http://hdl.handle.net/2282/256 Search the Channel search http://teora.hit.no/dspace/simple-search http://hdl.handle.net/2282/1338 Title: Confined granular flow in silos with inserts - Full-scale experiments <br/> <br/>Authors: Wójcik, M.; Tejchman, J.; Enstad, Gisle G. <br/> <br/>Abstract: The paper describes results of experimental investigations of confined granular flow in a silo with different inserts. Over 100 experiments were carried out with dry cohesionless sand in a large metal silo with and without inserts at Tel-Tek, dept. POSTEC, in Norway. Wall pressures and flow patterns were measured during both silo filling and emptying. Three different insert types were used in the silo: double cone, cone-in-cone and inverted cone. Different positions of inserts were also investigated. Experimental results with inserts were compared with those without inserts. Some design recommendations for silos equipped with inserts were worked out. http://hdl.handle.net/2282/1332 Title: Investigation of flow behaviour in biomass gasifier using Electrical capacitance Tomography (ECT) and pressure sensors <br/> <br/>Authors: Thapa, Rajan Kumar; Rautenbach, Christo; Halvorsen, Britt <br/> <br/>Abstract: The particles in a biomass gasifier are mainly a mixture of wood chips, char particles and bed material. The charwood particles have a significant lower density than the bed material, and also a wider range of particle sizes and larger mean particle diameter. The difference in particle properties may cause segregation and thereby influence on the fluidization properties and the flow behavior in the bed. The aim of this work is to study the fluidization properties in cold fluidized bed with different mixtures of particles. ZrO and plastic particles with a density ratio of 6, are used in the experiments to simulate the bed material and the char-wood particles in a biomass gasifier. Experiments are performed in cylindrical beds with uniform air distribution. The fluidization properties are studied using pressure sensors and Electrical Capacitance Tomography (ECT). The ECT system is a non-intrusive measurement system and is a suitable method for monitoring the internal flow behavior of fluidized bed. The experimental results show that the minimum fluidization velocities very much depend on the particle composition in the bed. The fluidization velocity reaches a maximum when 20% plastic particles are added to the ZrO powder and decreases again when the fraction of plastic beads are further increased. The theoretical minimum fluidization velocities for the different mixtures agree well with the experimental data. The standard deviations of the pressure and the ECT measurements showed that the fluidization velocities are higher in the lower part than in the higher part of the bed. This observation is more significant in the mixtures with high fraction of plastic particles. This indicates that the plastic particles moves upward in the bed and that mainly ZrO particles are present in the lower part of the bed. This is also visually observed during the experiments. Segregation can give low degree of particle motion in parts of the bed. Investigation of fluidization behavior of the different mixtures in this study may be useful as an initial step of analyzing the complex system of a bubbling fluidized bed gasifier http://hdl.handle.net/2282/1331 Title: Statistical diagnosis of a gas-solid fluidized bed using Electrical Capacitance Tomography <br/> <br/>Authors: Rautenbach, Christo; Melaaen, Morten Christian; Halvorsen, Britt <br/> <br/>Abstract: Fluidization experiments were performed using several particle size distributions of spherical glass particles, ranging from Geldart B to D. An Electrical Capacitance Tomography (ECT) tomograph was utilised in the present study and its usefulness as a diagnostic tool is illustrated. During the experiments a 10.4cm diameter tower was utilised and the tower was operated at atmospheric pressure and room temperature (cold fluidized bed). Statistical analysis were performed on the average solid fraction data obtained using the ECT tomograph. Using the time domain skewness and kurtosis the time series could be characterised and the quality of fluidization is determined at different superficial gas velocities (Azizpour, H., Sotudeh-Gharebagh, R., Zarghami, R., Abbasi, M., Mostoufi, N., and Mahjoob, M. (2011). Characterization of gas-solid fluidized bed hydrodynamics by vibration signal analysis. International Journal of Multiphase Flow, 37:788-793). Statistical analysis is also used to characterise the influence of small particles on the bed hydrodynamics. http://hdl.handle.net/2282/1330 Title: A comparative study between electrical capacitance tomography and time-resolved X-ray tomography <br/> <br/>Authors: Rautenbach, Christo; Mudde, Robert F.; Yang, X.; Melaaen, Morten Christian; Halvorsen, Britt <br/> <br/>Abstract: Modern day tomographs enable the research community to investigate the internal flow behaviour of a fluidized bed by non invasive methods that partially overcome the opaque nature of a dense bubbling bed. Each tomographic modality has its own limitations and advantages and in the present study two modern day tomographic systems were evaluated with respect to their performance on a cold dense fluidized bed. The two tomographs investigated are an Electrical Capacitance Tomography (ECT) tomograph and a time-resolved X-ray tomography tomograph. The study was performed on spherical glass particles with various particle size distributions that could mainly be classified as Geldart B or D particles. Two experimental towers were employed, one with a diameter of 10.4cm and the other 23.8cm while compressed air was used as fluidizing fluid during all of the experiments. Results obtained with both systems are provided in comprehensive figures and tables and some first results are obtained with the time-resolved X-ray tomography system. The bubble size measurements of both tomographs are compared with several theoretical correlations via the root mean square error of the predictions (RMSEP). With the results it was also concluded that a small amount of small particles can noticeably alter the fluidization hydrodynamics of a powder. The bubble frequencies are also presented to aid in understanding the hydrodynamic behaviour of the powders investigated. A comprehensive summary of the two tomographic modalities is also provided.