An experimental and numerical investigation of heat transfer enhancement in a three dimensional channel using wall mounted porous baffles was conducted. The module average heat transfer coefficients were measured in a uniformly heated rectangular channel with staggered positioned porous baffles. A numerical procedure was implemented, in conjunction with a commercially available Navier-Stokes solver, to model the turbulent flow in porous media. The Brinkman-Forchheimer-Extended Darcy model was used for modeling fluid flow through the porous baffles. Conventional, oneequation, and two-equation models were used for heat transfer modeling. The accuracy and characteristics of each model were investigated and discussed. The results were compared with experimental data. Baffles were mounted alternatively on the top and bottom walls. Heat transfer coefficients and pressure loss for periodically fully developed flow and heat transfer were obtained for different pore densities (10, 20, and 40 pores per inch (PPI)) with two different baffle heights ( / h h B D = 1/3 and 2/3), and two baffle thicknesses ( / t h B D = 1/3 and 1/12). The Reynolds number (Re) was varied from 20,000 to 50,000. To compare the effect of foam metal baffles, the data for conventional solid-type baffles was obtained for ( / t h B D =1/3). The maximum uncertainties associated with the module Nusselt number and friction factor were 5.8% and 4.3%, respectively. The experimental procedure was validated by comparing the data for the straight channel without baffles ( / h h B D = 0) with those in the literature. The use of porous baffles resulted in heat transfer enhancement as high as 300% compared to heat transfer in straight channels without baffles. However, the heat transfer enhancement per unit increase in pumping power was less than one for the range of parameters studied in this work. Correlation equations were developed for the heat transfer enhancement ratio and the heat transfer enhancement per unit increase in pumping power in terms of Reynolds number. The conventional theoretical model, the dispersion conductivity model, and the modified two-phase model using the local thermal non-equilibrium theory were considered. The results from each model were compared against the experimental data, and compared to each other to investigate the efficiency of each model. Also, the characteristics of each model were discussed.

The effective radiative conductivity of fibrous material is an important part of the evaluation of the thermal performance of fibrous insulators. To better evaluate this material property, a three-dimensional direct simulation model which calculates the effective radiative conductivity of fibrous material is proposed. Two different geometries are used in this analysis. The simplified model assumes that the fibers are in a cylindrical shape and does not require identically-sized fibers or a symmetric configuration. Using a geometry with properties resembling those of a fibrous insulator, a numerical calculation of the geometric configuration factor is carried out. The results show the dependency of thermal conductivity on temperature as well as the orientation of the fibers. The calculated conductivity values are also used in the continuum heat equation, and the results are compared to the ones obtained using the direct simulation approach, showing a good agreement. In continue, the simulated model is replaced by a realistic geometry obtained from X-ray micro-tomography. To study the radiative heat transfer mechanism of fibrous carbon, three-dimensional direct simulation modeling is performed. A polygonal mesh computed from tomography is used to study the effect of pore geometry on the overall radiative heat transfer performance of fibrous insulators. An robust procedure is presented for numerical calculation of the geometric configuration factor to study energy-exchange processes among small surface areas of the polygonal mesh. The methodology presented here can be applied to obtain accurate values of the effective conductivity, thereby increasing the fidelity in heat transfer analysis.

This study focuses on the numerical solution of a fourth-order cell problem obtained through a two- scale expansion approach applied to a higher gradient heat equation microscopic problem involving temperature distributions. The main objective is to investigate the temperature field within the macroscale domain and compute the effective conductivity using finite element methods. The research utilizes numerical techniques, specifically finite element methods, to solve the fourth-order cell problem and obtain the temperature distribution.

Cette de thèse comporte deux volets : Le premier, plutôt applicatif, concerne le design d'échangeurs à ailettes et à mousses ; le second, plus académique, traite des relations entre la texture des mousses métalliques et leurs propriétés thermophysiques effectives. Sur la première partie consacrée à l'amélioration des performances des échangeurs de chaleur Mota. Nous avons mis en place une méthode de dimensionnement multi-échelle adaptés aux batteries tubes-ailettes et aux échangeurs à mousse ; Nous avons développé et caractériser une architecture optimisée d'échangeur à mousse et à ailettes. Des gains de 50% ont été obtenus en termes d'efficacité énergétique et les solutions proposées sont actuellement en production.La deuxième partie concerne l'analyse des mécanismes de transferts dans les mousses et de la détermination de leurs propriétés effectives. Nous avons développé une approche basée sur la modélisation des transferts et écoulements à l'échelle du pore -confortée par le développement de bancs expérimentaux- pour déterminer ces propriétés. Nous avons réalisé une base de données de 900 mousses obtenues par élongation et cisaillement d'une cellule périodique de référence. Les propriétés effectives –tensorielles- de ces mousses ont été mesurées et leur dépendance à la morphologie et aux propriétés thermophysiques des phases a été étudiée.En conclusion, le dernier chapitre illustre la démarche naturelle de poursuite des travaux : Optimisation des géométries des échangeurs et des mousses selon les conditions applicatives. / This work is composed of two parts: the first one deals with the design of fins-and-tubes and metal foam heat exchangers; the second one deals with the relationship between foams morphology and their effective thermophysical properties. The first part is dedicated to Mota heat exchanger performance enhancement. We develop a multi-scale method to optimize both local heat transfer surfaces and global architecture of classical and foam units. We develop, using this method, new heat exchanger and we characterize it numerically and experimentally. An increase of 50% of energetic efficiency is obtained and new geometries are nowadays produced and commercialized. The second part deals with the analysis of transport phenomena in metal foams and the determination of their effectives properties. We develop an approach based on pore scale numerical simulation of conjugate heat transfer – validated by experimental results obtained on set-up developed for this study. We have generated 900 virtual samples obtained by deformation a periodic unit cell (Kelvin cell). Full effective properties tensors are determined. The influence of cell shape and classical geometrical parameters on physical properties is then studied. To conclude, in the last chapter, we present natural perspectives involved by this work: Geometrical optimization of heat exchanger architecture and foams morphology depending on the application; The use of a multi-scale approach to design modern –foam- heat exchangers.

This dissertation revisits, develops, and documents methods that can be used to calibrate spaceborne microwave radiometers once in orbit. The on-orbit calibration methods discussed within this dissertation can provide accurate and early results by utilizing Calibration Attitude Maneuvers (CAM), which encompasses Deep Space Calibration (DSC) and a new use of the Second Stokes (SS) analysis that can provide early and much needed insight on the performance of the instrument. This dissertation describes pre-existing and new methods of using DSC maneuvers as well as a simplified use of the SS procedure. Over TRMM's 17 years of operation it has provided invaluable data and has performed multiple CAMs over its lifetime. These maneuvers are analyzed to implement on-orbit calibration procedures that will be applied for future missions. In addition, this research focuses on the radiometric calibration of TMI that will be incorporated in the final processing (Archive/Legacy of the NASA TMI 1B11 brightness temperature data product). This is of importance since TMI's 17-year sensor data record must be vetted of all known calibration errors so to provide the final stable data for science users, specifically, climatological data records.