Breast cancer is the most common cancer among women. Statistics released by the American Cancer Society (1999) show that every 1 in 8 women in the United States is likely to get breast cancer during her lifetime. Thermography, also known as thermal or infrared imaging, is a procedure to determine if an abnormality is present in the breast tissue temperature distribution, which may indicate the presence of an embedded tumor. In the year 1982, the United States Food and Drug Administration (FDA) approved thermography as an adjunct method of detecting breast cancer, which could be combined with other established techniques like mammography. Although thermography is currently used to indicate the presence of an abnormality, there are no standard protocols to interpret the abnormal thermal images and determine the size and location of an embedded tumor. This research explores the relationship between the physical characteristics of an embedded tumor and the resulting temperature distributions on the skin surface. Experiments were conducted using a resistance heater that was embedded in agar in order to simulate the heat produced by a tumor in the biological tissue. The resulting temperature distribution on the surface was imaged using an infrared camera. In order to estimate the location and heat generation rate of the source from these temperature distributions, a genetic algorithm was used as the estimation method. The genetic algorithm utilizes a finite difference scheme for the direct solution of Pennes bioheat equation. It was determined that a genetic algorithm based approach is well suited for the estimation problem since both the depth and the heat generation rate of the heat source were accurately predicted. Thermography can prove to be a valuable tool in locating tumors if combined with such an algorithm. / Master of Science

It is critical for the construction industry to ensure that new building designs and materials, including wall and floor assemblies, provide an acceptable level of fire safety. A key fire safety requirement that is specified in building codes is the minimum fire resistance rating. A manufacturer of building materials (e.g., insulation or drywall) is currently required to perform full-scale fire furnace tests in order to determine the fire resistance ratings of assemblies that use their products. Due to the cost of these tests, and the limited number of test facilities, it can be difficult to properly assess the impact of changes to individual components on the overall fire performance of an assembly during the design process. It would be advantageous to be able to use small-scale fire tests for this purpose, as these tests are relatively inexpensive to perform. One challenge in using results of small-scale fire tests to predict full-scale fire performance is the difficulty in truly representing a larger product or assembly using a small-scale test specimen. Another challenge is the lack of established methods of scaling fire test results. Cone calorimeter tests were used to measure heat transfer through small-scale specimens that are representative of generic wall assemblies for which fire resistance ratings are given in the National Building Code of Canada. Test specimens had a surface area of 111.1 mm (4.375 in.) by 111.1 mm (4.375 in.), and consisted of single or double layers of gypsum board, stone wool insulation and spruce-pine-fir (SPR) studs. As the specimens were designed to represent a one-quarter scale model of a common wall design, with studs spaced at a centre-to-centre distance of 406.4 mm (16 in.), the wood studs were made by cutting nominal 2x4 studs (38 mm by 89 mm) into 9.25 mm by 89 mm (0.375 in. by 3.5 in.) pieces. The scaled studs were then spaced at a centre-to-centre distance of 101.6 mm (4 in.). Three types of gypsum board were tested: 12.7 mm (0.5 in.) regular and lightweight gypsum board, and 15.9 mm (0.625 in.) type X gypsum board. Temperature measurements were made at various points within the specimens during 70 min exposures to an incident heat flux of 35, 50 and 75 kW/m2 using 24 AWG Type K thermocouples and an infrared thermometer. Temperature measurements made during cone calorimeter tests were compared with temperature measurements made during fire resistance tests of the same generic assemblies and the result show a very good agreement for the first 25 min of testing at the unexposed side. A one-dimensional conduction heat transfer model was developed using the finite difference method in order to predict temperatures within the small-scale wall assemblies during the cone calorimeter tests. Constant and temperature-dependent thermal properties were used in the model, in order to study the effects of changes to materials and thermal properties on fire performance. A comparison of predicted and measured temperatures during the cone calorimeter tests of the generic wall assemblies is presented in this thesis. The model had varying degrees of success in predicting temperature profiles obtained in the cone calorimeter tests. Predicted and measured times for temperatures to reach 100C and 250C on the unexposed side of the gypsum board layer closest to the cone heater were generally within 10%. There was less agreement between predicted and measured times to reach 600C at this location, and the temperature increase on the unexposed side of the test specimen. The model did not do a good job in predicting temperatures in the insulated double layer walls. Sensitivity studies show that the thermal conductivity of the gypsum board has the most significant impact on the predicted temperature.

Cryosurgery is the destruction of undesired biological tissues by freezing. Modern cryosurgery is frequently performed as a minimally-invasive procedure, where multiple hypodermic, needle-shaped cryoprobes are inserted into the target area to be treated. The aim of the cryosurgeon is to maximize cryoinjury within a target region, while minimizing damage to healthy surrounding tissues. There is an undisputed need for temperature-field reconstruction during minimally invasive cryosurgery to help the cryosurgeon achieve this aim. The work presented in this thesis is a part of ongoing project at the Biothermal Technology Laboratory (BTTL), to develop hardware and software tools to accomplish real-time temperature field reconstruction. The goal in this project is two-fold: (i) to develop the hardware necessary for miniature, wireless, implantable temperature sensors, and (ii) to develop mathematical techniques for temperature-field reconstruction in real time, which is the focus of the work presented in this thesis. To accomplish this goal, this study proposes a computational approach for real-time temperature-field reconstruction, combining data obtained from various sensing modalities such as medical imaging, cryoprobe-embedded sensors, and miniature, wireless, implantable sensors. In practice, the proposed approach aims at solving the inverse bioheat transfer problem during cryosurgery, where spatially distributed input data is used to reconstruct the temperature field. Three numerical methods have been developed and are evaluated in the scope of this thesis. The first is based on a quasi-steady approximation of the transient temperature field, which has been termed Temperature Field Reconstruction Method (TFRM). The second method is based on analogy between the fields of temperature and electrical potential, and is thus termed Potential Field Analogy Method (PFAM). The third method is essentially a hybrid of TFRM and PFAM, which has shown superior results. Each of these methods has been benchmarked against a full-scale finite elements analysis using the commercial code ANSYS. Benchmarking results display an average mismatch of less than 2 mm in 2D cases and less than 3 mm in 3D cases for the location of the clinically significance isotherms of -22°C and -45°C. In an advanced stage of numerical methods evaluation, they have been validated against experimental data, previously obtained at the BTTL. Those experiments were conducted on a gelatin solution, using proprietary liquid-nitrogen cryoprobes and a cryoheater to simulate urethral warming. The design of the experiment was aimed at creating a 2D heat-transfer problem. Validation results against experimental data suggest an average mismatch of less than 2 mm, for the hybrid of TFRM + PFAM method, which is of the order of uncertainty in estimating the freezing front location based on ultrasound imaging.

The impinging solar receiver, bearing the merits of high heat transfer coefficient and compact structure, has a great potential in the field of solar dish Brayton system. Despite the wide application of cylindrical structure in the impinging solar receiver, the research on orifice array optimization against curvature surfaces is rare.In this paper, the main objective is to study the heat transfer and pressure drop characteristics of an orifice impinging array under a constant mass flow rate and a constant surface temperature boundary condition for the future impinging receiver design. Various orifice shapes were studied via numerical tools (Ansys Fluent 14.0) and their performances in both pressure drop and heat transfer coefficient were compared. The upstream fillet orifice was found to have the lowest pressure drop with moderate compromise in heat transfer coefficient. Moreover, a mathematical optimization model, based on empirical correlations, was developed for the orifice impinging array on the convex cylindrical surfaces. This model can provide an appropriate range of orifice number and orifice diameter, from which the key factors of the array including the ratio of height and orifice diameter H/D, orifice interval, number of orifices in each tier circumferential and tier numbers can be calculated. Several validation cases were also conducted by Ansys Fluent.

A new one-dimensional heat conduction model for predicting stem heating during fires is presented. The model makes use of moisture and temperature dependent thermal properties for bark and wood. Also, the thermal aspects of the processes of bark swelling, desiccation, and devolatilization are treated in an approximate fashion. Simulation with a surface flux boundary condition requires that these phenomena be accounted for. Previous models have used temperature-time boundary conditions, which prevents them from being directly coupled to fire behavior models. This model uses a flux-time profile for its boundary condition, making it possible to eventually couple it to fire behavior models. Cambial mortality predictions are made through the incorporation of a cell mortality model. The model was developed and validated with laboratory experiments on four species.

La presente tesis se ha llevado a cabo en el Instituto de Ingeniería Energética de la Universitat Politècnica de València y durante una estancia en el National Institute of Standards and Technology (NIST). El objetivo principal de la tesis es desarrollar un modelo de alta precisión para intercambiadores de calor de microcanales (MCHX), que tiene que ser útil, en términos de coste computacional, para tareas de diseño. En la opinión del autor, existen algunos inconvenientes cuando los modelos existentes se aplican a algunos diseños recientes de intercambiador de calor, tales como MCHXs, bien de tubos en serpentín o en paralelo. Por lo tanto, la primera etapa de la tesis identifica los fenómenos que tienen el mayor impacto en la precisión de un modelo para MCHX. Adicionalmente, se evaluó el grado de cumplimiento de varias simplificaciones y enfoques clásicos. Con este fin, se desarrolló el modelo de alta precisión Fin2D como una herramienta para llevar a cabo la investigación mencionada. El modelo Fin2D es una herramienta útil para analizar los fenómenos que tienen lugar, sin embargo requiere un gran coste computacional, y por tanto no es útil para trabajos de diseño. Es por ello que en base a los conocimientos adquiridos con el modelo Fin2D, se ha desarrollado un nuevo modelo, el Fin1Dx3. Este modelo tan sólo tiene en cuenta los fenómenos más importantes, reteniendo casi la misma precisión que Fin2D, pero con una reducción en el tiempo de cálculo de un orden de magnitud. Se introduce una novedosa discretización y un esquema numérico único para el modelado de la transferencia de calor del lado del aire. Este nuevo enfoque permite modelar los fenómenos existentes de forma consistente con mayor precisión y con mucho menos simplificaciones que los modelos actuales de la literatura. Por otra parte, se logra un coste razonable de cálculo para el objetivo fijado. La tesis incluye la validación experimental de este modelo tanto para un condensador y un enfriador de gas. Con e / Martínez Ballester, S. (2012). NUMERICAL MODEL FOR MICROCHANNEL CONDENSERS AND GAS COOLERS WITH AN IMPROVED AIR-SIDE APPROACH [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/17453

During hypersonic atmospheric entry, spacecraft are exposed to enormous aerodynamic heat. To prevent the payload from overheating, charring ablative materials are favored to be applied as the heat shield at the exposing surface of the vehicle. Accurate modeling not only prevents mission failures, but also helps reduce cost. Existing models were mostly limited to one-dimensional and discrepancies were shown against measured experiments and flight-data. To help improve the models and analyze the charring ablation problems, a multidimensional material response module is developed, based on a finite volume method framework. The developed computer program is verified through a series of test-cases, and through code-to-code comparisons with a validated code. Several novel models are proposed, including a three-dimensional pyrolysis gas transport model and an orthotropic material model. The effects of these models are numerically studied and demonstrated to be significant.

Thermally developing, electro-osmotically generated flow has been analyzed for a circular microtube under imposed constant wall temperature (CWT) and constant wall heat flux (CHF) boundary conditions. Established by a voltage potential gradient along the length of the microtube, the hydrodynamics of such a flow dictate either a slug flow velocity profile (under conditions of large tube radius-to-Debye length ratio, a/lambda_d) or a family of electro-osmotic flow (EOF) velocity profiles that depend on a/lambda_d. The imposed voltage gradient results in Joule heating in the fluid with an associated volumetric source of energy. For this scenario coupled with a slug flow velocity profile, the analytical solution for the fluid temperature development has been determined for both thermal boundary conditions. The local Nusselt number for the CHF boundary condition is shown to reduce to the classical slug flow thermal development for imposed constant wall heat flux, and is independent of Joule heating source magnitude. For the CWT boundary condition, a local minimum in the streamwise variation in local Nusselt number for moderate positive dimensionless inlet temperature is predicted. For negative dimensionless inlet temperature, which arises if the fluid entrance temperature is below the tube wall temperature, the fluid is initially heated, then cooled, resulting in a singularity in the local Nusselt number at the axial location of the heating/cooling transition. The thermal development length is considerably larger than for traditional pressure-driven flow heat transfer, and is a function of the magnitudes of Peclet number and dimensionless inlet temperature. For the EOF velocity profile scenario, numerical techniques were used to predict the fluid temperature development for both wall boundary conditions by utilizing a finite control volume approach. In addition to Joule heating as an energy source, viscous dissipation is also considered. The results predict that for decreasing a/lambda_d, the local Nusselt number decreases for all axial positions and the thermal development shortens for both wall boundary conditions. Viscous dissipation has significant effect only at intermediate values of a/lambda_d. Results predict local Nusselt numbers to increase for a CWT boundary condition and to decrease for an imposed constant wall heat flux with increasing viscous dissipation.