Användningen av kommunalt avfall för att producera förnybar energi, huvudsaklig biogas, uppfyller 8 av Sveriges 16 miljökvalitetsmål. Två typer av rötningsprocesser som används är kontinuerligt omrörda tankreaktorer (CSTR) och pluggflödesreaktorer (PFR). Rapportens syfte är att direkt jämföra de två reaktorkonfigurationerna, PFR och CSTR, med samma substratblandning. Båda reaktortyperna drevs med samma belastning (5,2 g VS/L dag), hydraulisk retentionstid (30 dagar) och driftstemperatur (520C). Två PFR-reaktorer drevs med återcirkulation av rötrester. Under projektets gång mättes olika parametrar, vilka var: pH, total gasvolym och gassammansättning, FOS/TAC (organiska syror/alkalinitet), flyktiga fettsyror (VFA), ammonium-kvävekoncentration och TS (torrsubstanshalt) och VS (organiska ämnen). Studieresultatet var uppdelat i två sektioner. Avsnitt 1 sammanfattar uppstartsperioden, där alla tre CSTR (D1-R, D2-NR och C1-NR) kördes i icke-återcirkulerande läge. Uppstartsperioden gjordes för att säkerställa reaktorernas stabilitet och det gällde att uppnå en liknande baslinje för detektion. Inom studien accepterades avvikelser för baslinjen inom intervallet 0-5%. För uppstartsperioden varierade den specifika metanproduktionen med 2 % mellan D1-NR och D2-R, D1-R och C1-NR med 6 %, och D2-NR och C1-NR med 8 %. För ammoniak-koncentrationen var skillnaden mellan D1-R och D2-NR 2 % och mellan D1-R och C1-NR 9 %, mellan D2-NR och C1-NR, 7%. Med dessa variationer togs beslutet att utesluta reaktor C1-NR från den experimentella perioden för projektet. Avsnitt 2 jämför PFR och CSTR återcirkulerat/icke återcirkulerat läge. En CSTR drevs med 30 % återcirkulation av rötrest och en CSTR drevs i icke-återcirkulationsläge. Att jämföra PFR och CSTR återcirkulerat/icke återcirkulerat läge visade att PFR:erna övervann båda CSTR:erna när det gäller den specifika metanproduktionen. Där PFR producerade 395±93 NL/KgVS och 372±42 (N)L/KgVS CSTR med återcirkulation 280±10 (N)L/KgVS och den icke-återcirkulerade CSTR producerade 250±7 (N)L/KgVS. NH4+-N-nivåerna mellan PFR och CSTR visade en skillnad på 1 g/L, där PFR var den med högre NH4+-N (2,53±0,39 g/L för PFR-A och 2,73±0,43 g/L för PFR-T). En av skillnaderna mellan de återcirkulerade och de icke-återcirkulerade CSTR:erna var VFA-koncentrationen. VFA-koncentrationen i de återcirkulerade var 1,05±0,90 g/L och 0,43±0,25 g/L i de icke-återcirkulerade. VFA-koncentrationen för PFR var i genomsnitt 0,28±0,12 g/L och 0,40 ±0,16 g/L. Graden av nedbrytning i CSTRs var 90-91%, och 63-65% i PFR. Den är möjligen felberäknad och visar en inkonsekvens mellan reaktorernas prestanda och specifik metanproduktion. / The use of municipal waste to produce renewable energy, in the form of biogas, fulfils eight of Sweden's sixteen environmental quality objectives. The most common technology to produce biogas is anaerobic digestion (AD). Two common types of AD processes are continuously stirred reactors (CSTR) and plug flow reactors (PFR). The thesis aims at directly comparing the two reactor configurations using the same substrate mix. For this, two PFRs (PFR-T and PFR-A) and three CSTRs (D1-R, D2-NR and C1-NR) were setup. All reactors were operated at the same organic loading rate (5.2 g VS/L-day), hydraulic retention time (30 days) and operational temperature (52°C). During the project, various parameters were measured to evaluate the reactor performance, such as pH, total gas volume and gas composition, FOS/TAC (organic acids/alkalinity), volatile fatty acids (VFA), ammonium-nitrogen concentration, and solid and volatile solid of digestate.   The study result was divided into two sections. Section 1 summarises the start-up period (42 days), where the CSTRs and the PFRs were operated under non-recirculation mode. The start-up period was done to ensure the stability of the reactors and was concerned with achieving a similar baseline for performance. For the start-up period, the specific methane production between D1-R and D2-NR varied by 2% while the variation between C1-NR and D2-NR was 8%. Likewise, for the ammonia concentration, the difference between D1-R and D2-NR was 2%, while C1-NR differed by 9% from D2-NR. Based on these findings, the decision was taken to exclude reactor C1-NR from the experimental period of the project.  Section 2 compares the PFR and CSTR. One CSTR was operated with 30% recirculation of digest, while the other CSTR was operated in non-recirculation mode. The two PFRs were operated with recirculation of digestate. The experiments showed that the PFRs outperformed both CSTRs regarding the specific methane production. The PFRs produced 395±93 (N)L/kg-VS and 372±42 (N)L/kg-VS. In contrast, the CSTR with recirculation reached 280±10 (N)L/kg-VS and the non-recirculated CSTR produced 250±7 (N)L/kg-VS. The NH4+-N levels for the PFRs and CSTRs showed a 1 g/L difference, with a higher value for the PFRs (2.53±0.39 g/L for PFR-A, and 2.73±0.43 g/L for PFR-T). One of the significant differences between the recirculated and the non-recirculated CSTRs was the VFA concentration. The VFA concentration in the recirculated and non-recirculated reactor was 1.05±0.90 g/L and 0.43±0.25 g/L, respectively. The VFA concentration for the two PFRs was on average 0.28±0.12 g/L and 0.40 ±0.16 g/L. The degree of degradation in the CSTRs was 90-91% compared to 63-65% in the PFRs. The degree of degradation is possibly miscalculated and shows an inconsistency between the reactor performance in terms of specific methane production.

<div>Adsorbent technology is widely used in many industrial applications including waste heat recovery, water purification, and atmospheric revitalization in confined habitations. Astronauts depend on adsorbent-based systems to remove metabolic carbon dioxide (CO₂) from the cabin atmosphere; as NASA prepares for the journey to Mars, engineers are redesigning the adsorbent-based system for reduced weight and optimal efficiency. These efforts hinge upon the development of accurate, predictive models, as simulations are increasingly relied upon to save cost and time over the traditional design-build-test approach. Engineers rely on simplified models to reduce computational cost and enable parametric optimizations. Amongst these simplified models is the axially dispersed plug-flow model for predicting the adsorbate concentration during flow through an adsorbent bed. This model is ubiquitously used in designing fixed-bed adsorption systems. The current work aims to improve the accuracy of the axially dispersed plug-flow model because of its wide-spread use. This dissertation identifies the critical model inputs that drive the overall uncertainty in important output quantities then systematically improves the measurement and prediction of these input parameters. Limitations of the axially dispersed plug-flow model are also discussed, and recommendations made for identifying failure of the plug-flow assumption.</div><div><br></div><div>An uncertainty and sensitivity analysis of an axially disperse plug-flow model is first presented. Upper and lower uncertainty bounds for each of the model inputs are found by comparing empirical correlations against experimental data from the literature. Model uncertainty is then investigated by independently varying each model input between its individual upper and lower uncertainty bounds then observing the relative change in predicted effluent concentration and temperature (<i>e.g.</i>, breakthrough time, bed capacity, and effluent temperature). This analysis showed that the LDF mass transfer coefficient is the largest source of uncertainty. Furthermore, the uncertainty analysis reveals that ignoring the effect of wall-channeling on apparent axial dispersion can cause significant error in the predicted breakthrough times of small-diameter beds.</div><div><br></div><div>In addition to LDF mass transfer coefficient and axial-dispersion, equilibrium isotherms are known to be strong lever arms and a potentially dominant source of model error. As such, detailed analysis of the equilibrium adsorption isotherms for zeolite 13X was conducted to improve the fidelity of CO₂ and H₂O on equilibrium isotherms compared to extant data. These two adsorbent/adsorbate pairs are of great interest as NASA plans to use zeolite 13X in the next generation atmospheric revitalization system. Equilibrium isotherms describe a sorbent’s maximum capacity at a given temperature and adsorbate (<i>e.g.</i>, CO₂ or H₂O) partial pressure. New isotherm data from NASA Ames Research Center and NASA Marshall Space Flight Center for CO₂ and H₂O adsorption on zeolite 13X are presented. These measurements were carefully collected to eliminate sources of bias in previous data from the literature, where incomplete activation resulted in a reduced capacity. Several models are fit to the new equilibrium isotherm data and recommendations of the best model fit are made. The best-fit isotherm models from this analysis are used in all subsequent modeling efforts discussed in this dissertation.</div><div><br></div><div>The last two chapters examine the limitations of the axially disperse plug-flow model for predicting breakthrough in confined geometries. When a bed of pellets is confined in a rigid container, packing heterogeneities near the wall lead to faster flow around the periphery of the bed (<i>i.e.</i>, wall channeling). Wall-channeling effects have long been considered negligible for beds which hold more than 20 pellets across; however, the present work shows that neglecting wall-channeling effects on dispersion can yield significant errors in model predictions. There is a fundamental gap in understanding the mechanisms which control wall-channeling driven dispersion. Furthermore, there is currently no way to predict wall channeling effects a priori or even to identify what systems will be impacted by it. This dissertation aims to fill this gap using both experimental measurements and simulations to identify mechanisms which cause the plug-flow assumption to fail.</div><div><br></div><div>First, experimental evidence of wall-channeling in beds, even at large bed-to-pellet diameter ratios (<i>d</i>_bed/<i>d</i>_p=48) is presented. These experiments are then used to validate a method for accurately extracting mass transfer coefficients from data affected by significant wall channeling. The relative magnitudes of wall-channeling effects are shown to be a function of the adsorption/adsorbate pair and geometric confinement (<i>i.e.</i>, bed size). Ultimately, the axially disperse plug-flow model fails to capture the physics of breakthrough when nonplug-flow conditions prevail in the bed.</div><div><br></div><div>The final chapter of this dissertation develops a two-dimensional (2-D) adsorption model to examine the interplay of wall-channeling and adsorption kinetics and the adsorbent equilibrium capacity on breakthrough in confined geometries. The 2-D model incorporates the effect of radial variations in porosity on the velocity profile and is shown to accurately capture the effect of wall-channeling on adsorption behavior. The 2-D model is validated against experimental data, and then used to investigate whether capacity or adsorption kinetics cause certain adsorbates to exhibit more significant radial variations in concentration compared than others. This work explains channeling effects can vary for different adsorbate and/or adsorbent pairs—even under otherwise identical conditions—and highlights the importance of considering adsorption kinetics in addition to the traditional <i>d</i>_bed/<i>d</i>_p criteria.</div><div><br></div><div>This dissertation investigates key gaps in our understanding of fixed-bed adsorption. It will deliver insight into how these missing pieces impact the accuracy of predictive models and provide a means for reconciling these errors. The culmination of this work will be an accurate, predictive model that assists in the simulation-based design of the next-generation atmospheric revitalization system for humans’ journey to Mars.</div>

Plug nozzle, a passive altitude adaptive nozzle, for futuristic SSTO applications, exhibits greater efficiency as compared to conventional nozzles over a wide range of altitudes. The plug nozzle comprises of a primary nozzle and a contoured plug; an under–expanded jet exiting the primary nozzle is allowed to further expand over the plug surface for altitude adaptation. At design condition the flow expands correctly to the ambient conditions on the full length plug surface, while at off design conditions the flow adapts to the ambient conditions through wave interactions within the nozzle core jet. Based on thrust to weight considerations, the full length plug is truncated and this results in a base flow rich in flow physics. In addition, the base flow exhibits an interesting transitional behaviour from open wake to a closed wake because of the wave interactions within the nozzle core jet. The plug surface flow can further exhibit flow complexities because of wave interactions resulting from the shear layer emanating from the splitter plates, in case of clustered plug flows. Considering these flow complexities, the design of the plug nozzles and analysing the associated flows can be a challenge to the aerodynamic community. An attempt has been made in understanding this class of flows in this thesis. This objective has been accomplished using both experimental and computational tools. In the present work, both the linear and annular plug nozzle geometries have been analysed for a wide range of pressure ratios spanning from 5to 80. The linear and annular nozzles have been designed for similar flow conditions and their respective design pressure ratios are 60and 66. From the experimental and computational results, it has been shown that the computational solver performs well in predicting the wave interactions on the plug surface. In addition the limitations of the computational solver in predicting the plug base flows in general has been brought out. This limitation in itself need not be considered as a serious handicap in the design and analysis of plug nozzle flows; this is because the plug base contribution to the thrust is very minimal, as has been brought out in this thesis. Apart from this the high quality experimental data generated is also of immense value to the CFD community as this also serves as a valuable data base for CFD code validation. For analysis, the plug flow field has been categorized into three different regimes based on the primary nozzle lip expansion fan extent. The flow field is categorised based on the reflection of the primary nozzle lip expansion fan from plug surface, base region shear layer and symmetry line downstream of the base region recirculation bubble. This flow division is particularly helpful in understanding the base wake characteristics with increasing pressure ratio. The base lip pressure and the base pressure variation have been discussed with respect to the primary nozzle lip expansion fan extent. In the open wake regime (or for low pressure ratios) the wave interactions within the core jet flow impinge on the base region shear layer. Because of these interactions it is difficult to propose an empirical model for open wake base pressure. In the closed wake regime (for higher pressure ratios), the base region recirculation bubble is completely under the shower of primary nozzle lip expansion fan. Hence the base lip pressure and base pressure are frozen with respect to stagnation conditions. Based on these insights it was possible to propose empirical models for linear and annular closed wake base pressure. Along with these, a mathematical model defining a reference pressure ratio PR∗, beyond which the closed wake base pressure is expected to be more than the ambient pressure has also been proposed. This is expected to serve as a good design parameter. In case of linear plug flows, this also serves the purpose of base wake transition, for the cases considered in this thesis. The flow expansion process or the primary nozzle lip expansion fan extent was also useful in understanding the differences between the linear and annular plug nozzle flow fields. In a linear plug nozzle, the flow expands only in the streamwise direction while in an annular plug nozzle the flow expands both along the streamwise and azimuthal directions. The flow expands at a faster rate in case of annular nozzle as against linear nozzle. Hence differences are observed between the linear and annular nozzle on plug and base surfaces. On the annular plug surface more wave interactions are observed because of faster expansion. With regard to base characteristics, faster expansion in annular plug nozzle, with respect to linear nozzle, results in a lower base lip pressure, lower base pressure and higher wake transition pressure ratio. The realistic cluster plug configurations have also been considered for the present studies. The effects of clustering on the plug nozzle flow field have been brought out by considering two different linear cluster nozzles and one annular cluster nozzle. The differences in the flow field of a simple and cluster plug nozzle has been discussed. In case of simple plug nozzle wave interactions are observed only in the stream wise direction, while in case of cluster plug nozzle three dimensional wave interactions are observed because of the splitter plates. Along the splitter plate differential end conditions introduce a curved recompression shock on the plug surface. This recompression shock in turn induces a streamwise vortex and also a secondary shock. It has been observed that differences between the simple and cluster plug surface pressure field are because of three dimensional wave interactions. Regarding the base pressure, differences between the simple and cluster geometries were observed for shorter truncation plug lengths (20% length plug). While for longer plug lengths (more than 34% length) the effects of clustering were reduced on the base pressure. Regarding the transition pressure ratio, differences were observed between simple and clustered plug nozzles for all the plug lengths considered. In addition, the performance of the plug nozzles has been carried out. From the analysis it was found that the primary nozzle and plug surface are major contributors towards thrust. The base surface contributes only about 2– 3% of the thrust at design condition. Hence, from a design point of view, a computational solver can be a useful tool considering its efficacy on the plug surface and in the primary nozzle.

Plug nozzle, a passive altitude adaptive nozzle, for futuristic SSTO applications, exhibits greater efficiency as compared to conventional nozzles over a wide range of altitudes. The plug nozzle comprises of a primary nozzle and a contoured plug; an under–expanded jet exiting the primary nozzle is allowed to further expand over the plug surface for altitude adaptation. At design condition the flow expands correctly to the ambient conditions on the full length plug surface, while at off design conditions the flow adapts to the ambient conditions through wave interactions within the nozzle core jet. Based on thrust to weight considerations, the full length plug is truncated and this results in a base flow rich in flow physics. In addition, the base flow exhibits an interesting transitional behaviour from open wake to a closed wake because of the wave interactions within the nozzle core jet. The plug surface flow can further exhibit flow complexities because of wave interactions resulting from the shear layer emanating from the splitter plates, in case of clustered plug flows. Considering these flow complexities, the design of the plug nozzles and analysing the associated flows can be a challenge to the aerodynamic community. An attempt has been made in understanding this class of flows in this thesis. This objective has been accomplished using both experimental and computational tools. In the present work, both the linear and annular plug nozzle geometries have been analysed for a wide range of pressure ratios spanning from 5to 80. The linear and annular nozzles have been designed for similar flow conditions and their respective design pressure ratios are 60and 66. From the experimental and computational results, it has been shown that the computational solver performs well in predicting the wave interactions on the plug surface. In addition the limitations of the computational solver in predicting the plug base flows in general has been brought out. This limitation in itself need not be considered as a serious handicap in the design and analysis of plug nozzle flows; this is because the plug base contribution to the thrust is very minimal, as has been brought out in this thesis. Apart from this the high quality experimental data generated is also of immense value to the CFD community as this also serves as a valuable data base for CFD code validation. For analysis, the plug flow field has been categorized into three different regimes based on the primary nozzle lip expansion fan extent. The flow field is categorised based on the reflection of the primary nozzle lip expansion fan from plug surface, base region shear layer and symmetry line downstream of the base region recirculation bubble. This flow division is particularly helpful in understanding the base wake characteristics with increasing pressure ratio. The base lip pressure and the base pressure variation have been discussed with respect to the primary nozzle lip expansion fan extent. In the open wake regime (or for low pressure ratios) the wave interactions within the core jet flow impinge on the base region shear layer. Because of these interactions it is difficult to propose an empirical model for open wake base pressure. In the closed wake regime (for higher pressure ratios), the base region recirculation bubble is completely under the shower of primary nozzle lip expansion fan. Hence the base lip pressure and base pressure are frozen with respect to stagnation conditions. Based on these insights it was possible to propose empirical models for linear and annular closed wake base pressure. Along with these, a mathematical model defining a reference pressure ratio PR∗, beyond which the closed wake base pressure is expected to be more than the ambient pressure has also been proposed. This is expected to serve as a good design parameter. In case of linear plug flows, this also serves the purpose of base wake transition, for the cases considered in this thesis. The flow expansion process or the primary nozzle lip expansion fan extent was also useful in understanding the differences between the linear and annular plug nozzle flow fields. In a linear plug nozzle, the flow expands only in the streamwise direction while in an annular plug nozzle the flow expands both along the streamwise and azimuthal directions. The flow expands at a faster rate in case of annular nozzle as against linear nozzle. Hence differences are observed between the linear and annular nozzle on plug and base surfaces. On the annular plug surface more wave interactions are observed because of faster expansion. With regard to base characteristics, faster expansion in annular plug nozzle, with respect to linear nozzle, results in a lower base lip pressure, lower base pressure and higher wake transition pressure ratio. The realistic cluster plug configurations have also been considered for the present studies. The effects of clustering on the plug nozzle flow field have been brought out by considering two different linear cluster nozzles and one annular cluster nozzle. The differences in the flow field of a simple and cluster plug nozzle has been discussed. In case of simple plug nozzle wave interactions are observed only in the stream wise direction, while in case of cluster plug nozzle three dimensional wave interactions are observed because of the splitter plates. Along the splitter plate differential end conditions introduce a curved recompression shock on the plug surface. This recompression shock in turn induces a streamwise vortex and also a secondary shock. It has been observed that differences between the simple and cluster plug surface pressure field are because of three dimensional wave interactions. Regarding the base pressure, differences between the simple and cluster geometries were observed for shorter truncation plug lengths (20% length plug). While for longer plug lengths (more than 34% length) the effects of clustering were reduced on the base pressure. Regarding the transition pressure ratio, differences were observed between simple and clustered plug nozzles for all the plug lengths considered. In addition, the performance of the plug nozzles has been carried out. From the analysis it was found that the primary nozzle and plug surface are major contributors towards thrust. The base surface contributes only about 2– 3% of the thrust at design condition. Hence, from a design point of view, a computational solver can be a useful tool considering its efficacy on the plug surface and in the primary nozzle.

This work thoroughly analyzes a previously created computational model for predicting characteristic properties of the combustion process in an experimental combustion chamber. Any found shortcomings of the original model are removed and the model is further improved prior to its application on 11 real cases of combustion tests performed at various conditions and with various fuels. Data provided by the model are confronted with the data obtained during the combustion tests and the model accuracy is evaluated, based on local heat flux along the length of the combustion chamber. Finally, the overall usefulness of the model is determined by the means of evaluating the acquired accuracy values, and further possibilities of model improvement and use are presented.

<p></p><p>This doctoral dissertation takes the reader through a journey where applied shear rheology and flow-velocimetry are used to understand the mesoscopic factors that control the flow behavior of three microstructured fluids. Three individual protocols that measure relative physical and mechanical properties of the flow are developed. Each protocol aims to advance the particular transformation of novel soft materials into a commercial product converging in the demonstration of the real the chemical, physical and thermodynamical factors that could potentially drive their successful transformation. </p> <p> </p> <p>First, this dissertation introduces the use of rotational and oscillatory shear rheometry to quantify the solvent evaporation effect on the flow behavior of polymer solutions used to fabricate isoporous asymmetric membranes. Three different A-B-C triblock copolymer were evaluated: polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(4-vinylpyridine) (ISV); polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(<i>N</i>,<i>N</i>-dimethylacrylamide) (ISD); and polyisoprene-<i>b</i>-polystyrene-<i>b</i>-poly(<i>tert</i>-butyl methacrylate) (ISB). The resulting evaporation-induced microstructure showed a solution viscosity and film viscoelasticity strongly dependent on the chemical structure of the triblock copolymer molecules. </p> <p> </p> <p>Furthermore, basic shear rheometry, flow birefringence, and advanced flow-velocimetry are used to deconvolute the flow-microstructure relationships of concentrated surfactant solutions. Sodium laureth sulfate in water (SLE₁S) was used to replicate spherical, worm-like, and hexagonally packed micelles and lamellar structures. Interesting findings demonstrated that regular features of flow curves, such as power-law shear thinning behavior, resulted from a wide variety of experimental artifacts that appeared when measuring microstructured fluids with shear rheometry.</p> <p> </p> <p>Finally, the successful integration of shear rheometry to calculate essential parameters to be used in a cost-effective visualization technique (still in development) used to calculate the dissolution time of polymers is addressed. The use of oscillatory rheometry successfully quantify the viscoelastic response of polyvinyl alcohol (PVA) solutions and identify formulations changes such as additive addition. The flow behavior of PVA solutions was correlated to dissolution behavior proving that the developed protocol has a high potential as a first screening tool.</p><br><p></p>