Phase-field modeling of vapor bubble growth in a microchannel

Anumerical model based on Cahn–Hilliard phase-field method is introduced for thefirst time in the literature to investigate the hydrodynamics and heat transfercharacteristics of a vaporized elongated bubble in a rectangular microchannel. In thesimulations, the initially nucleated bubble starts growing as it comes in contact withsuperheated water. The effects of the water inlet velocity and the bubble contact angleon the temporal evolution of the average heat transfer coefficient are also reported.Both qualitative and quantitative comparisons indicated that the numerically obtainedbubble shape and the growth rate are in very good agreement with the experimentalresults available in the literature

3D numerical modeling of boiling in a microchannel by arbitrary Lagrangian-Eulerian (ALE) method

The arbitrary Lagrangian-Eulerian method (ALE) is used to model the hydrodynamics and the heat transfer of an elongated vaporized bubble in a rnicrotube. The Navier-Stokes equations along with the energy equation are solved in ALE description as a single fluid with two subdomains and a moving mesh at the interface of the liquid and the vapor phases. The numerical framework is the commercial CFD code COMSOL multiphysics with the finite element method, which has been improved by external functions to the phase changing. In the simulations, the nucleated bubble comes in contact with superheated water and starts growing. The growth rate of the bubble in the proposed model and the thin liquid film between the elongated bubble and the channel wall are in a very good agreement with the analytical solution and the empirical correlation in the literature, respectively. The interactive effects of two elongated bubbles also are presented

EFFECTS OF THERMOPYHSICAL PROPERTIES AND ENTRANCE REGION ON THE DIMENSIONAL OPTIMIZATION OF MICROCHANNEL HEAT SINKS

Dimensional optimization of silicon microchannel heat sinks is performed by minimizing the total thermal resistance. Intel Core i7-900 Desktop Processor of chip core dimensions of 1.891 cm x 1.44 cm is considered as a reference processor which is reported to dissipate 130 W of heat. The properties are evaluated at the area weighted average of the fluid inlet and iteratively calculated outlet temperatures. The effects of the thermal and hydrodynamic entrance regions on heat transfer and flow are also investigated. The results of the optimization code agreed very well with available ones in the literature

The Arbitrary Lagrangian-Eulerian (ALE) Modeling of a Vapor Bubble Growth in a Microtube

A numerical model based on the arbitrary Lagrangian-Eulerian method (ALE) is introduced to investigate the hydrodynamics and the heat transfer of an elongated vaporized bubble in a microchannelin detail. The Navier-Stokes equations along the energy equation are solved in ALE description as a single fluid. The finite element method is used to discretize the equations. In simulations, the nucleated bubble comes in contact with superheated water and starts growing

Participating media exposed to collimated short-pulse irradiation - A Laguerre-Galerkin solution

A new method is developed for the solution of radiative transfer in a one-dimensional absorbing and isotropically scattering medium with short-pulse irradiation on one of its boundaries. The time-dependent radiative intensity is expanded in a series of Laguerre polynomials with time as the argument. Moments of the radiative transfer equation, as well as of the boundary conditions, then yield a set of coupled time-independent radiative transfer problems. This set, in turn, is reduced to a set of algebraic equations by the application of the Galerkin method. The transient transmittance and reflectance of the medium are evaluated for various values of the optical thickness, scattering albedo and pulse duration. It is demonstrated that the Laguerre-Galerkin method is not only easier to implement and more efficient but also yields more accurate results compared to the direct application of the Galerkin method. The results are in very good agreement with those available in the literature

Radiative transfer in participating media with collimated short-pulse Gaussian irradiation

Radiative transfer in a one-dimensional absorbing and isotropically scattering plane-parallel grey medium with a collimated short-pulse Gaussian irradiation on one of its boundaries is studied. The medium is non-emitting and the boundaries are non-reflecting and non-refracting. The Galerkin method is extended for the solution of the transient radiative transfer problem. The transient transmittance and reflectance of the medium are evaluated for various optical thicknesses, scattering albedos and pulse durations

Dimensional optimization of microchannel heat sinks with multiple heat sources

Dimensional optimization of silicon microchannel heat sinks is performed by minimizing the total thermal resistance. Intel Core i7-900 Desktop Processor of chip core dimensions of 1.891 cm x 1.44 cm is considered as a reference processor which is reported to dissipate 130 W of heat. The properties are evaluated at the area weighted average of the fluid inlet and iteratively calculated outlet temperatures. The effects of the thermal and hydrodynamic entrance regions on heat transfer and flow are also investigated. The study is unique in that the optimization has been performed for localized multiple heat sources, as well as for a uniform heat load condition. The results of the optimization agreed very well with available ones in the literature. (C) 2011 Elsevier Masson SAS. All rights reserved

Numerical simulation of flow boiling from an artificial cavity in a microchannel

Cahn Hilliard phase-field method is used to numerically simulate subcooled water boiling in which nucleation occurs from an artificial cavity on the inner surface of a microchannel. The boiling initiates from a cavity and the growth and departure of the nucleated bubbles from the cavity are simulated. The velocity, temperature and pressure distributions inside the microchannel have been analyzed. The bubble generation frequency increases by increasing inlet mass flux. For this case of study, the rising trend continues up to the mass flux of 64 kg/m(2) s. Further increase in the inlet mass flux does not accelerate the bubble formation. The radius and the shape of the generated bubble compared well with experimental data available in the literature

Entropy generation analysis and dimensional optimization of an evaporator for use in a microscale refrigeration cycle

Entropy generation in the evaporator of a microscale vapor compression refrigeration cycle is investigated under the effects of vapor quality, mass and heat flux, saturation temperature, and channel dimensions. For a variety of channel heights and mass flow rates, the optimum vapor quality, and the channel and fin widths yielding minimum entropy generation are obtained. The variation of heat transfer coefficient with vapor quality, and pressure drop with heat flux compare very well with literature. The vapor quality yielding the minimum entropy generation is found as 0.846. The optimum channel and fin widths are 66 and 50 mu m, respectively, for 700 mu m channel height. Heat transfer is the major source of the total entropy production for 200-400 mu m wide channels, while the contribution of pressure drop becomes comparable for narrower channels. The study is unique in the literature in pursuing an entropy generation minimization study for microscale two-phase flow