Development of a micro-heat exchanger with stacked plates using LTCC technology

A green ceramic tape micro-heat exchanger was developed using Low Temperature Co-fired Ceramics technology (LTCC). The device was designed by using Computational Aided Design software and simulations were made using a Computational Fluid Dynamics package (COMSOL Multiphysics) to evaluate the homogeneity of fluid distribution in the microchannels. Four geometries were proposed and simulated in two and three dimensions to show that geometric details directly affect the distribution of velocity in the micro-heat exchanger channels. The simulation results were quite useful for the design of the microfluidic device. The micro-heat exchanger was then constructed using the LTCC technology and is composed of five thermal exchange plates in cross-flow arrangement and two connecting plates, with all plates stacked to form a device with external dimensions of 26 x 26 x 6 mm(3).

INFLUENCE of THE EVAPORATOR POSITION IN STATIC DOMESTIC REFRIGERATORS

The temperature and velocity distributions of the air inside the cabinet of domestic refrigerators affect the quality of food products. If the consumer knows the location of warm and cold zones in the refrigerator, the products can be placed in the right zone. In addition, the knowledge of the thickness of thermal and hydrodynamic boundary layers near the evaporator and the other walls is also important. If the product is too close to the evaporator wall, freezing can occur, and if it is too close to warm walls, the products can be deteriorated. The aim of the present work is to develop a steady state computational fluid dynamics (CFD) model for domestic refrigerators working on natural convection regime. The Finite Volume Methodology is chosen as numerical procedure for discretizing the governing equations. The SIMPLE-Semi-Implicit Method for Pressure-Linked Equations algorithm applied to a staggered mesh was used for solving the pressure-velocity coupling problem. The Power-Law scheme is employed as interpolation function for the convective-diffusive terms, and the TDMA-Tri-Diagonal Matrix Algorithm is used to solve the systems of algebraic equations. The model is applied to a commercial static refrigerator, where the cabinet is considered an empty three-dimensional rectangular cavity with one drawer at the bottom of the cabinet, but without shelves. In order to analyze the velocity and temperature fields of the air flow inside the cabinet the evaporator temperature, Te, was varied from -20 degrees C to 0 degrees C, and nine different evaporator positions are evaluated for evaporator temperature of -15 degrees C. The cooling capacity of the evaporator for the steady state regime is also computed for each case. One can conclude that the vertical positioning of the evaporator inside the cabinet plays an important role on the temperature distribution inside the cabinet.

Fourth-order method for solving the Navier-Stokes equations in a constricting channel

A fourth-order numerical method for solving the Navier-Stokes equations in streamfunction/vorticity formulation on a two-dimensional non-uniform orthogonal grid has been tested on the fluid flow in a constricted symmetric channel. The family of grids is generated algebraically using a conformal transformation followed by a non-uniform stretching of the mesh cells in which the shape of the channel boundary can vary from a smooth constriction to one which one possesses a very sharp but smooth corner. The generality of the grids allows the use of long channels upstream and downstream as well as having a refined grid near the sharp corner. Derivatives in the governing equations are replaced by fourth-order central differences and the vorticity is eliminated, either before or after the discretization, to form a wide difference molecule for the streamfunction. Extra boundary conditions, necessary for wide-molecule methods, are supplied by a procedure proposed by Henshaw et al. The ensuing set of non-linear equations is solved using Newton iteration. Results have been obtained for Reynolds numbers up to 250 for three constrictions, the first being smooth, the second having a moderately sharp corner and the third with a very sharp corner. Estimates of the error incurred show that the results are very accurate and substantially better than those of the corresponding second-order method. The observed order of the method has been shown to be close to four, demonstrating that the method is genuinely fourth-order. © 1977 John Wiley & Sons, Ltd.

Simulação numérica de trocadores de calor multitubulares equipados com fitas helicoidais externamente aos tubos

Classical shell-and-tube heat exchangers are usually equipped with segmental baffles. These baffles serve two basic functions: (a) they provide tube supports, thereby preventing or reducing mechanical problems, such as sagging or vibration; (b) they direct the fluid flow over the tubes so as to introduce a cross-flow component, thereby increasing the heat transfer. Segmented baffles have several sources of performance loss, some due to various leakage flows and others caused by stagnation zones. A new concept of longitudinal flow heat exchanger - based on placing twisted tapes along the tube bundle subchannels - was developed to mitigate drawbacks of other types of tubular heat exchangers. In this paper, a numerical model has been implemented in order to simulate the thermal-hydraulic feature of tubular heat exchangers equipped either with segmental baffles or with subchannel twisted tapes. The tube bundle has been described by means of an equivalent porous medium type model, allowing a macroscopic description of the shell-side flow. The basic equations - continuity, momentum and energy - have been solved by using the finite volume method. Typical numerical results have been compared with experimental data, reaching a very good agreement. A comparative analysis of different types of heat exchangers has been carried out, revealing the satisfactory thermal-hydraulic efficiency level of the twisted tapes heat exchangers.

Study on transient ice formation of laminar flow inside externally supercooled rectangular duct

The transient process of solidification of laminar liquid flow (water) submitted to super-cooling was investigated both theoretically and experimentally. In this study an alternative analytical formulation and numerical approach were adopted resulting in the unsteady model with temperature dependent thermophysical properties in the solid region. The proposed model is based upon the fundamental equations of energy balance in the solid and liquid regions as well as across the solidification front. The basic equations and the associated boundary and initial conditions were made dimensionless by using the Landau transformation to immobilize the moving front and render the problem to a fixed plane type problem. A laminar velocity profile is admitted in the liquid domain and the resulting equations were discretized using the finite difference approach. The numerical predictions obtained were compared with the available results based on other models and concepts such as Neumann analytical model, the apparent thermal capacity model due to Bonacina and the conventional fixed grid energy model due to Goodrich. To obtain further comparisons and more validation of the model and the numerical solution, an experimental rig was constructed and instrumented permitting very well controlled experimental measurements. The numerical predictions were compared with the experimental results and the agreement was found satisfactory.

Object oriented modeling of piston engines

This work reports a conception phase of a piston engine global model. The model objective is forecast the motor performance (power, torque and specific consumption as a function of rotation and environmental conditions). Global model or Zero-dimensional is based on flux balance through each engine component. The resulting differential equations represents a compressive unsteady flow, in which, all dimensional variables are areas or volumes. A review is presented first. The ordinary differential equation system is presented and a Runge-Kutta method is proposed to solve it numerically. The model includes the momentum conservation equation to link the gas dynamics with the engine moving parts rigid body mechanics. As an oriented to objects model the documentation follows the UML standard. A discussion about the class diagrams is presented, relating the classes with physical model related. The OOP approach allows evolution from simple models to most complex ones without total code rewrite. Copyright © 2001 Society of Automotive Engineers, Inc.

Simulação numérica do escoamento de jatos impingentes axissimétricos confinados

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Simulação numérica de escoamentos incompressíveis pelo método de elementos finitos com esquema de Separação Baseado na Característica (CBS)

Pós-graduação em Engenharia Mecânica - FEIS

Estudo do escoamento ao redor de cilindros elípticos

Pós-graduação em Engenharia Mecânica - FEIS

Implementação e teste do método da fronteira imersa para a simulação do escoamento em torno de cilindros estacionários e rotativos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Modelagem numérica do escoamento em válvulas automáticas de compressores pelo Método da Fronteira Imersa

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Análise numérica de condensadores do tipo arame-sobre-tubo usados em refrigeradores domésticos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Modelagem do escoamento ao longo de evaporadores de serpentina com tubos aletados

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Análise numérica de evaporadores do tipo Roll-Bond usados em refrigeradores domésticos

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Estabilidade e controle dinâmico de roll waves

Pós-graduação em Engenharia Elétrica - FEIS