Cette thèse présente une étude numérique d’un séchoir solaire indirect à convection naturelle destiné à sécher les produits agricoles (les figues). La première partie analyse un séchoir solaire contenant une chambre de séchage couplée à un absorbeur inversé et une cheminée solaire. Les simulations ont été faites afin de déterminer les champs dynamique et thermique sous l’influence de la variation de la configuration de la cheminée solaire et la taille de l’ouverture d’admission. Les équations de conservations basées sur le modèle de turbulence k-ε standard sont résolues par la méthode des volumes finis à l’aide du code commercial ANSYS-Fluent. La deuxième partie analyse l’effet d’ajouter un stockage thermique sous forme d’un lit en gravier dans la chambre de séchage. Le lit est modélisé comme un milieu poreux. En plus, cette étude propose l’utilisation d’une deuxième entrée d'air dans la chambre de séchage afin d’assurer une distribution thermique plus homogène au niveau des claies et de garantir un séchage plus uniforme. / This thesis presents a numerical study of an indirect natural convection solar dryer for drying agricultural products (Figs). The first part analyzes a solar dryer containing a drying chamber coupled to a reversed absorber and a solar chimney. Simulations were made to determine the dynamic and thermal fields under the influence of the variation of the solar chimney configuration and the size of the inlet opening. The governing equations based on the standard k-ε turbulence model are solved by the finite volume method using the ANSYS-Fluent commercial code. The second part analyzes the effect of adding a thermal storage in the form of a gravel bed in the drying chamber. The bed is modeled as a porous medium. Furthermore, this study proposes the use of a second air inlet in the drying chamber in order to ensure a more homogeneous thermal distribution at the level of the racks and to guarantee a more uniform drying.

Interactions between combinatorics and statistical mechanics have provided many fruitful insights in both fields. A compelling example is Kuperberg’s solution to the alternating sign matrix conjecture, and its following generalisations. In this thesis we investigate two models from statistical mechanics which have received attention in recent years. The first is the fully packed loop model. A conjecture from 2001 by Razumov and Stroganov opened the field for a large ongoing investigation of the O(1) loop model and its connections to a refinement of the fully packed loop model. We apply a combinatorial bijection originally found by de Gier to an older conjecture made by Propp. The second model is the hard particle model. Recent discoveries by Fendley et al. and results by Jonsson suggests that the hard square model with cylindrical boundary conditions possess some beautiful combinatorial properties. We apply both topological and purely combinatorial methods to related independence complexes to try and gain a better understanding of this model.

The firing of fuel wood has been identified as one of themain causes of pollutant emissions from small-scale (<100kW) combustion of wood fuels. The emissions are a result ofinsufficient combustion efficiency. This thesis presents a newmeasurement method to analyse the thermochemical conversion ofbiofuels in general, as well as to explain the main reason ofthe inefficient combustion of fuel wood in particular. In general, small-scale combustion of biofuels are carriedout by means of packed-bed combustion (PBC)technology. Acomprehensive literature review revealed that textbooks,theories, and methods in the field of thermochemical conversionof solid fuels in the context of PBC are scarce. This authorneeded a theoretical platform for systematic research on PBC ofbiofuels. Consequently, a new system theory - the three-stepmodel - was developed, describing the objectives of, theefficiencies of, and the process flows between, the leastcommon functions (subsystems) of a PBC system. The three stepsare referred to as the conversion system, the combustionsystem, and the heat exchanger system (boiler system). A numberof quantities and concepts, such as solid-fuel convertibles,conversion gas, conversion efficiency, and combustionefficiency, are deduced in the context of the three-step model.Based on the three-step model a measurement method washypothetically modelled aiming at the central physicalquantities of the conversion system, that is, the mass flow andstoichiometry of conversion gas, as well as the air factor ofthe conversion system. An uncertainty propagation analysis ofthe constitutive mathematical models of the method was carriedout. It indicated that it should be possible to determine themass flow and stoichiometry of conversion gas within the rangesof relative uncertainties of ±5% and ±7%,respectively. An experimental PBC system was constructed,according to the criteria defined by the hypothetical method.Finally, the method was verified with respect to total massflow of conversion gas in good agreement with the verificationmethod. The relative error of mass flow of conversion gas wasin the range of ±5% of the actual value predicted by theverification method. One experimental series was conducted applying the newmeasurement method. The studied conversion concept correspondedto overfired, updraft, horizontal fixed grate, and verticalcylindrical batch reactor. The measurements revealed newinformation on the similarities and the differences in theconversion behaviour of wood chips, wood pellets, and fuelwood. The course of a batch conversion has proven to be highlydynamic and stochastic. The dynamic range of the air factor ofthe conversion system during a run was 10:1. The empiricalstoichiometry of conversion gas during a run was CH3.1O:CH0O0. Finally ,this experimental series revealed one ofthe main reasons why fuel wood is more difficult to burn thanfor example wood pellets. The relatively dry fuel wood (12-31g/m2,s) displayed a significantly lower time-integratedmean of mass flux of conversion gas than both the wood pellets(37-62 g/m2,s) and the wood chips (50-90 g/m2,s). The higher the mass flux of conversion gasproduced in the conversion system, the higher the combustiontemperature for a given combustion system, which in turn ispositively coupled to the combustion efficiency. In future work the method will be improved so thatmeasurements of combustion efficiency can be carried out. Othertypes of conversion concepts will be studied by the method. Keywords: Packed-bed combustion, thermochemical conversionof biomass, solid-fuel combustion, fuel-bed combustion, gratecombustion, biomass combustion, gasification, pyrolysis,drying.

Solid propellant gas generators that have high gas capacity are used for fast pressurization of inflatable devices or elastic shells. However, many applications such as control surface actuation, air bottle pressurization in rocket engines and safety systems of automobiles (airbags) require exit gases at near ambient temperature. A scheme suitable for short duration applications is passive cooling of gas generator gases by using a packed bed as compact heat exchanger. A study indicated that the mass flow rates of solid propellant gas generators for applications such as air bottle pressurization and control system actuators were of the order of 1 kg/s. Since pressure and enthalpy drop correlations for packed beds with mass flow rates (~1 kg/s) and packing sphere based Reynolds number (Red) ~ 9X104 were unavailable in open literature, an experimental investigation was deemed necessary. The objectives of the present study were (a) characterization of packed beds for pressure and enthalpy drop, (b) develop Euler and Nusselt number correlations at Red~105 and (c) evolve an engineering procedure for estimation of packed bed pressure and enthalpy drop. An experimental test facility with a hydrogen-air combustor was designed and fabricated for this purpose to characterize a variety of packed beds for pressure drop and heat transfer. Flow through separate packed beds consisting of 9.5mm and 5mm steel spheres and lengths ~200mm and ~300mm were studied in the sphere based Reynolds numbers (Red) range of 0.4X104 to 8.5X104. The average porosity (є) of the randomly packed beds was ~0.4. The ratios of packed bed diameter to packing diameter for 9.5mm and 5mm sphere packing were ~ 9.5 and 18 respectively. The inlet flow temperature was unsteady and a suitable arrangement using mesh of spheres was used at either ends to eliminate flow entrance and exit effects. Stagnation pressures were measured at entry and exit of the packed beds. The pressure drop factor fpd, (ratio of Euler number (Eu) to packed bed dimensions) for packed bed with 9.5mm spheres exhibited an asymptotically decreasing trend with increasing Reynolds number, and a correlation for the pressure drop factor is proposed as, fpd=Eu/ [6(1-є) (L/dp)] =125.3 Red-0.4; 0.8X104 < Red < 8.5X104 (9.5mm sphere packing). However, for packed beds with 5mm spheres the pressure drop factor fpd, was observed to increase in the investigated Reynolds number range. The correlation based for pressure drop factor is proposed as, fpd= Eu/ [6(1-є) (L/dp)] =0.0479 Red0.37; 0.4X104 < Red < 3.9X104 (5mm sphere packing). The pressure drop factor was observed to be independent of the inlet flow temperature. Gas temperatures were measured at the entry, exit and at three axial locations along centerline in the packed beds. The solid packing temperature was measured at three axial locations in the packed bed. At Red~104, the influence of gas phase and solid phase thermal conductivity on heat transfer coefficient was found to be negligible based on order of magnitude analysis and solid packing temperature data obtained from the experiments. Evaluation of sphere based Nusselt number (Nud) at axial locations in the packed bed indicated a length effect on the heat transfer coefficient, which was a function of Reynolds number and size of spheres used in packing. The arithmetic average of Nusselt numbers at different axial locations in the packed bed were correlated as Nud=3.85 Red0.5; 0.5X104 < Red < 8.5X104. The Nusselt numbers obtained in the experiments were consistent with corresponding literature data available at lower Reynolds numbers. In this experimental study Euler number correlations for pressure drop and Nusselt number correlations for heat transfer were obtained for packed beds at Red~105. An engineering model for estimation of packed bed pressure and enthalpy drop was evolved, which is useful for sizing of packed bed heat exchanger in solid propellant gas generation systems.

Naphthenic acids (NAs) comprise a complex mixture of alkyl-substituted acyclic and cycloaliphatic carboxylic acids. NAs are present in wastewaters at petroleum refineries and in the process waters of oil sands extraction plants where they are primarily retained in large tailing ponds in the Athabasca region of Northern Alberta. The toxicity of these waters, primarily caused by NAs, dictates the need for their treatment.Bioremediation is considered as one of the most cost-effective approaches for the treatment of these wastewaters. Ex-situ bioremediation conducted in a bioreactor optimizes the microbial growth and activity by controlling environmental conditions resulting in efficient conversion of the contaminants to less harmful compounds. In this work, a circulating packed bed bioreactor (CPBB), with improved mixing, mass transfer and biomass hold-up has been used to study biodegradation of several model NA compounds: namely trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), a mixture of cis- and trans- 4-methyl-cyclohexane acetic acid (4MCHAA), and octanoic acid as well co-biodegradation of these naphthenic acids with octanoic acid, using a mixed culture developed in our laboratory. The biodegradation rates achieved for trans-4MCHCA in the CPBB are far greater than those reported previously in the literatures. The maximum biodegradation rate of trans-4MCHCA observed during batch operation was 43.5 mg/L-h, while a rate of 209 mg/L-h was achieved during continuous operation. Although cis-4MCHAA is more resistant to biodegradation when compared with trans-4MCHCA, the experimental results obtained from this study indicated both isomers were effectively biodegraded in the CPBB, with the maximum biodegradation rates being as high as 2.25 mg/L-h (cis-4MCHAA) and 4.17 mg/L-h (trans-4MCHAA) during batch operations and 4.17 mg/L-h(cis-4MCHAA) and 7.80 mg/L-h (trans-4MCHAA) during the continuous operation. Optimum temperature for biodegradation of 4MCHAA was determined as 25 aC. Furthermore, the biodegradation rate of single ring NAs (trans-4MCHCA and 4MCHAA) were found to be significantly improved through utilization of octanoic acid as a co-substrate. For example, the maximum biodegradation rate of trans-4MCHCA obtained during batch operation with the presence of octanoic acid was 112 mg/L-h, which was 2.6 times faster than the maximum value of 43.5 mg/L-h when trans-4MCHCA was used as a sole substrate. Similarly, the highest biodegradation rates of cis-4MCHAA and trans-4MCHAA were 16.7 and 28.4 mg/L-h in the presence of octanoic acid, which were 7.4 and 6.8 times higher than the maximum rates of 2.25 and 4.17 mg/L-h in the absence of octanoic acid.

Naphthenic acids (NAs) comprise a complex mixture of alkyl-substituted acyclic and cycloaliphatic carboxylic acids. NAs are present in wastewaters at petroleum refineries and in the process waters of oil sands extraction plants where they are primarily retained in large tailing ponds in the Athabasca region of Northern Alberta. The toxicity of these waters, primarily caused by NAs, dictates the need for their treatment.Bioremediation is considered as one of the most cost-effective approaches for the treatment of these wastewaters. Ex-situ bioremediation conducted in a bioreactor optimizes the microbial growth and activity by controlling environmental conditions resulting in efficient conversion of the contaminants to less harmful compounds. In this work, a circulating packed bed bioreactor (CPBB), with improved mixing, mass transfer and biomass hold-up has been used to study biodegradation of several model NA compounds: namely trans-4-methyl-1-cyclohexane carboxylic acid (trans-4MCHCA), a mixture of cis- and trans- 4-methyl-cyclohexane acetic acid (4MCHAA), and octanoic acid as well co-biodegradation of these naphthenic acids with octanoic acid, using a mixed culture developed in our laboratory. The biodegradation rates achieved for trans-4MCHCA in the CPBB are far greater than those reported previously in the literatures. The maximum biodegradation rate of trans-4MCHCA observed during batch operation was 43.5 mg/L-h, while a rate of 209 mg/L-h was achieved during continuous operation. Although cis-4MCHAA is more resistant to biodegradation when compared with trans-4MCHCA, the experimental results obtained from this study indicated both isomers were effectively biodegraded in the CPBB, with the maximum biodegradation rates being as high as 2.25 mg/L-h (cis-4MCHAA) and 4.17 mg/L-h (trans-4MCHAA) during batch operations and 4.17 mg/L-h(cis-4MCHAA) and 7.80 mg/L-h (trans-4MCHAA) during the continuous operation. Optimum temperature for biodegradation of 4MCHAA was determined as 25 aC. Furthermore, the biodegradation rate of single ring NAs (trans-4MCHCA and 4MCHAA) were found to be significantly improved through utilization of octanoic acid as a co-substrate. For example, the maximum biodegradation rate of trans-4MCHCA obtained during batch operation with the presence of octanoic acid was 112 mg/L-h, which was 2.6 times faster than the maximum value of 43.5 mg/L-h when trans-4MCHCA was used as a sole substrate. Similarly, the highest biodegradation rates of cis-4MCHAA and trans-4MCHAA were 16.7 and 28.4 mg/L-h in the presence of octanoic acid, which were 7.4 and 6.8 times higher than the maximum rates of 2.25 and 4.17 mg/L-h in the absence of octanoic acid.

The objective of this work was to develop a novel enzyme immobilization scheme for supported lipase sol-gels and to evaluate the potential of the immobilized biocatalyst for the production of biodiesel in a packed bed reactor. Two sources of lipase (EC 3.1.1.3 triacylglycerol hydrolase) were used in this study and the transesterification of methanol and triolein to produce glycerol and methyl oleate was used as a model reaction of biodiesel production. A commercially available form of immobilized lipase, Novozym® 435, was used as a basis for comparison to the literature. Upon establishing a lipase sol-gel formulation technique, the experimental methodology for the transesterification reaction using Novozyme® 435 was developed. Subsequently, a series of inert materials were considered based on their suitability as supports for immobilized lipase sol-gels and the synthesis of methyl oleate. The value of a supported lipase sol-gel is to improve the activity and stability of the enzyme and develop an immobilized biocatalyst that is practical for use under packed bed reactor conditions. Of the six support materials considered (6-12 mesh silica gel, Celite® R633, Celite® R632, Celite® R647, anion exchange resin, and Quartzel® felt), the diatomaceous earth supports (Celite® R633, R632 and R647) exhibited high enzymatic activity, were thermally stable, and possessed high sol-gel adhesion. From the three types of diatomaceous earth considered, Celite® R632 supported lipase sol-gels were identified as the most promising supported lipase sol-gels for methyl oleate production via transesterification. Upon further evaluation, the Celite® R632 lipase sol-gels were found to achieve high methyl oleate percent conversions, glycerol-water absorption was only significant at glycerol levels higher than 75%, and the immobilized lipase had high stability upon storage at 4°C for 1.5 years. To determine the effects of methanol and glycerol inhibition as well as temperature on the reaction kinetics, a ping-pong bi-bi kinetic model was developed and validated over a range of methanol concentrations and temperatures. The optimal methanol concentration for the conditions tested was in the range of 1.3 M to 2.0 M, and increased with increasing temperature. The model developed was consistent with the experimental data and confirmed that glycerol inhibition and the presence of products had significant effects on the reaction kinetics. The methyl oleate production capabilities of the Celite® supported lipase sol-gel were investigated using a packed bed reactor and compared with Novozym® 435 under similar operating conditions. A kinetic and mass transfer based model was developed for the reactor system using a novel efficiency correlation to account for the effect of glycerol on the enzymatic activity. Increasing the flow rate (1.4 mL/min to 20 mL/min) increased the reaction rate, presumably due to the reduction of the glycerol inhibition effect on the immobilized biocatalyst. The Celite® supported lipase sol-gel was found to have superior performance over Novozym® 435 both under batch stirred tank reaction conditions and in a packed bed reactor (83% conversion for Celite® sol-gel vs. 59% conversion for Novozym® 435 at 20 mL/min in the packed bed reactor). Based on the results obtained, Celite® supported lipase sol-gels exhibited good performance for the transesterification of triolein with methanol to produce methyl oleate in both batch and packed bed reactors, and warrant further exploration for the enzymatic production of biodiesel.

Packed beds find extensive application in a wide variety of industries. The objective of the present work is to analyze and evaluate the effects of the wall on structural characteristics, hydrodynamics and heat transfer in packed beds of spheres. As a first attempt, spheres of uniform size are considered. The cylindrical wall of the bed confines the location of the particles thus leading to significant radial variations in void fraction and specific lateral surface area. The two characteristics at any given radial position r* are estimated by defining a concentric cylindrical channel (CCC) of an arbitrary thickness such that its boundaries are equidistant from the cylindrical surface passing through r* and accounting for the solid volumes or lateral surface areas of the segments of spheres (cap, slice, rod and annular ring) contained in the CCC and with centers lying within a distance of a particle radius from r*.The curved boundaries of the sphere segments are rigorously accounted for. The low aspect ratio beds (aspect ratio less than or equal to 2) show three distinct types of behavior. In beds of aspect ratio 2, the void fraction starts from a value of unity at the wall and decreases to a minimum and then increases to unity at the center of the bed. In beds with aspect ratio between l\/¯3/2, there is a continuous decrease in void fraction from unity at the wall to a fairly low value towards the axis and then a slight increase followed by another decrease. The profiles for aspect ratio less than l\/¯3/2 show a continuous decrease from a value of unity at the wall to zero towards the axis. In contrast, beds of high aspect ratio show heavily damped oscillations in the void fraction up to about five particle diameters from the wall and then a constant value. The lateral surface area variations in low aspect ratio beds show a steep fall from a very high value near the wall, and in high aspect ratio beds an oscillatory nature, though not as strong as in the corresponding void fraction profiles. The distribution of flow in packed beds for steady flow of an incompressible Newtonian fluid under isothermal conditions is modeled by using Ergun equation with Brinkman-type correction to account for the viscous effects in the region close to the wall. The confining effect of the wall is incorporated through the radial variations in void fraction and specific lateral surface area. The hydraulic radius in the region next to the wall is modified to take into account the resistance of the wall surface to flow. The resulting model equations with appropriate boundary conditions are solved numerically by collocation technique. The influence of aspect ratio in the range 1.25 to 20.3 and Reynolds number from 0.1 to 1000, the two most important factors affecting the flow behavior, is evaluated. The velocity profiles show a peak in the region close to the wall thus indicating severe channeling effect in this region. The magnitude and location of the peak depend on aspect ratio and Reynolds number. The model predictions agree remarkably with reported experimental data on velocity profiles in a bed of aspect ratio 10.7, and on the effect of Reynolds number on friction factors in beds of low aspect ratio. The radial variations in void fraction, velocity and effective thermal conductivity are incorporated in the two-dimensional pseudo-homogeneous steady-state model to analyze the wall effects on heat transfer in packed beds. Both constant wall temperature and constant wall flux boundary conditions are adopted. The equations are solved numerically using finite difference technique. The radial temperature profiles are seen to be fairly uniform in beds of low aspect ratio thus showing that the often made assumption of complete radial thermal mixing in low aspect ratio beds is valid. Beds of high aspect ratio show strong radial gradients. For constant heat flux condition the slope of the temperature profile remains constant after a small distance from the Inlet thus leading to thermally fully-developed flow. For this condition the heat transfer equations are solved analytically to obtain expressions for Nusselt number and the radial temperature profiles. There is a significant difference in the temperature profiles evaluated in the presence and absence of wall effects. Good agreement is found between the Nusselt numbers obtained from the model and reported experimental data.

<p>The firing of fuel wood has been identified as one of themain causes of pollutant emissions from small-scale (<100kW) combustion of wood fuels. The emissions are a result ofinsufficient combustion efficiency. This thesis presents a newmeasurement method to analyse the thermochemical conversion ofbiofuels in general, as well as to explain the main reason ofthe inefficient combustion of fuel wood in particular.</p><p>In general, small-scale combustion of biofuels are carriedout by means of packed-bed combustion (PBC)technology. Acomprehensive literature review revealed that textbooks,theories, and methods in the field of thermochemical conversionof solid fuels in the context of PBC are scarce. This authorneeded a theoretical platform for systematic research on PBC ofbiofuels. Consequently, a new system theory - the three-stepmodel - was developed, describing the objectives of, theefficiencies of, and the process flows between, the leastcommon functions (subsystems) of a PBC system. The three stepsare referred to as the conversion system, the combustionsystem, and the heat exchanger system (boiler system). A numberof quantities and concepts, such as solid-fuel convertibles,conversion gas, conversion efficiency, and combustionefficiency, are deduced in the context of the three-step model.Based on the three-step model a measurement method washypothetically modelled aiming at the central physicalquantities of the conversion system, that is, the mass flow andstoichiometry of conversion gas, as well as the air factor ofthe conversion system. An uncertainty propagation analysis ofthe constitutive mathematical models of the method was carriedout. It indicated that it should be possible to determine themass flow and stoichiometry of conversion gas within the rangesof relative uncertainties of ±5% and ±7%,respectively. An experimental PBC system was constructed,according to the criteria defined by the hypothetical method.Finally, the method was verified with respect to total massflow of conversion gas in good agreement with the verificationmethod. The relative error of mass flow of conversion gas wasin the range of ±5% of the actual value predicted by theverification method.</p><p>One experimental series was conducted applying the newmeasurement method. The studied conversion concept correspondedto overfired, updraft, horizontal fixed grate, and verticalcylindrical batch reactor. The measurements revealed newinformation on the similarities and the differences in theconversion behaviour of wood chips, wood pellets, and fuelwood. The course of a batch conversion has proven to be highlydynamic and stochastic. The dynamic range of the air factor ofthe conversion system during a run was 10:1. The empiricalstoichiometry of conversion gas during a run was CH_3.1O:CH₀O₀. Finally ,this experimental series revealed one ofthe main reasons why fuel wood is more difficult to burn thanfor example wood pellets. The relatively dry fuel wood (12-31g/m₂,s) displayed a significantly lower time-integratedmean of mass flux of conversion gas than both the wood pellets(37-62 g/m₂,s) and the wood chips (50-90 g/m₂,s). The higher the mass flux of conversion gasproduced in the conversion system, the higher the combustiontemperature for a given combustion system, which in turn ispositively coupled to the combustion efficiency.</p><p>In future work the method will be improved so thatmeasurements of combustion efficiency can be carried out. Othertypes of conversion concepts will be studied by the method.</p><p>Keywords: Packed-bed combustion, thermochemical conversionof biomass, solid-fuel combustion, fuel-bed combustion, gratecombustion, biomass combustion, gasification, pyrolysis,drying.</p>

<p>Interactions between combinatorics and statistical mechanics have provided many fruitful insights in both fields. A compelling example is Kuperberg’s solution to the alternating sign matrix conjecture, and its following generalisations. In this thesis we investigate two models from statistical mechanics which have received attention in recent years.</p><p>The first is the fully packed loop model. A conjecture from 2001 by Razumov and Stroganov opened the field for a large ongoing investigation of the O(1) loop model and its connections to a refinement of the fully packed loop model. We apply a combinatorial bijection originally found by de Gier to an older conjecture made by Propp.</p><p>The second model is the hard particle model. Recent discoveries by Fendley et al. and results by Jonsson suggests that the hard square model with cylindrical boundary conditions possess some beautiful combinatorial properties. We apply both topological and purely combinatorial methods to related independence complexes to try and gain a better understanding of this model.</p>