Nazia Afrin

Numerical Simulation of Thermal Damage to Living Biological Tissues Induced by Laser Irradiation Based on a Generalized Dual Phase Lag Model

A generalized dual phase lag (DPL) bioheat model based on the nonequilibrium heat transfer in living biological tissues is applied to investigate thermal damage induced by laser irradiation. Comparisons of the temperature responses and thermal damages between the generalized and classical DPL bioheat model, derived from the constitutive DPL model and Pennes bioheat equation, are carried out in this study. It is shown that the generalized DPL model could predict significantly different temperature and thermal damage from the classical DPL model and Pennes bioheat conduction model. The generalized DPL equation can reduce to the classical Pennes heat conduction equation only when the phase lag times of temperature gradient (τ T ) and heat flux vector (τ q ) are both zero. The effects of laser parameters such as laser exposure time, laser irradiance, and coupling factor on the thermal damage are also studied.

Uncertainty Analysis of Melting and Resolidification of Gold Film Irradiated by Nano- to Femtosecond Lasers Using Stochastic Method

A sample-based stochastic model is presented to investigate the effects of uncertainties of various input parameters, including laser fluence, laser pulse duration, thermal conductivity constants for electron, and electron-lattice coupling factor, on solid-liquid phase change of gold film under nano- to femtosecond laser irradiation. Rapid melting and resolidification of a free standing gold film subject to nano- to femtosecond laser are simulated using a two-temperature model incorporated with the interfacial tracking method. The interfacial velocity and temperature are obtained by solving the energy equation in terms of volumetric enthalpy for control volume. The convergence of variance (COV) is used to characterize the variability of the input parameters, and the interquartile range (IQR) is used to calculate the uncertainty of the output parameters. The IQR analysis shows that the laser fluence and the electron-lattice coupling factor have the strongest influences on the interfacial location, velocity, and temperatures.

Effects of Beam Size and Pulse Duration on the Laser Drilling Process

A two-dimensional axisymmetric transient laser drilling model is used to analyze the effects of laser beam diameter and laser pulse duration on the laser drilling process. The model includes conduction and convection heat transfer, melting, solidification and vaporization, as well as material removal resulting from the vaporization and melt ejection. The validated model is applied to study the effects of laser beam size and pulse duration on the geometry of the drilled hole. It is found that the ablation effect decrease with the increasing beam diameter due to the effect of increased vaporization rate, and deeper hole is observed for the larger pulse width due to the higher thermal ablation efficiency.

Numerical simulation of complex flow and heat transfer induced by localized laser heating on a urethane-coated substrate

ABSTRACT A three-dimensional numerical simulation is conducted for complex flow and heat transfer that incorporate solid–liquid–vapor phase change and surface chemical reaction induced by localized laser heating on a urethane-coated stainless-steel substrate. The surface chemical reaction due to laser irradiation on the urethane-coated stainless-steel substrate, and heat and mass transfer due to melting/vaporization of the stainless steel are considered. The entire problem is solved within one computational domain that includes two solid regions and one gaseous region through a penalty method. One of the solid region is the paint that will decompose via chemical reaction to generate gaseous products and then mix with the air, and the other one is the stainless steel that melting and vaporization can occur due to extremely high temperature in the process. Moreover, the gas phase is considered as a multicomponent system that consists of O2, N2, CO2, H2O, NO2, binder vapor, and stainless-steel vapor. In the present multiphysics simulation, the process of melting, vaporization and chemical reaction and the splash of the melted paint and stainless steel into the gas is observed.

Uncertainty analysis of thermal damage to living biological tissues by laser irradiation based on a generalized duel-phase lag model

ABSTRACT The effects of uncertainties of laser exposure time, phase lag times, blood perfusion coefficient, scattering coefficient, and diffuse reflectance of light on the thermal damage of living biological tissue by laser irradiation are investigated using a sample-based stochastic model. The variabilities of input and output parameters are quantified using the coefficient of variance (COV) and interquartile range (IQR), respectively. The IQR analysis concluded that phase lag times for temperature gradient and heat flux, laser exposure time, and blood perfusion rate have more significant influences on the maximum temperature and maximum thermal damage of the living biological tissue induced by laser irradiation than the diffuse reflectance of light and scattering coefficient.

MULTICOMPONENT GAS-PARTICLE FLOW AND HEAT/MASS TRANSFER INDUCED BY A LOCALIZED LASER IRRADIATION ON A URETHANE-COATED STAINLESS STEEL SUBSTRATE

A three-dimensional numerical simulation is conducted for a complex process in a laser-material system, which involves heat and mass transfer in a compressible gaseous phase and chemical reaction during laser irradiation on a urethane paint coated on a stainless steel substrate. A finite volume method (FVM) with a co-located grid mesh that discretizes the entire computational domain is employed to simulate the heating process. The results show that when the top surface of the paint reaches a threshold temperature of 560 K, the polyurethane starts to decompose through chemical reaction. As a result, combustion products CO2, H2O and NO2 are produced and chromium (III) oxide, which serves as pigment in the paint, is ejected as solid parcels from the paint into the gaseous domain. Variations of temperature, density and velocity at the center of the laser irradiation spot, and the concentrations of reaction reactant/products in the gaseous phase are presented and discussed, by comparing six scenarios with different laser powers ranging from 2.5 kW to 15 kW with an increment of 2.5 kW.