This project investigated the manufacturing of large diameter welded PTFE rings.This welding process is time consuming and can take over ten hours for one complete weld cycle. Additionally, the welds can have poor quality in the center of the material due to insufficient heating across the weld face. The goal of this research was to address these two issues by analyzing the current process to determine the root cause of weld failures while also determining the feasibility of reducing the weld cycle time. The scope of this thesis was to develop a model to better understand and simulate the current process which could then be used for design future improvements.<div><br></div><div>A MATLAB model of the current process was developed to simulate the transient heating cycle of the most common weld cycle for PTFE currently used by a manufacturer of PTFE seals. The data for the material properties was gathered from the manufacturer test data as well as from Lau et al. (1984). Temperature dependent material properties were used in the program because the PTFE is heated above its melting point during the weld cycle. Because of the complexity of this heat transfer problem, the heat flux in the model was tuned so that it accurately reflected the current process. This is because the goal of this study was not to determine the exact heat fluxas it was unknown, but to develop an accurate model. Thus, the heat flux was assumed and the model was then verified with process data. Results from the model were compared to validation results from a FLIR thermal camera. The model predicted the compared temperatures to within 3.1% error at both 15-minute and 90-minute intervals. Though there are many potential sources of error in the process and the thermal camera measurement, the model was deemed acceptable as a model of the current process. A semi-infinite heat analysis was calculated to simulate a hot plate welding method on the PTFE. This showed that the temperature of the weld face could be raised by 57.275°C. It is believed that a method similar to hot plate welding applied to PTFE could heat the material faster and more evenly than the current process, reducing the weld failures and cycle time.<br></div>

No description available.

A parallel domain decomposition Laplace transform Boundary Element Method, BEM, algorithm for the solution of large-scale transient heat conduction problems will be developed. This is accomplished by building on previous work by the author and including several new additions (most note-worthy is the extension to 3-D) aimed at extending the scope and improving the efficiency of this technique for large-scale problems. A Laplace transform method is utilized to avoid time marching and a Proper Orthogonal Decomposition, POD, interpolation scheme is used to improve the efficiency of the numerical Laplace inversion process. A detailed analysis of the Stehfest Transform (numerical Laplace inversion) is performed to help optimize the procedure for heat transfer problems. A domain decomposition process is described in detail and is used to significantly reduce the size of any single problem for the BEM, which greatly reduces the storage and computational burden of the BEM. The procedure is readily implemented in parallel and renders the BEM applicable to large-scale transient conduction problems on even modest computational platforms. A major benefit of the Laplace space approach described herein, is that it readily allows adaptation and integration of traditional BEM codes, as the resulting governing equations are time independent. This work includes the adaptation of two such traditional BEM codes for steady-state heat conduction, in both two and three dimensions. Verification and validation example problems are presented which show the accuracy and efficiency of the techniques. Additionally, comparisons to commercial Finite Volume Method results are shown to further prove the effectiveness.

The purpose of this study is to build, test, validate, and implement two heat transfer models, and couple them to an existing fluid flow solver, which can then be used for simulating multi-disciplinary problems. The first model is for heat conduction computations, the other one is a quasi-one-dimensional cooling channel model for water-cooled jacket structural analysis. The first model employs the integral, conservative form of the thermal energy equation, which is discretized by means of a finite-volume numerical scheme. A special algorithm is developed at the interface between the solid and fluid regions, in order to keep the heat flux consistent. The properties of the solid region materials can be temperature dependent, and different materials can be used in different parts of the domains, thanks to a multi-block gridding strategy. The cooling channel flow model is developed by using uasi-one-dimensional conservation laws of mass, momentum, and energy, taking into account the effects of heat transfer and friction. It is possible to have phase changes in the channel, and a mixture model is applied, which allows two phases to be present, as long as they move at the same bulk velocity and vapor quality does not exceed relatively small values. The coupling process of both models (with the fluid solver and with each other) is handled within the Loci system, and is detailed in this study. A hot-air nozzle wall problem is simulated, and the computed results are validated with available experimental data. Finally, a more complex case involving the water-cooled nozzle of a Rocket Based Combined Cycle(RBCC) gaseous oxygen/gaseous hydrogen thruster is simulated, which involves all three models, fully coupled. The calculated temperatures in the nozzle wall and at the cooling channel outlet compare favorably with experimental data.

No description available.

The study identifies a specific problem area related to students' misconceptions about heat and heat conduction. The aims of the study are to contribute knowledge about how practical activities with thermal cameras impact the interaction and understanding of heat conduction among intermediate-grade students. The study was conducted with 23 fifth-grade students in two different schools in Sweden. To address the study's purpose, groups of three to four students were observed during a designed activity in which we participated. This activity included discussions and experiments on heat conduction using a thermal camera. The activity was recorded on video and later analysed. The results of the study, presented in three experiments, indicate that the use of thermal cameras can effectively support students' understanding of heat conduction. Students articulate the concept of heat conduction and use it in discussions. Visualizing heat with the help of thermal cameras facilitates students in connecting theoretical concepts to practical situations and enhances their ability to explain and reason about the phenomenon. The study also highlights the teacher's role in guiding students in their development. Despite some difficulties in verbalizing their conclusions, students show increased awareness of heat conduction and its connection to different materials. The study thus emphasizes the potential of using thermal cameras to support teaching and improve students' understanding of how heat spreads. / Studien identifierar ett specifikt problemområde relaterat till elevers missuppfattningar om värme och värmeledning. Syften med studien är att bidra med kunskap om hur praktiska aktiviteter med värmekameror påverkar mellanstadieelevers interaktion och förståelse för hur värme sprids genom ledning. Studien är utförd på 23 elever i årskurs 5 på två olika skolor i Sverige.    För att besvara studiens syfte observerades grupper av tre till fyra elever under en designad aktivitet där vi deltog. I denna aktivitet ingick diskussioner och experiment om värmeledning där värmekamera användes. Aktiviteten videofilmades och analyserades senare.  Studiens resultat, presenterade i tre experiment, visar att användningen av värmekameror effektivt kan stödja elevernas förståelse för värmeledning. Eleverna uttrycker begreppet värmeledning och använder det i diskussioner. Visualiseringen av värme med hjälp av värmekameror underlättar för eleverna att koppla teoretiska begrepp till praktiska situationer och främjar deras förmåga att förklara och resonera kring fenomenet. Studien belyser också lärarens roll för att vägleda eleverna i deras utveckling. Trots vissa svårigheter att verbalisera sina slutsatser visar eleverna ökad medvetenhet om värmeledning och dess koppling till olika material. Studien betonar således potentialen i att använda värmekameror för att stödja undervisningen och förbättra elevernas förståelse för hur värme sprids.

<p dir="ltr">This Thesis is divided into four parts. Its main themes are the thermal transport characteristics of Surface Phonon-Polaritons (SPhPs) and Surface Plasmon Polaritons (SPPs).</p><p dir="ltr">Chapter 1 introduces the main problem at issue in this Thesis: the decline in thermal conductivity with decreasing thicknesses in electronic devices and the feasibility of optimizing polar semiconductors and metals to produce polaritons that augment heat dissipation at these length scales.</p><p dir="ltr">Chapter 2 discusses Surface Phonon-Polariton (SPhP)-mediated thermal conductivity, or radiation conduction, in polar semiconductors. It considers the propagation of SPhPs in the case of two semi-infinite planes consisting of air and a polar semiconductor with a dielectric function described by its transverse- and longitudinal-optical (TOLO) phonon energies. It characterizes twenty different polar semiconductors in terms of radiation conduction via SPhPs and proposes a Figure of Merit (FoM) that describes the effectiveness of polariton conductance using easily-measured TO and LO phonon energies and linewidths.</p><p dir="ltr">Chapter 3 considers the propagation of SPPs in the case of two semi-infinite planes consisting of air and a metal with a dielectric function described by the Lorentz-Drude (LD) model. This chapter characterizes the effectiveness of eleven different metals as radiation conductors via SPPs and relates polariton conductance to electrical resistivity. It proposes a FoM analogous to the Wiedemann-Franz law that relates the effectiveness of polariton conductance and thermal conductance to the material’s electron scattering or linewidth.</p><p dir="ltr">Chapter 4 chapter compares the relative effectiveness of SPhP- and SPP-mediated radiation conduction. It describes why SPPs demonstrate far higher polariton conductance values than SPhPs by highlighting the underlying mechanisms at work in both—that is, available modes of energy transmission and their respective mean free path lengths.</p>

The Thermal Radiation Group at Virginia Polytechnic Institute and State University has been working closely with scientists and engineers at NASA's Langley Research Center to develop accurate analytical and numerical models suitable for designing next-generation thin-film thermal radiation detectors for earth radiation budget measurement applications. The current study provides an analytical model of the notional thermal radiation detector that takes into account thermal transport phenomena, such as the contact resistance between the layers of the detector, and is suitable for use in parameter estimation. It was found that the responsivity of the detector can increase significantly due to the presence of contact resistance between the layers of the detector. Also presented is the effect of doping the thermal impedance layer of the detector with conducting particles in order to electrically link the two junctions of the detector. It was found that the responsivity and the time response of the doped detector decrease significantly in this case. The corresponding decrease of the electrical resistance of the doped thermal impedance layer is not sufficient to significantly improve the electrical performance of the detector. Finally, the "roughness effect" is shown to be unable to explain the decrease in the thermal conductivity often reported for thin-film layers / Master of Science

A unified and systematic study of one-dimensional heat conduction based on thermal relaxation is presented. Thermal relaxation is introduced through the constitutive equation (modified Fourier's law) which relates this heat flux and temperature. The resulting temperature and flux field equations become hyperbolic rather than the usual classical parabolic equations encountered in heat conduction. In this formulation, heat propagates at a finite speed and removes one of the anomalies associated to parabolic heat conduction, i.e., heat propagating at an infinite speed. In situations involving very short times, high heat fluxes, and cryogenic temperatures, a more exact constitutive relation must be introduced to preserve a finite speed to a thermal disturbance. The general one-dimensional temperature and flux formulations for the three standard orthogonal coordinate systems are presented. The general solution, in the temperature domain, is developed by the finite integral transform technique. The basic physics and mathematics are demonstrated by reviewing Taitel's problem. Then attention is turned to the effects of radially dependent systems, such as the case of a cylinder and sphere. Various thermal disturbances are studied showing the unusual physics associated with dissipative wave equations. The flux formulation is shown to be a viable alternative domain to develop the flux distribution. Once the flux distribution has been established, the temperature distribution may be obtained through the conservation of energy. Linear one-dimensional composite regions are then investigated in detail. The general temperature and flux formulations are developed for the three standard orthogonal coordinate systems. The general solution for the flux and temperature distributions are obtained in the flux domain using a generalized integral transform technique. Additional features associated with hyperbolic heat conduction are displayed through examples with various thermal disturbances. A generalized expression for temperature dependent thermal conductivity is introduced and incorporated into the one-dimensional hyperbolic heat equation. An approximate analytical solution is obtained and compared with a standard numerical method. Finally, recommendations for future analytical and experimental investigations are suggested. / Ph. D.

An experimental investigation was carried out to determine the feasibility of using thermal conductivity measurements to detect moisture concentrations in a highly porous glass fiber insulation. A new technique employing thermistor probes was used to measure thermal conductivity over a range of low moisture contents. The results indicate that the material's thermal conductivity is a strong nonlinear function of the moisture concentration. The sensitivity of the moisture content to thermal conductivity is greatest for moisture contents less than 25 per cent for the material tested. A numerical procedure for predicting the temperature and moisture distributions in a highly porous material is detailed. / Ph. D.