Thermal energy storage systems as an integral part of concentrated solar power plants improve the performance of the system by mitigating the mismatch between the energy supply and the energy demand. Using a phase change material (PCM) to store energy increases the energy density, hence, reduces the size and cost of the system. However, the performance is limited by the low thermal conductivity of the PCM, which decreases the heat transfer rate between the heat source and PCM, which therefore prolongs the melting, or solidification process, and results in overheating the interface wall. To address this issue, heat pipes are embedded in the PCM to enhance the heat transfer from the receiver to the PCM, and from the PCM to the heat sink during charging and discharging processes, respectively. In the current study, the thermal-fluid phenomenon inside a heat pipe was investigated. The heat pipe network is specifically configured to be implemented in a thermal energy storage unit for a concentrated solar power system. The configuration allows for simultaneous power generation and energy storage for later use. The network is composed of a main heat pipe and an array of secondary heat pipes. The primary heat pipe has a disk-shaped evaporator and a disk-shaped condenser, which are connected via an adiabatic section. The secondary heat pipes are attached to the condenser of the primary heat pipe and they are surrounded by PCM. The other side of the condenser is connected to a heat engine and serves as its heat acceptor. The applied thermal energy to the disk-shaped evaporator changes the phase of working fluid in the wick structure from liquid to vapor. The vapor pressure drives it through the adiabatic section to the condenser where the vapor condenses and releases its heat to a heat engine. It should be noted that the condensed working fluid is returned to the evaporator by the capillary forces of the wick. The extra heat is then delivered to the phase change material through the secondary heat pipes. During the discharging process, secondary heat pipes serve as evaporators and transfer the stored energy to the heat engine. Due to the different geometry of the heat pipe network, a new numerical procedure was developed. The model is axisymmetric and accounts for the compressible vapor flow in the vapor chamber as well as heat conduction in the wall and wick regions. Because of the large expansion ratio from the adiabatic section to the primary condenser, the vapor flow leaving the adiabatic pipe section of the primary heat pipe to the disk-shaped condenser behaves similarly to a confined jet impingement. Therefore, the condensation is not uniform over the main condenser. The feature that makes the numerical procedure distinguished from other available techniques is its ability to simulate non-uniform condensation of the working fluid in the condenser section. The vapor jet impingement on the condenser surface along with condensation is modeled by attaching a porous layer adjacent to the condenser wall. This porous layer acts as a wall, lets the vapor flow to impinge on it, and spread out radially while it allows mass transfer through it. The heat rejection via the vapor condensation is estimated from the mass flux by energy balance at the vapor-liquid interface. This method of simulating heat pipe is proposed and developed in the current work for the first time. Laboratory cylindrical and complex heat pipes and an experimental test rig were designed and fabricated. The measured data from cylindrical heat pipe were used to evaluate the accuracy of the numerical results. The effects of the operating conditions of the heat pipe, heat input, and portion of heat transferred to the phase change material, main condenser geometry, primary heat pipe adiabatic radius and its location as well as secondary heat pipe configurations have been investigated on heat pipe performance. The results showed that in the case with a tubular adiabatic section in the center, the complex interaction of convective and viscous forces in the main condenser chamber, caused several recirculation zones to form in this region, which made the performance of the heat pipe convoluted. The recirculation zone shapes and locations affected by the geometrical features and the heat input, play an important role in the condenser temperature distributions. The temperature distributions of the primary condenser and secondary heat pipe highly depend on the secondary heat pipe configurations and main condenser spacing, especially for the cases with higher heat inputs and higher percentages of heat transfer to the PCM via secondary heat pipes. It was found that changing the entrance shape of the primary condenser and the secondary heat pipes as well as the location and quantity of the secondary heat pipes does not diminish the recirculation zone effects. It was also concluded that changing the location of the adiabatic section reduces the jetting effect of the vapor flow and curtails the recirculation zones, leading to higher average temperature in the main condenser and secondary heat pipes. The experimental results of the conventional heat pipe are presented, however the data for the heat pipe network is not included in this dissertation. The results obtained from the experimental analyses revealed that for the transient operation, as the heat input to the system increases and the conditions at the condenser remains constant, the heat pipe operating temperature increases until it reaches another steady state condition. In addition, the effects of the working fluid and the inclination angle were studied on the performance of a heat pipe. The results showed that in gravity-assisted orientations, the inclination angle has negligible effect on the performance of the heat pipe. However, for gravity-opposed orientations, as the inclination angle increases, the temperature difference between the evaporator and condensation increases which results in higher thermal resistance. It was also found that if the heat pipe is under-filled with the working fluid, the capillary limit of the heat pipe decreases dramatically. However, overfilling of the heat pipe with working fluid degrades the heat pipe performance due to interfering with the evaporation-condensation mechanism. / Mechanical Engineering

The turbulent flow through a 90o pipe bend is complex with secondary flow that can affect pressure drop and heat/mass transfer. The mean and unsteady flow is studied using refractive index matched two-dimensional two-component (2D2C) Particle Image Velocimetry in a single 90o bend with Rc/D = 1.5 and at Re = 34800. The measurements were performed in a closed loop using a 1-inch diameter test section that was machined out of acrylic. The flow is imaged in the symmetric plane parallel to the axial flow and at different cross sectional planes including 0.25D and 1D upstream, 10o, 20o, 70o, 80o from the bend inlet and 0.25D and 1D downstream of the bend. The axial flow accelerates on the inner wall at the inlet and then moves towards the outer wall at 40o-50o. A shear layer is formed between high velocity fluid near the outer wall and the slower moving fluid at the inner wall side in the second half of the bend. The axial turbulent kinetic energy ((u^2 ) ̅+(v^2 ) ̅) is found to be high in regions corresponding to high velocity gradient regions: (i) at the outer wall near the inlet that extends up to the outlet, (ii) near the inner wall at 40o-50o, and (iii) at the shear layer formed near the inner wall. In the cross sectional planes, two vortices are formed and have a maximum strength at 80o from the bend inlet. The cross sectional turbulent kinetic energy ((v^2 ) ̅+(w^2 ) ̅) is found to be highest on the inner wall at the 80o plane. The snapshot Proper Orthogonal Decomposition (POD) technique is used to study the unsteady flow structures within the flow. There are long and short flow structures in the upstream pipe which can be related to Very Large Scale and Large Scale Motions. The secondary flow at 20o and further downstream cross sectional planes show evidence of unsteadiness as two vortices oscillate about the symmetry axis with low frequencies of St ~ 0.07, 0.13 and higher frequency at St ~ 0.3-0.6. The low frequency oscillations can be related to Very Large Scale Motions while high frequency oscillations are related to separation of the flow on the inner wall side. Evidence of swirl switching in the high frequency range (St ~ 0.3-0.5) is found at cross sectional plane 1D downstream. / Thesis / Master of Applied Science (MASc)

This thesis contains the details of an experimental study on the local void fraction measurements in large-diameter vertical pipes using optical fiber probes. The experiments were conducted in vertical transparent acrylic pipe of a 20-cm diameter. An experimental test facility used for performing of experiments, was designed as a low-pressure air-water loop, which can operate in either a natural circulation mode or a forced circulation mode. Radial void fraction profiles were measured using an optical fiber probe. An average cross-sectional void fraction was calculated by integration of the data obtained by the optical fiber probe. The average void fraction was also calculated using two-phase pressure-drop measurements . The results were compared and the resulting good accuracy of the optical fiber probe was determined. The flow regime results were plotted in terms of superficial gas and liquid velocities using flow regime maps of several researchers. Absence of the slug flow regime in large-diameter pipes was observed during the experiments. The data were correlated using the drift-flux model. A near unity distribution parameter showed that nearly uniform radial distribution of the void fraction dominates in two-phase flow through large-diameter vertical pipes. / Thesis / Master of Engineering (ME)

Non-uniform corrosion of copper and brass in potable water systems poses both economic and environmental problems associated with premature plumbing failures and release of metals. With respect to copper pitting corrosion, it was found that forensic testing (i.e., in pipe-loops) is the only investigative technique that can closely mimic conditions found in real water systems and produce unambiguous results; and, if used in combination with electrochemical techniques, it may also provide some mechanistic insights into the pitting process. Using pipe-loops, it was demonstrated that copper pitting in aggressive water qualities (i.e., chlorinated, high pH and low alkalinity) is deterministic and reproducible. Additionally, the effects of various chemical and physical factors on pitting were investigated. Overall, increased flow velocity and frequency, increased chlorine residual and decreased hardness were found to accelerate pitting; whereas increased phosphate and silica were found to decelerate pitting. Several mitigation strategies for copper pitting in aggressive water were further investigated, and experimental data were interpreted utilizing electrochemical theory to evaluate specific effects on the initiation and propagation phases of pitting. Surprisingly, it was found that decreased chlorine may delay pit initiation, however, even relatively low levels of chlorine may eventually initiate and propagate pits. Increased alkalinity appears to decelerate pit growth, but does not prevent pit initiation. NOM can delay pit initiation and propagation, although the potential for DBP formation in chlorinated waters makes inhibition by NOM an unfavorable alternative. At sufficient dosages, phosphate and silica corrosion inhibitors may completely stop pitting, consistent with the success of several field trials. At very low dosages, phosphate and silica may actually accelerate pinhole failures, so these inhibitors should not be under-dosed. While brass alloys exist that can limit dezincification problems, they are not always utilized in potable water applications due to high costs, and so dezincification is a re-emerging issue in some countries, including the US. Little research has been conducted in the past several decades regarding the effects of water chemistry, and almost no work has addressed the roles of physical factors associated with real plumbing systems. Thus, a comprehensive review of these topics was conducted. To better understand the effects of some factors associated with specific plumbing installations on dezincification and other brass corrosion types, a series of pipe-loop studies was carried out. It was confirmed that increased oxidant delivery rates to cathodic surfaces, either via increased oxidant concentration or increased flow velocity, can increase corrosion rates. Several key differences were observed with respect to corrosion of brass located in copper plumbing tube systems as opposed to plastic. When copper tubes contribute copper ions to water, brass corrosion becomes more selective for zinc; but if galvanic connections are made between the copper tubes and brass, selectivity for zinc is reduced while overall corrosion rates are accelerated. As opposed to copper tubing, plastic maintains oxidant (e.g., free chlorine) levels, and may thereby increase brass corrosion and build-up of corrosion by-products. Finally, it was found that increased temperature can significantly increase lead leaching from brass. Following recent outbreaks of brass dezincification failures, NSF/ANSI Standard 14 has been revised to require that all NSF 14-listed brass is dezincification resistant, as certified by satisfactory results from an accelerated test method (ISO 6509). Various brasses were tested using this method as well as a longer-term jar method utilizing real potable water. Results of the two tests were in good agreement with respect to dezincification, specifically; but some inconsistencies were observed with respect to uniform corrosion and lead leaching. / Ph. D.

Properties of both chemical contaminants and polymers can impact contaminant diffusivity and solubility in new and aged polyethylene materials for pipes and geomembranes. Diffusivity, solubility, polymer and chemical properties were measured for thirteen contaminants and six polyethylene materials that were new and/or aged in chlorinated water. Tree regression was used to select variables, and linear regression was used to develop predictive equations for contaminant diffusivity and solubility in polyethylene. Organic contaminant properties had greater predictive capability than polyethylene properties. Model coefficients significantly changed between new materials to chlorine-aged materials, indicating changes of polyethylene properties impact the interaction between contaminants and polymers. The metallic flavor of copper in drinking water influences the taste of water and can cause the taste problems for water utilities. The mechanism of metallic flavor caused by these metals is related to free or soluble ions. Free copper concentrations were measured at different pH in diluted artificial saliva using a cupric ion selective electrode. Three major proteins in human saliva: α-amylase, mucin and lactoferrin, were added in the artificial saliva and the impacts on the chemical speciation of copper were analyzed. Inorganic saliva components, typically phosphate, carbonate and hydroxide combined with copper and greatly influenced the levels of free copper in the oral cavity. Proteins such as α-amylase, mucin and lactoferrin also impacted the chemical speciation of copper, with different affinity to copper. Mucin had the greatest affinity with copper than α-amylase. / Master of Science

Composite materials are under consideration for the replacement of steel helical tendons in unbonded flexible pipes utilized by the offshore oil industry. Higher strength to weight ratios and increased corrosion resistance are the primary advantages of a composite material for this application. The current study focuses on the life prediction of a PPS/AS-4 carbon fiber composite proposed for the above employment. In order to accomplish this task, the properties of the material were experimentally characterized at varying temperatures, aging times and loadings. An analytic technique was developed to predict tensile rupture behavior from bend-compression rupture data. In comparison to tensile rupture tests, bend-compression rupture data collection are uncomplicated and efficient; thus, this technique effectively simplifies and accelerates the material characterization process. The service life model for the flexible pipe composite armor was constructed with MRLife, a well established performance simulation code for material systems developed by the Materials Response Group at Virginia Tech. In order to validate MRLife for the current material, experimental data are compared to life prediction results produced by the code. MRLife was then applied to predict the life of the flexible pipe composite armor in an ocean environment. This analysis takes into account the flexible pipe structure and the environmental and mechanical loading history of an ocean service location. Several parameter studies of a flexible pipe in a hypothetical environment were conducted. These analyses highlight certain loadings and conditions which are particularly detrimental to the life of the material. / Master of Science

Prestressed Concrete Cylinder Pipe (PCCP) is a large-diameter and high-pressure conduit for drinking water and wastewater transmission. Due to its large diameter, high pressure, and mode of breakdown, PCCP failures usually have catastrophic consequences. To mitigate failures, it is very important to assess the condition of the pipe and take proactive measures, such as repair, rehabilitation, or replacement. There are many challenges in assessing the condition of PCCP. PCCP has a complex structure with several layers of materials (e.g. mortar coating, prestressing wire, steel cylinder, and concrete core) working together under loading. This means that there are many factors that can cause pipe failure, and that failure mechanisms are complicated. Data collection could be difficult, and existing data are often unavailable or unreliable. Considerable research has been conducted by scholars and engineers in developing models to evaluate the condition of PCCP. There are mainly two types of models: statistical models, and numerical models using finite element method. Statistical models consider only a few factors, such as pipe age and failure rate, to predict the failure of PCCP. However, the failure of PCCP can be caused by many other factors including pipe material, and loading conditions. Models only considering a few factors are not robust enough for reliable results. The current numerical models assume that all broken wires are centrally distributed in the same location and broken wires have no prestress, thus all broken wires are completely removed from the model. These assumptions could be overly conservative when actual broken wires are distributed in different locations along the pipeline and broken wires have remaining prestress due to the bond between the wire and mortar coating. Therefore, a more comprehensive numerical model is needed to have a better understanding of the condition of PCCP. In this research, an extensive literature and practice review was conducted on PCCP failures to understand the critical factors that affect pipe condition. The available technologies commonly used to detect pipe defects were reviewed in order to better understand the accuracy and uncertainties of the collected data. Existing models were reviewed to better understand their limitations and to advance the research on condition analysis of PCCP using numerical models. Based on these comprehensive reviews, this dissertation proposed a numerical model to analyze the condition of PCCP for its long-term performance management. Detailed structural components such as concrete cores, prestressing wires, steel cylinder, and mortar coating were modelled. The interactions between different layers of pipe components were considered. An algorithm was proposed to account for the bond between the prestressing wire and mortar coating, which is a critical factor for the condition of PCCP with broken wires. A FORTRAN program was developed to assign linear stress distribution between the broken point and the full-prestress resuming point. The proposed numerical model was verified utilizing data from lab tests and forensic study. Lab test data helped to understand the functionality of the model and to verify the model parameters used in analyzing pipe components and the simulation of interactions between different layers. The forensic data helped to verify the model under actual field working conditions of the pipe. Validation of the proposed numerical model was conducted using a 66-inch Embedded Cylinder Pipe and two Lined Cylinder Pipes (42-inch and 48-inch, respectively) from a water utility. In the validation, field data were collected for model development. The simulation results were consistent with the field observation, which proved the validity and applicability of the proposed numerical model in practice. A series of sensitivity studies were conducted to investigate the impact of longitudinal and circumferential location on the structural integrity of the pipe. These investigations showed that considering the actual longitudinal and circumferential location of broken wires is very important to get accurate analysis of pipe condition, while assuming that all broken wires fail in one longitudinal location (assumptions by current numerical models for PCCP) will overestimate the actual damage to the pipe caused by broken wires. To consider the bedding condition, a critical factor for PCCP, the four most common bedding types found in practice were analyzed. Results show that poor bedding could lead to cracks in PCCP, which could cause corrosion in prestressing wires. Therefore, it is very important to account for bedding conditions in the PCCP analysis. The model presented in this dissertation is more comprehensive and robust compared with existing numerical models, and could provide a better understanding of the condition of PCCP. This is because the proposed model considers the contribution of remaining prestress in broken wires due to the bond between the wire and mortar coating. This model can consider the actual longitudinal and circumferential location of broken wires rather than centrally distribute them, and it can consider the actual bedding locations, and the interaction between different layers of materials. This model was calibrated using lab test data and forensic data, and was further validated using field data which showed consistence between simulation results and field observations. The proposed model does have limitations due to limited availability of data and assumptions. Material tests were not conducted to verify the material properties used in the model, which could cause accuracy issues in the results. A full-scale simulation of the interaction between prestressing wire and mortar coating was not considered because it could significantly increase the computation time. Lab tests were not conducted to verify the parameters used for the simulation of interaction between concrete core and steel cylinder which could lead to accuracy problems. Finally, it is acknowledged that the model was only validated in one water utility and validations in more geographically distributed utilities might further test the model's validity and robustness. Nonetheless, the comprehensiveness and robustness of this proposed model improved the analysis of the condition of PCCP. The findings and results of this research will provide guidance for better management of PCCP pipelines for water utilities, and provide reference for future research on numerical modeling of PCCP as well. / Ph. D.

Buried culvert has its contribution in improving the convenience and quality of human life. The research of buried culvert in the past decades makes it to serve people more widely and efficiently. The research project of Cross Canyon culvert is one of them. A computer program was used in this study. The overburden-dependent soil model was chosen to represent the stress states of the soil in the backfill. The triaxial shear test data were converted into an overburden-dependent soil model and then this converted soil model was modified. The modified soil model was obtained when the difference of the measured and computed crown vertical displacement was minimized. The parametric studies were done after the modified soil model was obtained. In this research, the parametric studies were (1) Effects of different inclusion material on the culvert, (2) Effects of polystyrene plank wrapped around the culvert, (3) Effects of concrete bedding, (4) Effects of compaction. It was found that the material of inclusion had great influence on the moments of the culvert between the position of crown and 45 degrees. The concrete bedding was not a good practice because the moments were increased largely compared with those moments without concrete bedding. Finally, the compaction did not have much effects on the behavior of the culvert. / Master of Science

M.S.

Abstract [en]Customization and product development are crucial for competitiveness, and modular product architectures enable adaptation and improvement without extensive changes. Originally introduced by Starr in 1965, modular solutions aim to minimize costs through maximum part combination. In sanitation engineering, where water and sewage systems are critical, high-quality, and customized solutions are required. Uponor, a leading player in the field, offers prefabricated water cabinet units to distribute water to various devices. Based on this, a question has been formulated for the study to address: How can a modular product architecture be applied to water cabinets in plumbing and HVAC systems to reduce component costs and production time? The study introduces fundamental concepts in product architecture and modularity, detailing how products can be divided into modules and designed to function independently yet collaboratively. Modularity enables increased flexibility, lower costs, and simpler product development, while component standardization streamlines manufacturing and facilitates adaptation to customer requirements. Additionally, pipe flow and its impact on water distribution systems are discussed, focusing on pressure drops and legionella risks. The study resulted in two new components contributing to cost reduction within the product family, thanks to the modular product architecture. The components enable the company to reduce costs by 38 - 46 SEK per cabinet. This is a cost reduction of 7.5% to 9% for the specific subsystem. Abstract [sv]Kundanpassning och produktutveckling är avgörande för konkurrenskraft, och modulära produktarkitekturer möjliggör anpassning och förbättring utan omfattande ändringar (Modrak & Soltysova, 2018 ,Bouchard, et al, 2023). Ursprungligen introducerades modulära lösningar av Starr ((1965, refererad i Amend, et al, 2022).) för att minimera kostnader genom maximal kombination av delar. Inom sanitetsteknik, där vatten- och avloppssystem är avgörande, krävs högkvalitativa och kundanpassade lösningar. Uponor, en ledande aktör inom området, erbjuder prefabricerade tappvattenskåp för att distribuera vatten i olika enheter. Baserat på det här har en fråga formulerats som studien syftar till att besvara: Hur kan en modulär produktarkitektur för tappvattenskåp inom VVS tillämpas för att minska komponentkostnader och produktionstiden? Den teoretiska referensramen presenterar grundläggande begrepp inom produktarkitektur och modularitet, samt hur produkter kan delas upp i moduler och designas för att fungera oberoende men samverka. Modularitet möjliggör ökad flexibilitet, lägre kostnader och enklare produktutveckling, medan standardisering av komponenter effektiviserar tillverkning och möjliggör anpassning till kundkrav. Dessutom diskuteras rörströmning och dess påverkan på vattenledningssystem, med fokus på tryckfall och risker för legionella bakterier. Studien resulterade i två nya komponenter som bidrar till sänkta kostnader inom produktfamiljen, tack vare den modulära produktarkitekturen. Komponenterna möjliggör för företaget att reducera kostnaderna med 38 - 46 kronor per skåp.