The extraction-condensing cogeneration system is a popular technology for heat and power integration which can be used by petrochemical process. To compare with back pressure system, extraction-condensing system has better flexibility for process control. However, the thermal efficiency of extraction- condensing system could be affected by the amount of effective heat to process. If the effective heat to process and the plant power demand were not well designed, the cogeneration system may violate government regulation of ¡§qualified cogeneration system¡¨ by MOEA, or the system economics can not meet investor¡¦s requirement. From another point of view, if the cogeneration system bias original design operating condition or it has to run under low loading, the energy efficiency will move away from the target. A 94.9 MW extraction-condensing system of a petrochemical plant was selected as an example. For the purpose of data requisition, the author established a model to predict main steam flow, extraction steam flow, and power generation load. Moreover, a set of equations for the calculation of heat rate of turbine plant was developed. Besides, a Microsoft Excel calculation sheet was programmed to compute real time plant thermal efficiency. The actual operation data was compared with computer simulation. Results show (1) To meet the regulation, the process steam shall exceed 100 t/h with rated power generation. (2) For the minimum generator load (about 20 MW), the effective heat to process must exceed 78% in order to ensure a 52% overall thermal efficiency. (3) Low load means low thermal efficiency of this system. Some energy conservation ideas of this cogeneration system were assessed. Four ideas were presented, including (1) Increase boiler feed water temperature during low evaporation load. (2) Recovering of flash steam vented from blow down tank for the heating of boiler combustion air. (3) Control of cooling tower fans speed by using frequency inverter. (4) Utilization of hydraulic coupled forced draft fan. The total benefit of these energy conservation ideas is 2,546.44 kilo-liter fuel oil equivalent.

The thesis deals with the creation for a numerical model of a solar collector with a phase change material as a heat storage medium. The model was implemented in Python. Using the created model, design optimization of several problems was carried out with the use of selected methods of heuristic optimization. The results of the behaviour of the created model and of design optimization were then analysed and evaluated.

Submitted by Renata Lopes (renatasil82@gmail.com) on 2017-11-07T12:20:00Z No. of bitstreams: 1 gessicalacerdasiqueira.pdf: 2914379 bytes, checksum: 13b701ceac7f6562db4c0a3167e60c32 (MD5) / Approved for entry into archive by Adriana Oliveira (adriana.oliveira@ufjf.edu.br) on 2017-11-09T14:37:17Z (GMT) No. of bitstreams: 1 gessicalacerdasiqueira.pdf: 2914379 bytes, checksum: 13b701ceac7f6562db4c0a3167e60c32 (MD5) / Made available in DSpace on 2017-11-09T14:37:17Z (GMT). No. of bitstreams: 1 gessicalacerdasiqueira.pdf: 2914379 bytes, checksum: 13b701ceac7f6562db4c0a3167e60c32 (MD5) Previous issue date: 2017-07-13 / Processos de transferência de calor com mudança de fase são de interesse em várias áreas da ciência, engenharia e aplicações industriais. Em processos de solidificação, por exemplo, a ocorrência de trincas e formações de vazios causados por uma redução na capacidade de resistir a esforços mecânicos geralmente são observados, e é de grande importância prever esses comportamentos para que possam ser evitados. Uma das formas de se estudar esses fenômenos e suas aplicações é através do uso de modelos matemáticos que possibilitam, através do uso de métodos de discretização temporal e espacial a realização de simulações computacionais. Dessa forma, este trabalho estudou e comparou diferentes formulações numéricas do método dos elementos finitos para problemas de transferência de calor com mudança de fase levando em consideração a condução como mecanismo de transferência de calor. Na metodologia usada, os processos de solidificação ou fusão foram tratados por meio de métodos baseados em malhas fixas. Diversos experimentos numéricos foram realizados para se analisar a adequabilidade dos métodos estudados e propostos neste trabalho e os resultados obtidos foram satisfatórios. / Heat transfer processes with phase change are of great interest in several areas of science, engineering and industrial applications. In some of these applications, such as in solidification processes, the occurrence of cracks and void formation caused by a reduction in the ability of the material to resist mechanical loadings are generally observed, and it is of great importance to predict these behaviors so that they can be circumvented. One of the ways to study these phenomena and their applications is through the use of mathematical models and executing of computer simulations. Thus, this work studied and compared different numerical formulations of the finite element method for the heat transfer problems with phase change considering only conduction as the main mechanism of heat transfer. In the methodology used, the solidification or melting processes were treated by means of numerical methods based on fixed meshs. Several numerical experiments were performed to analyze the suitability of the methods studied and proposed in this work and the results were satisfactory.

Cílem diplomové práce je vytvoření 2D numerického modelu pohybujícího se řezu s proměnnými okrajovými podmínkami skutečné geometrie plynulého odlévání a chlazení předlitku v prostředí MATLAB. Model se zabývá vysoce nelineárními termofyzikálními podmínkami oceli během tuhnutí a chlazení. V práci je simulovaná nejen nelinearita termofyzikálních podmínek, ale také nelinearita při fázové změně. Fázová změna je modelovaná pomocí metody entalpie, metody zdánlivé kapacity a metody teplotního zotavení. Všechny výsledky práce jsou porovnány z více hledisek, jako např. z hlediska přesnosti, rychlosti výpočtu, nebo vhodnosti časového diskretizačního kroku pro nelineární problémy, a paralelizace.