• Evaluation of the performance and economic viability of a novel low temperature carbon capture process

      Wilson, Paul; Lychnos, George; Clements, Alastair; Michailos, Stavros; Font Palma, Carolina; Diego, Maria E.; Pourkashanian, Mohamed; Howe, Joseph; PMW Technology Ltd; University of Sheffield; University of Chester (Elsevier, 2019-04-22)
      A novel Advanced Cryogenic Carbon Capture (A3C) process is being developed using low cost but high intensity heat transfer to achieve high CO2 capture efficiencies with a much reduced energy consumption and process equipment size. These characteristics, along with the purity of CO2 product and absence of process chemicals, offer the potential for application across a range of sectors. This work presents a techno-economic evaluation for applications ranging from 3% to 35%vol. CO2 content. The A3C process is evaluated against an amine-based CO2 capture process for three applications; an oil-fired boiler, a combined cycle gas turbine (CCGT) and a biogas upgrading plant. The A3C process has shown a modest life cost advantage over the mature MEA technology for the larger selected applications, and substantially lower costs in the smaller biogas application. Enhanced energy recovery and optimization offer significant opportunities for further reductions in cost.
    • Evaporation of liquid nitrogen droplets in superheated immiscible liquids

      Rebelo, Neville; Zhao, Huayong; Nadal, Francois; Garner, Colin; Williams, Andy; Loughborough University; University of Chester (Elsevier, 2019-08-22)
      Liquid nitrogen or other cryogenic liquids have the potential to replace or augment current energy sources in cooling and power applications. This can be done by the rapid evaporation and expansion processes that occur when liquid nitrogen is injected into hotter fluids in mechanical expander systems. In this study, the evaporation process of single liquid nitrogen droplets when submerged into n-propanol, methanol, n-hexane, and n-pentane maintained at 294 K has been investigated experimentally and numerically. The evaporation process is quantified by tracking the growth rate of the resulting nitrogen vapour bubble that has an interface with the bulk liquid. The experimental data suggest that the bubble volume growth is proportional to the time and the bubble growth rate is mainly determined by the initial droplet size. A comparison between the four different bulk liquids indicates that the evaporation rate in n-pentane is the highest, possibly due to its low surface tension. A scaling law based on the pure diffusion-controlled evaporation of droplet in open air environment has been successfully implemented to scale the experimental data. The deviation between the scaling law predictions and the experimental data for 2-propanol, methanol and n-hexane vary between 4% and 30% and the deviation for n-pentane was between 24% and 65%. The more detailed bubble growth rates have been modelled by a heuristic one-dimensional, spherically symmetric quasi-steady-state confined model, which can predict the growth trend well but consistently underestimate the growth rate. A fixed effective thermal conductivity is then introduced to account for the complex dynamics of the droplet inside the bubble and the subsequent convective processes in the surrounding vapour, which leads to a satisfactory quantitative prediction of the growth rate.
    • Evidence for the Perception of Time Distortion During Episodes of Alice in Wonderland Syndrome

      Jia, Yu; Miao. Ying; University of Chester; Aston University (Lippincott Williams & Wilkins, 2018-05-17)
      Alice in Wonderland syndrome (AIWS) is a rare perceptual disorder associated with sensation of one or several visual and/or auditory perceptual distortions including size of body parts, size of external objects, or passage of time (either speeding up or slowing down). Cause for AIWS is yet to be widely agreed, and the implications are widely varied. One of the research difficulties is the brevity of each episode, typically not exceeding few tens of minutes. This article presents a male adult in late 20s who has apparently experienced AIWS episodes since childhood, and infection has been ruled out. Reaction speed tests were conducted during and after AIWS episodes, across a span of 13 months. Statistically significant evidence is present for delayed response time during AIWS episodes when the patient claims to experience a sensation of time distortion: where events seem to move faster and people appear to speak quicker.
    • Evidence of Lipid Exchange in Styrene Maleic Acid Lipid Particle (SMALP) Nanodisc Systems

      Hazell, Gavin; Arnold, Thomas; Tognoloni, Cecilia; Barker, Robert; Clifton, Luke; Steinke, Nina-Juliane; Edler, Karen; University of Chester, University of Bath, University of Dundee, ISIS, Diamond Light Source (American Chemical Society, 2016-10-14)
      Styrene-alt-maleic Acid lipid particles (SMALPs) are self-assembled discoidal structures composed of a polymer belt and a segment of lipid bilayer, which are capable of encapsulating membrane proteins directly from the cell membrane. Here we present evidence of the exchange of lipids between such “nanodiscs” and lipid monolayers adsorbed at either solid-liquid or air-liquid interfaces. This behavior has important implications for the potential uses of nanodiscs, including the potential to control lipid composition within nanodiscs containing membrane proteins
    • Evolution of Neural Networks for Physically Simulated Evolved Virtual Quadruped Creatures

      Vaughan, Neil; Royal Academy of Engineering; University of Chester (Springer-Verlag, 2018-07-07)
      This work develops evolved virtual creatures (EVCs) using neuroevolution as the controller for movement and decisions within a 3D physics simulated environ-ment. Previous work on EVCs has displayed various behaviour such as following a light source. This work is focused on complexifying the range of behaviours available to EVCs. This work uses neuroevolution for learning specific actions combined with other controllers for making higher level decisions about which action to take in a given scenario. Results include analysis of performance of the EVCs in simulated physics environment. Various controllers are compared including a hard coded benchmark, a fixed topology feed forward artificial neural network and an evolving ANN subjected to neuroevolution by applying mutations in both topology and weights. The findings showed that both fixed topology ANNs and neuroevolution did successfully control the evolved virtual creatures in the distance travelling task.
    • The Evolution of Ransomware Variants

      Wood, Ashley; Eze, Thaddeus
      Abstract: This paper investigates how ransomware is continuing to evolve and adapt as time progresses to become more damaging, resilient and sophisticated from one ransomware variant to another. This involves investigating how each ransomware sample including; Petya, WannaCry and CrySiS/Dharma interacts with the underlying system to implicate on both the systems functionality and its underlying data, by utilising several static and dynamic analysis tools. Our analysis shows, whilst ransomware is undoubtedly becoming more sophisticated, fundamental problems exist with its underlying encryption processes which has shown data recovery to be possible across all three samples studied whilst varying aspects of system functionality can be preserved or restored in their entirety.
    • Evolutionary Robot Swarm Cooperative Retrieval

      Vaughan, Neil; Royal Academy of Engineering; University of Chester (Springer, 2018-07-07)
      In nature bees and leaf-cutter ants communicate to improve cooperation during food retrieval. This research aims to model communication in a swarm of auton-omous robots. When food is identified robot communication is emitted within a limited range. Other robots within the range receive the communication and learn of the location and size of the food source. The simulation revealed that commu-nication improved the rate of cooperative food retrieval tasks. However a counter-productive chain reaction can occur when robots repeat communications from other robots causing cooperation errors. This can lead to a large number of robots travelling towards the same food source at the same time. The food becomes de-pleted, before some robots have arrived. Several robots continue to communicate food presence, before arriving at the food source to find it gone. Nature-inspired communication can enhance swarm behaviour without requiring a central control-ler and may be useful in autonomous drones or vehicles.
    • Existence and regularity of solution for a Stochastic CahnHilliard / Allen-Cahn equation with unbounded noise diffusion

      Antonopoulou, Dimitra; Karali, Georgia D.; Millet, Annie; University of Chester (Elsevier, 2015-10-24)
      The Cahn-Hilliard/Allen-Cahn equation with noise is a simplified mean field model of stochastic microscopic dynamics associated with adsorption and desorption-spin flip mechanisms in the context of surface processes. For such an equation we consider a multiplicative space-time white noise with diffusion coefficient of linear growth. Applying technics from semigroup theory, we prove local existence and uniqueness in dimensions d = 1,2,3. Moreover, when the diffusion coefficient satisfies a sub-linear growth condition of order α bounded by 1 3, which is the inverse of the polynomial order of the nonlinearity used, we prove for d = 1 global existence of solution. Path regularity of stochastic solution, depending on that of the initial condition, is obtained a.s. up to the explosion time. The path regularity is identical to that proved for the stochastic Cahn-Hilliard equation in the case of bounded noise diffusion. Our results are also valid for the stochastic Cahn-Hilliard equation with unbounded noise diffusion, for which previous results were established only in the framework of a bounded diffusion coefficient. As expected from the theory of parabolic operators in the sense of Petrovsk˘ıı, the bi-Laplacian operator seems to be dominant in the combined model.
    • Existence of time periodic solutions for a class of non-resonant discrete wave equations

      Zhang, Guang; Feng, Wenying; Yan, Yubin; University of Chester (Springer, 2015-04-17)
      In this paper, a class of discrete wave equations with Dirichlet boundary conditions are obtained by using the center-difference method. For any positive integers m and T, when the existence of time mT-periodic solutions is considered, a strongly indefinite discrete system needs to be established. By using a variant generalized weak linking theorem, a non-resonant superlinear (or superquadratic) result is obtained and the Ambrosetti-Rabinowitz condition is improved. Such a method cannot be used for the corresponding continuous wave equations or the continuous Hamiltonian systems; however, it is valid for some general discrete Hamiltonian systems.
    • Existence theory for a class of evolutionary equations with time-lag, studied via integral equation formulations

      Baker, Christopher T. H.; Lumb, Patricia M.; University of Chester (University of Chester, 2006)
      In discussions of certain neutral delay differential equations in Hale’s form, the relationship of the original problem with an integrated form (an integral equation) proves to be helpful in considering existence and uniqueness of a solution and sensitivity to initial data. Although the theory is generally based on the assumption that a solution is continuous, natural solutions of neutral delay differential equations of the type considered may be discontinuous. This difficulty is resolved by relating the discontinuous solution to its restrictions on appropriate (half-open) subintervals where they are continuous and can be regarded as solutions of related integral equations. Existence and unicity theories then follow. Furthermore, it is seen that the discontinuous solutions can be regarded as solutions in the sense of Caratheodory (where this concept is adapted from the theory of ordinary differential equations, recast as integral equations).
    • An experimental and computational investigation of pressurised anaerobic digestion

      Wilkinson, Steve; Liang, Zhixuan (University of Chester, 2021-01)
      The aim of this work is to gain a greater understanding of the effect of headspace pressure on biogas production from anaerobic digestion. This is important to improve the energy content of the biogas i.e., increase the methane content and therefore reduce the need for upgrading to scrub out carbon dioxide. In addition, headspace pressure can potentially be used to provide energy for mixing and gas sparging, thereby removing the need for mechanical agitation. In this work, an existing computational model was adapted to investigate its prediction of the variation of biogas production as headspace pressure is increased above atmospheric. The simulation results were accompanied with experimental work using periodic venting of sealed laboratory bottles. The headspace pressure was inferred from the weight loss during venting to atmosphere. In addition, a fully instrumented, pressurised digestor system was designed and constructed in which headspace pressure could be measured directly. Experiments were conducted with headspace pressures of up to 3.4 barg. The biogas that accumulated in the headspace during the digestion process was sampled periodically to determine its composition. The results showed that biogas produced at higher pressures has a higher methane content. A mass balance for the headspace sampling process, which assumed no gas was released from the liquid during sampling, was compared to experimental measurements. This led to the discovery that the effective Henry’s constant for the solubility of carbon dioxide could be an order of magnitude lower in digestate than the known value for pure water. Both the adapted model and the laboratory-scale experiments showed that as the headspace pressure increases, the production rate of biogas decreases. The adapted model also gives slightly higher methane content for higher pressure. The model was then used to estimate the specific growth rates of bacteria used in the laboratory-scale experiments and the agreement was not good, which indicates further changes to the model are needed. The results show that the rate of biogas production reduces as the headspace pressure increases but the rate of decrease is not very steep. This same trend was also displayed for yeast fermentation, which was also studied as another model process for pressurised biological gas production. The variation of the rate of 𝐶𝑂2 evolution with pressure was also used to infer the concentration of dissolved 𝐶𝑂2 within the fermenting yeast cells. Finally, turning attention back to anaerobic digestion processes for energy, it is encouraging that at the relatively modest elevation of pressure required for sparging to give mixing (less than 0.5 barg), the reduction in biogas evolution is small. This small penalty might therefore be offset in a production scale system by the reduced costs of mixing and increased methane content of the biogas.
    • Experimental and process modelling study of integration of a micro-turbine with an amine plant

      Agbonghae, Elvis O.; Best, Thom; Finney, Karen N.; Font Palma, Carolina; Hughes, Kevin J.; Pourkashanian, Mohamed; University of Leeds (Elsevier, 2014-12-31)
      An integrated model of a micro-turbine coupled to a CO2 capture plant has been developed with Aspen Plus, and validated with experimental data obtained from a Turbec T100 microturbine at the PACT facilities in the UKCCS Research Centre, Beighton, UK. Monoethanolamine (MEA) was used as solvent and experimental measurements from the CO2 capture plant have been used to validate the steady-state model developed with Aspen Plus®. The optimum liquid/gas ratio and the lean CO2 loading for 90% CO2 capture has been quantified for flue gases with CO2 concentrations ranging from 3 to 8 mol%.
    • Experimental and theoretical study of a piezoelectric vibration energy harvester under high temperature

      Arroyo, Emmanuelle; Jia, Yu; Du, Sijun; Chen, Shao-Tuan; Seshia, Ashwin A.; University of Cambridge; University of Chester (IEEE, 2017-08-01)
      This paper focuses on studying the effect of increasing the ambient temperature up to 160 °C on the power harvested by an MEMS piezoelectric micro-cantilever manufactured using an aluminum nitride-on-silicon fabrication process. An experimental study shows that the peak output power decreases by 60% to 70% depending on the input acceleration. A theoretical study establishes the relationship of all important parameters with temperature and includes them into a temperature-dependent model. This model shows that around 50% of the power drop can be explained by a decreasing quality factor, and that thermal stresses account for around 30% of this decrease.
    • Experimental demonstration of a transparent graphene millimetre wave absorber with 28% fractional bandwidth at 140 GHz

      Wu, Bian; Tuncer, Hatice M.; Naeem, Majid; Yang, Bin; Cole, Matthew T.; Milne, William I.; Hao, Yang; Queen Mary University of London (Nature Publishing Group, 2014-02-19)
      The development of transparent radio-frequency electronics has been limited, until recently, by the lack of suitable materials. Naturally thin and transparent graphene may lead to disruptive innovations in such applications. Here, we realize optically transparent broadband absorbers operating in the millimetre wave regime achieved by stacking graphene bearing quartz substrates on a ground plate. Broadband absorption is a result of mutually coupled Fabry-Perot resonators represented by each graphene-quartz substrate. An analytical model has been developed to predict the absorption performance and the angular dependence of the absorber. Using a repeated transfer-and-etch process, multilayer graphene was processed to control its surface resistivity. Millimetre wave reflectometer measurements of the stacked graphene-quartz absorbers demonstrated excellent broadband absorption of 90% with a 28% fractional bandwidth from 125-165 GHz. Our data suggests that the absorbers’ operation can also be extended to microwave and low-terahertz bands with negligible loss in performance.
    • Experimental Exploration of CO2 Capture Using a Cryogenic Moving Packed Bed

      Cann, David; Willson, Paul; Font Palma, Carolina; University of Chester; PMW Technology Ltd; University of Chester (SSRN, 2018-10)
      This study examines a novel cryogenic post-combustion capture process, based on a moving bed of cold beads to freeze CO2 out of a flue gas, and this paper presents the first steps in experimental work. The preliminary experiments included the test of fluidization of bed material, if the flow rate of bed material can be kept constant in and out of the column and the estimation of heat transfer coefficient. The obtained results are encouraging for the running of the rig at cryogenic conditions.
    • Experimental exploration of cryogenic CO2 capture utilising a moving bed

      Font-Palma, Carolina; Willson, Paul; Cann, David G. (University of Chester, 2021-04)
      It is widely accepted that climate change is a result of the increase in greenhouse gases in the atmosphere. The continued combustion of fossil fuels and subsequent emission of CO2 is leading to an increase in global temperatures, which has led to interest in decarbonising the energy sector. Carbon capture and storage (CCS) is a method of reducing carbon emissions from fossil fuel power plants by capturing CO2 from exhaust gases and storing it in underground gas stores. Carbon capture using chemical solvents is the most matured technology for capturing emissions from the energy sector, however as the energy sector continues to decarbonise with the arrival of renewable sources focus is shifting to other industries to reduce their carbon footprint. Solvent carbon capture has disadvantages including requiring large equipment and large amounts of heat to regenerate solvent for capture, meaning it would be difficult to scale the technology down and apply it to other industrial applications. Cryogenic carbon capture (CCC) is one proposed method of CCS at smaller scale, which captures CO2 by freezing CO2 out of the exhaust gases as CO2 forms a frost on a heat transfer surface. One disadvantage of CCC is the accumulation of CO2 frost reduces the efficiency of the capture process. The process must be periodically shut down to regenerate the heat transfer surface and collect CO2 that has been frozen out of exhaust gases. This thesis proposes to overcome the frost accumulation through the use of a moving packed bed of small spherical metal beads as the heat transfer surface. As CO2 is fed into a capture column and freezes onto the metal beads, the metal beads are removed from the column, regenerated to recover the CO2, then cooled and recirculated back into the capture column. This prevents the accumulation of frost and allows continuous CO2 capture. There are many difficulties identified in this project, primarily a lack of knowledge on CO2 frost formation and how heat transfer in a moving bed affects frost formation. The research done on a purpose built experimental rig is critical in improving the future design work of a next generation moving bed CCC system. The frost accumulation in a capture column is known as a frost front, which advanced through the capture column at a fixed velocity until the column is saturated with frost. Experimental results had shown that the frost front velocity is predictable for varying CO2 concentrations and gas flow rates, with frost front velocities between 0.46-0.78 mm/s for CO2 concentrations between 4-18% v/v and 0.36-0.98 mm/s for gas flow rates between 50-120 LPM. These frost front velocity experiments in a fixed packed bed allowed the design of a moving packed bed column to set the bed flow rate to match the frost front velocity. The moving bed experiments show that the excessive accumulation of CO2 frost within the capture column can be prevented by utilising the moving bed. The successful development of a moving bed CCC system would result in a cost effective solution to the requirements of certain smaller applications that need to capture CO2, which make up a significant portion of emissions. In particular this technology is very economical for biogas upgrading, where the CO2 content of biogas must be removed before the gas can be introduced to the UK’s larger gas network. There is also a growing interest for use in shipping and other maritime applications, capturing CO2 from ship exhaust emissions during transit.
    • Exploration and Implementation of Augmented Reality for External Beam Radiotherapy

      John, Nigel W.; Vaarkamp, Jaap; Cosentino, Francesco (University of Chester, 2018-07-17)
      We have explored applications of Augmented Reality (AR) for external beam radiotherapy to assist with treatment planning, patient education, and treatment delivery. We created an AR development framework for applications in radiotherapy (RADiotherapy Augmented Reality, RAD-AR) for AR ready consumer electronics such as tablet computers and head mounted devices (HMD). We implemented in RAD-AR three tools to assist radiotherapy practitioners with: treatment plans evaluation, patient pre-treatment information/education, and treatment delivery. We estimated accuracy and precision of the patient setup tool and the underlying self-tracking technology, and fidelity of AR content geometric representation, on the Apple iPad tablet computer and the Microsoft HoloLens HMD. Results showed that the technology could already be applied for detection of large treatment setup errors, and could become applicable to other aspects of treatment delivery subject to technological improvements that can be expected in the near future. We performed user feedback studies of the patient education and the plan evaluation tools. Results indicated an overall positive user evaluation of AR technology compared to conventional tools for the radiotherapy elements implemented. We conclude that AR will become a useful tool in radiotherapy bringing real benefits for both clinicians and patients, contributing to successful treatment outcomes.
    • Exploring the electrochemical performance of graphite and graphene paste electrodes composed of varying lateral flake sizes

      Slate, Anthony J.; Brownson, Dale A. C.; Abo Dena, Ahmed S.; Smith, Graham C.; Whitehead, Kathryn A.; Banks, Craig E. (Royal Society of Chemistry (RSC), 2018)
    • Explosive solutions of a stochastic non-local reaction–diffusion equation arising in shear band formation

      Kavallaris, Nikos I.; University of Chester (Wiley, 2015-07-07)
      In this paper, we consider a non-local stochastic parabolic equation which actually serves as a mathematical model describing the adiabatic shear-banding formation phenomena in strained metals. We first present the derivation of the mathematical model. Then we investigate under which circumstances a finite-time explosion for this non-local SPDE, corresponding to shear-banding formation, occurs. For that purpose some results related to the maximum principle for this non-local SPDE are derived and afterwards the Kaplan's eigenfunction method is employed.
    • Exponential stability in p-th mean of solutions, and of convergent Euler-type solutions, of stochastic delay differential equations

      Baker, Christopher T. H.; Buckwar, Evelyn; Univesity College Chester ; Humboldt-Universität zu Berlin (Elsevier, 2005-12-15)
      This article carries out an analysis which proceeds as follows: showing that an inequality of Halanay type (derivable via comparison theory) can be employed to derive conditions for p-th mean stability of a solution; producing a discrete analogue of the Halanay-type theory, that permits the development of a p-th mean stability analysis of analogous stochastic difference equations. The application of the theoretical results is illustrated by deriving mean-square stability conditions for solutions and numerical solutions of a constant-coefficient linear test equation.