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Abstract In an effort to minimise electricity consumption and greenhouse gases emissions, the heating, ventilation and air-conditioning sector has focused its attention on developing alternative solutions to electrically-driven vapour-compression cooling. Liquid desiccant air-conditioning systems represent an energy-efficient and more environmentally friendly alternative technology for dehumidification and cooling, particularly in those cases with high latent loads to maintain indoor air quality and comfort conditions. This technology is considered particularly efficient in hot and humid climates. As a matter of fact, the choice of the desiccant solution influences the overall performance of the system. The current paper reviews the working principle of liquid desiccant systems, focusing on the thermodynamic properties of the desiccant solutions and describes an evaluation of the reference thermodynamic properties of different desiccant solutions to identify which thermodynamic, physical, transport property influences the liquid desiccant process and to what extent. The comparison of these thermodynamic properties for the commonly used desiccants is conducted to estimate which fluid could perform most favourably in the system. The economic factors and the effect of different applications and climatic conditions on the system performance are also described. The paper is intended to be the first step in the evaluation of alternative desiccant fluids able to overcome the problems related to the use of the common desiccant solutions, such as crystallization and corrosion to metals. Ionic liquids seem a promising alternative working fluid in liquid desiccant air-conditioning systems and their characteristics and cost are discussed.

Abstract The present work focuses on the numerical simulation of Moderate or Intense Low oxygen Dilution combustion condition, using the Partially-Stirred Reactor model for turbulence-chemistry interactions. The Partially-Stirred Reactor model assumes that reactions are confined in a specific region of the computational cell, whose mass fraction depends both on the mixing and the chemical time scales. Therefore, the appropriate choice of mixing and chemical time scales becomes crucial to ensure the accuracy of the numerical simulation prediction. Results show that the most appropriate choice for mixing time scale in Moderate or Intense Low oxygen Dilution combustion regime is to use a dynamic evaluation, in which the ratio between the variance of mixture fraction and its dissipation rate is adopted, rather than global estimations based on Kolmogorov or integral mixing scales. This is supported by the validation of the numerical results against experimental profiles of temperature and species mass fractions, available from measurements on the Adelaide Jet in Hot Co-flow burner. Different approaches for chemical time scale evaluation are also compared, using the species formation rates, the reaction rates and the eigenvalues of the formation rate Jacobian matrix. Different co-flow oxygen dilution levels and Reynolds numbers are considered in the validation work, to evaluate the applicability of Partially-Stirred Reactor approach over a wide range of operating conditions. Moreover, the influence of specifying uniform and non-uniform boundary conditions for the chemical scalars is assessed. The present work sheds light on the key mechanisms of turbulence-chemistry interactions in advanced combustion regimes. At the same time, it provides essential information to advance the predictive nature of computational tools used by scientists and engineers, to support the development of new technologies.

This study proposed a hybrid model consisting of a characteristic time combustion (CTC) model and a closed reactor model for the combustion modelling with detailed chemistry in RCCI engines. In the light of the basic idea of the CTC model of achieving chemical equilibrium in high temperature, this hybrid model uses the CTC model to solve the species conversion and heat release in the diffusion flame. Except for the diffusion flame, the auto-ignition in RCCI combustion is computed by a closed reactor model with the CHEMKIN library by assuming that the computational cells are closed reactors. The border of the transition between the CTC model and closed reactor model is determined by two criteria, a critical temperature and a critical Damkohler number. On the formulation of this hybrid model, emphasis is placed on coupling detailed chemistry into this hybrid model. A CEQ solver for species equilibrium calculations at certain temperature, pressure was embedded with CTC for detailed chemistry calculation. Then this combustion model was integrated with the CFD framework KIVA4 and the chemical library CHEMKIN-II and validated in a RCCI engine. The predicted in-cylinder pressure and heat release rate (HRR) show a good consistency with the data from the experiment and better accuracy than that computed from the sole closed reactor model. More importantly, it is observed that this model could save computational time compared with closed reactor model due to less stiff ordinary differential equations (ODEs) computation. A sensitivity analysis of the critical temperature and critical Damkohler number was conducted to demonstrate the effect of these two parameters in the current model.

Abstract Integrating low-carbon technologies (e.g. heat pumps, photovoltaic systems) in buildings influences the stability of the low-voltage grid, which therefore often requires to be reinforced. This article proposes a techno-economic methodology to identify the reinforcements needed to maintain grid stability at the lowest life-cycle cost. Novel contributions include the consideration of three-phase connection of low-carbon technologies as a reinforcement option and the fact that we study to what extent grid reinforcements can mitigate voltage unbalance issues. Additionally, to reduce computing time, a dummy island approach is used, whereby one feeder is modelled in detail and the remainder of the distribution island is represented by an aggregated load. Finally, random repetitions are proposed, to consider uncertainties related to building properties, occupants and the location of low-carbon technologies in the feeders. The methodology is applied to investigate the integration of heat pumps and photovoltaic systems in typical Belgian rural and urban grids. For the rural grid, heat pumps may lead to significant reinforcement costs (up to 1230 €/dwelling), mainly due to voltage stability problems. For the urban grid, heat pump and photovoltaic integration causes low reinforcement cost (

Abstract This study investigated in-situ and ex-situ biological methanation strategies for biogas upgrading potential. The addition and circulation of hydrogen with a ceramic gas diffuser unit revealed positive effects on the methanogenic process. A short-term maximum methane productivity of 2.5 L CH4 per L reactor volume per day (LVR−1 d−1) was obtained in-situ. Adverse effects of elevated dissolved hydrogen concentrations on acetogenesis became evident. Ex-situ methanation in a reactor subjected to gas recirculation for recurrent 24 h periods achieved methane formation rates of 3.7 L CH4 LVR−1 d−1. A biomethane with methane concentrations in excess of 96% successfully demonstrated the potential for gas grid injection. A theoretic model supplying gases continuously into a sequential ex-situ reactor system and steadily displacing the upgraded biogas confirmed similar methane formation performance and was advanced to a full-scale concept. Gas conversion efficiency of 95% producing biomethane at 85% methane content was attained. A hybrid model, where an in-situ grass digester is followed by an ex-situ reactor, is proposed as a novel upgrading strategy.

Abstract Carbon intensity is a valuable indicator for balancing economic growth and environmental pollution, and plays an important role in mitigating global climate change and promoting environmental sustainability. This study attempts to examine the impacts of export on carbon intensity by proposing a novel framework that targeting at the gap between export aggregate carbon intensity (EACI) and self aggregate carbon intensity (SACI) which constitute the total carbon intensity to reveal export effects. Multi-region input-output model was used to calculate EACI and SACI in 44 world regions in 2014. LMDI approach was further adopted to decompose the gap between EACI and SACI from sectoral perspective. Some main results are concluded. (1) On global scale, exports increased 7.2% in carbon intensity. On national scale, exports showed increased effects on most countries (42/44). The regional EACI/SACI ranged from 0.79 to 3.53. (2) Sectoral aggregate carbon intensity (ACI) of export decreased EACI by 51 g/$, while sectoral aggregate structure (AS) of export increased EACI by 186 g/$, resulting in 135 g/$ increase in EACI globally. (3) For most regions, although ACI of carbon-intensive sectors (Elec., Metal, Nonmetal, Trans., Chem. and Coke&petrol.) in exports was lower than that in self, the high AS of these sectors in exports resulted in EACI higher than SACI, causing pulling force of export on global carbon intensity. Thus reducing carbon-intensive industries’ weights in exports would have great effects on global and national carbon intensity mitigation.

Laboratory-created samples of methane hydrate (MH)-bearing media are a necessity because of the rarity and difficulty of obtaining naturally-occurring samples. The hypothesis that the inevitable heterogeneity in the phase saturations of the laboratory samples may lead to unreliable and non-repeatable results provided the impetus for this study, which aimed to determine the conditions under which maximum uniformity can be achieved. To that end, we designed four experiments involving different multi-stage cooling regimes (in terms of their duration and number of stages) to induce MH formation under excess-water conditions. In the absence of direct visualization capabilities, we analysed the experimental results by means of numerical simulation, which provided high-resolution predictions of the spatial distributions of the phase saturations in the cores and enabled the estimation of the parameters controlling the kinetic MH-formation behaviour through history-matching. Analysis of the numerical results indicated that, under the conditions of the experiments and with the design of the reactor, significant heterogeneities in phase saturation distributions were observed in all cases, leading to the conclusion that it is not possible to obtain cores with uniform phase saturation. Additionally, contrary to expectations, heterogeneities increased with the number of cooling stages and the duration of cooling, and this was attributed to imperfect insulation of the upper part of the reactor. A set of simulations involving perfect insulation of the reactor top confirmed the validity of this assumption: (a) predicting the formation of high-uniformity MH-bearing cores that became more homogeneous as the number of cooling stages and the length of the cooling period increased; and (b) providing important information for the improvement of the standard design of the experimental apparatus for the laboratory creation of MH-bearing cores using the excess water method.