The processes of dissolution and hydrate forming behind the shock wave in the gas–liquid medium with gas mixture bubbles

The processes of dissolution and hydrate forming behind the front of the shock wave, propagating in liquid with bubbles of carbon dioxide and nitrogen mixture, have been experimentally studied under various initial pressures, medium temperatures and surfactant concentrations in water. The theoretical model of this process is presented for the gas–liquid medium with bubbles of multicomponent gas mixture with consideration of accompanying heat effects. Numerical solutions to this problem were found. Close fit of calculation results and experimental data was achieved. Experimental data on profiles of gas content, times of dissolution and hydrate forming were generalized on the basis of the suggested model.     

Investigation of rotating detonation wave fueled by “ethylene-acetylene-hydrogen” mixture

In this study, the stable operating range and basic characteristics including the pressure and speed of a rotating detonation are researched. The fuel is an “ethylene–acetylene–hydrogen” mixture, examined at three mixing ratios of 2:1:4, 2.2:1:4, and 1.8:1:4 (ethylene:acetylene:hydrogen). The pressure of the rotating detonation wave (RDW) increases when the equivalence ratio (ER) is near the stoichiometric ratio, but it is little affected by the flow rate. The detonation wave speed maintains at 1200–1400 m/s, approximately 70% of the Chapman-Jouguet (C-J) speed, which is hardly impacted by the ER and flow rate. The speed of the RDW in the long-duration tests is higher than in the short-duration tests, and the time taken for the formation of a stable RDW is longer. The stable operating range is broadened and speed is increased with the increase in the acetylene and hydrogen in the mixture. The instabilities in the RDW are found to be correlated with the planar acoustic waves, whereas the mechanisms of the decoupling and re-ignition of the RDW are explained from the perspective of thermoacoustic coupling.     

Flame–vortex interaction driven combustion dynamics in a backward-facing step combustor

The combustion dynamics of propane–hydrogen mixtures are investigated in an atmospheric pressure, lean, premixed backward-facing step combustor. We systematically vary the equivalence ratio, inlet temperature and fuel composition to determine the stability map of the combustor. Simultaneous pressure, velocity, heat release rate and equivalence ratio measurements and high-speed video from the experiments are used to identify and characterize several distinct operating modes. When fuel is injected far upstream from the step, the equivalence ratio entering the flame is temporally and spatially uniform, and the combustion dynamics are governed only by flame–vortex interactions. Four distinct dynamic regimes are observed depending on the operating parameters. At high but lean equivalence ratios, the flame is unstable and oscillates strongly as it is wrapped around the large unsteady wake vortex. At intermediate equivalence ratios, weakly oscillating quasi-stable flames are observed. Near the lean blowout limit, long stable flames extending from the corner of the step are formed. At atmospheric inlet temperature, the unstable mode resonates at the 1/4 wavemode of the combustor. As the inlet temperature is increased, the 5/4 wavemode of the combustor is excited at high but lean equivalence ratios, forming the high-frequency unstable flames. Higher hydrogen concentration in the fuel and higher inlet temperatures reduce the equivalence ratios at which the transitions between regimes are observed. We plot combustion dynamics maps or the response curves, that is the overall sound pressure level as a function of the equivalence ratio, for different operating conditions. We demonstrate that numerical results of strained premixed flames can be used to collapse the response curves describing the transitions among the dynamic modes onto a function of the heat release rate parameter alone, rather than a function dependent on the equivalence ratio, inlet temperature and fuel composition separately. We formulate a theory for predicting the critical values of the heat release parameter at which quasi-stable to unstable and unstable to high-frequency unstable modes take place.     

Auto-ignition model based on tabulated detailed kinetics and presumed temperature PDF – Application to internal combustion engine controlled by thermal stratifications

The prediction of the auto-ignition sensitivity to the temperature in new engine combustors is a challenge in the community of numerical combustion. This paper is devoted to the modeling of temperature fluctuations for the simulation of reactive flows in real internal engine configurations. It aims at validating the temperature fluctuation equation model Truffin and Benkenida and its coupling with the ECFM3Z combustion model of Colin and Benkenida. Especially, this study focuses on the auto-ignition process which is described by the TKI (Tabulated Kinetics for Ignition) model of Knop and Jay. TKI is based on a tabulation method for reaction rates and its coupling with the temperature fluctuation is achieved through a presumed PDF approach. The integral limits for the PDF integration are determined locally through transport equations with appropriate closures on isothermal walls. The resulting model, called TKI–υ_T, is applied on Homogeneous Charge Compression Ignition (HCCI) combustion mode engine for which the only source of thermal stratification is wall heat loss. Comparisons with experiments demonstrate the impact of temperature fluctuations and the ability of the model to improve the prediction of the auto-ignition model.     

Electric system management through hydrogen production – A market driven approach in the French context

Hydrogen is usually presented as a promising energy carrier that has a major role to play in low carbon transportation, through the use of fuel cells. However, such a development is not expected in the short term. In the meantime, hydrogen may also contribute to reduce carbon emissions in diverse sectors among which methanol production. Methanol can be produced by combining carbon dioxide and hydrogen, hence facilitating carbon dioxide emission mitigation while providing a beneficial tool to manage the electric system, if hydrogen is produced by alkaline electrolysis operated in a variable way driven by the spot and balancing electricity markets. Such a concept is promoted by the VItESSE² project (Industrial and Energy value of CO₂ through Efficient use of CO₂-free electricity - Electricity Network System Control & Electricity Storage). Through the proposed market driven approach, hydrogen production offers a possibility to help managing the electric system, together with an opportunity to reduce hydrogen production costs.     

Numerical simulation of fluid–structure interaction in stenotic arteries considering two layer nonlinear anisotropic structural model

The unsteady non-Newtonian blood flow in symmetric stenotic arteries is numerically simulated considering fluid–structure interaction (FSI) using the code ADINA. A two layer hyperelastic anisotropic structural model is used for the compliant arterial wall. The pressure used as outlet boundary condition was obtained running a CFD simulation for each stenosis with a physiologically-realistic time variation of pressure at inlet for different velocities. The obtained pressure drop increases in potential form with the inlet velocity for a fixed stenosis severity. The FSI results show that the maxima velocity and WSS at throat increase in exponential form with stenosis severity. The minimum and maximum effective stress at throat for stenosis severity of S = 70% ranged between 47 kPa and 96 kPa at diastole and systole, respectively.     

Constitutive equations and wave propagation in Green–Naghdi type II and III thermoelectroelasticity

In this article we extend the theory of thermoelasticity devised by Green and Naghdi to the framework of finite thermoelectroelasticity. Both isotropic and transversely isotropic bodies are considered and thermodynamic restrictions on their constitutive relations are obtained by virtue of the reduced energy equality. In the second part, a linearized theory for transversely isotropic thermopiezoelectricity is derived from thermodynamic restrictions by constructing the free energy as a quadratic function of the 11 second-order invariants of the basic fields. The resulting theory provides a natural extension of the (linear) Green and Naghdi theory for types II and III rigid heat conductors. As a particular case, we derive the linear system which rules the processes depending on the symmetry axis coordinate only.     

Development and comparison of two-bed silica gel–water adsorption chillers driven by low-grade heat source

A novel silica gel–water adsorption chiller (driven by hot water of 60–90 °C) with three vacuum chambers has been built in Shanghai Jiao Tong University (SJTU). This chiller was an improvement of an earlier deigned chiller and it integrated two single-bed systems (basic system) with only one vacuum valve. The performance of the chiller was tested and compared with the former adsorption chiller. The results show that the cooling power and COP of the chiller are 8.70 kW and 0.39 for the heat source temperature of 82.5 °C, cooling water temperature of 30.4 °C and chilled water outlet temperature of 12 °C. For a higher chilled water outlet temperature of about 16 °C, the COP increases to 0.43 while the cooling power is about 11.0 kW. Compared with that of the former chiller, the COP of this chiller increases by 20%.     

Fast turbulent deflagration and DDT of hydrogen–air mixtures in small obstructed channel

An experimental study of flame propagation, acceleration and transition to detonation in hydrogen–air mixture in 2-m long rectangular cross-section channel filled with obstacles located at the bottom wall was performed. The initial conditions of the hydrogen–air mixture were 0.1 MPa and 293 K. Three different cases of obstacle height (blockage ratio 0.25, 0.5 and 0.75) and four cases of obstacle density were studied with the channel height equal to 0.08 m. The channel width was 0.11 m in all experiments. The propagation of flame and pressure waves was monitored by four pressure transducers and four in-house ion probes. The pairs of transducers and probes were placed at various locations along the channel in order to get information about the progress of the phenomena along the channel. To examine the influence of mixture composition on flame propagation and DDT, the experiments were performed for the compositions of 20%, 25% and 29.6% of H₂ in air by volume. As a result of the experiments the deflagration and detonation regimes and velocities of flame propagation in the obstructed channel were determined.     

Solar hybrid cooling system for high-tech offices in subtropical climate – Radiant cooling by absorption refrigeration and desiccant dehumidification

A solar hybrid cooling design is proposed for high cooling load demand in hot and humid climate. For the typical building cooling load, the system can handle the zone cooling load (mainly sensible) by radiant cooling with the chilled water from absorption refrigeration, while the ventilation load (largely latent) by desiccant dehumidification. This hybrid system utilizes solar energy for driving the absorption chiller and regenerating the desiccant wheel. Since a high chilled water temperature generated from the absorption chiller is not effective to handle the required latent load, desiccant dehumidification is therefore involved. It is an integration of radiant cooling, absorption refrigeration and desiccant dehumidification, which are powered up by solar energy. In this study, the application potential of the solar hybrid cooling system was evaluated for the high-tech offices in the subtropical climate through dynamic simulation. The high-tech offices are featured with relatively high internal sensible heat gains due to the intensive office electric equipment. The key performance indicators included the solar fraction and the primary energy consumption. Comparative study was also carried out for the solar hybrid cooling system using two common types of chilled ceilings, the passive chilled beams and active chilled beams. It was found that the solar hybrid cooling system was technically feasible for the applications of relatively higher cooling load demand. The annual primary energy consumption of the solar hybrid cooling system was lower than that of the conventional vapour compression refrigeration system up to 36.5%. Between the two options of chilled ceilings, the passive chilled beams were more energy-efficient to work with the solar hybrid cooling system in the hot and humid climate. Harnessing solar energy for driving air-conditioning would help in reducing the carbon emission, hence alleviating the climate change.     

The role of hydrogen in the edge dislocation mobility and grain boundary-dislocation interaction in α-Fe

The atomistic mechanisms of dislocation mobility depending on the presence of hydrogen were investigated for two edge dislocation systems that are active in the plasticity of α-Fe, specifically ½<111>{110} and ½<111>{112}. In particular, the glide of the dislocation pile-ups through a single crystal, as well as transmission of the pile-ups across the grain boundary were evaluated in bcc iron crystals that contain hydrogen concentrations in different amounts. Additionally, the uniaxial tensile response under a constant strain rate was analyzed for the aforementioned structures. The results reveal that the presence of hydrogen decreases the velocity of the dislocations – in contrast to the commonly invoked HELP (Hydrogen-enhanced localized plasticity) mechanism -, although some localization was observed near the grain boundary where dislocations were pinned by elastic stress fields. In the presence of pre-exisiting dislocations, hydrogen-induced hardening was observed as a consequence of the restriction of the dislocation mobility under uniaxial tension. Furthermore, it was observed that hydrogen accumulation in the grain boundary suppresses the formation of new grains that leads to a hardening response in the stress-strain behaviour which can initiate brittle fracture points.     

High temperature creep,fatigue and creep–fatigue interaction in engineering materials

An attempt has been made to systematize the criterion for the crack initiation, the crack growth and the final fracture in creep, fatigue and creep–fatigue interaction conditions at high temperatures. Reference has been made to the systematically designed studies performed hitherto by the authors and colleagues, including the comparative study on the similarity and the dissimilarity between creep and fatigue. Further research as complexity science and engineering is emphasized.     

Redirection of sunlight by microstructured components – Simulation,fabrication and experimental results

This paper presents a non-tracking microstructured light redirecting device, which can be integrated into architectural glass. When fixed in the upper area of a window above eye level it redirects the light from solar altitudes between 15° and 65° and illuminates a room without causing glare.Ray-tracing calculations are employed as a tool for identifying suitable configurations and geometries. The results of the simulations show the advantage of combinations of lens-like with prism-like geometries in comparison to conventional microprism arrays regarding the overall light redirection efficiency as well as the producibility. The redirecting device is more lightweight, gives better integration options and is producible in a more economic manufacturing process as systems with similar performance. Measurements of cast silicone prototypes (100 mm × 100 mm × 4 mm) confirmed the simulation results. By now the performance has also been shown by large scale industrially produced acrylic panels with dimensions of 1500 mm × 400 mm × 4 mm.     

Prospective national and regional environmental performance: Boundary estimations using a combined data envelopment – stochastic frontier analysis approach

The environmental performance of regions and largest economies of the world – actually, the efficiency of their energy sectors – is estimated for the period 2010–2030 by using forecasted values of main economic indicators. Two essentially different methodologies, data envelopment analysis and stochastic frontier analysis, are used to obtain upper and lower boundaries of the environmental efficiency index. Greenhouse gas emission per unit of area is used as a resulting indicator, with GDP, energy consumption, and population forming a background of comparable estimations. The dynamics of the upper and lower boundaries and their average is analyzed. Regions and national economies having low level or negative dynamics of environmental efficiency are determined.     

Combined Heat Transfer by Natural Convection – Conduction and Surface Radiation in an Open Cavity Under Constant Heat Flux Heating

Combined heat transfer by natural convection-conduction and surface radiation in an open cavity heated by constant flux is studied here. The laminar flow is solved numerically by employing the SIMPLE algorithm with QUICK scheme. The numerical results show that both radiation and solid conduction increase the average total Nusselt number. The average total Nusselt number is a linear increasing function of emissivity when emissivity is larger than 0.2. The heat conduction of a conductive wall increases the total cooling effect, but its effect is close to a limit when the conductivity ratio exceeds 100. The increase due to radiation ranged from 54.1% to 64.0%.     

Power generation in thermochemical and electrochemical systems – A thermodynamic theory

In this paper power limits and other performance indicators are investigated in various power generation systems with downgrading or upgrading of resources. Energy flux (power) is created in a power generator located between a resource fluid (‘upper’ fluid 1) and the environmental fluid (‘lower’ fluid, 2). Transfer phenomena, fluid properties and conductance values of dissipative layers or conductors influence the rate of power yield. While temperatures T_i of participating media are only necessary variables to describe purely thermal systems, in the present work both temperatures and chemical potentials μ_k are essential. This case is associated with engines propelled by fluxes of both energy and substance (chemical and electrochemical engines).Optimization methods are applied to determine power generation limits which are important performance indicators for various energy converters, such as thermal, solar, chemical, and electrochemical engines. Methodological similarity is shown when analysing power limits in thermal machines and fuel cells. Numerical approaches are based on the methods of dynamic programing (DP) or Pontryagin’s maximum principle. In view of the limitation of DP to systems with low dimensionality of state vector, we focus here on the Pontryagin’s method, which involves discrete canonical algorithms derived from the process Hamiltonian. Some new or relatively unknown properties of these algorithms are described in the context of their application to power systems.In fuel cells and other electrochemical systems downgrading or upgrading of resources may also occur. However, we restrict here to the steady-state fuel cells. An approximate (topology-ignoring) analysis shows that, in linear systems, only at most 1/4 of power dissipated in the natural transfer process can be transformed into mechanical or electric power. This indicator may be viewed as a new form of the second law efficiency. The relevant experimental data obtained at the institute of Power Engineering are also presented in this paper.     

Solar industrial process heating in Australia – Past and current status

Thirty years ago in Australia, there was a significant research, development and demonstration programme in solar industrial process heating (SIPH). This activity was led principally by the Commonwealth Science and Industrial Research Organisation, the country’s main scientific research body. Other state government bodies also funded demonstration projects. Today, there is very little SIPH activity at any level in Australia. The contrast with the progress in other renewable energy technologies like wind and solar photovoltaic systems is striking. While the implementation of these technologies has progressed, SIPH has gone backwards. If Australia is to decarbonise its economy at the rate required, a massive deployment of solar thermal technology in those industries which use large quantities of low temperature hot water is also required. Recent developments nationally and internationally may rekindle new applications of solar thermal energy use by industry. This paper reviews the past achievements in SIPH in Australia and describes the lessons learned in order to better prepare for any new wave of SIPH activity.