Neste trabalho é apresentada a avaliação da inversão da sacarose em um sistema constituído de um Evaporador de filme descendente com promotor de película. Foi feita a modelagem da inversão considerando-se os balanços de massa e de entalpia e a cinética de inversão no tubo de evaporação. Os principais parâmetros considerados foram: constante cinética (k), taxa de evaporação(mv), concentração de açúcares totais (C), vazão do líquido no tubo de evaporação (q), pH, temperatura (T) e tempo de residência no tubo de evaporação (T). Usaram-se dois métodos para a resolução do modelo, a primeira através da integração numérica do modelo (Runge Kutta de 4ta ordem) e a outra através de equacionamento simplificado a partir valores médios das propriedades, pH, e calculando as constantes cinéticas nas temperaturas efetivas em cada zona do tubo de evaporação, Tefa (zona de aquecimento) e Tefe (zona de evaporação), possibilitando assim, a integração analítica do modelo. Foram calculados os valores do volume do líquido (V) através dos dois métodos. Os resultados foram expressos em função da vazão do líquido (q). Verificou-se que os resultados calculados pelos dois métodos foram muito próximos. Os modelos desenvolvidos podem ser aplicados para a otimização do processo de evaporação visando à minimização da inversão da sacarose. O método desenvolvido possibilita a determinação do tempo de residência no tubo de evaporação. / In this work the evaluation of sucrose inversion in a system formed by falling film Evaporator with Promoter of film is presented. The modeling was made considering: mass and enthalpy balances and the kinetic of inversion in the evaporation tube. The mean parameters investigated were: kinetic constant (k), evaporation rate (mv), concentration of total sugars (C), volumetric velocity of the liquid in the evaporation tube (q), pH, temperature (T) and residence time in the evaporation tube (T). Two methods was used to solve the model, the first by numeric integration (Runge Kutta 4th Order) and the other by analytic integration of simplified model considering mean values of properties and pH, and the kinetic constant calculates at effective temperatures in each zone of the evaporation tube, Tefa and Tefe, allowed the analytic integration of the model. The volume of liquid in the evaporation tube (V) was calculated by the two methods (numeric integration and simplified methods). The results were expressed as a function of liquid flow rate (q). It was verified that the values obtained by the two methods were very closed. These models can be used for the optimization of the evaporation process emphasizing the minimization of the sucrose inversion. The methodology could be used for the determination of the residence time in the evaporation tube.

O processo de pasteurização tem como objetivo garantir a segurança e qualidade nutricional do alimento e aumentar sua vida de prateleira. O conhecimento da distribuição do tempo de residência (DTR) do alimento em cada etapa do processo contínuo é importante para uma avaliação adequada do processo e das alterações que causa no alimento. Este trabalho tem como objetivo estudar a DTR em um processo de pasteurização contínuo assistido por micro-ondas aplicado a alimentos líquidos e propor modelos de escoamento para representá-la. Para isso, foram realizados experimentos de estímulo-resposta com alimentação tipo pulso por técnica condutimétrica utilizando uma solução saturada de NaCl como traçador. Com isso, foram obtidas as curvas de DTR do sistema completo, dos trocadores de calor das seções de pré-aquecimento e resfriamento, de seis tubos de retenção com diferentes diâmetros e comprimentos (volumes entre 40 e 125 mL) e do sistema de aquisição de dados de condutividade elétrica. Os experimentos foram realizados em quatro vazões volumétricas (0,5, 0,7, 0,9 e 1,1 L/min), a temperatura ambiente (19 a 26 °C) e como fluido de trabalho foi utilizada uma corrente de alimentação de água com concentração 0,5 g/L de NaCl para estabilizar a leitura de condutividade elétrica. Foram realizadas três repetições por vazão para o processo completo, trocadores de calor e tubos de retenção, e cinco repetições por vazão para o sistema de aquisição de dados, dada a maior sensibilidade. Observou-se a necessidade de realizar o procedimento de convolução numérica para avaliar a distorção na curva de DTR do processo causada pelo escoamento na célula do sistema de aquisição de dados. Foram testados cinco modelos de escoamento: dispersão axial, compartimentado PFR+CSTR, tanques em série, convecção generalizada e y-laminar. O critério de ajuste dos modelos foi a minimização do erro quadrático entre valores experimentais e calculados da curva E(t). Os modelos de dispersão axial e y-laminar foram o que apresentaram melhor ajuste para os tubos de retenção e o modelo de convecção generalizada apresentou melhor ajuste para os trocadores de calor. O regime de escoamento durante os experimentos variou entre laminar e de transição (valores de Reynolds entre 1259 e 4238). Os resultados para o sistema completo e trocadores de calor foram satisfatórios, para os tubos de retenção foi observada uma grande incerteza nos valores dos parâmetros e foi observada a importância da convolução numérica em sistemas de pequeno volume. / Pasteurization process aims to ensure the safety and nutritional quality of the food and increase its shelf life. The knowledge of residence time distribution (RTD) of the food in each step of continuous processes is important to evaluate the process and changes that it causes in foods. This work aims to study the RTD in a continuous pasteurization process assisted by microwave applied to liquid foods and propose flow models to represent it. For this reason, stimulus-response experiments by pulse injection were conducted by conductimetric technique using a saturated solution of NaCl as a tracer. Thus, it was obtained the RTD of the complete process, heat exchangers of preheating section and cooling section, six retention tubes with different diameters and lengths (volumes between 40 and 125 mL) and of the electrical conductivity data acquisition system. The experiments were carried out at four volumetric flow rates (0.5, 0.7, 0.9 and 1.1 L/min), at room temperature (19 to 26 °C) and water with 0.5 g/L of NaCl was used as the work fluid to stabilize the electrical conductivity reading. Three repetitions per volumetric flow rate were performed for the complete process, heat exchangers and holding tubes, and five repetitions per volumetric flow rate were performed for the data acquisition system, given the higher sensibility. It was observed the need to apply the numerical convolution procedure to evaluate the distortion in the RTD curve of the process caused by the flow through the data acquisition system. Five flow models were tested: axial dispersion, PFR+CSTR association, tanks in series, generalized convection and y-laminar. The adjustment criterion of the parameters was the minimization of the quadratic error between experimental and calculated E(t) values. The axial dispersion and y-laminar models provided the best adjustments for the holding tubes and the generalized convection model provided the best adjustment for the heat exchangers. The flow regime during the experiments varied between laminar and transition (Reynolds values between 1259 and 4238). The results for the complete system and heat exchangers were satisfactory, for the holding tubes was observed a great uncertainty in the parameters values and was observed the importance of numerical convolution in small volume systems.

The current work has developed a CFD model to characterise a pseudo-annular photocatalytic bubble column reactor. The model development was divided into three stages. Firstly, hydrodynamic assessment of the multiphase fluid flow in the vessel, which incorporated residence time distribution analysis both numerically and experimentally for validation purposes. Secondly, the radiation distribution of the UV source was completed. The final stage incorporated the kinetics for the degradation the model pollutant, sodium oxalate. The hydrodynamics were modelled using an Eulerian-Eulerian approach to the multiphase system with the standard k- turbulence model. This research established that there was significant deviation in the fluid behaviour in the pseudo-annular reactor when compared with traditional cylindrical columns due to the nature of the internal structure. The residence time distribution study showed almost completely mixed flow in the liquid phase, whereas the gas phase more closely represented plug flow behaviour. Whilst there was significant dependence on the superficial gas flow rate the mixing behaviour demonstrated negligible dependence on the liquid superficial velocity or the liquid flow direction, either co- or counter- current with respect to the gas phase. The light distribution was modelled using a conservative variant of the Discrete Ordinate method. The model examined the contribution to the incident radiation within the reactor of both the gas bubbles and titanium dioxide particles. This work has established the importance of the gas phase in evaluating the light distribution and showed that it should be included when examining the light distribution in a gas-liquid-solid three-phase system. An optimal catalyst loading for the vessel was established to be 1g/L. Integration of the kinetics of sodium oxalate degradation was the final step is developing the complete CFD model. Species transport equations were employed to describe the distribution of pollutant concentration within the vessel. Using a response surface methodology it was shown that the reaction rate exhibited a greater dependency on the lamp power that the lamp length, however, the converse was true with the quantum efficiency. This work highlights the complexity of completely modelling a photocatalytic system and has demonstrated the applicability of CFD for this purpose.

<p>The hypothetical assumption that chloride is conservative in the soil has been debated for the last decade. The results of the recent years of study in chlorine biogeochemistry show that chloride is non-conservative but rather participates in complex biogeochemical reactions in the soil. These interactions in nature inform the development of simplified hydrochemical model of chloride dynamics in the soil that is driven on soil routine component of HBV hydrological model. This novel attempt affords the opportunity to explore chlorine biogeochemistry further by evaluating the biological processes such as microbial biomass that predominate chlorine cycles in the same order of magnitude as earlier studied abiotic factors. Data from soil lysimeter experiment with different inputs treatments were used in the calibration and validation of both the hydrological and biogeochemical model. The results show that (1) model efficiency reduces with decreasing water residence and with increasing soil organic matter. (2) Longer water residence time (low water input), high chloride and high nitrogen input loads relatively enhance maximum biomass accumulation in a shorter time span. (3) Chloride retention time reduces with increasing chloride loads under short water residence. (4) Microbial biomass growth rate is highest under high chloride input treatments. (5) Biomass death rates shows reducing trend under short water residence (High water input). Further researches are therefore suggested for possible model expansion and to make the results of this model plausible under field conditions.</p>

The hypothetical assumption that chloride is conservative in the soil has been debated for the last decade. The results of the recent years of study in chlorine biogeochemistry show that chloride is non-conservative but rather participates in complex biogeochemical reactions in the soil. These interactions in nature inform the development of simplified hydrochemical model of chloride dynamics in the soil that is driven on soil routine component of HBV hydrological model. This novel attempt affords the opportunity to explore chlorine biogeochemistry further by evaluating the biological processes such as microbial biomass that predominate chlorine cycles in the same order of magnitude as earlier studied abiotic factors. Data from soil lysimeter experiment with different inputs treatments were used in the calibration and validation of both the hydrological and biogeochemical model. The results show that (1) model efficiency reduces with decreasing water residence and with increasing soil organic matter. (2) Longer water residence time (low water input), high chloride and high nitrogen input loads relatively enhance maximum biomass accumulation in a shorter time span. (3) Chloride retention time reduces with increasing chloride loads under short water residence. (4) Microbial biomass growth rate is highest under high chloride input treatments. (5) Biomass death rates shows reducing trend under short water residence (High water input). Further researches are therefore suggested for possible model expansion and to make the results of this model plausible under field conditions.

The purposes of this study are to understand the surface water distributions and vertical profiles of Ra-226 in the northern South China Sea (SCS), and to estimate the mean residence time of Pb-210 based on the extent of radioactive disequilibrium relative to Ra-226. Seawater samples of 20-liter size were collected during four Ocean Researcher I (ORI) cruises conducted in 2000, 2001, 2002 and 2003 (Cruise 575 in March, Cruise 606 in April, Cruise 662 in October, and Cruise 688 in July) for Ra-226 measurements. Surface water Ra-226 in the study area varies between 10 and 16 dpm/100 kg with higher values at stations closer to the landmass of coastal China. The surface water Ra-226 distribution shows seasonal variation: the western Philippine Sea (WPS) surface water with low Ra-226 content enters the SCS and moves mainly northwestward in summer; this water shifts toward the center in autumn. Ra-226 profiles in the northern SCS generally show an increase from the surface toward the bottom, quite similar to that of the open ocean. However, Ra-226 is systematically higher in the northern SCS than in the western North Pacific above 1500m. This may be attributed to higher Ra-226 input from the vast area of the shelf and slope in the SCS. Below this depth, Ra-226 displays large variation in some of the profiles but the mean values are quite comparable to those of the western North Pacific at the corresponding depth. The deep water in the SCS basin probably derives its Ra from the underlying sediments similar to the case in open oceans. The Pb-210/Ra-226 activity ratio in the study area ranges between 1.4 and 2.7 in the surface water with higher values at the stations closer to the Luzon Strait due to lower Ra-226 over there. The excess Pb-210 over Ra-226 in the surface water due to atmospheric input may penetrate to a depth of about 200 to 500m. Below this depth, Pb-210 becomes deficient because it is scavenged and removed by settling particulates. Below 1000m, the Pb-210/Ra-226 activity ratio varies around 0.7 to 0.5. Box model calculations within a mixed layer of 50m in the area yield a mean residence time of about 1 yr for Pb-210 if an atmospheric Pb-210 flux of 1.05 dpm/cm2/y is adopted. The activity ratio of about 0.5 to 0.7 in the deep water corresponds to a Pb-210 mean residence time of about 30 to 70 yrs with respect to particulate scavenging. These values are quite comparable to those determined from the Pacific deep water, suggesting that Pb-210 in the SCS deep water is scavenged and removed by sinking particulates at a rate similar to that in the deep open oceans.

The study of catalytic oxidation on the removal of NO was investigated over the Cu-catalysts . The Cu-catalysts , including Cu/TiO2 , Cu/Al2O3 and Cu/SiO2 , were prepared by impregnation method . Alougth NO2 , the product of this reaction , has higher toxicity than NO , but it might be removed completely by absorption with H2O or alkalinal solution for its high solubility . The experiments can be divided into three parts , i.e. , the screen of test catalysts , the effect of operating factors on the conversion of NO and the kinetic model . In the first part , the activity of test catalysts , which were prepared by mixing three various sources of Cu-ions¡]i.e., Cu(NO3)2 , Cu(CH3COO)2 , and CuSO4¡^with three different types of support¡]i.e., TiO2 , Al2O3 , and SiO2¡^, and were compared in form of conversion on NO to find the best catalyst . The results show that the mixture Cu(NO3)2 / TiO2 has the good performance on the conversion of NO , and also has more wider operating in range of temperature . In order to find the optimal loading of Cu on Cu(NO3)2 / TiO2 , additional test of various dosage over the catalysts was conduct in series . It is found that 8wt.% of Cu loading on Cu(NO3)2 / TiO2 is the most economic dosage . Therefore , we select this type of Cu oxide as the best catalyst in the following work . In the second part , the effect of NO inlet concentration , space velocity and humidity on the conversion of NO were performed . The results show that the conversion of NO decreases with the increasing of [NO]in when [NO]in is larger than 1000ppm¡Fthe conversion of NO is not changed with [NO]in when [NO]in is lower than 1000ppm . The better space velocity is 15000hr-1 , i.e.,the empty bed residence time is 0.24 second . The reaction on NO conversion would be restrained by higher humidity contenting in inlet gas stream , but the effect of inhibition on NO conversion is not significant . Finally , the kinetics of the oxidation of NO over 8wt.% Cu(NO3)2 / TiO2 was obtained by integral method .It is found that the oxidations of NO can be described by first order reversible reaction and the observed activation energy are 15.8 kcal/mole¡]forward reaction¡^and 25.9 kcal/mole¡]backward reaction¡^, respectively . By comparing the conversion of predicted NO with the experimentals , we can find the suitable operation conditions in application of the kinetic model : the inlet concentration of NO in a range of 300-1000ppm , the empty-bed residence time ranging from 0.12-0.48 second , and the absolute humidity ranging from 4854 to 42475ppm .

The study site, Ta-pon Bay, is located in southwestern Taiwan that has the total volume of 9.92 x 106 m3, surface area of 4.46 x 106 m2, and an average depth of 2.19 m. The Ta-pon Bay is a shallow and semi-enclosed lagoon. The tidal regime at the Ta-pon Bay inlet is mixed, with diurnal dominance. There is noticeable amount of land-derived freshwater inflow in Ta-pon Bay and the mixing between the sea water and freshwater is largely determined by the tide. In order to understand the tidal exchange process between Ta-pon Bay and the coastal sea, the observation focused on the physiographic and hydrographic characteristics of this lagoon. The bathymetry of the study area was also surveyed. From the spatial sediment grain-size distribution pattern, the high energy region is at the inlet and the low energy region is in the interior of the lagoon. Our observation results indicate that freshwater outflow from the Kao-ping River was not transported into Ta-pon Bay. Tides are also the dominant cause for the water level fluctuations in the lagoon. In our winter observation, the local wind effects and atmospheric forcing dominated the subtidal sea surface fluctuations. In summer observation, the subtidal variability was strongly influenced by freshwater inflow. In Ta-pon Bay, the spatial salinity distribution was controlled by the flood and ebb tides, and the spatial temperature distribution was controlled by the different seasons. The tidal prism model can help us understand the tidal exchange between a shallow coastal lagoon and the open sea, and estimate the volume of freshwater inflow, return flow factor, and the turn-over time. Furthermore, we used a one-dimensional model to simulate the hydrodynamics of tidal inlet. The model results show good agreement with observations. We found that the superelevation of the lagoon was 20 cm. This mean sea level difference was caused by freshwater inflow and accumulation of lagoonward tidal transport of water.

Stochastic compartment models are widely used in modeling processes for biological populations. The residence time has been especially useful in describing the system dynamics in the models. The direct calculation of the distribution for the residence time of stochastic multi-compartment models is very complicated even with a relatively simple model and often impossible to calculate directly. This dissertation presents an analytical method to obtain the moment generating function for stochastic multi-compartment models and describe the distribution of the residence times, especially systems with nonexponential lifetime distributions. A common method for obtaining moments of the residence time is using the coefficient matrix, however it has a limitation in obtaining high order moments and moments for combined compartments in a system. In this dissertation, we first derive the bivariate moment generating function of the residence time distribution for stochastic two-compartment models with general lifetimes. It provides any order of moments and also enables us to approximate the density of the residence time using the saddlepoint approximation. The approximation method is applied to various situations including the approximation of the bivariate distribution of residence times in two-compartment models or approximations based on the truncated moment generating function. Special attention is given to the distribution of the residence time for multi-compartment semi-Markov models. The cofactor rule and the analytic approach to the two-compartment model facilitate the derivation of the moment generating function. The properties from the embedded Markov chain are also used to extend the application of the approach. This approach provides a complete specification of the residence time distribution based on the moment generating function and thus provides an easier calculation of high-order moments than the approach using the coefficient matrix. Applications to drug kinetics demonstrate the simplicity and usefulness of this approach.

Growth and development over the past one hundred years has resulted in the construction of causeways and navigational channels in Tampa Bay. Urbanization has lead to bathymetric alterations of the bay, and thus has effectively changed the residual salinity, flow fields, and transport time in Tampa Bay. In this study a numerical ocean model of Tampa Bay was first used to simulate the circulation for 2001-2003 using present day bathymetry. Then, an identical simulation was performed using the bathymetry generated from 1879 depth soundings. The residual (30-day time average) circulation fields and salinity, along with transport times was intercompared for different freshwater inflow conditions to investigate the impacts of these physical alteration. The salinity for the "present" simulation is about 3 psu higher than the "1879" simulation in the areas of upper Middle Tampa Bay, Lower Hillsborough Bay and Old Tampa Bay, a result of a stronger axial pressure gradient associated with the deeper more extensive channels. Velocities are up to 10 cm/s higher in the "present" run than in the "1879" simulation in the areas where water must converge and diverge through the narrow openings of the bridges/causeways. Transport time is short (~10 days) during strong residual circulation, and long (~90 days) during weak residual circulation. Bridges and causeways are associated with longer transport times (~90 days), except in the area North of the Courtney Campbell Causeway. The navigational channel is associated with long transport times during dry periods and short transport time during wet periods.