Concentrated solar power (CSP) has the potential of fulfilling the world’s electricity needs. Parabolic-trough system using synthetic oil as the HTF with operating temperature between 300 and 400o C, is the most matured CSP technology. A thermal storage system is required for the stable and cost effective operation of CSP plants. The current storage technology is the indirect two-tank system which is expensive and has high energy consumption due to the need to prevent the storage material from freezing. Latent heat storage (LHS) systems offer higher storage density translating into smaller storage size and higher performance but suitable phase change materials (PCMs) have low thermal conductivity, thus hindering the realization of their potential. The low thermal conductivity can be solved by heat transfer enhancement in the PCM. There is also lack of suitable commercially-available PCMs to cover the operating temperature range. In this study, a hybrid cascaded storage system (HCSS) consisting of a cascaded finned LHS and a high temperature sensible or concrete tube register (CTR) stages was proposed and analysed via modelling and simulation. Fluent CFD code and the Dymola simulation environment were employed. A validated CFD phase change model was used in determining the heat transfer characteristics during charging and discharging of a finned and unfinned LHS shell-and-tube storage element. The effects of various fin configurations were investigated and heat transfer coefficients that can be used for predicting the performance of the system were obtained. A model of the HCSS was then developed in the Dymola simulation environment. Simulations were conducted considering the required boundary conditions of the system to develop the best design of a system having a capacity of 875 MWhth, equivalent to 6 hours of full load operation of a 50 MWe power plant. The cascaded finned LHS section provided ~46% of the entire HCSS capacity. The HCSS and cascaded finned LHS section have volumetric specific capacities 9.3% and 54% greater than that of the two-tank system, respectively. It has been estimated that the capital cost of the system is ~12% greater than that of the two-tank system. Considering that the passive HCSS has lower operational and maintenance costs it will be more cost effective than the twotank system considering the life cycle of the system. There is no requirement of keeping the storage material above its melting temperature always. The HCSS has also the potential of even lower capital cost at higher capacities (>6 hours of full load operation).

Thermodynamic and thermoeconomic aspects of 12.5 kW residential solar-thermal power generating systems suitable for distributed, decentralized power generation paradigm are presented in this thesis. The design of a meso-scale power system greatly differs from centralized power generation. As a result, this thesis provides guidance in the selection of the power cycle and operating parameters suitable for meso-scale power generation. Development of standard thermodynamic power cycle computer simulations provides means for evaluation of the feasibility of meso-scale solar-thermal power generation. The thermodynamic power cycles considered in this study are the Rankine cycle, the organic Rankine cycle with toluene, R123, and ethylbenzene as working fluids, the Kalina cycle, and the Maloney-Robertson cycle. From a strictly thermodynamic perspective, the cycles are evaluated based on first- and second-law efficiencies. Additionally, the study includes economic feasibility through thermoeconomic characterization that encompasses a meso-scale cost model for solar-thermal power generation systems. Key results from this study indicate that a R123 organic Rankine cycle is the most cost-effective cycle implementation for operating conditions in which the maximum temperature is limited below 240C. For temperatures greater than 240C and less than 375C, the toluene and ethylbenzne organic Rankine cycles outperform the other cycles. The highest first law efficiency of 28% of the Kalina cycle exceeds all other cycles at temperatures between 375C and 500C. However, when considering cycle cost and overall feasibility, including thermodynamic and thermoeconomic performance, the Maloney-Robertson and Kalina cycles have poor performance on a cost-to-efficiency basis.

The heat flux demands for electronics cooling applications are quickly approaching the limits of conventional thermal management systems. To meet the demand of next generation electronics, a means for rejecting high heat fluxes at low temperatures in a compact system is an urgent need. To answer this challenge, in this work a gasketed chevron plate heat exchanger in conjunction with a slurry consisting of highly endothermic solid ammonium carbamate and a heat transfer fluid. A reduced-order 1-dimensional model was developed and used to solve the coupled equations for heat, mass, and momentum transfer. The feasibility of this chosen design for satisfying the heat rejection load of 2kW was also explored in this study. Also, a decomposition reaction using acetic acid and sodium bicarbonate was conducted in a plate heat exchanger (to simulate a configuration similar to the ammonium carbamate reactions). This enabled the experimental validation of the numerical predictions for the momentum transfer correlations used in this study (which in turn, are closely tied to both the heat transfer correlations and chemical kinetics models). These experiments also reveal important parameters of interest that are required for the reactor design. A numerical model was developed in this study and applied for estimating the reactor size required for achieving a power rating of 2 kW. It was found that this goal could be achieved with a plate heat exchanger weighing less than 70 kg (~100 lbs) and occupying a volume of 29 L (which is roughly the size of a typical desktop printer). Investigation of the hydrodynamic phenomena using flow visualization studies showed that the flow patterns were similar to those described in previous studies. This justified the adaptation of empirical correlations involving two-phase multipliers that were developed for air-water two-phase flows. High-speed video confirmed the absence of heterogeneous flow patterns and the prevalence of bubbly flow with bubble sizes typically less than 0.5 mm, which justifies the use of homogenous flow based correlations for vigorous gas-producing reactions inside a plate heat exchanger. Absolute pressure measurements - performed for experimental validation studies - indicate a significant rise in back pressure that are observed to be several times greater than the theoretically estimated values of frictional and gravitational pressure losses. The predictions from the numerical model were found to be consistent with the experimental measurements, with an average absolute error of ~26%

Thesis (M.E. Mechanical Engineering)--University of Waikato, 2007. / Title from PDF cover (viewed May 6, 2008) Includes bibliographical references (p. 102-108)

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008. / Committee Chair: Sheldon Jeter; Committee Member: Sam Shelton; Committee Member: Srinivas Garimella

Thesis (Ph.D. (Physics & Electronics)) - Rhodes University, 2009 / A thesis submitted in partial fulfilment of the requirements for the degree of Master of Science

Thesis (M.S.M.E)--Baylor University, 2009. / Includes bibliographical references (p. 133-134).

L'utilisation de la réfrigération secondaire permet de réduire l'impact environnemental des systèmes frigorifiques grâce à une réduction de l'utilisation de gaz à effet de serre, néanmoins un tel procédé abaisse l'efficacité des systèmes. Afin de rendre ce procédé plus efficace et viable, l'utilisation de fluide à forte densité énergétique ainsi qu'un couplage avec un dispositif de stockage thermique a été envisagé comme réponse à une problématique industrielle de distribution de froid (climatisation, procédés de refroidissement). Un montage expérimental constitué d'une boucle de circulation et d'un réacteur de formation a été utilisé afin d'évaluer les caractéristiques de charge et décharge d'un réseau utilisant des fluides diphasiques. Cette étude a également permis l'élaboration et la validation de modèles prédictifs (réservoir de stockage, échangeur de chaleur, écoulement) de dynamique de stockage et déstockage pour différents matériaux. Ces modèles ont ensuite été appliqués au cas d'un réseau industriel afin d'étudier l'impact du matériau de stockage choisi sur le dimensionnement du système, sur la consommation énergétique mais aussi sur sa viabilité économique. Ainsi, les résultats ont d'abord montré que l'utilisation d'un dispositif améliorait l'efficacité d'un système et que le retour sur investissement dépendait des scénarios de stockage envisagés. Enfin, une forte dépendance sur le choix du matériau a également été soulevée. / The use of secondary refrigeration can reduce cooling system impact on environment by greenhouse gas reduction, nevertheless this kind of technology reduce the system efficiency. The use of high energetic density and thermal energy storage was considered to improve system efficiency and to answer to industrial cooling process issue (air-conditioning, cooling process or temperature preservation). An experimental set-up composed by a stired tank reactor and circulation loop was used in order to evaluate the charging and discharging dynamic of a cooling district using phase change slurry. This experimental study offers the opportunity to elaborate and validate further models (stirred tank reactor, heat exchanger, flow behavior) to predict the charging and discharging behaviors for various storage materials. Then, these models were used in the case of an industrial system to observe the impact of the storage material or system sizing, energy consumption and economic sustainability. Thus, results show that the impact of the storage device on system energy efficiency and the return on investment depends on storage scenarios. Finally the impact of the chosen material on system efficiency was pointed out.

abstract: Phase Change Material (PCM) plays an important role as a thermal energy storage device by utilizing its high storage density and latent heat property. One of the potential applications for PCM is in buildings by incorporating them in the envelope for energy conservation. During the summer season, the benefits are a decrease in overall energy consumption by the air conditioning unit and a time shift in peak load during the day. Experimental work was carried out by Arizona Public Service (APS) in collaboration with Phase Change Energy Solutions (PCES) Inc. with a new class of organic-based PCM. This "BioPCM" has non-flammable properties and can be safely used in buildings. The experimental setup showed maximum energy savings of about 30%, a maximum peak load shift of ~ 60 min, and maximum cost savings of about 30%. Simulation was performed to validate the experimental results. EnergyPlus was chosen as it has the capability to simulate phase change material in the building envelope. The building material properties were chosen from the ASHRAE Handbook - Fundamentals and the HVAC system used was a window-mounted heat pump. The weather file used in the simulation was customized for the year 2008 from the National Renewable Energy Laboratory (NREL) website. All EnergyPlus inputs were ensured to match closely with the experimental parameters. The simulation results yielded comparable trends with the experimental energy consumption values, however time shifts were not observed. Several other parametric studies like varying PCM thermal conductivity, temperature range, location, insulation R-value and combination of different PCMs were analyzed and results are presented. It was found that a PCM with a melting point from 23 to 27 °C led to maximum energy savings and greater peak load time shift duration, and is more suitable than other PCM temperature ranges for light weight building construction in Phoenix. / Dissertation/Thesis / M.S. Mechanical Engineering 2010

O aumento da população e o desenvolvimento da economia criam a necessidade de expansão de mais de quatro mil Megawatts da energia nova por ano no Sistema Interligado Nacional (SIN). O sistema elétrico brasileiro é peculiar, devido a sua grande capacidade, extensão continental e grande dependência na energia renovável hídrica. Outra peculiaridade é a capacidade potencial de inserção de outras formas da energia renováveis “verdes” no sistema. Embora as vantagens ambientais das energias renováveis, elas têm limitações, são variáveis e dependentes das condições climáticas. Para que o setor elétrico brasileiro possa atuar com confiabilidade com mais energia renovável deve haver concomitante mais energia firme de origem térmica disponível. Assim o trabalho analisa, na perspectiva global, o estado da arte e as tendências das fontes de geração elétrica, sob o ponto de vista de disponibilidade, preço e sustentação ambiental. De forma especial, o trabalho analisa as opções de geração térmica no Brasil. Conclui pela necessidade do Brasil priorizar o uso dos recursos disponíveis dentro de suas fronteiras como o carvão mineral para garantir a geração térmica elétrica auto-suficiente. O trabalho demonstra as vantagens sociais e de desenvolvimento de uma indústria do carvão para as regiões produtoras. Aponta também a necessidade de implementação de tecnologias modernas a fim de atender à legislação ambiental, que gradativamente deve aumentar as restrições das emissões poluentes, na medida em que as tecnologias forem desenvolvidas. / The population and economy growth in Brazil generate the necessity of an expansion higher than four thousand Megawatts of new electric energy per year. The Brazilian Electrical System is peculiar because of its continental extension and also its strong dependence in renewable energy (hydro). Another reason for its peculiarity is the potential of inserting other forms of renewable and “green” energy in the system. Although the environmental advantages of the “renewable”, these kinds of energies are variable and dependant of the weather conditions. In order to the electrical system be more reliable, its operation must be combined with a larger addition of thermal energy. Thus this report analyses thermal generation option in Brazil. Looking at the developed countries trends in diversify power generation, the article indicates the advantages and the priority of using, in Brazil, internal resources like coal to guarantee the self-sufficient thermal generation electrical capacity. The dissertation demonstrates the social advantages to develop the coal industry for the producers region, witch are poor areas in Brazil. The proposition points the need of implement modern technologies in order to attend the environmental legislation, which must increase the emissions restrictions as these technologies are developed.