Dans ce travail, on présente une étude des performances d’un capteur solaire plan double passe destiné à la production de l’air chaud permettant d’alimenter et d’améliorer les techniques de séchage. On analyse les cas d’un absorbeur avec et sans ailettes.Les modèles théoriques relatifs au capteur à air double passe avec et sans ailettes ont été établis et résolus numériquement à l’aide de codes élaborés en Fortran pour obtenir une approche globale de leur comportement ou alors à l’aide de Comsol multiphysique pour une étude plus locale. Un dispositif expérimental a été conçu pour valider les résultats obtenus numériquement. Une des particularités du capteur mis au point au laboratoire est relative à son système d'isolation. À cet effet, un matériau local composé de tiges de mil broyées (biosourcé) a été réalisé dans le but d’augmenter les performances du capteur solaire. Les propriétés des matériaux biosourcés utilisés pour l’isolation ont été identifiées à l’aide de moyens existant au laboratoire. Une comparaison des températures mesurées et calculées a permis de valider les deux approches expérimentale et numérique. L’évaluation des performances a montré une forte influence du débit et du rayonnement solaire sur le rendement énergétique du capteur solaire double passe avec ailettes. L’approche globale des bilans thermique au sein du capteur solaire repose principalement sur une bonne connaissance des coefficients d’échange entre le fluide caloporteur et l’absorbeur, un travail d’estimation de ces coefficients d’échange convectif est proposé dans la dernière partie de ce travail.Mots clés : Capteur solaire, double passe, tige de mil broyée, matériau biosourcé, modélisation numérique, expérimentale, performance. / In this work, we present a study of the performance of a double pass flat solar collector for the production of hot air to supply and improve drying techniques. The cases of an absorber with and without fins are analyzed.Theoretical models for the double pass solar collector with and without fins have been established and solved numerically using codes developed in Fortran to obtain a global approach. Comsol Multi-physics code is used for a more local study. An experimental device has been designed to validate the results obtained numerically. One of the particularities of the solar collector developed in the laboratory is its insulation system. For this, a local bio-sourced material composed of crushed millet stems has been developed to increase the performance of the solar collector. The properties of the bio-sourced materials used for insulation were characterized by using available laboratory testing model. A comparison of the measured and calculated temperatures validated both the experimental and numerical approaches. The performance evaluation showed a strong influence of the flow rate and solar radiation on the energy efficiency of the double pass finned solar collector. The global approach to heat balances within the solar collector is mainly based on the heat transfer coefficients between the fluid and the absorber. An estimation of these coefficients is proposed in the last part of this work.Keywords: Solar collector, double pass, millet rod crushed, biosourced material, numerical modeling, experiment, performance.

Among sources of renewable energy, development of tidal energy has traditionally been plagued by relatively high costs and limited availability of sites with sufficiently high tidal amplitudes or flow velocities. However, many recent technology developments and improvements, both in design (e.g. dynamic tidal power, tidal lagoons) and turbine technology (e.g. new axial turbines, crossflow turbines), showed that the economic and environmental costs may be brought down to competitive levels comparing to other conventional energy sources. It has long been identified that the Bay of Fundy is one of the world’s premier locations for the development of tidal power generating systems, since it has some of the world’s largest tidal ranges. Consequently, several proposals have been made in the recent years to find economical ways to harness the power of tides. Presently, there is considerable interest in installing tidal lagoons in the Bay of Fundy. The lagoon concept involves temporarily storing seawater behind an impoundment dike and generating power by gradually releasing the impounded seawater through conventional low-head hydroelectric turbines. A tidal lagoon will inherently modify the tides and tidal currents regime in the vicinity of the lagoon, and possibly induce effects that may be felt throughout the entire Bay of Fundy. The nature of these hydrodynamic impacts will likely depend on the size of the tidal lagoon, its location, and its method of operation. Any changes in the tidal hydrodynamics caused by a tidal lagoon may also impact on the transport of sediments throughout the region and upset ecosystems that are well adapted to existing conditions. The scale and character of the potential hydrodynamic impacts due to tidal lagoons operating in the Bay of Fundy have not been previously investigated. The present study endeavours to investigate these potential impacts to help the development of sustainable, science-based policies for the management and development of clean energy for future generations. After outlining fundamental aspects of tidal power projects taken in consideration in the Bay of Fundy, an analysis of present knowledge on tidal lagoons was conducted in order to provide a focus for subsequent investigations. Hydrodynamic modeling was used to quantify any of the potential hydrodynamic changes induced in the Bay of Fundy due to the presence of tidal lagoons. In the last part of the thesis, new relationships were derived in order to describe the amount of energy removed from tidal lagoons associated with its hydrodynamic impacts.

In this study, a numerical model is developed for determining coupled heat and moisture transfer in a run-around membrane energy exchanger (RAMEE) using two counter/cross flow exchangers and with a salt solution of MgCl2 as the coupling fluid. The counter/cross flow exchanger is a counter-flow exchanger with cross-flow inlet and outlet headers. The model is two-dimensional, steady-state and based on the physical principles of conservation of momentum, energy, and mass. The finite difference method is used in this model to discretize the governing equations.<p> The heat transfer model is validated with effectiveness correlations in the literature. It is shown that the difference between the numerical model and correlations is less than ¡À2% and ¡À2.5% for heat exchangers and run around heat exchangers (RAHE), respectively. The simultaneous heat and moisture transfer model is validated with data from another model and experiments. The inter-model comparison shows a difference of less than 1%. The experimental validation shows an average discrepancy of 1% to 17% between the experimental and numerical data for overall total effectiveness. At lower NTUs the numerical and experimental results show better agreement (e.g. within 1-4% at NTU=4).<p> The model for RAHE is used to develop new effectiveness correlations for the geometrically more complex counter/cross flow heat exchangers and RAHE systems. The correlations are developed to predict the response of the exchangers and overall system to the change of different design characteristics as it is determined by the model. Discrepancies between the simulated and correlated results are within ¡À2% for both the heat exchangers and the RAHE systems.<p> It is revealed by the model that the overall effectiveness of the counter/cross flow RAMEE depends on the entrance ratio (the ratio of the length of the inlet and outlet headers to the length of the exchanger, xi/x0), aspect ratio (the ratio of the height to the length of the exchanger, y0/x0), number of heat transfer units (NTU), heat capacity rate ratio (Cr*), number of mass transfer units (NTUm), and the mass flow rate ratio of pure salt in desiccant solution to dry air (m*). Beside these dimensionless parameters, the performance of the RAMEE system is affected by the liquid-air flow configuration and the operating inlet temperature and humidity.<p> This study concludes that the maximum effectiveness of the RAMEE system with two counter/cross flow exchangers occurs when NTU and NTUm are large (e.g. greater than 10). At any NTU, the overall effectiveness of the RAMEE system increases with Cr* until it reaches a maximum value when Cr*= . Increasing Cr* above causes the overall effectiveness to decrease slightly. Therefore, to achieve the maximum overall effectiveness of the system, Cr* must be close to . is a function of NTU and operating conditions e.g., with NTU=10, and under AHRI summer and winter operating conditions, respectively. The exchangers in the RAMEE system are needed to have a small aspect ratio (e.g. y0/x0<0.2) and small entrance ratio (e.g. xi/x0<0.1) to get the maximum overall effectiveness of a RAMEE system using two counter/cross flow exchangers. Such a RAMEE system has a total effectiveness 6% higher and 1.5% lower compared to the same cross-flow and counter-flow RAMEE, respectively (at NTU=10, Cr*¡Ö3, y0/x0=0.2 and xi/x0=0.1).

It is well established that the temperature gradients in the interiors of internally-heated mantle convection models are subadiabatic (e.g. Parmentier et al., 1994; Bunge et al., 1997, 2001). The subadiabatic gradients have been explained to arise due to a balance between vertical advection and internal heating, however, a detailed analysis of the energy balance in the subadiabatic regions has not been undertaken. In this research, I examine in detail the energy balance in a suite of two-dimensional convection calculations with mixed internal and basal heating, depth-dependent viscosity and continents. I find that there are three causes of subadiabatic gradients. One is the above-mentioned balance, which becomes significant when the ratio of internal heating to surface heat flux is large. The second mechanism involves the growth of the overshoot (maximum and minimum Temperatures along a geotherm) of the geotherm near the lower boundary where the dominant balance is between vertical and horizontal advection. The latter mechanism is significant even in relatively weakly internally heated calculations. For time-dependent calculations, I find that local secular cooling can be a dominant term in the energy equation and can lead to subadiabaticity. However, it does not show its signature on the shape of the time-averaged geotherm. I also compare the basal heat flux with parameterized calculations based on the temperature drop at the core-mantle boundary, calculated both with and without taking the subadiabatic gradient into account and I find a significantly improved fit with its inclusion.<p> I also explore a wide range of parameter space to investigate the dynamical interaction between effects due to surface boundary conditions representing continental and oceanic lithosphere and the endothermic phase boundary at 660 km-depth in two-dimensional Cartesian coordinate convection calculations. I find that phase boundary induced mantle layering is strongly affected by the wavelength of convective flows and mixed surface boundary conditions strongly increase the horizontal wavelength of convection. My study shows that for mixed cases the effects of the surface boundary conditions dominate the effects of the phase boundary. I show that the calculations with complete continental coverage have the most significantly decoupled lower and upper mantle flows and substantial thermal and mechanical layering. Unlike the free-slip case where the surface heat flux decreases substantially with increasing magnitude of the Clapeyron slope, surface heat flux is shown to be almost independent of the Clapeyron slope for mixed boundary condition cases. Although very different when not layered, models with free and mixed surfaces have very similar planforms with very large aspect ratio flows when run with large magnitudes of the Clapeyron slope. I also calculate the critical boundary layer Rayleigh number as a measure of the thermal resistance of the surface boundary layer. My results show that the thermal resistance in the oceanic and the continental regions of the mixed cases are similar to fully free and no-slip cases, respectively. I find that, even for purely basally heated models, the mantle becomes significantly subadiabatic in the presence of partial continental coverage. This is due to the significant horizontal advection of heat that occurs with very large aspect ratio convection cells.

This thesis presents an axisymmetric numerical model to simulate interfacial flows near a sharp corner, where contact line pinning occurs. The method has been used to analyze drop imbibition into a capillary. To evaluate the performance of the numerical method, for a liquid drop initially placed partially within a capillary, a thermodynamic model has also been developed, to predict equilibrium states. The first part of this thesis presents an axisymmetric VoF algorithm to simulate interfacial flows near a sharp corner. (1) A new method to exactly calculate the normals and curvatures of any circle with a radius as small as the grid size is presented. This method is a hybrid least squares height function technique which fits a discretized osculating circle to a curve, from which interface normals and curvature can be evaluated. (2) A novel technique for applying the contact angle boundary condition has been devised, based on the definition of an osculating circle near a solid phase. (3) A new flux volume construction technique is presented, which can be applied to any split advection scheme. Unlike the traditional approach where the flux volumes are assumed rectangular, the new flux volumes can be either trapezoidal or triangular. The new technique improves the accuracy and consistency of the advection scheme. (4) Explicit PLIC reconstruction expressions for axisymmetric coordinates have been derived. (5) Finally, a numerical treatment of VoF for contact line motion near a sharp corner is presented, base on the idea of contact line pinning and an edge contact angle. The second part of the thesis is on the imbibition of a drop into an open capillary. A thermodynamic analysis based on minimization of an interfacial surface energy function is presented to predict equilibrium configurations of drops. Based on the drop size compared to the hole size, the equilibrium contact angle, and the geometry of the capillary, the drop can be totally imbibed by the capillary, or may not wet the capillary at all. The thesis concludes with application of the numerical scheme to the same problem, to examine the dynamics of wetting or dewetting of a capillary. All of the simulations yield results that correspond to the equilibrium states predicted by the thermodynamic analysis, but offer additional insight on contact line motion and interface deformation near the capillary edge.

In this thesis, a numerical model for coupled heat and moisture transfer in a run around membrane energy exchanger (RAMEE) with a liquid desiccant as a coupling fluid is developed. The numerical model is two dimensional, transient and is formulated using the finite difference method with an implicit time discretization. The model for the case of only heat transfer for a single heat exchanger is compared to an available analytical solution and good agreement is obtained. It is shown that the discrepancy between the numerical and theoretical dimensionless bulk outlet temperature of the fluids is less than 4% during the transient period. The model is also validated for the case of simultaneous heat and moisture transfer using experimental data measured during the laboratory testing of a RAMEE system. The results for both sensible and latent effectiveness showed satisfactory agreement at different operating conditions. However, there are some discrepancies between the simulation and the experimental data during the transient times. It is proposed that these discrepancies may be due to experimental flow distribution problems within the exchanger. The maximum average absolute differences between the measured and simulated transient effectivenesses were 7.5% and 10.3% for summer and winter operating conditions, respectively.<p> The transient response of the RAMEE system for step changes in the inlet supply air temperature and humidity ratio is presented using the numerical model. In addition, the system quasi steady state operating conditions are predicted as the system approaches its steady state operating condition. The effect of various dimensionless parameters on the transient response is predicted separately. These included: the number of heat transfer units, thermal capacity ratio, heat loss/gain ratio, storage volume ratio and the normalized initial salt solution concentration. It is shown that the initial salt solution concentration and the storage volume of the salt solution have significant impacts on the transient response of the system and the heat loss/gain rates from/to the circulated fluid flow can change the system quasi steady effectiveness substantially. The detailed study of the transient performance of the RAMEE is useful to determine the transient response time of the system under different practical situations.

Closed-loop ground source heat pumps (GSHPs) are used to transfer thermal energy between the subsurface and conditioned spaces for heating and cooling applications. A basic GSHP is composed of a ground heat exchanger (GHX), which is a closed loop of pipe buried in the shallow subsurface circulating a heat exchange fluid, connected to a heat pump. These systems offer an energy efficient alternative to conventional heating and cooling systems; however, installation costs are higher due to the additional cost associated with the GHX. By further developing our understanding of how these ground loops interact with the subsurface, it may possible to design them more intelligently, efficiently, and economically. To gain insight into the physical processes occurring between the GHX and the subsurface and to identify efficiencies and inefficiencies in GSHP design and operation, two main research goals were defined: comprehensive monitoring of a fully functioning GSHP and intensive simulation of these systems using computer models. A 6-ton GSHP was installed at a residence in Elora, ON. An array of 64 temperature sensors was installed on and surrounding the GHX and power consumption and temperature sensors were installed on the system inside the residence. The data collected were used to help characterize and understand the function of the system, provide motivation for further investigations, and assess the impact of the time of use billing scheme on GSHP operation costs. To simulate GSHPs, two computer models were utilized. A 3D finite element model was employed to analyse the effects of pipe configuration and pipe spacing on system performance. A unique, transient 1D finite difference heat conduction model was developed to simulate a single pipe in a U-tube shape with inter-pipe interactions and was benchmarked against a tested analytical solution. The model was used to compare quasi-steady state and transient simulation of GSHPs, identify system performance efficiencies through pump schedule optimization, and investigate the effect of pipe length on system performance. A comprehensive comparison of steady state and pulsed simulation concludes that it is possible to simulate transient operation using a steady state assumption for some cases. Optimal pipe configurations are identified for a range of soil thermal properties. Optimized pump schedules are identified and analysed for a specific heat pump and fluid circulation pump. Finally, the effect of pipe spacing and length on system performance is characterized. It was found that there are few design inefficiencies that could be easily addressed to improve general design practice.

This thesis presents an axisymmetric numerical model to simulate interfacial flows near a sharp corner, where contact line pinning occurs. The method has been used to analyze drop imbibition into a capillary. To evaluate the performance of the numerical method, for a liquid drop initially placed partially within a capillary, a thermodynamic model has also been developed, to predict equilibrium states. The first part of this thesis presents an axisymmetric VoF algorithm to simulate interfacial flows near a sharp corner. (1) A new method to exactly calculate the normals and curvatures of any circle with a radius as small as the grid size is presented. This method is a hybrid least squares height function technique which fits a discretized osculating circle to a curve, from which interface normals and curvature can be evaluated. (2) A novel technique for applying the contact angle boundary condition has been devised, based on the definition of an osculating circle near a solid phase. (3) A new flux volume construction technique is presented, which can be applied to any split advection scheme. Unlike the traditional approach where the flux volumes are assumed rectangular, the new flux volumes can be either trapezoidal or triangular. The new technique improves the accuracy and consistency of the advection scheme. (4) Explicit PLIC reconstruction expressions for axisymmetric coordinates have been derived. (5) Finally, a numerical treatment of VoF for contact line motion near a sharp corner is presented, base on the idea of contact line pinning and an edge contact angle. The second part of the thesis is on the imbibition of a drop into an open capillary. A thermodynamic analysis based on minimization of an interfacial surface energy function is presented to predict equilibrium configurations of drops. Based on the drop size compared to the hole size, the equilibrium contact angle, and the geometry of the capillary, the drop can be totally imbibed by the capillary, or may not wet the capillary at all. The thesis concludes with application of the numerical scheme to the same problem, to examine the dynamics of wetting or dewetting of a capillary. All of the simulations yield results that correspond to the equilibrium states predicted by the thermodynamic analysis, but offer additional insight on contact line motion and interface deformation near the capillary edge.

In this thesis, a numerical model for coupled heat and moisture transfer in a run around membrane energy exchanger (RAMEE) with a liquid desiccant as a coupling fluid is developed. The numerical model is two dimensional, transient and is formulated using the finite difference method with an implicit time discretization. The model for the case of only heat transfer for a single heat exchanger is compared to an available analytical solution and good agreement is obtained. It is shown that the discrepancy between the numerical and theoretical dimensionless bulk outlet temperature of the fluids is less than 4% during the transient period. The model is also validated for the case of simultaneous heat and moisture transfer using experimental data measured during the laboratory testing of a RAMEE system. The results for both sensible and latent effectiveness showed satisfactory agreement at different operating conditions. However, there are some discrepancies between the simulation and the experimental data during the transient times. It is proposed that these discrepancies may be due to experimental flow distribution problems within the exchanger. The maximum average absolute differences between the measured and simulated transient effectivenesses were 7.5% and 10.3% for summer and winter operating conditions, respectively.<p> The transient response of the RAMEE system for step changes in the inlet supply air temperature and humidity ratio is presented using the numerical model. In addition, the system quasi steady state operating conditions are predicted as the system approaches its steady state operating condition. The effect of various dimensionless parameters on the transient response is predicted separately. These included: the number of heat transfer units, thermal capacity ratio, heat loss/gain ratio, storage volume ratio and the normalized initial salt solution concentration. It is shown that the initial salt solution concentration and the storage volume of the salt solution have significant impacts on the transient response of the system and the heat loss/gain rates from/to the circulated fluid flow can change the system quasi steady effectiveness substantially. The detailed study of the transient performance of the RAMEE is useful to determine the transient response time of the system under different practical situations.

In this study, a numerical model is developed for determining coupled heat and moisture transfer in a run-around membrane energy exchanger (RAMEE) using two counter/cross flow exchangers and with a salt solution of MgCl2 as the coupling fluid. The counter/cross flow exchanger is a counter-flow exchanger with cross-flow inlet and outlet headers. The model is two-dimensional, steady-state and based on the physical principles of conservation of momentum, energy, and mass. The finite difference method is used in this model to discretize the governing equations.<p> The heat transfer model is validated with effectiveness correlations in the literature. It is shown that the difference between the numerical model and correlations is less than ¡À2% and ¡À2.5% for heat exchangers and run around heat exchangers (RAHE), respectively. The simultaneous heat and moisture transfer model is validated with data from another model and experiments. The inter-model comparison shows a difference of less than 1%. The experimental validation shows an average discrepancy of 1% to 17% between the experimental and numerical data for overall total effectiveness. At lower NTUs the numerical and experimental results show better agreement (e.g. within 1-4% at NTU=4).<p> The model for RAHE is used to develop new effectiveness correlations for the geometrically more complex counter/cross flow heat exchangers and RAHE systems. The correlations are developed to predict the response of the exchangers and overall system to the change of different design characteristics as it is determined by the model. Discrepancies between the simulated and correlated results are within ¡À2% for both the heat exchangers and the RAHE systems.<p> It is revealed by the model that the overall effectiveness of the counter/cross flow RAMEE depends on the entrance ratio (the ratio of the length of the inlet and outlet headers to the length of the exchanger, xi/x0), aspect ratio (the ratio of the height to the length of the exchanger, y0/x0), number of heat transfer units (NTU), heat capacity rate ratio (Cr*), number of mass transfer units (NTUm), and the mass flow rate ratio of pure salt in desiccant solution to dry air (m*). Beside these dimensionless parameters, the performance of the RAMEE system is affected by the liquid-air flow configuration and the operating inlet temperature and humidity.<p> This study concludes that the maximum effectiveness of the RAMEE system with two counter/cross flow exchangers occurs when NTU and NTUm are large (e.g. greater than 10). At any NTU, the overall effectiveness of the RAMEE system increases with Cr* until it reaches a maximum value when Cr*= . Increasing Cr* above causes the overall effectiveness to decrease slightly. Therefore, to achieve the maximum overall effectiveness of the system, Cr* must be close to . is a function of NTU and operating conditions e.g., with NTU=10, and under AHRI summer and winter operating conditions, respectively. The exchangers in the RAMEE system are needed to have a small aspect ratio (e.g. y0/x0<0.2) and small entrance ratio (e.g. xi/x0<0.1) to get the maximum overall effectiveness of a RAMEE system using two counter/cross flow exchangers. Such a RAMEE system has a total effectiveness 6% higher and 1.5% lower compared to the same cross-flow and counter-flow RAMEE, respectively (at NTU=10, Cr*¡Ö3, y0/x0=0.2 and xi/x0=0.1).