The aim of the thesis, is to find the transient force applied by an individual transient liquid slug on an elbow at the end of a horizontal line due to an impact. The liquid slug is driven by pressurized air in a tank located upstream of the pipeline. The time dependent pressure distribution along the elbow and a vertical extension segment after the elbow was solved, with a 1-D numerical approach along a curved line mesh. For this purpose / firstly, a 3-D axial turbulent velocity profile function was assumed for the slug, with its shape allowed to sway towards the convex side of the elbow along the curved mesh with the aid of a calibration tool. Then, the pressure values were calculated by using 1-D application of Reynolds Equations in cylindrical polar and cartesian coordinates for the elbow and the vertical extension segment, respectively. The transient force acting on the elbow and the following vertical extension segment was found by using these calculated pressure values and applying conservation of momentum principle over the volume elements selected along the elbow and the vertical extension segment. For the analysis of the slug motion from the pressurizer tank to the elbow, a previously written computer code BOZKUS-2 was utilized. Then, the elbow and the vertical extension segment calculations in this study were made with a new code KAYHAN, which is an improved version of BOZKUS-2. The calculated transient force and impact pressures at the elbow were also compared with those from previous studies.

The goal of the work described in this report was the experimental investigation of the mixing of coolant with different quality (temperature, boron concentration) in nuclear reactors on the way from the cold leg through the downcomer and lower plenum to the core inlet in a systematic way. The obtained data were used for the clarification of the mixing mechanisms and form a data basis for the validation of computational fluid dynamics (CFD) codes. For these purposes, experiments on slug mixing have been performed at two test facilities, modelling different reactor types in scale 1:5, the Rossendorf and Vattenfall test facilities. The corresponding accident scenario is the start-up of first main coolant pump (MCP) after formation of a slug of lower borated water during the reflux-condenser mode phase of a small break loss of coolant accident (LOCA). The matrices for the experiments were elaborated on the basis of the key phenomena, being responsible for the coolant mixing during pump start-up. Slug mixing tests have also been performed at the VVER-1000 facility of EDO Gidropress to meet the specifics of this reactor type. The mixing of slugs of water of different quality is also very important for pre-stressed thermal shock (PTS) situations. In emergency core cooling (ECC) situations after a LOCA, cold ECC water is injected into the hot water in the cold leg and downcomer. Due to the large temperature differences, thermal shocks are induced at the reactor pressure vessel (RPV) wall. Temperature distributions near the wall and temperature gradients in time are important to be known for the assessment of thermal stresses. One of the important phenomena in connection with PTS is thermal stratification, a flow condition with a vertical temperature profile in a horizontal pipe. Due to the fluctuating character of the flow, this may cause thermal fatigue in the pipe. Besides of thermal fatigue, a single thermal shock can also be relevant for structural integrity, if it is large enough, especially in the case, that the brittle fracture temperature of the RPV material is reduced due to radiation embrittlement. Therefore, additional to the investigations of slug mixing during re-start of coolant circulation, the mixing of slugs or streams of water with higher density with the ambient fluid in the RPV was investigated. The aim of these investigations was to study the process of turbulent mixing under the influence of buoyancy forces caused by the temperature differences. Heat transfer to the wall and thermal conductivity in the wall material have not been considered. Experiments on density driven mixing were carried out at the Rossendorf and the Fortum PTS facilities.

Grasslands comprise the greatest biome by land area, are sensitive to environmental factors affected by climate change, and can impact future climate change through their ability to store and release greenhouse gasses (GHGs). I performed two studies: 1) evaluated the effects of increased temperature and precipitation on slug herbivory/abundance and pasture forage production; 2) quantified different homeowner lawn system effects on soil-to-atmosphere GHG emissions. Climate change will likely affect pasture forage production, with implications for slug herbivory and abundance. I found little evidence that slugs have or will have significant effects on pasture production or plant community. Warming altered the abundance of slugs and modified seasonal trends, increasing slug abundance in spring/winter and reducing it in late-summer/fall, through both direct effects and changes in plant community and forage quality. Home lawns vary in levels of management, influencing the exchange of GHGs. I quantified the effects of three common home lawn systems of central Kentucky on GHG emissions, but found no significant differences in CO2, N2O, and NH3 fluxes. My research suggests that slug herbivory is not a dominant ecological process in Kentucky pastures and that common home lawn systems have similar soil-to-atmosphere GHG emissions.

Accurate hydraulic conductivity values are necessary for understanding groundwater flow. Methods for estimating hydraulic conductivity show limitations because measured values vary several orders of magnitude in high permeability aquifers. Slug tests, while cost and time efficient, result in values lower than expected. It is proposed that underdamped behavior of water in a well is similar to mass on a damped spring; hence, models constructed to simulate behavior independent of aquifer effects might replicate some tests. The Poiseuille and Darcy-Weisbach models, and extensions of these models considering entry/exit effects, are applied to an aquifer-free laboratory test, and real wells. Aquifer-free laboratory tests are modeled well using both Poiseuille and Darcy-Weisbach models with entry/exit effects. The Poiseuille model for wells does not agree with observed data, possibly because of high Reynolds numbers. The Darcy-Weisbach model does agree with well data significantly better, although the friction factor relies on a single Reynolds number.

The goal of the work described in this report was the experimental investigation of the mixing of coolant with different quality (temperature, boron concentration) in nuclear reactors on the way from the cold leg through the downcomer and lower plenum to the core inlet in a systematic way. The obtained data were used for the clarification of the mixing mechanisms and form a data basis for the validation of computational fluid dynamics (CFD) codes. For these purposes, experiments on slug mixing have been performed at two test facilities, modelling different reactor types in scale 1:5, the Rossendorf and Vattenfall test facilities. The corresponding accident scenario is the start-up of first main coolant pump (MCP) after formation of a slug of lower borated water during the reflux-condenser mode phase of a small break loss of coolant accident (LOCA). The matrices for the experiments were elaborated on the basis of the key phenomena, being responsible for the coolant mixing during pump start-up. Slug mixing tests have also been performed at the VVER-1000 facility of EDO Gidropress to meet the specifics of this reactor type. The mixing of slugs of water of different quality is also very important for pre-stressed thermal shock (PTS) situations. In emergency core cooling (ECC) situations after a LOCA, cold ECC water is injected into the hot water in the cold leg and downcomer. Due to the large temperature differences, thermal shocks are induced at the reactor pressure vessel (RPV) wall. Temperature distributions near the wall and temperature gradients in time are important to be known for the assessment of thermal stresses. One of the important phenomena in connection with PTS is thermal stratification, a flow condition with a vertical temperature profile in a horizontal pipe. Due to the fluctuating character of the flow, this may cause thermal fatigue in the pipe. Besides of thermal fatigue, a single thermal shock can also be relevant for structural integrity, if it is large enough, especially in the case, that the brittle fracture temperature of the RPV material is reduced due to radiation embrittlement. Therefore, additional to the investigations of slug mixing during re-start of coolant circulation, the mixing of slugs or streams of water with higher density with the ambient fluid in the RPV was investigated. The aim of these investigations was to study the process of turbulent mixing under the influence of buoyancy forces caused by the temperature differences. Heat transfer to the wall and thermal conductivity in the wall material have not been considered. Experiments on density driven mixing were carried out at the Rossendorf and the Fortum PTS facilities.

Counter-Current Flow Limitation (CCFL) is of importance for PWR safety analyses in several accident scenarios connected with loss of coolant. Basing on the experiences obtained during a first series of hot leg tests now new experiments on counter-current flow limitation were conducted in the TOPFLOW pressure vessel. The test series comprises air-water tests at 1 and 2 bar as well as steam-water tests at 10, 25 and 50 bar. During the experiments the flow structure was observed along the hot leg model using a high-speed camera and web-cams. In addition pressure was measured at several positions along the horizontal part and the water levels in the reactor-simulator and steam-generator-simulator tanks were determined. This report documents the experimental setup including the description of operational and special measuring techniques, the experimental procedure and the data obtained. From these data flooding curves were obtained basing on the Wallis parameter. The results show a slight shift of the curves in dependency of the pressure. In addition a slight decrease of the slope was found with increasing pressure. Additional investigations concern the effects of hysteresis and the frequencies of liquid slugs. The latter ones show a dependency on pressure and the mass flow rate of the injected water. The data are available for CFD-model development and validation.

Thermally developing, electro-osmotically generated flow has been analyzed for a circular microtube under imposed constant wall temperature (CWT) and constant wall heat flux (CHF) boundary conditions. Established by a voltage potential gradient along the length of the microtube, the hydrodynamics of such a flow dictate either a slug flow velocity profile (under conditions of large tube radius-to-Debye length ratio, a/lambda_d) or a family of electro-osmotic flow (EOF) velocity profiles that depend on a/lambda_d. The imposed voltage gradient results in Joule heating in the fluid with an associated volumetric source of energy. For this scenario coupled with a slug flow velocity profile, the analytical solution for the fluid temperature development has been determined for both thermal boundary conditions. The local Nusselt number for the CHF boundary condition is shown to reduce to the classical slug flow thermal development for imposed constant wall heat flux, and is independent of Joule heating source magnitude. For the CWT boundary condition, a local minimum in the streamwise variation in local Nusselt number for moderate positive dimensionless inlet temperature is predicted. For negative dimensionless inlet temperature, which arises if the fluid entrance temperature is below the tube wall temperature, the fluid is initially heated, then cooled, resulting in a singularity in the local Nusselt number at the axial location of the heating/cooling transition. The thermal development length is considerably larger than for traditional pressure-driven flow heat transfer, and is a function of the magnitudes of Peclet number and dimensionless inlet temperature. For the EOF velocity profile scenario, numerical techniques were used to predict the fluid temperature development for both wall boundary conditions by utilizing a finite control volume approach. In addition to Joule heating as an energy source, viscous dissipation is also considered. The results predict that for decreasing a/lambda_d, the local Nusselt number decreases for all axial positions and the thermal development shortens for both wall boundary conditions. Viscous dissipation has significant effect only at intermediate values of a/lambda_d. Results predict local Nusselt numbers to increase for a CWT boundary condition and to decrease for an imposed constant wall heat flux with increasing viscous dissipation.

[pt] O escoamento trifásico na indústria do petróleo é caracterizado pela presença das fases gás, óleo e água. A presença da terceira fase (água) traz complexidade a esse processo, visto que pode provocar a formação de diversos novos padrões de escoamento, além dos já conhecidos para escoamento bifásico. Adicionalmente, a presença de uma fase líquida dispersa na outra pode formar uma emulsão, alterando significativamente a viscosidade e, assim, influenciando diretamente na perda de carga. O foco do presente trabalho é na previsão do padrão de golfadas com dispersões de água e óleo utilizando um modelo transiente unidimensional de Dois Fluidos. A presença da água é modelada através da solução da equação de conservação de massa para a fase água. Visando prever com precisão a queda de pressão, assim como a distribuição das frações volumétricas de cada fase ao longo do domínio, desenvolveu-se um modelo de fechamento algébrico para avaliar o escorregamento entre as fases líquidas. Com o modelo proposto, os resultados obtidos para a velocidade de escorregamento no escoamento água/óleo foram comparados com dados experimentais e de outros modelos, apresentando um excelente desempenho. O modelo foi então utilizado para analisar o escoamento trifásico no padrão de golfadas. As previsões para a queda de pressão e características das golfadas (comprimento, frequência e velocidade de translação) foram comparadas com dados experimentais da literatura e os resultados são promissores. / [en] The three-phase flow in the oil industry is characterized by the presence of the gas, oil and water phases. The presence of the third phase (water) adds complexity to this process, since it can cause the formation of several new flow patterns in addition to those already known for two-phase flow. Additionally, the presence of a dispersed phase into another can form an emulsion, altering significantly the viscosity and consequently influencing directly the pressure drop. The focus of this job is in the prediction of the slug flow with dispersions of water and oil using a one-dimensional transient Two Fluid model. The presence of water in the flow is modelled with the solution of an equation of conservation of mass. Intending to predict with precision the pressure drop, as the volumetric phase distribution of each phase throw the domain, an algebraic closure model was inserted to assess the slip between the liquid phases. With the proposed model, the results obtained for the slip velocity of the water/oil flow were compared with experimental data and other models, showing excellent performance. The model was then used to analyze the three-phase flow in the slug pattern. The predictions for pressure drop and characteristics of the slugs (length, frequency and translation velocity) have been compared with experimental data from the literature and the results are promising.

The Spanish slug (Arion vulgaris) is a problem both for commercial farmers and home gardeners in Europe, and it can negatively impact biodiversity. To limit its dispersal, it is important to understand the links between habitat use and behaviour. I tested if mowing had an effect on the movement pattern of the Spanish slug in a meadow. My hypothesis was that the slugs should move shorter distances during the day and longer distances at night if the grass was cut short than if the grass was kept high, because high grass may offer protection and food resources. I collected 92 Spanish slugs and tagged them with PIT tags. Sixty-eight slugs survived the tagging, and they were released in a meadow in Sätila, Sweden. The meadow was divided into two equally sized sections and 34 slugs were released in each section. On day one after releasing the slugs, 17 slugs were found alive and within the test area, those were included in the test.  In a first part of the study, I measured the movement of the slugs by a mobile antenna without altering the habitat. Before the second part of the test, I mowed the meadow in one section and kept the other section unaltered. The measurements from the telemetry survey showed that the slugs were moving faster at night than during the day time in both sections (mean ± SE = 25,8 ± 6,4 at night and 5.9 ± 1,7 cm/h during the day). In the second part of the test where the grass in one section had been cut, there was a slight trend that the slugs were moving slower at night in the short grass (25,9 ± 8,8) than in the high grass (48,8 ± 9,4 cm/h), in contrast to my hypothesis. The corresponding daytime values were 26,6 ± 9,0 in the short grass and 13,9 ± 3,4 cm/h in the high grass. My study was carried out under humid weather conditions. If the study was to be repeated in dry conditions, this may result in the slugs being exposed to sunlight during daytime, which would potentially impact their diel behaviour in the two habitats. / Mördarsniglar (Arion vulgaris) är ett problem för både privata och kommersiella odlare och de kan påverka den biologiska mångfalden negativt. Habitatets betydelse för deras beteende är viktigt att förstå för att lära sig mer om hur sniglarna potentiellt kan begränsas. Jag testade om kortklippt gräs påverkar sniglarnas rörelsemönster så att de rör sig mer på natten och kortare sträckor dagtid jämfört med sniglar i högt gräs, där de potentiellt har mer skydd och tillgång till föda. Jag samlade in 92 mördarsniglar och försedde dem med varsin PIT-tag. Sextioåtta sniglar överlevde till testets start och släpptes ut i ett ängsområde i Sätila, Sverige. Området delades upp i två lika stora delar, 34 sniglar placerades i vardera delen. I en första försöksomgång av studien behölls båda delarna oklippta. Inför den andra försöksomgången, klippte jag gräset i den ena delen medan jag lät den andra vara oklippt. Efter utsläppet återfanns 17 sniglar vid liv inom studieområdet och dessa inkluderades i studien. Mätningarna från den första försöksomgången visade att sniglarna rörde sig mer på natten (medelvärde ± SE) 25,8 ± 6,4 än på dagen 5.9 ± 1,7 cm/h i båda delarna. I den andra försöksomgången, fanns en icke-signifikant tendens till att sniglarna rörde sig mindre på natten i delen med klippt gräs (25,9 ± 8,8) än i delen med oklippt gräs (48,8 ± 9,4 cm/h; tvärtemot vad jag hade förväntat mig. Dagtid var medelhastigheten 26,6 ± 9,0 i det kortklippta gräset och 13,9 ± 3,4 cm/h i det oklippta långa gräset. Studien genomfördes i fuktigt väder. Att istället mäta sniglarnas rörelser under torr väderlek skulle potentiellt kunna påverka resultatet eftersom sniglarna då blir mer utsatta dagtid för solinstrålning, framförallt i det korta gräset.

No description available.