Numerical Simulation of Solid and Porous Fins’ Impact on Heat Transfer Performance in a Differentially Heated Chamber

The development of different industrial fields, including mechanical and power engineering and electronics, demands the augmentation of heat transfer in engineering devices. Such enhancement can be achieved by adding extended heat transfer surfaces to the heated walls or heat-generating elements. This investigation is devoted to the numerical analysis of natural convective energy transport in a differentially heated chamber with isothermal vertical walls and a fin system mounted on the heated wall. The developed in-house computational code has been comprehensively validated. The Forchheimer–Brinkman extended Darcy model has been employed for the numerical simulation of transport phenomena in a porous material. The partial differential equations written, employing non-primitive variables, have been worked out by the finite difference technique. Analysis has been performed for solid and porous fins with various fin materials, amounts and heights. It has been revealed that porous fins provide a very good technique for the intensification of energy removal from heated surfaces.

Conjugate heat transfer in the mode of thermal gravitational-capillary convection in the model of a fuel tank, after a sudden heating of the sidewall

The evolution of unsteady gravitational-capillary convection in a layer of ethyl alcohol with a free surface after sudden electric heating of one of the vertical walls of a rectangular cavity was investigated numerically. The effect of the incoming flow of hot liquid on the time evolution of the temperature field on the opposite thin metal wall of the cavity was investigated. The calculations were carried out by the finite element method in the conjugate two-dimensional formulation with the Prandtl number Pr = 16, and the range of Grashof numbers determined by the heat flux density, 33·103 ≤ Gr ≤ 28·106. It is shown that the maximum local temperature gradients occur on the wall near the liquid-gas interface.

Influence of thermal gravitational-capillary convection on temperature fields in a thin wall

The development of convective flow in a layer of ethyl alcohol when heating one of the vertical walls of a rectangular cavity was investigated experimentally. Thermal films were obtained, whose processing allowed plotting in time the distribution of temperature and temperature gradients on the free surface of the liquid layer and the opposite thin vertical wall of the cavity after the flow of heated liquid on it.

Effect of inclination angle on bioconvection in porous square cavity containing gyrotactic microorganisms and nanofluid

The current article investigates the effect of inclination angle on thermo-bioconvection within the porous-square shaped cavity filled with gyrotactic type microorganisms and nanofluid. The Darcy law with Boussinesq estimation is used for the momentum equation in porous media. The transformed governing equations are solved by Galerkin’s method of finite elements. The effect of inclination angle in the square cavity is interpreted by varying the angle from [Formula: see text] to [Formula: see text]. The effect of inclination on different quantities, for instance, Rayleigh number, bioconvective Rayleigh number, Peclet number, Brownian motion, heat source/sink, and ratio of buoyancy, is discussed. Further, the mean quantities of Nusselt number [Formula: see text], Sherwood number [Formula: see text], and density number [Formula: see text] are analyzed at vertical walls. A quantitative outcome of the study is that the maximum values of [Formula: see text], [Formula: see text], and [Formula: see text] are found for the angle [Formula: see text] and [Formula: see text].

Global exact controllability of ideal incompressible magnetohydrodynamic flows through a planar duct

This article is concerned with the global exact controllability for ideal incompressible magnetohydrodynamics in a rectangular domain where the controls are situated in both vertical walls. First, global exact controllability via boundary controls is established for a related Elsässer type system by applying the return method, introduced in [Coron J.M., Math. Control Signals Systems, 5(3) (1992) 295--312]. Similar results are then inferred for the original magnetohydrodynamics system with the help of a special pressure-like corrector in the induction equation. Overall, the main difficulties stem from the nonlinear coupling between the fluid velocity and the magnetic field in combination with the aim of exactly controlling the system. In order to overcome some of the obstacles, we introduce ad-hoc constructions, such as suitable initial data extensions outside of the physical part of the domain and a certain weighted space.

A Measurement of ‘Walking-the-Wall’ Dynamics: An Observational Study Using Accelerometry and Sensors to Quantify Risk Associated with Vertical Wall Impact Attenuation in Trampoline Parks

This study illustrates the application of a tri-axial accelerometer and gyroscope sensor device on a trampolinist performing the walking-the-wall manoeuvre on a high-performance trampoline to determine the performer dynamic conditions. This research found that rigid vertical walls would allow the trampolinist to obtain greater control and retain spatial awareness at greater levels than what is achievable on non-rigid vertical walls. With a non-rigid padded wall, the reaction force from the wall can be considered a variable force that is not constrained, and would not always provide the feedback that the trampolinist needs to maintain the balance with each climb up the wall and fall from height. This research postulates that unattenuated vertical walls are safer than attenuated vertical walls for walking-the-wall manoeuvres within trampoline park facilities. This is because non-rigid walls would provide higher g-force reaction feedback from the wall, which would reduce the trampolinist’s control and stability. This was verified by measuring g-force on a horizontal rigid surface versus a non-rigid surface, where the g-force feedback was 27% higher for the non-rigid surface. Control and stability are both critical while performing the complex walking-the-wall manoeuvre. The trampolinist experienced a very high peak g-force, with a maximum g-force of approximately 11.5 g at the bottom of the jump cycle. It was concluded that applying impact attenuation padding to vertical walls used for walking-the-wall and similar activities would increase the likelihood of injury; therefore, padding of these vertical surfaces is not recommended.

Numerical simulation of coupled diffuse radiation and natural convection in a cubic cavity heated from bottom

We present, a three-dimensional numerical simulation of coupled natural convection with diffuse radiation in a cubic cavity whose all four vertical walls are isothermal, the bottom wall is convectively heated and the top wall is insulated. All walls are treated as black, diffuse and opaque for radiation. The simulations are carried out for the fixed Rayleigh (Ra=105) and Prandtl numbers (Pr=0.71) for a transparent and participating medium. The flow visualization technique Q-criteria has been used for analysis of the flow structure. The isothermal surfaces inside the cavity form vertical co-axially convergent-divergent three-dimensional open and closed nozzles, while inside the cavity Q-criteria reveals the formation of Jellyfish like flow structure. The cavity contains four conical vortices whereas each vortex is occupied in tetrahedron space.

A Simulation Survey on the Effects of Progressing Faults Within the SCAS of a Flight Control Actuator for Helicopters

Stability Control Augmentation Systems (SCAS) are widely adopted to enhance the flight stability of rotary-wing aircraft operating in difficult aerodynamic conditions, such as low altitude missions, stationary flight nearby vertical walls or in presence of heavy gusts. Such systems are based upon small electro-hydraulic servosystems controlled in position through a dedicated servovalve. The SCAS operates with limited authority over the main control linkage translating the pilot input in the movement of the main flight control actuator. Being critical for the operability of the helicopter, the definition of a Prognostics and Health Management (PHM) framework for the SCAS systems would provide significant advantages, such as better risk mitigation, improved availability, and a reduction in the occurrences of unpredicted failures which still represent one of the most known downsides of helicopters. This paper provides the results of a preliminary analysis on the effects of the inception and progression of several degradation types within a simulated SCAS system. Signals usually available within such devices are hence combined with measurements provided by additional sensors to check the feasibility of a PHM system with and without dedicated sensors. The resulting features selection process shows that although the dedicated measurements are required to design a complete PHM system, it appears nonetheless possible to obtain valuable information on the health status of the SCAS system without resorting to additional sensors.