1,203 research outputs found
CO<sub>2</sub> cycles
No full textCO2-based (both transcritical and supercritical) cycle systems have emerged as a promising option for power generation thanks to their robust thermodynamic performance as well as advantages offered by CO2 as a working fluid, which is nontoxic, nonflammable, and robust to decomposition at high-temperature conditions. Good thermodynamic performance in these systems is promoted by the good thermal match that can be achieved between the cycle and heat source(s), again as a consequence of the thermodynamic properties of CO2. Heat from fossil-fuel combustion as well as solar, geothermal, biomass heat and waste-heat recovery are all potential application areas for CO2 cycle systems, covering heat-source temperatures over a wide range from 300 °C to 1200 °C, with a thermodynamic efficiency of 20%–65%. When the turbine inlet temperature is ~500 °C the thermal efficiency of supercritical (s-CO2) cycle systems reaches ~30%, but a thermal efficiency of 60% can be achieved when the turbine inlet temperature reaches 1200 °C. Moreover the high density of CO2 in the supercritical region allows compact component and system design, which is particularly advantageous in space-limited applications. Although the technology has not yet been deployed widely, economic performance projections of s-CO2 cycle systems have been performed. A variety of such assessments have predicted that (1) the specific investment cost of s-CO2 cycle systems will fall in the range 900–1650 /MWh, (3) the unit cost of electricity of s-CO2 cycle systems in solar applications can reach 0.07–0.09 $/kWh, and (4) a total cost saving of up to 30% can be achieved by CO2 cycle systems relative to steam Rankine cycle systems. Research on CO2 cycle systems is extensive and spans diverse areas from component (especially turbomachine and heat exchanger) design, cycle innovation and optimization, thermodynamic and economic analyses, prototype construction, and experimental testing, all aimed at overcoming the challenges associated with high-temperature/high-pressure operation and the significant variations in the working fluid properties near the supercritical region. This chapter aims to summarize previous numerical and experimental studies on CO2 power cycle systems, present comparisons with other power generation technologies, propose future research directions, and provide valuable information and guidance for the development and demonstration of this promising technology in suitable practical applications
Innovation and advancement of thermal processes for the production, storage, utilization and conservation of energy in sustainable engineering applications
No full textThis vision article accompanies a special issue of Applied Thermal Engineering dedicated to the 16th Conference on Sustainable Development of Energy, Water and Environment Systems (SDEWES) held in Dubrovnik in 2021, and summarizes a selection of papers presented at the conference. At the focal point are a range of topics related to thermal processes as these arise in energy production, storage, utilization and conservation, covering fundamental research, the development of technical solutions for diverse sustainable engineering applications, technoeconomic analyses, and issues relating to the potential and integration of technologies from higher-level approaches. Thermal processes are the basis of numerous sustainable engineering applications and their understanding and improvement are increasingly required in the context of improved resource use efficiency and reduced environmental impact. Applications of interest include thermal systems used in buildings, thermochemical processes, seawater treatment, thermal storage solutions and renewable energy resource use. Emerging challenges in this space have given an opportunity to scientists, researchers and engineers to actively contribute to the development of relevant technological solutions, which are covered briefly in the present article
Cooling with carbon dioxide
No full textWith a growing global demand for cooling and more restrictive legislation coming into force concerning the selection of refrigerants, the refrigeration industry is looking for new alternatives. Nareshkumar Handagama, Martin White and Christos Markides discuss the role that carbon dioxide could play
Performance of working fluid mixtures in an ORC-CHP system for different heat demand segments
No full textOrganic Rankine cycle (ORC) power systems are being increasingly deployed for waste heat recovery and
conversion to power in several industrial settings. In the present paper, we investigate the deployment of
working-fluid mixtures in ORCs operating in combined heat and power mode (ORC-CHP) with shaft power
provided by the expanding working fluid and heating provided by the cooling-water exiting the ORC
condenser. Using the flue gas from a refinery boiler as the waste-heat source and with working fluids
comprising normal alkanes, refrigerants and their subsequent mixtures, the ORC-CHP system is
demonstrated as being capable of delivering over 20 MW of net shaft power and up to 15 MW of heating,
leading to a fuel energy savings ratio (FESR) in excess of 20%. Single-component working fluids such as
pentane appear to be optimal at low hot-water supply temperatures. Working-fluid mixtures become optimal
at higher temperatures, with the working-fluid mixture combination of octane and pentane giving an ORCCHP
system design with the highest efficiency. However, in most CHP applications, the fluctuation of heat
demand can determinate a discharge of heating, in particular when a waste-heat source makes profitable the
system operation also in only electricity mode, and if thermal storage options are not considered. For this
reason, the influence of heat demand intensity on the global system conversion efficiency and optimal
working fluid selection is also explored
ORC cogeneration systems in waste-heat recovery applications
No full textThe performance of organic Rankine cycle (ORC) systems operating in combined heat and power (CHP) mode is investigated. The
ORC-CHP systems recover heat from selected industrial waste-heat fluid streams with temperatures in the range 150 °C – 330 °C. An
electrical power output is provided by the expanding working fluid in the ORC turbine, while a thermal output is provided by the cooling
water exiting the ORC condenser and also by a second heat-exchanger that recovers additional thermal energy from the heat-source
stream downstream of the evaporator. The electrical and thermal energy outputs emerge as competing objectives, with the latter favoured
at higher hot-water outlet temperatures and vice versa. Pentane, hexane and R245fa result in ORC-CHP systems with the highest exergy
efficiencies over the range of waste-heat temperatures considered in this work. When maximizing the exergy efficiency, the second heatexchanger
is effective (and advantageous) only in cases with lower heat-source temperatures (< 250 °C) and high heat-delivery/demand
temperatures (> 60 °C) giving a fuel energy savings ratio (FESR) of over 40%. When maximizing the FESR, this heat exchanger is
essential to the system, satisfying 100% of the heat demand in all cases, achieving FESRs between 46% and 86%
Operational strategies for a photovoltaic-thermal system integrated with an electric air-to-water heat pump
No full textIn this study, operational strategies are investigated for an air-based photovoltaic-thermal (PV-T) system integrated with a domestic air-to-water heat pump. The PV-T system is used to simultaneously generate electricity and heat ambient air, which serves as the heat source for the heat pump. By utilising a variable-speed fan to regulate airflow, the PV-T system outlet temperature is adjusted, and the focus is on how different outlet temperatures impact the PVT system electrical and thermal efficiency, heat pump performance, and overall electricity requirements for heating. The performance of the integrated system is examined for a case study of a household application in north Italy. The optimal PV-T outlet temperature is found to be between 30 – 35 °C, resulting in only 5% less electricity production than an equivalent PV system with equal nominal electricity capacity, while reducing overall electricity required for heating by over 15% compared to PV-integrated heat pumps
Introduction: Christos Tsiolkas and Contemporary Australia — The Outsider Artist
No full textChristos Tsiolkas is regularly acknowledged as one of the most important writers working in Australia—indeed, the world—today. However, his proclivity for the public essay (in venues such as The Monthly), as well as his willingness to speak out on important social and political issues (such as refugees and marriage equality), casts him not only as an important writer, but also as a critical public figure in contemporary Australia. This collection of articles takes the range of Tsiolkas’s works (both fiction and non-fiction, as well as their television and cinematic adaptations) as their impetus, using these as a model to explore the significance of Tsiolkas’s intellectual contribution to Australian public life. As such, these articles work across genre, across theories, across national and international borders, and across disciplines in order to make clear Tsiolkas’s contemporary significance. Building on recent book-length studies on the author, including Andrew McCann’s Christos Tsiolkas and the Fiction of Critique: Politics, Obscenity, Celebrity (2015) and my own Christos Tsiolkas: The Utopian Vision (2017), what these articles hold in common is an assertion that Tsiolkas’s fiction and non-fiction always and everywhere serve a political and social purpose. As I have argued elsewhere, Tsiolkas’s writing ultimately suggests the ways in which we can shape a better future for Australia
A rational lens on prioritizing emission reductions via removal versus abatement
No full textMatthias Mersch is a postdoctoral researcher in the Clean Energy Processes (CEP) Laboratory in the Department of Chemical Engineering at Imperial College London. He holds an MSc in energy engineering from RWTH Aachen University and a PhD in chemical engineering from Imperial College London, working in collaboration with the Centre for Environmental Policy. Matthias works at the interface between detailed technology modeling and whole-energy system optimization.
Marwan Sendi is a senior engineer in the Life Cycle Assessment Group at Saudi Aramco’s Technology Strategy and Planning Department, where he focuses on technology assessment and net-zero strategy. He holds a PhD from Imperial College London, where his research centered on geospatial modeling of chemical processes and energy systems, including direct air capture systems.
Christos N. Markides is a professor of clean energy technologies and head of the Clean Energy Processes (CEP) Laboratory at Imperial College London, with an interest in the development of next-generation energy technologies and systems. He is editor-in-chief of the journal Applied Thermal Engineering and founding editor-in-chief of the journal AI Thermal Fluids. Professor Markides has authored over 400 journal articles and books.
Niall Mac Dowell is a professor of future energy systems at Imperial College London. He is a chartered engineer and is a fellow of both the Institution of Chemical Engineers and the Royal Society of Chemistry. Professor Mac Dowell has 20 years of experience in the energy transition and has published more than 200 books, papers, and technical reports on this subject. He has consulted widely for a range of public and private organizations who are active in implementing the net-zero transition
System-level techno-economic comparison of residential low-carbon heating and cooling solutions
No full textThis paper studies portfolios of electricity- and hydrogen-driven heat pumps, electricity- and hydrogen-driven boilers and thermal energy storage technologies from an energy system perspective. Thermodynamic and component-costing models of heating and cooling technologies are integrated into a whole-energy system cost optimisation model to determine configurations of heating and cooling systems that minimise the overall system cost. Case studies focus on two archetypal systems (North and South) that differ in terms of heating and cooling demand and availability profiles of solar and wind generation. Modelling results suggest that optimal capacities for heating and cooling technologies vary significantly depending on system properties. Between 83 % and 100 % of low-carbon heat is supplied by electric heat pump technologies, with the rest contributed by electric or hydrogen boilers, supplemented by heat storage. Air-to-air electric heat pumps emerge as a significant contributor to both heating and cooling, although their contribution may be constrained by the compatibility with existing heating systems and the inability to provide hot water. Nevertheless, they are found to be a useful supplementary source of space heating that can displace between 20 and 33 GWth of other heating technologies compared to the case where they do not contribute to space heating
Design and operational control strategy for optimum off-design performance of an ORC plant for low-grade waste heat recovery
No full textThe applicability of organic Rankine cycle (ORC) technology to waste heat recovery (WHR) is currently experiencing growing interest and accelerated technological development. The utilization of low-to-medium grade thermal energy sources, especially in the presence of heat source intermittency in applications where the thermal source is characterized by highly variable thermodynamic conditions, requires a control strategy for off-design operation to achieve optimal ORC power-unit performance. This paper presents a validated comprehensive model for off-design analysis of an ORC power-unit, with R236fa as the working fluid, a gear pump, and a 1.5 kW sliding vane rotary expander (SVRE) for WHR from the exhaust gases of a light-duty internal combustion engine. Model validation is performed using data from an extensive experimental campaign on both the rotary equipment (pump, expander) and the remainder components of the plant, namely the heat recovery vapor generator (HRVH), condenser, reservoirs, and piping. Based on the validated computational platform, the benefits on the ORC plant net power output and efficiency of either a variable permeability expander or of sliding vane rotary pump optimization are assessed. The novelty introduced by this optimization strategy is that the evaluations are conducted by a numerical model, which reproduces the real features of the ORC plant. This approach ensures an analysis of the whole system both from a plant and cycle point of view, catching some real aspects that are otherwise undetectable. These optimization strategies are considered as a baseline ORC plant that suffers low expander efficiency (30%) and a large parasitic pumping power, with a backwork ratio (BWR) of up to 60%. It is found that the benefits on the expander power arising from a lower permeability combined with a lower energy demand by the pump (20% of BWR) for circulation of the working fluid allows a better recovery performance for the ORC plant with respect to the baseline case. Adopting the optimization strategies, the average efficiency and maximum generated power increase from 1.5% to 3.5% and from 400 to 1100 W, respectively. These performances are in accordance with the plant efficiencies found in the experimental works in the literature, which vary between 1.6% and 6.5% for similar applications. Nonetheless, there is still room for improvement regarding a proper design of rotary machines, which can be redesigned considering the indications resulting from the developed optimization analysis
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