330 results found
Taleb AI, Sapin PMC, Barfuß C, et al., 2017, CFD Analysis of Thermally Induced Thermodynamic Loses in the Reciprocating Compression and Expansion of Real Gases, 1st International Seminar on Non-Ideal Compressible-Fluid Dynamics for Propulsion and Power, Publisher: IOP Publishing: Conference Series, ISSN: 1742-6588
The efficiency of expanders is of prime importance in determining the overallperformance of a variety of thermodynamic power systems, with reciprocating-piston expandersfavoured at intermediate-scales of application (typically 10–100 kW). Once the mechanical lossesin reciprocating machines are minimized (e.g. through careful valve design and operation), lossesdue to the unsteady thermal-energy exchange between the working fluid and the solid walls ofthe containing device can become the dominant loss mechanism. In this work, gas-spring devicesare investigated numerically in order to focus explicitly on the thermodynamic losses that arisedue to this unsteady heat transfer. The specific aim of the study is to investigate the behaviourof real gases in gas springs and to compare this to that of ideal gases in order to attain a betterunderstanding of the impact of real-gas effects on the thermally induced losses in reciprocatingexpanders and compressors. A CFD-model of a gas spring is developed in OpenFOAM. Threedifferent fluid models are compared: (1) an ideal-gas model with constant thermodynamicand transport properties; (2) an ideal-gas model with temperature-dependent properties; and(3) a real-gas model using the Peng-Robinson equation-of-state with temperature and pressure-dependent properties. Results indicate that, for simple, mono- and diatomic gases, like helium ornitrogen, there is a negligible difference in the pressure and temperature oscillations over a cyclebetween the ideal and real-gas models. However, when considering heavier (organic) molecules,such as propane, the ideal-gas model tends to overestimate the pressure compared to the real-gasmodel, especially if the temperature and pressure dependency of the thermodynamic propertiesis not taken into account. In fact, the ideal-gas model predicts higher pressures by as much as25% (compared to the real-gas model). Additionally, both ideal-gas models underestimate thethermall
White M, Oyewunmi OA, Haslam A, et al., 2017, Incorporating Computer-Aided Working-Fluid Design in the System Optimisation of an Organic Rankine Cycle Using the SAFT-γ Mie Equation of State, SAFT 2017 Conference
White MT, Oyewunmi OA, Haslam AJ, et al., 2017, High-efficiency industrial waste-heat recovery through computer-aided integrated working-fluid and ORC system optimisation, The 4th Sustainable Thermal Energy Management International Conference (SusTEM 2017)
In this paper, we develop a mixed-integer non-linear programming optimisation framework that combines working-fluid thermodynamic property predictions from a group-contribution equation of state, SAFT- Mie, with a thermodynamic description of an organic Rankine cycle. In this model, a number of working-fluids are described by their constituent functional groups (i.e., -CH3, -CH2, etc.), and integer optimisation variables are introduced in the description of the structure of the working-fluid. This facilitates combining the computer-aided molecular design of novel working-fluids with the power system optimisation into a single framework, thus removing subjective and pre-emptive screening criteria, and simultaneously moving towards the next generation of tailored working-fluids and optimised organic Rankine cycle systems for industrial waste-heat recovery applications. The thermodynamic model is first validated against an alternative formulation that uses (pseudo-experimental) thermodynamic property predictions from REFPROP, and against an optimisation study taken from the literature. Furthermore, molecular feasibility constraints are defined and validated in order to ensure all feasible working-fluid candidates can be found. Finally, the optimisation problem is formulated using the functional groups from the hydrocarbon family, and applied to three industrial waste-heat recovery case studies. The results demonstrate the potential of this framework to drive the search for the next generation of organic Rankine cycles, and to provide meaningful insights into which working-fluids are the optimal choices for a targeted application.
Willich C, Markides CN, White AJ, 2017, An investigation of heat transfer losses in reciprocating devices, APPLIED THERMAL ENGINEERING, Vol: 111, Pages: 903-913, ISSN: 1359-4311
Ramos Cabal A, Chatzopoulou MA, Guarracino I, et al., 2017, Hybrid photovoltaic-thermal solar systems for combined heating, cooling and power provision in the urban environment, 4th Sustainable Thermal Energy Management International Conference (SusTEM 2017)
Charogiannis, Denner, van Wachem, et al., 2017, Detailed Hydrodynamic Characterization of Harmonically Excited Falling-Film Flows: A Combined Experimental and Computational Study, Physical Review Fluids, Vol: 2, Pages: 014002-014002, ISSN: 2469-990X
We present results from the simultaneous application of planar laser-induced uorescence (PLIF)and particle image/tracking velocimetry, complemented by direct numerical simulations, aimed atthe detailed hydrodynamic characterization of harmonically excited liquid- lm ows falling underthe action of gravity. The experimental campaign comprises four di erent aqueous-glycerol solutionscorresponding to four Kapitza numbers (Ka= 14, 85, 350, 1800), spanning the Reynolds numberrangeRe= 2:3
Herrando M, Ramos A, Zabalza I, et al., 2017, Energy performance of a solar trigeneration system based on a novel hybrid PVT panel for residential applications, Pages: 1090-1101
© 2017. The Authors. The overall aim of this work is to assess the performance of high-efficiency solar trigeneration systems based on a novel hybrid photovoltaic-thermal (PVT) collector for the provision of domestic hot water (DHW), space heating (SH), cooling and electricity to residential single-family households. To this end, a TRNSYS model is developed featuring a novel hybrid PVT panel based on a new absorber-exchanger configuration coupled via a thermal store to two alternative small-scale solar heating and cooling configurations, one based on an electrically-driven vapour-compression heat pump (PVT+HP) and one on a thermally-driven absorption refrigeration unit (PVT+AR). The energy demands of a single-family house located in three different climates, namely Seville (Spain), Rome (Italy) and Paris (France), are estimated using EnergyPlus. Hourly transient simulations of the complete systems considering real weather data and reasonable areas for collector installation (< 30 m2) are conducted over a year. The household energy demands covered by the two systems indicate that the PVT+HP configuration is the most promising for the locations of Rome and Paris, covering more than 74% the DHW demand, 100% of the space heating and cooling demands, as well as an important share of the electricity demand. Meanwhile, for Seville, the PVT+AR configuration appears as a promising alternative, covering more than 80% of the DHW, around 70% of the cooling and electricity, and 54% of the space heating demands.
Kheirabadi AN, Freeman J, Cabal AR, et al., 2017, EXPERIMENTAL INVESTIGATION OF AN AMMONIA-WATER DIFFUSION-ABSORPTION REFRIGERATOR (DAR) AT PART LOAD, ASME Summer Heat Transfer Conference, Publisher: AMER SOC MECHANICAL ENGINEERS
Charogiannis A, Markides CN, 2017, APPLICATION OF LASER-INDUCED FLUORESCENCE, PARTICLE VELOCIMETRY AND INFRARED THERMOGRAPHY TO HEATED FALLING-FILM FLOWS, ASME Summer Heat Transfer Conference, Publisher: AMER SOC MECHANICAL ENGINEERS
Herrando M, Guarracino I, del Amo A, et al., 2017, Energy Characterization and Optimization of New Heat Recovery Configurations in Hybrid PVT Systems, 11th ISES EuroSun Conference, Publisher: INTL SOLAR ENERGY SOC, Pages: 1228-1239
Chatzopoulou MA, Markides CN, 2016, Modelling of advanced combined heat and power systems in building applications, 2nd Thermal and Fluid Engineering Conference TFEC2017
Mellor AV, Guarracino I, Llin LF, et al., 2016, Specially designed solar cells for hybrid photovoltaic-thermal generators, 43rd IEEE Photovoltaic Specialists Conference, Publisher: IEEE
The performance of hybrid photovoltaic-thermal systems can be improved using PV cells that are specially designed to generate both electricity and useful heat with maximum efficiency. Present systems, however, use standard PV cells that are only optimized for electrical performance. In this work, we have developed two cell-level components that will improve the thermal efficiency of PV-T collectors, with minimal loss of electrical efficiency. These are a spectrally-selective low-emissivity coating to reduce radiative thermal losses, and a nanotextured rear reflector to improve absorption of the near-infrared part of the solar spectrum for heat generation.
Le Brun N, Hewitt GF, Markides CN, 2016, Transient freezing of molten salts in pipe-flow systems: application to the direct reactor auxiliary cooling system (DRACS), Applied Energy, Vol: 186, Pages: 56-67, ISSN: 0306-2619
The possibility of molten-salt freezing in pipe-flow systems is a key concern for the solar-energy industry and a safety issue in the new generation of molten-salt reactors, worthy of careful consideration. This paper tackles the problem of coolant solidification in complex pipe networks by developing a transient thermohydraulic model and applying it to the ‘Direct Reactor Auxiliary Cooling System’ (DRACS), the passive-safety system proposed for the Generation-IV molten-salt reactors. The results indicate that DRACS, as currently envisioned, is prone to failure due to freezing in the air/molten-salt heat exchanger, which can occur after approximately 20 minutes, leading to reactor temperatures above 900 °C within 4 hours. The occurrence of this scenario is related to an unstable behaviour mode of DRACS in which newly formed solid-salt deposit on the pipe walls acts to decrease the flow-rate in the secondary loop, facilitating additional solid-salt deposition. Conservative criteria are suggested to facilitate preliminary assessments of early-stage DRACS designs. The present study is, to the knowledge of the authors, the first of its kind in serving to illustrate possible safety concerns in molten-salt reactors, which are otherwise considered very safe in the literature. Furthermore, and from a broader prospective, the analytical tools developed in this study can also be applied to examine the freezing propensity of molten-salt flows in other complex piping systems where standard, finite element approaches are computationally too expensive.
Zhang K, Chen X, Markides CN, et al., 2016, Evaluation of ejector performance for an organic Rankine cycle combined power and cooling system, Applied Energy, Vol: 184, Pages: 404-412, ISSN: 0306-2619
Power-generation systems based on organic Rankine cycles (ORCs) are well suited and increasingly employed in the conversion of thermal energy from low temperature heat sources to power. These systems can be driven by waste heat, for example from various industrial processes, as well as solar or geothermal energy. A useful extension of such systems involves a combined ORC and ejector-refrigeration cycle (EORC) that is capable, at low cost and complexity, of producing useful power while having a simultaneous capacity for cooling that is highly desirable in many applications. A significant thermodynamic loss in such a combined energy system takes place in the ejector due to unavoidable losses caused by irreversible mixing in this component. This paper focuses on the flow and transport processes in an ejector, in order to understand and quantify the underlying reasons for these losses, as well as their sensitivity to important design parameters and operational variables. Specifically, the study considers, beyond variations to the geometric design of the ejector, also the role of changing the external conditions across this component and how these affect its performance; this is not only important in helping develop ejector designs in the first instance, but also in evaluating how the performance may shift (in fact, deteriorate) quantitatively when the device (and wider energy system within which it functions) are operated at part load, away from their design/operating points. An appreciation of the loss mechanisms and how these vary can be harnessed to propose new and improved designs leading to more efficient EROC systems, which would greatly enhance this technology’s economic and environmental potential. It is found that some operating conditions, such as a high pressure of the secondary and discharge fluid, lead to higher energy losses inside the ejector and limit the performance of the entire system. Based on the ejector model, an optimal design featuring a sm
Morgan RG, Ibarra R, Zadrazil I, et al., 2016, On the role of buoyancy-driven instabilities in horizontal liquid–liquid flow, International Journal of Multiphase Flow, Vol: 89, Pages: 123-135, ISSN: 0301-9322
Horizontal flows of two initially stratified immiscible liquids with matched refractive indices, namely an aliphatic hydrocarbon oil (Exxsol D80) and an aqueous-glycerol solution, are investigated by combining two laser-based optical-diagnostic measurement techniques. Specifically, high-speed Planar Laser-Induced Fluorescence (PLIF) is used to provide spatiotemporally resolved phase information, while high-speed Particle Image and Tracking Velocimetry (PIV/PVT) are used to provide information on the velocity field in both phases. The two techniques are applied simultaneously in a vertical plane through the centreline of the investigated pipe flow, illuminated by a single laser-sheet in a time-resolved manner (at a frequency of 1–2 kHz depending on the flow condition). Optical distortions due to the curvature of the (transparent) circular tube test-section are corrected with the use of a graticule (target). The test section where the optical-diagnostic methods are applied is located 244 pipe-diameters downstream of the inlet section, in order to ensure a significant development length. The experimental campaign is explicitly designed to study the long-length development of immiscible liquid–liquid flows by introducing the heavier (aqueous) phase at the top of the channel and above the lighter (oil) phase that is introduced at the bottom, which corresponds to an unstably-stratified “inverted” inlet orientation in the opposite orientation to that in which the phases would naturally separate. The main focus is to evaluate the role of the subsequent interfacial instabilities on the resulting long-length flow patterns and characteristics, also by direct comparison to an existing liquid–liquid flow dataset generated in previous work, downstream of a “normal” inlet orientation in which the oil phase was introduced over the aqueous phase in a conventional stably-stratified inlet orientation. To the best knowledge of the authors this
Freeman J, Ramos Cabal A, Mac Dowel N, et al., 2016, An experimentally validated model of a solar-cooling system based on an ammonia-water diffusion-absorption cycle, The 8th International Conference on Applied Energy – ICAE2016
An experimentally validated thermodynamic model of a domestic-scale solar-cooling system based on an ammonia-water diffusion-absorption refrigeration (DAR) cycle is presented. The model combines sub-component descriptions of a DAR unit and a suitably sized (matched) solar-collector array, which are validated separately;outdoor tests are performed on an evacuated-tube (ET) collector over a range of solar-irradiance conditions, while a 150-W (nominal rating) DAR unit is tested in the laboratory with a thermal input provided by controlled electrical heaters. A COP of 0.2 is reported for the DARunit when operating with a generator temperature of 155 °C and a system charge pressure of 20.7 bar. Using the experimentally validated solar-cooling system model, it is found that the area of the collector array required to power the system depends strongly on the type of collector. Annual simulations are also performed in various geographical regions order to predict the system’s cooling output. It is found that a single DAR unit with a 3-m2 ET arrayhas the potential to provide 150-200 kWh per year of coolingin a southern European climate, which amounts approximately to the per capita demand for space cooling in residential dwellings in the same region.
White AJ, McTigue JD, Markides CN, 2016, Analysis and optimisation of packed-bed thermal reservoirs for electricity storage applications, PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART A-JOURNAL OF POWER AND ENERGY, Vol: 230, Pages: 739-754, ISSN: 0957-6509
Oyewunmi OA, Kirmse CJW, Markides CN, 2016, HEAT EXCHANGER ANALYSIS OF AZEOTROPE MIXTURES IN ORGANIC RANKINE CYCLES, UK Heat Transfer Conference
Delangle ACC, 2016, MODELLING AND OPTIMISATION OF A DISTRICT HEATING NETWORK’S MARGINAL EXTENSION
District heating networks have a key role to play in tackling greenhouse gas emissions associated with urban energy systems. In this context, renewed attention has recently been paid to them and there is a global trend towards the acceleration of district heating expansion. If several existing networks even plan to extend, little work has been carried out on district heating networks expansion in the literature. The following thesis develops a methodology to find the best district heating network expansion strategy under given constraints. After analysing the heat demand and establishing buildings connection scenarios, the model developed optimises the energy centre expansion over a twelve years’ time horizon. Spatial expansion aspects are also included. The optimisation approach was applied to the case of the Barkantine district heating network in the Isle of Dogs, London. The model demonstrated that depending on the optimisation performed (costs or greenhouse gas emissions), some connection strategies have to be privileged. It also proved that district heating scheme’s financial viability may be affected by the connection scenario chosen, highlighting the necessity of planning strategies for district heating networks. The proposed approach can be adapted to other district heating network schemes and modified to integrate more aspects and constraints.
Georgiou S, Markides CN, Shah N, 2016, Decarbonisation of food supply chains from an energetic perspective through optimisation and technological modelling: A holistic approach, Perspectives on Environmental Change DTP Conference 2016
Oyewunmi OA, Simó Ferré-Serres, Steven Lecompte, et al., 2017, An assessment of subcritical and trans-critical organic Rankine cycles for waste-heat recovery, The 8th International Conference on Applied Energy – ICAE2016, Publisher: Elsevier, ISSN: 1876-6102
Organic Rankine cycle (ORC) systems are increasingly being deployed for waste-heat recovery and conversion in industrial settings. Using a case study of an exhaust flue-gas streamat a temperature of 380 °C as the heat source, an ORC system power output in excess of 10MW is predicted at exergy efficiencies ranging between 20% and 35%. By comparison with available experimental data, the thermodynamic properties (including those in the supercritical region) of working fluids are shown to be reliably predicted by the SAFT-VR Mie equation of state; this verification is quite important as this is the first time that the SAFT-VR Mie equation of state is used forthermodynamic property predictionof working fluids in their supercriticalstateintrans-critical ORC systems.Various cycle configurations and the use of working-fluid mixtures are also investigated. ORC systems operating on trans-critical cycles and those incorporating an internal heat exchanger(IHE)are seen to be beneficial from a thermodynamic perspective, they are,however,more expensive than the simpleORC system considered (subcritical cycle with no IHE).Furthermore, ORC systems using pure working fluids are associated withslightly lower costs than those with fluid mixtures. It is concluded thatabasicORCsystem utilizingpure working fluidsshowsthe lowest specific investment cost(SIC)in the case study considered.
Lecompte S, Oyewunmi OA, Markides C, et al., 2016, Preliminary experimental results of an 11 kWe organic Rankine cycle, The 8th International Conference on Applied Energy – ICAE2016, Publisher: Elsevier, ISSN: 1876-6102
The organic Rankine cycle(ORC)is considered a viable technology forconvertinglow-and medium-temperature heat to electricity. However,many of ORC systems in practical applications operate in off-design conditions. In order to characterize thisoperation, experimental data is needed. In this paper, the commissioning of an 11 kWe ORC is described with special attention to the processingof the data. A filtering algorithm is introduced to isolate steady-state working points. This filter is thenappliedtothe raw experimental data. In addition,the reliability of the experimental data is evaluated by investigating the heat balancesover the heat exchangers and error propagation of the measurementuncertainties. The result of this work is a test-setup which is fully ready for high-accuracyand reliablemeasurements,including the post-processingsteps. In the future, off-design models will be validatedwith the acquired experimental dataand especially two-phase expansion will be further investigated.
Cedillos D, Acha Izquierdo S, Shah N, et al., 2016, A Technology Selection and Operation (TSO) optimisation model for distributed energy systems: Mathematical formulation and case study, Applied Energy, Vol: 180, Pages: 491-503, ISSN: 1872-9118
This paper presents a model which simultaneously optimises the selection and operation of technologies for distributed energy systems in buildings. The Technology Selection and Operation (TSO) model enables a new approach for the optimal selection and operation of energy system technologies that encompasses whole life costing, carbon emissions as well as real-time energy prices and demands; thus, providing a more comprehensive result than current methods. Utilizing historic metered energy demands, projected energy prices and a portfolio of available technologies, the mathematical model simultaneously solves for an optimal technology selection and operational strategy for a determined building based on a preferred objective: minimizing cost and/or minimizing carbon emissions. The TSO is a comprehensive and novel techno-economic model, capable of providing decision makers an optimal selection from a portfolio of available energy technologies. The current portfolio of available technologies is composed of various combined heat and power (CHP) and organic Rankine cycle (ORC) units. The TSO model framework is data-driven and therefore presents a high level of flexibility with respect to time granularity, period of analysis and the technology portfolio. A case study depicts the capabilities of the model; optimisation results under different temporal arrangements and technology options are showcased. Overall, the TSO model provides meaningful insights that allow stakeholders to make technology investment decisions with greater assurance.
Le Brun N, Markides C, 2016, Framework for the energetic assessment of South and South-East Asia fixed chimney bull’s trench kiln, ICIEA 2016, Publisher: EDP Sciences
One of the major sources of fuel consumption and greenhouse gas emission in South and South-East Asia is brick manufacturing. One of the most commonly implemented technologies for brick manufacturing in this region is the fixed chimney Bull’s trench kiln (FCBTK). This type of technology largely depends on manual labour and is very inefficient when compared to more modern technologies. Because the adoption of more advanced technologies is hindered by the socio-economical background, the much needed innovations in the brick sector are necessarily related to improving/modifying the FCBTK already operational. However, few scientific studies have been conducted on FCBTK probably due to the basic level of technological development. Such studies are however important to systematically and methodologically assess the challenges and solutions in FCBTK. In this study we develop a thermo-energetic model to evaluate the importance of the parameters pertained to FCBTK construction and operation. The prospective of this study is to build an initial thermo-energetic framework that will serve as a basis to investigate possible energetic improvements.
Le Brun N, Markides C, 2016, A transient model for simulating the freezing process of molten-salt coolants, ICIEA 2016, Publisher: EDP Sciences
Even though molten salts have many useful characteristic, especially as coolants for nuclear reactors, they are prone to freezing due to their high melting point. The solidification of the salt inside the piping system could cause structural damage and stop the flow of coolant with possible serious problems. Modelling the freezing process is therefore of primary importance for nuclear safety. In this study a quasi-steady thermo-hydraulic model has been derived and implemented to describe the transient freezing of molten salts. The partial differential equations describing the solidification/melting of the salt are solved numerically using a combination of standard explicit and implicit methods. Validation of the model is presented based on previous experimental studies for two separate cases.
White MT, Oyewunmi OA, Haslam AJ, et al., 2016, Integrated working-fluid design and ORC system optimisation for waste-heat recovery using CAMD and the SAFT-γ Mie equation of state, 3rd Annual Engine ORC Consortium Workshop
Freeman J, Guarracino I, Unamba CK, et al., 2016, Developing a test bed for small-scale ORC expanders in waste-heat recovery applications, 3rd Annual Engine ORC Consortium Workshop
Charogiannis A, Pradas M, Denner F, et al., 2016, Hydrodynamic characteristics of harmonically excited thin-film flows: Experiments and computations, 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics
Oyewunmi OA, Ferré-Serres S, Markides C, 2016, Supercritical organic Rankine cycles in waste-heat recovery using SAFT-VR Mie, 3rd International Meeting of Specialists on Heat Transfer and Fluid Dynamics at Supercritical Pressure (HFSCP2016)
Ibarra R, Morgan R, Zadrazil I, et al., 2016, Investigation of oil-water flow in horizontal pipes using simultaneous two-line planar laser-induced fluorescence and particle velocimetry, HEFAT, 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics
The flow of oil and water in pipes represents a challenging configuration in multiphase flows due to complex hydrodynamics which are still not fully understood. This can be observed in the large number of flow regimes encountered, which extend from smooth stratified flows to complex dispersions such as droplets of oil-in-water and water-in-oil. These flow configurations are the result of the inherent properties of the liquid phases, e.g., their densities and viscosities, interfacial tension and contact angle, as well as of flow conditions and related phenomena, such as turbulence, which have a direct effect on the interface instabilities giving rise to flow regime transitions. In this paper, experimental data are reported that were acquired at low water cuts and low mixture velocities using an aliphatic oil (Exxsol D140) and water as the test fluids in an 8.5 m long and 32 mm internal diameter horizontal pipe. A copper-vapour laser, emitting two narrow-band laser beams, and two high-speed cameras were used to obtain quantitative simultaneous information of the flow (specifically, spatiotemporally resolved fluid-phase and velocity information in both phases) based on simultaneous two-line Planar Laser-Induced Fluorescence (PLIF) and Particle Image and Tracking Velocimetry (PIV/PTV). To the best knowledge of the authors this is the first such instance of the application of this combined technique to these flows. It is found that the rms of the fluctuating velocity show peaks in high shear regions, i.e. at the pipe wall and interface.
This data is extracted from the Web of Science and reproduced under a licence from Thomson Reuters. You may not copy or re-distribute this data in whole or in part without the written consent of the Science business of Thomson Reuters.