Spelling suggestions: "subject:"athermal energy"" "subject:"ephermal energy""
71 |
PERFORMANCE ANALYSIS FOR A RESIDENTIAL-SCALE ICE THERMAL ENERGY STORAGE SYSTEMAndrew David Groleau (17499033) 30 November 2023 (has links)
<p dir="ltr">Ice thermal energy storage (ITES) systems have long been an economic way to slash cooling costs in the commercial sector since the 1980s. An ITES system generates cooling in the formation of ice within a storage tank. This occurs during periods of the day when the cost of electricity is low, normally at night. This ice is then melted to absorb the energy within the conditioned space. While ITES systems have been prosperous in the commercial sector, they have yet to take root in the residential sector.</p><p dir="ltr">The U.S. Department of Energy (DoE) has published guidelines for TES. The DoE guidelines include providing a minimum of four hours of cooling, shifting 30-50% of a space’s cooling load to non-peak hours, minimizing the weight, volume, complexity, and cost of the system, creating a system than operates for over 10,000 cycles, enacting predictive control measures, and being modular to increase scale for larger single-family and multi-family homes [1]. The purpose of this research is to develop a model that meets these guidelines.</p><p dir="ltr">After extensive research in both experimental data, technical specifications, existing models, and best practices taken from the works of others a MATLAB model was generated. The modeled ITES system is comprised of a 1m diameter tank by 1m tall. Ice was selected as the PCM. A baseline model was constructed with parameters deemed to be ideal. This model generated an ITES system that can be charged in under four hours and is capable of providing a total of 22.18 kWh of cooling for a single-family home over a four-hour time period. This model was then validated with experimental data and found to have a root mean squared error of 0.0959 for the system state of charge. During the validation both the experimental and model estimation for the water/ice within the tank converged at the HTF supply temperature of -5.2°C.</p><p dir="ltr">With the model established, a parametric analysis was conducted to learn how adjusting a few of the system parameters impact it. The first parameter, reducing the pipe radius, has the potential to lead to a 152.6-minute reduction in charge time. The second parameter, varying the heat transfer fluid (HTF) within the prescribed zone of 0.7 kg/s to 1.2 kg/s, experienced a 4.8-minute increase in charge time for the former and a decrease in charge time by 5.4 minutes for the latter. The third parameter, increasing the pipe spacing and consequently increasing the ratio of mass of water to mass of HTF, yielded a negative impact. A 7.1mm increase in pipe spacing produced a 16.6-minute increase in charge time. Meanwhile, a 14.2mm increase in pipe spacing created a 93.3-minute increase in charge time and exceeded the charging time limit of five hours.</p><p dir="ltr">This functioning model establishes the foundation of creating a residential-scale ITES system. The adjustability and scalability of the code enable it to be modified to user specifications. Thus, allowing for various prototypes to be generated based on it. The model also lays the groundwork to synthesize a code containing an ITES system and a heat pump operating as one. This will aid in the understanding of residential-scale ITES systems and their energy effects.</p>
|
72 |
Thermal energy storage design for emergency coolingBasgall, Lance Edgar January 1900 (has links)
Master of Science / Department of Mechanical and Nuclear Engineering / Donald L. Fenton / Emergency cooling systems are applied to any application where the loss of cooling results in damage to the product, loss of data, or equipment failure. Facilities using chilled water for cooling that experience an electrical power outage, even a small one, would cause the chiller to shut down for 20 minutes or more. If emergency cooling is not available, temperatures would continue to increase to dangerous levels, potentially damaging the facility. Examples of facilities that could be protected by having emergency cooling systems are data centers, hospitals, banks, control rooms, laboratories, clean rooms, and emergency shelters among others.
This project addresses the current lack of information and methods needed to correctly design emergency cooling systems. Three application uses were investigated for the possible benefits of having emergency cooling systems. The software TRNSYS was used to simulate five typical emergency cooling systems for each of the three applications. The characteristics and differences of the systems developed from the simulations were then analyzed and documented.
The five systems simulated include a pressurized chilled water tank (parallel), atmospheric chilled water tank (parallel and series), low temperature chilled water tank (parallel), and ice storage tank (series). Simulations showed that low temperature chilled water tanks were less stratified than regular chilled water tanks by approximately 10%. Simulations also showed that the differences between atmospheric and pressurized tanks were negligible. Each tank discharged energy in the same manner and managed to replenish itself in the same amount of time. Examination of the different system configurations showed that tanks in series with the thermal load have issues with recharging due to its inability to isolate itself from the thermal load. It was also observed that while low temperature chilled water and ice storage tanks had the potential of reducing the storage tank volume, the amount of time ragged cooling will last is decreased by at least a factor of two.
The examination of the five systems produced the desired design methodologies needed to address the lack of information on emergency cooling systems. With the reported information designers can effectively engineer systems to meet their needs.
|
73 |
The Application of Microencapsulated Biobased Phase Change Material on TextileHagman, Susanna January 2016 (has links)
The increasing demand for energy in combination with a greater awareness for our environmental impact have encouraged the development of sustainable energy sources, including materials for energy storage. Latent heat thermal energy storage by the use of phase change material (PCM) have become an area of great interest. It is a reliable and efficient way to reduce energy consumption. PCMs store and release latent heat, which means that the material can absorb the excess of heat energy, save it and release it when needed. By introducing soy wax as a biobased PCM and apply it on textile, one can achieve a thermoregulation material to be used in buildings and smart textiles. By replacing the present most used PCM, paraffin, with soy wax one cannot only decrease the use of fossil fuel, but also achieve a less flammable material. The performance of soy wax PCM applied on a textile fabric have not yet been investigated but can be a step towards a more sustainable energy consumption. The soy wax may also broaden the application for PCM due to its low flammability. The aim is to develop an environmental friendly latent heat thermal energy storage material to be used within numerous application fields.
|
74 |
Discrete and porous computational fluid dynamics modelling of an air-rock bed thermal energy storage systemLouw, Andre Du Randt 04 1900 (has links)
Thesis (MScEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Concentrating solar power promises to be a potential solution for meeting the
worlds energy needs in the future. One of the key features of this type of renewable
energy technology is its ability to store energy effectively and relatively
cheaply. An air-rock bed thermal energy storage system promises to be an effective
and reasonably inexpensive storage system for concentrating solar power
plants. Currently there is no such storage system commercially in operation
in any concentrating solar power plant, and further research is required before
such a system can be implemented. The main research areas to address are
the thermal-mechanical behaviour of rocks, rock bed pressure drop correlations
and effective and practical system designs. Recent studies have shown that the
pressure drop over a packed bed of rocks is dependant on various aspects such
as particle orientation relative to the flow direction, particle shape and surface
roughness. The irregularity and unpredictability of the particle shapes make it
difficult to formulate a general pressure drop correlation. Typical air-rock bed
thermal design concepts consist of a large vertical square or cylindrical vessel in
which the bed is contained. Such system designs are simple but susceptible to
the ratcheting effect and large pressure drops. Several authors have proposed
concepts to over-come these issues, but there remains a need for tools to prove
the feasibility of the designs.
The purpose of this paper is to investigate aDEM-CFD coupled approach that
can aid the development of an air-rock bed thermal energy storage system. This
study specifically focuses on the use of CFD. A complementary study focusses
on DEM. The two areas of focus in this study are the pressure drop and system
design. A discrete CFD simulation model is used to predict pressure drop over packed beds containing spherical and irregular particles. DEM is used to create
randomly packed beds containing either spherical or irregularly shaped particles.
This model is also used to determine the heat transfer between the fluid
and particle surface. A porous CFD model is used to model system design concepts.
Pressure drop and heat transfer data predicted by the discrete model, is
used in the porous model to describe the pressure drop and thermal behaviour
of a TES system.
Results from the discrete CFD model shows that it can accurately predict the
pressure drop over a packed bed of spheres with an average deviation of roughly
10%fromresults found in literature. The heat transfer between the fluid and particle
surface also is accurately predicted, with an average deviation of between
13.36 % and 21.83 % from results found in literature. The discrete CFD model for
packed beds containing irregular particles presented problems when generating
a mesh for the CFD computational domain. The clump logic method was used
to represent rock particles in this study. This method was proven by other studies
to accurately model the rock particle and the rock packed bed structure using
DEM. However, this technique presented problems when generating the surface
mesh. As a result a simplified clump model was used to represent the rock particles.
This simplified clump model showed characteristics of a packed bed of
rocks in terms of pressure drop and heat transfer. However, the results suggest
that the particles failed to represent formdrag. This was attributed to absence of
blunt surfaces and sharp edges of the simplified clumpmodel normally found on
rock particles. The irregular particles presented in this study proved to be inadequate
for modelling universal characteristics of a packed bed of rocks in terms of
pressure drop. The porous CFD model was validated against experimental measurement
to predict the thermal behaviour of rock beds. The application of the
porous model demonstrated that it is a useful design tool for system design concepts. / AFRIKAANSE OPSOMMING: Gekonsentreerde sonkrag beloof om ’n potensiële toekomstige oplossing te
wees vir die wêreld se groeiende energie behoeftes. Een van die belangrikste eienskappe
van hierdie tipe hernubare energie tegnologie is die vermoë om energie
doeltreffend en relatief goedkoop te stoor. ’n Lug-klipbed termiese energie
stoorstelsel beloof om ’n doeltreffende en redelik goedkoop stoorstelsel vir gekonsentreerde
sonkragstasies te wees . Tans is daar geen sodanige stoorstelsel
kommersieël in werking in enige gekonsentreerde sonkragstasie nie. Verdere navorsing
is nodig voordat so ’n stelsel in werking gestel kan word. Die belangrikste
navorsingsgebiede om aan te spreek is die termies-meganiese gedrag van klippe,
klipbed drukverlies korrelasies en effektiewe en praktiese stelsel ontwerpe. Onlangse
studies het getoon dat die drukverlies oor ’n gepakte bed van klippe afhanklik
is van verskeie aspekte soos partikel oriëntasie tot die vloeirigting, partikel
vormen oppervlak grofheid. Die onreëlmatigheid en onvoorspelbaarheid van
die klip vorms maak dit moeilik om ’n algemene drukverlies korrelasie te formuleer.
Tipiese lug-klipbed termiese ontwerp konsepte bestaan uit ’n groot vertikale
vierkantige of silindriese houer waarin die gepakte bed is. Sodanige sisteem
ontwerpe is eenvoudig, maar vatbaar vir die palrat effek en groot drukverliese.
Verskeie studies het voorgestelde konsepte om hierdie kwessies te oorkom, maar
daar is steeds ’n behoefte aanmetodes om die haalbaarheid van die ontwerpe te
bewys.
Die doel van hierdie studie is om ’n Diskreet Element Modelle (DEM) en numeriese
vloeidinamika gekoppelde benadering te ontwikkel wat ’n lug-klipbed termiese energie stoorstelsel kan ondersoek. Hierdie studie fokus spesifiek op
die gebruik van numeriese vloeidinamika. ’n Aanvullende studie fokus op DEM.
Die twee areas van fokus in hierdie studie is die drukverlies en stelsel ontwerp.
’n Diskrete numeriese vloeidinamika simulasie model word gebruik om drukverlies
te voorspel oor gepakte beddens met sferiese en onreëlmatige partikels.
DEM word gebruik om lukraak gepakte beddens van óf sferiese óf onreëlmatige
partikels te skep. Hierdie model is ook gebruik om die hitte-oordrag tussen die
vloeistof en partikel oppervlak te bepaal. ’n Poreuse numeriese vloeidinamika
model word gebruik omdie stelsel ontwerp konsepte voor te stel. Drukverlies en
hitte-oordrag data, voorspel deur die diskrete model, word gebruik in die poreuse
model om die drukverlies- en hittegedrag van ’n TES-stelsel te beskryf. Resultate van die diskrete numeriese vloeidinamikamodel toon dat dit akkuraat
die drukverlies oor ’n gepakte bed van sfere kan voorspel met ’n gemiddelde
afwyking van ongeveer 10%van die resultatewat in die literatuur aangetref word.
Die hitte-oordrag tussen die vloeistof en partikel oppervlak is ook akkuraat voorspel,
met ’n gemiddelde afwyking van tussen 13.36%en 21.83%van die resultate
wat in die literatuur aangetref word. Die diskrete numeriese vloeidinamika model
vir gepakte beddens met onreëlmatige partikels bied probleme wanneer ’n
maas vir die numeriese vloeidinamika, numeriese domein gegenereer word. Die
"clump"logika metode is gebruik om klip partikels te verteenwoordig in hierdie
studie. Hierdiemetode is deur ander studies bewys om akkuraat die klip partikel
en die klip gepakte bed-struktuur te modelleer deur die gebruik van DEM. Hierdie
tegniek het egter probleme gebied toe die oppervlak maas gegenereer is. As
gevolg hiervan is ’n vereenvoudigde "clump"model gebruik om die klip partikels
te verteenwoordig. Die vereenvoudigde "clump"model vertoon karakteristieke
eienskappe van ’n gepakte bed van klippe in terme van drukverlies en hitte oordrag.
Die resultate het egter getoon dat die partikels nie vorm weerstand verteenwoordig
nie. Hierdie resultate kan toegeskryf word aan die afwesigheid van
gladde oppervlaktes en skerp kante, wat normaalweg op klip partikels gevind
word, in die vereenvoudigde "clump"model. Die oneweredige partikels wat in
hierdie studie voorgestel word, blykomnie geskik tewees vir die modellering van
die universele karakteristieke eienskappe van ’n gepakte bed van klippe in terme
van drukverlies nie. Die poreuse numeriese vloeidinamika model is met eksperimentele
metings bevestig omdie termiese gedrag van klipbeddens te voorspel.
Die toepassing van die poreuse model demonstreer dat dit ’n nuttige ontwerp
metode is vir stelsel ontwerp konsepte.
|
75 |
Automatic positioner and control system for a motorized parabolic solar reflectorPrinsloo, Gerhardus Johannes 12 1900 (has links)
Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Most rural African villages enjoy high levels of sunlight, but rolling out solar
power generation technology to tap into this renewable energy resource at remote
rural sites in Africa pose a number of design challenges. To meet these
challenges, a project has been initiated to design, build and test/evaluate a
knock down 3 kW peak electrical stand-alone self-tracking dual-axis concentrating
solar power system.
This study focusses on the mechatronic engineering aspects in the design
and development of a dynamic mechatronic platform and digital electronic
control system for the stand-alone concentrating solar power system. Design
specifications require an accurate automatic positioner and control system for
a motorized parabolic solar reflector with an optical solar harnessing capacity
of 12 kWt at solar noon. It must be suitable for stand-alone rural power generation.
This study presents a conceptual design and engineering prototype
of a balanced cantilever tilt-and-swing dual-axis slew drive actuation means
as mechatronic solar tracking mobility platform for a ∼12 m2 lightweight
parabolic solar concentrator. Digital automation of the concentrated solar
platform is implemented using an industrial Siemens S7-1200 programmable
logic controller (PLC) with digital remote control interfacing, pulse width modulated
direct current driving, and electronic open loop/closed loop solar tracking
control. The design and prototype incorporates off-the-shelf components
to support local manufacturing at reduced cost and generally meets the goal
of delivering a dynamic mechatronic platform for a concentrating solar power
system that is easy to transport, assemble and install at remote rural sites
in Africa. Real-time experiments, conducted in the summer of South Africa,
validated and established the accuracy of the engineering prototype positioning
system. It shows that the as-designed and -built continuous solar tracking
performs to an optical accuracy of better than 1.0◦ on both the azimuth and
elevation tracking axes; and which is also in compliance with the pre-defined
design specifications.
Structural aspects of the prototype parabolic dish are evaluated and optimized
by other researchers while the Stirling and power handling units are under
development in parallel projects. Ultimately, these joint research projects
aim to produce a locally manufactured knock down do-it-yourself concentrated
solar power generation kit, suitable for deployment into Africa. / AFRIKAANSE OPSOMMING: Landelike gebiede in Afrika geniet hoë vlakke van sonskyn, maar die ontwerp
van betroubare sonkrag tegnologie vir die benutting van hierdie hernubare
energie hulpbron by afgeleë gebiede in Afrika bied verskeie uitdagings. Om
hierdie uitdagings te oorkom, is ’n projek van stapel gestuur om ’n afbreekbare
3 kW piek elektriese alleenstaande selfaangedrewe dubbel-as son-konsentreeder
te ontwerp, bou en te toets.
Hierdie studies fokus op die megatroniese ingenieurs-aspekte in die ontwerp
en ontwikkeling van ’n dinamiese megatroniese platform en ’n digitale
elektroniese beheerstelsel vir die alleenstaande gekonsentreerde sonkrag stelsel.
Ontwerp spesifikasies vereis ’n akkurate outomatiese posisionering en beheer
stelsel vir ’n motor aangedrewe paraboliese son reflekteerder met ’n optiesekollekteer-
kapasiteit van 12 kWt by maksimum sonhoogte, en veral geskik wees
vir afgeleë sonkrag opwekking. Hierdie studie lewer ’n konsepsuele ontwerp en
ingenieurs-prototipe van ’n gebalanseerde dubbelas swaai-en-kantel swenkrat
aandrywingsmeganisme as megatroniese sonvolg platform vir ’n ∼12 m2 liggewig
paraboliese son konsentreerder. Digitale outomatisering van die son konsentreerder
platform is geimplementeer op ’n industriële Siemens S7-1200 programmeerbare
logiese beheerder (PLB) met ’n digitale afstandbeheer koppelvlak,
puls-wydte-gemoduleerde gelykstroom aandrywing en elektroniese ooplus
en geslote-lus sonvolg beheer. Die ontwerp en prototipe maak gebruik van
beskikbare komponente om lae-koste plaaslike vervaardiging te ondersteun en
slaag in die algemeen in die doel om ’n dinamiese megatroniese platform vir ’n
gekonsentreerde sonkrag stelsel te lewer wat maklik vervoer, gebou en opgerig
kan word op afgeleë persele in Afrika. Intydse eksperimente is gedurende die
somer uitgevoer om die akkuraatheid van die prototipe posisionering sisteem
te evalueer. Dit toon dat die sisteem die son deurlopend volg met ’n akkuraatheid
beter as 1.0◦ op beide die azimut en elevasie sonvolg asse, wat voldoen
aan die ontwerp spesifikasies.
Strukturele aspekte van die prototipe paraboliese skottel word deur ander
navorsers geëvalueer en verbeter terwyl die Stirling-eenheid en elektriese sisteme
in parallelle projekte ontwikkel word. Die uiteindelike doel met hierdie
groepnavorsing is om ’n plaaslik vervaardigde doen-dit-self sonkrag eenheid te
ontwikkel wat in Afrika ontplooi kan word.
|
76 |
Investigation of solar applicable gas cyclesGopalakrishna, Sandeep 22 April 2013 (has links)
This thesis presents the thermodynamic and economic assessment of gas power cycles for 100 MW solar thermal power generation systems. A gas power cycle for solar power generation is a totally different technology from the current state of the art solar power generation systems. As a result, this thesis provides an assessment of the solar power generation systems with gas power cycles and provides guidance in the selection of design and operating parameters for gas power cycle based solar power generation system. The gas power cycle based power generation systems are assessed by means of thermodynamic and economic models developed and simulated using commercial thermodynamic analysis software. The gas cycle based power generation systems considered in this study are Cold Gas Turbine, High Temperature Solar Gas Turbine and Lorentz Cycle Gas Turbine. The system models are assessed for their thermodynamic performance using theory based turbo-machinery models with practical performance and loss data. In addition, extensive cost models have been developed for assessing the economic performance of the system models to determine their practical feasibility. The results from this study indicate that the most economical power generation system is the HTSGT system for a high peak cycle temperature utilizing the central receiver power tower solar collector system. The LCGT system also has a comparable performance at the same operating temperature. The CGT system assessed for operating with parabolic trough solar collector system at a lower peak cycle temperature had an inferior performance compared to the current state of the art technology for the power generation using parabolic troughs.
|
77 |
A Techno-Economic Framework for the Analysis of Concentrating Solar Power Plants with StorageGuédez, Rafael January 2016 (has links)
Concentrating solar power plants can integrate cost-effective thermal energy storage systems and thereby supply controllable power on demand, an advantage against other renewable technologies. Storage integration allows a solar thermal power plant to increase its load factor and to shift production to periods of peak demand. It also enables output firmness, providing stability to the power block and to the grid. Thus, despite the additional investment, storage can enhance the performance and economic viability of the plants. However, the levelized cost of electricity of these plants yet remains higher than for other technologies, so projects today are only viable through the provision of incentives or technology-specific competitive bid tenders. It is the variability of the solar resource, the myriad roles that storage can assume, and the complexity of enhancing the synergies between the solar field, the storage and the power block, what makes the development of adequate policy instruments, design and operation of these plants a challenging process. In this thesis a comprehensive methodology for the pre-design and analysis of concentrating solar power plants is presented. The methodology is based on a techno-economic modeling approach that allows identifying optimum trade-off curves between technical, environmental, and financial performance indicators. A number of contemporary plant layouts and novel storage and hybridization concepts are assessed to identify optimum plant configurations, in terms of component size and storage dispatch strategies. Conclusions highlight the relevance between the sizing of key plant components, the operation strategy and the boundaries set by the location. The interrelation between critical performance indicators, and their use as decisive parameters, is also discussed. Results are used as a basis to provide recommendations aimed to support the decision making process of key actors along the project development value chain of the plants. This research work and conclusions are primarily meant to set a stepping stone in the research of concentrating solar power plant design and optimization, but also to support the research towards understanding the value of storage in concentrating solar power plants and in the grid. / Koncentrerad solkraft erbjuder möjligheten att integrera kostnadseffektiv termisk energilagring och därmed behovsstyrd kraftkontroll. Detta är en viktig fördel jämfört med andra förnybara energiteknologier. Lagringsintegration tillåter solkraftsanläggningar att öka sin lastfaktor och skifta produktion till tider med största efterfrågan. Vidare möjliggör lagring fast elproduktion vilket leder till förbättrad nät- och kraftturbinstabilitet. Därför kan termisk lagring öka anläggningsprestanda och ekonomiskt värde trots ökande initiala kapitalkostnader. I termer av specifik elproduktionskostnad (LCOE) ligger koncentrerade solkraftsanläggningar med lagring fortfarande högre än andra kraftteknologier och anläggningsprojekt blir endast lönsamma genom subventionsmodeller eller teknologispecifika konkurrensutsatta anbudsförfaranden. Att hitta adekvata policylösningar och optimala design och operationsstrategier är en utmanande process eftersom det gäller att hitta rätt balans mellan variabel solinstrålning, lagring av energi och tid för produktion genom optimal design och operation av solmottagarfält, kraftblock och lagringskapacitet. I denna avhandling presenteras en omfattande metodik för pre-design och analys av koncentrerande solkraftverk. Metodiken baseras på en tekno-ekonomisk modelleringsansats som möjliggör identifiering av optimala avvägningssamband för tekniska, ekonomiska och miljöprestanda indikatorer. Metodiken tillämpas på ett antal moderna anläggningslayouter och lagrings- och hybridiseringskoncept för att identifiera optimal kraftanläggningsdesign i termer av komponentprestanda och lagringsanvändningsstrategier. I slutsatsen poängteras relevansen av att hitta rätt storlek på nyckelkomponenter i relation till lagringsstrategi och randvillkoren som ges av konstruktionsläget för optimal ekonomisk och miljömässig prestanda. Resultaten används för att formulera rekommendationer till nyckelaktörer i beslutsprocessen genom hela kraftanläggningens värdekedja från politisk beslutsfattare till anläggningsingenjör. Forskningen och slutsatserna i detta arbete skall i första hand ta ett steg framåt för optimering och design av solkraftsanläggningar men även tillhandahålla en metodik för utvärdering av lagringslösningar och dess specifika värde för solkraftsanläggningar och elnätet. / <p>QC 20160829</p>
|
78 |
Strategic raw material supply for the particleboard-producing industry in Europe : Problems and challengesTrischler, Johann January 2016 (has links)
Particleboard was invented to increase the utilization of wood and it soon became an important core material for furniture production. Nowadays, other industries such as the pulp and papermaking industry and the thermal energy recovery industry claim the same type of raw material. This leads to increasing competition and higher prices than in the past when that kind of wood raw material was widely available and of low price. The particleboard-producing industry is therefore seeking opportunities to reduce the competition and ensure the future supply of lignocellulosic raw material for their products. The purpose of the work summarised in this thesis was to investigate the strategic supply of lignocellulosic raw materials for particleboard production and to evaluate alternatives for the supply of lignocellulosic raw material for particleboard production. To encompass the complex field of strategic raw material supply, several publications have considered different stages along the supply chain. These papers range from empirical studies to practical tests on a laboratory scale. In this thesis, some of the papers are linked together, building the base for the overall results. The results show that the task of increasing the supply of lignocellulosic raw material as primary raw material source is limited by several factors, but that improved product design coupled with a suitable recycling concept can greatly increase the availability of lignocellulosic raw material as a secondary source. Alternatively, the use of non-wood plants might be an opportunity to substitute wood as raw material but there are still some problems relating to the particle properties which must be overcome first.
|
79 |
Development of a cascaded latent heat storage system for parabolic trough solar thermal power generationMuhammad, Mubarak Danladi January 2014 (has links)
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).
|
80 |
Development of a rotary thermomagnetic motor for thermal energy conversion. / Desenvolvimento de um motor termomagnético rotativo para conversão de energia térmica.Ferreira, Lucas Diego Rodrigues 22 November 2018 (has links)
Thermomagnetic motors can represent an alternative for the conversion of heat into mechanical energy, limited by the critical transition temperature (TC) of the used magnetic materials. Thus, by using materials with a TC close to room temperature, the energy available in the form of low-grade heat sources can be converted into useful mechanical work. This thesis proposes the development of a thermomagnetic motor to be operated with heat sources at temperatures in the range from 343 to 353 K, and a heat sink at room temperature, using water as the heat transfer fluid, presenting a novel approach to the construction of thermomagnetic devices. The design of this thermomagnetic motor was developed with the intent of producing a rotary movement, working similarly to an electric stepper motor, where instead of the electromagnetic coils being activated by an electric current, plates of a magnetic material change their magnetization state, due to a change in their temperature caused by the heat transfer with the heat transfer fluid. The analysis of the thermomagnetic motor proposed was done with the adoption of an integrated approach of numerical simulation and experimental validation. The evaluation of the motor is divided into the three main physical phenomena it encompasses: the magnetic field source, the heat transfer processes involved in the change of temperature of the magnetic material, and the system dynamics and power production. Each of these systems was modeled using computational tools. These models were then validated according to the data measured, obtained from a test stand of an idealized thermomagnetic motor, and for a rotary thermomagnetic motor. This methodology allowed a more comprehensive understanding of the critical working principles of the motor developed, and with that a fast advancement of the technology through a validated computational model. The computational models helped to identify the critical components to be improved in the development of these motors. These parameters can be guidelines for the design of thermomagnetic motors. One of the ways identified to produce a significant performance improvement, in the simulations, was the adoption of a control strategy that promotes the regeneration of heat in the plates of magnetic material, through which an improvement in the efficiency of 2.7 times could be achieved. / Motores termomagnéticos representam uma alternativa para a conversão de calor em energia mecânica, limitada apenas pela temperatura crítica da transição termomagnética (TC) dos materiais magnéticos. Ao usar materiais com TC próximo à temperatura ambiente, pode-se realizar a conversão da energia contida nas chamadas fontes pobres de calor, produzindo trabalho mecânico útil. Esta tese propõe o desenvolvimento de um motor termomagnético para operação com fontes de calor com temperaturas entre 343 e 353 K, e resfriamento à temperatura ambiente, utilizando a água como fluído de troca térmica, apresentando uma abordagem inovadora para dispositivos termomagnéticos. O motor foi projetado para produção de movimento rotativo de um eixo, per meio de um princípio similar ao de um motor de passo, no qual em vez de bobinas ativadas pela passagem de corrente elétrica, placas de material magnético sofrem uma mudança em seu estado de magnetização, devido à mudança de temperatura, causada pela troca de calor com a água. A análise do motor termomagnético proposto foi realizada com a adoção de uma abordagem integrada de simulações numéricas e validação experimental, dividindo a avaliação dos motores nos três principais fenômenos físicos envolvidos em seu funcionamento: a fonte de campo magnético, o processo de troca térmica envolvido na mudança de temperatura do material magnético, a dinâmica do sistema e produção de potência. Cada um destes sistemas foi modelado usando ferramentas computacionais. Os resultados obtidos foram então validados utilizando dados experimentais, obtidos a partir da construção e caracterização de uma bancada de testes para um motor termomagnético idealizado, e também para o motor termomagnético rotativo construído. Esta metodologia propiciou maior entendimento das funções críticas do motor desenvolvido, e possibilitou ainda sua otimização, através do estudo dos modelos computacionais validados. Os parâmetros obtidos ajudaram a identificar componentes críticos para melhoria no projeto do motor rotativo construído, e servem também como guias gerais para projetos de motores termomagnéticos. Um dos componentes com elevado potencial de melhoria foi a adoção de uma estratégia de controle para a regeneração do calor nas placas de material magnético, o que possibilitou, nas simulações, uma melhoria até 2,7 vezes na eficiência.
|
Page generated in 0.0639 seconds