Orientador: Roger Josef Zemp / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-25T15:18:44Z (GMT). No. of bitstreams: 1 Silva_IgorMacieldeOliveirae_M.pdf: 2922871 bytes, checksum: 4b7ffbcbf31e3be71d4453d00d6c7592 (MD5) Previous issue date: 2014 / Resumo: Sistemas de água de resfriamento são o método mais comum de rejeição de calor na indústria. Sistemas convencionais de água de resfriamento recirculante possuem uma rede de trocadores de calor em uma configuração paralela, demandando grande quantidade de circulação de água e torres de resfriamento. Embora a reutilização de água de resfriamento reduza a quantidade de água que é necessária no sistema e aumente o desempenho e capacidade da torre de resfriamento, a queda de pressão na rede de trocadores de calor pode aumentar devido ao seu arranjo em série-paralelo. Este estudo introduz uma metodologia para projetar diferentes sistemas de água de resfriamento e para analisar os impactos da reutilização de água sobre a queda de pressão na rede de trocadores de calor e sobre a torre de resfriamento. A partir de um modelo de super-estrutura, utiliza-se um algoritmo combinatorial com o auxílio da ferramenta de otimização Solver do Microsoft Excel para resolver um problema não-linear (NLP) de cada estrutura de rede de trocadores de calor. A queda de pressão em redes de trocadores de calor é avaliada por uma metodologia baseada na Teoria dos Grafos e utiliza os algoritmos de ordenação por topologia e de caminho crítico. Utiliza-se o método de Merkel para modelar a altura de uma torre de resfriamento e poder avaliar o volume necessário de uma torre de resfriamento para cada rede de trocadores de calor. Um estudo de caso é utilizado para ilustrar cada passo a medida que a metodologia é desenvolvida, buscando prover fundamentos para um estágio conceitual durante o projeto de um sistema de água de resfriamento / Abstract: Cooling water systems are the most common method of waste heat disposal in industry. Conventional recirculating cooling water systems have a heat exchanger network in a parallel arrangement, demanding not only substantial cooling water flow, but also large cooling towers. Although cooling water reuse reduces the amount of water that is recirculated in the system, thereby increasing the cooling tower capacity and performance, the pressure drop in the heat exchanger network may significantly increase due to series-parallel arrangements. This study introduces a methodology to design different cooling water systems and to analyse the cooling water reuse impacts on the heat exchanger network pressure drop and on the cooling tower size. From a superstructure model, a combinatorial algorithm in conjunction with the optimisation tool Solver in Microsoft Excel is used to solve a non-linear problem for each heat exchanger network structure. Pressure drop in heat exchanger networks is evaluated by a methodology that is based on Graph Theory and that uses topological sorting and critical path algorithms. Merkel's method is used to model the cooling tower height and to assess the required cooling tower volume for each heat exchanger network. A case study is used to illustrate each step as the methodology is developed, aiming to provide a basis for a conceptual stage during the cooling water system design / Mestrado / Engenharia Química / Mestre em Engenharia Química

The sample used for evaporative cooling system is Fabric defender 750 with Shelltite finish. From the experimental data and equations we have diffusion coefficient of 20.9 ± 3.71 x 10-6 m2/s for fabric with one layer with 17%-20% fluctuations from the theory, 27.8 ± 4.5 x 10-6 m2/s for fabric with two layers with 6%-14% fluctuations from the theory and 24.9 ± 4.1 x 10-6 m2/s for fabric with three layers with 13%-16% fluctuations from the theory. Since the thickness of the fabric increases so the mass transport rate decreases so the mass transport resistance should be increases. The intrinsic mass resistances of Fabri-1L, Fabri-2L and Fabri-3L are respectively 104 ± 10.2 s/m, 154 ± 23 s/m and 206 ± 26 s/m from the experiment.

Ground source cooling is commonly used for cooling of electronics in protected sites. Sometimes the boreholes are combined with free cooling from the air using a dry cooler to reduce the amount and length of the boreholes, which is the biggest part of the costs. The dry cooler can have two different running modes. In unloading mode the dry cooler is started at a certain temperature and the fans are slowed down at low temperatures so that the cooling power never exceeds the cooling demand. The extracted cooling is used to unload the boreholes. In recharging mode the dry cooler is started at a certain temperature and is operating at full capacity below this temperature. The excess cooling that is extracted in this mode is used to recharge the boreholes. The numerical simulation tool COMSOL Multiphysics was used to evaluate the borehole performance. The software can simulate tilted boreholes with good accuracy and makes it possible to adjust the geometry in any desired way. In this thesis, the performance of a 100 kW ground source cooling system is evaluated for a number of cases both with and without dry coolers in different running modes and sizes. The best solution in respect to life cycle cost, technical feasibility and environmental impact is chosen to be an unloading case with a dry cooler with 100 kW capacity at 8 °C. Using only boreholes gives less carbon dioxide emissions but much higher costs.

Transpiration cooling as potential replacement of multi-hole effusion cooling for gas turbine engines combustion liner application is investigated by comparing their cooling film effectiveness based on the mass transfer analogy (CFEM). Pressure sensitive paint was used to measure CFEM over PM surfaces which was found to be on average 40% higher than multi-hole effusion cooling. High porosity PM with low resistance to flow movement were found to offer uneven distribution of exiting coolant, with large amounts leaving the trailing edge, leading to lopsided CFEM. Design of anisotropic PM based on PM properties (porosity, permeability, and inertia coefficient) were investigated using numerical models to obtain more uniform CFEM. Heat transfer analysis of different PM showed that anisotropic samples offered better thermal protection over isotropic PM for the same porosity. Comparison between cooling film effectiveness obtained from temperatures CFET against CFEM revealed large differences in the predicted protection. This is attributed to the assumptions made to apply CFEM, nonetheless, CFEM remains a good proxy to study and improve transpiration cooling. A method for creating a CAD model of designed PM is proposed based on critical characteristics of transpiration cooling for future use in 3D printing manufacturing.

Building energy simulation has become a useful tool for predicting cooling, heating and electrical loads for facilities. Simulation models have been validated throughout the years by comparing simulation results to actual measured values. The simulations have become more accurate as approaches were changed to be more comprehensive in their ability to model building features. These simulation models tend to require considerable experience in determining input parameters and large amounts of time to construct the models. As a result of the large number of man-hours required, simplified models have been sought and used. Simplified models are particularly useful for conducting preliminary assessments of energy conservation measures. These simplified models often use linear relationships in order to estimate conditions such as infiltration, energy usage, and temperature gradients. Studies have been performed in order to validate popular models such as ASHRAE's Bin or Modified Bin methods. A useful measure would be to determine the accuracy of a simplified model to establish error bounds. Having a simplified model and establishing its error bounds, technical estimations from such models could be used in selected applications with more confidence. The error bound relative to DOE-2 predictions, for a proposed simplified model denoted IEC, for estimating a commercial building's cooling load are presented along with two actual-building test cases for validation purposes. The sensitivity of the error to various building parameters such as minimum make-up air, cooling capacity oversize, and internal equipment load was investigated. The error bound was determined to be within ±15 per cent for both cases and almost all variations. / Master of Science

Though the least squares technique has many advantages, its possible limitations as applied in the atmospheric sciences have not yet been fully explored in the literature. The assumption that the atmosphere responds either in phase or out of phase to the solar input is ubiquitous. However, our analysis found this assumption to be incorrect. If not properly addressed, the possible consequences are bias in the linear trend coefficient and attenuation of the solar response coefficient. Using USU Rayleigh lidar temperature data, we found a significant phase offset to the solar input in the temperatures that varies ±5 years depending on altitude. In addition to introducing a phase offset into the linear regression model, we argue that separating what we identify as the solar-noise is to be preferred because (1) the solar-noise can contain important physical information, (2) its omission could lead to spurious conclusions about the significance of the solar-proxy coefficient, and (3) its omission could also bias the solar proxy coefficient. We also argue that the Mt. Pinatubo eruption caused a positive temperature perturbation in our early mesopause temperatures, exerting leverage on the linear trend coefficient. In the upper mesosphere, we found a linear cooling trend of greater than -1.5 K/year, which is possibly exaggerated because of leverage from the earlier temperatures and/or collinearity. In the middle mesosphere we found a cooling trend of -1 K/year to near zero. We use the autocorrelation coefficient of the model residuals as a physical parameter. The autocorrelation can provide information about how strongly current temperatures are affected by prior temperatures or how quickly a physical process is occurring. The amplitudes and phases of the annual oscillation in our data compare favorably with those from the OHP and CEL French lidars, as well has the HALOE satellite instrument measurements. The semiannual climatology from the USU temperatures is similar to that from the HALOE temperatures. We also found that our semiannual and annual amplitudes and phases compare favorably with those from the HALOE, OHP, and CPC data.

Let X be a space and let S ⊂ X with a measure of set size |S| and boundary size |∂S|. Fix a set C ⊂ X called the constraining set. The constrained isoperimetric problem asks when we can find a subset S of C that maximizes the Følner ratio FR(S) = |S|/|∂S|. We consider different measures for subsets of R^2,R^3,Z^2,Z^3 and describe the properties that must be satisfied for sets S that maximize the Folner ratio. We give explicit examples.

Electricity has become so ingrained in everyday life that the current generation has no knowledge of life without it. The majority of power generation in the United States is the result of turbines of some form. With such widespread utilization of these complex rotating machines, any increase in efficiency translates into improvements in the current cost of energy. These improvements manifest themselves as reductions in greenhouse emissions or possible savings to the consumer. The most important temperature regarding turbine performance is the temperature of the hot gas entering the turbine, denoted turbine inlet temperature. Increasing the turbine inlet temperature allows for increases in power production as well as increases in efficiency. The challenge with increasing this temperature, currently the hottest temperature seen by the turbine, is that it currently already exceeds the melting point of the metals that the turbine is manufactured from. Active cooling of stationary and rotating components in the turbine is required. Cooling flows are taken from bleed flows from various stages of the compressor as well as flow from the combustor shell. This cooling flow is considered wasted air as far as performance is concerned and can account for as much as 20% of the mass flow in the hot gas path. Lowering the amount of air used for cooling allows for more to be used for performance gain. Various technologies exist to allow for greater turbine inlet temperatures such as various internal channel features inside of turbine blades, film holes on the surface to cool the outside of the airfoil as well as thermal barrier coatings that insulate the airfoils from the hot mainstream iv flow. The current work is a study of the potential performance impact of coupling two effusion technologies, transpiration and discrete hole film cooling. Film cooling and transpiring flows are individually validated against literature before the two technologies are coupled. The coupled geometries feature 13 film holes of 7.5mm diameter and a transpiring strip 5mm long in the streamwise direction. The first coupled geometry features the porous section upstream of the film holes and the second features it downstream. Both geometries use the same crushed aluminum porous insert of nominal porosity of 50%. Temperature sensitive paint along with an ‘adiabatic’ Rohacell surface (thermal conductivity of 0.029W/m-K) are used to measure adiabatic film cooling effectiveness using a scientific grade high resolution CCD camera. The result is local effectiveness data up to 50 film hole diameters downstream of injection location. Data is laterally averaged and compared with the baseline cases. Local effectiveness contours are used to draw conclusions regarding the interactions between transpiration and discrete hole film cooling. It is found that a linear superposition method is only valid far downstream from the injection location. Both coupled geometries perform better than transpiration or the discrete holes far downstream of the injection location. The coupled geometry featuring the transpiring section downstream of the film holes matches the transpiration effectiveness just downstream of injection and surpasses both transpiration and film cooling further downstream.

One of the main goals of recent turbine film cooling research has been to improve the overall efficiency of the turbine by slightly increasing film cooling efficiency. This has a twofold effect. Firstly by increasing the effectiveness of the cooling being done. it is possible to increase the inlet temperature of the combusted air coming into the turbine which in tum increases turbine performance. Secondly by increasing the cooling efficiency less air is required. for cooling. This means that less air will be redirected from the compressor for cooling purposes, allowing more air to reach the combustor to be burned and used for power or thrust generation. Even though much bulk flow pulsation research has been conducted in the past, little research has studied the effect of film coolant pulsation on cooling effectiveness. Previous studies that have been conducted on the effect of film pulsation have provided conflicting results, therefore more research is required. This project provides experimental data and analysis which study, and show the effects that low frequency pulsations (5.55 and 11.11 Hz) at two different blowing rations (.5 and .75) have on film cooling effectiveness. In addition a Kulite dynamic pressure probe was placed at the entrance to the coolant holes in order to provide the actual blowing ratio felt by the holes. The study concluded that film pulsation increases film cooling effectiveness mainly through. a reduction in the amount of coolant gas needed to provide adequate film cooling. In addition to providing some initial data, the study also lays the groundwork for additional research to delve further into film pulsation and answer unanswered questions, which will be conducted at a later time.

A segment of transpiring wall is installed near a row of unshaped film holes. The effects on the aerodynamic performance and cooling downstream of the row of cylindrical holes in the presence of transpiration is studied numerically. The changes in behavior of the film due to relative positioning of the injection sources and blowing ratios are predicted to understand the sensitivity of cooling and aerodynamic losses on the relative positioning of the two sources and each blowing ratio. The results indicate that a coupling of the two sources allows a more efficient use of coolant by generating a more uniform initial film resulting in improved component durability through reduction of hot- streaks. With careful optimization the discrete holes can be placed farther apart laterally operating at a lower blowing ratio with a transpiration segment making the large deficits in cooling effectiveness mid-pitch less severe, overall minimizing coolant usage. Addition of transpiration increases the aerodynamic losses associated with injection. This effect can be arguably small compared to corresponding thermal benefits seen by coupling the two. Comparisons of linear superposition predictions of the two independent sources with the corresponding coupled scenario indicate the two films positively influence one another and outperform predictions. The interaction between the two films is dependent upon the relative placement of the transpiration; all relative placements have an overall beneficial effect on the cooling seen by the protected wall. An increase in area-averaged film cooling effectiveness of 300% is seen along with only a 50% increase in loss coefficient by injecting an additional 10% coolant. In this study the downstream placement of transpiration is found to perform best of the three geometries tested while considering cooling, aerodynamic losses, local uniformity and manufacturing feasibility. With further study and optimization this technique can potentially provide more effective thermal protection at a lower cost of aerodynamic losses and spent coolant. A method of measuring the local temperature of a porous wall is also discussed. Measurements are taken with temperature sensitive paint applied in thin coats to the wall. This technique was validated on a 40PPI, 7% relative density aluminum porous coupon. Measurements of discharge coefficients as well as downstream effectiveness data are included to verify the flow through the porous wall was unaltered by applying the paint. A maximum deviation in film-cooling effectiveness of 9% between the two cases with the majority of data falling within 4% was found, very similar to the experimental uncertainty of the rig. This excellent agreement between the repeated tests showed that by applying thermal paint to a wall of such porosity does not significantly affect the flow exiting the wall and hence the measurement technique can readily be applied to transpiration cooling studies at this scale. Methods of filtering the temperature sensitive paint on the porous wall are presented.