theoretical results are presented.

A method for activated carbon production from pine nut shells by pyrolysis technology followed by steam-gas activation is considered. The process of thermal decomposition of sample in an inert environment was studied; the main stages of the process were identified; the residual mass was determined. The iodine adsorption activity, total pore volume, mass fraction of moisture, mass fraction of ash, and specific surface area were found. The experiments have shown that the production technology is efficient and the raw material is promising for activated carbon production.

This article studies the flow of Ostwald–de Waele ternary nanofluid over a permeable shrinking sheet. The governing partial differential equations are converted into ordinary differential equations using similarity variables and solved analytically. The article includes closed-form algebraic solutions and graphical flow dynamics analysis, dependent on Darcy number, volume fraction, and mass transpiration. The study shows that the presence of porous media significantly upsurges the mass transpiration and magnitude of skin friction. The calculation uses a combination of Titanium dioxide (TiO₂), Cobalt ferrite (CoFe(_{2}O_{4})), and Magnesium oxide (MgO) nanoparticles in pure water, and the ternary nanofluid performs better than the conventional fluid in terms of thermal conductivity. This is important in the fields of manufacturing, machine operations, and engineering, where improving heat transfer is crucial.