Submitted in fulfilment of the requirements for M.Tech.: Electrical Engineering, Durban University of Technology, 2017. / Industrial plants are excellent sources of waste heat and provide many opportunities for energy harvesting using thermo-electric principles. A thermoelectric generator (TEG) is utilized in this study for harvesting expended heat from various sources. The main challenge associated with this type of technology lies in the creation of a sufficient thermal gradient between the hot side and the cold side of the TEG device. This is necessary for the module to generate an appreciable quantity of electrical energy. The performance of the TEG generator is tested using different configurations, different heat sources and different cooling methods. Heat sources included electrically driven devices, gas, biomass and gel fuel. Expended heat from different sites within an industrial environment was also chosen for operating the TEG device. The power produced by the generator is sufficient to operate low power LED lights, a DC radio receiver and a cellular phone charger. / M

Conventional understanding of quality of energy suggests that heat is a low grade form of energy. Hence converting this energy into useful form of work was assumed difficult. However, this understanding was challenged by researchers over the last few decades. With advances in solar, thermal and geothermal energy harvesting, they believed that these sources of energy had great potential to operate as dependable avenues for electrical power. In recent times, waste heat from automobiles, oil and gas and manufacturing industries were employed to harness power. Statistics show that US alone has a potential of generating 120,000 GWh/year of electricity from oil , gas and manufacturing industries, while automobiles can contribute upto 15,900 GWh/year. Thermoelectric generators (TEGs) can be employed to capture some of this otherwise wasted heat and to convert this heat into useful electrical energy. This field of research as compared to gas turbine industry has emerged recently over past 30 decades. Researchers have shown that efficiency of these TEGs modules can be improved by integrating heat transfer augmentation features on the hot side of these modules. Gas turbines employ advanced technologies for internal and external cooling. These technologies have applications over wide range of applications, one of which is thermoelectricity. Hence, making use of gas turbine technologies in thermoelectrics would surely improve the efficiency of existing TEGs. This study makes an effort to develop innovative technologies for gas turbine as well as thermoelectric applications. The first part of the study analyzes heat transfer augmentation from four different configurations for low aspect ratio channels and the second part deal with characterizing improvement in efficiency of TEGs due to the heat transfer augmentation techniques. / Master of Science

As wearable technology and wireless sensor nodes become more and more ubiquitous, the batteries required to power them have become more and more unappealing as they limit lifetime and scalability. Energy harvesting from body heat provides a solution to these limitations. Energy can be harvested from body heat using thermoelectric generators, or TEGs. TEGs provide a continuous, scalable, solid-state energy source ideal for wearable and wireless electronics and sensors. Unfortunately, current TEG technology produces low power (< 1 mW) at a very low voltage (20-90 mV) and require the load to be matched to the TEG internal resistance for maximum power transfer to occur. This thesis research proposes a power management integrated circuit (PMIC) that steps up ultralow voltages generated by TEGs to a regulated 3 V, while matching the internal resistance. The proposed boost converter aims to harvest energy from body heat as efficiently and flexibly as possible by providing a regulated 3 V output that can be used by a variable load. A comparator-based burst mode operation affords the converter a high conversion ratio at high efficiency, while fractional open circuit voltage maximum power point tracking ensures that the controller can be used with a variety of TEGs and TEG setups. This control allows the converter to boost input voltages as low as 50 mV, while matching a range of TEG internal source resistances in one stage. The controller was implemented in 0.25 µm CMOS and taped out in February 2016. Since these fabricated chips will not be completed and delivered until May 2016, functionality has only been verified through simulation. Simulation results are promising and indicate that the peak overall efficiency is 81% and peak low voltage, low power efficiency is 73%. These results demonstrate the the proposed converter can achieve overall efficiencies comparable to current literature and low power efficiencies better than similar wide range converters in literature. / Master of Science

Master of Science / Department of Electrical and Computer Engineering / William B. Kuhn / This work was a part of NASA EPSCoR Project NNX11AM05A: Biosensor Networks and Telecommunication Subsystems for Long Duration Missions, EVA Suits, and Robotic Precursor Scout Missions. The project’s main goal is the development of a wireless sensor network inside an astronaut’s spacesuit. Antennas are essential components in a wireless network. Since this antenna will be used inside the spacesuit it is important to consider both the physical size limitations and the desired antenna polarization. After exploring the WWVB radio station antenna which provides the preferred vertical polarization and has a suitable aspect ratio, the top hat antenna seemed promising for intrasuit communication. The design of a top hat antenna is outlined. Then, the antennas were tested using 433 MHz radios in a full scale model spacesuit. This spacesuit was designed specifically to model the behavior of aluminized mylar in the real suit. Test results support the feasibility of an intrasuit wireless network. If a gateway radio is placed on the chest or back, a sensor could be placed anywhere on the body and provide an adequate signal. These initial tests did not include a matching network, but the additional link-margin afforded by a matching network, even an imperfect match, is considered. Energy harvesting is explored as an alternative to batteries powering the intrasuit radio. In the oxygen rich environment of a spacesuit, even the smallest spark can be catastrophic. A variety of energy harvesting options are explored with a focus on thermal energy harvesting. The temperature difference between the human skin and the astronaut’s Liquid Cooling and Ventilation Garment can be used to produce a small voltage. To increase the voltage a step-up converter is implemented. Final integration of the two systems with a biosensor is left for on-going work in the three year NASA project.

Procedure for site discovery, system design, and optimization of power harvesting systems is developed with an emphasis on application to air compressors. Limitations for the usage of infrared pyrometers is evaluated. A system of governing equations for thermoelectric generators is developed. A solution method for solving the system of equations is created in order to predict power output from the device. Payback analysis is proposed for determining economic viability. A genetic algorithm is used to optimize the power harvesting system payback with changing quantities and varieties of thermoelectric generators, as well as the back work put into cooling the thermoelectric generators. Experimental data is taken for laboratory simulation of a power harvesting system under varying resistive load and thermal conductances in order to confirm the working model. A power harvester is designed for and installed on a consumer grade portable air compressor. Experimental data is compared against the model's prediction. As a case study, a system is designed for a water-cooled power harvesting system. Thermoelectric generator power harvesters are found to be economically infeasible for typical installations at current energy prices. Changes in parameters which would increase economic feasibility of the power harvesting system are discussed.

Procedure for site discovery, system design, and optimization of power harvesting systems is developed with an emphasis on application to air compressors. Limitations for the usage of infrared pyrometers is evaluated. A system of governing equations for thermoelectric generators is developed. A solution method for solving the system of equations is created in order to predict power output from the device. Payback analysis is proposed for determining economic viability. A genetic algorithm is used to optimize the power harvesting system payback with changing quantities and varieties of thermoelectric generators, as well as the back work put into cooling the thermoelectric generators.Experimental data is taken for laboratory simulation of a power harvesting system under varying resistive load and thermal conductances in order to confirm the working model. A power harvester is designed for and installed on a consumer grade portable air compressor. Experimental data is compared against the model's prediction. As a case study, a system is designed for a water-cooled power harvesting system.Thermoelectric generator power harvesters are found to be economically infeasible for typical installations at current energy prices. Changes in parameters which would increase economic feasibility of the power harvesting system are discussed.

Performance of two different waste heat recovery systems (one based on Rankine cycle and the other one using thermoelectricity) combined with non-hybrid, mild-hybrid and full hybrid systems are investigated. The vehicle under investigation was a 440hp Scania truck, loaded by 40 tons. Input data included logged data from a long haulage drive test in Sweden.All systems (waste heat recovery as well as hybrid) are implemented and simulated in Matlab/Simulink. Almost all systems are modeled using measured data or performance curves provided by one manufacturer. For Rankine system results from another investigation were used.Regardless of practical issues in implementing systems, reduction in fuel consumption for six different combination of waste heat recovery systems and hybrid systems with different degrees of hybridization are calculated. In general Rankine cycle shows a better performance. However, due to improvements achieved in laboratories, thermoelectricity could also be an option in future.This study focuses on “system” point of view and therefore high precision calculations is not included. However it can be useful in making decisions for further investigations.

This thesis presents a low power DC-DC converter suitable for harvesting energy from high impedance thermoelectric generators (TEGs) for the use in body powered electronics. The chip has been fabricated in a 130nm CMOS technology. To meet the power demands of body powered networks, a novel dual-path architecture capable of efficiently harvesting power at levels below 5 μW has been developed. To control the converter, a low power control loop has been developed. The control loop features a low-power clock and a pulse counting system that is capable of matching the converter impedance with high impedance TEGs. The system consumes less than 900nW of quiescent power and maintains an efficiency of 68% for a load of 5 μW. / Graduation date: 2013

Conducting polymers (CP) have received great attention in both academic and industrial areas in recent years. They exhibit unique characteristics (electrical conductivity, solution processability, light weight and flexibility) which make them promising candidates for being used in many electronic applications. Recently, there is a renewed interest to consider those materials for thermoelectric generators that is for energy harvesting purposes. Therefore, it is of great importance to have in depth understanding of their thermal and electrical characteristics. In this diploma work, the thermal conductivity of PEDOT:PSS is investigated by applying 3-omega technique which is accounted for a transient method of measuring thermal conductivity and specific heat. To validate the measurement setup, two benchmark substrates with known properties are explored and the results for thermal conductivity are nicely in agreement with their actual values with a reasonable error percentage. All measurements are carried out inside a Cryogenic probe station with vacuum condition. Then a bulk scale of PEDOT:PSS with sufficient thickness is made and investigated. Although, it is a great challenge to make a thick layer of this polymer since it needs to be both solid state and has as smooth surface as possible for further gold deposition. The results display a thermal conductivity range between 0.20 and 0.25 (W.m-1.K-1) at room temperature which is a nice approximation of what has been reported so far. The discrepancy is mainly due to some uncertainty about the exact value of temperature coefficient of resistance (TCR) of the heater and also heat losses especially in case of heaters with larger surface area. Moreover, thermal conductivity of PEDOT:PSS is studied over a wide temperature band ranging from 223 - 373 K.

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.