An Inverse Algorithm to Estimate Spatially Varying Thermal Contact Resistance

Characterization of the thermal contact resistance is important in modeling of multi-component thermal systems which feature mechanically mated surfaces. Thermal resistance is phenomenologically quite complex and depends on many parameters including surface characteristics of the interfacial region and contact pressure. In general, the contact resistance varies as a function of pressure and is non-uniform along the interface. An inverse problem is formulated to estimate the variation of the contact resistance. A two-dimensional model is considered where the contact resistance is sought along the contact line at the interface between two regions. Temperature measured at discrete locations using embedded sensors placed in proximity to the interface provides the additional information required to solve the inverse problem. Given current estimates of the contact resistance as a function of position along the interface, a forward problem is solved, and a quadratic objective function is formulated to evaluate the difference between predicted temperatures at the sensors and those measured. A genetic algorithm is used to minimize the objective function and obtain the best estimate of the contact resistance. A boundary element method is used to solve the forward temperature field problem. Numerical simulations are carried out to demonstrate the approach. Random noise is used to simulate the effect of input uncertainties in measured temperatures at the sensors.

Tin Solidification in the Presence of Turbulent Natural Convection

The solidification process of tin, inside a closed cavity, is numerically investigated by the finite volume method. A non-orthogonal system of coordinates is employed to adapt to the irregular geometry, with a moving mesh to account for the changing domain size. The momentum equations are solved for the contravariant velocity components. The SIMPLEC algorithm handles the coupling between velocity and pressure. A special treatment is given at the liquid-solid interface to obtain the momentum and energy balance. The phase change process is strongly influenced by natural convection in the melt. At the beginning of the process, the cavity is full of liquid, and the natural convection slightly influences the interface shape. But as the liquid region diminishes during the process, the influence of natural convection increases. Further, at the same time as the liquid size region is reduced, the intensity of the flow increases, and the flow can became turbulent, affecting the heat flux at the interface and consequently the size of the solid region. Therefore, the purpose of the paper is to analyze the influence of the turbulent regime on the kinetics of the solidification process. The turbulent flow is taken into account by a low Reynolds number model. The influence of the Rayleigh number on the velocity and temperature field is investigated.

Cartesian Based Finite Volume Formulation for LES of Mixed Convection in a Vertical Turbulent Pipe Flow

A numerical study was performed to investigate the effects of heating and buoyancy on the turbulent structures and transport in turbulent pipe flow. Isoflux wall boundary conditions with low and high heating were imposed. The compressible filtered Navier-Stokes equations were solved using a second order accurate finite volume method. Low Mach number preconditioning was used to enable the compressible code to work efficiently at low Mach numbers. A dynamic subgrid-scale stress model accounted for the subgrid-scale turbulence. The results showed that strong heating caused distortions of the flow structures resulting in reduction of turbulent intensities, shear stresses, and turbulent heat flux, particularly near the wall. The effect of heating was to raise the mean streamwise velocity in the central region and reduce the velocity near the wall resulting in velocity distributions that resembled laminar profiles for the high heating case.

The Influence to Thermal Resistance to Conduction in Rotary Regenerators

The present work is devoted to the modeling of rotary regenerators. A mathematical model is proposed based on a number of simplifying assumptions, the validity of which is discussed in light of actual regenerator design figures. The results are presented in ε-NTU analysis. It is shown that the often neglected thermal resistance offered by the storage material might imply in substantial reduction on the regenerator effectiveness.

Parallel Multiblock Mixed Finite Element Method for Elliptic Problems on Unstructured Grids

In this paper, we develop a general multiblock mixed finite element method for solving 2D and 3D elliptic problems by different unstructured grids on both serial and parallel platforms. Detailed implementations and numerical results are presented.

Turbulent Heat Transfer in a Backward-Facing Step Flow Using a Non-Linear k-ε Model

This work presents numerical results for heat transfer in turbulent flow past a backward-facing step. It is shown that nonlinear k-ε models perform better than their linear counterparts when simulations are compared with experimental values. Wall functions are used for simplicity of the simulations. The finite-volume technique is employed for discretizing the transport equation set on a non-orthogonal grid system. The SIMPLE method is used for correcting the pressure field. Results for the reattachment length using the non-linear model are closer to the experimental values when compared with similar calculations using the standard linear closure.

A Pseudo-Spectral Numerical Scheme for the Simulation of Convective Flows

This paper focuses on the development and validation of a pseudo-spectral numerical scheme, based on a variational formulation, for the solution of the three-dimensional, time-dependent governing equations in wall bounded forced and natural convective flows. One of the novel aspects of this numerical scheme is the use of rescaled Legendre-Lagrangian interpolants to represent the velocity and temperature in the vertical direction. These interpolants were obtained by dividing the Legendre Lagrangian interpolants of same order by the square root of the corresponding weight used for Gauss-Lobatto quadrature. By rescaling the interpolants in such a manner, the mass matrix resulting from the variational formulation becomes the identity matrix, thus simplifying the numerical algorithm. Two specific problems have been investigated as part of the validation process: Steady and unsteady channel flow driven by an external streamwise oscillating pressure gradient and Rayleigh Be´nard convection. In all cases, comparison with exact solutions and published results yield excellent agreement.

Conjugate Heat Transfer in a Rotor-Stator System With Through-Flow

The conjugate heat transfer in a stationary cylindrical cavity with a rotating disk and fluid through-flow is analysed at various rotational speeds ranging from 10000 to 50000 rpm by using a finite volume commercial code. The numerical model and code are validated for a problem, which involves rotation and fluid through-flow. A reduction of the thermal boundary layer thickness and increase in the heat transfer coefficients are observed with increase in the rotational speed. Marked differences are noticed between the Nusselt numbers obtained from the conjugate and constant temperature analyses.

A Multi-Mechanics Approach to Computational Heat Transfer

We present a turbulent combustion code for modeling heat transfer in fires that arise in accident scenarios. The code is a component of a multi-mechanics framework and is based on a domain-decomposition, message-passing approach to parallel computing. The turbulent combustion code is based on a vertex-centered, finite-volume scheme for 3D unstructured meshes. The multi-mechanics nature of the frameworks allows us to couple to a conduction heat transfer code for conjugate heat transfer problems or a participating media radiation code for radiation transport in soot-laden flows. We describe our numerical methods, our approach to parallel computing, and the multi-mechanics frameworks. We demonstrate parallel performance using some example verification problems.

Field Validation of a Systematic Approach to Modeling of Glass Delivery Systems

In the fiberglass production process, glass is produced from various batch ingredients in a glass furnace. The molten glass is then delivered, through a delivery system that is often called the front-end system, to the various downstream forming operations. Front-end systems consist of various covered channels and forehearths. One of the major tasks of a front-end system is to insure that the glass is conditioned to the stringent specifications required by the forming operations. Improperly designed and/or operated front-end delivery systems can cause a number of problems to the forming operations, ranging from poor conversion efficiency (resulting in waste generation) due to glass defects to shortened service life. In today’s business environment, improvement in productivity, reduction in energy consumption, and minimization or elimination of waste generation have become priorities in managing and optimizing manufacturing operations. CFD has become an increasingly important tool for glass manufacturers to guide and optimize such system designs and operations. The current front-end model is developed to simultaneously simulate the chemically reacting turbulent flows in the superstructure and the laminar glass flow with strong buoyancy effects. Radiation from the superstructure wall surfaces and burner flames and internal radiation within the glass is modeled with the discrete ordinates (DO) radiation model in FLUENT. The turbulent reacting flow in the combustion space is calculated to obtain the flame shapes and lengths to accurately determine the heat transfer rate to the molten glass. The laminar glass flow, which is strongly influenced by natural convection, is calculated with temperature dependent physical properties. Simulations of the two radically different flow regimes are coupled through the interface boundary conditions in terms of temperature and heat flux continuity. Significant efforts were made to validate this approach with field measurements. Vertical temperature profiles were obtained in the glass melt as well as the combustion space at several strategically selected locations. The measurements were performed using two 6-element thermocouples housed in a platinum sheath. This coupled approach is expected to provide an effective tool that can be used to guide field operations as well as future system designs.