Prilling is a spray solidification process of producing spherical beads, or prills, typically for fertilizers like urea and ammonium nitrate. The process involves molten material passing through perforated rotating containers, forming spiraling jets and breaking up into droplets due to a Rayleigh-Plateau instability by surface tension. These droplets undergo heat exchange with a cooling air stream and turn into solid prills. However, controlling prill size and shape remains challenging due to complex fluid dynamics, thermal effects, and non-Newtonian material properties. This research focuses on understanding jet breakup under the influence of thermal effects and body forces related to gravity and rotation (centrifugal and Coriolis forces). The overarching goal is to optimize the prilling process for a desired narrow prill size distribution by predicting and controlling the jet breakup process. A fundamental and holistic approach was taken based on a combination of experiments, stability analysis and various types of numerical simulations.
The study begins by exploring the dynamics of a spiraling liquid jet emitted from a rotating orifice. Using experiments, linear stability analysis and a nonlinear slender-jet model, the influence of the body forces from rotation and gravity on jet thinning and breakup is quantified. Imposed mechanical vibrations within the nozzle modulate the jet conditions at nozzle exit, enabling control over the jet breakup length and droplet size. The findings reveal that spiraling jets behave similarly to straight jets under gravity, where the body forces influence the thinning rate of the base jet and local base jet conditions control the growth rate of unstable jet perturbations. This insight opens pathways for more precise control mechanisms in various jet-based industrial applications....@en

Capacitive deionisation (CDI) is a desalination technology that removes ionic species from water through electrostatic attraction. Recently, a new CDI cell architecture has been developed with multiple channels and electrodes. Here, the ions are driven to migrate from channel to channel to desalinate the water. The inner electrodes of such a cell function as selective membranes when charged, therefore called capacitive membrane electrodes (CME). This thesis used an experimental approach to investigate the effect of the electrostatic charge and the microstructure of the CMEs on the permselectivity of these CMEs. Five different CMEs were tested in a cell to determine their permselectivities. A porometer (utilising the capillary flow technique) was used to determine the pore size distributions of the CMEs. When comparing the data from both measurements, it was found that CMEs with a higher fluid permeability also showed lower ionic resistances. A lower ionic resistance indicates a lower permselectivity. To achieve good desalination performance in multi-channel CDI, CMEs must offer low ionic resistance when ions are driven from low salinity to high salinity, while still being permselective when ions want to migrate back from high to low salinity.

As the global economy continues to expand, the demand for natural gas has surged, leading to a significant increase in LNG consumption. LNG offers a pipeline-free transportation solution, but its integration with standard natural gas systems requires an evaporation process. Currently, LNG evap- oration is commonly achieved through self-consuming processes, seawater, or air evaporators. However, there is growing interest in leveraging the cold exergy of LNG for other processes. With carbon storage gaining prominence due to climate change concerns, integrating LNG evaporation and CO2 liquefaction systems could offer potential cost reductions in the overall process. Singapore could be an optimal location for such an integrated system due to the increasing LNG imports and the desire to become carbon-neutral requiring CO2 exports. The research of this thesis therefore will be: ”How can the LNG evaporation process be integrated with a carbon-dioxide liquefaction process at an LNG terminal in Singapore?” Existing research primarily focuses on self-consuming processes or CO2 purification, leaving a gap in understanding non self-consuming systems for integrating LNG evaporation and CO2 liquefaction at cryogenic temperatures. This study aims to fill this gap by comparing various heat transfer systems and evaluating their technical and economic feasibility. Three systems have been set up to be compared: a Direct heat exchanger system, an intermediate Propane loop and an Organic Rankine cycle. The Organic Rankine cycle has been optimized based on the net power output, first and second law efficiency of the system. Subsequently, the three systems have been compared showing that the Organic Rankine cycle is dominant in technical performance, both being self sustaining and holding a second law efficiency of 82.3%, which is 5% higher than the other designed systems. Additionally, the Organic Rankine cycle has a specific net power output of 7.3 kWh per ton CO2 liquefied, which can be utilized for other processes. After this, a financial assessment is performed on the three systems based on the internal rate of return and net present value of the systems. The Direct heat exchanger showed to be dominant in terms of internal rate of return and net present value ($313M and 534.1%, respectively). The Propane loop would be the second best system in terms of internal rate of return (79.5%). The Organic Rankine cycle could provide a higher net present value than the Propane loop ($285M and $267M, respectively), assuming that constant flows could be guaranteed and no additional evaporator is required. The Direct heat exchanger would be the financial best choice for Vopak but is limited by the high risk of frost formation in the exchangers, making it an unfit choice for this application. While the Organic Rankine cycle could provide an interesting alternative due to it’s higher net present value and power generation, the system complexity, generated electricity value uncertainty and initial investment make it a less attractive choice. Based on the techno-economic analysis in its entirety, the Propane loop was determined to be the best system to combine CO2 liquefaction and LNG evaporation.

Crystallization is one of the most widely used purification and separation processes applied in a multitude of industries such as pharmaceuticals, food & beverages, agriculture, and fine chemicals. However, the initial step of the crystallization process, nucleation, is still poorly understood and highly stochastic. As a result, most crystallization processes lack proper control over the properties of the crystals produced. Among many techniques for achieving better control over the nucleation process, the application of non-photochemical laser induced nucleation (NPLIN) has gathered significant interest. This is because of its potential to improve product quality in crystallization processes by directly controlling the nucleation rate, both spatially and temporally. Additionally, NPLIN can induce crystallization in solutions that would otherwise take a long time to nucleate, offering a unique advantage over traditional methods. However, despite its promising capabilities, NPLIN is not widely used in practice yet. The fundamental mechanism behind NPLIN is not fully understood, making it unclear how it should be applied effectively in practice and for which systems NPLIN could be beneficial.

This Ph.D. project aims to delve into the fundamental mechanisms of NPLIN, by examining how specific laser and solution parameters influence nucleation kinetics, leveraging innovative experimental setups. Laser parameters being studied include laser-exposed volume, laser irradiation position, laser intensity, and laser wavelength, and solution parameters include supersaturation levels, solution filtration, and the presence of impurities or dopants, particularly nanoparticles.

The thesis begins with a comprehensive review of the experimental and computational literature on NPLIN. It then presents a detailed study on the effect of the laser-exposed volume and laser irradiation position on the nucleation probability within partly illuminated supersaturated aqueous potassium chloride solutions. An increase in the laser-exposed volume resulted in a higher nucleation probability and a higher number of crystals per nucleated sample. Furthermore, laser irradiation, particularly through the air/solution interface, not only enhances nucleation probability but also influences the formation of different crystal morphologies. These observations are partly explained by the Nanoparticle Heating mechanism and the Dielectric Polarization model (Chapter 2).

The research then transitions to a microfluidic platform, which allows for high-throughput and crystallization detection using the deep learning method. This innovative approach addresses the need for large data sets in NPLIN research, which has been a significant challenge due to the manual nature of traditional experiments. The study examines the effects of laser intensity, wavelength, supersaturation, solution filtration, and intentional doping on nucleation probability in supersaturated potassium chloride solutions. Higher laser intensities and increased supersaturation significantly enhance nucleation probabilities. The laser wavelength effect was only observed for 355 nm at higher laser intensities. Solution filtration suppresses the NPLIN effect, whereas the addition of nanoparticles as dopants into the solution not only increases the NPLIN probabilities but also affects the crystal morphology. The results highlight the importance of impurities in the solution and support the hypothesis that nanoparticle or impurity heating could be the key mechanism in understanding NPLIN (Chapter 3).

The study finally investigated the effects of solution filtration, laser intensity, and nanoparticle properties including nanoparticle concentration and material on NPLIN probability in supersaturated aqueous urea solutions. The study highlights the significant role of impurities in NPLIN, demonstrating that doping with different nanoparticle materials leads to varied nucleation probabilities. In particular, gold nanoparticles were found to enhance nucleation more effectively than silica nanoparticles. Additionally, it was observed that NPLIN probabilities followed a Poisson distribution to changes in nanoparticle concentration and laser intensity respectively. The findings in this chapter enhance our understanding of the critical role of impurities in comprehending the NPLIN mechanism (Chapter 4).@en

Crystallization is one of the most common separation techniques in chemical industry. Nonetheless, the nucleation step in the crystallization process is little understood. This makes it difficult to gain control over the crystallization process and more specifically crystal properties. Nucleation mechanics is therefore studied thoroughly. Non-Photochemical LaserInduced Nucleation has shown to be a promising technique for getting a hold on nucleation and with that crystal properties such as crystal shape, size and morphology. Althoug Non-photochemical Laser-Induced Nucleation is promising, its mechanism has not yet been uncovered and thus requires subsequent research. This research can be very intensive as it commonly requires the study of a lot of samples. Microfluidics can drastically reduce the amount of work for conducting experiments, since it allows for multiple samples, independent droplets, to be studied in a short time. In this study, a previously designed microfluidic setup is used to study two aspects of Non-Photochemical Laser-Induced Nucleation. First, the influence of time on the nucleation process is investigated by increasing the droplet pathway in an improved version of the microfluidic setup, via a longer capillary and a FEP tube coil. Second, the nanoparticle heating mechanism is explored by filtration of a supersaturated KCl solution and doping of a filtered supersaturated solution with iron oxide nanoparticles. Control cooling and laser irradiation experiments are conducted with these solutions to study the effect of nanoparticles on Non-Photochemical Laser-Induced Nucleation. Results show that increasing the droplet pathway is not that simple because of a coating issue of the capillary that can possibly be solved by trial and error and the formation of dead zones and back flow in the FEP tube coil. The effect of time on the nucleation probability in Non-Photochemical Laser-Induced Nucleation has therefore not been studied up to a satisfying result. Removal of nanoimpurities from a supersaturated KCl soltuion upon filtration gives a significantly lower nucleation probability compared to an unfiltered solution. Addition of iron oxide nanoparticles on the other hand increases the nucleation probability to 100%. These results highly support the nanoparticle heating model.

Crystallization is one of the most sought after separation and purification technique in the process industries. However, the fundamental understanding on the formation of crystals poses quite a challenge due to the inherent complexity and stochasticity associated with the process. In the past, several attempts put forth to control crystal nucleation have been anything but successful. But, more recently, the use of lasers to control primary nucleation have led to promising prospects.

In the current study, efforts were made to explore the phenomena behind Non-Photochemical Laser Induced Nucleation (NPLIN). Experiments were carried out starting with a confined microfluidic system for both supersaturated aqueous potassium permanganate and potassium chloride solutions and later extended to unconfined geometry with potassium chloride solutions. A single nanosecond laser pulse of 532 nm wavelength was employed to create vapour bubbles and the resulting crystal formation was quantified.

To begin with, a quadratic relationship between the laser energy supplied and the maximum radius of the bubble formed was observed. By systematically varying both the supplied laser energy and the solution supersaturation, the probability of crystal formation for various energy–supersaturation combinations were studied. A minimum laser energy threshold for crystal formation was observed to be a function of solution supersaturation. The results obtained in this study will aid in developing a numerical model that can apriori predict the minimum necessary laser and supersaturation conditions required for any given salt to undergo NPLIN.

Nephrolithiasis is a disease of the urinary tract system, caused by accumulating waste products which form small stones. It is known to affect people all over the world, with a prevalence in populations as high as 16.7 % in North East Thailand and 18.5 % in uranium workers in Eastern Tennessee, USA. The most found stones are Calcium (𝐶𝑎)Oxalate (𝑂𝑥)based crystals, which form when their concentrations are supersaturated in the kidney, thus exceeding their solubility limit. The most common forms of CaOxcrystals in urine are the stable Calcium Oxalate Monohydrate (COM) and the metastable Calcium Oxalate Dihydrate (COD). If they grow too large and get stuck, medical surgery is necessary to prevent kidney failure. It is therefore necessary to understand this form of biomineralization within the human body to ensure proper treatment and prevention. This study focuses on mimicking the situation in the collecting duct of the kidney. This is done in a 295𝑥45 𝜇𝑚T-shaped microchannel, wherin a 𝐶𝑎solution enters through one inlet and an 𝑂𝑥solution through a second, such that the combined fluid flowing through the main channel is supersaturated. 𝐶𝑎 and 𝑂𝑥 are dissolved in either water or artificial urine based on the works of Streit et al. In this manner, the following effects are studied: the effect of varying average velocity, the effect of adding an amount of the natural inhibitor Osteopontin in the 𝑂𝑥-inlet, and the effect of changing the 𝐶𝑎 to 𝑂𝑥 ratio in urine conditions. Besides the microfluidic experiments, three models are applied to understand the ongoing phenomena: the Surface Reaction Model (SRM)as an analytical model of the transport-reaction kinetics at the crystal surface, the Analytical Microchannel Model (AMM) as an analytical model of the momentum and mass transport through the microchannel, and the COMSOL model as a numerical model of the microchannel made in the Matlab program COMSOL. With the latter momentum and mass transport through the channel are calculated and the mass transport results are combined with Jess Urine Expert to calculate supersaturation profiles at the channel bottom, where the crystals grow. The number for the transport reaction kinetics of the crystal surface points out that the surface reaction limits the growth, not the mass transport. LowDamköhler numbers for the transport-reaction kinetics in the entire microchannel also point this out.

Crystallization is an important process occurring in the nature, pharmaceutical, and food industries. It is one of many widely used unit operations for the separation and purification of chemicals industrially. Despite its far-reaching application in fine chemicals and active pharmaceutical ingredients production, the stochastic nature of nucleation makes it difficult to obtain crystals with reproducible properties like size, structure, purity, and polymorphic form. The accidental discovery of Non-Photochemical Laser-Induced Nucleation (NPLIN) in 1996 emerged as a novel technique to tame the crystallization process. Since the laser provided better spatiotemporal control over crystal properties in a solution, NPLIN gained abundant traction over the past decades in the vial and microfluidic scaled experiments.
On the contrary, this research studies the NPLIN effect in potassium chloride (KCl) solution on a liter scale. A batch cooling crystallizer coupled with an irradiation source in the form of the laser beam is investigated here as proof of the concept study. NPLIN experiments were conducted in batch crystallizer and were compared with the control experiments. Interestingly, the laser source reduced the induction time of nucleation compared to control experiments. This phenomenon showed that nucleation kinetics can be controlled using laser properties. Furthermore, it was observed experimentally that the nuclei generated by laser in an undersaturated solution can be grown to a detectable size provided the supersaturation is increased. It was also observed that the crystal number density was more with the multiple pulses as compared to a single pulse owing to the large exposed volume by irradiation of multiple pulses in agitated bulk solution. Finally, the offline particle size distribution (PSD) comparison was done. The dominant size of crystals was 100-200 microns for the control experiment whereas, it was 300-500 microns for the NPLIN experiment. It revealed a clear shift in the peak of the dominant size of crystals indicating a growth dominant event in NPLIN experiments. Appealingly, the nature of PSD generated by laser irradiation was found similar in all repetitions. It is hypothesized that the laser generates the seeds which grow in the metastable region.
This research study provides the basis for the NPLIN study in the system resembling industrial conditions. This, in turn, will aid in the understanding of the nucleation process and, ultimately, the optimization of industrial crystallization. The results obtained can also be used to develop mathematical models for particle size distribution.

Crystallization is one of the most widely used purification and separation processes. Nevertheless, the initial step of the crystallization process, nucleation, is still poorly understood and highly stochastic. As a result, most crystallization processes lack fine control over the produced crystal properties. Non­ photochemical Laser Induced Nucleation is seen as a promising technique to optimize crystallization processes, by decreasing the induction time and potentially offering more control over crystal size, amount and morphology. However, as its underlying mechanism has not yet been unveiled its appli­ cation is still limited. Further study of the phenomenon is thus essential, yet limited by the stochastic nature of the process. Past research has been laborious and time­consuming, due to the substantial number of samples needed to attain statistical significance of the results. Microfluidics could offer a solution to this issue, since it allows for the study of copious amounts of independent samples in short time frames, whilst using less resources. In this study, a microfluidic system previously designed and validated within Eral Lab was further improved. Once improved, the system was used to study the effects of common NPLIN parameters such as supersaturation, laser intensity and laser wavelength on the nucleation probability in thousands of independent micro droplets. The experiments were performed using KCl solutions of both 1.05 and 1.10 supersaturation index and irradiated with light of three different wavelengths and four different laser intensities. Control cooling experiments were conducted to serve as a reference and measure the effectiveness of irradiation. Results indicated that, increasing the supersaturation increases the nucleation probability. However, small differences between both supersaturations were observed, potentially indicating a supersatura­ tion dependent laser intensity threshold. A threshold possibly explained by the Nanoparticle Heating model used to describe Non­photochemical Laser Induced Nucleation. Laser irradiation of 1.05 su­ persaturated solutions was seen to be effective with light of all colours at higher laser intensities (≥ 50 MW/cm2). In contrast, for 1.10 supersaturated solutions irradiation was, in most cases, already effective at lower laser intensities (≥ 25 MW/cm2). No significant wavelength effect was observed, besides irradiation with 355 nm light at higher laser intensities (≥ 50 MW/cm2) to be more effective on 1.10 supersaturated solutions. Further analysis of the data was done by investigating the ability of common nucleation models, such as the Classical Nucleation Theory and the Dielectric Polarization model, to describe the behaviour. Results of the Classical Nucleation Theory were highly uncertain due to a limited amount of data points at varying supersaturations. Yet, indicated a heterogeneous influence on the nucleation probability in both the control cooling and laser irradiation experiments. The Dielectric Polarization model was not able to properly describe the nucleation events observed in the experiments, as lability parameters calculated for the experiments were inconsistent with literature and suffered from significant errors.

Electroreduction of CO2 into high-valued chemicals is a promising way to reduce CO2 emissions while simultaneously producing bulk chemicals currently produced from fossil-fuel feedstocks. The downside of this process is that conversion rates are low, meaning the resulting product stream is a complex gas mixture consisting primarily of reactants and by-products and a relatively small amount of product. This study focuses on the development of a new downstream separation process to capture ethylene from a mock-up reaction mixture (mole fractions C2H4/CO2/CO/H2/H2O : 20/55/15/15/5), based on low driving forces and suitable for application in a 100kW test case within the e-Refinery. An extensive literature study of numerous separation techniques for gases was conducted and adsorption was chosen as the most suitable option. After screening of various adsorbents, active carbon was selected as the most potential sorbent. Based on a selectivity analysis, the primary focus was on the behaviour of C2H4/CO2 on active carbon. Using a simple, custom-build set-up, transient breakthrough experiments were performed for this gas mixture and the resulting selectivity for an equivolume feed, yielded a lower separation performance than expected based on the ideal adsorption solution theory, respectively a selectivity of 1.5–1.7 versus 3.2–3.5. Additionally a theoretical model was developed using MATLAB, which described the velocity profile inside the adsorber column and could qualitatively predict breakthrough behaviour. Further analysis led to the conclusion that for a more accurate quantitative match between experimental and numerical results, isotherm parameters should be obtained from the same type of active carbon. Ultimately this technique could be used to increase the ethylene content in a CO2-bearing stream and pave the way for a new, energy-efficient method to obtain hydrocarbons, ethylene in this case, from an electrolyzer cell.

This thesis describes a study into pairwise particle interactions within a Hele-Shaw geometry, using stop-flow lithography. By exposing a photoreactive mixture to a strong UV-pulse, a hydrogel is formed. The shape of this hydrogel is controlled by masking part of the light beam. This process takes place while the Hele-Shaw channel is placed on the stage of a microscope, which allows these hydrogel particles to be viewed and tracked. Improvements were made to increase the accuracy and precision of the experimental set-up. No- tably, the initially present mismatch of intra-pair particle thickness was greatly reduced by changing the method of particle pair production. By tracking these pairs of particles, information is obtained regarding their motions and velocity relative to one another. Experiments were performed for a selection of particle shapes and compared to numerical simulations of identical geometries. Simulations predicted that attractive and repulsive velocities should be noticed depending on the separation distance and shape of the particles. Qualitatively, the experiments agree to a certain extent with the simulations. It was demonstrated that the pairwise interactions are indeed dependent on their shape. Furthermore, the magnitude of these interactions qualitatively matched with the experimental data. Quantitatively, the experimental data did not agree with the simulations, but strong evidence was presented to indicate that the UV-light hitting the sample was not uniformly distributed. This results in a discrepancy in particle thickness between the pair, which skews the experimental data. Novel insights were gained on the applicability of the current literature model on hydrogel particle propagation. In contrast to the current model, it was experimentally demonstrated that the shape and (in-plane) size of the particle affects its thickness.

Separation of particles from suspensions has been an integral part of many industrial, chemical and biological processes. Traditional methods such as sieving, flocculation, centrifugation etc. have many demerits. This has lead to an interest in unconventional separation methods that use physical properties of the particles. Acoustophoresis is one such method that has gained popularity in recent times. Acoustophoretic separation is based on the density contrast between the particles and the medium, as well as the size of the particles. A particle in a medium in which an acoustic field has been applied, experiences an acoustic force. This acoustic force is greater in standing waves than traveling waves, which is why acoustophoretic devices generally use standing wave fields. Particles with positive contrast factor are pushed to the pressure nodes; once the particles reach the nodes, they are trapped. If the medium is in flow, the particles also experience drag force. The interplay between the drag and the acoustic force forms the basis for separation. Standing wave fields can further be distinguished as static fields or dynamic acoustic fields (DAF). In a static field, the nodes are stationary, while in DAF, there is movement of the nodes, caused by variation of source frequency. Here, the tendency of different-sized particles to follow the nodal movement gives rise to separation. DAF devices seem preferable when separation needs to be done on a larger scale.In this thesis, two novel DAF devices were studied; one device works on the principle of frequency sweeping, while the other works on frequency modulation. Both devices are 3D printed, and have two inlets and two exits, with separation occurring in an acoustic chamber where the DAF acts. Both devices are multi-nodal & milli-fluidic. The samples to be separated consist of polyethylene particles of a continuous size distribution between 32-106 µm, dispersed in water. The devices were tested at a total channel flow rate of 1000 mlh-1 (Reynolds number of 20). The aim was to understand how varying the flow and acoustic field parameters affect the separation/filtration performance of the devices. This was done by defining a “threshold size” or the cut-off size at which the entire particle distribution is divided into two separate distributions. Flow and acoustic field parameters were adjusted to see how the threshold size increases/decreases.The analysis for each device was done by a parametric study using Design of Experiments (DOE). First the available features (both design and operation) were studied and suitable parameters and their values were selected. The DOE was then designed, having 27 combinations of parameters known as ‘runs’. Each run of the DOE was first simulated on an available 2D COMSOL model, followed by experimental validation. The DOE was then analysed using both theoretical and actual values, to find out the parameters that had the maximum effect on the threshold size, and their respective trends.

A cylindrical column of fluid breaks into drops under the action of surface tension when other forces are relatively small. This phenomenon is called the capillary break-up. Since the introduction of the seminal theory of inertial-capillary jet instability by Rayleigh in the late 19th century, this phenomenon has seen a rich influx of academic research and industrial interests over the past few decades. The theory suggests that out of all the unstable wavelengths only the most unstable wavelength determines the drop size. But in reality, random background perturbations and non-linear pinch-off dynamics result in bi-modal drop size distribution. The two peaks in the bi-modal distribution correspond to the formation of main drops and satellite drops. The main drops are the desired product of the industry and the satellite drops are relatively smaller in size and are discarded by post-production processes like sieving. To reduce post-production processes and ensure repeatability, the industrial demand is to have a "narrow uni-modal" drop size distribution. Meaning, elimination of satellite drops and having uniform-sized main drops. Narrow distribution is achieved by employing finite-amplitude perturbation on the jet. This way the jet is not affected by the random background perturbation as the finite-amplitude perturbation dominates the break-up process. But this does not ensure satellite drop elimination. Uni-modality is achieved when the satellite drops merge with the main drops. Merging happens when the satellite and the main drop have different velocities and follow the same trajectory. The amplitude of the sinusoidal perturbation can be tuned to have this merging condition. The externally perturbed jet finds its application in a plethora of industrial processes such as powder production, combustion, micro-encapsulation, extreme ultraviolet rays (EUV) and, laser-plasma production (LPP), ink-jet printing, etc. The focus of this thesis is the production of crystalline fertilizer pellets from the capillary break-up of a spiralling jet of molten fertilizer. This process is called rotary prilling. Experimental studies in spiraling jets without external perturbation also shows bi-modal distribution of drops. The fine satellite drops produced in prilling process are a potential safety hazard as they can cause dust explosions which can be detrimental to air quality. Expensive filters and wet scrubbers are placed inside the prilling tower to remove the fine satellite drops. Hence uni-modal drop size distribution in prilling is highly beneficial for both economic and environmental reasons. As perturbed spiralling jets are not studied in detail in the existing literature, this thesis employs sinusoidal perturbations on spiraling water jets and aims to achieve uni-modal drop size distribution. While the straight jets have a nearly constant base flow, the spiraling jets have a base flow that accelerates due to the centrifugal and Coriolis forces in the downstream direction. As a result of mass conservation the accelerating base flow results in jet stretching in the downstream direction. The evolution of perturbations on such a stretched jet not only depends on surface tension and inertial forces of the local jet radius, but also on the wavelength that is excited initially. Hence the evolution of perturbations on straight jets with constant base flow is an eigen-value problem whereas, on a stretched jet it is an initial value problem. When the stretching rate is faster than the capillary growth rate damping of the surface perturbations will occur. For the process parameters investigated in this thesis, the capillary growth rate is faster resulting in negligible damping. The other effect of jet stretching is that the wavelengths are also stretched, that is the wavelength that is excited initially becomes longer in the downstream direction, thus the wavenumber decreases. The linear spatial instability theory for spiraling jets is experimentally validated in this thesis. For the set of non-dimensional numbers chosen in this thesis, uni-modal distribution of drops is achieved by tuning the frequency and amplitude of the sinusoidal perturbation. Uni-modality is observed when the non-dimensional wavenumber near break-up is approximately 0.7 and the amplitude is tuned accordingly. As the wavenumber decreases in downstream direction the wavenumber excited at the nozzle should be greater than 0.7.

Kidney stone disease influences 10% of people in the world [36]. Calcium oxalate (CaOx) stones are the most common stones found in the kidney stone. In this research, ANSYS/Fluent CFD was used to determine the supersaturation profile in the microchannel for different constant flow rates and Ca and Ox inlet concentrations. The growth of the CaOx stones is studied by performing experiments in a microfluidic channel under an optical microscopy. The growth of the CaOx stones is also investigated by using a combined transport-kinetics model which couple both mass transport and CaOx precipitation
reaction at the surface of the crystal. It is shown that the crystal growth rate increases with solution supersaturation increasing and decreases with the crystal size increasing. The findings also indicated that in cases of low bulk solution supersaturation and low surface reaction constant values,
the crystal growth rates are controlled by the surface reaction kinetics and independent on the species transport. When the bulk solution supersaturation and surface reaction constant values are high, the Ca and Ox surface concentrations become lower than the bulk solution concentration values. Thus,
the crystal growth rates are controlled by the species transport. The presented study also shows that in the presence of inhibitor osteopontin, the crystal growth rate was decreased.

Kidney stones may be uncommon is certain parts of the world. On the other hand, considering the percentage of cases in the western world, one can say it is worrisome. Anyone can have kidney stones, which may be easily passed out of the kidney through the urine. It only becomes a cause for concern when the stones grow beyond a certain size. They can cause flank and abdominal pains, fever, painful urination, etc., and can subsequently result in kidney failure if the patient has only one kidney present. In that case, a kidney stone patient may require the attention of a nephrologist. Advancement in technology has provided conventional techniques such as ureteroscopy (URS), percutaneous nephrolithotomy (PNL) and shockwave lithotripsy (SWL) for treating kidney stones. One may wonder what exactly these stones are. They are nothing extraordinary but rather made of calcium oxalate (CaOx) crystals which are formed from a supersaturated urine. CaOx crystal which is a product of crystallization occurs in two forms, calcium oxalate monohydrate (COM) and calcium oxalate dihydrate (COD). Crystallization is a very simple and effective purification and phase separation process used in the chemical and pharmaceutical industry. This process is usually influenced by many factors such as concentration, temperature, mixing, impurities, etc. The presence of oxalate in urine is a major contributor to the formation of kidney stones. High concentration of oxalate combines with calcium to form CaOx. On the other hand, injury to the kidney tubular epithelial cells results in the expression of Hyaluronic acid (HA). HA has since been considered as a binding agent which causes the retention of kidney stones. Furthermore, some scientists are of the idea that HA may also influence the formation of kidney stones. A novel method was developed to study the nucleation kinetics of CaOx in artificial urine under the influence of varying oxalate and HA concentrations. The method involved crystallizing CaOx (COM, COD) in emulsions (micro-droplets) that were generated by and stored in a microfluidic device. Incorporating polarized lightmicroscopy also allowed COM and COD to be detected at the same time. The cumulative probability distribution as a function of induction time for COM and COD was determined and fitted to the Weibull model. The induction time is the average time at which the first crystal is detected in the droplets. As was expected, higher oxalate concentration shortened the induction time for both COM and COD. Surprisingly, increasing HA concentration induced the formation of COM whiles inhibiting the formation of COD. In general, the frequency of COD was always less than that of COM. In conclusion, the idea that HA played a role in the formation of kidney stones was confirmed. This was the most important part of the research.

Non-photochemical laser-induced nucleation (NPLIN) is a crystallisation method in which a highly structured phase is formed out of solution by exposure to a laser beam. NPLIN offers unprecedented spatiotemporal control and characterisation of nucleation. NPLIN is energy efficient compared to conventional crystallisation methods and can be implemented in continuous microfluidic reactors, enabling sustainable operation. However, its working principles are not yet fully understood. This study contains an evaluation of four proposed mechanisms and a description of an experimental setup involving an ultrahigh speed camera. Two mechanisms describe interaction of molecular polarisation with the electric field, either isotropically known as dielectric polarisation (DP), or anisotropically via the optical Kerr effect (OKE). The other two mechanisms involve cavitation bubble formation by nanoparticle heating through light absorption. This work contains a refined description of this so-called cavity-induced nucleation where its consequences are distinguished into two mechanisms, either based on concentration enhancement (CICEN) or due to pressure enhancement (CIPEN). Novel theoretical calculations in conjunction with experimental data suggest that NPLIN phenomena are based on DP or CICEN, potentially operating in concert. It is conjectured that the influence of DP and
CICEN can be quantified further by development of a topological description of DP, simulations of CICEN and relating nucleation probabilities to the metastable zone width of various solutes. The calculations suggest that OKE and CIPEN have little significance because involved energies are several orders of magnitude
below kBT . The proposed setup allows for observing the NPLIN phenomena and establishing dependence on cavitation bubbles, providing empirical validation. Solutions to experimental problems are provided, including reduction of sample fluid evaporation, aligning the nucleation site with the region of interest of the camera and removing image noise.

Crystallization is a process known to humankind for centuries. Everyday items can be a result of crystallization, e.g. snowflakes being formed in cold weather and sugar that is obtained from glucose-water solutions. Crystallization follows from the process which is called nucleation. This phenomenon is explained in two different theories: classical nucleation theory and two-step nucleation theory. Also, two different ways of crystallization can be distinguished: heterogeneous nucleation, which is nucleation that evolves from external surfaces and homogeneous nucleation, which obviously evolves without the help of external surfaces. Methods to perform crystallization, based on aforementioned mechanisms, are useful for production scale facilities as it is a very useful method to separate chemicals in manufacturing processes. However, large scale crystallization processes are known to be hard to control and energy intensive, something that does not fit into today’s society. To keep up with the global demand for sustainable production novel crystallization methods need to be established. A promising finding, 20 years ago, consisted of laser-induced nucleation. By means of a laser, Garetz et al.[1] were able to induce crystallization, calling it non-photochemical laser induced nucleation (NPLIN). Up to this date, it is not known what mechanisms underlie the observed behavior. Because the phenomenon was only observed at the milliliter range, it is important to understand the mechanisms before further upscaling can be done. Over the course of the last decade, 4 mechanisms have been proposed: Optical Kerr effect, Isotropic electronic polarization, nano-impurities, and shockwaves. During the discovery of NPLIN, it was found that the wavelengths and power intensity were incapable of creating a photochemical effect on the compound used. For this reason, the LIN was ascribed to nonphotochemical behavior. In this research, more detail is provided on this presumed non-photochemical effect. An experimental build is established to perform multiple experiments for detecting radicals and obtain consensus on the attributed name. Initial tests revealed that there is no particular interaction between the solute and laser electric field. Throughout the research, several factors were found to play a role in observed NPLIN behavior. Over the course of this project, glycine samples started to turn yellow due to the degradation of glycine. pH was found to be an important factor for polymorphic control, however, it was constant for all samples since glycine acted as a buffering agent. Future research with new chemicals should keep track of the pH together with polymorphism. Glass geometries tests showed that container curvatures are affecting the polarization of the laser and thus the outcomes for polymorphic structures. At last, the effect of impurities on NPLIN was elaborated. Doping samples intentionally with nanoimpurities resulted in higher crystallization probabilities. On the other hand, reducing the impurity levels also decreased the nucleation probability. It is concluded that impurities are highly correlated to nucleation performance. Moreover, the laser-interaction volume is also affecting the nucleation probability in significant amounts. Supplementary research is required to obtain a set of operating parameters that have an effect on NPLIN behavior. With such a model, NPLIN can be controlled and a state of the art production scale laser induced nucleation unit becomes the new standard.

Kidney stone disease is an increasing worldwide issue. There is a current lack of understanding of the exact mechanisms involved, partially due to the need for experimental instrumentation able to mimic the microenvironmental conditions present in vivo. As crystal nucleation often initiates at liquid-solid interfaces, the interface morphology plays a significant role in the rate of nucleation. Within the nephron, the functional unit of the kidney, four distinct segments can be distinguished that contain different surface morphologies. Particularly, the cells lining these segments contain protrusions in the shape of nanopillars that vary in length, diameter and spacing. Exploiting the opportunities provided by organ-on-chip technology, we designed and manufactured a microfluidic device proposed to increase our understanding of the exact mechanisms that drive kidney stone crystallization. We used two-photon polymerization to fabricate surfaces that contain these morphologies in materials possessing a Young’s modulus matching the value of the biological structures. After optimizing design and process parameters like laser power and scanning speed, we manufactured nanopillars with diameters in the range of 150-250 nm and aspect ratios up to 100 with which we can mimic the protrusions in the nephron. Pillar arrays were printed on a glass slide, and assembled with a polydimethylsiloxane (PDMS) microfluidic component (channels 150 um wide). We used high-resolution 3D printing to create master molds used for PDMS soft-lithography. After precise alignment, the two components were brought together and clamped mechanically with a 3D printed holder to ensure a watertight seal between the glass and PDMS. This microfluidic device was used to study crystallization of the most common type of kidney stone, calcium oxalate monohydrate (COM). Because of the chip dimensions combined with a surface morphology this device closely resembles a human nephron.

In the past decades, fossil fuels have become an increasing concern, due them being a non-renewable energy source and due to the environmental concerns related to the production and use of this fuel. This has led to increasingly more research in the value of bio-sourced lignocellulosic biomass such as Empty Fruit Bunch (EFB) fibres from the palm oil industry. EFB fibres are a major by-product of the palm oil industry and globally, over 30 million tons are produced annually. Due to its biomass characteristic, it is a potential source of energy in processes such as anaerobic digestion, however, its complex structure results in poor biological degradation. A pretreatment such as a hydrothermal (HT) pretreatment can be used, to improve the biodegradability, prior to anaerobic digestion; however, this is an energy intensive process and has led to investigating the use of alternative energy sources for the pretreatment such as solar power. The geographical position of Malaysia is beneficial to make use of solar radiation as an alternative energy source. Concentrated Solar Power (CSP) is a technology that is gaining more interest as a way to convert solar radiation into usable energy and in particular the Fresnel lens. This research investigates if a Fresnel lens can be used to improve the biodegradability of the EFB fibres and analysed what effect this pretreatment has on the fibres (in terms of the solar radiation and the duration of exposure). Two conditions are investigated; wet (water and EFB fibre mixture) and dry conditions (dry fibres in an inert environment). These two pretreatments are compared to a conventional HT pretreatment in terms of the biodegradability based on the Biomethane Potential (BMP). From the experimental results, it was found that the Fresnel lens can achieve very high temperatures (>400oC) and possesses fast heating rates resulting in a predominantly photothermal pretreatment. The biodegradability of the EFB fibres (using the Fresnel lens) was significantly improved in comparison to the HT pretreatment under the wet conditions; however, based on the analytical methods used in this research, no conclusive explanation can be given to why the biodegradability increased. Possible explanations are increased available surface area and pore size, which will need to be further researched. The dry condition pretreatment was too inhomogeneous to observe a significant improvement in the biodegradability. However, based on the overall biodegradability and the structural changes observed in the EFB fibres, it is expected that with improved operating conditions that this pretreatment will also improve the biodegradability. Overall, based on this research, the CSP pretreatment has potential to be used as alternative to the conventional HT pretreatment and the surface area for the CSP required by this process is estimated to be 2% of the actual plantation size. Therefore, CSP pretreatment has potential to be feasible in large-scale, however process efficiency needs to be improved due to the low efficiency of the lens and high energy requirements. Secondly, and most importantly, an economic analysis is crucial to validate the economic feasibility of implementing such a pretreatment.

Kidney stones disease is a serious healthy issue in modern society. The amount of patients getting kidney stones are increasing every year. This trend can be caused my numerous reasons like dietary and living conditions. The main point is that the number of kidney stone disease patients need to be lowered. The first step to achieve this is by getting a better understanding of the process of kidney stone formation. The focus will be on calcium oxalate which is the main constituent of kidney stones. In this study we present a microfluidic method to quantify nucleation kinetics of calcium oxalate as function of supersaturation, pH and in the presence of inhibitors (Magnesium, Osteopontin). We have optimized the design of the microfluidic device to minimize the droplet coalescence. Kinetic parameters were obtained through fitting of the probability of nucleation curves measured for over a hundred microdroplets. Nucleation kinetics was seen to increase with an increase in supersaturation, as expected. At pH 6.0 the kinetics dramatically slows down compared to pH’s 3.6 and 8.6. As the inhibitor concentration increases the kinetics will decrease, this is the case for both magnesium and osteopontin.