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Numerical Investigations of an Integrated Phase-Change-Material Solar Collector
No full textThe objective of this study is to optimize the thermal performance of a solar collector. The solar collector is coupled to a building slab with a PCM layer. A mathematical model for the thermal behavior of the studied system is developed using the enthalpy method. The model parameters are defined and the resulting equations are solved iteratively. Several simulations were carried out to optimize the proposed heating system. The results show that the inlet temperature fluctuations are less pronounced than those at the outlet
Analysis of Natural Convection in a Nanofluid-Filled Open Cavity with a Sinusoidal Boundary Condition in the Presence of a Magnetic Field
No full textThis paper examines natural convection in an open cavity with a sinusoidal thermal boundary condition. The cavity is filled with a water-Al2O3 nanofluid and subjected to a magnetic field. The Lattice Boltzmann method (LBM) is applied to solve the coupled equations of flow and temperature. The study has been carried out considering parameters in the following ranges: Rayleigh number of the base fluid, Ra = 103 to 106, Hartmann number varied from Ha = 0 to 60, phase deviation γ = 0, π4, π2, 3 π4 and π and solid volume fraction of nanoparticles between π = 0 and 6%. Results show that the heat transfer rate decreases with the Hartmann number and increases with Rayleigh number. At Ha = 30 and Ra = 103 - 105, for all phase deviations the addition of nanoparticles increases the heat transfer rate. Also, at low Rayleigh number (Ra ≤ 104) the highest heat transfer rate is obtained for γ = π2
Dynamics of the Moving Load Acting on the Hydro-elastic System Consisting of the Elastic Plate, Compressible Viscous Fluid and RigidWall
Get PDFThe subject of the paper is the study of the dynamics of the moving load acting on the hydro-elastic system consisting of the elastic plate, compressible viscous fluid and rigid wall. Under this study the motion of the plate is described by linear elastodynamics, and the motion of the compressible viscous fluid is described by the linearized Navier-Stokes equations. Numerical results are obtained for the case where the material of the plate is steel, but the fluid material is Glycerin. According to these results, corresponding conclusions related to the influence of the problem parameters, such as fluid viscosity, plate thickness, fluid depth, fluid compressibility and initial stresses on the inter-phase normal stress and normal and tangent velocities of the fluid caused by the load which moves with constant velocity, are made. In particular, it is established that the influence of the fluid viscosity of the aforementioned quantities becomes more considerable under lower velocities of the moving load. Moreover, it is established that there exists a critical velocity of the moving load under which a resonance type event takes place
Time-Dependent J-Integral Solution for Semi-elliptical Surface Crack in HDPE
Get PDFThis work focuses on a linear elastic analysis by the finite element method and the development of a shape function, commonly known as geometrical correction factor, for the case of semi-elliptical crack in a cylindrical rod. We used the same shape function to analyze the behavior of the rod in the case of a viscoelastic medium materialized by a polymeric material such as HDPE. A linear viscoelastic model calibrated from a relaxation test was developed and implemented in Abaqus. Results showed a relatively good performance, compared with finite element method
Analytical Solution of Thermo-elastic Stresses and Deformation of Functionally Graded Rotating Hollow Discs with Radially Varying Thermo-mechanical Properties under Internal Pressure
Get PDFExact analytical solution for functionally graded hollow discs under internal pressure, thermal load and rotation are provided in this paper. Material properties of discs, i.e. elastic modulus, density and thermal expansion coefficient are assumed to vary in radial direction. Two power functions are assumed for property dependency to study various types of functional grading of materials in the discs. Assuming small deformations, a differential equation is obtained and solved for the Airy stress function. The effects of various grading functions on the stress and deformation distribution are studied and an optimum value for the power is obtained
Design, Optimization and CFD Simulation of a Nozzle for Industrial Cleaning Processes based on High-Pressure Water Jets
Get PDFThree different kinds of nozzles, normally used in industrial processes for the cleaning of material surface by means of water jets at high pressure (a Cylindrical Contracting, a Taper Contracting and Stepped nozzle), are numerically simulated with the express intent to optimize the related efficiency (cleaning effectiveness). Although some of them are found to display interesting properties, simulation results indicate that a helix nozzle displays the best jetting performances. It is shown that, as compared to improvements obtained by simply changing the jetting angle, revolving the fluid released from the helix nozzle can be used to create a grinding wheel on the cleaning surface, exerting a significant shearing action on the material to be cleaned
On the Formation Mechanism and Characteristics of High-Pressure Percussion Pulsed Water Jets
Get PDFAlthough the socalled percussion-pulsed-water jet technique is currently recognized as an effective means for breaking hard rocks, it can’t be extensively employed due to insufficient systematic research on the related flow-field structure. Considered as one of the rock breaking technologies with the highest potential of development and application, this method is characterized by water hammer effects, a high-frequency impact pressure and high-speed side flows. The typical (impact and extrusion) pistons used for this technique collide several times to form the multi-pulsed jet. Here we analyze these features through a combined experimental-numerical investigation. The number of pulses and kinetic parameters of the jet are studies as a function of the mass of piston, the speed of the impact piston before collision, the diameter of water chamber, the water depth in the chamber and the nozzle diameter. Interestingly, the jet pressure and velocity first increase from zero and then decrease following a non-linear (quadratic) law. As the mass of the extrusion piston is reduced, the number of pulses increases. We also study in detail the typical umbrella-shaped configuration of the pulsed jet by means of a VOF numerical method. We show the existence of a back jet and a front jet transporting fluid away from the central regions under the action of air friction and resistance. With the loss of acceleration, the jet moves backward giving rise to an umbrella structure. The formation of the umbrella shape is observed to improve the degree of convergence. A low-velocity layer is identified at the front of the jet, where the turbulent kinetic energy is relatively high
Investigating Creep Performance and Predicting Rupture Time for Rotating FGM Disc under Different Thermal Gradients
Get PDFA mathematical model is developed to describe the steady state creep in a rotating Al-SiCp disc having a non-linear thickness profile and distribution of SiC particles along the radial direction. The model is used to investigate the effect of imposing three different kinds of radial temperature profiles viz. linear, parabolic and exponential with fixed values of inner and outer surface temperatures, on the creep stresses and strain rates. It is noticed that by increasing the temperature exponent (nT), the radial stress (over the entire radius) and tangential stress (near the inner radius) increase in the disc. However, the tangential stress decreases near the outer radius. The radial and tangential strain rates in the functionally graded (FG) disc reduce significantly with the increase in exponent nT. Besides reduction in the magnitude, the distribution of strain rates also become relatively more uniform throughout with the increase in nT. It is concluded that FG disc operating under exponential temperature profile performs better. It is also revealed that amongst several FG discs operating under radial thermal gradients, with different values of temperature exponent (nT) but having the same average and fixed outer surface temperature, the FGM disc with lower value of nT exhibits the maximum creep life
Enhanced External Counterpulsation Treatment May Intervene The Advanced Atherosclerotic Plaque Progression by Inducing The Variations of Mechanical Factors: A 3D FSI Study Based on in vivo Animal Experiment
Get PDFGrowing evidences suggest that long-term enhanced external counterpulsation (EECP) treatment can inhibit the initiation of atherosclerotic lesion by improving the hemodynamic environment in aortas. However, whether this kind procedure will intervene the progression of advanced atherosclerotic plaque remains elusive and causes great concern in its clinical application presently. In the current paper, a pilot study combining animal experiment and numerical simulation was conducted to investigate the acute mechanical stress variations during EECP intervention, and then to assess the possible chronic effects.
An experimentally induced hypercholesterolemic porcine model was developed and the basic hemodynamic measurement was performed in vivo before and during EECP treatment. Meanwhile, A 3D fluid-structure interaction (FSI) model of blood vessel with symmetric local stenosis was developed for the numerical calculation of some important mechanical factors. The results show that EECP augmented 12.21% of the plaque wall stress (PWS), 57.72% of the time average wall shear stress (AWSS) and 43.67% of the non-dimensional wall shear stress gradient (WSSGnd) at throat site of the stenosis. We suggest that long-term EECP treatment may intervene the advanced plaque progression by inducing the significant variations of some important mechanical factors, but its proper effects will need a further research combined follow-up observation in clinic
Numerical Study for a Class of Variable Order Fractional Integral-differential Equation in Terms of Bernstein Polynomials
Get PDFThe aim of this paper is to seek the numerical solution of a class of variable order fractional integral-differential equation in terms of Bernstein polynomials. The fractional derivative is described in the Caputo sense. Four kinds of operational matrixes of Bernstein polynomials are introduced and are utilized to reduce the initial equation to the solution of algebraic equations after dispersing the variable. By solving the algebraic equations, the numerical solutions are acquired. The method in general is easy to implement and yields good results. Numerical examples are provided to demonstrate the validity and applicability of the method