Search

Composite thermochemical energy storage (TCES) represents an exciting field of thermal energy storage which could address the issue of seasonal variance in renewable energy supply. However, there are open questions about their performance and the root cause of some observed phenomena. Some researchers have observed the breakdown of particles in their production phase, and in their use. This study seeks to investigate the underlying cause of this breakdown. SEM and EDX analysis have been conducted on MgCl2 impregnated 13X zeolite composites of differing diameters, as well as LiX zeolite. This was done in order to study the level of impregnation of salt into the zeolitematrix, as well as the effect this impregnation process has on themorphology of the zeolite. Analysis was conducted using ImageJ software to study the effect of the impregnation process on the diameter of the particles. It has been found that a by weight impregnation concentration of magnesium chloride of 11.90% for the LiX zeolite, and 7.59% and 5.26% for the large diameter 13X zeolite and the small diameter 13X zeolite respectively has been achieved. It has been found that the impregnation process significantly affects themorphology of 13X zeolite particles, causing large fissures to form, and eventually resulting in the previously found breakdown of these particles. It has been verified that a primary factor influencing the breakdown of the 13X zeolite particles is the efflorescence and sub-fluorescence phenomena, which leads to a build-up of crystals in the zeolite pores. It has also been found that prolonged impregnation times and the use of high concentration salt solutions in the soaking process can induce significant crystal growth which also leads to the breakdown of these particles. Results demonstrate that LiX zeolite is the optimum host matrix choice in these conditions. These results will allow for the design of more resilient composite TCES particles. [ABSTRACT FROM AUTHOR]

• Smaller/lighter materials which dominate retrofit are poorly characterised in datasets. • Materials are poorly named, described, or are absent in LCA datasets. • LCA for retrofit may not yield reliable information for design decisions. • Embodied energy coefficients may be more reliable than embodied carbon ones. • Reporting only carbon could lead to externalisation of impacts, not avoidance. Low energy domestic retrofit consumes materials, such as insulation, membranes and glazing, with smaller quantities of structural timber, steel or concrete, which have associated embodied impacts from resource extraction, manufacture and end-of-life treatments. In retrofit design, coefficients for material embodied impacts vary widely between sources and can lead to different results in a life cycle energy or carbon analysis, and perhaps different material choices in retrofit implementation. This paper considers how and why results differ between sources, and whether such data is suitable for making climate-beneficial design decisions. Embodied energy and carbon coefficients for 18 key retrofit materials were obtained from two widely used LCA databases and their similarity was quantified. The data collected illustrates that 70% embodied energy and embodied carbon data is within 20%, but that 30% of data was more than 20% different. Consistency of product naming and the absence in the datasets of key retrofit materials are factors identified contributing to variation, and present real constraints in practice. Furthermore, this exercise showed that embodied impacts for the types of materials most prominent in retrofits are less-well characterised than other major construction materials, and presents another layer of uncertainty. The data showed embodied energy was more consistent between sources than embodied carbon. This raises doubts about the predominant use of embodied carbon over energy for such analyses and establishes that a focus on embodied carbon over embodied energy has less power to reduce greenhouse gas emissions than considering both metrics together. It is concluded that obtaining such data with confidence is challenging and requires expertise in LCA, and is therefore unlikely to be accessible to most retrofit designers. Datasets need to be more complete and offer higher confidence to ensure delivery of high quality and meaningful results for climate-beneficial design decisions. [ABSTRACT FROM AUTHOR]

A simplified transient model for fixed-bed reactors was extended to account for the heat sink effect of the phase change material diluent in the Fischer-Tropsch reactor energy balance. The resulting model was found to accurately approximate the more rigorous two-dimensional model with significantly less computational requirements even at the hotspot, where the reactor enthalpy balance is most sensitive. As anticipated, the presence of the encapsulated phase change material in the reactor induced thermal inertia, thereby restricting the temperature ramp rate in the reactor to acceptably safe operational limits for the catalyst. Although there was a reduction in both the CH4 and C5+ productivity, the reduction in CH4 production was up to four times that of the C5+ at the same coolant temperature. [ABSTRACT FROM AUTHOR]

The dynamic velocity range of particle image velocimetry (PIV) is determined by the maximum and minimum resolvable particle displacement. Various techniques have extended the dynamic range, however flows with a wide velocity range (e.g., impinging jets) still challenge PIV algorithms. A new technique is presented to increase the dynamic velocity range by over an order of magnitude. The multiple pulse separation (MPS) technique (i) records series of double-frame exposures with different pulse separations, (ii) processes the fields using conventional multi-grid algorithms, and (iii) yields a composite velocity field with a locally optimized pulse separation. A robust criterion determines the local optimum pulse separation, accounting for correlation strength and measurement uncertainty. Validation experiments are performed in an impinging jet flow, using laser-Doppler velocimetry as reference measurement. The precision of mean flow and turbulence quantities is significantly improved compared to conventional PIV, due to the increase in dynamic range. In a wide range of applications, MPS PIV is a robust approach to increase the dynamic velocity range without restricting the vector evaluation methods. [ABSTRACT FROM AUTHOR]

Synthetic jets are used for active flow control and enhanced heat transfer, and are typically generated by an orifice connected to a cavity with movable diaphragm actuator. Low-power operation is achieved by matching actuator and Helmholtz resonance frequencies. This brief communication presents an analytical model derived from simplified gas dynamics, for estimating the synthetic jet velocity and actuator deflection, based on a cavity pressure measurement. Model closure is provided by a damping force in the orifice, which agrees with established pressure loss correlations for steady flow through short ducts. The model is validated against experimental data obtained for an axisymmetric synthetic jet. The valid frequency range extends from zero, over the Helmholtz resonance frequency, up to a geometry-dependent limit frequency. This model presents a reference against which synthetic jet velocity can be calibrated. [ABSTRACT FROM AUTHOR]

• Improved methods for embodied energy could reduce life cycle energy in retrofits. • Fabric first retrofit design is not well supported by typical life cycle energy approaches. • A prescriptive life cycle approach could improve design decisions for materials and systems. • A framework providing focused life cycle impacts for fabric first retrofit measures is proposed. Reduction of energy for space heating through retrofit interventions is imperative to meet carbon reduction targets in many temperate climates. A Life Cycle approach to retrofit design has the potential to reveal the balance between projected operational energy savings, and embodied energy invested in an intervention, and therefore optimise the extent of retrofit. However, life cycle energy analysis (LCEA) suffers from inconsistent methodologies across studies, and is rarely used for retrofit projects. A preliminary meta-analysis was conducted, drawing on LCEA data from domestic new builds and retrofits from the last twenty years. Whilst recent literature conversations indicate that embodied energy increases with decreasing operating energy, the meta-analysis is inconsistent with this. This review critiques the limitations and sources of variation in LCEA, focuses on how these compromise its value as part of the building design process and when comparing between projects, and recommends approaches which add value for building designers. This review has identified a need for research to elucidate a transferrable approach for determining the lowest life cycle energy for any retrofit, and also a need for a more robust data set of domestic retrofit LCEA. [ABSTRACT FROM AUTHOR]