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Abstract Thermal energy storage systems for both heat and cold are necessary for many industrial processes. High energy density and high power capacity are desirable properties of the storage. The use of latent heat increases the energy density of the storage tank with high temperature control close to the melting point. Tube in PCM tank is a very promising system that provides high packing factor. This work presents an experimental study of a PCM tank for cold storage applications. Two different configurations and different flow rates of the heat transfer fluid were studied. The effectiveness of the PCM storage system was defined as that of a heat exchanger. The results showed that the heat exchange effectiveness of the system did not vary with time, decreased with increasing flow rate and increased with increasing heat transfer area. The effectiveness was experimentally determined to only be a function of the ratio m ˙ /A. This equation was found to be adequately be used to design a PCM storage system, and a case study is presented. It was shown that the tube in tank design together with a low temperature PCM is suitable as a thermal storage facility for cold storage.

A commercial drum chipper was fed alternately and piecewise with poplar stems and poplar tops, in order to determine the effect of piece size and tree part on machine performance. Chipping stems required most of the available power (231 kW) delivered by the tractor, whereas chipping tops took about half that much. However, productivity was twice as high with stems, compared to tops (i.e. 25 and 11 t h-1 of oven dry wood, respectively). As a consequence, specific fuel consumption per unit product was 15% lower with stems, compared to tops - i.e. 0.61 and 0.72 L m-3, respectively. Mean feeding speed was 0.37 m s-1 for stems and 0.41 m s-1 for tops, but the difference was not significant (p = 0.1677). Productivity and fuel consumption were strongly related to piece size, but tree part had its own additional effect, independent from size and possibly related to form. When chipping tops it is advisable to feed more pieces at a time, in order to partly compensate for the effect of piece size. Operators expecting to chip primarily small-size materials may acquire special chipper versions with wider drums and additional side rollers, for smoother mass feeding. oThe same chipper was tested with poplar stems and tops.oChipping stems resulted in higher productivity and lower fuel consumption.oChipping stems required most of the available tractor power.oChip particle size distribution was about the same for both feedstocks. © 2013 Elsevier Ltd.

In Italy, olive tree groves may offer up to a million tonnes of dry biomass per year as pruning residue. Searching for a cost-effective way to tap this potential, the authors tested a new machine, capable of recovering pruning residue at the same time as pruning. The pre-commercial prototype was tested on four different plots and compared to a simpler tractorbase mechanical pruning unit. The authors conducted detailed time-studies in order to determine machine productivity and residue recovery cost. The integrated machine can treat between 0.2 and 0.6 ha h(-1), producing between 0.33 and 1.03 tonnes of fresh residue hour(-1). Its integrated residue recovery function does not slow the pruning, which actually proceeds faster than with the tractor-base unit, due to the more efficient multiple-disc cutting bar. The marginal cost of residue recovery hovers around 40-45 (sic) fresh tonne(-1). However, the new machine must not be considered just as a biomass harvester, but rather as a mechanical pruning unit with an integrated biomass recovery function. Its main benefit derives from the capacity of performing a very effective mechanical pruning, and the residue recovery function is a secondary benefit yet unavailable on standard pruning machines. Its deployment must be seen in the context of a general effort to modernize olive grove management and to develop an integrated biomass production system, rather than as a further attempt to build a specialised biomass supply chain.

Recent needs of reducing pollutant emissions of internal combustion engines have pushed the development of non-conventional ignition systems. One of the most promising techniques appears to be the so-called Turbulent Jet Ignition (TJI) system, in which a jet of high-energy reactive gases is generated by means of a pilot combustion in a pre-chamber and used to initiate the main combustion event in the cylinder. Considering the complex nature of some phenomena typical of TJI systems, 3D CFD studies are essential to provide a detailed analysis for an efficient design. In this study, numerical simulations of an active pre-chamber TJI system applied to a lean operating methane engine were performed to provide a thorough analysis of the combustion process that characterizes such a technology. The numerical model was validated against experimental measurements carried out on an optically accessible single cylinder spark-ignition engine equipped with the pre-chamber prototype. The numerical simulations provided an insight view of both physical and chemical phenomena occurring inside the pre-chamber otherwise difficult to achieve by experiments alone. The evolution of some species of interest was analyzed in order to study the main charge ignition process, as well as the overall combustion progress. The results show that the main charge ignition is made possible by the large amount of energy and active radicals released from the pre-chamber and this ensures an overall stable and faster combustion in lean conditions. The performance improvements of the TJI system with respect to a traditional spark-ignition engine were evaluated in terms of efficiency and pollutant emission levels.

This paper presents a multicriteria formulation for multiyear dynamic transmission expansion planning problems. This formulation considers three criteria: investment costs, operation costs, and the expected energy not supplied. The solution algorithm adopts an interactive decision-making approach that starts at a nondominated solution of the problem. This solution is identified transforming two of the three criteria in constraints specifying aspiration levels and using afterwards simulated annealing to deal with the integer nature of investment decisions. After obtaining this first solution, the decision maker can alter the aspiration levels and run the application again to obtain a new solution. Once an expansion plan is accepted, the algorithm computes long-term marginal costs, reflecting both investment and operation costs. These costs are more stable than short-term ones and inherently address the revenue reconciliation problem well known in short-term approaches. The developed algorithm is tested using a case study based on the Portuguese 400/220/150-kV transmission network.

This article examines whether the energy consumption–GDP relationship is in long-term equilibrium for EU-15 countries. Unlike many previous works, we apply a nonlinear unit root test introduced by Kapetanios et al. (2003a) and extended by Chong et al. (2008) that identifies not only deterministic cointegration, but also the stronger concept of stochastic cointegration. The results yield a clear pattern: Austria, Denmark, Italy, the Netherlands, Portugal and Spain must achieve greater emissions reductions between 2009 and 2012 to reach their respective Kyoto targets.

Electricity generation integrated with xylose degradation was investigated in a two-chamber mediator-less microbial fuel cell (MFC). Voltage output followed saturation kinetics as a function of xylose concentration for concentration below 9.7 mM, with a predicted maximum of 86 mV (6.3 mW m(-2) or 116 mW m(-3)) and half-saturation constant (K(s)) of 0.29 mM. Xylose concentrations from 0.5 mM to 1.5 mM resulted in coulombic efficiencies and maximum voltage ranging from 41+/-1.6% to 36+/-1.2% and 55+/-2.0 mV to 70+/-3.0 mV respectively. Xylose degradation rate increased with increasing xylose concentration up to 9.7 mM and the predicted maximum degradation rate was 0.13 mM h(-1) and K(s) of 3.0 mM. Stirring by nitrogen in the anode chamber led to 99+/-2.3 mV maximum voltage (8.4+/-0.4 mW m(-2) or 153+/-7.1 mW m(-3)) and 5.9+/-0.3% coulombic efficiency at MFC running time 180 h, which were respectively 17+/-1.2% and 37+/-1.8%, higher than those without stirring. The COD removal under stirring was 22.1+/-0.3%, which was slightly lower than that of 23.7+/-0.4% under no stirring. However, stirring resulted in 59% lower xylose degradation rate. This work demonstrates that xylose can be used in the MFC for electricity production. Comparatively higher electricity generation and coulombic efficiency can be obtained by adjusting initial xylose concentration and applying stirring in the anode chamber.

Abstract Because of the high content of alkaline metals, biomass has very reactive ashes and these have a strong impact upon pyrolysis and combustion phenomena. From the study of the evolution with the combustion temperature, of the kinetic and diffusive data of several wood chars, it was found that the Quercus ilex (holm oak) char had an unexpected evolution of the heterogeneous phase reaction rate constant. Scanning electronic microscopy analysis of the ashes and thermogravimetric analysis of the char where performed, and the results shown that close to 750 °C there is a loss of mass associated with the release of inorganic matter, especially potassium and phosphorus, which have a known influence on the combustion process and the subsequent kinetic data collection.