Array jet impingement cooling experiments were performed on flat and grooved surfaces with the surface at a constant temperature. For the flat surface, power and temperature measurements were performed to obtain convection coefficients under a wide range of operating conditions such as jet speed, orifice to surface stand-of distance, and open area percentage. Cooling performance (CP) was calculated as the ratio between heat transfer and fan power. An empirical model was developed to predict jet impingement heat transfer taking into account the entrainment effects. Experimental results showed that jet impingement can provide high transfer rates with lower rates of cooling cost in comparison to contemporary conventional techniques in the industry. CP values over 279 were measured which are significantly higher than the standard values of 70 to 95 in current technology. The model enhanced prediction accuracy by taking into account the entrainment effects; an effect that is rarely considered in the literature. Experiments on the grooved surfaces were performed at dry and wet surface conditions. Under dry conditions, results showed 10%~55% improvement in heat transfer when compared to the flat surface. Improvement percentage tends to be higher at wider gaps between the array of orifices and the grooved surface. An improvement of 30%~40% was observed when increasing Re either by increasing orifice diameter or jet speed. Similar improvement was observed at higher flow open area percentages. No significant improvement in heat transfer resulted from decreasing the size of the grooves from 3.56mm to 2.54mm. Similarly, no noticeable change in heat transfer resulted from changing the relative position of the jets striking the surface at the top of the grooves to the bottom of the grooves. Deeper grooves with twice the depth gave statistically similar average heat transfer coefficients as shallower grooves. Under wet conditions, a hybrid cooling technique approach was proposed by using air jets impinging on a grooved surface with the grooves containing water. The approached is proposed and evaluated experimentally for its feasibility as an alternative for cooling towers of thermoelectric power plants. Convection heat and mass transfer coefficients were measured experimentally using the heat mass transfer analogy. Results showed that hybrid jet impingement provided high magnitudes of heat flux at low jet speeds and flow rates. High coefficients of performance CP > 3000, and heat fluxes > 8,000W/m2 were observed. Hybrid jet impingement showed 500% improvement as compared to jet impingement on a dry flat surface. CP values of hybrid jet impingement is 600% to 1,500% more as compared to performance of air-cooled condensers and wet cooling towers. Water use for hybrid jet impingement cooling is efficient since evaporation energy is absorbed from the surface directly instead of cooling air to near wet-bulb temperature. / PHD / This thesis explored the possibility of using air jets on the outside surface of a device that is used to condense steam. An experiment apparatus was used to imitate the conditions of steam condensation in the lab. A flat metallic surface was heated by placing an electric heater beneath it. The metallic surface was cooled using air jets coming out of orifices situated above the hot metallic surface. A fan, connected to an electric motor, was used to create the air jets. The amount of heat transfer was measured by measuring the electric power the heater consumed. This measured power was compared to the power needed to run the fan. The ratio of heat transfer to fan power is called the coefficient of performance CP. The CP values of more than 200 were obtained when air jets were used meaning that we need one kilowatt of mechanical power to remove 200 kilowatts of heat. This CP value is 300% more than the current technology used in the industry where CP ranges from 70 to 90. This means that we can build very efficient steam condensers for power plants. This type of condensers that uses air jets allows the power plant to be efficient and to be able to increase the amount of power generated without extra cost. Further enhancement of the CP can be achieved by making the hot surface grooved instead of flat with the grooves containing water. Air jets, coming out of orifices situated above the grooved surface, were used for cooling. The CP values of more than 3,000 were obtained when air jets were used with wet grooved surface. This CP values is 1,500% more than the current technology used in the industry. This type of condensers that uses air jets on wet grooves allows the power plant to be efficient and to be able to tremendously increase the amount of power generated without extra power and water costs.

Eco-friendly non-CFC refrigerants were introduced in the Air Conditioning and Refrigeration industry during the last few years to reduce damage to the stratospheric ozone layer. The HFC refrigerant R-134a, which has zero Ozone Depletion Potential (ODP), is being used extensively as a replacement for R-12 and also in some centrifugal chillers as a replacement for R-11. However, the disadvantage of R-134a is its comparatively high global warming potential (GWP). Owing to energy crisis and also to reduce the indirect warming impact resulting from electrical energy usage, the new refrigeration systems should be operated at the lowest possible condensing temperatures. In view of this, several active and passive techniques for augmentation of condensation heat transfer and reduction of condensation temperature are gaining increasing attention. Passive augmentation methods are more popular than active ones. To this end, micro-finned tubes of various geometrical shapes are being explored for compact heat exchangers in the refrigeration industry as the best choice. Towards understanding the enhancement in condensation heat transfer coefficients in micro-finned tubes, a test facility has been fabricated to measure the condensing coefficients for R-134a refrigerant. Condensation experiments have been conducted on single plain and finned tubes of outer diameter 19 mm with a refrigerant saturation temperature of 400C and tube wall temperatures 350C, 320C, 300C and 280C respectively. Water is used as the cooling medium inside the tubes with the flow rate varying from 180 lph to 600 lph. The condensing coefficient typically ranged from 0.9 – 1.4 kW/(m2 K) for plain tubes and from 4.2 to 5.8 kW/(m2 K) for the finned tubes. The results of the plain v tube are found to compare favourably with the Nusselt’s theory, leading to a validation of the experimental procedure. Upon comparing the results of finned and plain tubes, it is found that provision of fins result in an enhancement factor of 3.6 to 4.6 in the condensation heat transfer coefficients. This level of enhancement is larger than that resulting from the enhanced surface area of the finned tube surface, suggesting that, apart from the extended area, the surface tension forces play an important role in the augmentation process by driving the condensate from the fin crests to the valleys in between the fins. The measured augmentation factors have also been cross-checked using the Wilson plot method. Detailed error analysis has been performed to quantify the uncertainty in the condensation heat transfer coefficient. The performance of a bank of tubes has been determined based on the measurements carried out on practical condensers of two large chillers with refrigerating capacities of 500 TR and 550 TR. On comparing the finned tube bank results and the single finned tube results, it is found that the average condensation heat transfer coefficient in a bank of tubes having N rows varies as N ¯1/6. The deterioration is in agreement with the relation proposed by Kern.

Submitted by Pedro Silva Filho (pfsilva@ipen.br) on 2017-11-22T17:15:11Z No. of bitstreams: 0 / Made available in DSpace on 2017-11-22T17:15:11Z (GMT). No. of bitstreams: 0 / O excessivo processo de urbanização da Região Metropolitana de São Paulo resultou na perda das características naturais dos seus cursos d\'água ocasionando profundas alterações nos regimes de vazão e de qualidade. O objetivo desse estudo foi avaliar a concentração de metais tóxicos, os semi-metais As, Sb e Se e os elementos terras raras, presentes em amostras de sedimento superficiais coletadas nos Reservatórios Billings, Guarapiranga e Rio Grande. Os elementos Ag, Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb, Sb, Se e Zn foram determinados pela técnica de Espectrometria de Emissão Ótica com Plasma Indutivamente Acoplado (ICP OES). Alguns elementos maiores, traço e elementos terras raras (Ce, Eu, La, Lu, Nd, Sm, Tb e Yb) foram determinados pela técnica de Análise por Ativação Neutrônica Instrumental (INAA). A concentração de Hg total foi determinada pela técnica Espectrometria de Absorção Atômica com Geração de Vapor Frio (CVAAS). A validação das metodologias foi realizada por meio da análise de materiais de referência certificados. Para avaliar as possíveis fontes de contaminação antrópicas foram utilizadas as ferramentas de fator de enriquecimento (FE) e o índice de geoacumulação (IGeo). Os resultados obtidos pelas técnicas foram comparados com os valores orientadores TEL e PEL estabelecidos pelo CCME (Canadian Council of Ministers of the Environment) e adotados pela CETESB. Todos os pontos analisados apresentaram valores > TEL para todos os metais e dois pontos da represa Billings (BILL02100 e 02030), valores > PEL para As, Cr, Cu, Hg, Ni, Pb e Zn, provavelmente em decorrência do recebimento das águas do Rio Pinheiros e das bacias de drenagem do ribeirão Cocaia e Bororé. Os valores de FE e IGeo calculados apontaram possíveis contaminações antrópicas para Sb e Se para os elementos determinados por ICP OES e de As, Cr, Sb e Zn, por INAA. O reservatório Billings apresentou, em geral, as maiores concentrações para os elementos analisados, indicando uma má qualidade de seus sedimentos. Este estudo confirma a necessidade de um monitoramento frequente da qualidade do sedimento nos reservatórios estudados como procedimento indispensável para avaliação periódica da qualidade das bacias, considerando sua importância no fornecimento de água para a Região Metropolitana de São Paulo. / Dissertação (Mestrado em Tecnologia Nuclear) / IPEN/D / Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP

<div>Thermal desalination of high salinity water resources is crucial for increasing freshwater supply, but efficiency enhancements are badly needed. Nanomaterial enhancements and novel condensation regimes offer enormous potential for improving promising technologies like membrane distillation (MD). In this work, we first examined nanofluids for MD, including the role of nanoscale physics, and model system-level energy efficiency enhancements. Our model included the dominant micro-mixing from Brownian motion in fine particle nanofluids (copper oxide) and the unusually high axial conduction from phonon resonance through Van der Waals interaction in carbon nanotube nanofluids. Carbon nanotubes resulted in a consistent, wide range of improvements; while copper oxide particles showcased diminishing returns after a concentration of 0.7%, where Brownian motion effects reduced. However, the enhancements at higher concentrations from liquid layering around nanoparticles were impractical in MD, since the related high surfactant levels compromised the membrane hydrophobicity and promoted fouling. Dilute solutions of metallic nanofluids can be actively integrated to enhance the performance of MD, whereas stronger nanofluid solutions should be limited to heat exchangers that supply thermal energy to MD systems. We then investigated slippery liquid infused porous surfaces (SLIPS) for enhanced condensation rates in MD. Dropwise condensation heat transfer was modelled considering the effects of the departing, minimum droplet radii and the interfacial thermal resistances. Effective droplet shedding from these surfaces led to an experimental thermal efficiency of 95%. Alternatively, porous condensers with superior wicking properties and conductive heat transfer offered a robust solution to high salinity desalination. We modelled the onset of flooding in porous condensers using Darcy’s law for porous media, including the effects of the condenser permeability and determined the optimal condenser thickness at varying system length scales. The increased active area of condensation resulted in a significant enhancement (96.5%) in permeate production and 31.7% improvement in experimental thermal efficiency. However, porous condensers were only compatible with flat plate module designs limiting their practicality.</div>

Thesis focuses on a detailed technical description of all important parts of secondary circuit in Dukovany power plant and its connection to other systems of power plant. In thesis are analyzed significant adjustments which have been made during the entire operation of power plant including in particular the actions associated with project called Utilization of project reserves of units EDU. In the main part of the thesis were carried out calculations of the power plant's power for states before and after the modernization and there is also analyzed the impact of individual changes on the whole power plant. These changes are with the entire secondary circuit drawn in the T-s diagram.