Modelling and development of thermo-mechanical energy storage

Pumped thermal energy storage (PTES) and liquid air energy storage (LAES) are two technologies that use mechanically-driven thermodynamic cycles to store electricity in the form of high-grade thermal energy, employing abundant materials that are kept in large insulated tanks. Both technologies are free from geographic constraints, providing a significant advantage over competing methods such as pumped hydro or compressed air energy storage. The focus of this thesis is on the analysis, modelling and development of these technologies. A number of PTES systems have been proposed based on different thermodynamic cycles. A variant based on the Joule-Brayton cycle employing liquid storage media is studied here. An analytical study is presented that reveals how the performance of the cycle varies along a range of operating conditions. Generally, the same strategies that minimise compression/expansion losses also maximise heat exchanger losses, which results in optimal points at certain operating conditions. A numerical model is developed to find these optima while accounting for real fluid properties. Employing a regenerative heat exchanger is found useful to adapt the cycle to the operating temperature ranges of the storage liquids and to increase the performance of the cycle. A new combined cycle that integrates PTES and LAES is presented. The fundamental advantage is that the cold thermal reservoirs that would be required by the separate cycles are replaced by a single heat exchanger that acts between them, thereby saving significant amounts of storage media per unit of energy stored. Several configurations are possible and these are studied and optimised. The most advanced configuration reaches a round-trip efficiency of 71 % under nominal conditions, compared to 65 % for stand-alone PTES and 61 % for LAES. A further adaptation of the combined cycle is presented which only employs water and liquid air as storage media, dramatically reducing the cost of energy capacity. The performance of the heat exchangers is found to have a significant impact on the overall performance of the various cycles. For this reason, an optimisation procedure is developed to obtain heat exchanger designs that minimise entropy generation for a given amount of material. These designs are used when estimating the costs of energy capacity and power capacity of each cycle. Results indicate that the best cycle configurations would be competitive with reported costs for pumped hydro and compressed air energy storage.This PhD project was funded by a Peterhouse Graduate Studentship

GiD 2008. 4th Conference on advances and applications of GiD

The extended use of simulation programs has leaned on the advances in user-friendly interfaces and in the capability to generate meshes for any generic complex geometry. More than ten years of development have made Gid grow to become one of the more popular pre ans postprocessing systems at international level. The constant dialogue between the GiD development team and the users has guided the development of giD to cover the pre-post needs of many disciplines in science and engineering. Following gthis philosophy, the biannual GiD Conference has become an important forum for discussion and interchange of experiences among the GiD community. This monograph includes the contributions of the participants to the fourth edition of the GiD Conference held in the island of Ibiza from 8-9 May 2008

Numerical modelling of additive manufacturing process for stainless steel tension testing samples

Nowadays additive manufacturing (AM) technologies including 3D printing grow rapidly and they are expected to replace conventional subtractive manufacturing technologies to some extents. During a selective laser melting (SLM) process as one of popular AM technologies for metals, large amount of heats is required to melt metal powders, and this leads to distortions and/or shrinkages of additively manufactured parts. It is useful to predict the 3D printed parts to control unwanted distortions and shrinkages before their 3D printing. This study develops a two-phase numerical modelling and simulation process of AM process for 17-4PH stainless steel and it considers the importance of post-processing and the need for calibration to achieve a high-quality printing at the end. By using this proposed AM modelling and simulation process, optimal process parameters, material properties, and topology can be obtained to ensure a part 3D printed successfully

Design and Analysis of Pulse Tube Refrigerator

After decades of rapid development, the absence of moving parts in the cold head, low vibration, long lifetime and high reliability, pulse tube refrigerators are the most promising cryo-coolers. Because of these momentous advantages, they are widely used in Superconducting Quantum Interference Devices (SQUIDs), cooling of infrared sensors, low noise electronic amplifiers, missiles and military helicopters, superconducting magnets, liquefaction of gases, gamma ray spectrometers, liquefaction of gases, X-ray devices and high temperature superconductors etc. It has also got wide applications in preservation of live biological materials as well as in scientific equipment. It is essential to accurate modelling of the pulse tube cryocooler and predicts its performance, thereby arrive at optimum design. At the current stage of worldwide research, such accurate models are not readily available in open literature. Further, the complexity of the periodic flow in the PTR makes analysis difficult. Although different models are available to simulate pulse tube cryocoolers, the models have its limitations and also range of applicability. In order to accurately predict and improve the performance of the PTR system a reasonably thorough understanding of the thermos fluid- process in the system is required. One way to understand the processes is by numerically solving the continuum governing equations based on fundamental principles, without making arbitrary simplified assumptions. The recent availability of powerful computational fluid dynamics (CFD) software that is capable of rigorously modelling of transient and multidimensional flow and heat transfer process in complexgeometries provides a good opportunity for analysis of PTRs. Performance evaluation and parametric studies of an Inertance tube pulse tube refrigerator (ITPTR) and an orifice pulse tube refrigerator (OPTR) are carried out. The integrated model consists of individual models of the components, namely, the compressor, after cooler, regenerator, cold heat exchanger, pulse tube, warm heat exchanger, inertance tube or orifice, and the reservoir. In the first part of the study, the commercial CFD package, FLUENT is used for investigating the transport phenomenon inside the ITPTR. The local thermal equilibrium and thermal non-equilibrium of the gas and the matrix is taken into account for the modelling of porous zones and the results are compared. The focus of the second part of the study is to establish the most important geometrical dimension and operating parameters that contribute to the performance of ITPTR and OPTR. The numerical investigation procedure for these investigations is conducted according to the Response surface methodology (RSM) and the results are statistically evaluated using analysis of variance method. Finally a multi-objective evolutionary algorithm is used to optimize the parameters and for an optimized case the phasor diagram is discussed

Development and optimization of small-scale axial turbines for distributed cryogenic energy storage system

This research aims to study in a comprehensive way a different power generation cryogenic energy storage cycles and effective strategies for developing an optimized design of small scale nitrogen axial turbines as the expanders for these cycles within the capacities that can be used for small/medium size buildings, rural, and remote off-grid communities. The hybrid open-closed Rankine cycle have been chosen as the case study for nitrogen turbine analysis for expansion ratios ranged from 1.5 to 3. New turbine design methodology has been developed which integrates one dimension preliminary design method (mean-line method) and three dimensional CFD simulations, and expe1imental validation testing. This turbine methodology was expanded to include developing optimization parametrization technique, a parametric study of four different blade configurations (lean, sweep, twist, and bow), and development of a novel dual stage non-repeated annular area small-scale axial nitrogen turbine. In order to validate the CFD simulation, the design methodology, and to investigate the effects of blade height on small-scale axial turbines performance, a test rig using compressed air was developed. Three manufactured axial turbines with different blade heights ( 4mm, 6mm, and 8mm) were manufactured and tested at various operating conditions

ECOS 2012

The 8-volume set contains the Proceedings of the 25th ECOS 2012 International Conference, Perugia, Italy, June 26th to June 29th, 2012. ECOS is an acronym for Efficiency, Cost, Optimization and Simulation (of energy conversion systems and processes), summarizing the topics covered in ECOS: Thermodynamics, Heat and Mass Transfer, Exergy and Second Law Analysis, Process Integration and Heat Exchanger Networks, Fluid Dynamics and Power Plant Components, Fuel Cells, Simulation of Energy Conversion Systems, Renewable Energies, Thermo-Economic Analysis and Optimisation, Combustion, Chemical Reactors, Carbon Capture and Sequestration, Building/Urban/Complex Energy Systems, Water Desalination and Use of Water Resources, Energy Systems- Environmental and Sustainability Issues, System Operation/ Control/Diagnosis and Prognosis, Industrial Ecology

Radial turbine expander design, modelling and testing for automotive organic Rankine cycle waste heat recovery

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University LondonSince the late 19th century, the average temperature on Earth has risen by approximately 1.1 °Cbecause of the increased carbon dioxide (CO2) and other man-made emissions to the atmosphere. The transportation sector is responsible for approximately 33% of the global CO2 emissions and 14% of the overall greenhouse gas emissions. Therefore, increasingly stringent regulations in the European Union require CO2 emissions to be lower than 95 2/ by 2020. In this regard, improvements in internal combustion engines (ICEs)must be achieved in terms of fuel consumption and CO2 emissions. Given that only up to 35% of fuel energy is converted into mechanical power, the wasted energy can be reused through waste heat recovery (WHR) technologies. Consequently, organic Rankine cycle (ORC) has received significant attention as a WHR technology because of its ability to recover wasted heat in low- to medium-heat sources. The Expansion machine is the key component in ORC systems, and its performance has a direct and significant impact on overall cycle efficiency. However, the thermal efficiencies of ORC systems are typically low due to low working temperatures. Moreover, supersonic conditions at the high pressure ratios are usually encountered in the expander due to the thermal properties of the working fluids selected which are different to water.Therefore, this thesis aims to design an efficient radial-inflow turbine to avoid further efficiency reductions in the overall system. To fulfil this aim, a novel design and optimisation methodology was developed. A design of experiments technique was incorporated in the methodology toexplorethe effects of input parameters on turbine performance and overall size. Importantly, performance prediction modelling by means of 1D mean-line modelling was employed in the proposed methodology to examine the performance of ORC turbines at constant geometries. The proposed methodology was validated by three methods: computational fluid dynamics analysis, experimental work available in the literature, and experimental work in the current project.Owing to the lack of actual experimental works in ORC-ICE applications, a test rig was built around a heavy-duty diesel engine at Brunel University London and tested at partial load conditions due to the requirement for a realistic off-high representation of the performance of the system rather than its best (design) point, while taking into account the limitation of the engine dynamometer employed. Results of the design methodology developed for this projectpresented an efficient single-stage high-pressure ratio radial-inflow turbine with a total to static efficiency of 74.4% and an output power of 13.6 kW.Experimental results showed that the ORC system had a thermal efficiency of 4.3%, and the brake-specific fuel consumption of the engine was reduced by 3%. The novel meanlineoff designcode (MOC) was validated with the experimental works from three turbines. In comparison with the experimental results conducted at Brunel University London, the predicted and measured results were in good agreement with a maximum deviation of 2.8%.Innovate U

Model-based development of high-pressure membrane contactors for natural gas sweetening

Membrane separation and chemical solvent absorption technologies are both widely employed for Natural Gas (NG) Sweetening. A new hybrid process combining the advantages of both technologies, called membrane contactor (MBC), has been drawing significant attention over the past decade. MBC is considered a promising process for intensification purposes, as it can provide high specific surface areas, independent control over the gas and liquid flow rates, modularity, and compactness. Nevertheless, no literature to date has conducted a process-wide assessment of using MBC for NG sweetening, and therefore, its intensification potential cannot be systematically quantified. This challenge is the motivation of the research presented in this thesis. The main objective of this work is to develop process-wide modeling of NG sweetening using MBC to enable MBC process design and performance assessment. A predictive mathematical model of high-pressure MBC for NG sweetening with alkanolamines as the chemical solvent was developed. The model explicitly accounts for the rates of mass transfer through the membrane, diffusion, and chemical reaction in the liquid phase. A combination of 1-d and 2-d mass-balance equations to predict the CO2 absorption flux was considered, whereby the degree of membrane wetting itself is calculated using the Laplace-Young equation based upon knowledge of the membrane pore-size distribution, fluid flow configuration, and operating condition. The MBC model can also predict the solvent evaporative losses and the hydrocarbon (HC) absorption into amine solvent, which is important to maintain the CO2 absorption performance in MBC and to quantify the potential solvent make-up and product loss. Then, a full-scale steady-state MBC-based NG sweetening process was developed whereby the MBC model (absorption section) is integrated with the conventional solvent regeneration model (desorption section) in the gPROMS ProcessBuilder environment. The predictive capability of the model was tested using two sets of membranes with different characteristics, against data from two experimental settings; a lab-scale MBC module, where the purification is conducted using binary gas mixtures of CH4/CO2 and N2/CO2; and a pilot-scale MBC module operated under industrially relevant conditions at a NG processing plant in Malaysia. The important operation and design parameters such as the CO2 partial pressure, gas and liquid flowrates, pressure, temperature, liquid CO2 loading, membrane area and fiber length were varied to determine the performance of MBC. The model results clearly showed the change in the CO2 absorption performance and the energy consumption related to the variables. All model predictions showed a close agreement with the measured CO2 absorption fluxes, energy consumptions and the HC absorption and recovery from the solvent. The MBC model provided valuable research recommendations, whereby approximately 80% increase of CO2 absorption performance was achieved in MBC pilot plant by operating a smaller diameter of hollow fiber membrane in a horizontal orientation. The integrated process model is used to analyse the effects of various design configuration and operating conditions, such as the lean and semi-lean operations to meet sales gas specification. The experimental data and model analysis has confirmed the advantages of semi-lean operation in terms of energy reduction and physical footprint. Finally, a model based scale-up of a commercial MBC for NG sweetening was conducted to gauge its intensification potential. Overall, the scaled-up MBC commercial module showed promising prospects, whereby (i) the predicted reboiler energy per ton of CO2 removed is lower than the conventional amine absorption column by 12 - 50%; (ii) the predicted amine loss rate per treated gas and per ton of CO2 removed are lower compared to the typical loss rates reported in a conventional amine-based processes; and (iii) a potential savings of US$ 0.96-1.1 million 〖"yr" 〗^"-1" from the HC recovery can be realized, subject to further sweetening of the flash gas. Nevertheless, the MBC may require larger footprint than conventional absorption column due to horizontal operation. Going forward, the MBC model can be used to provide research and development targets, such as the improvement in membrane specific surface area and the hydrophobicity to enable commercial MBC modules to be stacked, thereby improving the intensification potential in terms of footprint.Open Acces