System analysis and integration studies for a 15-micron horizon radiance measurement experiment

Systems analysis and integration studies for 15-micron horizon radiance measurement experimen

Experimental validation of the recovery effect in batteries for wearable sensors and healthcare devices discovering the existence of hidden time constants

Wearable sensors and healthcare devices use small lightweight batteries to power their typical operations of monitoring and tracking. It becomes absolutely vital to effectively utilise all the available battery charge for device longevity between charges. The electrochemical recovery effect enables the extraction of more power from the battery when implementing idle times in between use cycles, and has been used to develop various power management techniques. However, there is no evidence concerning the actual increase in available power that can be attained using the recovery effect. Also, this property cannot be generalised on all the battery chemistries since it is an innate phenomenon, relying on the anode/cathode material. Indeed recent developments suggest that recovery effect does not exist at all. This paper presents experimental results to verify the presence and level of the recovery effect in commonly used battery chemistries in wearable sensors and healthcare devices. The results have revealed that the recovery effect significantly does exist in certain batteries, and importantly we show that it is also comprised of two different time constants. This novel finding has important implications for the development of power management techniques that utilise the recovery effect with application in a large range of battery devices

On battery recovery effect in wireless sensor nodes

With the perennial demand for longer runtime of battery-powered Wireless Sensor Nodes (WSNs), several techniques have been proposed to increase the battery runtime. One such class of techniques exploiting the battery recovery effect phenomenon claims that performing an intermittent discharge instead of a continuous discharge will increase the usable battery capacity. Several works in the areas of embedded systems and wireless sensor networks have assumed the existence of this recovery effect and proposed different power management techniques in the form of power supply architectures (multiple battery setup) and communication protocols (burst mode transmission) in order to exploit it. However, until now, a systematic experimental evaluation of the recovery effect has not been performed with real battery cells, using high accuracy battery testers to confirm the existence of this recovery phenomenon. In this paper, a systematic evaluation procedure is developed to verify the existence of this battery recovery effect. Using our evaluation procedure we investigated Alkaline, Nickel-Metal Hydride (NiMH) and Lithium-Ion (Li-Ion) battery chemistries, which are commonly used as power supplies for WSN applications. Our experimental results do not show any evidence of the aforementioned recovery effect in these battery chemistries. In particular, our results show a significant deviation from the stochastic battery models, which were used by many power management techniques. Therefore, the existing power management approaches that rely on this recovery effect do not hold in practice. Instead of a battery recovery effect, our experimental results show the existence of the rate capacity effect, which is the reduction of usable battery capacity with higher discharge power, to be the dominant electrochemical phenomenon that should be considered for maximizing the runtime of WSN applications. We outline power management techniques that minimize the rate capacity effect in order to obtain a higher energy output from the battery

Modelling the recovery effect in batteries and supercapacitors for wearable sensors: discovering the existence of hidden time constants

Wearable devices, including health care monitors and aids, are very popular and extremely pervasive. They allow a user to sense physiological parameters and movement, can process sensed data to derive contextualised information, and also communicate with the wider world to allow remote health monitoring and enable health interventions. The inevitable march of technological invention pushes wearables to have more functionality, process more and sense more. As such, the demands on their power source increases. However, users demand small and lightweight wearable devices which place physical constraints on the power source, thus limiting the available power. To address these two conflicting positions, it seems sensible to consider ways to manage the wearable power source intelligently. It becomes absolutely vital to effectively utilise all the available power for device longevity between charges. Rechargeable batteries are popular in wearable devices. While rechargeable batteries have good energy density, their charge rate can be limited and they can be relatively heavy. Supercapacitors are likely to also be adopted as power sources for wearable sensors; in particular where the sensor mechanism relies on energy harvesting. A specific advantage of supercapacitors over batteries is their maintained performance over large numbers of discharge cycles and they are relatively light weight. It is known in the literature that the electrochemical recovery effect can enable the extraction of more power from the battery when implementing idle times in between discharge cycles, and it has been used to develop various power management techniques. However, there is no evidence concerning the actual increase in available power that can be obtained by exploiting the recovery effect. Also, this property cannot be generalised across all battery chemistries since it is an innate phenomenon, relying on the anode/cathode material. Indeed recent developments suggest that recovery effect does not exist at all. This thesis examines the recovery effect in batteries and presents controlled experiments and results, to verify the presence, and level, of the recovery effect in commonly used battery chemistries that are typically found in wearable sensors and healthcare devices. While the literature analysed the recovery effect using active current and zero discharge current, this work has identified that wearable devices still have a small current drawn from the power source when in idle mode, therefore a novel active and idle discharge circuit was designed to model the recovery effect in the typical operation of wearable devices. The results have revealed that the recovery effect significantly does exist in certain batteries, and a novel contribution from this research has been the identification that the recovery response can be modelled using two different time constants. The time constants reflect the difference in charge carrier movement from the available charge well and the bounded charge well leading to the proposal from this work to model the recovery effect using a two-tank model. This novel finding has important implications for the development of power management techniques that utilise the recovery effect, with application in a large range of battery operated devices. Furthermore, this thesis also has examined the recovery effect in supercapacitors and has for the first time demonstrated that the recovery effect also exists in supercapacitors

Assessment of alternative power sources for mobile mining machinery

Alternative mobile power sources for mining applications were assessed. A wide variety of heat engines and energy systems was examined as potential alternatives to presently used power systems. The present mobile power systems are electrical trailing cable, electrical battery, and diesel - with diesel being largely limited in the United States to noncoal mines. Each candidate power source was evaluated for the following requirements: (1) ability to achieve the duty cycle; (2) ability to meet Government regulations; (3) availability (production readiness); (4) market availability; and (5) packaging capability. Screening reduced the list of candidates to the following power sources: diesel, stirling, gas turbine, rankine (steam), advanced electric (batteries), mechanical energy storage (flywheel), and use of hydrogen evolved from metal hydrides. This list of candidates is divided into two classes of alternative power sources for mining applications, heat engines and energy storage systems

Thermal modeling of industrial-scale vanadium redox flow batteries in high-current operations

A cell-resolved model that simulates the dynamic thermal behavior of a Vanadium Redox Flow Battery during charge and discharge is presented. It takes into account, at a cell level, the reversible entropic heat of the electrochemical reactions, irreversible heat due to overpotentials, self-discharge reactions due to ion crossover, and shunt current losses. The model accounts for the heat transfer between cells and toward the environment, the pump hydraulic losses and the heat transfer of piping and tanks. It provides the electrolyte temperature in each cell, at the stack inlet and outlet, along the piping and in the tanks. Validation has been carried out against the charge/discharge measurements from a 9kW/27kWh VRFB test facility. The model has been applied to study a VRFB with the same stack but a much larger capacity, operating at \uf0b1400 A for 8 h, in order to identify critical thermal conditions which may occur in next-generation industrial VRFB stacks capable to operating at high current density. The most critical condition has been found at the end a long discharge, when temperatures above 50\ub0C appeared, possibly resulting in \u3016VO\u3017_2^+ precipitation and battery faults. These results call for heat exchangers tailored to assist high-power VRFB systems

Analysis of spacecraft anomalies

The anomalies from 316 spacecraft covering the entire U.S. space program were analyzed to determine if there were any experimental or technological programs which could be implemented to remove the anomalies from future space activity. Thirty specific categories of anomalies were found to cover nearly 85 percent of all observed anomalies. Thirteen experiments were defined to deal with 17 of these categories; nine additional experiments were identified to deal with other classes of observed and anticipated anomalies. Preliminary analyses indicate that all 22 experimental programs are both technically feasible and economically viable

Challenges to the Integration of Renewable Resources at High System Penetration

Successfully integrating renewable resources into the electric grid at penetration levels to meet a 33 percent Renewables Portfolio Standard for California presents diverse technical and organizational challenges. This report characterizes these challenges by coordinating problems in time and space, balancing electric power on a range of scales from microseconds to decades and from individual homes to hundreds of miles. Crucial research needs were identified related to grid operation, standards and procedures, system design and analysis, and incentives, and public engagement in each scale of analysis. Performing this coordination on more refined scales of time and space independent of any particular technology, is defined as a “smart grid.” “Smart” coordination of the grid should mitigate technical difficulties associated with intermittent and distributed generation, support grid stability and reliability, and maximize benefits to California ratepayers by using the most economic technologies, design and operating approaches

Descriptive analysis of viability of fuel saving in commercial aircraft through the application of photovoltaic cells

This paper presents the analysis of the technical feasibility to use a photovoltaic system to supply the electrical demand on two referential commercial aircraft, Airbus A340–300 and Cessna Conquest 441. The methodology approach comprises a process given by the selection of the photovoltaic technology, the calculation of the available solar radiation, the determination of the electrical demand, the layout definition of solar cells, the photovoltaic system capacity calculation, the estimation of the photovoltaic system weight, the estimation of fuel savings for photovoltaic system equipped aircrafts, and finally, the extrapolation of results to other aircrafts. The study concludes that the use of photovoltaic technology to supply power to the aircraft electrical system can result viable from the point of view of operational profitability, generating savings in fuel consumption. These fuel savings depend on the type of aircraft, the flying route and schedules of operation.El documento sera publicado en la versión impresa de la revista Volume 51, November 2015, Pages 138–15