Measurement of the thermal conductivity of thin solid films with a thermal comparator

A direct-reading thermal comparator was used to measure the thermal conductivities of several thin solid films. This new application of the thermal comparator was based on heat flow modelling using the thermal constriction resistance, generalized here for the case of a film on the surface of an infinite half-space. Four dielectric optical coating materials were tested, and found to have thermal conductivities significantly lower than those for the same material in bulk form. The finite element method was used to estimate the minimum sample dimensions required for accurate results, and the variation of the thermal constriction resistance with the assumed mode of heat flow between the comparator probe tip and the test specimen

High precision modelling of thermal perturbations with application to Pioneer 10 and Rosetta

This thesis deals with the exact numerical determination of thermal recoil pressure (TRP) and solar radiation pressure (SRP) for complex satellite geometries. The basic equations for both perturbations are introduced and expanded into a generic numerical approach based on finite element modeling and ray-tracing. The method is applied to the missions Pioneer 10 and Rosetta. For Pioneer 10, it is found that the so-called Pioneer anomaly can fully be explained by the recoil resulting from anisotropic heat radiation. In case of Rosetta, observed discrepancies of ESAs SRP models are resolved as unmodeled TRP. Furthermore both SRP and TRP are analysed for the first Earth fly-by. Here both effects can be excluded as causes of the observed fly-by anomaly

Implementation of B-splines in a Conventional Finite Element Framework

The use of B-spline interpolation functions in the finite element method (FEM) is not a new subject. B-splines have been utilized in finite elements for many reasons. One reason is the higher continuity of derivatives and smoothness of B-splines. Another reason is the possibility of reducing the required number of degrees of freedom compared to a conventional finite element analysis. Furthermore, if B-splines are utilized to represent the geometry of a finite element model, interfacing a finite element analysis program with existing computer aided design programs (which make extensive use of B-splines) is possible. While B-splines have been used in finite element analysis due to the aforementioned goals, it is difficult to find resources that describe the process of implementing B-splines into an existing finite element framework. Therefore, it is necessary to document this methodology. This implementation should conform to the structure of conventional finite elements and only require exceptions in methodology where absolutely necessary. One goal is to implement B-spline interpolation functions in a finite element framework such that it appears very similar to conventional finite elements and is easily understandable by those with a finite element background. The use of B-spline functions in finite element analysis has been studied for advantages and disadvantages. Two-dimensional B-spline and standard FEM have been compared. This comparison has addressed the accuracy as well as the computational efficiency of B-spline FEM. Results show that for a given number of degrees of freedom, B-spline FEM can produce solutions with lower error than standard FEM. Furthermore, for a given solution time and total analysis time B-spline FEM will typically produce solutions with lower error than standard FEM. However, due to a more coupled system of equations and larger elemental stiffness matrix, B-spline FEM will take longer per degree of freedom for solution and assembly times than standard FEM. Three-dimensional B-spline FEM has also been validated by the comparison of a three-dimensional model with plane-strain boundary conditions to an equivalent two-dimensional model using plane strain conditions

Geometrical modelling and numerical analysis of thermal behaviour of textile structures

The thermal properties of fabric are an important factor in the understanding of the thermo-physiological comfort of clothing. The principal aim of this research was to develop novel numerical methods, Graphical User Interface (GUI) plug-ins and experimental setup to evaluate the effective thermal conductivity and thermal resistance of different textile structures which has significant impact on the thermal comfort of clothing. The numerical methods also include the analysis of the effect of fibre orientation, thermal anisotropy of fibre, temperature dependent thermal conductivity and fibre volume fraction on the effective thermal conductivity and thermal resistance of textile fabrics. The research covers the development of geometrical models of woven, knitted, nonwoven and the composites fabric structures, evaluation of their thermal properties by using finite element method, creation of user friendly plug-ins and the extended application tools. Micro and mesoscopic scale modelling approaches were used to investigate the effective thermal conductivity and thermal resistance of textile structures. Various techniques, including scanning electron microscopy, x-ray microtomography and experimental method have been adopted to obtain the actual 3D dimensional parameters of the fabrics for finite element analysis. Research revealed that, the thermal anisotropy of fibres, fibres material orientation and temperature dependent thermal conductivity of fibre have significant impact on the effective thermal conductivity of fabrics because experimental and simulated results were highly correlated with the consideration of above mentioned factors. In addition a unique technique has been developed in modelling fabric coated by microencapsulated phase change material for temperature stable textile and clothing system. User friendly GUI plug-ins have been developed to generate both microscopic and mesoscopic scale models for finite element analysis. The plug-ins were developed by using Abaqus/CAE as a platform. The GUI Plug-ins enable automatic model generation and property analysis of knitted fabrics and composites. Apart from finite element analysis of various fabric structures, an experimental device has been developed for testing thermal conductivity of fabrics which is capable of testing small sample size within very short period of time. The device was validated by commercial available apparatus for testing of fabric thermal conductivity

B-spline finite elements for plane elasticity problems

The finite element method since its development in the 1950âÂÂs has been used extensively in solving complex problems involving partial differential equations. The conventional finite element methods use piecewise Lagrange interpolation functions for approximating displacements. The aim of this research is to explore finite element analysis using B-spline interpolation. B-splines are piecewise defined polynomial curves which provide higher continuity of derivatives than piecewise Lagrange interpolation functions. This work focuses on the implementation and comparison of the B-spline finite elements in contrast with the conventional finite elements. This thesis observes that the use of B-spline interpolation functions can reduce the computational cost significantly. It is an efficient technique and can be conveniently implemented into the existing finite element programs

Integrated polysilicon thermistors for microfluidic sensing

This thesis documents results related to the design, fabrication, and testing of integrated polysilicon thermistors for microfluidic sensing in experimental investigations of micro impinging jet cooling and microchannel flow. Such experimental study has yielded fundamental understanding and practical design guidelines of these two microfluidic applications. Novel MEMS devices fabricated include temperature imagers, MEMS nozzles and nozzle arrays, and micro fluidic couplers. A technology for suspended microchannels with integrated polysilicon thermistors has been developed and used for microchannel flow study and flow-rate sensing. Theoretical models have been developed to analyze such micro thermal and fluidic phenomena. In the micro impinging jet cooling study, a MEMS-based heat transfer measurement paradigm has been successfully developed for the first time. This includes technology for MEMS device fabrication, an experimental setup well suited for microscale thermal study, and accurate and efficient data processing techniques. Sensing and heating are integrated into a single thermal imager chip, which allows temperature measurement over a large area at very high spatial resolution. The heat transfer data demonstrate the excellent promise of micro-impinging-jet heat transfer, and provide useful rules for designing impinging-jet-based micro heat exchangers for IC packages. In the investigation of micro channel flow, suspended microchannels with integrated thermistors have successfully been designed and fabricated to study the basic science of micro-scale channel flow. Considerable discrepancies between existing theory and experimental data have been observed, and an improved flow model that accounts for the effects of compressibility, boundary slip, fluid acceleration, non-parabolic fluid velocity profile and channel-wall bulging has been proposed to address such discrepancies. In addition, micro fluidic couplers have been designed and fabricated as the fluidic interface connection between micro fluidic systems and the external macro environment. The experiments show that MEMS couplers are capable of handling pressures as high as 1200 psig. Finally, this thesis presents the development of liquid flow sensors. Resolution of 0.4 nL/min and a capability of bubble detecting have been demonstrated. A numerical model is developed to understand device operation and to guide the design process. Excellent agreement has been found between numerical and experimental results

Transient Heat Transfer in Vertical Ground Heat Exchangers

RÉSUMÉ: Cette thèse porte sur le transfert de chaleur en régime transitoire à l’intérieur et au voisinage de puits géothermiques verticaux. Un modèle hybride analytique-numérique unidimensionnel du transfert de chaleur dans les puits géothermiques est d’abord présenté. Dans ce modèle, le transfert de chaleur à l’intérieur du puits est traité numériquement alors que pour l’extérieur du puits la méthode de la source cylindrique est utilisée. Cette approche unidimensionnelle s’appuie sur plusieurs hypothèses qui sont rigoureusement présentées. De plus, plusieurs intervalles de temps doivent être considérés à partir du temps de résidence du fluide dans le puits jusqu’au pas de temps des simulations énergétiques en passant par le pas de temps des simulations numériques dans le puits. Le modèle hybride est validé avec succès en le comparant à des résultats numériques et à des résultats d’une expérience de terrain. Il est ensuite utilisé dans des simulations énergétiques d’une pompe à chaleur géothermique mono étagée reliée à un puits géothermique et opérant sur une saison de chauffage. Deux types de simulations sont réalisés, d’abord en considérant la capacité thermique du puits et ensuite en la négligeant. Les résultats montrent que le coefficient de performance (COP) annuel de la pompe à chaleur peut être sous-estimé de 4 à 4.6% lorsque les simulations ne tiennent pas compte de la capacité thermique du coulis et du fluide dans le puits géothermique. Une part importante de ce travail a porté sur la conception, la construction, et la mise en service d’une installation expérimentale à échelle réduite (1/100) pour l’étude du transfert de chaleur transitoire au voisinage de puits géothermiques dans un bac à sable. Cette installation comprend : i) un puits géothermique d’une longueur de 1.23 m muni d’un tube en U précisément positionné et rempli de petites billes de verre qui agissent comme coulis; ii) une soixantaine de thermocouples étalonnés et localisés précisément dans le bac au moyen de fils tendus permettant de mesurer la température du sable; iii) du sable de qualité laboratoire dont on connait les propriétés thermiques; iv) de l’équipement de conditionnement du fluide caloporteur permettant d’alimenter le puits avec le débit et la température voulus. Cette installation expérimentale s’est avérée être indispensable pour la validation du modèle numérique bi-dimensionnel et axi-symmétrique développé dans le cadre de cette thèse. Les résultats numériques issus de ce modèle se comparent très favorablement aux résultats expérimentaux alors que la plupart des résultats sont à l’intérieur de la bande d’incertitude expérimentale----------ABSTRACT: Transient heat transfer inside and in the vicinity of vertical ground heat exchangers is the main focus of the present thesis. A hybrid analytical-numerical one-dimensional model is presented where heat transfer in the borehole is treated numerically and ground heat transfer is handled with the classic cylindrical heat source analytical solution. The one-dimensional approach imposes several assumptions which are rigorously presented. As well, the model requires careful treatment of the various time periods from the residence time of the fluid in the borehole to the energy simulation time and including the time steps of the numerical simulation. The hybrid model is successfully validated against analytical solutions and field data. It is used in simulations over an entire heating season with a single-stage geothermal heat pump linked to a borehole. Two sets of simulations are performed: with and without borehole thermal capacity. Results show that for a typical borehole, the annual heat pump coefficient of performance (COP) can be underestimated by 4 to 4.6% when the borehole simulations do not account for the grout and fluid thermal capacities. A significant level of effort went into the design, construction, and commissioning of a small-scale (1/100) experimental sand tank to study transient heat transfer in the vicinity of boreholes. The main features of the facility include: i) an instrumented 1.23 m long borehole with a carefully positioned U-tube and filled with well-characterized small glass beads which act as the grout; ii) a string rack instrumented with some 60 calibrated thermocouples precisely located for sand temperature measurement; iii) laboratory-grade sand with known thermal properties; iv) fluid conditioning equipment that allow to feed the facility with user-specified inlet temperature and flow rate. The experimental facility proved to be invaluable for validating a two-dimensional axi-symmetric numerical model developed for this study. Comparison results show that the numerical results are in very good agreement with the experimental data with most of the results lying within the experimental uncertainty. The measured azimuthal temperature variation at the borehole wall seems to corroborate recent findings obtained using the analytical multipole method

Movement artefact rejection in impedance pneumography.

Impedance pneumography is a non-invasive and a very convenient technique for monitoring breathing. However, a major drawback of this technique is that it is impossible to monitor breathing due to large artefacts introduced by the body movements. The aim of this project was to develop a technique for reducing these 'movement artefacts'. In the first stage of the project, experimental and theoretical studies were carried out to identify an 'optimum' electrode placement that would maximise the 'sensitivity' of measured thoracic impedance to lung resistivity changes. This maximum sensitivity was obtained when the drive and the receive electrode pairs were placed in two different horizontal planes. This sensitivity was also found to increase with increase in electrode spacing. In the second stage, the optimum electrode placement was used to record thoracic impedance during movements. Movement artefacts occurred only when the electrodes moved from their initial location along with the skin, during movements. Taking into consideration these observations, a strategy was decided for placing 4 electrodes in one plane so that movement artefacts could be reduced by combining the two independent measurements. Further studies showed that movement artefacts could be reduced using a strategic 6- electrode placement in three dimensions. It was also possible to detect obstructive apnoea, as the amplitude of the breathing signal was higher than that due to obstructive apnoea and this difference was statistically significant. In these studies, the main cause of movement artefacts was identified as the movement of electrodes with the skin. A significant reduction in movement artefacts was obtained using the 6-electrode placement. This advantage of the 6-electrode placement proposed in this project, can be of great use in clinical applications such as apnoea monitoring in neonates. Further studies can be carried out to determine an optimum frequency of injected current to achieve reduction in residual movement artefacts

Cumulative Index to NASA Tech Briefs, 1963 - 1966

Cumulative index of NASA Tech Briefs dealing with electrical and electronic, physical science and energy sources, materials and chemistry, life science, and mechanical innovation