Thermal energy storage (TES) is widely recognized as a means to integrate renewable energies into the electricity production mix on the generation side, but its applicability to the demand side is ...also possible. In recent decades, TES systems have demonstrated a capability to shift electrical loads from high-peak to off-peak hours, so they have the potential to become a powerful instrument in demand-side management programs (DSM). Thermal storage is a technology that ensures energy security, efficiency and environmental quality. Of particular interest are applications where TES systems help manage the mismatch between availability of renewable electricity and the demand for electricity in buildings where hot water, heating and cooling are delivered by heat pumps and air conditioning for example. Thus this paper demonstrates the state of the art of present applications of thermal storage for demand-side management. A particular focus of this work is the attention paid to the characteristics of DSM and their relationship to different thermal storage systems. If TES effectiveness for the abovementioned applications is demonstrated, TES devices have a small percentage of the potential market. Therefore challenges and guidelines for a development plan are suggested.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Heat pumps are seen as a promising technology for load management in the built environment, in combination with the smart grid concept. They can be coupled with thermal energy storage (TES) systems ...to shift electrical loads from high-peak to off-peak hours, thus serving as a powerful tool in demand-side management (DSM). This paper analyzes heat pumps with radiators or underfloor heating distribution systems coupled with TES with a view to showing how a heat pump system behaves and how it influences the building occupants' thermal comfort under a DSM strategy designed to flatten the shape of the electricity load curve by switching off the heat pump during peak hours (16:00–19:00). The reference scenario for the analysis was Northern Ireland (UK). The results showed that the heat pump is a good tool for the purposes of DSM, also thanks to the use of TES systems, in particular with heating distribution systems that have a low thermal inertia, e.g. radiators. It proved possible to achieve a good control of the indoor temperature, even if the heat pump was turned off for 3 h, and to reduce the electricity bill if a “time of use” tariff structure was adopted.
► Heat pump heating systems with thermal energy storage are considered. ► System behavior is investigated during a DSM strategy for reducing peak energy demand. ► Heat pump heating systems demonstrate to be able to have an active role in DSM programs. ► A TES system must be coupled with the heat pump in presence of low thermal inertia heating distribution systems. ► Central role played by incentives schemes to promote this technology.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Measurements of 21 cm Epoch of Reionization (EoR) structure are subject to systematics originating from both the analysis and the observation conditions. Using 2013 data from the Murchison Widefield ...Array (MWA), we show the importance of mitigating both sources of contamination. A direct comparison between results from Beardsley et al. and our updated analysis demonstrates new precision techniques, lowering analysis systematics by a factor of 2.8 in power. We then further lower systematics by excising observations contaminated by ultra-faint RFI, reducing by an additional factor of 3.8 in power for the zenith pointing. With this enhanced analysis precision and newly developed RFI mitigation, we calculate a noise-dominated upper limit on the EoR structure of Δ2 ≤ 3.9 × 103 mK2 at k = 0.20 h Mpc−1 and z = 7 using 21 hr of data, improving previous MWA limits by almost an order of magnitude.
In 2010, a tissue‐engineered trachea was transplanted into a 10‐year‐old child using a decellularized deceased donor trachea repopulated with the recipient's respiratory epithelium and mesenchymal ...stromal cells. We report the child's clinical progress, tracheal epithelialization and costs over the 4 years. A chronology of events was derived from clinical notes and costs determined using reference costs per procedure. Serial tracheoscopy images, lung function tests and anti‐HLA blood samples were compared. Epithelial morphology and T cell, Ki67 and cleaved caspase 3 activity were examined. Computational fluid dynamic simulations determined flow, velocity and airway pressure drops. After the first year following transplantation, the number of interventions fell and the child is currently clinically well and continues in education. Endoscopy demonstrated a complete mucosal lining at 15 months, despite retention of a stent. Histocytology indicates a differentiated respiratory layer and no abnormal immune activity. Computational fluid dynamic analysis demonstrated increased velocity and pressure drops around a distal tracheal narrowing. Cross‐sectional area analysis showed restriction of growth within an area of in‐stent stenosis. This report demonstrates the long‐term viability of a decellularized tissue‐engineered trachea within a child. Further research is needed to develop bioengineered pediatric tracheal replacements with lower morbidity, better biomechanics and lower costs.
This case presents a 4‐year follow‐up of a tissue‐engineered pediatric tracheal transplant and reports on the longterm viability of this approach and areas for further research.
Full text
Available for:
BFBNIB, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Elevated operating temperatures reduce the solar to electrical conversion efficiency of building integrated photovoltaic devices (BIPV). Phase change materials (PCM) can be used to passively limit ...this temperature rise although their effectiveness is limited by their low thermal conductivities and crystallisation segregation during solidification. This paper presents an experimental evaluation of the effects of convection and crystalline segregation in a PCM as a function of efficiency of heat transfer within the finned PV/PCM system. The thermal performances of bulk PCM with crystallisation segregation for different internal fin arrangements are presented. It is noted that the addition of internal fins improves the temperature control of the PV in a PV/PCM system.
Display omitted
► Phase change materials (PCM) can be used to passively limit the temperature rise on PV. ► Effectiveness is limited by low thermal conductivities and crystallization segregation. ► Experimental evaluation of the effects of convection and crystalline segregation. ► Internal fins improves the temperature control of the PV in a PV/PCM system.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
•Large thermal units are increasingly required to operate cyclically.•Cyclic operation causes fatigue damage which they were not designed to withstand.•The resulting costs are usually overlooked in ...renewable energy integration studies.•A model for estimating maintenance costs in cycling duty scenarios is presented.
In many power systems large thermal generating units, which were primarily designed to resist creep damage caused by base load operation throughout an effective service life of more than 40years, are being operated cyclically as a result of market liberalization and the rapid expansion of intermittent renewable energy sources. This type of off-design operation results in accelerated rates of life consumption due to the initiation of fatigue-related damage mechanisms which these units were not designed to withstand. This issue is of particular concern to the owners and operators of thermal generators in the Irish all-island system because of the significantly increased levels of cycling duty that their units will be required to perform as a result of plans to integrate very high levels of wind power by 2020. The impacts of cyclic operation on unit operating costs, scheduling and availability has largely been overlooked in renewable energy integration studies. The authors draw on the results of recent studies in Ireland and elsewhere to relate fatigue-life consumption (measured in total lifetime starts) and damage accumulation (measured in annual maintenance costs) to create a model which can be used to forecast lifetime hot, warm and cold per-start costs for a typical base load unit in a range of market and wind-penetration scenarios.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
7.
Viscoplastic slender-body theory Hewitt, D. R.; Balmforth, N. J.
Journal of fluid mechanics,
12/2018, Volume:
856
Journal Article
Peer reviewed
Open access
The theory of slow viscous flow around a slender body is generalized to the situation where the ambient fluid has a yield stress. The local flow around a cylinder that is moving along or ...perpendicular to its axis, and rotating, provides a first step in this theory. Unlike for a Newtonian fluid, the nonlinearity associated with the viscoplastic constitutive law precludes one from linearly superposing solutions corresponding to each independent component of motion, and instead demands a full numerical approach to the problem. This is accomplished for the case of a Bingham fluid, along with a consideration of some asymptotic limits in which analytical progress is possible. Since the yield stress of the fluid strongly localizes the flow around the body, the leading-order slender-body approximation is rendered significantly more accurate than the equivalent Newtonian problem. The theory is applied to the sedimentation of inclined cylinders, bent rods and helices, and compared with some experimental data. Finally, the theory is applied to the locomotion of a cylindrical filament driven by helical waves through a viscoplastic fluid.
Experiments that pursue detection of signals from the Epoch of Reionization (EoR) are relying on spectral smoothness of source spectra at low frequencies. This article empirically explores the effect ...of foreground spectra on EoR experiments by measuring high-resolution full-polarization spectra for the 586 brightest unresolved sources in one of the Murchison Widefield Array (MWA) EoR fields using 45 h of observation. A novel peeling scheme is used to subtract 2500 sources from the visibilities with ionospheric and beam corrections, resulting in the deepest, confusion-limited MWA image so far. The resulting spectra are found to be affected by instrumental effects, which limit the constraints that can be set on source-intrinsic spectral structure. The sensitivity and power-spectrum of the spectra are analysed, and it is found that the spectra of residuals are dominated by point spread function sidelobes from nearby undeconvolved sources. We release a catalogue describing the spectral parameters for each measured source.
Biomass fuelled trigeneration is the term given to the system which is the on-site generation of electricity, heat and cooling simultaneously, using biomass as the fuel source. As a form of the ...renewable energy sources biomass is not intermittent, location-dependent or very difficult to store. If grown sustainably, biomass can be considered to be CO2 neutral. Biomass, therefore, would be a promising option for the future to contribute both to the reduction of greenhouse gases and to the solution of replacing fossil fuels in power plants. For a wide range of commercial buildings, biomass trigeneration offers an economical solution of providing power, heat and cooling which is more environmentally friendly than conventional methods.
This work focuses on the modelling, simulation and techno-economic analysis of small scale biomass trigeneration applications. The Organic Rankine Cycle (ORC) integrated with conventional combustion provides electricity for building use. The waste heat recovered from the ORC system and exhaust gases is used to supply hot water to space heating and excess heat is also used to drive an absorption cooling system. In order to use energy resources most efficiently, the proposed process is modelled and simulated using the ECLIPSE process simulation package. Based on the results achieved, the key technical and environmental issues have been examined. The study also investigates the impact of different biomass feedstock on the performance of trigeneration plant, biomass ash content ranges from 0.57 to 14.26% ash and a range of moisture content 10.6–33.51%. The calorific value across the biomass sources ranges between 16.56 and 17.97MJ/kg daf. Finally, an economic evaluation of the system is performed along with sensitivity analyses such as capital investments, plant load factors and fuel costs. The results show that the maximum efficiencies and the best breakeven electricity selling price for the cases considered in this study are as follows: 11.1% and 221 £/MWh for power only, 85.0% and 87 £/MWh for combined heat and power and 71.7% and 103 £/kWh for trigeneration respectively.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A yield stress is added to Taylor's (1952, Proc. Royal Soc. A, 211, 225-239) model of a microscopic organism with a wavy cylindrical tail swimming through a viscous fluid. Viscoplastic slender-body ...theory is employed for the task, generalising existing results for Bingham fluid to the Herschel–Bulkley constitutive model. Numerical solutions are provided over a range of the two key parameters of the problem: the wave amplitude relative to the wavelength, and a Bingham number which describes the strength of the yield stress. Numerical solutions are supplemented with discussions of various limits of the problem in which analytical progress is possible. If the wave amplitude is sufficiently small, the yield stress of the material inevitably dominates the flow; the resulting ‘plastic locomotion’ results in swimming speeds that depend strongly on the swimming gait, and can, in some cases, even be negative. Conversely, when the yield stress is large, swimming becomes possible at the wave speed, with the swimmer sliding or burrowing along its centreline with a relatively high efficiency.
PDF
