Multiphase modelling of the characteristics of close coupled gas atomization

Not withstanding the high demand of metal powder for automotive and High Tech applications, there are still many unclear aspects of the production process. Only recentlyhas supercomputer performance made possible numerical investigation of such phenomena. This thesis focuses on the modelling aspects of primary and secondary atomization. Initially two-dimensional analysis is carried out to investigate the influence of flow parameters (reservoir pressure and gas temperature principally) and nozzle geometry on final powder yielding. Among the different types, close coupled atomizers have the best performance in terms of cost and narrow size distribution. An isentropic contoured nozzle is introduced to minimize the gas flow losses through shock cells: the results demonstrate that it outperformed the standard converging-diverging slit nozzle. Furthermore the utilization of hot gas gave a promising outcome: the powder size distribution is narrowed and the gas consumption reduced. In the second part of the thesis, the interaction of liquid metal and high speed gas near the feeding tube exit was studied. Both axisymmetric andnon-axisymmetric geometries were simulated using a 3D approach. The filming mechanism was detected only for very small metal flow rates (typically obtained in laboratory scale atomizers). When the melt flow increased, the liquid core overtook the adverse gas flow and entered in the high speed wake directly: in this case the disruption isdriven by sinusoidal surface waves. The process is characterized by fluctuating values of liquid volumes entering the domain that are monitored only as a time average rate: it is far from industrial robustness and capability concept. The non-axisymmetric geometry promoted the splitting of the initial stream into four cores, smaller in diameter and easier to atomize. Finally a new atomization design based on the lesson learned from previous cases simulation is presented

Influence of theory and experiment on the most probable value of seven principal physical constants

Thesis (M.A.)--Boston University, 1944. This item was digitized by the Internet Archive

Performance Evaluation of an Indirect Evaporative Cooler

peer reviewedNowadays, buildings are responsible for 40% of energy consumption in the European Union, according to the International Energy Agency (IEA). To reach the European objective aiming for CO2 neutrality of buildings, the IEA has developed the Energy in Buildings and Communities program (EBC), from which Annex 85 on Indirect Evaporative Cooling (IEC) is part of. This work contributes to assess the energy performance of indirect evaporative coolers in mixed-humid climates. A reference cooling system has been chosen as a base case to evaluate the performance of the IEC. The reference cooling system is composed of terminal units, a chiller, and a cooling tower as primary cooling system. In the upgraded cooling system, the cooling tower has been replaced by an indirect evaporative cooler. The latter is a modified version of the cooling tower that comprises an additional heat exchanger for air-pre-cooling. The energy consumption of both systems over a one-year period are then compared, including auxiliaries consumption. The possibility to perform free chilling has also been investigated. The models used to describe each system component are overviewed as well as their limitations. The annual energy consumption of the systems has been computed using three control methods: temperature control, flow rate control and optimized operation. While free chilling has a significant impact on the energy consumption (30% reduction), the IEC has a more moderate effect (up to 5% reduction). It is also shown that the advantage of the IEC over the cooling tower is directly dependent on the temperature difference between the dry bulb temperature and the dew point temperature

Concatenation of convolutional and block codes Final report

Comparison of concatenated and sequential decoding systems and convolutional code structural propertie