311 results found
Herrando Zapater M, Ramos Cabal A, Zabalza I, et al., 2019, A comprehensive assessment of alternative absorber-exchanger designs for hybrid PVT-water collectors, Applied Energy, Vol: 235, Pages: 1583-1602, ISSN: 0306-2619
In this paper, 26 alternative absorber-exchanger designs for hybrid PV-Thermal (PVT) solar collectors are proposed and compared against a reference-case, commercial sheet-and-tube PVT collector. The collectors involve different geometric design features based on the conventional sheet-and-tube configuration, and also on a newer flat-box structure constructed from alternative polymeric materials with the aim of maintaining or even improving heat transfer and overall (thermal and electrical) performance while achieving reductions in the overall weight and cost of the collectors. The main contributions of this research include: (i) the development and validation of a detailed 3-D computational finite-element model of the proposed PVT collector designs involving multi-physics processes (heat transfer, fluid dynamics and solid mechanics); (ii) results from comparative techno-economic analyses of the proposed PVT designs; and, (iii) further insights from thermal stress and structural deformation analyses of the proposed collectors, which are crucial for ensuring long lifetimes and especially important in the case of polymeric collectors. The results show that, in general, the flat-box designs (characterised by a thin absorber plate) are not sensitive to the flow-channel size or construction material, at least within the range of investigation. A PVT collector featuring a polycarbonate (PC) flat-box design with 3 × 2 mm rectangular channels appears to be a particularly promising alternative to commercial PVT collectors, achieving a slightly improved thermal performance compared to the reference case (with a 4% higher optical efficiency and 15% lower linear heat-loss coefficient), while also lowering the weight (by around 9%) and investment cost (by about 21%) of the collector. The structural analysis shows that the maximum von Mises stress experienced in the absorber-exchanger of the PC flat-box collector is considerably lower than that in the copper sheet-and-tube c
Franchini S, Charogiannis A, Markides CN, et al., 2019, Calibration of astigmatic particle tracking velocimetry based on generalized Gaussian feature extraction, Advances in Water Resources, Vol: 124, Pages: 1-8, ISSN: 0309-1708
Flow and transport in porous media are driven by pore scale processes. Particle tracking in transparent porous media allows for the observation of these processes at the time scale of ms. We demonstrate an application of defocusing particle tracking using brightfield illumination and a CMOS camera sensor. The resulting images have relatively high noise levels. To address this challenge, we propose a new calibration for locating particles in the out-of-plane direction. The methodology relies on extracting features of particle images by fitting generalized Gaussian distributions to particle images. The resulting fitting parameters are then linked to the out-of-plane coordinates of particles using flexible machine learning tools. A workflow is presented which shows how to generate a training dataset of fitting parameters paired to known out-of-plane locations. Several regression models are tested on the resulting training dataset, of which a boosted regression tree ensemble produced the lowest cross-validation error. The efficiacy of the proposed methodology is then examined in a laminar channel flow in a large measurement volume of 2048, 1152 and 3000 μm in length, width and depth respectively. The size of the test domain reflects the representative elementary volume of many fluid flow phenomena in porous media. Such large measurement depths require the collection of images at different focal levels. We acquired images at 21 focal levels 150 μm apart from each other. The error in predicting the out-of-plane location in a single slice of 240 μm thickness was found to be 7 μm, while in-plane locations were determined with sub-pixel resolution (below 0.8 μm). The mean relative error in the velocity measurement was obtained by comparing the experimental results to an analytic model of the flow. The estimated displacement errors in the axial direction of the flow were 0.21 pixel and 0.22 pixel at flows rates of 1.0 mL/h and 2.5 mL/h, respectively. These resu
Simpson M, Chatzopoulou MA, Oyewunmi O, et al., 2019, Technoeconomic analysis of internal combustion engine – organic Rankine cycle cogeneration systems in energy-intensive buildings, 10th International Conference on Applied Energy, Publisher: Elsevier, Pages: 2354-2359, ISSN: 1876-6102
Organic Rankine cycle (ORC) systems are a promising technology for converting heat to useful power, especially in combined heat and power (CHP) applications with significant quantities of surplus heat that would otherwise be wasted. Beyond the technical performance of these systems, their economic feasibility is crucially important for their wider deployment. In this study, a technoeconomic optimisation of CHP systems is performed in which ORC engines convert heat recovered from internal combustion engines (ICEs), and specifically from both the ICE hot-water output and exhaust-gas stream. The overall aim is to evaluate the impact of the ORC power output and of the components’ design and capital cost on the financial viability of a relevant project, while evaluating a range of candidate working fluids. Results indicate that ORC designs optimised for maximum power output correspond to higher specific investment cost (SIC), with the best performing fluids achieving a SIC of £2100 per kW. In contrast, optimisation for minimum SIC returns values as low as £1700 per kW, or 20% lower. For systems designed and optimised for maximum power, a large fraction of jacket water heat is recovered, while for minimum SIC the utilisation drops to minimise the size and cost of the heat exchangers. The best-performing ORC designs for minimum SIC have discounted payback periods (DPPs) of 4 – 5 years, while those optimised for power output have DPPs of 6 – 7 years, however, the net present values (NPVs) of the latter designs are up to 27% higher than the former. Therefore, there is a trade-off to consider over the project life between high-capacity ORC engines with a high SIC and longer DPP, and designs with minimal SIC but lower power output, shorter DPP and lower NPV. The effect of increasing the amount of hot water required by the building is also analysed, and the ORC engine is shown to be sensitive to this factor for some work
Wang K, Herrando M, Pantaleo AM, et al., 2019, Thermoeconomic assessment of a PV/T combined heating and power system for University Sport Centre of Bari, 10th International Conference on Applied Energy (ICAE2018), Publisher: Elsevier, Pages: 1229-1234, ISSN: 1876-6102
This paper presents a thermoeconomic analysis of a solar combined heating and power (S-CHP) system based on hybridphotovoltaic-thermal (PV/T) collectors for the University Sport Centre (USC) of Bari, Italy. Hourly demand data for space heating,swimming pool heating, hot water and electricity provision as well as the local weather data are used as inputs to a transient modeldeveloped in TRNSYS. Economic performance is evaluated by considering the investment costs and the cost savings due to thereduced electricity and natural gas consumptions. The results show that 38.2% of the electricity demand can be satisfied by thePV/T S-CHP system with an installation area of 4,000 m2. The coverage increases to 81.3% if the excess electricity is fed to thegrid. In addition, the system can cover 23.7% of the space heating demand and 53.8% of the demands for the swimming pool andhot water heating. A comparison with an equivalent gas-fired internal combustion engine (ICE) CHP system shows that the PV/Tsystem has a higher payback time, i.e., 11.6 years vs. 3 years, but outperforms the ICE solution in terms of CO2 emission reduction,i.e., 435 tons CO2/year vs. 164 tons CO2/year. This work suggests that the proposed PV/T S-CHP system has a good potential ofdecarbonisation, while the economic competitiveness should be further enhanced to boost its deployment.
Harraz AA, Freeman J, Wang K, et al., 2019, Diffusion-absorption refrigeration cycle simulations in gPROMS using SAFT-γ Mie, Energy Procedia, Vol: 158, Pages: 2360-2365, ISSN: 1876-6102
Diffusion-absorption refrigeration (DAR) is a clean thermally-powered refrigeration technology that can readily be activated by low- to medium-grade renewable heat. There is an ongoing interest in identifying or designing new working fluids for performance improvement, particularly in solar applications with non-concentrating solar collectors providing heat at temperatures < 150 °C. In this work, the state-of-the-art statistical associating fluid theory (SAFT) is adopted for predicting the thermodynamic properties of suitable DAR working fluids. A first-law thermodynamic analysis is performed in the software environment gPROMS for a DAR cycle using ammonia as the refrigerant, water as the absorbent and hydrogen as the auxiliary gas. The simulation results show good agreement with experimental data generated in a prototype DAR system with a nominal cooling capacity of 100 W. In particular, at a charge pressure of 17 bar and when delivering cooling at 5 °C, the model results agree with experimental COP data to within ± 7 % over a range of heat inputs from 150 to 500 W. The maximum coefficient of performance (COP) is estimated to be 0.24 at a heat input of 250 W. The group-contribution SAFT-γ Mie equation of state is of particular interest as it offers good agreement with experimental data and provides flexibility in extending the model to test different working fluids with a high degree of fidelity. A methodology is also presented that allows the DAR thermodynamic analysis and working-fluid modelling to be integrated into a more general technology optimisation framework.
Chatzopoulou MA, Lecompte S, De Paepe M, et al., 2019, Off-design operation of ORC engines with different heat exchanger architectures in waste heat recovery applications, ICAE2018 - 10th International Conference on Applied Energy, Publisher: Elsevier, Pages: 2348-2353, ISSN: 1876-6102
Organic Rankine cycle(ORC)engines in waste-heat recovery applications experience variable heat-source conditions (i.e. temperature and mass flow ratevariations). Therefore maximisingthe ORC system performance under off-design conditions is of key importance, for the financial viability and wider adoption of these systems. In this paper,the off-design performance of an ORC engineis investigated, with screw expander andtwoheat exchanger (HEXs)architectures, while recovering heat from an internal combustion engine (ICE).Unlike previous studieswhere the ORC expanderand HEXsperformance is assumed fixed duringoff-design operation, in this work we consider the time-varying characteristics of the system components.Firstly, nominal system sizing results indicate that the screw expander isentropic efficiency exceeds 80%,whilethe plate HEXs (PHEXs) heat transferarea requirements are 50% lower,than the respective ones for double pipe (DPHEX) design. Next, the ORC engine operation is optimised at part-load (PL) ICE conditions.Although, the HEXs heat transfer coefficients decrease by 30% with part-load, the HEX effectiveness increasesby up to 20%, due to higher temperature difference across the working fluids.Findingsalso reveal that the PHEX performance is less sensitive to the off-design operation. Optimum off-design power output maps indicatethattheORC enginePL reduces to 72%, for ICE PL of 60%, while ORCengines with PHEXsgenerate slightlymore power,for the same heat source conditions. Overall, the modelling tool developed predictsthe ORC performance over an operating envelope and allows the selection of optimal designs and sizes of ORC HEXsand expanders.The findings can be used by ORC plant operators to optimise the ORC engine power output, given the varying heat source conditions observed on their site,and by ORC vendors to inform HEX andexpander design decisions.
Ibrahim D, Oyewunmi O, Haslam A, et al., COMPUTER-AIDED WORKING FLUID DESIGN AND POWER SYSTEM OPTIMIZATION USING THE SAFT-γ MIE EQUATION OF STATE, 4th Thermal and Fluids Engineering Conference (TFEC)
Juggurnath D, Dauhoo MZ, Elahee MK, et al., 2019, Numerical simulations of condensing R134a flows in horizontal pipes, Pages: 413-422
© 2019 Begell House Inc. All rights reserved. Three-dimensional numerical simulations were performed of condensing R134a flows in a smooth horizontal pipe with an inner diameter of 8.4 mm and a length of 1.5 m, and validated against experimental results. A constant mass flux of 100 kg m-2 s-1 was considered and the influence of vapour qualities (0.25 to 0.75) and saturation temperatures (30 ?C and 40 ?C) on the resulting flow regimes and heat transfer characteristics of these flows were investigated. The volume-of-fluid (VOF) method was employed in the numerical framework to track and reconstruct the interface between the liquid and vapour phases. The simulations, given the imposed flow conditions, produced stratified wavy flow which are in agreement with the expected flow pattern based on the El Hajal flow pattern map. The heat transfer coefficient in the numerically simulated flows were found to be in good agreement (within 1.3%) with corresponding experimentally-measured values. From the simulations, the liquid-phase height at the bottom of the pipe was observed to be smaller with increasing vapour quality, which results in an increase in the heat transfer coefficient. A thicker film thickness and lower heat transfer coefficient were noted at the higher saturation temperature.
Harraz AA, Najjaran A, Sacks R, et al., 2019, Experimentally validated simulations of a diffusion absorption refrigeration system, Pages: 1045-1056
© ECOS 2019 - Proceedings of the 32nd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems. All rights reserved. Diffusion absorption refrigeration (DAR) is a small-scale, thermally-driven cooling technology that operates passively without the need for mechanical or electrical inputs. Due to the lack of a compressor, DAR systems are charged with an auxiliary gas to enable single-pressure operation. Although DAR units have a simple construction and are easy to operate, their modelling presents challenges arising from the complexity of the physical processes that take place and govern operation. Few experimentally validated models offer a reliable prediction of the DAR system performance over a wide range of operating conditions. This paper combines results from experimental investigations on a laboratory-scale ammonia-water-hydrogen DAR system with a nominal cooling output of ∼100 W with model predictions of the performance characteristics of this system. In previous work, the DAR cycle was modelled using first-law thermodynamic analysis in the gPROMS environment for a single cooling delivery temperature and a single-charge pressure, using a group-contribution equation-of-state based on the statistical associating fluid theory (SAFT). Here, extended model validation is performed to investigate the effect of key operating parameters on system performance, including the generator heat input (varied from 150 W to 700 W), the cooling delivery temperature (set to two levels: 5 ◦C and 23 ◦C) and the system charge pressure (18 bar and 21 bar). The measured coefficient of performance (COP) was between 0.02 and 0.29. The present model predicts the maximum COP well over the heat-input range from 250 W to 550 W. Hence, the model shows good agreement with experiments, particularly when the heat-input rate is at or below the system’s design-point. Conclusions are drawn concerning the ability of models to
Charogiannis A, Denner F, Van Wachem B, et al., 2018, Experimental investigations of liquid falling films flowing under an inclined planar substrate, Physical Review Fluids, Vol: 3, ISSN: 2469-990X
We report on detailed and systematic experiments of thin liquid films flowing as a result of the action of gravity under an inverted planar substrate. A measurement technique based on planar laser-induced fluorescence (PLIF) was developed and applied to a range of such flows in order to provide detailed space- and time-resolved film-height information. Specifically, the experimental campaign spanned three inclination angles (β=−15∘, −30∘, and −45∘, in all cases negative with respect to the vertical), two water-glycerol solutions (with Kapitza numbers of Ka=13.1 and 330), and flow Reynolds numbers covering the range Re=0.6–193. The collection optics were arranged so as to interrogate a spanwise section of the flow extending about 40mm symmetrically on either side the centerline of the film span (80mm in total), at a distance 330 mm downstream of the flow inlet. A range of flow regimes, typically characterized by strong three dimensionality and pronounced rivulet formation, were observed depending on the imposed inlet flow conditions. In the lower liquid Kapitza number Ka(=13.1) flows and depending on the flow Re, the free surface of the film was populated by smooth rivulets or regular sequences of solitary pulses that traveled over the rivulets. In the higher liquid Ka(=330) flows, rivulets were observed typically above Re≈30, depending also on the inclination angle, and grew in amplitude until quasi-two-dimensional fronts developed intermittently that were associated with distinct thin-film regions of varying length and frequency. These regions are of particular interest as they are expected to affect strongly the heat and mass transfer capabilities of these flows. The occurrence of the fronts was more pronounced, with higher wave frequencies, in film flows at smaller negative inclinations for the same flow Re. The rivulet amplitude was found to increase at larger inclinations for the same Re and showed a nonmonotonic trend with in
Riverola A, Mellor A, Alvarez DA, et al., 2018, Experimental and theoretical study of the infrared emissivity of crystalline silicon solar cells, IEEE 44th Photovoltaic Specialist Conference (PVSC), Publisher: IEEE, Pages: 1339-1341, ISSN: 0160-8371
Sacks RE, Markides C, 2018, Compressed air energy storage – a new heat-integration, liquid-compression approach, Energy Learning
Herrando M, Ramos A, Freeman J, et al., 2018, Technoeconomic modelling and optimisation of solar combined heat and power systems based on flat-box PVT collectors for domestic applications, Energy Conversion and Management, Vol: 175, Pages: 67-85, ISSN: 0196-8904
We investigate solar combined heat and power (S-CHP) systems based on hybrid photovoltaic-thermal (PVT) collectors for the simultaneous provision of domestic hot water (DHW), space heating (SH) and power to single- family homes. The systems include PVT collectors with a polycarbonate flat-box structure design, a water storage tank, an auxiliary heater and a battery storage subsystem. A methodology is developed for modelling the en- ergetic and economic performance of such PVT-based S-CHP systems, which is used to optimally size and operate systems for covering the energy demands of single-family reference households at three selected locations: Athens (Greece), London (UK) and Zaragoza (Spain). The results show that optimised systems are capable of covering ∼65% of the annual household electricity demands in Athens, London and Zaragoza when employing 14.0, 17.0 and 12.4 m2 collector array areas respectively, while also covering a significant fraction of the thermal energy demands in Athens (∼60%) and Zaragoza (∼45%); even in London, almost 30% of the reference household’s thermal demand is covered by such a system. A corresponding economic analysis reveals that, despite the suitability of Athens’ weather conditions for implementing such solar-energy systems, the payback time (PBT) of the optimised S-CHP system in Athens is 15.6 years in contrast to the 11.6 years predicted for Zaragoza, due to the lower electricity prices in Greece. On the other hand, the high carbon emission factor of the electricity grid in Greece makes these systems particularly promising at this location. Specifically, the in- vestigated systems have the potential to displace 3.87, 1.65 and 1.54 tons of CO2 per year in Athens, London and Zaragoza, when substituting the conventional means for household energy provision (i.e. grid electricity and gas- fired boilers). Furthermore, it is demonstrated that the optimised systems outperform benchmark equivalent systems comprisin
Mellor A, Alonso Alvarez D, Guarracino I, et al., 2018, Roadmap for the next-generation of hybrid photovoltaic-thermal solar energy collectors, Solar Energy, Vol: 174, Pages: 386-398, ISSN: 0038-092X
For hybrid photovoltaic-thermal collectors to become competitive with other types of solar energy converters, they must offer high performance at fluid outlet temperatures above 60 °C, as is required for space heating and domestic hot water provision, which together account for nearly 50% of heat demand. A roadmap is presented of the technological advances required to achieve this goal. Strategies for reducing convective, radiative and electrical losses at elevated temperature are discussed, and an experimental characterisation of a novel transparent low-emissivity coating for photovoltaic solar cells is presented. An experimentally-validated simulation formalism is used to project the performance of different combinations of loss-reduction strategies implemented together. Finally, a techno-economic analysis is performed to predict the price points at which the hybrid technologies along the roadmap become competitive with non-hybrid photovoltaic and solar thermal technologies. The most advanced hybrid technology along the roadmap employs an evacuated cavity, a transparent low-emissivity coating, and silicon heterojunction photovoltaic cells.
Sorrentino A, Pantaleo AM, Markides C, et al., 2018, Energy performance and profitability of biomass boilers in commercial sector: the case study of Sainsbury’s stores in the UK, 73rd Conference of the Italian Thermal Machines Engineering Association (ATI 2018), Publisher: Elsevier, Pages: 539-646, ISSN: 1876-6102
Commercial buildings or shopping malls are characterized by large thermal and electrical energy consumptions with high variability of energy demand. Therefore, there is a large interest to explore novel renewable energy generation systems for these applications. A novel flexible configuration of biomass-fired CHP system with organic Rankine cycle(ORC) is here proposedand applied to the case study of Sainsbury’s supermarkets in the UK.The proposed configuration adoptsa molten salt (MS) circuitto transfer heat from the biomass furnace to the ORC plant. A thermal Energy Storage (TES) is proposedtoimprove the flexible operation of the plantand reduce the size of the biomass boiler. Molten salts have been preferredto thermal oil as they have no fire risks and low environmental impactand can be used as medium for a Two Tank TES with a “direct heating” scheme. The planthas beenanalysedusing real input data of biomass boiler installed, conversion efficiency and heat demand from the store. The model is informed by hourly energy costs and electricity feed in tariff in order to define optimal size and operation of the bottoming ORC for the specific case study of large commercial energy end userin the UK.The results show that the use of thermal storage in a biomass-fired ORC plant can improve the boiler efficiency and reduce the biomass consumption in thermal-load following operating mode and increase the investment profitability.
Ramos A, Chatzopoulou MA, Freeman J, et al., 2018, Optimisation of a high-efficiency solar-driven organic Rankine cycle for applications in the built environment, Applied Energy, Vol: 228, Pages: 755-765, ISSN: 0306-2619
Energy security, pollution and sustainability are major challenges presently facing the international community, in response to which increasing quantities of renewable energy are to be generated in the urban environment. Consequently, recent years have seen a strong increase in the uptake of solar technologies in the building sector. In this work, the potential of a solar combined heat and power (CHP) system based on an organic Rankine cycle (ORC) engine is investigated in a domestic setting. Unlike previous studies that focus on the optimisation of the ORC subsystem, this study performs a complete system optimisation considering both the design parameters of the solar collector array and the ORC engine simultaneously. Firstly, we present thermodynamic models of different collectors, including flat-plate and evacuated-tube designs, coupled to a non-recuperative sub-critical ORC architecture that delivers power and hot water by using thermal energy rejected from the engine. Optimisation of the complete system is first conducted, aimed at identifying operating conditions for which the power output is maximised. Then, hourly dynamic simulations of the optimised system configurations are performed to complete the system sizing. Results are presented of: (i) dynamic 3-D simulations of the solar collectors together with a thermal energy storage tank, and (ii) of an optimisation analysis to identify the most suitable working fluids for the ORC engine, in which the configuration and operational constraints of the collector array are considered. The best performing working fluids (R245fa and R1233zd) are then chosen for a whole-system annual simulation in a southern European climate. The system configuration combining an evacuated-tube collector array and an ORC engine is found to be best-suited for electricity prioritisation, delivering an electrical output of 3,605 kWh/year from a 60 m2 collector array. In addition, the system supplies 13,175 kWh/year in the form of domes
White M, Oyewunmi OA, Chatzopoulou M, et al., 2018, Computer-aided working-fluid design, thermodynamic optimisation and technoeconomic assessment of ORC systems for waste-heat recovery, Energy, Vol: 161, Pages: 1181-1198, ISSN: 0360-5442
The wider adoption of organic Rankine cycle (ORC) technology for power generation or cogeneration from renewable or recovered waste-heat in many applications can be facilitated by improved thermodynamic performance, but also reduced investment costs. In this context, it is suggested that the further development of ORC power systems should be guided by combined thermoeconomic assessments that can capture directly the trade-offs between performace and cost with the aim of proposing solutions with high resource-use efficiency and, importantly, improved economic viability. This paper couples, for the first time, the computer-aided molecular design (CAMD) of the ORC working-fluid based on the statistical associating fluid theory (SAFT)-γ Mie equation of state with thermodynamic modelling and optimisation, in addition to heat-exchanger sizing models, component cost correlations and thermoeconomic assessments. The resulting CAMD-ORC framework presents a novel and powerful approach with extended capabilities that allows the thermodynamic optimisation of the ORC system and working fluid to be performed in a single step, thus removing subjective and pre-emptive screening criteria that exist in conventional approaches, while also extending to include cost considerations relating to the resulting optimal systems. Following validation, the proposed framework is used to identify optimal cycles and working fluids over a wide range of conditions characterised by three different heat-source cases with temperatures of 150 °C, 250 °C and 350 °C, corresponding to small- to medium-scale applications. In each case, the optimal combination of ORC system design and working fluid is identified, and the corresponding capital costs are evaluated. It is found that fluids with low specific-investment costs (SIC) are different to those that maximise the power output. The fluids with the lowest SIC are isoheptane, 2-pentene and 2-heptene, with SICs of £5620, £2760 an
Wang Y, Markides CN, Chachuat B, 2018, Optimization-based investigations of a thermofluidic engine for low-grade heat recovery, IFAC-PapersOnLine, Vol: 51, Pages: 690-695, ISSN: 2405-8963
This paper presents an analysis of the non-inertive-feedback thermofluidic engine (NIFTE) under cyclic steady-state conditions. The analysis is based on a nonlinear model of NIFTE that had previously been validated experimentally, and applies an optimization-based approach to detect the cyclic steady states (CSS). The stability of the CSS is furthermore determined by analyzing their monodromy matrix. It is found that NIFTE can exhibit multiple CSS for certain values of the design parameters, which may be either stable or unstable, a result that had not been reported before. Subsequently, a parametric study is conducted by varying key design parameters, revealing that higher efficiencies could be achieved by controlling the engine at different CSS, including unstable ones. Lastly, the paper investigates the trade-offs between efficiency and work output in NIFTE.
McTigue JD, Markides C, White AJ, 2018, Performance response of packed-bed thermal storage to cycle duration perturbations, Journal of Energy Storage, Vol: 19, Pages: 379-392, ISSN: 2352-152X
Packed-bed thermal stores are integral components in numerous bulk electricity storage systems and may also be integrated into renewable generation and process heat systems. In such applications, the store may undergo charging and discharging periods of irregular durations. Previous work has typically concentrated on the initial charging cycles, or on steady-state cyclic operation. Understanding the impact of unpredictable charging periods on the storage behavior is necessary to improve design and operation. In this article, the influence of the cycle duration (or ‘partial-charge’ cycles) on the performance of such thermal stores is investigated. The response to perturbations is explained and provides a framework for understanding the response to realistic load cycles.The packed beds considered here have a rock filler material and air as the heat transfer fluid. The thermodynamic model is based on a modified form of the Schumann equations. Major sources of exergy loss are described, and the various irreversibility generating mechanisms are quantified.It is known that repeated charge-discharge cycles lead to steady-state behavior, which exhibits a trade-off between round-trip efficiency and stored exergy, and the underlying reasons for this are described. The steady state is then perturbed by cycles with a different duration. Short duration perturbations lead to a transient decrease in exergy losses, while longer perturbations increase it. The magnitude of the change in losses is related to the perturbation size and initial cycle period, but changes of 1–10 % are typical. The perturbations also affect the time to return to a steady-state, which may take up to 50 cycles. Segmenting the packed bed into layers reduces the effect of the perturbations, particularly short durations.Operational guidelines are developed, and it is found that packed beds are more resilient to changes in available energy if the store is not suddenly over-charged (i.e. longer
Wang K, Herrando M, Pantaleo AM, et al., 2018, Thermodynamic and economic assessments of a hybrid PVT-ORC combined heating and power system for swimming pools, Heat Powered Cycles Conference 2018
The thermodynamic and economicperformance of a solar combined heatand power(S-CHP) system based on an array of hybrid photovoltaic-thermal (PVT) collectorsandan organic Rankine cycle (ORC)engineis considered for the provision of heating and power to swimming poolfacilities. Priority is given to meeting the thermaldemand of the swimming pool,in order to ensure a comfortable condition for swimmers in colderweather conditions, while excessthermal output from the collectorsat highertemperatures is converted toelectricityby the ORC engine inwarmerweather conditions. The thermodynamic performance of this system and its dynamic characteristicsare analysed on the basis of a transient thermodynamic model. Various heat losses and gains are considered in accordance toenvironmental and user-relatedfactorsfor both indoor and outdoor swimming pools. A case study is then performed for the swimming pool atthe UniversitySportCentre (USC)of Bari, Italy. The results show thatemployinga zeotropic mixture of R245fa/R227ea (30/70%) as the ORC working fluidallows such an ORC systemto generate~50% more power than when usingpure R236eadue to the better temperature matchof the cycle tothe low-temperature hot-water heat sourcefrom the output of the PVT collectors.Apart from generatingelectricity, the ORC enginealso alleviatesPVT collectoroverheating,and reducesthe required size of the hot-water storage tank. With an installation of 2000 m2of PVT collectors, energetic analysesindicate that the proposedS-CHP systemcan cover 84-96% of the thermal demand of the swimming pool during the warm summer months and 61% of itsannually integratedtotal thermal demand. In addition, the system produces a combined (from thecollectors andORC engine) of 328 MWhofelectricityper year, corresponding to 36% of the total electricity demand of the USC, with ~4% coming from the ORC engine.Theanalysis suggestsa minimum payback time of 12.7yearswith anopt
Georgiou S, Aunedi M, Strbac G, et al., 2018, Application of liquid-air and pumped-thermal electricity storage systems in low-carbon electricity systems, Heat Powered Cycles - HPC-2018
In this study, we considertwo medium-to large-scale electricity storage systems currently under development, namely ‘Liquid-Air Energy Storage’ (LAES) and ‘Pumped-Thermal Electricity Storage’ (PTES). Consistent thermodynamic models and costing methodologies for the twosystems are presented,with the objective of integrating the characteristics of these technologies intoa whole-electricity system assessment model,andassessingtheirsystem-levelvalue in different scenarios for power system decarbonisation.It is found that the value of storage variesgreatlydepending on the cumulative installed capacity of storage in the electrical system, withthe storage technologies providinggreater marginal benefits at low penetrations. Two carbon target scenarios showed similar results, with a limited effect of the carbon target on the system value of storage (althoughit is noted thatthis may change for even more ambitious carbon targets). On the other hand, the location and installed capacity of storage plants isfound to have a significantimpact on the system value and acceptable cost of thesetechnologies. The whole-system value of PTES was foundto be slightly higher than that of LAES, driven by a higher storage duration and efficiency,however, due to the higher power capital cost of PTES, this becomes less attractive for implementation at lower volumes than LAES.
Georgiou S, Shah N, Markides C, 2018, A thermo-economic analysis and comparison of pumped-thermal and liquid-air electricity storage systems, Applied Energy, Vol: 226, Pages: 1119-1133, ISSN: 0306-2619
Efficient and affordable electricitystorage systemshave a significant potential tosupport thegrowth and increasingpenetration of intermittent renewable-energy generationinto the gridfrom an energy system planning and management perspective,whiledifferencesin the demand and price ofpeak and off-peak electricity can make its storage of economicinterest. Technical (e.g.,roundtrip efficiency,energy andpower capacity)as well aseconomic (e.g.,capital, operating and maintenance costs)indicators are anticipatedto have a significantcombined impact on the competitiveness of anyelectricity storage technology or systemunder considerationand, ultimately, will cruciallydetermine their uptake and implementation.In this paper,we present thermo-economicmodels of two recentlyproposedmedium-to large-scale electricity storage systems, namely ‘Pumped-Thermal Electricity Storage’ (PTES) and ‘Liquid-Air Energy Storage’ (LAES), focusing on system efficiency and costs. The LAESthermodynamic model isvalidated against datafrom anoperationalpilot plant in the UK; no such equivalent PTES plant exists, although one is currently underconstruction. Ascommonwith most newly proposedtechnologies, the absenceof cost dataresults tothe economic analysis and comparisonbeinga significant challenge.Therefore, acosting effort for the two electricity storage systems that includes multiple costing approaches based on the module costing technique is presented,with the overriding aim of conducting a preliminary economic feasibility assessment and comparison of the two systems. Based on the results, it appears that PTES has the potential to achievehigher roundtrip efficiencies,althoughthis remains to be demonstrated. LAESperformance isfound to be significantly enhanced through the integration and utilisation of waste heat (and cold)streams.In terms of economicson the other hand,and at the
Chatzopoulou MA, Markides C, 2018, Thermodynamic optimisation of a high-electrical efficiency integrated internal combustion engine – organic Rankine cycle combined heat and power system, Applied Energy, Vol: 226, Pages: 1229-1251, ISSN: 0306-2619
Organic Rankine cycle (ORC) engines are suitable for heat recovery from internal combustion engines (ICE) in combined heat and power (CHP) systems. However, trade-offs must be considered between ICE andORC engine performance in such integrated solutions. The ICE design and operational characteristics influence its own performance along withthe exhaust-gas conditions available as heat source to the ORC engine, impacting ORC design and performance, while the heat-recovery heat exchanger (ORC evaporator) will affect the ICE operation. In this paper, an integrated ICE-ORC CHP whole-system optimisation framework is presented. This differs from other efforts in that we develop and apply a fully-integrated ICE-ORC CHP optimisation framework, considering the design and operation of both the ICE and ORC enginessimultaneously within the combined system, to optimise the overall system performance. A dynamic ICE model is developed and validated, along with a steady-state model of subcritical recuperative ORC engines. Both naturally aspirated and turbocharged ICEs are considered, of two different sizes/capacities. Nine substances (covering low-GWP refrigerants and hydrocarbons) are investigated as potential ORC working fluids. The integrated ICE-ORC CHP system isoptimised for eithermaximum total power output, or minimum fuel consumption. Resultshighlight that by optimising the complete integrated ICE-ORC CHP system simultaneously, the total power output increases by up to 30% in comparison to a nominal system design. In the integrated CHP system,the ICE power output is slightly lower than that obtained for optimal standalone ICE application, as the exhaust-gas temperature increases to promote the bottoming ORC engine performance, whose power increasesby 7%. The ORC power output achieved accounts for up to 15% of the total power generated by the integrated system, increasing the system efficiency by up to 11%. When only power optimisation is performed, the
Pantaleo AM, de palma P, Fordham J, et al., 2018, Integrating cogeneration and intermittent waste-heat recovery in food processing: Microturbines vs. ORC systems in the coffee roasting industry, Applied Energy, Vol: 225, Pages: 782-796, ISSN: 0306-2619
Coffee roasting is a highly energy intensive process wherein a large quantity of heat is discharged from the stack at medium-to-high temperatures. Much of the heat is released from the afterburner, which is required to remove volatile organic compounds and other pollutants from the flue gases. In this work, intermittent waste-heat recovery via thermal energy storage (TES) and organic Rankine cycles (ORCs) is compared to combined heat and power (CHP) based on micro gas-turbines (MGTs) for a coffee roasting plant. With regard to the former, a promising solution is proposed that involves recovering waste heat from the flue gas stream by partial hot-gas recycling at the rotating drum coffee roaster, and coupling this to a thermal store and an ORC engine for power generation. The two solutions (CHP + MGT prime mover vs. waste-heat recovery + ORC engine) are investigated based on mass and energy balances, and a cost assessment methodology is adopted to compare the profitability of three system configurations integrated into the selected roasting process. The case study involves a major Italian roasting plant with a 500 kg per hour coffee production capacity. Three options are investigated: (i) intermittent waste-heat recovery from the hot flue-gases with an ORC engine coupled to a TES system; (ii) regenerative topping MGT coupled to the existing modulating gas burner to generate hot air for the roasting process; and (iii) non-regenerative topping MGT with direct recovery of the turbine outlet air for the roasting process. The results show that the profitability of these investments is highly influenced by the natural gas and electricity prices and by the coffee roasting production capacity. The CHP solution via an MGT appears as a more profitable option than waste-heat recovery via an ORC engine primarily due to the intermittency of the heat-source availability and the high electricity cost relative to the cost of natural gas.
White MT, Markides CN, Sayma AI, 2018, Working-Fluid Replacement in Supersonic Organic Rankine Cycle Turbines, JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER-TRANSACTIONS OF THE ASME, Vol: 140, ISSN: 0742-4795
Georgiou S, Acha S, Shah N, et al., 2018, A generic tool for quantifying the energy requirements of glasshouse food production, Journal of Cleaner Production, Vol: 191, Pages: 384-399, ISSN: 0959-6526
Quantifying the use of resources in food production and its environmental impact is key to identifying distinctive measures which can be used to develop pathways towards low-carbon food systems. In this paper, a first-principle modelling approach is developed, referred to as gThermaR (Glasshouse-Thermal Requirements). gThermaR is a generic tool that focuses on the energy requirements of protected heated production, by integrating holistic energy, carbon, and cost modelling, food production, data analytics and visualization. The gThermaR tool employs historic data from weather stations, growing schedules and requirements specific to grower and product needs (e.g. set-point temperatures, heating periods, etc.) in order to quantify the heating and cooling requirements of glasshouse food production. In the present paper, a case study is reported that employs a database compiled for the UK. Another relevant feature of the tool is that it can quantify the effects that spatial and annual weather trends can have on these heating and cooling requirements. The main contribution of this work, therefore, concerns the development a tool that can provide a simple integrated approach for performing a wide range of analyses relevant to the thermal requirements of heated glasshouses. The tool is validated through collaborations with industrial partners and showcased in a case study of a heated glasshouse in the UK, offering the capacity to benchmark and compare different glasshouse types and food growth processes. Results from the case study indicate that a significant reduction in the heating requirement and, therefore, carbon footprint, of the facility can be achieved by improving key design and operational parameters. Results indicate savings in the peak daily and annual heating requirements of 44-50% and 51-57% respectively, depending on the region where the glasshouse is located. This improvement is also reflected in the carbon emissions and operating costs for the different en
Cherdantsev A, An J, Charogiannis A, et al., 2018, Cross-validation of PLIF and BBLIF towards the detailed study of gas-sheared liquid films in downward annular flows, 19th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics
This paper is devoted to the development and application of two spatiotemporally resolved optical techniquescapable of liquid film thickness measurements in downward annular (co-current) gas-liquid flows, namely PlanarLaser-Induced Fluorescence (PLIF) and Brightness-Based Laser-Induced Fluorescence (BBLIF). A single laser sheet is used to excite the liquid film, which has been doped with a fluorescent dye, along a longitudinal/vertical planenormal to the pipe wall. Two cameras (one for each technique) are placed at different angles to the plane of the lasersheet in order to recover independently the shape of the gas-liquid interface along this section. The effect of theangle between the laser sheet and the PLIF camera axis is also investigated. It is found that, at film regions wherethe gas-liquid interfaceis smooth, the conventional approach used for interpreting PLIF data is vulnerable to totalinternal reflection of the fluorescent light at the free surface, which leads to an overestimation of the film thicknessthat increases as the angle between the laser sheet and the camera axis is decreased. Nonetheless, local features suchas light intensity maxima or minima can often be located within the fluorescent signal that correctly identify theinterface, which in these conditions also coincides with the BBLIF film-thickness measurement. The BBLIFmeasurement, on the other hand, can lead to localized overestimation of the film thickness at flow regions withsignificant wave activity, i.e. steep slopes or agitated films, and around gas bubbles entrained into the liquid film, or an underestimation inside the gas bubbles. Correction procedures are developed to compensate distortions causedby both methods that would make these techniques more accurate for standalone employment. The simultaneousapplication of both techniqu
Wright SF, Charogiannis A, Voulgaropoulos V, et al., 2018, Laser-based measurements of stratified liquid-liquid pipe flows interacting with jets in cross-flow, 19th International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics
At low velocities, horizontal liquid-liquid flows uder go gravitation ally-induced stratification, which in many practical applications complicatessignificantly the direct measurement of the average properties of theflow. The extent of flow stratification, however, can be limited through in line mixing leading to the formation of liquid-liquid dispersions withmore homogenous properties. In this work, we focus on the use of‘active’ mixing methods using jets in cross flows (JICFs). In this paper,a dedicated experimental flow facility for the investigation of such flowsis presented, along with the accompanying laser-based optical measurement techniques and associated algorithms that have beendeveloped for this investigation. The facility allows simultaneous,space-and time-resolved phase and velocity information to be generatedvia plan ar laser-induced fluorescence (PLIF) and particle velocimetry(PIV/ PTV), with stereo-PIV used to provide information on the third (out-of-plane) velocity component. Preliminary experimental results arepresented which demonstrate the capabilities of this arrangementfor optically examining stratified liquid-liquid flows interacting withJICFs, leading to new insights into these complex flows. The key resultsinclude phenomena of jets interacting with the liquid-liquid inter face,recirculation zones that lead to further mixing, the presence of complexcompound droplets, droplet size distributions, and water concentrationprofiles.
Georgiou S, Shah N, Markides C, Potential for Carbon Savings from the Deployment of Liquid-Air and Pumped-Thermal Electricity Storage Systems, Offshore Energy and Storage 2018
Herrando M, Pantaleo AM, Wang K, et al., Technoeconomic assessment of a PVT-based solar combined cooling heating and power (S-CCHP) system for the university campus of Bari, 13th Conference on Sustainable Development of Energy, Water and Environment Systems - SDEWES Conference, Publisher: SEDWES
In thiswork weanalyse the year-round technoeconomicperformance of a solar combined cooling, heating and power (S-CCHP)system that features polymeric flat-box PVT collectorscoupled via a thermal store to an absorptionchiller. The hourly space heating (SH), cooling and electricitydemands of the University Campus of Bari are used as inputs to amodeldeveloped in TRNSYS.Current electricity and gas prices are considered in order to estimate the annual cost savings which, together with the system’s investment cost, allow an estimation of itspayback time (PBT). The results are then compared to a PV systemthat matchesthe electricity demand of the Campus (including the electricity required to run the current HVAC system for air-conditioning).The results show that the main limiting factorfor the implementationof the S-CCHP systemis the roof-space availability in this application. Asystem with aninstalled power of 1.68MWpcan cover14% of the SH, 66% of the cooling and 17% oftheelectricaldemands of the Campus. The system’s PBTis estimated at 19.3years, which is 3 times higher than the PBTof a PV system of the same installed power, nevertheless,the proposed S-CCHPsystemhas the potential to displace 1,170tons CO2/year, or 50% more than theequivalentPV solution.
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