An autonomous wave-powered desalination system

The potential for an autonomous wave-powered desalination system is considered and it is identified that the most promising configuration is a reverse osmosis (RO) plant utilising a pressure exchanger-intensifier for energy recovery. A numerical model of the RO plant with a pressure exchanger-intensifier is developed that shows that a specific energy consumption of less than 2.0 kW h/m3 over a wide range of sea-water feed conditions, making it particularly suitable for use with a variable power source such as wave energy. A numerical model of the combined wave-power and desalination plant is also developed that shows that it is possible to supply the desalination plant with sea-water directly pressurised by the wave energy converter, eliminating the cost and energy losses associated with converting the energy into electricity and back to pressurised water. For a typical sea-state the specific hydraulic energy consumption of the desalination plant is estimated to be 1.85 kW h/m3 whilst maintaining a recovery-ratio of less than 25 to 35% to avoid the need for chemical pre-treatment to eliminate scaling problems. It is suggested that the economic potential for wave-powered desalination depends on these energy and cost savings more than compensating for the reduction in membrane life that occurs with variable feed conditions.

Two-dimensional hygrothermal transfer in porous building materials

A two-dimensional mathematical model for evaluating the simultaneous heat and moisture migration in porous building materials was proposed. Vapor content and temperature were chosen as the principal driving potentials. The numerical solution was based on the control volume finite difference technique with fully implicit scheme in time. Two validation experiments were developed in this study. The evolution of transient moisture distributions in both one-dimensional and two-dimensional cases was measured. A comparison between experimental results and those obtained by the numerical model proves that they are fully consistent with each other. The model can be easily integrated into a whole building heat, air and moisture transfer model. Another main advantage of the present numerical method lies in the fact that the required moisture transport properties are comparatively simple and easy to determine.

An Investigation of Compressor Map Width Enhancement and a Detailed Analysis of Inducer Flow Field

This paper describes an investigation of various shroud bleed slot configurations of a centrifugal compressor using CFD with a manual multi-block structured grid generation method. The compressor under investigation is used in a turbocharger application for a heavy duty diesel engine of approximately 400 hp. The baseline numerical model has been developed and validated against experimental performance measurements. The influence of the bleed slot flow field on a range of operating conditions between surge and choke has been analysed in detail.
The impact of the returning bleed flow on the incidence at the impeller blade leading edge due to its mixing with the main through-flow has also been studied. From the baseline geometry, a number of modifications to the bleed slot width have been proposed, and a detailed comparison of the flow characteristics performed. The impact of slot variations on the inlet incidence angle has been investigated, highlighting the improvement in surge and choked flow capability. Along with this, the influence of the bleed slot on stabilising the blade passage flow by the suction of the tip and over-tip vortex flow by the slot has been considered near surge.

Computational Investigation of Inlet Distortion at High Angles of Attack

Lip separation is one of the primary sources of inlet distortion, which can result in a loss in fan stability. High angles of incidence are one of several critical causes of lip separation. There have been many studies into inlet performance at high incidence, including the resulting distortion levels when lip separation occurs. However, the vast majority of these investigations have been carried out experimentally, with little in the way of computational results for inlet performance at high incidence. The flow topology within an inlet when lip separation has occurred is also not well understood. This work aims to demonstrate a suitable model for the prediction of inlet flows at high incidence using ANSYS CFX, looking at both the performance of the inlet and the separated flow topology within the inlet. The attenuating effect of the fan is also investigated, with particular emphasis on the flow redistribution ahead of the fan. The results show that the model used is suitable for predicting inlet performance in adverse operating conditions, showing good agreement with experimental results. In addition, the attenuation of the distortion by the fan is also captured by the numerical model.

The UMIST database for astrochemistry 1995

We report the release of a new version of the UMIST database for astrochemistry. The database contains the rate coefficients of 3864 gas-phase reactions important in interstellar and circumstellar chemistry and involves 395 species and 12 elements. The previous (1990) version of this database has been widely used by modellers. In addition to the rate coefficients, we also tabulate permanent electric dipole moments of the neutral species and heats of formation. A numerical model of the chemical evolution of a dark cloud is calculated and important differences to that calculated with the previous database noted.

MODELED DIFFUSION-CONTROLLED RESPONSE AND RECOVERY BEHAVIOR OF A NAKED OPTICAL FILM SENSOR WITH A HYPERBOLIC-TYPE RESPONSE TO ANALYTE CONCENTRATION

The diffusion-controlled response and recovery behaviour of a naked optical film sensor (i.e., with no protective membrane) with a hyperbolic-type response [i.e., S0/S = (1 + Kc), where S is the measured value of the absorbance or luminescence intensity of one form of the sensor dye in the presence of the analyte, S0 is the observed value of S in the absence of analyte and K is a constant] to changes in analyte concentration, c, in a system under test is approximated using a simple model, and described more accurately using a numerical model; in both models it is assumed that the system under test represents an infinite reservoir. Each model predicts the variations in the response and recovery times of such an optical sensor, as a function of the final external analyte concentration, the film thickness (I) and the analyte diffusion coefficient (D). From an observed signal versus time profile for a naked optical film sensor it is shown how values for K and D/I2 can be extracted using the numerical model. Both models provide a qualitative description of the often cited asymmetric nature of the response and recovery for hyperbolic-type response naked optical film sensors. It is envisaged that the models will help in the interpretation of the response and recovery behaviour exhibited by many naked optical film sensors and might be especially apposite when the analyte is a gas.

Quantifying contributions of domestic wastewater treatment systems to nutrient fluxes in stream headwaters

Effective implementation of the Water Framework Directive requires a reappraisal of conventional approaches to water quality monitoring. Quantifying the impact of domestic wastewater treatment systems (DWWTS) in Irish catchments is further complicated by high levels of natural heterogeneity. This paper presents a numerical model that couples attenuation to flow along different hydrological pathways contributing to river discharge; this permits estimation of the impact of DWWTS to overall nutrient fluxes under a range of geological conditions. Preliminary results suggest high levels of attenuation experienced
before DWWTS effluent reaches bedrock play a significant role in reducing its ecological impact on aquatic receptors. Conversely, low levels of attenuation in systems discharging directly to surface water may affect water quality more significantly, particularly during prolonged dry periods in areas underlain by low productivity aquifers (>60% of Ireland), where dilution capacity is limited.

Design and testing of transonic linear cascade tunnel with optimized slotted walls

In linear cascade wind tunnel tests, a high level of pitchwise periodicity is desirable to reproduce the azimuthal periodicity in the stage of an axial compressor or turbine. Transonic tests in a cascade wind tunnel with open jet boundaries have been shown to suffer from spurious waves, reflected at the jet boundary, that compromise the flow periodicity in pitch. This problem can be tackled by placing at this boundary a slotted tailboard with a specific wall void ratio s and pitch angle a. The optimal value of the s-a pair depends on the test section geometry and on the tunnel running conditions. An inviscid two-dimensional numerical method has been developed to predict transonic linear cascade flows, with and without a tailboard, and quantify the nonperiodicity in the discharge. This method includes a new computational boundary condition to model the effects of the tailboard slots on the cascade interior flow. This method has been applied to a six-blade turbine nozzle cascade, transonically tested at the University of Leicester. The numerical results identified a specific slotted tailboard geometry, able to minimize the spurious reflected waves and regain some pitchwise flow periodicity. The wind tunnel open jet test section was redesigned accordingly. Pressure measurements at the cascade outlet and synchronous spark schlieren visualization of the test section, with and without the optimized slotted tailboard, have confirmed the gain in pitchwise periodicity predicted by the numerical model. Copyright © 2006 by ASME.

Evaluation of a substructured soft Real-time Hybrid Test for performing Seismic analysis of complex structural systems

The hybrid test method is a relatively recently developed dynamic testing technique that uses numerical modelling combined with simultaneous physical testing. The concept of substructuring allows the critical or highly nonlinear part of the structure that is difficult to numerically model with accuracy to be physically tested whilst the remainder of the structure, that has a more predictable response, is numerically modelled. In this paper, a substructured soft-real time hybrid test is evaluated as an accurate means of performing seismic tests of complex structures. The structure analysed is a three-storey, two-by-one bay concentrically braced frame (CBF) steel structure subjected to seismic excitation. A ground storey braced frame substructure whose response is critical to the overall response of the structure is tested, whilst the remainder of the structure is numerically modelled. OpenSees is used for numerical modelling and OpenFresco is used for the communication between the test equipment and numerical model. A novel approach using OpenFresco to define the complex numerical substructure of an X-braced frame within a hybrid test is also presented. The results of the hybrid tests are compared to purely numerical models using OpenSees and a simulated test using a combination of OpenSees and OpenFresco. The comparative results indicate that the test method provides an accurate and cost effective procedure for performing
full scale seismic tests of complex structural systems.

Energetic beams of negative and neutral hydrogen from intense laser plasma interaction

We present observations of intense beams of energetic negative hydrogen ions and fast neutral hydrogen atoms in intense (5 × 10 W/cm) laser plasma interaction experiments, which were quantified in numerical calculations. Generation of negative ions and neutral atoms is ascribed to the processes of electron capture and loss by a laser accelerated positive ion in the collisions with a cloud of droplets. A comparison with a numerical model of charge exchange processes provides information on the cross section of the electron capture in the high energy domain.

Modeling target bulk heating resulting from ultra-intense short pulse laser irradiation of solid density targets

Isochoric heating of solid-density matter up to a few tens of eV is of interest for investigating astrophysical or inertial fusion scenarios. Such ultra-fast heating can be achieved via the energy deposition of short-pulse laser generated electrons. Here, we report on experimental measurements of this process by means of time-and space-resolved optical interferometry. Our results are found in reasonable agreement with a simple numerical model of fast electron-induced heating. (C) 2013 AIP Publishing LLC.

Testing Tidal Turbines - Part 1: Steady Towing Tests vs Tidal Moored Tests

Tidal turbines have been tested extensively at many scales in steady state flow. Testing medium- or full-scale devices in turbulent flow has been less thoroughly examined. The differences between turbine performances in these two different states are needed for testing method verification and numerical model validation. The work in this paper documents the performance of a 1/10 scale turbine in steady state pushing tests and tidal moored tests. The overall performance of the device appears to decrease with turbulent flow, though there is increased data scatter and therefore, reduced uncertainty. At maximum power performance, as velocity increases the mechanical power and electrical power reduction from steady to unsteady flow increases. The drive train conversion efficiency also decreases. This infers that the performance for this turbine design is affected by the presence of turbulent flow.

Electrical conduction and rheological behaviour of composites of poly(epsilon-caprolactone) and MWCNTs

Two mechanisms of conduction were identified from temperature dependent (120 K-340 K) DC electrical resistivity measurements of composites of poly(c-caprolactone) (PCL) and multi-walled carbon nanotubes (MWCNTs). Activation of variable range hopping (VRH) occurred at lower temperatures than that for temperature fluctuation induced tunneling (TFIT). Experimental data was in good agreement with the VRH model in contrast to the TFIT model, where broadening of tunnel junctions and increasing electrical resistivity at T > T-g is a consequence of a large difference in the coefficients of thermal expansion of PCL and MWCNTs. A numerical model was developed to explain this behavior accounting for a thermal expansion effect by supposing the large increase in electrical resistivity corresponds to the larger relative deformation due to thermal expansion associated with disintegration of the conductive MWCNT network. MWCNTs had a significant nucleating effect on PCL resulting in increased PCL crystallinity and an electrically insulating layer between MWCNTs. The onset of rheological percolation at similar to 0.18 vol% MWCNTs was clearly evident as storage modulus, G' and complex viscosity, vertical bar eta*vertical bar increased by several orders of magnitude. From Cole-Cole and Van Gurp-Palmen plots, and extraction of crossover points (G(c)) from overlaying plots of G' and G '' as a function of frequency, the onset of rheological percolation at 0.18 vol% MWCNTs was confirmed, a similar MWCNT loading to that determined for electrical percolation. 

Tailoring the nonlinear frequency coupling between odd harmonics for the optimisation of charged particle dynamics in capacitively coupled oxygen plasmas

The influence of nonlinear frequency coupling in an oxygen plasma excited by two odd harmonics at moderate pressure is investigated using a numerical model. Through variations in the voltage ratio and phase shift between the frequency components changes in ionization dynamics and sheath voltages are demonstrated. Furthermore, a regime in which the voltage drop across the plasma sheath is minimised is identified. This regime provides a significantly higher ion flux than a single frequency discharge driven by the lower of the two frequencies alone. These operating parameters have potential to be exploited for plasma processes requiring low ion bombardment energies but high ion fluxes. 

An Investigation of Compressor Map Width Enhancement and the Inducer Flow Field Using Various Configurations of Shroud Bleed Slot

This paper describes an investigation of various shroud bleed slot configurations of a centrifugal compressor using CFD with a manual multi-block structured grid generation method. The compressor under investigation is used in a turbocharger application for a heavy duty diesel engine of approximately 400hp. The baseline numerical model has been developed and validated against experimental performance measurements. The influence of the bleed slot flow field on a range of operating conditions between surge and choke has been analysed in detail. The impact of the returning bleed flow on the incidence at the impeller blade leading edge due to its mixing with the main through-flow has also been studied. From the baseline geometry, a number of modifications to the bleed slot width have been proposed, and a detailed comparison of the flow characteristics performed. The impact of slot variations on the inlet incidence angle has been investigated, highlighting the improvement in surge and choked flow capability. Along with this, the influence of the bleed slot on stabilizing the blade passage flow by the suction of the tip and over-tip vortex flow by the slot has been considered near surge.