Imperial College London

ProfessorChristosMarkides

Faculty of EngineeringDepartment of Chemical Engineering

Professor of Clean Energy Technologies
 
 
 
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Contact

 

+44 (0)20 7594 1601c.markides Website

 
 
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Location

 

404ACE ExtensionSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

275 results found

Pantaleo AM, markides C, fordham J, Oyewunmiet al., 2017, Intermittent waste heat recovery: Investment profitability of ORC cogeneration for batch, gas-fired coffee roasting, ICAE 2017, Publisher: Elsevier, Pages: 575-582, ISSN: 1876-6102

Coffee roasting is a highly energy intensive process with much of the energy being lost in intermittent cycles as discharged heatfrom the stack. In this work, combined heat and power (CHP) systems based on micro gas-turbines (MGT) are investigated forproviding heat to the roasting process. Much of the heat released in a coffee roaster is from the afterburner that heats up the fluegases to high temperatures in order to remove volatile organic compounds (VOCs) and other pollutants. An interesting solutionfor utilizing waste heat is assessed through energy and material balances of a rotating drum coffee roasting with partial hot gasrecycling. A cost assessment methodology is adopted to compare the profitability of three proposed system configurationsintegrated into the process. The case study of a major coffee torrefaction plant with 500 kg/h production capacity is assumed tocarry out the thermo-economic assessment, under the Italian energy framework. The CHP options under investigation are:(i) regenerative topping MGT coupled to the existing modulating gas burner to generate hot air for the roasting process;(ii) intermittent waste-heat recovery from the hot flue-gases through an organic Rankine cycle (ORC) engine coupled to athermal storage buffer; and (iii) non-regenerative topping MGT with direct recovery of turbine outlet air for the roasting processby means of an afterburner that modulates the heat demand of the roasting process. The results show that the profitability of theseinvestments is highly influenced by the natural gas/electricity cost ratio, by the coffee torrefaction production capacity and by theintermittency level of discharged heat. The MGT appears as a more profitable option than waste-heat recovery via the ORCengine due to the intermittency of the heat source and the relatively high electricity/heat cost ratio.

Conference paper

Pantaleo AM, markides, Oyewunmi, Chatzopoulou, white M, haslamet al., 2017, Integrated computer-aided working-fluid design and thermoeconomic ORC system optimisation, ORC-2017, Publisher: Elsevier, Pages: 152-159, ISSN: 1876-6102

The successful commercialisation of organic Rankine cycle (ORC) systems across a range of power outputs and heat-source temperatures demands step-changes in both improved thermodynamic performance and reduced investment costs. The former can be achieved through high-performance components and optimised system architectures operating with novel working-fluids, whilst the latter requires careful component-technology selection, economies of scale, learning curves and a proper selection of materials and cycle configurations. In this context, thermoeconomic optimisation of the whole power-system should be completed aimed at maximising profitability. This paper couples the computer-aided molecular design (CAMD) of the working-fluid with ORC thermodynamic models, including recuperated and other alternative (e.g., partial evaporation or trilateral) cycles, and a thermoeconomic system assessment. The developed CAMD-ORC framework integrates an advanced molecular-based group-contribution equation of state, SAFT-γ Mie, with a thermodynamic description of the system, and is capable of simultaneously optimising the working-fluid structure, and the thermodynamic system. The advantage of the proposed CAMD-ORC methodology is that it removes subjective and pre-emptive screening criteria that would otherwise exist in conventional working-fluid selection studies. The framework is used to optimise hydrocarbon working-fluids for three different heat sources (150, 250 and 350 °C, each with mcp = 4.2 kW/K). In each case, the optimal combination of working-fluid and ORC system architecture is identified, and system investment costs are evaluated through component sizing models. It is observed that optimal working fluids that minimise the specific investment cost (SIC) are not the same as those that maximise power output. For the three heat sources the optimal working-fluids that minimise the SIC are isobutane, 2-pentene and 2-heptene, with SICs of 4.03, 2.22 and 1.84 £/W res

Conference paper

Georgiou S, Acha Izquierdo S, Shah N, Markides Cet al., 2017, Assessing, benchmarking and analyzing heating and cooling requirements for glasshouse food production: a design and operation modelling framework, 1st International Conference on Sustainable Energy and Resource Use in Food Chains, ICSEF 2017, Publisher: Elsevier, Pages: 164-172, ISSN: 1876-6102

Growing populations, increase in food demand, society’s expectations for out of season products and the dependency of the food system on fossil fuels stress resources due to the requirements for national production and from importation of products from remote origins. Quantifying the use of resources in food production and their environmental impacts is key to identifying distinctive measures which can develop pathways towards low carbon food systems. In this paper, a modelling approach is presented which can quantify the energy requirements of heated glasshouse food production. Based on the outputs from the model, benchmarking and comparison among different glasshouse types and growers is possible. Additionally, the effect of spatial and annual weather trends on the heating and cooling requirements of glasshouses are quantified. Case study results indicate that a reduction in heating requirements of about 50%, and therefore an equivalent carbon footprint reduction, can be achieved by replacing a single glass sealed cover with a double glass sealed cover.

Conference paper

Oyewunmi OA, Lecompte S, De Paepe M, Markides CNet al., 2017, Thermoeconomic analysis of recuperative sub- and transcritical organic Rankine cycle systems, 4th International Seminar on ORC Power Systems, Publisher: Elsevier, Pages: 58-65, ISSN: 1876-6102

There is significant interest in the deployment of organic Rankine cycle (ORC) technology for waste-heat recovery and power generation in industrial settings. This study considers ORC systems optimized for maximum power generation using a case study of an exhaust flue-gas stream at a temperature of 380°C as the heat source, covering over 35 working fluids and also considering the option of featuring a recuperator. Systems based on transcritical cycles are found to deliver higher power outputs than subcritical ones, with optimal evaporation pressures that are 4-5 times the critical pressures of refrigerants and light hydrocarbons, and 1-2 times those of siloxanes and heavy hydrocarbons. For maximum power production, a recuperator is necessary for ORC systems with constraints imposed on their evaporation and condensation pressures. This includes, for example, limiting the minimum condensation pressure to atmospheric pressure to prevent sub-atmospheric operation of this component, as is the case when employing heavy hydrocarbon and siloxane working fluids. For scenarios where such operating constraints are relaxed, the optimal cycles do not feature a recuperator, with some systems showing more than three times the generated power than with this component, albeit at higher investment costs.

Conference paper

Unamba CK, White M, Sapin P, Freeman J, Lecompte S, Oyewunmi OA, Markides CNet al., 2017, Experimental investigation of the operating point of a 1-kW ORC system, 4th International Seminar on ORC Power Systems (ORC), Publisher: Elsevier Science BV, Pages: 875-882, ISSN: 1876-6102

The organic Rankine cycle (ORC) is a promising technology for the conversion of waste heat from industrial processes as well as heat from renewable sources. Many efforts have been channeled towards maximizing the thermodynamic potential of ORC systems through the selection of working fluids and the optimal choice of operating parameters with the aim of improving overall system designs, and the selection and further development of key components. Nevertheless, experimental work has typically lagged behind modelling efforts. In this paper, we present results from tests on a small-scale (1 kWel) ORC engine consisting of a rotary-vane pump, a brazed-plate evaporator and a brazed-plate condenser, a scroll expander with a built-in volume ratio of 3.5, and using R245fa as the working fluid. An electric oil-heater acted as the heat source, providing hot oil at temperatures in the range 120-140 °C. The frequency of the expander was not imposed by an inverter or the electricity grid but depended directly on the attached generator load; both the electrical load on the generator and the pump rotational speed were varied in order to investigate the performance of the system. Based on the generated data, this paper explores the relationship between the operating conditions of the ORC engine and changes in the heat-source temperature, pump and expander speeds leading to working fluid flow rates between 0.0088 kg/s and 0.0337 kg/s, from which performance maps are derived. The experimental data is, in turn, used to assess the performance of both the individual components and of the system, with the help of an exergy analysis. In particular, the exergy analysis indicates that the expander accounts for the second highest loss in the system. Analysis of the results suggests that increased heat-source temperatures, working-fluid flow rates, higher pressure ratios and larger generator loads improve the overall cycle efficiency. Specifically, a 46% increase in pressure ratio from 2.4

Conference paper

Markides C, Charogiannis A, 2017, Application of planar laser-induced fluorescence for the investigation of interfacial waves and rivulet structures in liquid films flowing down inverted substrates, Interfacial phenomena and heat transfer, Vol: 4, Pages: 235-252, ISSN: 2169-2785

We investigate the interfacial topology of liquid-film flows falling under an inverted planarsubstrate by conducting space- and time-resolved film-height measurements. A planarlaser-induced fluorescence (PLIF) technique is employed for this purpose, with a twocameraarrangement that allows us to image a region of the flow extending ≈ 40 mm oneither side of the centre of the film span, at a distance 330 mm downstream of the flowinlet. The substrate inclination angle is set to β = −30 °, the working fluid comprises 82%glycerol and 18% water (by weight), and the flow Reynolds number, Re, is varied in therange Re = 0.6 − 8.2. The uncertainty associated with the instantaneous film-height measurementis estimated at less than 3%. Depending on the flow Re, we observe a range ofinteresting flow regimes typically characterised by pronounced rivulet formation and spatiotemporalcoherence, which deviate from expectations of liquid-films flows falling overplanar substrates. Over the range Re = 0.6 − 3.5, a series of regime transitions take place,followed by the generation of regular, in both space and time, 3-D solitary pulses ‘riding’over rivulet flow structures. These waves grow with increasing flow Re, as more liquidis drawn away from the rivulet troughs due to gravity. Finally, the wave frequencies andrivulet wavelengths are investigated by employment of power spectral density (PSD) andwavelet analyses. The application of PSD analysis offers superior resolution in the frequencydomain when performed on temporally varying film-height data, whereas waveletanalysis is preferred when considering the spatially varying film-height data due to thelimited spatial extent and low number of captured rivulets in the imaged region.

Journal article

Acha Izquierdo S, lambert R, Shah N, Markides C, delangle Aet al., 2017, Modelling and optimising the marginal expansion of an existing district heating network, Energy, Vol: 140, Pages: 209-223, ISSN: 0360-5442

Although district heating networks have a key role to play in tackling greenhouse gas emissions associated with urban energy systems, little work has been carried out on district heating networks expansion in the literature. The present article develops a methodology to find the best district heating network expansion strategy under a set of given constraints. Using a mixed-integer linear programming approach, the model developed optimises the future energy centre operation by selecting the best mix of technologies to achieve a given purpose (e.g. cost savings maximisation or greenhouse gas emissions minimisation). Spatial expansion features are also considered in the methodology.Applied to a case study, the model demonstrates that depending on the optimisation performed, some building connection strategies have to be prioritised. Outputs also prove that district heating schemes' financial viability may be affected by the connection scenario chosen, highlighting the necessity of planning strategies for district heating networks. The proposed approach is highly flexible as it can be adapted to other district heating network schemes and modified to integrate more aspects and constraints.

Journal article

Wright SF, Zadrazil I, Markides CN, 2017, A review of solid–fluid selection options for optical-based measurements in single-phase liquid, two-phase liquid–liquid and multiphase solid–liquid flows, Experiments in Fluids, Vol: 58, ISSN: 1432-1114

Experimental techniques based on optical measurement principles have experienced significant growth in recent decades. They are able to provide detailed information with high-spatiotemporal resolution on important scalar (e.g., temperature, concentration, and phase) and vector (e.g., velocity) fields in single-phase or multiphase flows, as well as interfacial characteristics in the latter, which has been instrumental to step-changes in our fundamental understanding of these flows, and the development and validation of advanced models with ever-improving predictive accuracy and reliability. Relevant techniques rely upon well-established optical methods such as direct photography, laser-induced fluorescence, laser Doppler velocimetry/phase Doppler anemometry, particle image/tracking velocimetry, and variants thereof. The accuracy of the resulting data depends on numerous factors including, importantly, the refractive indices of the solids and liquids used. The best results are obtained when the observational materials have closely matched refractive indices, including test-section walls, liquid phases, and any suspended particles. This paper reviews solid–liquid and solid–liquid–liquid refractive-index-matched systems employed in different fields, e.g., multiphase flows, turbomachinery, bio-fluid flows, with an emphasis on liquid–liquid systems. The refractive indices of various aqueous and organic phases found in the literature span the range 1.330–1.620 and 1.251–1.637, respectively, allowing the identification of appropriate combinations to match selected transparent or translucent plastics/polymers, glasses, or custom materials in single-phase liquid or multiphase liquid–liquid flow systems. In addition, the refractive indices of fluids can be further tuned with the use of additives, which also allows for the matching of important flow similarity parameters such as density and viscosity.

Journal article

Pantaleo, Fordham J, Oyewunmi OA, Markideset al., Optimal sizing and operation of on-site combined heat and power systems for intermittent waste-heat recovery, 9th International Conference on Applied Energy (ICAE2017), Publisher: Elsevier, ISSN: 1876-6102

Coffee roasting is a highly energy intensive process with much of the energy being lost in intermittent cycles as discharged heatfrom the stack. In this work, combined heat and power (CHP) systems based on micro gas-turbines (MGT) are investigated forproviding heat to the roasting process. Much of the heat released in a coffee roaster is from the afterburner that heats up the fluegases to high temperatures in order to remove volatile organic compounds (VOCs) and other pollutants. An interesting solutionfor utilizing waste heat is assessed through energy and material balances of a rotating drum coffee roasting with partial hot gasrecycling. A cost assessment methodology is adopted to compare the profitability of three proposed system configurationsintegrated into the process. The case study of a major coffee torrefaction plant with 500 kg/h production capacity is assumed tocarry out the thermo-economic assessment, under the Italian energy framework. The CHP options under investigation are:(i) regenerative topping MGT coupled to the existing modulating gas burner to generate hot air for the roasting process;(ii) intermittent waste-heat recovery from the hot flue-gases through an organic Rankine cycle (ORC) engine coupled to athermal storage buffer; and (iii) non-regenerative topping MGT with direct recovery of turbine outlet air for the roasting processby means of an afterburner that modulates the heat demand of the roasting process. The results show that the profitability of theseinvestments is highly influenced by the natural gas/electricity cost ratio, by the coffee torrefaction production capacity and by theintermittency level of discharged heat. The MGT appears as a more profitable option than waste-heat recovery via the ORCengine due to the intermittency of the heat source and the relatively high electricity/heat cost ratio.

Conference paper

Freeman J, Guarracino I, Kalogirou SA, Markides CNet al., 2017, A small-scale solar organic Rankine cycle combined heat and power system with integrated thermal-energy storage, Heat Powered Cycles Conference 2016, Publisher: Elsevier, Pages: 1543-1554, ISSN: 1873-5606

In this paper, we examine integrated thermal energy storage (TES) solutions for a domestic-scale solar combined heat and power (S-CHP) system based on an organic Rankine cycle (ORC) engine and low-cost non-concentrating solar-thermal collectors. TES is a critical element of solar-thermal systems. It can allow, depending on how it is implemented, improved matching to the end-user demands, improved load factors, higher average efficiencies and overall performance, as well as reduced component and system sizes and costs, especially in climates with high solar-irradiance variabilities. The operating temperature range of the TES solution must be compatible with the solar-collector array and with the ORC engine operation in order to maximise the overall performance of the system. Various combinations of phase change materials (PCMs) and solar collectors are compared and the S-CHP system's electrical performance is simulated for selected months in the contrasting climates of Cyprus and the UK. The key performance indicator of the ORC engine (net-work output) and the required TES volume are compared and discussed. The PCM-TES solutions that enable the best summer performance from an ORC engine sized for a nominal ~1-kWe output in combination with a 15-m2 solar collector array result in diurnal volume requirements as low as ~100 L in Cyprus and 400 - 500 L in the UK. However, the required TES volume is strongly in influenced by the choice of operational strategy for the system in order to match the domestic load profiles. In a full-storage strategy in which electrical energy generation from the ORC engine is offset to match the week-day evening peak in demand, it is found that a ~20% higher total daily electrical output per unit storage volume can be achieved with a PCM compared to liquid water as a sensible storage medium. The isothermal operation of the PCM during phase-change allows for a smaller diurnal storage temperature swing and a higher energy conversion efficiency

Conference paper

Oyewunmi OA, Kirmse CJW, Pantaleo AM, Markides CNet al., 2017, Performance of working-fluid mixtures in ORC-CHP systems for different heat-demand segments and heat-recovery temperature levels, Energy Conversion and Management, Vol: 148, Pages: 1508-1524, ISSN: 0196-8904

In this paper, we investigate the adoption of working-fluid mixtures in ORC systems operating in combined heat and power (CHP) mode, with a power output provided by the expanding working fluid in the ORC turbine and a thermal energy output provided by the cooling water exiting (as a hot-water supply) the ORC condenser. We present a methodology for selecting optimal working-fluids in ORC systems with optimal CHP heat-to-electricity ratio and heat-supply temperature settings to match the seasonal variation in heat demand (temperature and intermittency of the load) of different end-users. A number of representative industrial waste-heat sources are considered by varying the ORC heat-source temperature over the range 150–330 °C. It is found that, a higher hot-water outlet temperature increases the exergy of the heat-sink stream but decreases the power output of the expander. Conversely, a low outlet temperature (~30 °C) allows for a high power-output, but a low cooling-stream exergy and hence a low potential to heat buildings or to cover other industrial thermal-energy demands. The results demonstrate that the optimal ORC shaft-power outputs vary considerably, from 9 MW up to 26 MW, while up to 10 MW of heating exergy is provided, with fuel savings in excess of 10%. It also emerges that single-component working fluids such as n-pentane appear to be optimal for fulfilling low-temperature heat demands, while working-fluid mixtures become optimal at higher heat-demand temperatures. In particular, the working-fluid mixture of 70% n-octane + 30% n-pentane results in an ORC-CHP system with the highest ORC exergy efficiency of 63% when utilizing 330 °C waste heat and delivering 90 °C hot water. The results of this research indicate that, when optimizing the global performance of ORC-CHP systems fed by industrial waste-heat sources, the temperature and load pattern of the cogenerated heat demand are crucial factors affecting the selection of the working fl

Journal article

Simpson M, Rotolo G, Sapin P, De Palma P, White AJ, Markides CNet al., 2017, Thermodynamic performance maps of reciprocating-piston expanders for operation at off-design and part-load conditions, 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Publisher: ICHMT

Renewable energy sources, such as solar-thermal or geothermal heat, and low-/medium-grade industrial waste-heat can be converted into useful power and/or heating with a variety of technologies, including organic Rankine cycle (ORC) and vapour-compression heat-pump systems. The thermodynamic performance and cost of these technologies depends crucially on the efficiency of key components, including the compressor or expander used. Reciprocating-piston machines can be advantageous over turbomachines and other positive-displacement machines at intermediate scales (~10s-100s of kW) thanks to their ability to operate with relatively high isentropic efficiencies at large expansion ratios. However, modelling the thermodynamic losses in reciprocating-piston expanders, with a view towards designing high-performance machines, is a complex undertaking. The aim of this paper is to develop a spatially-lumped, yet dynamic model of a piston expander suitable for early-stage engineering design, that can provide simplification without sacrificing accuracy. The unsteady heat transfer between the gas and the cylinder walls, and the mass leakage are predicted independently with correlations available in the literature and simplified one-dimensional models, respectively. However, the turbulence induced by the mass intake through the piston rings can affect the gas-to-wall heat transfer. In order to address this dependency two complementary approaches are used. Compression and expansion processes are simulated in a gas spring configuration (i.e. without valve systems) using a computational fluid dynamics (CFD) model developed using the open-source code OpenFOAM, where the loss mechanisms are solved directly. The results are then compared with predictions from the heuristic lumped model based on heat tr

Conference paper

Najjaran Kheirabadi A, Freeman J, Ramos Cabal A, Markides Cet al., EXPERIMENTAL PERFORMANCE ANALYSIS OF AN AMMONIA-WATER DIFFUSION ABSORPTION REFRIGERATION CYCLE, ASME 2017 Summer Heat Transfer Conference

Conference paper

Oyewunmi OA, Pantaleo AM, markides CN, ORC cogeneration systems in waste-heat recovery applications, 9th International Conference on Applied Energy (ICAE2017), Publisher: Elsevier, ISSN: 1876-6102

The performance of organic Rankine cycle (ORC) systems operating in combined heat and power (CHP) mode is investigated. TheORC-CHP systems recover heat from selected industrial waste-heat fluid streams with temperatures in the range 150 °C – 330 °C. Anelectrical power output is provided by the expanding working fluid in the ORC turbine, while a thermal output is provided by the coolingwater exiting the ORC condenser and also by a second heat-exchanger that recovers additional thermal energy from the heat-sourcestream downstream of the evaporator. The electrical and thermal energy outputs emerge as competing objectives, with the latter favouredat higher hot-water outlet temperatures and vice versa. Pentane, hexane and R245fa result in ORC-CHP systems with the highest exergyefficiencies over the range of waste-heat temperatures considered in this work. When maximizing the exergy efficiency, the second heatexchangeris effective (and advantageous) only in cases with lower heat-source temperatures (< 250 °C) and high heat-delivery/demandtemperatures (> 60 °C) giving a fuel energy savings ratio (FESR) of over 40%. When maximizing the FESR, this heat exchanger isessential to the system, satisfying 100% of the heat demand in all cases, achieving FESRs between 46% and 86%.

Conference paper

Sapin PMC, Simpson M, White AJ, Markides Cet al., 2017, Lumped dynamic analysis and design of a high-performance reciprocating-piston expander, 30th International Conference on Efficiency, Cost, Optimisation, Simulation and Environmental Impact of Energy Systems., Publisher: ECOS

A spatially-lumped dynamic model of a reciprocating-piston expander is presented in this paper. The model accounts for the three main loss mechanisms in realistic piston machines, namely: pressure losses through the intake and exhaust valves, heat transfer between the gas and the surrounding cylinder walls, and the mass leakagebetween the compression/expansion chamber and the crankcasethrough the piston rings. The model also accounts for real-gas effects with the fluid properties calculated from the NIST database using REFPROP. The numerical calculations are first compared with experimental pressure-volume-temperature data obtained on a custom reciprocating-piston gas spring over a range of oscillation frequencies. The comparison between numerical and experimental results shows good agreement. It also allows the most accurate heat transfer correlationto be selectedfor calculating the gas-to-wallin-cylinderheat transfer. The semi-heuristic modelling tool is thenused to design an expander forspecific pressure ratiosand mass flowrate, and to predict the thermodynamic performance of the piston device over arange of part-load conditions.

Conference paper

Chatzopoulou MA, Markides CN, 2017, Advancements in organic Rankine cycle system optimisation for combined heat and power applications: components sizing and thermoeconomic considerations, 30th International Conference on Efficiency, Cost, Optimisation, Simulation and Environmental Impact of Energy Systems, Publisher: ECOS

There is great interest in distributed combined heat and power (CHP) generation in the built environment due to the higher overall efficienciesattained in comparison to separate provision of these vectors. Organic Rankine cycle (ORC) systems are capable of generating additional electricity from the thermal outputs of CHP engines, improving the electrical conversion efficiency and power-to-heat ratio of suchsystems. Thermodynamic analysis and technical feasibility are at the core of the development of these systems, whilea critical factor for the wider adoption of ORC systems concerns their economic proposition. Obtainingcredible estimates of system costs requires correct sizing of individual components. This work focuses on the thermodynamic optimisation, sizing and costing of ORC units in CHP applications, over a range of heat-source temperatures. The working fluids examined include R245fa, R1233zd, Pentane and Hexane, due to their good performance and favourable environmental characteristics. The optimalcycles obtained can increase the power-to-heat ratio of the complete CHP-ORCsystem by up to 65%.Alternative equipment sizing methods are then applied for each fluid and the resultant component sizes are compared. The cost estimates obtained from the alternative methods are also compared to real ORC application. Based on this, a hybrid costing method is proposed andapplied to an ORC system design,in order to obtain the specific investment cost (SIC). The results indicate that as the heat source temperature increases, the power output increases, resultingin larger and more expensive components. Nevertheless, the SIC drops from 17GBP/W for low-power outputs to 1.1GBP/W for high-temperature/high-power outputs.

Conference paper

Herrando M, Ramos A, Zabalza I, Markides CNet al., 2017, Structural characterization and energy performance of novel hybrid PVT solar-panels through 3-D FEM and CFD simulations, ECOS 2017

Hybrid Photovoltaic-Thermal (PVT) panels generate both power and heat from the same area with overall efficiencies up to 70%. This work assesses the performance of novel hybrid PVT solar panels considering alternative geometries and materials that maximize heat transfer while allowing weight and cost reductions. A three-dimensional (3-D) model previously developed and validated using 3-D Finite-Element and Computational Fluid-Dynamics (FEM and CFD) software is used for this purpose. The most promising configurations and materials for the absorber-exchanger unit of the proposed PVT panel are studied to analyse their energy performance and behaviour in terms of a thermal-stress assessment. Apart from an assessment of the steady-state performance, for the type of solar PVT panels considered, especially those made of polymeric materials, it is important to evaluate the thermal expansion that the collector suffers, so as to verify whether the associated thermal stresses and strains are within the limits that guarantee a proper performance during its lifetime. The most promising PVT panel is then integrated within a Solar Combined Heat and Power (S-CHP) system for power and heating provision to a single-family house located in Zaragoza (Spain), in order to assess its daily energy performance through transient simulations on half-hourly basis. The results show that these novel polymeric PVT panel configurations are a promising alternative to commercial PVT panel designs, achieving an improved thermal performance compared to a reference case (4% higher optical efficiency and 15% lower heat loss coefficient), while suffering lower strains in most of the PVT layers. Furthermore, the novel polycarbonate 3×2 mm flat-box configuration has the potential to cover, on average, around 50% of the total space heating and Domestic Hot Water (DHW) demand and around 87% of the total electricity demand (including lighting, cooling and home appliances).

Conference paper

Georgiou S, Dowell NM, Shah N, Markides CNet al., 2017, Thermo-economic comparison of liquid-air and pumped-thermal electricity storage, 30th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, ECOS 2017

© 2017 IMEKO An efficient and affordable electricity storage system can assist the increasing penetration of intermittent renewable-energy generation, while the difference in the demand and price of peak and off-peak electricity can make its storage of financial interest. Technical indicators (e.g., roundtrip efficiency, energy and power density) along with economic indicators (e.g., capital, operating and maintenance costs) are expected to have a substantial combined impact on the competitiveness of any electricity storage technology or system under consideration. In this paper we will present thermodynamic models of two newly proposed medium- to large-scale electricity storage systems, namely ‘Liquid-Air Energy Storage’ (LAES) and ‘Pumped-Thermal Electricity Storage’ (PTES). The LAES model is validated against data from a pilot plant in operation in the UK; no such equivalent PTES plant exists. As with most new technologies, the lack of cost information makes the economic analysis and comparison a significant challenge. A costing effort for the two systems based on the module costing technique is also presented with the overriding aim of performing a preliminary economic feasibility assessment of the two systems. Based on initial results, PTES achieves higher roundtrip efficiencies, although the performance of LAES is found to be significantly enhanced through the utilisation of waste heat (and cold) streams. In terms of costs, LAES is estimated to have lower capital costs by roughly £600/kW. The most expensive components in both systems are the compression and expansion devices.

Conference paper

Ramos Cabal Alba RA, Chatzopoulou M, Freeman James JF, Markides Christos CNMet al., 2017, Optimisation of a high-efficiency solar-driven organic Rankine cycle for applications in the built environment, The 30th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems, Publisher: ECOS

Recent years have seen a strong increase in the uptake of solar technologies in the built environment. Incombined heat and power (CHP) or cogeneration systems, the thermodynamic and economic ‘value’ of theelectrical output is usually considered to be greater than that of (an equivalent) thermal output, and thereforethe prioritisation of the electrical output in terms of system-level optimisation has been driving much of theresearch, innovation and technology development in this area. In this work, the potential of a solar CHPtechnology based on an organic Rankine cycle (ORC) engine is investigated. We present thermodynamicmodels developed for different collectors, including flat-plate collectors (FPC) and evacuated-tube collectors(ETC) coupled with a non-recuperative sub-critical ORC architecture to deliver power and hot water by usingthermal energy rejected from the engine. Results from dynamic 3-D simulations of the solar collectors togetherwith a thermal energy storage (TES) tank are presented. TES offers an important buffering capability duringperiods of intermittent solar radiation, as well as the potential for demand-side management (DSM). Resultsare presented of an optimisation analysis to identify the most suitable working fluids for the ORC unit, in whichthe configuration and operational constraints of the collector array are taken into account. The most suitableworking fluids (R245fa and R1233zd) are then chosen for a whole-system optimisation performed in a southernEuropean climate. The system configuration with an ETC array is found to be best-suited for electricityprioritisation, delivering an electrical output of 3,605 kWh/yr from a 60 m2 array. In addition, the system supplies13,175 kWh/yr in the form of domestic hot water, which is equivalent to more than 6 times the average annualhousehold demand. A brief cost analysis and comparison with photovoltaic (PV) systems are also performed.

Conference paper

Handagama N, White M, Markides CN, 2017, Cooling with carbon dioxide, Energy World, Pages: 28-29, ISSN: 0307-7942

With 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.

Journal article

Efstratiadi M-A, Acha S, Shah N, Markides CNet al., 2017, Analysis of Closed Loop Water-Cooled Refrigeration Systems for the Food Retail Industry: A UK Case Study, 2017 ASHRAE ANNUAL CONFERENCE PAPERS, ISSN: 2578-5257

Journal article

Pantaleo, Rotolo G, De Palma P, Amirante R, Oyewunmi OA, Chatzopoulou, Markides C, Simpson Met al., Thermo-economic optimization of small-scale ORC systems for heat recovery from natural gas internal combustion engines for stationary power generation, 4th Annual Engine ORC Consortium Workshop for the Automotive and Stationary Engine Industries

Conference paper

Ibarra R, Matar OK, Markides CN, 2017, Flow structures in low-inclination stratified oil-water pipe-flows using laser-based diagnostic techniques, International Conference on Multiphase Production, Publisher: BHR Group, Pages: 71-85

In this work, a novel two-line laser-based diagnostic measurement technique was developed and applied to obtain combined space- and time-resolved phase and velocity information in low-inclination upward (<+5°) stratified flows of oil (Exxsol D140) and water. The strength of this technique is in enabling direct measurements in the non-refractive-index-matched fluids of interest, as opposed to substitute (optically matched) fluids whose properties may be less representative of those in real field-applications. The experimental test-section consisted of a 32-mm internal diameter pipe with a total length of 8.5 m. Results reveal interesting interactions between the co-flowing liquid phases. The velocity gradients at the interface are enhanced at high pipe inclinations for upward flows as the oil and water velocities increase and decrease, respectively. This also has a direct effect on the velocity fluctuations (quantified through their rms) and on the interfacial instabilities, which in turn affect the local velocity distributions in both phases.

Conference paper

Pantaleo AM, Camporeale SM, Miliozzi A, Russo V, Mugnozza GS, Markides CN, Shah Net al., 2017, Thermo-economic assessment of an externally fired hybrid CSP/biomass gas turbine and organic Rankine combined cycle, 8th International Conference on Applied Energy (ICAE), Publisher: Elsevier, Pages: 174-181, ISSN: 1876-6102

This paper focuses on the thermo-economic analysis of a hybrid solar-biomass CHP combined cycle composed by a 1.3-MW externally fired gas-turbine (EFGT) and a bottoming organic Rankine cycle (ORC) plant. The primary thermal energy input is provided by a hybrid concentrating solar power (CSP) collector-array coupled to a biomass boiler. The CSP collector-array is based on parabolic-trough concentrators (PTCs) with molten salts as the heat transfer fluid (HTF) upstream of a fluidized-bed furnace for direct biomass combustion. Thermal-energy storage (TES) with two molten-salt tanks (one cold and one hot) is considered, as a means to reducing the variations in the plant's operating conditions and increasing the plant's capacity factor. On the basis of the results of the thermodynamic simulations, upfront and operational costs assessments, and considering an Italian energy policy scenario, the global energy conversion efficiency and investment profitability are estimated for 2 different sizes of CSP arrays and biomass furnaces. The results indicate the low economic profitability of CSP in comparison to only biomass CHP, because of the high investment costs, which are not compensated by higher electricity sales revenues.

Conference paper

Pantaleo AM, Camporeale SM, Markides CN, Mugnozza GS, Shah Net al., 2017, Energy performance and thermo-economic assessment of a microturbine-based dual-fuel gas-biomass trigeneration system, 8th International Conference on Applied Energy (ICAE), Publisher: Elsevier, Pages: 764-772, ISSN: 1876-6102

The focus of this paper is on the energy performance and thermo-economic assessment of a small scale (100 kWe) combined cooling, heat and power (CCHP) plant serving a tertiary/residential energy demand fired by natural gas and solid biomass. The plant is based on a modified regenerative micro gas-turbine (MGT), where compressed air exiting the recuperator is externally heated by the hot gases produced in a biomass furnace. The flue gases after the recuperator flow through a heat recovery system (HRS), producing domestic hot water (DHW) at 90 °C, space heating (SH), and also chilled water (CW) by means of an absorption chiller (AC). Different biomass/natural gas ratios and an aggregate of residential end-users in cold, average and mild climate conditions are compared in the thermo-economic assessment, in order to assess the trade-offs between: (i) the lower energy conversion efficiency and higher investment cost when increasing the biomass input rate; (ii) the higher primary energy savings and revenues from feed-in tariffs available for biomass electricity exported into the grid; and (iii) the improved energy performance, sales revenue and higher investment and operational costs of trigeneration. The results allow for a comparison of the energy performance and investment profitability of the selected system configuration, as a function of the heating/cooling demand intensity, and report a global energy efficiency in the range of 25-45%, and IRR in the range of 15-20% assuming the Italian subsidy framework.

Conference paper

Mariaud A, Acha S, Ekins-Daukes N, Shah N, Markides CNet al., 2017, Integrated optimisation of photovoltaic and battery storage systems for UK commercial buildings, Applied Energy, Vol: 199, Pages: 466-478, ISSN: 1872-9118

Decarbonising the built environment cost-effectively is a complex challenge public and private organisations are facing in their effort to tackle climate change. In this context, this work presents an integrated Technology Selection and Operation (TSO) optimisation model for distributed energy systems in commercial buildings. The purpose of the model is to simultaneously optimise the selection, capacity and operation of photovoltaic (PV) and battery systems; serving as a decision support framework for assessing technology investments. A steady-state mixed-integer linear programming (MILP) approach is employed to formulate the optimisation problem. The virtue of the TSO model comes from employing granular state-of-the-art datasets such as half-hourly electricity demands and prices, irradiance levels from weather stations, and technology databases; while also considering building specific attributes. Investment revenues are obtained from reducing grid electricity costs and providing fast-frequency response (FFR) ancillary services. A case study of a distribution centre in London, UK is showcased with the goal to identify which technologies can minimise total energy costs against a conventional system setup serving as a benchmark. Results indicate the best technology configuration is a combination of lithium-ion batteries and mono-crystalline silicon PVs worth a total investment of £1.72 M. Due to the available space in the facility, the preferred PV capacity is 1.76 MW, while the battery system has a 1.06 MW power capacity and a 1.56 MWh energy capacity. Although PV performance varies across seasons, the solution indicates almost 30% of the energy used on-site can be supplied by PVs while achieving a carbon reduction of 26%. Nonetheless, PV and battery systems seem to be a questionable investment as the proposed solution has an 8-year payback, despite a 5-year NPV savings of £300k, implying there is still a performance gap for such systems to be massively

Journal article

Pantaleo AM, Camporeale SM, Miliozzi A, Russo V, Shah N, Markides CMet al., 2017, Novel hybrid CSP-biomass CHP for flexible generation: thermo-economic analysis and profitability assessment, Applied Energy, Vol: 204, Pages: 994-1006, ISSN: 1872-9118

This paper focuses on the thermo-economic analysis of a 2.1-MWe and 960 kWt hybrid solar-biomass combined heat and power (CHP) system composed of a 1.4-MWe Externally Fired Gas-Turbine (EFGT) and a 0.7-MWe bottoming Organic Rankine Cycle (ORC) power plant. The primary thermal energy input is provided by a hybrid Concentrating Solar Power (CSP) collector array covering a total ground area of 22,000–32,000 m2, coupled to a biomass boiler. The CSP collector array is based on parabolic-trough concentrators (PTCs) with molten salts as the heat transfer fluid (HTF), upstream of a 4.5–9.1 MWt fluidized-bed furnace for direct biomass combustion. In addition, two molten-salt tanks are considered that provide 4.8–18 MWh (corresponding to 1.3–5.0 h) of Thermal Energy Storage (TES), as a means of reducing the variations in the plant’s operating conditions, increasing the plant’s capacity factor and total operating hours (from 5500–6000 to 8000 h per year). On the basis of the results of the thermodynamic simulations, upfront and operational costs assessments, and considering an Italian energy policy scenario (feed-in tariffs, or FiTs, for renewable electricity), the global energy conversion efficiency and investment profitability of this plant are estimated for different sizes of CSP and biomass furnaces, different operation strategies (baseload and modulating) and cogenerative vs. electricity-only system configurations. Upfront costs in the range 4.3–9.5 MEur are reported, with operating costs in the range 1.5–2.3 MEur annually. Levelized costs of energy from around 100 Eur/MWh to above 220 Eur/MWh are found, along with net present values (NPVs) from close to 13,000 to −3000 kEur and internal rates of return (IRRs) from 30% down to almost zero when prioritizing electrical power generation (i.e., not in cogenerative mode). In all cases the economic viability of the systems deteriorate for larger CSP section sizes. The

Journal article

Lecompte S, Oyewunmi OA, Markides C, Lazova M, Kaya A, van den Broek M, De Paepe Met al., 2017, Case study of an organic Rankine cycle (ORC) for waste heat recovery from an electric arc furnace (EAF), Energies, Vol: 10, ISSN: 1996-1073

The organic Rankine cycle (ORC) is a mature technology for the conversion of waste heat to electricity. Although many energy intensive industries could benefit significantly from the integration of ORC technology, its current adoption rate is limited. One important reason for this arises from the difficulty of prospective investors and end-users to recognize and, ultimately, realise the potential energy savings from such deployment. In recent years, electric arc furnaces (EAF) have been identified as particularly interesting candidates for the implementation of waste heat recovery projects. Therefore, in this work, the integration of an ORC system into a 100 MWe EAF is investigated. The effect of evaluations based on averaged heat profiles, a steam buffer and optimized ORC architectures is investigated. The results show that it is crucial to take into account the heat profile variations for the typical batch process of an EAF. An optimized subcritical ORC system is found capable of generating a net electrical output of 752 kWe with a steam buffer working at 25 bar. If combined heating is considered, the ORC system can be optimized to generate 521 kWe of electricity, while also delivering 4.52 MW of heat. Finally, an increased power output (by 26% with combined heating, and by 39% without combined heating) can be achieved by using high temperature thermal oil for buffering instead of a steam loop; however, the use of thermal oil in these applications has been until now typically discouraged due to flammability concerns.

Journal article

Lecompte S, Oyewunmi OA, Markides CN, Lazova M, Kaya A, Ameel B, van den Broek M, De Paepe Met al., Potential of organic Rankine Cycles (ORC) for waste heat recovery on an electric arc furnace (EAF), 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT2017), Publisher: ICHMT

The organic Rankine cycle (ORC) is a mature technology to convert low temperature waste heat to electricity. While several energy intensive industries could benefit from the integration of an ORC, their adoption rate is rather low. One important reason is that the prospective end-users find it difficult to recognize and realise the possible energy savings. In more recent years, the electric arc furnaces (EAF) are considered as a major candidate for waste heat recovery. Therefore, in this work, the integration of an ORC coupled to a100 MWe EAF is investigated. The effect of working with averaged heat profiles, a steam buffer and optimized ORC architectures is investigated. The results show that it is crucial to take into account the heat profile variations for the typical batch process of an EAF. An optimized subcritical ORC(SCORC) can generate an electricity output of 752 kWe with a steam buffer working at 25 bar. However, the use of a steam buffer also impacts the heat transfer to the ORC. A reduction up to 61.5% in net power output is possible due to the additional isothermal plateau of the steam

Conference paper

White MT, Oyewunmi OA, Haslam A, Markides Cet al., Exploring optimal working fluids and cycle architectures for organic Rankine cycle systems using advanced computer-aided molecular design methodologies, 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics (HEFAT2017), Publisher: ICHMT

The combination of computer-aided molecular design(CAMD) with an organic Rankine cycle (ORC) power-systemmodel presents a powerful methodology that facilitates an in-tegrated approach to simultaneous working-fluid design andpower-system thermodynamic or thermoeconomic optimisation.Existing CAMD-ORC models have been focussed on simplesubcritical, non-recuperated ORC systems. The current workintroduces partially evaporated or trilateral cycles, recuperatedcycles and working-fluid mixtures into the ORC power-systemmodel, which to the best knowledge of the authors has not beenpreviously attempted. A necessary feature of a CAMD-ORCmodel is the use of a mixed-integer non-linear programming(MINLP) optimiser to simultaneously optimise integer working-fluid variables and continuous thermodynamic cycle and eco-nomic variables. In this paper, this feature is exploited by in-troducing binary optimisation variables to describe the cycle lay-out, thus enabling the cycle architecture to be optimised along-side the working fluid and system conditions. After describingthe models for the alternative cycles, the optimisation problemis completed for a defined heat source, considering hydrocar-bon working fluids. Two specific case studies are considered,in which the power output from the ORC system is maximised.These differ in the treatment of the minimum heat-source outlettemperature, which is unconstrained in the first case study, butconstrained in the second. This is done to replicate scenariossuch as a combined heat and power (CHP) plant, or applicationswhere condensation of the waste-heat stream must be avoided.In both cases it is found that a working-fluid mixture can per-form better than a pure working fluid. Furthermore, it is foundthat partially-evaporated and recuperated cycles are optimal forthe unconstrained and constrained case studies respectively.

Conference paper

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