Infiltration into inclined fibrous sheets

The flow from line and point sources through an inclined fibrous sheet is studied experimentally and theoretically for wicking from a saturated region and flow from a constant-flux source. Wicking from a saturated line generates a wetted region whose length grows diffusively, linearly or tends to a constant, depending on whether the sheet is horizontal or inclined downwards or upwards. A constant-flux line source generates a wetted region which ultimately grows linearly with time, and is characterized by a capillary fringe whose thickness depends on the relative strength of the source, gravitational and capillary forces. Good quantitative agreement is observed between experiments and similarity solutions.Capillary-driven and constant-flux source flows issuing from a point on a horizontal sheet generate a wetted patch whose radius grows diffusively in time. The flow is characterized by the relative strength of the source and spreading induced by the action of capillary forces, gamma. As gamma increases, the fraction of the wetted region which is saturated increases. Wicking from a saturated point corresponds to gamma = gamma(c), and spreads at a slower rate than from a line source. For gamma < gamma(c), the flow is partially saturated everywhere. Good agreement is observed between measured moisture profiles, rates of spreading, and similarity solutions.Numerical solutions are developed for point sources on inclined sheets. The moisture profile is characterized by a steady region circumscribed by a narrow boundary layer across which the moisture content rapidly changes. An approximate analytical solution describes the increase in the size of the wetted region with time and source strength; these conclusions are confirmed by numerical calculations. Experimental measurements of the downslope length are observed to be slightly in excess of theoretical predictions, though the dependence on time, inclination and flow rate obtained theoretically is confirmed. Experimental measurements of cross-slope width are in agreement with numerical results and solutions for short and long times. The affect of a percolation threshold is observed to ultimately arrest cross-slope transport, placing a limitation on the long-time analysis

Smart windows: Thermal modelling and evaluation

Copyright @ 2014 The Authors. Published by Elsevier Ltd. This is an open access article shared under the CC BY license (http://creativecommons.org/licenses/by/3.0/).A numerical investigation of the performance of a multi paned smart window integrated with water-cooled high efficiency third generation GaAsP/InGaAs QWSC (∼32% efficiency) solar cells illuminated by two-axis tracking solar concentrators at 500× in the inter pane space is presented. Optimising system parameters such as optical concentration ratio and coolant (water) flow rate is essential in order to avoid degradation in system performance due to high cell temperatures and thermal stresses. Detailed modelling of the thermo-fluid characteristics of the smart windows system was undertaken using a finite volume CFD package. Results of this analysis which considered the conductive, convective and radiative heat exchange processes taking place in the interior of the smart window system as well as the heat exchange to the internal and external ambient environment are presented.Engineering and Physical Sciences Research Counci

Quantitative LEED I-V and ab initio study of the Si(111)-3x2-Sm surface structure and the missing half order spots in the 3x1 diffraction pattern

We have used Low Energy Electron Diffraction (LEED) I-V analysis and ab initio calculations to quantitatively determine the honeycomb chain model structure for the Si(111)-3x2-Sm surface. This structure and a similar 3x1 recontruction have been observed for many Alkali-Earth and Rare-Earth metals on the Si(111) surface. Our ab initio calculations show that there are two almost degenerate sites for the Sm atom in the unit cell and the LEED I-V analysis reveals that an admixture of the two in a ratio that slightly favours the site with the lower energy is the best match to experiment. We show that the I-V curves are insensitive to the presence of the Sm atom and that this results in a very low intensity for the half order spots which might explain the appearance of a 3x1 LEED pattern produced by all of the structures with a 3x2 unit cell.Comment: 10 pages, 13 figures. Preliminary work presented at the the APS March meeting, Baltimore MD, 2006. To be published in Phys. Rev. B. April/May 200

Using Kriging regression to improve the stability and diversity in NSGA-II

This is the author accepted manuscript. The final version is available from IBPSANon-dominated sorting genetic algorithm version 2 (NSGA-II) is a multi-objective optimisation method. NSGA-II is often used to optimise the design of building. This paper details small improvements to this algorithm using ‘fitness approximation’ methods. Fitness approximation is used speed up the conversion of NSGA-II. Radial basis functions networks have been shown to be useful for this. Although there are many types of fitness approximation function that could be use for this purpose, Kriging methods have not yet been tested. In this paper, Kriging models are compared to standard NSGA-II. The results show that Kriging-based fitness approximation slightly improves upon standard NSGAII. More work is needed to test this method on different building types as well as more complex problems, such as those associated with HVAC design.The authors would like to thank for EPSRC for funding this research [Ref: EP/M021890/1

Efficient summertime overheating analysis using decomposed weather files

This is the author accepted manuscript. The final version is available from IBPSA via the link in this record.Overheating within European buildings is a big problem and the building design plays a significant role in any health-related outcomes. We show that heatwaves can be extracted from historic data based on how they affect buildings, rather than how they affect the external temperature. We propose a simple way of rating heatwaves based on the severity of their effect on the internal environment.The authors would like to thank the Engineering and Physical Sciences Research Council (EPSRC) for their support [Grant no: EP/M021890/1]

An integrated study of parallel valveless micropumps

This paper was presented at the 2nd Micro and Nano Flows Conference (MNF2009), which was held at Brunel University, West London, UK. The conference was organised by Brunel University and supported by the Institution of Mechanical Engineers, IPEM, the Italian Union of Thermofluid dynamics, the Process Intensification Network, HEXAG - the Heat Exchange Action Group and the Institute of Mathematics and its Applications.We describe an analytical, computational and experimental study of parallel valveless micropumps. A one dimensional model of a parallel micropump is presented and compared with available experimental data. The model confirms the linear decrease of the volume flux with pressure rise which is consistent with the experiments. The computational study showed a similar linear decrease but highlighted the effect of turbulence closures on the rectified mean flow, with the experimental data sitting between the turbulent and laminar closure regimes. The experimental study confirmed the importance of the displacement distance of fluid through the nozzle compared to nozzle length in the setting whether the flow regime is streaming or rectified. General conclusions are made about how to improve the pumping efficiency of micropumps.This study is supported by the Dorothy Hodgkin Postgraduate Award (DHPA) of the Engineering and Physical Sciences Research Council (EPSRC) of United Kingdom and Ebara Research Co. Ltd of Japan

STM and ab initio study of holmium nanowires on a Ge(111) Surface

A nanorod structure has been observed on the Ho/Ge(111) surface using scanning tunneling microscopy (STM). The rods do not require patterning of the surface or defects such as step edges in order to grow as is the case for nanorods on Si(111). At low holmium coverage the nanorods exist as isolated nanostructures while at high coverage they form a periodic 5x1 structure. We propose a structural model for the 5x1 unit cell and show using an ab initio calculation that the STM profile of our model structure compares favorably to that obtained experimentally for both filled and empty states sampling. The calculated local density of states shows that the nanorod is metallic in character.Comment: 4 pages, 12 figures (inc. subfigures). Presented at the the APS March meeting, Baltimore MD, 200

Injection of gaseous hydrogen into a natural gas pipeline

The injection of pure hydrogen at a T-junction into a horizontal pipe carrying natural gas is analysed computationally to understand the influence of blending and pipe geometry (diameter ratio, various 90° orientations) on mixing, for a target of 4.8–20% volume fraction hydrogen blend. The strongly inhomogeneous distribution of hydrogen within the pipe flow and on the pipe walls could indicate the location of potential pipe material degradation including embrittlement effects. The low molecular mass of hydrogen reduces the penetration of a side-branch flow and increases the buoyancy forces leading to stratification with high hydrogen concentrations on the upper pipe surface, downstream of the branch. Top-side injection leads to the hydrogen concentration remaining >40% for up to 8 pipe diameters from the injection point for volumetric dilutions ( D) less than 30%. Under-side injection promotes mixing within the flow interior and reduces wall concentration at the lower surface, compared to top-side injection. The practical implications for these results, in terms of mixing requirements and the contrasting constraint of codes of practice and energy demands, are discussed

A comparison between Gaussian Process emulation and Genetic Algorithms for optimising energy use of buildings

Computing speed has increased greatly over recent years. Building designers can now simulate complex building models in a short time. However, even with short simulation times, building optimisation routines can still take too long for some applications. In this paper, we compare how well genetic algorithms (GAs) and Gaussian process emulation with sequential optimisation (GPESO) optimise a building to minimise the energy use. The GA approach performs a GA routine on an EnergyPlus model and the GPESO technique creates a Gaussian Process emulator (GPE) also based on the EnergyPlus model. The GPESO uses an expected improvement algorithm to sequentially improve the GPE. The results show that the GPESO technique outperforms the GA in terms of minimising the number of simulations required and the solution obtained.This work was supported by the Engineering and Physical Sciences Research Council [EPSRC grant number EP/J002380/1]