Torres de resfriamento são equipamentos muito utilizados na indústria e que muitas vezes operam sob condições adversas, particularmente, temperatura de água acima dos 50°C na entrada da torre. Nesta condição, tem-se alta taxa de evaporação e eventualmente condição de alto transporte de massa, normalmente não considerado no equacionamento de torres de resfriamento. Apresenta-se assim uma análise comparativa de diferentes métodos de cálculo de torres de resfriamento: Merkel, Poppe e o modelo proposto. No modelo proposto neste estudo, consideram-se os balanços diferenciais de massa e energia e os mecanismos de transporte simultâneo de calor e massa, na condição de alto transporte de massa e de supersaturação do ar, caso o vapor de água condense na forma de névoa. Para os casos em que há saturação do ar, os balanços diferenciais de massa e energia passam a contemplar este fenômeno a partir do momento em que ocorre a saturação. O modelo matemático desenvolvido consiste de equações diferenciais ordinárias e equações auxiliares, e foi implementado em uma interface Matlab. Os principais parâmetros investigados foram: as vazões de água e ar, a temperatura de bulbo úmido do ar, a temperatura da água na entrada da coluna e a altura da torre. A partir das simulações matemáticas, foram obtidos resultados de temperaturas do ar, da água e da umidade do ar ao longo da coluna, para os diferentes métodos. / Cooling towers are equipment widely used in industrial plants, where these operate under severe conditions such as cooling water inlet temperatures above 50oC. Under this condition, there are high evaporation of water and high mass transfer, generally not considered in performance analysis of a cooling tower. This work presents and analyzes the differences between the proposed model and the Merkel and Poppe approaches. The proposed model in this work is based on differential equations for energy and mass balances and on the mechanisms of combined heat and mass transfers, at high mass transfer condition and considering the supersaturated air from the height of the tower that the excess of water vapor condenses as a mist. At the point that the air became supersaturated, the differential equations for energy and mass balances start to consider the supersaturation phenomena. The mathematical model developed in this work is composed by ordinary differential equations and auxiliary equations which were solved at Matlab. The parameters investigated were water and air mass flow rates, air wet bulb temperature, water inlet temperature and tower height. The results of air and water temperatures, humidity air across the tower height are presented for each method analyzed.

The content of this diploma thesis is solution of production technology of cooling tower component. A model the cooling tower according to customer specifications is designed. There are selected 2 plates from steel construction that will be machined by plasma cutting. The technology of production of the plates is also proposed. Technical and economic evaluation of production compares 2 versions of plate production using unconventional metal cutting methods.

The following thesis looks into modeling a chilled water system equipped with variable speed drives on different piece of equipment and optimization of system setpoints to achieve energy savings. The research was done by collecting data from a case-study and developing a system of component models that could be linked to simulate the overall system operation.

[pt] O crescimento microbiológico em águas de sistemas de resfriamento pode resultar na formação de biofilme, o qual pode causar problemas de biocorrosão, perdas de carga em tubulações, redução de taxa de transferência de calor e obstrução de fluxo. Os principais e tradicionais biocidas utilizados no controle microbiológico de águas de resfriamento são os compostos à base de cloro. Entretanto, nos últimos anos o ácido peracético tornou-se uma alternava aos compostos clorados, uma vez que este biocida deixa como resíduo apenas o acetato o qual é biodegradável e não forma subprodutos organoclorados. Este trabalho analisou a aplicação do ácido peracético comparando-o com o hipoclorito de sódio no controle microbiológico e na corrosividade de materiais, empregando uma árvore de teste em escala de laboratório. Foi investigada a taxa de corrosão dos materiais metálicos de aço carbono, cobre e aço inoxidável, além da efetividade na redução da contagem bacteriana. Os experimentos foram realizados em condições de fluxo turbulento, pH 8 e temperatura de 32 C empregando uma água de estudo real, carregada de matéria orgânica (DQO = 350 mg/L). As concentrações usadas de ácido peracético foram 0,75; 1,0 e 3,0 mg/L e de hipoclorito de sódio foram 1,0 e 3,0 mg/L. O ácido peracético na concentração de 3,0 mg/L reduziu a carga bacteriana de 1,5x10 (elevado a 5) UFC/mL para 5,24x10 (elevado a 3) UFC/mL. Comparado ao hipoclorito de sódio, o ácido peracético foi menos corrosivo para o aço carbono em todas as concentrações. Na concentração de 1,0 mg/L a taxa de corrosão do cobre em ácido peracético foi menor do que na solução de hipoclorito de sódio. Já na concentração de 3,0 mg/L ocorreu o inverso. Não foi observada corrosão significativa no aço inoxidável para os biocidas estudados. / [en] Microbiological growth in cooling systems water may result in biofilm formation, which can cause problems of bio-corrosion, pressure drop in the pipes, reduction of heat transfer rate and flow obstruction. The main and traditional biocides applied in microbiological control of cooling waters are the chlorine based compounds. However, in recent years, peracetic acid has become an alternative to chlorinated compounds, since this biocide leaves as residue only the acetate, which is biodegradable and does not form chlorinated organic byproducts. This work analyzed the application of peracetic acid comparing to sodium hypochlorite in the microbiological control and material corrosivity using a laboratory scale test tree. The corrosion rate of carbon steel, copper and stainless steel alloys in addition to the effectiveness in reducing the bacterial count. The experiments were carried out under conditions of turbulent flow, pH 8 and temperature of 32 C using a real industrial test water loaded with organics (COD = 350 mg/L). Peracetic acid concentrations used were 0.75, 1.0 and 3.0 mg/L and sodium hypochlorite were 1.0 and 3.0 mg/L. Peracetic acid at the concentration of 3.0 mg/L decreased the bacterial load from 1.5x10 (raised to 5) UFC/mL to 5.24x10 (raised to 3) UFC/mL. Peracetic acid compared to sodium hypochlorite was less corrosive to carbon steel at all concentrations. At the concentration of 1.0 mg/L the corrosion rate of copper in peracetic acid was lower than in sodium hypochlorite solution. At the concentration of 3.0 mg/L, the reverse occurred. No significant corrosion was observed in stainless steel for the biocides studied.

Neste trabalho foi realizada a modelagem fenomenológica do desempenho de uma torre de resfriamento de água e de um sistema de duas torres de resfriamento em série, com temperatura de água de entrada de até 65 ºC. Verificou-se a validade do modelo através de comparação dos resultados previstos com os obtidos em ensaios em uma unidade piloto. Em seguida, através de simulação matemática, a partir do modelo desenvolvido, foi feito o estudo de diversos casos de aplicação. Estudou-se a influência das principais variáveis de operação (vazão de ar, vazão de água e temperatura de bulbo úmido) no desempenho de torres de resfriamento acopladas (em série e em paralelo) e no custo operacional. Verifica-se que a variável de maior influência é a vazão de água que circula pela torre. / This is a study about the phenomenological modeling of the performance of a water cooling tower and a system of two cooling towers in series, with water temperature input up to 65°C. The validity of model was verified by comparing the expected results with those obtained in tests on a pilot plant. After this, through a mathematical simulation, based on the model developed, several cases of application were analyzed. It was studied the influence of main operating variables (air flow, water flow and wet bulb temperature) on the performance of couples cooling towers (in series and parallel) and on operational cost. It was verified the most influential variable is the water flow rate through the tower.

Neste trabalho foi realizada a modelagem fenomenológica do desempenho de uma torre de resfriamento de água e de um sistema de duas torres de resfriamento em série, com temperatura de água de entrada de até 65 ºC. Verificou-se a validade do modelo através de comparação dos resultados previstos com os obtidos em ensaios em uma unidade piloto. Em seguida, através de simulação matemática, a partir do modelo desenvolvido, foi feito o estudo de diversos casos de aplicação. Estudou-se a influência das principais variáveis de operação (vazão de ar, vazão de água e temperatura de bulbo úmido) no desempenho de torres de resfriamento acopladas (em série e em paralelo) e no custo operacional. Verifica-se que a variável de maior influência é a vazão de água que circula pela torre. / This is a study about the phenomenological modeling of the performance of a water cooling tower and a system of two cooling towers in series, with water temperature input up to 65°C. The validity of model was verified by comparing the expected results with those obtained in tests on a pilot plant. After this, through a mathematical simulation, based on the model developed, several cases of application were analyzed. It was studied the influence of main operating variables (air flow, water flow and wet bulb temperature) on the performance of couples cooling towers (in series and parallel) and on operational cost. It was verified the most influential variable is the water flow rate through the tower.

Industrial and mining sectors are amongst the largest single energy consumers in South Africa, making them a primary focus for implementing energy saving initiatives. Refrigeration systems on mines are responsible for consuming up to25 % of the electrical energy consumption on a typical South African deep level mine. Ample opportunities to reduce the energy consumption of these systems exists, as many of the current systems rely on old technology and function under partial or inadequate control management. In compiling this thesis, various energy saving strategies on deep level mines were investigated. In specific, the effects of controlling and improving the cooling auxiliaries. Scenarios were investigated and simulated, where after an optimum solution was implemented. Implementations, such as the ones covered in this dissertation, form part of the IDM (Integrated Demand Management) energy efficiency incentive introduced by Eskom, where funding is made available based on actual power saving; ensuring that the projects will be financially viable to the clients. Reduced electrical energy consumption realised from the abovementioned projects were measured, captured and compared to the consumption before project implementation to determine the achieved savings. Savings of up to 30 % of the plant installed capacity were realised, providing average savings of up to 2.3 MW per day. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013

Industrial and mining sectors are amongst the largest single energy consumers in South Africa, making them a primary focus for implementing energy saving initiatives. Refrigeration systems on mines are responsible for consuming up to25 % of the electrical energy consumption on a typical South African deep level mine. Ample opportunities to reduce the energy consumption of these systems exists, as many of the current systems rely on old technology and function under partial or inadequate control management. In compiling this thesis, various energy saving strategies on deep level mines were investigated. In specific, the effects of controlling and improving the cooling auxiliaries. Scenarios were investigated and simulated, where after an optimum solution was implemented. Implementations, such as the ones covered in this dissertation, form part of the IDM (Integrated Demand Management) energy efficiency incentive introduced by Eskom, where funding is made available based on actual power saving; ensuring that the projects will be financially viable to the clients. Reduced electrical energy consumption realised from the abovementioned projects were measured, captured and compared to the consumption before project implementation to determine the achieved savings. Savings of up to 30 % of the plant installed capacity were realised, providing average savings of up to 2.3 MW per day. / Thesis (MIng (Mechanical Engineering))--North-West University, Potchefstroom Campus, 2013

This diploma thesis deals with the problematics of fan cooling towers. The very first part of the text is research, focusing mainly on the theory of cooling and the function of fan cooling towers in general. The following chapter deals with the water resource management of the Dukovany nuclear power plant and the specification of its objects of forced draft cooling towers. The second part describes a computational model created to determine the cooling performance of these towers under the given input conditions. In the following chapters, the results from the computational model are compared with the available data from warranty measurements and with the provided characteristics. The final pages deal with the study of the influence of changes in input parameters on the cooling performance and the research of the behavior of the cooling towers under extreme weather conditions.

Grootvlei Power Station’s thermal efficiency had been on a steady declining trend since it was re-commissioned in 2008, which had tremendous financial implications to the company at the time of writing. The main contributory factor to the thermal efficiency losses was identified to be the condenser backpressure losses that the station was experiencing. This loss was responsible for approximately 17% of the total efficiency losses. Therefore an investigation was conducted to determine the potential impact of the condenser backpressure loss on the thermal efficiency and the financial implications thereof. The deliverables were to determine the cause of the condenser backpressure loss and propose possible resolutions, to quantify the financial effect and to produce a cost benefit analysis in order to justify certain corrective actions. Grootvlei Power Station is one of the older power stations in South Africa and it was used as the first testing facility for dry-cooling in South Africa. It consists of six 200MW units, two of which are dry-cooled units. In 1990 it was mothballed and due to rising power demands in South Africa, it was re-commissioned in 2008. Thermal efficiency has been playing a great role due to the power constraints and therefore it was deemed necessary to conduct this study. The approach that was used was one of experimental and quantitative research and analyses, incorporating deductive reasoning in order to test various hypotheses of factors that could have been contributing to the backpressure losses. In order to do so, a logic diagram was designed which could be used to aid in the identification of possible causes of the condenser backpressure losses. The logic diagram was able to identify whether the problem had to do with the cooling tower or the condenser. It was able to identify which area on the condenser was defective i.e. whether the pumps were not performing, or whether the air ejectors were not performing. It was also able to indicate whether the inefficiency was due to air ingress or fouling. Alongside the logic diagram, a condenser efficiency analysis was used in order to strengthen and improve on the investigation. This analysis was able to identify whether the condenser was experiencing fouling conditions, air ingress, passing valves or low cooling water flow. After the investigation commenced, it was decided to focus on the two largest contributing units since the largest contributor was a dry-cooled unit and the second largest contributor was a wet-cooled unit, thus some comparison between the units was incorporated. The condenser efficiency analysis on Unit 3 (wet-cooled unit) indicated a low cooling water flow, fouling as well as air ingress. The logic diagram indicated poor cooling tower performance, high air ingress as well as fouling. Further tests and analyses as well as visual inspections confirmed these phenomena and condenser fouling was identified to be the largest contributor to the backpressure loss on this unit. The condenser efficiency analysis on Unit 6 indicated that air was entering the condenser. The logic diagram indicated that a segment of the backpressure loss was due to poor cooling tower performance. Inspection of the cooling tower indicated damage and leaks. A cooling tower performance test was conducted and the result of the test indicated that the tower was in need of cleaning. Further analyses according to the logic diagram indicated that the condenser was experiencing air ingress which concurred with the condenser efficiency analysis. A helium test, condensate extraction pump pressure test as well as a flood test was conducted on this unit and various air in-leakage points were identified. The financial implications of the backpressure losses were investigated and found to be costing millions each month. The condenser backpressure loss was contributing more than 2% to the thermal efficiency loss. The cost benefit analysis indicated that the cost of cleaning the condenser on Unit 3 would be made up within six months and a return on investment of 16,6% was calculated. The cost benefit analysis motivates for extended outage times for the purpose of cleaning the condensers from a financial perspective. Therefore, it was recommended to clean the condenser on Unit 3 and fix all known defects on the unit as well as on Unit 6. The cooling towers were recommended to be refurbished. Further investigation was recommended to determine the feasibility of installing an online cleaning system on the wet-cooled units’ condensers such as a Taprogge system. Alternative investigation methods were suggested such as smoke stick analyses for air ingress determination. It was also recommended to review the maintenance strategies that were being used since many of the defects were found to be maintenance related. If the identified problem areas are attended to, the condenser backpressure loss will decrease and the condensers transfer heat more efficiently which will lead to financial gains for Grootvlei Power Station as well as efficiency gains, plant reliability and availability gains. / MIng (Development and Management Engineering), North-West University, Potchefstroom Campus, 2015