In the face of the internationally tightened requirements and regulations for CO2 emissions from the transportation sector, waste heat recovery using a thermoelectric generator (TEG) has become the most significant research interest. A vehicular TEG, converting otherwise wasted thermal energy from engines to electricity directly for use in the vehicle systems, is a promising approach for vehicle original equipment manufacturers (OEMs) to reduce fuel consumption and lower CO2 emissions. This thesis aims to explore the main challenges to be faced in the commercialization of TEGs. Based on a review of the literature, four research gaps have been identified, which are respectively: * Translating the material improvements into TEG Performance, * Transient behaviors of vehicular TEGs under driving cycles, * Fuel saving percentage and cost-benefit estimation of TEG, * Bidirectional characteristic of TEM and bifunctional vehicular TEG. To directly address these research gaps, a quasi-static TEM model, a dynamic TEG model, a semi-empirical vehicular TEG model, and a dual-model TEM model have been respectively developed and validated through experiments on both TEM test rigs and TEG engine test benches. These developed models are used as tools to investigate the performance of TEG, parameters sensitivity, and integration effects. Model-based TEG control, TEG cost benefit ratio and feasibility of a bifunctional TEG are also explored based on the developed models. The simulation results show that TEG power generation is highly sensitive to the heat transfer coefficient of hot side heat exchanger and thermal contact resistance. The TEG installation position is identified as the most important integration effect. It has been found by the simulation result that the fuel saving with TEG installed upstream of the three-way catalyst (TWC) is 50% higher than the fuel saving with TEG installed downstream of the TWC. The fuel saving percentage for a skutterudite vehicular TEG, which can generate around 400-600W in constant speed 120km/h, is 0.5-3.6% depending on the integration position in the exhaust line. A 3-minute faster warm-up effect of engine oil can be obtained when the bifunctional TEG works in engine warm-up mode with electrical current applied.

Transport Membrane Condenser (TMC) is an innovative technology based on the property of a nano-scale porous material which can extract both waste heat and water from exhaust gases. This technology tremendously improves the efficiency of boilers and gas/coal combustors by lowering waste heat and increasing water recovery. Contaminants in the flue gases, such as CO2, O2, NOx, and SO2 are inhibited from passing through the membrane by the membrane’s high selectivity. The condensed water through these tubes is highly pure and can be used as the makeup water for many industrial applications. The goal of this research is to investigate the heat transfer, condensation rate, pressure drop and overall performance of crossflow heat exchangers. In this research, a numerical model has been developed to predict condensation of water vapor over and inside of nano-porous layers. Both capillary condensation inside the nanoscale porous structure of the TMC and the surface condensation were considered in the proposed method using a semi-empirical model. The transport of the water vapor and the latent heat of condensation were applied in the numerical model using the pertinent mass, momentum, turbulence and energy equations. By using the proposed model and simulation procedure, the effect of various inlet parameters such as inlet mass flow rate, inlet temperature, and water vapor content of the inlet flow on the performance of the cross-flow TMC heat exchanger was studied to obtain the optimum performance of the heat exchangers at different working conditions. The performance of the TMC heat exchangers for inlet flue gas rate 40 to 120 kg/h, inlet water rate 60 to 140 kg/h, inlet flue gas relative humidity 20 to 90%, and tube pitch ratio 0.25 to 2.25 has been studied. The obtained results show that the water condensation flux continuously increases with the increase of the inlet flue-gas flow rate, water flow rate, and the flue-gas humidity. The total heat flux also follows the same trend due to the pronounced effect of the latent heat transfer from the condensation process. The water condensation flux and the overall heat transfer increase at the beginning for small values of the tube pitches and then decreases as the tube pitch increases furthermore. In addition to the cross-flow TMC heat exchangers, the performance of a shell and tube TMC heat exchanger for high pressure and temperature oxy-combustion applications has been investigated. The performance analysis for a 6-heat exchanger TMC unit shows that heat transfer of the 2-stage TMC unit is higher than the 2-stage with the same number of the heat exchanger in each unit.

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.

Refrigeration systems employing the NH3-H2O absorption cycle provide cooling using a thermal energy input. This cycle relies on the zeotropic nature of the refrigerant - absorbent pair: because of the difference in boiling temperatures between NH3 and H2O, they can be separated through selective boiling in the desorber. Desorbers with counter-current flow of the solution and generated vapor enable efficient heat and mass transfer between the two phases, reducing the absorbent content in the generated vapor. Flow visualization experiments at temperatures, concentrations and pressures representative of operating conditions are necessary to understand the heat and mass transfer processes and flow regime characteristics within the component. In this study, a Flooded Column desorber, which accomplishes desorption of the refrigerant vapor through a combination of falling-film and pool boiling, was fabricated and tested. Refrigerant-rich solution enters the top of the component and fills a column, which is heated by an adjacent heated microchannel array. The vapor generated within the component is removed from the top of the component, while the dilute solution drains from the bottom. Flow visualization experiments showed that the Flooded Column desorber operated most stably in a partially flooded condition, with a pool-boiling region below a falling-film region. It was found that the liquid column level was dependent on operating conditions, and that the pool-boiling region exhibits aggressive mixing between the vapor and solution phases. Heat transfer coefficients were calculated from the data for the pool-boiling region, and were compared with the predictions of several mixture pool-boiling correlations from the literature. The correlations from the literature were in general unable to predict the data from this study adequately. It was found that the Flooded Column desorber yielded higher heat transfer coefficients within the pool-boiling region than those predicted by these correlations. Therefore, modifications to existing mixture boiling correlations are suggested based on the findings of this study. The resulting modified correlation predicts 33 of the 35 data points from this study within ±40%, with an average absolute error of 19%.

The purpose of this thesis is to experimentally determine the feasibility of an ejector based, waste heat recovery driven refrigeration system applied to the data center environment in order to reduce operational cooling costs. A comprehensive literature review is detailed to determine the current state of the ejector refrigeration research and assess the initial direction of this thesis. A simplified model was created to perform preliminary performance estimations and system sizing before constructing an experimental system apparatus to evaluate the model predictions. The pressures and temperatures used in the model and instituted in the experimental system are based on the maximum temperatures typically observed in computing servers (50-75°C). Precision controlled heaters are used to simulate the computer server heat, and R245fa is used as the working fluid. Performance results ranged from 0.06 to 0.13.

The diffusion absorption refrigeration (DAR) cycle is a promising technology for fully thermally driven cooling. It is well suited to applications in medicine refrigeration and air-conditioning in off-grid settings. However, design and engineering knowhow for the technology is limited; therefore, system development has historically been an iterative and expensive process. Additionally, conventional system designs require high-grade energy input for operation, and are unsuitable for low-temperature solar- or waste-heat activated applications. In the present effort, component- and system-level DAR engineering analyses are performed. Detailed bubble-pump generator (BPG) component models are developed, and are validated experimentally and with direct simulations. Investigations into the BPG focus on the Taylor flow pattern in the intermediate Bond number regime, which has not yet been thoroughly characterized in the literature, and has numerous industry applications, including nuclear fuel processing and well dewatering. A coupling-fluid heated BPG design is also investigated experimentally for low-source-temperature operation. Phase-change simulation methodologies are developed to rigorously study the continuously developing flow pattern in this BPG configuration. Detailed component-level models are also formulated for all of the other DAR heat and mass exchangers, and are integrated to yield a complete system-level model. Results from these modeling studies are applied to develop a novel fully passive low-source-temperature (110 - 130°C) DAR system that delivers refrigeration grade cooling. This design achieves operation at target conditions through the use of alternate working fluids (NH3-NaSCN-He), the coupling-fluid heated BPG, and a novel absorber configuration. The complete DAR system is demonstrated experimentally, and evaluated over a range of operating conditions. Experimental results are applied to assess and refine component- and system- level models.

This research project was about the combined organic Rankine cycle which extracted energy from the exhaust gas of a diesel engine. There was a study about significant properties of suitable working fluids. The chosen working fluid, R134a, was used to operate at the dry condition when it exited the steam piston engine. Furthermore, R134a is environmentally friendly with low environmental impact. It was also compatible with sealing materials. There were calibrations for the components of the combined Rankine cycle. The efficiency of the heat exchanger converting exhaust heat from the diesel engine to vaporize R134a was 89%. The average efficiency of the generator was 50%. The hydraulic pump used for the combined Rankine cycle showed a transporting problem, as vapor-lock occurred when the pump ran for about 1 minute. The output of the combined Rankine cycle was normalized to compensate for the parasitic losses of a virtual vane pump used in hydraulic systems for the 6 liter diesel engines. There were three different vane pump widths from different pumps to compare frictional loss. The pump with the smallest vane width presented the least frictional mean effective pressure (fmep) (0.26 kPa) when scaled with the displacement of the GMC Sierra 6 liter diesel engine. The power output of the Rankine cycle was scaled to brake mean effective pressure (bmep) to compare with the frictional mean effective pressure. The maximum bmep was at 0.071 kPa when diesel engine had rotational speed at 2190 RPM. The power outputs of the organic Rankine compensated partially the frictional loss of the vane pumps in the 6 liter diesel engine. By using R134a, the condensing pressure was 0.8 MPa; hence, the power outputs from steam engine were limited. Therefore, refrigerants with lower condensing pressure were needed. There were proposal for improvement of the organic Rankine by substituting R134a by R123 (0.1 MPa), R21 (0.2 MPa), and R114 (0.25 MPa) . / text

This thesis was concerned with the proof of concept for mid-grade, 250-500oC, industrial waste heat recovery using a thermally regenerative electrochemical system. Proposed thermally regenerative electrochemical systems are limited to high operating temperatures (> 900oC) and suffer from poor conversion efficiencies (< 20%). As such, a single chamber design that is free of moving parts was presented in this work. The concept for this novel regenerative system relies on gravity and a liquid medium to convey dissolved sodium hydride in a hydride-borohydride solution from cold to hot regions in a continuous circuit. Such a liquid transport medium could allow for operation below 500oC while stabilizing the hydride from thermal decomposition. Investigations on this system were carried out using a custom pressure differential thermal analyzer that was able to operate above temperatures of 700oC and pressures of 2.2MPa. The results of the experiments provided valuable information concerning the phase diagrams of various hydride-borohydride mixtures. The eutectic composition of the NaH-KBH4 system was found to be 43 mole% NaH. The corresponding eutectic temperature (503oC) was determined using the differential cooling curves. Appreciable NaH decomposition was noticed in mixtures above 59.0 mole% NaH. Mixtures up to 42.5 mole% KH in KBH4 were also investigated. The eutectic composition of the KH-KBH4 binary system was determined by extrapolating the liquidus curve to intersect the solidus curve. The KH-KBH4 eutectic temperature was found to be 390oC at 66 mole% KH. The experimental work successfully demonstrates that thermally unstable hydrides can be obtained in the liquid phase below their melting points, under moderate pressures, when mixed with alkali borohydrides. This significantly lowers the achievable operating temperature of the thermally regenerative electrochemical systems currently proposed. The use of the single chamber design with a hydride-borohydride liquid medium offers numerous advantages including: reduced maintenance, reduced operating temperature, reduced system weight, reduced parasitic losses, increased voltage, and increased reliability. The viability for mid-grade industrial waste heat recovery requires construction of a prototype which optimizes power outputs and explores the hydrodynamic transport of material. / Thesis (Master, Mining Engineering) -- Queen's University, 2009-09-24 14:33:22.627

Globally, there are vast amounts of low-grade heat sources from industrial waste and renewables that can be converted into electricity through advanced thermodynamic power cycles and appropriate working fluids. In this thesis, experimental research was conducted to investigate the performance of a small-scale Organic Rankine Cycle (ORC) system under different operating conditions. The experimental setup consisted of typical ORC system components, such as a turboexpander with a high speed generator, a scroll expander, a finned-tube condenser, an ORC pump, a plate evaporator and a shell and tube evaporator. R245fa was selected as the working fluid, on account of its appropriate thermophysical properties for the ORC system and its low ozone depletion potential (ODP). The test rig was fully instrumented and extensive experiments carried out to examine the influences of several important parameters, including heat source temperature, ORC pump speed, heat sink flow velocity, different evaporators and with or without a recuperator on overall R245fa ORC performances. In addition, in terms of the working fluid’s environmental impact, temperature match of the cycle heat processes and system compactness, CO2 transcritical power cycles (T-CO2) were deemed more applicable for converting low-grade heat to power. However, the system thermal efficiency of T-CO2 requires further improvement. Subsequently, a test rig of a small-scale power generation system with T-CO2 power cycles was developed with essential components connected; these included a plate CO2 supercritical heater, a CO2 transcritical turbine, a plate recuperator, an air-cooled finned-tube CO2 condenser and a CO2 liquid pump. Various preliminary test results from the system measurements are demonstrated in this thesis. At the end, a theoretical study was conducted to investigate and compare the performance of T-CO2 and R245fa ORCs using low-grade thermal energy to produce useful shaft or electrical power. The thermodynamic models of both cycles were developed and applied to calculate and compare the cycle thermal and exergy efficiencies at different operating conditions and control strategies. In this thesis, the main results showed that the thermal efficiency of the tested ORC system could be improved with an increased heat source temperature in the system with or without recuperator. When the heat source temperature increased from 145 oC to 155 oC for the system without recuperator, the percentage increase rates of turbine power output and system thermal efficiency were 13.6% and 14% respectively while when the temperature increased from 154 oC to 166 oC for the system with recuperator, the percentage increase rates were 31.2% and 61.97% respectively. In addition, the ORC with recuperator required a relative higher heat source temperature, which is comparable to a system without recuperator. On the other hand, at constant heat source temperatures, the working fluid pump speed could be optimised to maximise system thermal efficiency for ORC both with and without recuperator. The pressure ratio is a key factor impacting the efficiencies and power generation of the turbine and scroll expander. Maximum electrical power outputs of 1556.24W and 750W of the scroll expander and turbine were observed at pressure ratio points of 3.3 and 2.57 respectively. For the T-CO2 system, the main results showing that the CO2 mass flow rate could be directly controlled by varying the CO2 liquid pump speeds. The CO2 pressures at the turbine inlet and outlet and turbine power generation all increased with higher CO2 mass flow rates. When CO2 mass flow rate increased from 0.2 kg/s to 0.26kg/s, the maximum percentage increase rates of measured turbine power generation was 116.9%. However, the heat source flow rate was found to have almost negligible impact on system performance. When the thermal oil flow rate increased from 0.364kg/s to 0.463kg/s, the maximum percentage increase rate of measured turbine power generation was only 14.8%. For the thermodynamic analysis, with the same operating conditions and heat transfer assumptions, the thermal and exergy efficiencies of R245fa ORCs are both slightly higher than those of T-CO2. However, the efficiencies of both cycles can be enhanced by installing a recuperator at under specific operating conditions. The experiment and simulation results can thus inform further design and operation optimisations of both the systems and their components.

Lately, car manufacturers have been put to a big challenge to reduce the CO2 emission of their entire fleets. Norms of pollutant emissions limit the ways to achieve the desired CO2 emission goals, as some of the solutions that would lead to lower CO2 emission also lead to higher pollutant emission. Waste Heat Recovery (WHR) could be a good solution to lower the CO2 emission of the Internal Combustion Engine (ICE) without increasing the pollutant emission. In the present thesis different WHR strategies are analysed and the results suggested it would be interesting to further study the Brayton cycle machine. Air Brayton Cycle (ABC) represents a way to recover a part of the heat energy of the ICE exhaust gases and transform it into mechanical energy. Recovered mechanical energy would then be returned to the crankshaft of the ICE, thereby reducing the amount of energy that has to be liberated by combustion of fuel which lowers the fuel consumption and CO2 emission. The study of ABC started with an analysis of the ideal cycle in order to obtain the theoretical maximum of the system. The study continued with an analysis of the semi ideal cycle where all losses are taken into account only by two efficiency coefficients. This analysis showed that for the diesel engine efficiency of the ABC is very low because of the low exhaust gas temperature. For the gasoline engine the cycle could be viable when the ICE is working under steady condition and higher load. These conditions could be fulfilled when the vehicle is driven on the highway. Detailed analysis was aimed at determining the cycle main losses. They were determined to be: pumping losses, losses caused by heat transfer and mechanical losses. Taking into account these main losses along with other direct and indirect losses it was concluded that the cycle is not viable for the types of the WHR machines that were considered in this study. In order for the cycle to be viable some other either existing or new machine type should be tested, that would lower the main losses and offer good isentropic and mechanical efficiency for desired conditions. / Últimamente los fabricantes de automóviles se han puesto el gran reto de reducir la emisión de CO2 en la totalidad de sus flotas. Las nuevas normativas para la reducción de las emisiones contaminantes limitan los medios para lograr los objetivos deseados en la emisión de CO2 porque algunas de las soluciones que llevan a la reducción en la emisión de CO2 también dan lugar a un incremento en la emisión de otros contaminantes. La recuperación de calor residual (WHR) podría ser una buena solución para reducir las emisiones de CO2 del motor de combustión interna (ICE) sin poner en peligro la emisión de contaminantes. En la presente Tesis se analizaron diferentes estrategias de WHR y se concluyó que sería interesante estudiar más a fondo la máquina de ciclo Brayton. El Ciclo Brayton de Aire (ABC) permite recuperar una parte del calor de los gases de escape del ICE y transformar este calor en energía mecánica. La energía mecánica recuperada se devuelve al cigüeñal del ICE, reduciendo de ese modo la cantidad de energía que tiene que ser liberada por la combustión del combustible, lo cual permite reducir el consumo de combustible y las emisiones de CO2. En esta Tesis se estudia el ABC mediante un análisis del ciclo ideal con el fin de obtener el máximo teórico del sistema. El modelo se mejora con un análisis del ciclo semi-ideal donde se tienen en cuenta todas las pérdidas mediante el uso de dos coeficientes generales. Este análisis muestra que para el motor diesel la eficiencia del ciclo ABC es muy baja debido a la baja temperatura del gas de escape. Para el motor de gasolina el ciclo podría ser viable cuando el ICE está trabajando bajo condiciones estacionarias y una carga mayor. Estas condiciones se podrían cumplir cuando el vehículo está circulando en autopista. El análisis detallado de este ciclo tiene como objetivo determinar las pérdidas principales de ciclo. Las pérdidas principales se identificaron como: las pérdidas de bombeo, las pérdidas causadas por la transferencia de calor y las pérdidas mecánicas. Teniendo en cuenta estas pérdidas principales junto con otras pérdidas directas e indirectas, se concluyó que el ciclo no es viable para los tipos de máquinas WHR que fueron considerados en este estudio. Para que el ciclo sea viable se tiene que buscar alguna otra máquina existente o un nuevo tipo de máquina que reduzca las principales pérdidas y ofrezca un buen rendimiento isentrópico y mecánico para las condiciones deseadas. / Últimament els fabricants d'automòbils s'han posat el gran repte de reduir l'emissió de CO2 de la totalitat de les seues flotes. Les noves normatives de reducció de les emissions contaminants limiten els mitjans per assolir els objectius desitjats d'emissió de CO2 perquè algunes de les solucions que porten a la reducció en l'emissió de CO2 també donen lloc a un increment a l'emissió de altres contaminants. La recuperació de calor residual (WHR) podria ser una bona solució per reduir les emissions de CO2 del motor de combustió interna (ICE) sense posar en perill l'emissió de contaminants. En la present Tesi s'han analitzat diferents estratègies WHR i es va concloure que seria interessant estudiar més a fons el cicle Brayton. El Cicle Brayton d'Aire (ABC) representa una manera de recuperar una part de la calor dels gasos d'escapament de l'ICE i transformar calor a l'energia mecànica. L'energia mecànica recuperada es retorna al cigonyal de l'ICE reduint d'aquesta manera la quantitat d'energia que ha de ser alliberada per la combustió del combustible permitint la reducció del consum de combustible i les emissions de CO2. En aquesta Tesi s'ha començat estudiant un ABC amb una anàlisi del cicle ideal per tal d'obtenir el màxim teòric del sistema. Este model es millora amb una anàlisi del cicle semiideal on es tenen en compte totes les pèrdues amb tan sols dos coeficients d'eficiència. Aquesta anàlisi va mostrar que per al motor dièsel l'eficiència del cicle ABC és molt baixa a causa de la baixa temperatura del gas d'escapament. Per al motor de gasolina el cicle podria ser viable quan l'ICE està treballant sota condicions estacionàries i una càrrega més gran. Aquestes condicions es podrien complir quan el vehicle està circulant en autopista. L'anàlisi detallada del cicle va tenir com a objectiu determinar les pèrdues principals de cicle. Les pèrdues principals es van identificar com: les pèrdues de bombament, les pèrdues causades per la transferència de calor i les pèrdues mecàniques. Tenint en compte aquestes pèrdues principals juntament amb altres pèrdues directes i indirectes, es va concloure que el cicle no és viable per als tipus de màquines WHR que van ser considerats en aquest estudi. Perquè el cicle puga ser viable s'ha de buscar alguna altra màquina existent o un nou tipus de màquina que puga reduir les principals pèrdues i puga oferir un bon rendiment isentròpic i mecànic per a les condicions desitjades. / Kleut, P. (2016). Recuperation of the exhaust gases energy using a Brayton cycle machine [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/76807 / TESIS