Win Jin Chang

Estimation of surface heat flux and temperature distributions in a multilayer tissue based on the hyperbolic model of heat conduction

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to solve the inverse hyperbolic heat conduction problem in estimating the unknown time-dependent surface heat flux in a skin tissue, which is stratified into epidermis, dermis, and subcutaneous layers, from the temperature measurements taken within the medium. Subsequently, the temperature distributions in the tissue can be calculated as well. The concept of finite heat propagation velocity is applied to the modeling of the bioheat transfer problem. The inverse solutions will be justified based on the numerical experiments in which two different heat flux distributions are to be determined. The temperature data obtained from the direct problem are used to simulate the temperature measurements. The influence of measurement errors on the precision of the estimated results is also investigated. Results show that an excellent estimation on the time-dependent surface heat flux can be obtained for the test cases considered in this study.

Computational Modeling of Micro-Fluid Flow in a Tubular Microchannel

This paper develops models for micro-fluid flow in tubular microchannels with uniform or varying cross-sections. The fluid flow is governed by the pressure drop, the capillary force, and the viscous force. The governing equation developed for the flow incorporates two geometry parameters, namely the cross-section perimeter, S, and the cross-section area, A. In a microchannel with a uniform cross-section, the governing equation reduces to a linear initial value problem which can be solved analytically. However, in the case of a varying cross-section, the two geometry parameters vary as a function of the flow front position, L, and the nonlinear initial value problem must be solved numerically. The computational models developed in this study will be able to provide accurate predictions of the micro-fluid flow behavior in microchannels with uniform or varying cross-sections.

An inverse problem in estimating the laser irradiance and thermal damage in laser-irradiated biological tissue with a dual-phase-lag model

Abstract The aim of this study is to solve an inverse heat conduction problem to estimate the unknown time-dependent laser irradiance and thermal damage in laser-irradiated biological tissue from the temperature measurements taken within the tissue. The dual-phase-lag model is considered in the formulation of heat conduction equation. The inverse algorithm used in the study is based on the conjugate gradient method and the discrepancy principle. The effect of measurement errors and measurement locations on the estimation accuracy is also investigated. Two different examples of laser irradiance are discussed. Results show that the unknown laser irradiance and thermal damage can be predicted precisely by using the present approach for the test cases considered in this study.

Mechanical Behaviors of Nanoimprinted Cu-Ni Alloys Using Molecular Dynamics Simulation

Molecular dynamics (MD) simulation with a tight-binding potential is used to studied the mechanical behaviors of nanoimprinted Cu-Ni alloys before and after annealing. The annealing process consists of three different stages. Initially, there is a gradual heating from the original temperature of 300 K to the specified annealing temperature of 823 K and then it is followed by a period of constant heating at that temperature, after which the specimen temperature is allowed to cool gradually to the original temperature. The results showed that when the punch is advancing, the punching force obtained from the simulation with a tight-binding potential is lower than with the Morse potential. The internal energy of Cu-Ni alloys decreased with increasing the temperature and the component of Cu during the annealing process. In addition, comparing the residual stress in the Cu-Ni alloys with and without annealing treatment, the stress is significantly released after annealing.