An Ultra-Fast TSP on a CNT Heating Layer for Unsteady Temperature and Heat Flux Measurements in Subsonic Flows

In this paper, the authors demonstrate the application of a modified Ru(phen)-based temperature-sensitive paint which was originally developed for the evaluation of unsteady aero-thermodynamic phenomena in high Mach number but short duration experiments. In the present work, the modified TSP with a temperature sensitivity of up to −5.6%/K was applied in a low Mach number long-duration test case in a low-pressure environment. For the demonstration of the paint’s performance, a flat plate with a mounted cylinder was set up in the High-Speed Cascade Wind Tunnel (HGK). The test case was designed to generate vortex shedding frequencies up to 4300 Hz which were sampled using a high-speed camera at 40 kHz frame rate to resolve unsteady surface temperature fields for potential heat-transfer estimations. The experiments were carried out at reduced ambient pressure of p∞ = 13.8 kPa for three inflow Mach numbers being Ma∞=[0.3;0.5;0.7]. In order to enable the resolution of very low temperature fluctuations down to the noise floor of 10−5 K with high spatial and temporal resolution, the flat plate model was equipped with a sprayable carbon nanotube (CNT) heating layer. This constellation, together with the thermal sensors incorporated in the model, allowed for the calculation of a quasi-heat-transfer coefficient from the surface temperature fields. Besides the results of the experiments, the paper highlights the properties of the modified TSP as well as the methodology.

Influence of Ultrasonic Waves on Current-Voltage Characteristics and Polarization Effects of Si-N-P Radiation Receivers

The currents of n-p junctions and polarization effects caused by the capture processes of diffusion Si-receivers (detectors) of radiation exposed by ultrasound have been analyzed in this work. It was found that there are local concentrations of impurity atoms with an effective size l>6μm30μm in Si-n-p radiation receivers. They determine the behavior of the signal amplitude in different intervals of electric and temperature fields. It was found that at Е>1500V/cm and T>168K, the efficiency of collecting nonequilibrium charge carriers significantly increases and doublets of spectral α-lines and “humps” disappear at the temperature dependences of the signal amplitude. The main physical processes and mechanisms that determine the appearance of the phenomenon of "polarization" of Si-n-p-detectors were investigated. This phenomenon is caused by the existence of local gold atoms, which arise in the process of manufacturing technology of Si-n-p-receivers and act as effective trapping centers.

Analysis of Thermal Performances in a Ventilated Room Using LBM-MRT: Effect of a Porous Separation

This article demonstrates the feasibility of porous separation on the performance of displacement ventilation in a rectangular enclosure. A jet of fresh air enters the cavity through an opening at the bottom of the left wall and exits through an opening at the top of the right wall. The porous separation is placed in the center of the cavity and its height varies between 0.2 and 0.8 with three values of thickness, 0.1, 0.2, and 0.3. The heat transfer rate was calculated for different intervals of Darcy (10−6 ≤ Da ≤ 10), Rayleigh (10 ≤ Ra ≤ 106), and Reynolds (50 ≤ Re ≤ 500) numbers. The momentum and the energy equations were solved by the lattice Boltzmann method with multiple relaxation times (LB-MRT). Schemes D2Q9 and D2Q5 were chosen for the velocity and temperature fields, respectively. For porous separation, the generalized Darcy–Brinkman–Forchheimer model was adopted. It is represented by a term added in the standard LB equations. For the dynamic domain, numerical simulations revealed complex flow structures depending on all control parameters. The results showed that the thermal field, mainly in the second compartment, is very dependent on the size and permeability of the porous separation. However, they have no influence on the transfer rate.

Effect of Heat Source Position in Fluid Flow, Heat Transfer and Entropy Generation in a Naturally Ventilated Room

In this study, a 3D numerical study of free ventilated room equipped with a discrete heat source was performed using the Finite Volume Method (FVM). To ensure good ventilation, two parallel openings were created in the room. A suction opening was located at the bottom of the left wall and another opening was located at the top of the opposite wall; the heat source was placed at various positions in order to compare the heating efficiency. The effects of Rayleigh number (103 ≤ Ra ≤ 106) for six heater positions was studied. The results focus on the impact of these parameters on the particle trajectories, temperature fields and on the heat transfer inside the room. It was found that the position of the heater has a dramatic effect on the behavior and topography of the flow in the room. When the heat source was placed on the wall with the suction opening, two antagonistic behaviors were recorded: an improvement in heat transfer of about 31.6%, compared to the other positions, and a low Rayleigh number against 22% attenuation for high Ra values was noted.

Induced magnetic field and viscous dissipation on flows of two immiscible fluids in a rectangular channel

The unsteady, magneto-hydrodynamic generalized Couette flows of two immiscible fluids in a rectangular channel with isothermal walls under the influence of an inclined magnetic field and an axial electric field have been investigated. Both fluids are considered electrically conducting and the solid boundaries are electrically insulated. Approximate analytical solutions for the velocity, induced magnetic, and temperature fields have been determined using the Laplace transform method along with the numerical Stehfest's algorithm for the inversion of the Laplace transforms. Also, for the nonlinear differential equation of energy, a numerical scheme based on the finite differences has been developed. A particular case has been numerically and graphically studied to show the evolution of the fluid velocity, induced magnetic field, and viscous dissipation in both flow regions.

A Special Extrusion-shear Manufacturing Method for Magnesium Alloy Rods Based on Finite Element Numerical Simulation and Experimental Verification

To research the influences of process parameters on a special extrusion-shearmanufacture method for magnesium alloy rods, deform-3d software with finite elementsimulations has been used to analyze the material flows of deformed magnesium alloysAZ31B during the extrusion-shear (ES) process, as well as the grain sizes anddistribution of extrusion loads, stresses and strains, and blank temperatures. Temperaturefields, stress fields, strain fields and temperature fields varying with different blankpreheating temperatures, extrusion speed and extrusion ratios were simulated. Influences ofdifferent extrusion conditions and different die structures on microstructures of rods prepared by ES process has been researched. Extrusion forces decrease with the increasing extrusion temperatures, decreasing extrusion ratios, increasing die channel angles and decreasing friction coefficients. The flow velocities of metal in the ES die increase with development of ES process. Increasing the channel angles and reducing the friction factors would increase the outflow velocities of metal, but it has little effect on the uniformity of metal flow. The increase in friction and extrusion speed would increase the temperatures of the ES die. The ES process can prepare finer and more uniform microstructures than those prepared by direct extrusion under the same conditions.

A Five Variable Refined Plate Theory For Thermal Buckling Analysis Uniform And Nonuniform Of Cross-Ply Laminated Plates

This research is devoted to investigating the thermal buckling analysis behaviour of laminated composite plates subjected to uniform and non-uniform temperature fields by applying an analytical model based on a refined plate theory (RPT) with five unknown independent variables. The theory accounts for the parabolic distribution of the transverse shear strains through the plate thickness and satisfies the zero-traction boundary condition on the surface without using shear correction factors; hence a shear correction factor is not required. The governing differential equations and associated boundary conditions are derived by using the virtual work principle and solved via Navier-type analytical procedure to obtain critical buckling temperature. Results are presented for: uniform and linear cross-ply lamination with symmetry and antisymmetric stacking, simply supported boundary condition, different aspect ratio (a/b), various orthogonality ratio (E1/E2), varying ratios of coefficient of uniform and linear thermal expansion (α2⁄α1), uniform and linearly varying temperature thickness ratio (a/h) and numbers of layers on thermal buckling of the laminated plate. It can be concluded that this theory gives good results compared to other theories.

Practical application of natural convective heat exchange of electrical equipment with air

This paper provides the physical and mathematical model of the air flow in a volume, containing electrical equipment with the heat-generating and heat-absorbing surfaces. The model predicts the temperature fields and air flow velocities across the volume. Using the developed model, we calculate the values of heat fluxes in the vicinity of the thermostated electrical equipment for three different cases: natural convective, forced and mixed modes of the airflow. The possibility of beneficial use of natural convective air flows for the transfer of thermal energy is analyzed. The results are applied in an industrial enterprise. Energy consumption for ventilation is significantly reduced.

CFD Study on the Air Temperature Field inside Fire-Rated Duct of Pressurisation System

Avoiding overheating of the supply air inside the fire-rated duct of pressurisation system is crucial for the escape and rescue of the building occupants during the development of a fire. The simulation scenarios are established concerning three cross-sectional dimensions of ducts and four inner air velocities. Based on the performance criteria of insulation specified in the international standard of ISO 834-1, the temperature fields of supply air inside different fire-rated ducts and corresponding safety are analysed based on the assumption that the exterior of fire-rated ducts is in a consistent state of being subjected to fire.

Determination of Thermomechanical Stresses in Elements of Vehicles’ Braking Systems

The main objective of the study was to develop a model and analyze the thermomechanical behavior of the hub material of the vehicle brake disk. The simulation strategy was based on the solution of the three-dimensional problem of the theory of elasticity for the case of effect of external loads and temperature fields on the metal structure element of the vehicle brakes. To solve this type of task of the theory of elasticity, the differential equations of the second order were used for the first time. Adaptation of the proposed model, completed in the article, has proved the correctness of use of these equations in modeling the thermomechanical processes with determination of stresses and displacements in unevenly heated rotary cylinders of the final length. The proposed method can be applied with high efficiency in stress strain state simulation of individual parts of vehicles.