Suspension pipe flows can exhibit a behaviour called core-peaking where the particles accumulate in the centre of the pipe. This is due to shear-induced migration, where particles migrate towards areas of the flow with lower shear rate. While this concept is well documented, the exact causes are still unknown. Experimental research can uncover how this behaviour is impacted by different flow properties. This knowledge can be used to predict whether a given system will display core peaking behaviour. Knowing this a priori is convenient, as core peaking can impact the pressure drop in the pipe flow significantly. This thesis investigates the applicability of an experimental method that uses light attenuation to measure volume fraction distributions in a suspension pipe flow. Investigating this method is worthwhile as it is relatively quick and affordable compared to other methods like MRI. The theoretical relationship between the concentration of a substance and the attenuation of light is given by the Beer-Lambert law. However, this linear law does not hold for dense suspensions. To account for this, a set of calibration experiments was done in a setup where the path length was varied consistently. The results give a relationship between the attenuation and the amount of particles, expressed as the product of the volume fraction and the path length. This relationship is initially linear before it transitions to a cube root function for higher particle loadings. This change is thought to be due to multiple scattering becoming more prominent when more particles are present. The found calibration curve was then applied to attenuation measurements that were done in a pipe flow setup. However, the resulting volume fractions deviate significantly from the values expected based on the known amount of particles in the flows. This deviation suggests that there are significant differences between these pipe flow experiments and the calibration experiments that cause a difference in the measured attenuation for the same particle loadings. The volume fraction distributions that were found are thus not quantitatively correct, but by comparing them, the accuracy of this method can still be defined. Because the behaviour in the pipe flow is axisymmetric, the radial volume fraction distributions can be found from a single measured projection with the inverse Abel transform. However, the measured attenuation profiles were not symmetric. This means that the resulting radial volume fraction profiles are not actual representations of the real volume fraction distributions. This also means that the current data cannot be used to study particle migration in detail. Nevertheless, the accuracy of the method can be determined by looking a the measured attenuation profiles directly. Even at small path lengths, a difference of 1% in volume fraction was measured successfully. This proves that the proposed experimental method is in theory accurate enough to be used to measure volume fraction distributions in suspension pipe flows. To apply this method successfully, the identified improvements to the experimental setup and processing will need to be implemented. Additional research will be necessary to verify if these improvements are sufficient. ... Read more

Particle-laden pipe flows are ubiquitous in industrial applications. Examples are industries like dredging, slurry transport, and the transport of reactants and products in chemical industries. One of the most important factors in these transport processes is the friction coefficient which relates directly to the pumping power which is a significant parameter for industries when viewed from an economic standpoint. The migration of particles in dense suspensions can significantly impact the friction coefficient in pipe flow. The clustering of particles in the core can lead to a reduction in the friction factor compared to a well-mixed particle suspension. This reduction is attributed to the decreased effective viscosity near the pipe wall. While the development lengths of single-phase flows are well known, limited knowledge exists regarding the development of velocity and concentration profiles in suspension flows.

The goal of this thesis is to study the development of neutrally buoyant suspension pipe flows. The experimental setup was validated using pressure drop measurements and the entrance length for single-phase pipe flow was obtained. The experiments for suspension flows involved varying the suspension Reynolds number and volume fractions keeping the particle size constant. Ultrasound imaging technique is used to circumvent the opacity of the suspension to study the development of suspension pipe flow. The inlet conditions for concentration were characterized, obtaining a uniform distribution at the inlet. Measurements are conducted at various locations downstream of the pipe and the velocity of the dispersed phase is obtained using ultrasound imaging velocimetry. Additionally, insights into the development of the concentration profile are obtained by checking the convergence towards a fully developed intensity profile, despite the fact that the image intensity doesn’t directly correlate to concentration profiles. The velocity profiles and intensity profiles were analyzed to understand the effect of radial migration on both concentration and velocity profiles. The entrance lengths for concentration and velocity were obtained for volume fractions ranging from 0.17 to 0.25 and suspension Reynolds numbers ranging from 500-2000. The results obtained revealed that the entrance length for concentration was greater than the entrance length for velocity. Scaling of the concentration entrance length with suspension Reynolds number and volume fractions were determined, and suspension Reynolds number scaled with an exponent of -1.62 and volume fraction scaled with an exponent of -2.1. This implies that the entrance length decreases with an increase in suspension Reynolds number and volume fraction. However, no definite trend was observed for the velocity entrance length. ... Read more

The phenomenon of lateral migration of neutrally buoyant rigid spheres is studied experimentally for Poiseuille Flow. The study relied on the particle migration technique to capture the distribution of particles radial position at different flow parameters. In this thesis, the varying experimental parameters are flow Reynolds number and particle concentration. These two parameters have been reported to have an opposing effect on the migration. Reynolds number is varying at Re=200-1200 and the particle concentration at φ = 0.05-0.5% . The results reveal that an increase in Reynolds number and particle concentration causes the migration to develop at a longer distance from the inlet. The migration is said to be developed when the particles have migrated to the region between the tube-axis and tube-wall. An increase in particle concentration shows a similar effect with the Reynolds number on the migration which the migration develop at a longer distance. An interesting result occurred at high particle concentration, at which the significance of the Reynolds number in altering the migration is decreasing. The study is also conducted to the secondary phenomena following the migration, the generation of inner annulus and the formation of trains of particles. It is shown that the variation of Reynolds number and particle concentration are significantly affected these secondary phenomena. ... Read more

The main goal of this master thesis is to reproduce by CFD computations the characteristic cavitation dynamics in a venturi which were experimentally discovered at TU Delft by Jahangir and al. The different cavitation regimes were obtained by modifying the global static pressure and flow velocity in the flow loop. Based on this, three different cloud cavitation shedding regimes were identified. One of the mechanisms appears at high cavitation number and can be attributed to the presence of a re-entrant liquid jet. Another dominant shedding mechanism was found at lower cavitation number, with the presence of propagating bubbly shock waves. A transition regime was also observed where both mechanisms seem to coexist. A two phases flow model is implemented in the open-source software OpenFOAM. The transition regime from the bubbly shock to the re-entrant jet dominated regime will be identified and compared to experimental findings. The three cavitation shedding regimes will be investigated by using different cavitation numbers. The simulations will mostly be conducted using an inviscid and incompressible solver. ... Read more