Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2009. / Committee Chair: Joshi, Yogendra; Committee Member: Gallivan, Martha; Committee Member: Graham, Samuel; Committee Member: Yeung, Pui-Kuen; Committee Member: Zhang, Zhuomin. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 66-69). Also available via the Internet.

Thesis (M.Sc.)(Metallurgy)--University of Pretoria, 2004. / Includes summary. Includes bibliographical references.

Thesis (Ph. D.)--Mechanical Engineering, Georgia Institute of Technology, 2006. / Marc Smith, Committee Member ; P.K. Yeung, Committee Member ; Benjamin Shapiro, Committee Member ; Sheldon Jeter, Committee Member ; Yogendra Joshi, Committee Chair.

Organic Rankine Cycle (ORC) heat engines convert low-grade heat to other forms of energy such as electrical and mechanical energy. They achieve this by vaporizing and expanding the organic fluid at high pressure, turning the turbine which can be employed to run an alternator or any other mechanism as desired. Conventional Rankine Cycles operate with steam at temperatures above 400 ℃. The broad aspect of the research focussed on the generation of electricity to cater for household needs. Solar energy would be used to heat air which would in turn heat rocks in an insulated vessel. This would act as an energy storage in form of heat from which a heat transfer fluid would collect heat to supply the ORC heat engine for the generation of electricity. The objective of the research was to optimize power output of the ORC heat engine operating at temperatures between 25℃ at the condenser and 90 to 150℃ at the heat source. This was achieved by analysis of thermal energy, mechanical power, electrical power and physical parameters in connection with flow rate of working fluid and heat transfer fluids.

M.Tech. (Mechanical Engineering) / Please refer to full text to view abstract

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Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The focus of this thesis is on South Africa's first micro space satellite SUNSAT, and the thermal modelling thereof. Background theory with relevance to thermal management and control of satellite systems and subsystems is presented. The mission profile and subsystem makeup of SUNSAT is also briefly discussed, with emphasis placed on the physical structure, possible orbit paths, internal heat generation, and the environmental heating. The environmental heating on the satellite surfaces from the direct and reflected earth solar radiation, as well as the earth emitted infrared radiation, is determined from the developed computer program ORBIT-FLUX. This program was used in tandem with numerical programs (developed in house), as well as an outsourced program TAS (Thermal Analysis Systems) to model SUNSAT for two possible orbit paths. The resistance-capacitance formulation method was used to develop the numerical programs, which served initially to establish the validity ofTAS. The first approximated thermal model of SUNSA T's batteries was the 7 lumped-mass model that focused on the batteries since their overheating is the suspected reason for SUNSA T'S failure to complete its mission. A numerical program as well as a similar TAS model was developed, and the results showed correlation to within 3°C. A lumped-mass model of SUNSAT was also developed, both numerically and using TAS. The models were tested and the results showed that the temperatures of the models were sensitive to changes in internal heating as well as varying emissivity and absorptivity. The numerical and TAS lumped-mass model results did not correlate well, possibly due to the higher number of control volumes used in the TAS lumped-mass model. The TAS SUNSAT 2 model was developed as advancement on the lumped-mass model. The higher number of control volumes and the effect of adding solar panels gave a more realistic model of SUNSA T. The results did not show good correlation with actual SUNSA T temperature data possibly due to the fact that the solar panels were not mounted on the model body as they were on SUNSA T; but the TAS SUNSA T 2 model did set the platform for the more advanced TAS SUNSAT 3 model. This thermal model included the effects of the solar panel mountings, and had a higher number of control volumes, which gave a better physical representation of the SUNSAT subsystems. The model was tested for possible orbit paths of SUNSA T. The results showed excellent correlation to actual SUNSA T data. For the comparison of the TAS SUNSA T 3 model results with data from SUNSAT for July 1999 showed that the SUNSA T battery temperature was modelled to within 8°C. And for June 2000, this same comparison was to within 1°C. A thermal management and control case study was done on a simple system (which included a cubic box and an internal solid block with heat generation) to illustrate the effects of using various passive and active thermal control hardware to regulate temperatures. The results showed that internal surfaces painted black provide for maximum heat sharing, and lowest block temperatures. The block temperatures were found to be very sensitive to changes in the cube external optical surface properties. A slight increase in emissivity lowered the block temperature, while a slight increase in absorptivity increased the block temperature. Heat pipes were also found to lower the temperatures of the block and immediate subsystems by providing a path of low thermal resistance to the flow of heat from the block directly to the radiator. The effect of thermal insulation was also investigated. For the two materials (rubber and plastic) that were tested, it was noticed that although insulation material does give more thermal control and predictability over a subsystem by thermally isolating it from its environment, it can cause a subsystem that has heat generation to become too hot. Recommendations were made relating to future micro satellite thermal management and control with regard to; thermal modelling techniques, acquisition of tried software, positioning of temperature sensors for optimisation of thermal data, and the verification of optical surface properties by physical measurement. / AFRIKAANSE OPSOMMING: Hierdie tesis fokus op Suid-Afrika se eerste mikro ruimte satelliet, SUNSAT, en die termiese ontwikkeling daarvan. Agtergrond teorie met betrekking tot die termiese bestuur en kontrole van die satelliet-sisteme en subsisteme word aangebied. Die missie-profiel en die samestelling van die subsisteme word ook kortliks bespreek met die klem op die fisiese strukture, moontlike wentelbane, interne hitte-opwekking, en die omgewingsverhitting. Die omgewingsverhitting op die oppervlaktes van die satelliet, veroorsaak deur direkte en weerkaatste aardlson bestraling, sowel as deur infrarooi bestraling afkomstig van die aarde, word bepaal deur die ontwikkelde rekenaarprogram ORBIT-FLUX. Hierdie program word gebruik in tandem met numeriese programme (intern ontwikkel), so weI as 'n uitgekontrakteerde program TAS (Termiese Analiese Sisteme) om SUNS AT vir twee moontlike wentelbane te modelleer. Die weerstandskapasitansie formuleringsmetode is gebruik om die numeriese programme te ontwikkel. Hierdie programme is oorspronklik gebruik om die validiteit van TAS vas te stel. Die eerste benaderde termiese model van SUNSAT se batterye was die 7 gekonsentreerdemassa model wat gefokus het op die batterye aangesien daar vermoed is dat oorverhitting van die batterye die rede is waarom SUNSAT nie sy missie voltooi het nie. 'n Numeriese program so weI as 'n gelyksoortige TAS model is ontwikkel en die resultate korreleer tot binne 3°C. 'n Gekonsentreerde-massa model van SUNSA T is ook ontwikkel, numeries en met gebruik van TAS. Die modelle is getoets en die resultate toon dat die temperature van die modelle gevoelig is vir veranderinge in interne hitte sowel as vir wissellende uitstralingsvermoe en absorpsievermoe, Die numeriese- en die TAS gekonsentreerde-massa model resultate het nie goed met mekaar korrelleer nie, moontlik weens die hoe aantal kontrole volumes wat in die TAS gekonsentreerde-massa model gebruik is. Die TAS SUNSA T 2 model is 'n verdere ontwikkeling van die gekonsentreerde-massa model. Die hoer aantal kontrole volumes en die byvoeging van solarpanele het tot gevolg gehad dat hierdie 'n meer realistiese model van SUNSA T is. Die resultate het nie goed gekorrelleer met die temperatuurdata van die werklike SUNSAT nie, moontlik weens die feit dat die solarpanele nie op die bakwerk monteer is, soos in die geval van SUNSA T nie. Nietemin het het die TAS SUNSAT 2 model gelei tot die meer gevorderde TAS SUNSAT 3 model. Hierdie termiese model het die solarpaneel montuur ingesluit en het 'n hoer aantal kontrole volumes gehad, wat 'n beter fisiese weergawe van die SUNSAT subsisteme tot gevolg gehad het. Die model is getoets vir moontlike wentelbane van SUNSAT. Die resultate het 'n hoe korrellasie getoon met die data van die werklike SUNSAT. 'n Vergelyking van die TAS SUNSAT 3 model resultate met data van SUNSAT vir Julie 1999 wys dat die SUNSAT battery temperatuur dieselfde is tot binne 8°C. Vergelyk met die resultate vir Junie 2000 was dit binne 1°C. 'n Termiese bestuurs- en kontrolestudie is gedoen op 'n eenvoudige sisteem (insluitende 'n kubieke boks en 'n interne soliede blok met hitte opwekking) om die uitwerking van die gebruik van passiewe en aktiewe termiese kontrole hardeware wat temperature reguleer, te illustreer. Die resultate toon dat interne oppervlaktes wat swart geverf is, lei tot die maksimum hitte-deling, en die laagste bloktemperature. Daar is gevind dat bloktemperature baie gevoelig is vir veranderinge in die eienskappe van die kubus se eksterne optiese oppervlaktes. 'n Effense vermedering van uitstralingsvermoe verlaag die bloktemperatuur, terwyl 'n effense vermedering van absorpsievermoe die bloktemperatuur verhoog. Daar is ook gevind dat hittepype die temperatuur van die blok en onmiddelike subsisteme verlaag deur om 'n pad van lae termiese weerstand teen die vloei van hitte vanaf die blok, direk na die verkoeler te verskaf. Die uitwerking van termiese isolasie is ook ondersoek. In die geval van die twee materiale (rubber en plastiek) wat getoets is, is daar opgemerk dat, alhoewel isolasie materiaal meer termiese beheer oor die subsisteem en voorspelbaarheid tot gevolg gehad het deurdat die subsisteem termies van die omgewing isoleer is, kan dit veroorsaak dat die subsisteem te warm word. Aanbevelings is gemaak met betrekking tot toekomstige mikro satelliet bestuur en kontrole en wel in verband met die volgende: termiese modelleringstegnieke, die aanskaffing van getoetste sagteware, die plasing van temperatuut sensors vir die beste termiese data, en die verifikasie van die eienskappe van optiese oppervlaktes deur fisiese meting.

In recent years, high strength concrete (HSC) is becoming an attractive alternative to traditional normal strength concrete (NSC), and is used in a wide range of applications. With the increased use of HSC, concern has developed regarding the behavior of such concrete in fire. Until now, the fire performance of HSC is not fully understood and more research is needed. Full-scale fire testing is time consuming and expensive, and the real fire scenario is different from the standard fire. Performance-based assessment methods, including numerical analysis and simplified method, are being accepted in an increasing number of countries. In this dissertation, the fire testing results both of HSC and NSC are presented, performance-based numerical models are developed to study the fire performance of reinforced concrete (RC) members, and simplified calculation methods are proposed to estimate the load capacity of fire-damaged RC columns/beams. A detailed and comprehensive literature review is presented that provides background information on the high temperature behavior of concrete materials and RC members, as well as information on fire performance assessment procedures and objectives. The fire testing results of seven batches of HSC and NSC are presented and discussed. The test results indicated that the post-fire re-curing results in substantial strength and durability recovery, and its extent depends upon the types of concrete, temperature level, and re-curing age. The fire tests also showed that violent explosive reduced the risk of HSC explosive spalling. The surface crack widths were also reduced during the re-curing process, and in most cases, they were found within the maximum limits specified by the American Concrete Institute (ACI) building code. / Numerical models are developed herein to investigate the behavior in fire of RC columns and beams. The models have been validated against fire test data available in literature, and used to conduct parametric studies, which focused on the size effect on fire resistance of RC columns, and the effect of concrete cover thickness on fire endurance of RC beams. Simplified calculation methods have been developed to predict the load capacity of fire damaged RC columns/beams. This method is validated by five case studies, including thirty-five RC columns tested by other investigators. The predicted results are compared with the experimental results, and the good agreement indicates the adequacy of the simplified method for practical engineering applications. / by Lixian Liu. / Thesis (Ph.D.)--Florida Atlantic University, 2009. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2009. Mode of access: World Wide Web.

The performance of a novel micro-thermodielectric power generation device (MTDPG) was investigated in order to determine if thermodielectric power generation can compete with current portable power generation technologies. Thermodielectric power generation is a direct energy conversion technology that converts heat directly into high voltage direct current. It requires dielectric (i.e., capacitive) materials whose charge storing capabilities are a function of temperature. This property is exploited by heating these materials after they are charged; as their temperature increases, their charge storage capability decreases, forcing them to eject a portion of their surface charge to an appropriate electronic storage device. Previously, predicting the performance of a thermodielectric power generator was hindered by a poor understanding of the materials thermodynamic properties and the affect unsteady heat transfer losses have on system performance. In order to improve predictive capabilities in this study, a thermodielectric equation of state was developed that describes the relationship between the applied electric field, the surface charge stored by the thermodielectric material, and its temperature. This state equation was then used to derive expressions for the material's thermodynamic states (internal energy, entropy), which were subsequently used to determine the optimum material properties for power generation. Next, a numerical simulation code was developed to determine the heat transfer capabilities of a micro-scale parallel plate heat recuperator (MPPHR), a device designed specifically to a) provide the unsteady heating and cooling necessary for thermodielectric power generation and b) minimize the unsteady heat transfer losses of the system. The previously derived thermodynamic equations were then incorporated into the numerical simulation code, creating a tool capable of determining the thermodynamic performance of an MTDPG, in terms of the thermal efficiency, percent Carnot efficiency, and energy/power density, when the material properties and the operating regime of the MPPHR were varied. The performance of the MTDPG was optimized for an operating temperature range of 300 500 K. The optimization predicted that the MTDPG could provide a thermal efficiency of 29.7 percent. This corresponds to 74.2 percent of the Carnot efficiency. The power density of this MTDPG depends on the operating frequency and can exceed 1,000,000 W/m3.