Experimental Analysis and Design Improvements on Combined Viper Expansion Work Recovery Turbine and Flow Phase Separation Device Applied in R410A Heat Pump

In light of recent trends towards energy efficiency and environmental consciousness, the heating, ventilation, air conditioning and refrigeration (HVAC&R) industry has been pushing for technological developments to meet both of these needs. As such, several solutions for harnessing the energy released from refrigerants during the expansion process of a conventional vapor-compression cycle have been developed to increase overall cycle efficiency. The study presented in this paper focuses on investigating the potential impact of installing an energy recovery expansion device known as the Viper Expander into an R410A heat pump. The Viper Expander operates by using a nozzle to accelerate the high pressure R410A into a high velocity jet of fluid impinging on a micro-turbine impeller. The impeller is coupled to a generator, which harvests the kinetic energy of the refrigerant by converting it into electrical energy that can be fed back into one of the system components, such as a fan or compressor motor. Previous Viper Expander iterations have not met performance expectations and thus, a major redesign was pursued. To improve the Viper Expander design, flow visualization of the two-phase refrigerant leaving the nozzle has been performed. Additionally, a housing redesign that will allow the Viper Expander to act as both an expansion work recovery device as well as a flash tank economizer has been proposed and modeled as a system solution

Two-phase flow modelling and application to high performance heat pumps

Reverse cycles allow environmental and waste heat to be converted into process heat, providing energy in an efficient and environmentally sustainable manner. Systems that perform such cycles are called heat pumps or chillers, depending on whether the useful effect sought is heating or cooling, respectively. Only the term “heat pump” will be used in this thesis, including all the useful effects they can provide. The uses of such a technology range from buildings to the process industry, and in recent years they have become technologically mature and ready for intensive use. Despite this, there are many technological difficulties in using heat pumps, especially given the stringent demands associated with reducing pollution and global warming. Modern heat pumps must be efficient, durable, use environmentally friendly fluids, and be able to integrate flexibly into complex systems, such as power plants or process industries. There is also a trend in recent years to increase the operating temperatures of heat pumps to replace the use of fossil fuels, thus electrifying thermal users. In such a framework, this thesis specifically addresses high speed two-phase flows, which may occur in heat pump cycles and which, if properly managed, may significantly contribute to enhance their performance. In particular, this thesis will mainly present modelling and experimental work about two-phase flow expansion, to recover power in place of lamination valves. Secondly, this thesis also starts the investigation of heat pump compressor surge, potentially subject to two-phase flow if spray intercooling is employed: research on this latter topic is started here but deems further investigations in the near future. In the introductory section, fundamentals of reverse cycle operation are recalled, and then the state of the art of contemporary research is reviewed. In the first part of this thesis modeling and experimental analyses regarding the use of high-speed two-phase flows within heat pumps are shown. Considering replacing common expansion valves with turbines or ejectors, it is necessary to have designer friendly models that can predict the physical characteristics of high-speed two phase flows. To begin with, a model for the analysis of two-phase supersonic nozzles is shown, demonstrating its potential for low-quality initial conditions of the refrigerant, which are not adequately studied in the open literature and are representative of the pressurized liquid downstream the heat pump condenser. After that, a novel statistical model for the analysis of maximum flow rates in supersonic nozzles is introduced, limited to CO2 as refrigerant. Maximum two-phase flow rates under sonic conditions represent a technical problem of great complexity, which is addressed here with a different approach from what is commonly shown in physical models in the open literature, since here it is devoted specifically to the preliminary design of nozzles. In the second part, experimental measurements made on a static bladeless turbine test-rig expanding two-phase flow are reported. Bladeless turbines can be a viable substitute for throttling valves, as they suffer less than conventional turbines from erosion problems due to high-speed two-phase flows. The measurements provided both qualitative results, through optical measurements, and quantitative results, through pressure measurements, with the goal of providing a validated basis for CFD models. The third part of the thesis is devoted to the experimental analysis of the stable and unstable operation of centrifugal compressors within inverse closed loops, potentially subject to two-phase flow, in terms of droplet ingestion at compressor intake, either due to spray intercooling or to liquid entrainment from the evaporator. This topic is sparsely covered in the literature, and it is of definite interest for improving the performance of heat pumps. This section is closed with a brief exposition of the ultimate future goal, which is that of two-phase compression. Finally, an example of experimental integration of a heat pump within a combined cycle is shown, this being one of the possible new applications of high performance heat pumps. The coupling between the two systems required a long work of interfacing between technologies that are well known but have quite different features and operational requirements. As concluding remark, this thesis aims to contribute to the future enhancement of heat pump performance providing the scientists with new tools and evidences for dealing with two-phase flows, both for energy harvesting in expansion as well as for compressor work reduction in compression

Study of Organic Rankine Cycles for Waste Heat Recovery in Transportation Vehicles

Regulations for ICE-based transportation in the EU seek carbon dioxide emissions lower than 95 g CO2/km by 2020. In order to fulfill these limits, improvements in vehicle fuel consumption have to be achieved. One of the main losses of ICEs happens in the exhaust line. Internal combustion engines transform chemical energy into mechanical energy through combustion; however, only about 15-32% of this energy is effectively used to produce work, while most of the fuel energy is wasted through exhaust gases and coolant. Therefore, these sources can be exploited to improve the overall efficiency of the engine. Between these sources, exhaust gases show the largest potential of Waste Heat Recovery (WHR) due to its high level of exergy. Regarding WHR technologies, Rankine cycles are considered as the most promising candidates for improving Internal Combustion Engines. However, the implementation of this technology in modern passenger cars requires additional features to achieve a compact integration and controllability in the engine. While industrial applications typically operates in steady state operating points, there is a huge challenge taking into account its impact in the engine during typical daily driving profiles. This thesis contributes to the knowledge and characterization of an Organic Rankine Cycle coupled with an Internal Combustion Engine using ethanol as working fluid and a swash-plate expander as expansion machine. The main objective of this research work is to obtain and quantify the potential of Organic Rankine Cycles for the use of residual energy in automotive engines. To do this, an experimental ORC test bench was designed and built at CMT (Polytechnic University of Valencia), which can be coupled to different types of automotive combustion engines. Using these results, an estimation of the main variables of the cycle was obtained both in stationary and transient operating points. A potential of increasing ICE mechanical efficiency up to 3.7% could be reached at points of high load installing an ORC in a conventional turbocharged gasoline engine. Regarding transient conditions, a slightly simple and robust control based on adaptive PIDs, allows the control of the ORC in realistic driving profiles. High loads and hot conditions should be the starting ideal conditions to test and validate the control of the ORC in order to achieve high exhaust temperatures that justify the feasibility of the system. In order to deepen in the viability and characteristics of this particular application, some theoretical studies were done. A 1D model was developed using LMS Imagine.Lab Amesim platform. A potential improvement of 2.5% in fuel conversion efficiency was obtained at the high operating points as a direct consequence of the 23.5 g/kWh reduction in bsfc. To conclude, a thermo-economic study was developed taking into account the main elements of the installation costs and a minimum Specific Investment Cost value of 2030 €/kW was obtained. Moreover, an exergetic study showed that a total amount of 3.75 kW, 36.5% of exergy destruction rate, could be lowered in the forthcoming years, taking account the maximum efficiencies considering technical restrictions of the cycle components.Las normativas anticontaminantes para el transporte propulsado por motores de combustión interna alternativos en la Unión Europea muestran límites de emisión menores a 95 g CO2/km para el año 2020. Con el fin de cumplir estos límites, deberán ser realizadas mejoras en el consumo de combustible en los vehículos. Una de las principales pérdidas en los Motores de Combustión Interna Alternativos (MCIA) ocurre en la línea de escape. Los MCIA transforman la energía química en energía mecánica a través de la combustión; sin embargo, únicamente el 15-32% de esta energía es eficazmente usada para producir trabajo, mientras que la mayor parte es desperdiciada a través de los gases de escape y el agua de refrigeración del motor. Por ello, estas fuentes de energía pueden ser utilizadas para mejorar la eficiencia global del vehículo. De estas fuentes, los gases de escape muestran un potencial mayor de recuperación de energía residual debido a su mayor contenido exergético. De todos los tipos de Sistemas de Recuperación de Energía Residual, los Ciclos Rankine son considerados como los candidatos más prometedores para mejorar la eficiencia de los MCIA. Sin embargo, la implementación de esta tecnología en los vehículos de pasajeros modernos requiere nuevas características para conseguir una integración compacta y una buena controlabilidad del motor. Mientras que las aplicaciones industriales normalmente operan en puntos de operación estacionarios, en el caso de los vehículos con MCIA existen importantes retos teniendo en cuenta su impacto en el modo de conducción cotidianos. Esta Tesis contribuye al conocimiento y caracterización de un Ciclo Rankine Orgánico acoplado con un Motor de Combustión Interna Alternativo utilizando etanol como fluido de trabajo y un expansor tipo Swash-plate como máquina expansora. El principal objetivo de este trabajo de investigación es obtener y cuantificar el potencial de los Ciclos Rankine Orgánicos (ORC) para la recuperación de la energía residual en motores de automoción. Para ello, una instalación experimental con un Ciclo Rankine Orgánico fue diseñada y construida en el Instituto Universitario "CMT - Motores Térmicos" (Universidad Politécnica de Valencia), que puede ser acoplada a diferentes tipos de motores de combustión interna alternativos. Usando esta instalación, una estimación de las principales variables del ciclo fue obtenida tanto en puntos estacionarios como en transitorios. Un potencial de mejora en torno a un 3.7 % puede ser alcanzada en puntos de alta carga instalando un ORC en un motor gasolina turboalimentado. Respecto a las condiciones transitorias, un control sencillo y robusto basado en PIDs adaptativos permite el control del ORC en perfiles de conducción reales. Las condiciones ideales para testear y validar el control del ORC son alta carga en el motor comenzando con el motor en caliente para conseguir altas temperaturas en el escape que justifiquen la viabilidad de estos ciclos. Para tratar de profundizar en la viabilidad y características de esta aplicación particular, diversos estudios teóricos fueron realizados. Un modelo 1D fue desarrollado usando el software LMS Imagine.Lab Amesim. Un potencial de mejora en torno a un 2.5% en el rendimiento efectivo del motor fue obtenido en condiciones transitorias en los puntos de alta carga como una consecuencia directa de la reducción de 23.5 g/kWh del consumo específico. Para concluir, un estudio termo-económico fue desarrollado teniendo en cuenta los costes de los principales elementos de la instalación y un valor mínimo de 2030 €/kW fue obtenido en el parámetro de Coste Específico de inversión. Además, el estudio exergético muestra que un total de 3.75 kW, 36.5 % de la tasa de destrucción total de exergía, podría ser reducida en los años futuros, teniendo en cuenta las máximas eficiencias considerando restricciones técnicas en los componentes del ciclo.Les normatives anticontaminants per al transport propulsat per motors de combustió interna alternatius a la Unió Europea mostren límits d'emissió menors a 95 g·CO2/km per a l'any 2020. Per tal d'acomplir aquests límits, s'hauran de realitzar millores al consum de combustible dels vehicles. Una de les principals pèrdues als Motors de combustió interna alternatius (MCIA) ocorre a la línia d'escapament. Els MCIA transformen l'energia química en energia mecànica a través de la combustió; però, únicament el 15-32% d'aquesta energia és usada per produir treball, mentre que la major part és desaprofitada a través dels gasos d'escapament i l'aigua de refrigeració del motor. Per això, aquestes fonts d'energia poden ser utilitzades per millorar l'eficiència global del vehicle. Considerant aquestes dues fonts d'energia, els gasos d'escapament mostren un potencial major de recuperació d'energia residual debut al seu major contingut exergètic. De tots els tipus de Sistemes de Recuperació d'Energia Residual, els Cicles Rankine són considerats com els candidats més prometedors per millorar l'eficiència dels MCIA. No obstant, la implementació d'aquesta tecnologia en els vehicles de passatgers moderns requereix un desenvolupament addicional per aconseguir una integració compacta i una bona controlabilitat del motor. Mentre que les aplicacions industrials normalment operen en punts d'operació estacionaris, en el cas dels vehicles amb MCIA hi han importants reptes a solucionar tenint en compte el funcionament en condicions variables del motor i el seu impacte en la manera de conducció quotidiana del usuari. Aquesta Tesi contribueix al coneixement i caracterització d'un Cicle Rankine Orgànic (ORC) acoblat amb un motor de combustió interna alternatiu (MCIA) utilitzant etanol com a fluid de treball i un expansor tipus Swash-plate com a màquina expansora. El principal objectiu d'aquest treball de recerca és obtenir i quantificar el potencial dels ORCs per a la recuperació de l'energia residual en motors d'automoció. Per aconseguir-ho, una instal·lació experimental amb un ORC va ser dissenyada i construïda a l'Institut "CMT- Motores Térmicos" (Universitat Politècnica de València). Esta installació pot ser acoblada a diferents tipus de MCIAs. Mitjançant assajos experimentals en aquesta installació, una estimació de les principals variables del cicle va ser obtinguda tant en punts estacionaris com en punts transitoris. Un potencial de millora al voltant d'un 3.7% pot ser aconseguida en punts d'alta càrrega instal·lant un ORC acoblat a un motor gasolina turboalimentat. Pel que fa a les condicions transitòries, un control senzill i robust basat en PIDs adaptatius permet el control del ORC en perfils de conducció reals. Les condicions ideals per a testejar i validar el control de l'ORC són alta càrrega al motor començant amb el motor en calent per aconseguir altes temperatures d'escapament que justifiquen la viabilitat d'aquests cicles. Per tractar d'aprofundir en la viabilitat i característiques d'aquesta aplicació particular, diversos estudis teòrics van ser realitzats. Un model 1D va ser desenvolupat usant el programari LMS Imagine.Lab Amesim. Un potencial de millora al voltant d'un 2.5% en el rendiment efectiu del motor va ser obtingut en condicions transitòries en els punts d'alta càrrega com una conseqüència directa de la reducció de 23.5 g/kWh al consum específic. Per concloure, un estudi termo-econòmic va ser desenvolupat tenint en compte els costos dels principals elements de la installació i un valor mínim de 2030 €/kW va ser obtingut en el paràmetre del Cost Específic d'Inversió. A més, l'estudi exergètic mostra que un total de 3.75 kW, 36.5% de la taxa de destrucció total d'exergia, podria ser recuperat en un pròxim, considerant restriccions tècniques en els components del cicle i tenint en compte les màximes eficiències que es poden aconseguir.Royo Pascual, L. (2017). Study of Organic Rankine Cycles for Waste Heat Recovery in Transportation Vehicles [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/84013TESI

performances of an orc power unit for waste heat recovery on heavy duty engine

Abstract Reciprocating internal combustion engines (ICE) are still the most used in the sector of the on-the-road transportation, both for passengers and freight. CO2 reduction is the actual technological driver, considering the worldwide greenhouse reduction targets committed by most governments. In ICE more than one third of the fuel energy used is rejected to the environment as thermal waste through the exhaust gases. Therefore, a greater fuel economy could be achieved, if this energy was recovered and converted into useful mechanical or electrical power. This recovery appears very interesting, in particular for those engines that run at almost steady working conditions, like marine, agricultural, industrial or long-hauling vehicle applications. In this paper, an ORC-based power unit was tested on a heavy duty diesel engine. Energetic and exergetic analyses have been carried out in order to assess the real performances of the ORC unit and to individuate differences with the theoretical ones. A single stage impulse axial turbine has been tested in this work, complete with an electric variable speed generator and an AC/DC converter. The tests demonstrated that the energy conversion chain is not negligible at all and an overall net efficiency of the power unit was around 2-3 % with respect to a 10% of thermodynamic efficiency

Performance evaluation of organic Rankine cycle architectures : application to waste heat valorisation

In our society, there is an ever increasing need for electricity. However, today most of the electricity is generated by burning fossil fuels in a thermal power plant. A proposed alternative is to make use of low temperature heat from renewable sources (geothermal and solar) or waste heat (excess heat that is dumped into the atmosphere) in an organic Rankine cycle (ORC) to generate electricity. The purpose of the presented work is to support further adoption of ORC technology. To achieve this, two main challenges need to be resolved. First, sound criteria should be devised to compare and size ORCs and secondly the performance of the ORC should be increased further. From literature it is clear that novel ORC architectures have the opportunity to increase the performance of the basic subcritical ORC. However these studies are not cross comparable. As such, a new screening approach is created which rigorously compares and quantifies the potential of three different ORC architectures. Secondly, the sizing and the financial appraisal of the ORC is tackled by introducing a multi-objective optimization which combines financial and thermodynamic criteria in the optimization objectives. Finally, experimentally validated part-load models of the ORC were developed. These part-load models are crucial to predict the actual power output of time varying heat sources like waste heat streams. In addition, the models permit to investigate the concept of retrofitting existing subcritical ORCs to work under the more optimal working regime of partial evaporation

Conversion of a scroll compressor to an expander for organic Rankine cycle: modeling and analysis

Conversion of a scroll compressor to an expander for organic Rankine Cycle: modeling and analysi

Design and Algorithm-based optimisation of Axial ORC turbine and transient cycles incorporating novel machine Learning tools

The flue gas stacks of industrial steam boilers can be considered an untapped waste heat source, which is characterised as highly intermittent. Although Organic Rankine Cycles pose strong potential to reuse such low-grade heat, the component and system levels analysis of ORCs to efficiently utilise these highly intermittent heat sources in a techno-economic fashion is still an unanswered research question. Such a holistic approach ultimately expedites the commercial adoption of ORCs to utilise a broader range of waste heat sources achieving the highest possible techno-economic benefits. To answer this research question, emphasising scale ORCs that employ axial flow turbines owing to their scalability and superior isentropic efficiency, this thesis undertakes turbine and cycle configuration optimisation by integrating the Craig and Cox loss model to simulate a small-scale axial flow ORC turbine. The transient waste heat of an actual industrial steam boiler stack was employed as a heat source to investigate ten novel cycle configurations. The optimisation was undertaken using parametric, metaheuristic (nature-inspired) and mathematics-based optimisers. Artificial Neural Networks (ANNs) and genetic algorithms (GAs)-based on the loss model led to an optimised turbine configuration that improved turbine total-to-static efficiency and cycle efficiency by 5.2% and 0.24%, respectively. The recuperative cycle proved the optimal thermodynamic configuration, with a 26.5% increase in mean power generation. Furthermore, a multi-objective analysis revealed the recuperative cycle integrated with an air preheater as the optimum thermo-economic configuration, with a 48.9% improvement in the combined overall value of the multiple objectives, including the Specific Investment Cost and mean power, achieving the final payback within 1.72 years. The ideal configuration was observed as a strong function of the Levelized cost of fuel and electricity prices. Application of a mathematical technique based on the non-linear programming by quadratic Lagrangian algorithm was validated for single- and multi-objective cycle configuration optimisations, providing results comparable to the well-established metaheuristic-based genetic algorithm, with a computational efficiency of greater than one order of magnitude. The overall approach of the direct loss model, artificial neural network- and genetic algorithm-based turbine optimisation, parametric cycle pre-optimisation, mathematical technique-based component optimisation and payback evaluation can be considered a blueprint for the future evaluation and design of organic Rankine cycles utilising transient waste heat sources