Wen Lih Chen

A Nonlinear Inverse Problem in Estimating the Heat Generation in Rotary Friction Welding

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown time-dependent heat generation at the interface of cylindrical bars during rotary friction welding process from the knowledge of temperature measurements taken within the stationary bar. In the direct problem, the heat capacity and thermal conductivity are functions of temperature; hence, this is a nonlinear inverse problem. The temperature data obtained from the direct problem are used to simulate the temperature measurements, and the effect of the errors in these measurements upon the precision of the estimated results is also considered. Results show that an excellent estimation on the time-dependent heat generation can be obtained for the test cases considered in this study. The current methodology can be applied to the prediction of heat generation in rotary friction welding.

Estimation of the Transient Heat Transfer Rate at the Boundary of an Electronic Chip Packaging

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown time-dependent heat transfer rate at the electronic-packaging/heat-sink-assembly interface from the knowledge of temperature measurements taken within the packaging. The temperature data obtained from the direct problem are used to simulate the temperature measurements, and the effect of the errors in these measurements upon the precision of the estimated results is also considered. Results show that an excellent estimation on the time-dependent heat transfer rate can be obtained for the test case considered here.

Three-Dimensional Pipe Fouling Layer Estimation by Using Conjugate Gradient Inverse Method

In this study, a conjugate gradient method based inverse algorithm is applied to estimate the unknown three-dimensional fouling-layer profiles on the inner wall of a piping system using simulated temperature measurements taken on the pipe wall. The temperature data obtained from the direct problem are used to simulate the exact temperature measurements. Results show that an excellent estimation on the fouling-layer profiles can be obtained for the two cases investigated in this study. The technique presented here can be used as an alternative to ultrasonic waves fouling detection techniques to provide crucial information for the optimization of cleaning schedule for piping systems.

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.

Estimating the absorptivity in laser processing by inverse methodology

In the present study, a conjugate gradient method is applied to estimate the unknown time-dependent laser absorptivity during a laser processing, based on available temperature measurements. It is assumed that no prior information is available for the functional form of the unknown absorptivity. But depending on the temperature history at a measuring position, the unknown time-dependent absorptivity can be estimated by an inverse analysis. The accuracy of the current method is examined by using the simulated exact and inexact temperature measurements. Results show that excellent agreement on the absorptivity can be obtained for all the test cases considered in this study. Subsequently, accurate melting depth and temperature distributions can also be returned. The methodology presented here can also be applied to other various applications, such as calculating the cutting forces in nanomachining by atomic force microscopy (AFM), and estimating the heat sources in a X-ray lithographic process.

Simultaneous Estimation of Boundary Heat Flux and Convective Heat Transfer Coefficient of a Curved Plate Subjected to a Slot Liquid Jet Impingement Cooling

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to simultaneously estimate the unknown boundary heat flux and convective heat transfer coefficient in a curved plate cooled by an impinging slot jet from the knowledge of temperature measurements taken within the plate. Subsequently, the distributions of temperature in the plate can be determined. It is assumed that no prior information is available on the functional forms of the heat flux and convective heat transfer coefficient; hence the procedure is classified as the function estimation in inverse calculation. The temperature data obtained from the direct problem are used to simulate the temperature measurements, and the effect of the errors and locations in these measurements upon the precision of the estimated results is also considered. Results show that an excellent estimation on the heat flux and convective heat transfer coefficient and temperature distributions can be obtained for the two test cases considered in this study.

A parametric study on the effects of displacer-cylinder-circumferential-wall thermal conditions on the performance of a γ-type LTD Stirling engine

ABSTRACT Regarding a Stirling engine’s heat source and heat sink, most of the studies in the literature focus only on the magnitude of temperature difference between them. However, different Stirling engines adopt very different heat-source and heat-sink configurations. This study is aimed at understanding the effects of different displacer-cylinder-wall thermal conditions on engine performance using computational fluid dynamics (CFD). Results include p–V diagrams, heat flux distributions, temperature variations, and effects of three displacer-cylinder-wall parameters on indicated power and efficiency. It is found that the thermal conditions on the displacer-cylinder-circumferential wall (DCCW) impose significant effects on engine performance. Within the ranges of parameters investigated in this study, extending the coverage of heat source and heat sink on this wall improves up to 28% in indicated power at the cost of losing about 10% in efficiency, proving the significance of DCCW conditions on engine performance.

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.

Integrating Domestic Air Conditioner with Solar Water Heater of the Development of an Energy-Saving Heating System

The current thesis proposed the integration of air conditioners that exhaust heat with solar energy to enhance the overall efficiency of thermal energy conversion. The analysis of thermal storage tanks of different volumes revealed that a two-ton air conditioner operating for an hour produced double energy than normal sunshine for a day. With thermal storage tanks of fixed volume, the integration of air conditioners of different tons with solar energy indicated that air conditioners of less tons produced faster and more efficient energy conversion. Therefore, the current thesis proposed that the modification of condenser in domestic air conditioner into water-cooled condenser not only enhanced the energy efficiency of air conditioners but also increased hot water supplies since hot water from air conditioners could be integrated into solar water heaters. By doing so, energy conservation and carbon reduction could be achieved.

The Modified Maximum Shear Stress Failure Theory of Ductile Material

In this study, the maximum and smallest vertical principle stresses σ1 and σ3 as well as maximum shear stress τmax distributions, obtained from Mohr circle in each quadrant, are used to investigate the applicability of various ductile material failure theories. Based on the yield tensile stress σyt equals to yield compressive stress σyc (σyt=σyc=σy) and the known practical yield shear stress and yield stress ratio τy/σy=0.42~0.75 of ductile materials, we prove that the maximum vertical stress failure theory cannot be applied to the first quadrant (σ1>σ3≧0) as well as the third quadrant (σ30 and σ3<0). In this study, the modified maximum shear stress failure line can be fit all ductile material depending on τy/σy=0.42~0.75 in all quadrants, thus the more reasonable results can be obtained.