Showing items 1 - 9 of 9

Your selections:

A numerical investigation into the behaviour of cracks in uPVC pipes under pressure

  • Authors: Cassa, Amanda Marilu
  • Date: 2012-07-19
  • Subjects: Pipe - Fluid dynamics , Numerical analysis , Piping , Finite element method
  • Type: Thesis
  • Identifier: uj:8843 , http://hdl.handle.net/10210/5255
  • Description: D.Ing. , This study is a numerical investigation into the behaviour of cracks in uPVC pipes under pressure. This study is a continuation of a Masters dissertation which showed that leakage exponents vary significantly from the theoretical orifice exponent of 0.5 for cracks in pipes for different materials. This study looks at the behaviour of cracks in more detail and specifically with regard to the parameters of the pipe and crack. Using Finite Element Analysis the relationship between the pressure head and the leak area in pipes with longitudinal, spiral and circumferential cracks was investigated. It was found that the longitudinal, spiral and circumferential crack areas increase linearly with pressure. The slope of this linear relationship depends on various parameters, including loading state, pipe dimensions and pipe material properties. The effect that the individual pipe parameters had on the pressure-area slope was investigated. These parameters included the material properties of the pipe (Young’s modulus, Poisson’s ratio and longitudinal stress), the geometry of the pipe (internal diameter and wall thickness) as well as the geometry of the crack (length of the crack and the width of the crack). Once the effect of the pressure-area slope m is known, the link between the conventional leakage exponent N1 and the pressure-area slope m was further investigated and the effect of each parameter on the leakage exponent N1 was found. Using various data techniques the above data was combined and processed to find mathematical relationships that give reasonable descriptions of the pressure-area slopes of longitudinal, spiral and circumferential cracks. Once these equations for the pressure-area slopes were determined it was possible to obtain three new relationships for leakage from longitudinal, spiral and circumferential cracks.
  • Full Text:

Numerical analysis of the convective heat transfer in a combustor cooling jacket

  • Authors: Gutierrez, Gustavo , Jen, Tien-Chien , Yan, Tuan-Zhou
  • Date: 2003
  • Subjects: Combustor cooling , Convective heat transfer , Numerical analysis
  • Language: English
  • Type: Conference proceedings
  • Identifier: http://hdl.handle.net/10210/16022 , uj:15729 , Citation: • Gutierrez, G., Jen, T.C., and Yan, T., 2003, “Numerical Analysis of the Convective Heat Transfer in a Combustor Cooling Jacket,” International Mechanical Engineering and Congress Exposition, November 16-21, 2003, Washington, D.C., Vol. 3, pp. 29-37. IMECE2003-42912. ISSN: 0-7918-3718-1.
  • Description: Abstract: In any combustors and chemical reactors, to achieve high efficiency it is very important to maintain the high gas temperature inside the combustion chamber without significant deterioration of the materials of the walls. Thus, a critical aspect of the design of a combustor or reactor is the development of a method to cool the inner walls of a combustor such that the temperatures on the inner wall are well below the temperature a material can sustain. A typical method to cool a combustor chamber is to use a cooling jacket adjacent to the inner wall of the combustor. In general, the efficiency of this cooling jacket depends on the heat removal capability of the cooling water and the flow channel geometry. It is critically important to control these parameters to enhance the performance of the combustion chamber by decreasing the inner wall temperature below its material limit Sφ : source term in the generic property φ Vr ,Vθ , Vz : reduced velocities in the r, θ , and z direction respectively [m/s] T : temperature [ºC] Tinn : inner temperature [ºC] T∞ : ambient temperature [ºC] U0 : inlet velocity [m/s] Greek ρ : density [kg/m3] φ : generic property μ : dynamic viscosity [kg/m-s] Γ : diffusivity for the generic property φ Ω : angular velocity [rad/s] This study considers a cylindrical combustor, rotating around its axis. A detailed investigation of the fluid flow and heat transfer processes throughout the cooling jacket is performed. A two-dimensional axial symmetric Navier-Stokes equations and energy equation as a conjugate problem are solved. The flow patterns and temperature distributions of the cooling jacket under the effect of rotation are presented. Also, local friction factor and Nusselt number are calculated along the axial direction.
  • Full Text:

Transient heat transfer analysis on a heat pipe with experimental validation

  • Authors: Gutierrez, Gustavo , Catano, Juan , Jen, Tien-Chien , Liao, Quan
  • Date: 2006
  • Subjects: Numerical analysis , Heat transfer , Heat pipes
  • Type: Article
  • Identifier: uj:5270 , http://hdl.handle.net/10210/14939
  • Description: In this study, a transient analysis of the performance of a heat pipe with a wick structure is performed. A complete formulation of the equation governing the operation of a heat pipe during transient conditions are presented and discussed. For the vapor flow, the conventional Navier-Stokes equations are used. For the liquid flow in the wick structure, which is modeled as a porous media, volume averaged Navier-Stokes equations are adopted. The energy equation is solved for the solid wall and wick structure of the heat pipe. The energy and momentum equations are coupled through the heat flux at the liquid-vapor interface that defines the suction and blowing velocities for the liquid and vapor flow. The evolution of the vaporliquid interface temperature is coupled through the heat flux at this interface that defines the mass flux to the vapor and the new saturation conditions to maintain a fully saturated vapor at all time. A control volume approach is used in the development of the numerical scheme. A parametric study is conducted to study the effect of different parameters that affect the thermal performance of the heat pipe. And experimental setup is developed and numerical res ults are validated with experimental data. The results of this study will be useful for the heat pipe design and implementation in processes that are essentially transient.
  • Full Text:

Numerical analysis in interrupted cutting tool temperatures

  • Authors: Jen, Tien-Chien , Gutierrez, Gustavo , Eapen, Sunil
  • Date: 2011
  • Subjects: Numerical analysis , Cutting tools , Cutting temperatures
  • Type: Article
  • Identifier: uj:5243 , ISSN 1040-7782 , http://hdl.handle.net/10210/14843
  • Description: In any cutting process, plastic deformation involved in chip formation and friction between the tool and the workpiece produces heat by the conversion of mechanical energy. A portion of this heat conducts into the tool and results in high temperatures near the cutting edge. As the temperature increases, the tool becomes softer and wears more rapidly, thus having a negative impact on tool life. In many cutting processes, tool life, or tool wear, is the major limitation to the process viability. Increased temperature also affects the dimensional accuracy of the products and machining efficiency. Because of these considerations, it is crucial to be able to predict accurately the tool temperature. Cutting temperatures have been studied widely for a number of years. Most research, however, has been restricted to steady state temperatures in relatively simple processes, such as orthogonal cutting or cylindrical turning, in which the cutting speed, feed rate, and the depth of cut are constant [1^3, 17, 21, 24]. In most industrial machining processes, however, these parameters vary with time so that a steady state temperature assumption may not be valid.
  • Full Text:

A numerical analysis of machining induced residual stresses of Grade 5 titanium alloy

  • Authors: Laubscher, R.F. , Styger, G. , Oosthuizen, G.A.
  • Date: 2014-06
  • Subjects: Numerical analysis , Machining , Residual stresses , Titanium alloys
  • Type: Article
  • Identifier: uj:5055 , http://hdl.handle.net/10210/13603
  • Description: Machining induced residual stresses may have a significant effect on the mechanical performance of machined parts. AdvantEdge is an advanced finite element code dedicated to the modelling of the machining process. This paper describes a comparative evaluation of modelling results obtained with AdvantEdge with experimental results obtained during turning of Grade 5 (Ti6Al4V) titanium alloy. A two dimensional orthogonal turning process is modelled and compared with experimental data. Comparisons are made relative to residual stress, cutting force and cutting temperature for various different cutting parameters including cutting speed, feed rate and cut depth.
  • Full Text:

Numerical solutions for a class of nonlinear volterra integral equation

  • Authors: Mamba, Hlukaphi Sithando
  • Date: 2015-11-11
  • Subjects: Volterra equations , Integral equations , Numerical analysis , Mathematical analysis
  • Type: Thesis
  • Identifier: uj:14546 , http://hdl.handle.net/10210/15077
  • Description: M.Sc. (Applied Mathematics) , Numerous studies on linear and nonlinear Volterra integral equations (VIEs), have been performed. These studies mainly considered the existence and uniqueness of the solution, and numerical solutions of these equations. In this work, a class of nonlinear (nonstandard) Volterra integral equation that has received very little attention in the literature is considered. The existence and uniqueness of the solution for the nonlinear VIE is proved using the contraction mapping theorem in the space C[0; d]. Collocation methods, repeated trapezoidal rule and repeated Simpson's rule are used to solve the nonlinear (nonstandard) VIE. For the collocation solutions we considered two cases: implicit Euler method and implicit midpoint method. Examples are used to compare the performance of these methods and the results show that the repeated Simpson's rule performs better than the other methods. An analysis of the collocation solution and the solution by the repeated trapezoidal rule is performed. Su cient conditions for existence and uniqueness of the numerical solution are given. The collocation methods and repeated trapezoidal rule yield convergence of order one.
  • Full Text:

On the numerical solution of double-diffusive convection in regular and nanofluid flow

Numerical analysis of the cold gas dynamic spray surface coating process

Development of composite metal membrane using cold gas dynamic spray for hydrogen separation : a numerical simulation approach

  • 1
  • Disclaimer
  • Privacy
  • Copyright
  • Contact