A comparative study of electrical potential sensors and Ag/AgCl electrodes for characterising spontaneous and event related electroencephalagram signals

For exactly 90 years researchers have used electroencephalography (EEG) as a window into the activities of the brain. Even now its high temporal resolution coupled with relatively low cost compares favourably to other neuroimaging techniques such as magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI). For the majority of this time the standard electrodes used for non-invasive monitoring of electrical activities of the brain have been Ag/AgCl metal electrodes. Although these electrodes provide a reliable method for recording EEG they suffer from noise, such as offset potential drift, and usability issues, for example, difficult skin preparation and cross-coupling of adjacent electrodes. In order to tackle these issues a prototype Electric Potential Sensor (EPS) device based on an auto-zero operational amplifier has been developed and evaluated. The absence of 1/f noise in these devices makes them ideal for use with signal frequencies of ~10 Hz or less. The EPS is a novel active ultrahigh impedance capacitively coupled sensor. The active electrodes are designed to be physically and electrically robust and chemically and biochemically inert. They are electrically insulated (anodized) and scalable. A comprehensive study was undertaken to compare the results of neural signals recorded by the EPS with a standard commercial EEG system. These studies comprised measurements of both free running EEG and Event Related Potentials (ERPs). Results demonstrate that the EPS provides a promising alternative, with many added benefits compared to standard EEG sensors, including reduced setup time, elimination of sensor cross-coupling, lack of a ground electrode and distortion of electrical potentials encountered when using standard gel electrodes. Quantitatively, highly similar signals were observed between the EPS and EEG sensors for both free running and evoked brain activity with cross correlations of higher than 0.9 between the EPS and a standard benchmark EEG system. Future developments of EPS-based neuroimaging include the implementation of a whole head ultra-dense EPS array, and the mapping of distributions of scalp recorded electrical potentials remotely

Metal foam heat exchangers for thermal management of fuel cell systems

The present study explores the possibility of using metal foams for thermal management of fuel cells so that air-cooled fuel cell stacks can be commercialized as replacements for currently-available water-cooled counterparts. Experimental studies have been conducted to examine the heat transfer enhancement from a thin metal foam layer sandwiched between two bipolar plates of a cell. To do this, effects of the key parameters including the free stream velocity and characteristics of metal foam such as porosity, permeability, and form drag coefficient on heat and fluid flow are investigated. The improvements as a result of the application of metal foam layers on fuel cell systems efficiency have been analyzed and discussed. Non-optimized results have shown that to remove the same amount of generated heat, the air-cooled fuel cell systems using aluminum foams require half of the pumping power compared to water-cooled fuel cell systems

Metal foam heat exchangers for thermal management of fuel cell systems – An experimental study

The present study explores the possibility of using metal foams for thermal management of fuel cells so that air-cooled fuel cell stacks can be commercialized as replacements for currently-available watercooled counterparts. Experimental studies have been conducted to examine the heat transfer enhancement from a thin metal foam layer sandwiched between two bipolar plates of a cell. To do this, effects of the key parameters including the free stream velocity and characteristics of metal foam such as porosity, permeability, and form drag coefficient on temperature distribution, heat and fluid flow are investigated. The improvements as a result of the application of metal foam layers on fuel cell systems efficiency have been analyzed and discussed. Empirical results were in an agreement with previous numerical studies and have shown that to remove the same amount of generated heat, the air-cooled fuel cell systems using aluminum foams require half of the pumping power compared to water-cooled fuel cell systems. The critical coolant temperature difference for Proton Exchange Membrane (PEM) fuel cell systems was considered in which the applied foam layer created a uniform temperature distribution across the graphite plates

Finned tubes versus metal foams as air-cooled heat exchangers

A numerical study has been conducted to predict the velocity and temperature field for a metal foam-wrapped tube bundle in cross flow. The numerical data, produced by ANSYS-FLUENT, are sufficient to encompass ranges of key parameters including the free stream velocity and characteristics of metal foam such as porosity, permeability, and form drag coefficient. The new design system has been compared to the conventional finned-tube design data generated by the QGECE at the University of Queensland. It is shown that while the heat transfer rate increases significantly, compared to the finned tubes, the pressure drop increase is within acceptable range. As a case study, the steel natural draft dry cooling tower designed by QGECE is considered in which 20-40% material cost reduction are estimated by making use of metal foam heat exchangers

Numerical study of turbulent convective cooling of vertical heat-generating rods using supercritical water

The heat-generating rod with an inner diameter of 10.2 mm and the pitch-to-diameter ratio (P/D) of 1.098 is studied for mass flux ranging between 550 and 1270 kg/ms and heat flux of 560 kW/m at pressures of 25MPa. V2F eddy viscosity turbulence model is used and, to isolate the effect of buoyancy, constant values are used for thermo-physical properties with Boussinesq approximation for the density variation with temperature in the momentum equations. The computed Nusselt number normalized by that of the same Reynolds number with no buoyancy against the buoyancy parameter proposed by Jackson and Hall's criterion. A significant decrease in Nusselt number was observed in the range of 10 < Gr/Re Pr < 10 before entering a serious heat transfer deterioration regime. Based on an analysis of the shear-stress distribution in the turbulent boundary layer, it is found that the same mechanism that leads to impairment of turbulence production and thus heat transfer, in a vertical tube is present in square lattice heat-generating rod bundles at supercritical pressure.Convection heat transfer in upward flows of supercritical water in rectangular tight rod bundles is numerically investigated using the commercially-available CFD software ANSYS Fluen

CFD simulation and FE analysis of a high pressure ratio radial inflow turbine

The present study investigates a coupled CFD&FE analysis of a high pressure ratio single stage radial-inflow turbine applied in the Sundstrans Power Systems T-100 Multipurpose Small Power Unit. ANSYS turbomachinary package is applied to create 3D geometry of one blade passage, including the stator, rotor and diffuser. CFD simulations are performed with ANSYS-CFX in which three-dimensional Reynolds-Averaged Navier-Stokes equations are solved subject to appropriate boundary conditions. CFD results are then imported to ANSYS Steady-State Thermal and Static Structural module enabling thermal stress and blade deformation analysis. The von Mises stress distribution is calculated by means of finite element analysis (FEA). Centrifugal forces acting on the turbine wheel are considered along with thermal stresses. Once validated against available experimental data, numerical (CFD-FEA) results are extended to cases where no experimental data could be found in the literature allowing for better understanding of the performance of such radial inflow turbines at higher rpms where significant centrifugal forces can affect the integrity of the turbine

Heat transfer augmentation and opimisation in a solar enhanced natural draft dry cooling tower

Different heat transfer surface extension techniques are considered in order to improve the performance of an air-cooled heat exchanger and an optimisation process on a Solar Enhanced Natural Draft Dry Cooling Tower (SENDDCT) is conducted by Queensland Geothermal Energy Centre of Excellence (QGECE), as the air-cooled condenser of a geothermal power plant. The conventional method of extending the heat transfer area by means of fins is compared with a modern technique being the application of a thin metal foam layer to the outer surface of the tube. Aiming at maximizing the heat transfer enhancement and minimizing the total pressure drop, different tube bundle arrangements are numerical investigated by ANSYS-Fluent where the number of rows and tube spacing are systematically changed. An optimum design ispresented for an existing tower to be equipped with solar panels to afterheat the air leaving the heat exchanger bundles arranged vertically around the tower skirt

A time frequency approach to CFAR detection

Simultaneous analysis of signals in time and frequency domains is a standard approach in many signal processing applications including some detection. Parameters of clutter, noise and interference, and in some cases Doppler specifications, are the basis for most of current CFAR target detection techniques. When these parameters are unknown, most of current detection methods do not perform well. In this paper, a detection approach is introduced using time-frequency (TF) signal analysis. The method is non-parametric and by analysis of the spectrogram of the input, the presence of target signal is localized in time domain. Then, the signal detection is achieved using an adaptive thresholding