Hung-Yi Li

A genetic algorithm for inverse radiation problems

Abstract An inverse radiation analysis for simultaneous estimation of the single scattering albedo, the optical thickness and the phase function, from the knowledge of the exit radiation intensities is presented. A genetic algorithm is adopted as the optimizer to search the parameters of the radiation system. The study shows that the single scattering albedo and the optical thickness can be estimated accurately even with noisy data. The estimation of the phase function is more difficult than that of the single scattering albedo and the optical thickness.

Performance of finned tube heat exchangers operating under frosting conditions

In this paper, the performance of flat plate finned tube heat exchangers operating under frosting conditions was investigated experimentally. Heat exchangers of single and multiple tube row(s) were tested to show the effects of various parameters on heat transfer performance. The parameters include temperature and relative humidity of air, flow rate of air, refrigerant temperature, fin pitch, and row number. The time variations of heat transfer rate, overall heat transfer coefficient, and pressure drop of heat exchangers presented.

Inverse Radiation Problem in Two-Dimensional Rectangular Media

An inverse radiation analysis is presented for estimating the unknown source term in a two-dimensional absorbing, emitting, scattering rectangular medium of known optical properties from the knowledge of the radiation intensities exiting the boundaries. The inverse problem is solved by using a least-squares method that minimizes the error between the exit radiation intensities calculated and the experimental measurements. The effects of the measurement errors, anisotropic scattering, single-scattering albedo, and optical thickness on the accuracy of the inverse analysis are investigated. Although the source term is a function of the space variables, the inverse algorithm presented requires measurements of the outgoing radiation intensities only at the center of each boundary. The study shows that the source term can be estimated accurately, even with noisy data.

Identification of wall heat flux for turbulent forced convection by inverse analysis

Abstract An inverse problem for turbulent forced convection between parallel flat plates is investigated. The space- and time-dependent heat flux at the upper wall is estimated from the temperature measurements taken inside the flow. In the present study, the conjugate gradient method is adopted for the estimation of the unknown wall heat flux. No prior information is needed for the functional form of the wall heat flux in the inverse analysis. The effects of the measurement errors, the functional form of the wall heat flux, and the location of the sensors on the accuracy of the estimation are investigated. The reconstruction of the wall heat flux is satisfactory when simulated exact or noisy data are input to the inverse analysis. The sensitivity coefficients are discussed in this paper. As expected, it is shown that the accuracy of the estimation can be improved when the sensors are located closer to the upper wall.

Radiation effects on mixed convection heat transfer in a vertical square duct

Abstract A numerical study has been made of the interaction of the thermal radiation with laminar mixed convection for a gray fluid (a gas that may have particulates in suspension) in a vertical square duct. Using the vorticity-velocity method, the three-dimensional Navier–Stokes equations and energy equations were solved simultaneously. The integro-differential radiative transfer equation was solved by the discrete ordinates method. Results are presented for a wide range of governing parameters. The effects are emphasized of thermal buoyancy and radiative transfer on the development of velocity and temperature fields, the friction factor and the Nusselt number. The results show that radiation significantly affects the total Nusselt number Nut and tends to reduce the buoyancy effects. In addition, radiation speeds the development of the temperature field.

Inverse Radiation Problem for Simultaneous Estimation of Temperature Profile and Surface Reflectivity

A method is presented for simultaneous estimation of the unknown temperature distribution and the diffuse surface reflectivity in an absorbing, emitting, and isotropically scattering medium from the knowledge of the exit radiation intensities. The inverse radiation problem is recast as an optimization problem in finite-dimensional space and the conjugate gradient method of minimization is then used for its solution. The scheme is stable, insensitive to the initial guess, and in the absence of measurement errors the estimated solution converges to the exact result. 25 refs.

Estimation of the temperature profile in a cylindrical medium by inverse analysis

Abstract An inverse radiation problem for determining the unknown temperature distribution in a one-dimensional absorbing, emitting, scattering cylindrical medium from the knowledge of the exit radiation intensities is presented. The inverse radiation problem is constructed as an optimization problem in finite-dimensional space and the conjugate gradient method is used for its solution.

A two-dimensional cylindrical inverse source problem in radiative transfer

Abstract This paper presents an approach for the estimation of the source term in a two-dimensional cylindrical absorbing, emitting, and scattering gray medium without having sensors inside the medium. The inverse source problem is solved by minimizing the square of the errors between the calculated exit radiation intensities and the simulated experimental data. The conjugate gradient method is employed for the solution of this minimization problem. The effects of the measurement errors, the source term, and the optical thickness on the accuracy of the estimation in the inverse analysis are examined.

Estimation of thermal properties in combined conduction and radiation

Abstract An inverse conduction–radiation problem for simultaneous estimation of the single scattering albedo, the optical thickness, the conduction-to-radiation parameter, and the scattering phase function from knowledge of the exit radiation intensities is presented. The inverse problem is solved by using the conjugate gradient method to minimize the error between the calculated exit intensities and the experimental data. The effects of the measurement errors, the conduction-to-radiation parameter, the single scattering albedo, the scattering phase function, and the optical thickness on the accuracy of the inverse analysis are investigated. The results show that the single scattering albedo and the optical thickness can be estimated accurately for exact and noisy data. Estimation of the conduction-to-radiation parameter and the scattering phase function is more difficult than that of the single scattering albedo and the optical thickness because the prediction of the former properties is more sensitive to the measurement errors.

Inverse Convection Problem for Determining Wall Heat Flux in Annular Duct Flow

An inverse problem for unsteady forced convection in an annular duct is presented. The simulated temperature data taken at the outer wall are used to estimate the time-dependent axially varying surface heat flux distribution at the inner wall of the annular passage. No prior information on the functional form of the unknown wall heat flux is needed in the inverse method. The effects of the functional form of the wall heat flux, the number of the measurement points, and the measurement errors on the accuracy of the estimation are investigated. The reconstruction of the timewise and spatial variations of the wall heat flux is satisfactory even if the estimated function is not smooth