Small-scale thermoelastic damping in micro-beams utilizing the modified couple stress theory and the dual-phase-lag heat conduction model

In this article, the size-dependent behavior of micro-beams with the thermoelastic damping (TED) phenomenon is studied. The coupled thermoelasticity equations are derived on the basis of the modified couple stress theory (MCST) and dual-phase-lag (DPL) heat conduction model. By solving these coupled equations simultaneously, a closed-form expression for the TED parameter in micro-beams is presented which considers the small-scale effects incorporation. Then, the effect of various parameters on TED in micro-beams, such as micro-beam height, the type of material, boundary conditions, and aspect ratio is investigated. The results show that the influence of utilizing non-classical continuum and thermoelasticity theories on the amount of TED and the critical thickness is significant in small scales.     

The phase change thermoelastic analysis of biological tissue with variable thermal properties during cryosurgery

Abstract

In this work, the coupling phase change heat transfer process and thermal stress behavior of biological tissue during cryosurgery are studied in the context of a generalized thermoelastic theory. The nonlinear governing equations are constructed while considering the variable thermal properties and solved by a time-domain finite element method based on the effective heat capacity formulation. A 2-D tumor and normal tissue model is adopted for simulating the freezing process in cryosurgery. The effects of temperature-dependent thermal properties and relaxation time on the responses of biological tissue are discussed and illustrated graphically.     

An analytical study of the PEM fuel cell with axial convection in the gas channel

A quasi two-dimensional mathematical model for a polymer electrolyte membrane (PEM) fuel cell is developed with consideration of axial convection in the gas channel and analytical solutions are obtained. A half-cell model which contains the cathode gas channel, gas diffuser, catalyst layer, and the membrane is investigated. To account for the effect of gas velocity in the gas channel, axial convection is included in the oxygen transport equation of the gas channel. Expressions for the oxygen mass fraction distribution in the gas channel, gas diffuser, and catalyst layer, and the current density and the membrane phase potential in the catalyst layer and membrane are derived. The solutions are presented in the form of infinite series. The polarization curve is also expressed as a function of the surface overpotential. Due to the advantage of the closed-form solutions this model can be easily employed as a diagnostic tool for PEM fuel cell simulations.     

Effect of variable viscosity and thermal conductivity on heat transfer in a circular porous passage with axial conduction

In this study, heat transfer in a circular porous passage with axial conduction and variable viscosity and thermal conductivity numerically has been investigated. Heat transfer for the different values of Da and Pe is investigated. The results found show that Nusselt distribution with variable viscosity does not significantly differ from that with constant viscosity in both thermally developing and fully developed regions. However, in the developing region there is a significant difference between Nusselt distribution with variable thermal conductivity and Nusselt distribution with constant thermal conductivity. In the fully developed region Nusselt distribution with variable and constant thermal conductivities does not drastically differ. © 2012 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.21028     

Fourier finite element model for prediction of thermal buckling in disc clutches and brakes

Numerical analyses are performed on thermal buckling of annular rings using a reduced Fourier method. The stress stiffness matrix is derived from the geometric nonlinearity in the Green strains with a predefined circumferential wave number. The method is first validated through the commercial software Abaqus using an axisymmetric model. It is then implemented to solve more general nonaxisymmetric problems with multiple waves along thecircumference. It is shown that there exists a particular wave number with which the buckling temperature reaches a minimum. This research has potential applications in automotive clutch and brake designs against thermal buckling.     

An analytical model for the transverse permeability of gas diffusion layer with electrical double layer effects in proton exchange membrane fuel cells

An analytical model is presented for the transverse permeability of gas diffusion layer (GDL) based on an ordered array of parallel charged circular cylinders at the steady state. The formula of calculating the permeability of the transverse direction is given by solving the fluid momentum equation in a unit cell. In the present approach, the proposed model is explicitly related to the porosity and fiber radius of fibrous porous media, the zeta potential, and the physical properties of the electrolyte solution. Besides, the effects of these parameters (the porosity, unit cell aspect ratio, fiber radius, and molar concentration) on the transverse permeability are discussed detailedly. The model predictions are compared with the previous studies in the available literature, and good agreement is found.     

Interaction among competitive producers in the electricity market: An iterative market model for the strategic management of thermal power plants

The liberalization of the electricity sector requires utilities to develop sound operation strategies for their power plants. In this paper, attention is focused on the problem of optimizing the management of the thermal power plants belonging to a strategic producer that competes with other strategic companies and a set of smaller non-strategic ones in the day-ahead market. The market model suggested here determines an equilibrium condition over the selected period of analysis, in which no producer can increase profits by changing its supply offers given all rivals’ bids. Power plants technical and operating constraints are considered. An iterative procedure, based on the dynamic programming, is used to find the optimum production plans of each producer. Some combinations of power plants and number of producers are analyzed, to simulate for instance the decommissioning of old expensive power plants, the installation of new more efficient capacity, the severance of large dominant producers into smaller utilities, the access of new producers to the market. Their effect on power plants management, market equilibrium, electricity quantities traded and prices is discussed.