Thesis (M.S. in mechanical engineering)--Washington State University, August 2006. / Includes bibliographical references (p. 77-81).

No description available.

Low-temperature waste heat recovery is an important component of generating a more efficient, cost-effective and environmentally-friendly energy source. To meet this goal, thermo-electrochemical cells (TECs) are cost-effective electrochemical devices that produce a steady electric current under an applied temperature difference between their electrodes. However, current TECs have low conversion efficiencies. On this project, I developed a comprehensive multiscale model that couples the governing equations in TECs. The model was used to understand the fundamental principles and limitations in TECs, and to find the optimum cell thickness, aspect ratio and number of cells in a series stack. Doped multiwall carbon nanotubes (MWCNTs) were then explored as alternative electrodes for TECs. One of the main objectives of this dissertation is to study multiwall carbon nanotube/ionic liquid (MWCNT/IL) mixtures as alternative electrolytes for TECs. Previous authors showed that the addition of carbon nanotubes (CNTs) to a solvent-free IL electrolyte improves the efficiency of dye solar cells by 300%. My research plan involved a spectroscopy analysis of imidazolium-based ionic liquids (IILs) mixed with MWCNTs using impedance spectroscopy and nuclear magnetic resonance. The results show that the combination of interfacial polarization and ion pair dissociation effects reduces mass transfer resistances and enhances the power of TECs at low wt% of MWCNTs. This happens in spite of reduced open circuit voltage due to percolated networks.

Thesis (Ph.D.)--University of Rhode Island, 2005. / Adviser: Stanley Barnett. Includes bibliographical references.

Every day, huge amounts of energy are used by all sectors of the economy. From transport to industries, energy constitutes the base of development and people’s way of living. Besides, the energetic demand of millions of individuals must be satisfied with resources that are in constant depletion while the consumption is growing at a 2% rate every year. The consequence of such increase is that in the last decade energy costs have risen extremely fast. Societies must now find a way of maintaining the actual social-economic growth whilst reducing the energy demand in order to ensure sustainable development. Ice hockey arenas in Sweden have an average energy consumption of more than 1000 MWh per year, and around 42% of the total is used by the refrigeration system to cool the rink surface. The core of these units is the chiller, a machine that removes heat from a cold refrigerant and as a product of this chilling process, waste heat is generated. This energy can be exhausted to the environment or recovered for heating purposes. The main aim of this study is to investigate the uses given to the waste heat in Läkerol Arena, in Gävle. Some alternatives have been proposed and analysed in order to diminish the amount of rejected heat. Other objectives set in this project are to examine the possibility of reducing the dependence on district heating and to determine the efficacy of insulating the ground below the heating pipes that prevent permafrost. Nowadays the heat recovery system is used to preheat tap water until 30ºC and then up to 60ºC, to warm the air sent to the main rink area and to prevent the creation of permafrost in the ground below the main arena. The unused energy is sent to ambient with six big fans placed on the roof. The first additional use for waste heat proposed in this study is to design a heating system just for the resurfacing water. The current method in Läkerol Arena is to mix hot tap water with cold water. The problem is that the first one is three times more expensive than the second, so installing a unit that warms only cold cheap water up to 30ºC would result into saving 18760 SEK per season. Although this solution does not reduce the waste heat sent to the environment, it does reduce the demand of the desuperheater and increases the demand in the glycol circuit by 7%. Another option is to build a pit to melt the snow generated in the ice rinks. This solution would increase the use of the waste heat by 26% and bring annual savings of 32198 SEK, since it would not be necessary to rent any transport service to remove this snow. Besides, the emissions of CO2 would be reduced by 43774 kg. The possibility of sending part of the produced heat to a nearby building has also been investigated. The suggestion made in this study is to use part of the waste heat to warm the air for the ventilation of the Gefle Tennisklubb, an indoor tennis facility located at 150 m of the ice hockey arena. It has been calculated that this ventilation unit has an average heating demand of 9,1 kW. Results showed that in average this would represent 2% of the total heating capacity of the chillers and annual savings of 39858 SEK and 6880 kg of CO2 sent to the environment. The option of installing a heat pump in the hockey facility has also resulted beneficial. The purpose of such equipment is to cover the demand of district heating from the arena, which is currently used for radiators, radiant floor and 4 small ventilation units. After analysing average consumptions and talking with an expert, it has been decided that the best option is to install a ground source heat pump with a heating capacity of 415 kW. The interesting aspect about the heat pump is its efficiency, being it over the 300% (COP of 3,26). Although it means an important economic investment, this technology would save the arena around 239264 SEK every year and reduce CO2 emissions by 58331 kg. Finally, the installation of an insulation layer below the heating pipes has been analysed. The purpose was to see if this measure would be energy efficient. A simulation has been done with the educational version of the software ANSYS 14.5, and the results show that with a 100 mm insulation layer placed under the heated sand below the tubes, the heating demand is reduced by 44 kW (–54,6%), while the cooling demand increases by 5 kW (+1,1%). At the end this alternative has been dismissed since the installation would be too expensive and more heat would be sent to the environment, which is counter-productive. To sum up, with all the measures being installed, the arena would reduce the waste heat sent to the environment by 175,5 kW. It would represent the 49% of the total capacity generated (currently it is around 85% of the total waste heat). Besides, the annual emission of CO2 would decrease by 109 tonnes, the equivalent to 22 American cars. Finally, in terms of money, all the measures would bring total savings of 68880 SEK per year. The study concludes with three suggestions to continue with further research. The ideas are to investigate the possibility of introducing a filtering system for the water obtained in the snow pit, the viability of installing renewable energy sources to supply the electricity for the heat pump and study the efficiency of reducing the condensing temperature of the chillers.

Strict emissions legislation and energy security debates have spurred extensive research in alternative fuels and renewable energies. Literature research has shown the need for improvements in internal combustion engines (ICE) due to their low efficiencies. Significant gains in efficiency can be accomplished with the use of waste heat recovery (WHR) techniques. Organic rankine cycles (ORC) with turbocompounding harness the waste heat from an ICE to improve efficiency and fuel economy while reducing brake-specific emissions. A mathematical model was developed to explore the potential gains in 1st and 2nd law efficiencies. The model approaches the evaluations of the ORC from a practical and a theoretical method. The practical method in evaluation 1 limits the outlet exhaust gas temperatures from the evaporator to prevent the formation of condensation. The performance of the ORC is then evaluated and compared to the evaluation 2. In the theoretical method, in evaluation 2, the effect of pinch point on the evaporator and the entire cycle was analyzed. This analysis was conducted for R113, a dry fluid, and propane, a wet fluid, in order to analyze the differences in the two types of fluids. R113 showed a 13% – 22% and a 6% – 14.7% increase in 1st and 2nd law efficiencies, respectively. Propane showed a 9% – 17.4% and a 2% – 8.5% increase in 1st and 2nd law efficiencies, respectively. It was also shown that as the pinch point temperature decreases the 2nd law efficiencies increased. It was concluded that use of ORC with turbocompounding is an effective method for waste heat recovery in order to increase ICE efficiency.

Growing concerns regarding climate change, the increase in demand for energy and the efficient utilization of energy have become of major interest in applications of heating and power generation. A large portion of the energy input to these applications is lost, due to their typical inefficiencies, in the form of waste thermal energy which, if captured and utilized, can offer an abundant source of energy for electricity generation and heating purposes. The use of thermoelectric generators (TEGs) of different designs in waste heat recovery applications has been pursued over the past few decades as the generation of electrical power using TEGs has become viable compared to other conventional systems at low temperatures. This study focuses on the implementation of an annular design for integrated TEG modules in a heat exchanger device for waste heat recovery and the investigation of the effect of different TEG design parameters on the device performance. The integration of the annular TEG design in the heat exchanger was studied using a developed numerical model to investigate the interaction between the heat transfer and the thermoelectric effects and evaluate the performance under specific operating conditions. The heat transferred from the exhaust to the water flow through the TEGs was modelled using a thermal network for the heat flow, coupled with an electrical circuit for the power output. The model was validated using experimental results of the first generation of the TEG device with good agreement (3-6 %) between the predicted and measured performance results: power output, efficiency and the exhaust and water flow temperatures. With the objectives of maximizing the power output and improving the power characteristics, a half annular TEG design was presented. It was able to generate the same power output with double the voltage and half the current, thus improved the power characteristics required for functional operation, compared to the full annular design. The effect of the annular TEG design dimensions on the device performance was studied for a multi-row heat exchanger using the numerical model. The results showed that a maximum power output can be obtained at optimum TEG diameter ratio and thickness. In addition, the TEGs performance was studied under different electrical connection configurations in series and in parallel. The series connection between TEG rows showed better power output characteristics with lower current output, minimal power loss due to temperature mismatch and higher voltage output. The effect of heat exchanger design considerations such as the axial heat conduction was also investigated using the numerical model and the results were compared with an ANSYS model for verification. Good agreement was demonstrated and the results showed a decrease in the total power output of multiple TEG rows when axial conduction of heat was allowed between the TEGs hot-side surfaces in the heat exchanger. A dimensions map was created for annular TEGs integrated in a heat exchanger combining the effects of varying the TEG diameter ratio and thickness on the power output. Further, a dimensionless design parameter (β) was introduced to locate the maximum power region on the map. Using the map as a design tool, the dimensions of the annular TEG modules in a heat exchanger were determined to maximize the power output under a typical current output constraint in order to improve the system power characteristics. Using the map, it was shown that the current output could be reduced by 46 % of its value at the maximum power available on the map and the resultant power output could be maintained at 98 % of its maximum value. This also resulted in a 48% reduction in the TEG material volume and an increased voltage output of the device. As a result, the power output was maximized, the current output was limited to reduce losses in the power management system components and material volume reduction was achieved which would increase the device power density and reduce its overall cost. / Thesis / Master of Applied Science (MASc)

Thesis (Ph. D.)--University of Rhode Island, 2005. / Typescript. Includes bibliographical references (leaves 120-121).

A city’s characteristics of mixed-use zoning, diverse built form, high-density development, and residual heat generation by urban processes, present potential for optimizing the thermal energy end-use of certain waste streams. A method was developed to identify sources of waste thermal energy and heat demand clusters in a mixed-use jurisdiction and design a preliminary primary network of a district heating system based on these waste heat sources. The method applies systems analysis, energy potential mapping (GIS spatial analysis) and network optimization (linear programming) techniques. The method is implemented using a case study of data for peninsular Halifax. Finally, the method and implementation’s influence on climate change (i.e. a reduction in GHG emissions) and energy security, two central themes of this research, are discussed.

This work focuses on an innovative Rotary Displacer SE (RDSE) configuration for Stirling engines (SEs). RDSE features rotary displacers instead of reciprocating displacers (found in conventional SE configurations), as well as combined compression and expansion spaces. Guided by the research question "can RDSE as a novel configuration achieve a higher efficiency compared to conventional SE configurations at comparable operating conditions?", the goal of this study is to characterize, analyze, and optimize RDSE which is pursued in three technical stages. It is observed the RDSE prototype has an optimum phase angle of > 90° and thermal efficiency of 15.5% corresponding to 75.2% of the ideal (Carnot) efficiency at the source and sink temperatures of 98.6° C and 22.1° C, respectively. Initial results indicate that 125° phase angle provides more power than that of the theoretically optimum 90° phase angle. The results also show comparable B_n and significantly higher W_n values (0.047 and 0.465, respectively) compared to earlier studies, and suggest the RDSE could potentially be a competitive alternative to other SE configurations. Furthermore, due to lack of a regenerator, the non-ideal effects calculated in the analytical approach have insignificant impact (less than 0.03 kPa in 100 kPa). The clearance volume in the shuttled volume has a dramatic negative effect and reduces the performance up to 40%. Ultimately, utilizing CFD, it is proved that the existing geometry is relatively optimized where the optimum phase angle is 121° and geometric ratio D\/L for the displacer is 0.49.