Valerie Eveloy

Environment and Usage Monitoringof Electronic Products for Health Assessment and Product Design

Abstract The life-cycle environmental and usage conditions of a product or system can be monitored and analyzed to assess its on-going health, provide advance warning of failure, and provide information to improve the design and qualification of fielded and future products. The challenge lies in the implementation of this method in application conditions. This paper presents methods to effectively collect and analyze life-cycle environmental and usage data for in-situ health assessments. An integrated hardware-software micro-programmable module for health and usage monitoring of electronic products in their application environment is presented. The hardware incorporates local sensors, and on-board processing power using embedded software. These data processing capabilities are intended to enable immediate and localized processing of the raw sensor data to reduce the power and memory consumption anticipated during load monitoring. Guidelines are also provided to develop a life cycle monitoring plan, that encompasses the selection of environmental and usage parameters. A case study is presented to illustrate the methodology.

Enhancement of photovoltaic solar module performance for power generation in the Middle East

Despite the abundance of solar energy in the Middle East, the efficiency and reliability of photovoltaic (PV) modules is severely affected by elevated cell operating temperature, which reduces the effectiveness of sun tracking techniques. In this study the potential of water-cooling to improve the electrical performance of stationary and sun-tracked PV modules is experimentally investigated for application at off-shore oil and gas facilities in the Persian Gulf. In parallel with measurements of PV module electrical characteristics and operating temperature, global solar irradiation, ambient air and cooling water temperatures, wind velocity and relative humidity are also recorded. In autumn conditions in the United Arab Emirates (24.43°N, 54.45°E), water-cooling is found to reduce PV module operating temperature by up to 30°C relative to passive cooling conditions, depending on operating conditions. Using water-cooling, power output is enhanced for a significant portion of the day for fixed geographical South facing modules (e.g., 22% at solar noon, and 13% at 2 p.m.) relative to passive cooling, and even more significantly for sun-tracked modules (e.g., 20% at 2 p.m.). Sun tracking enhances power output by 16% and 24% for passively- and water-cooled modules, respectively, at for example 2 p.m. The incorporation of water-cooling and sun tracking is the most effective, with enhancements in output power of on order 40% at for example 2 p.m. relative to passively-cooled, fixed South facing operation. In winter conditions (e.g., December), modest reductions in operating temperature and improvements in electrical performance are obtained using water-cooling and/or sun tracking, which may not justify the associated capital and operating costs.

Numerical Heat Transfer Predictive Accuracy for an In-Line Array of Board-Mounted Plastic Quad Flat Back Components in Free Convection

Numerical predictive accuracy is assessed for board-mounted electronic component heat transfer in free convection, using a computational fluid dynamics code dedicated to the thermal analysis of electronic equipment. This is achieved by comparing numerical predictions with experimental measurements of component junction temperature and component-PCB surface temperature, measured using thermal test chips and infrared thermography, respectively. The printed circuit board (PCB) test vehicle considered is populated with fifteen 160-lead PQFP components generating a high degree of component thermal interaction. Component numerical modeling is based on vendor-specified, nominal package dimensions and material thermophysical properties. To permit both the modeling methodology applied and solver capability to be carefully evaluated, test case complexity is incremented in controlled steps, from individually to simultaneously powered component configurations. Component junction temperature is predicted overall to within ±5°C (7%) of measurement, independently of component location on the board. However, component thermal interaction is found not to be fully captured.

Performance investigation of thermally enhanced polymer composite materials for microelectronics cooling

Driven by the low density, corrosion resistance, manufacturability, and low raw material and manufacturing costs of polymer composite materials, significant attention is being devoted to the innovation, characterization, and implementation of such materials. In this study the thermal and mechanical properties of a broad range of commercially available, injection moldable, thermally enhanced polymer composite materials are reviewed to help identify candidate materials that could replace conventional metal alloys in microelectronics cooling heat sink and heat exchanger applications. The material property characterization data reviewed consists of vendor data generated in accordance with applicable characterization standards. From twenty seven commercially-available polymeric composite materials, two promising groups of materials, namely polyphenylene sulfide (PPS) and polyimide 66 (PA66), are identified.A preliminary investigation of exchanger heat transfer rate is undertaken using computational fluid dynamics (CFD) to identify the envelope of thermally enhanced composite material thermal conductivities required for effective heat transfer in gas-liquid heat exchanger applications. The thermal performance of a thermally enhanced PPS, parallel plate cross-flow air-water heat exchanger prototype is shown numerically and experimentally to be comparable to that of a conventional aluminum exchanger having the same geometry, demonstrating the potential feasibility of replacing conventional metallic heat exchangers with thermally enhanced polymeric composite heat exchangers in microelectronic air-liquid cooling applications. Review of thermal and mechanical properties of polymer composite materials.Promising materials identified for heat exchangers in microelectronics cooling.Numerical assessment of polymer composite heat exchanger thermal performance.Heat transfer feasibility of replacing metallic exchangers with polymer composites.

Experimental characterization of thermally enhanced polymer composite heat exchangers

The latest developments in thermally enhanced polymer composite materials have opened opportunities in the design and fabrication of novel effective heat exchangers, having excellent heat transfer characteristics, chemical resistance, and both lower weight and cost compared with metallic materials. In this study, a thermally enhanced polyphenylene sulfide (PPS) polymer parallel plate cross-flow air-water heat exchanger prototype is manufactured by injection molding and experimentally characterized. The polymeric exchanger thermofluid performance is found to be comparable to that of a conventional aluminum exchanger having the same geometry, demonstrating its potential for air-liquid cooling of electronic equipment.

An experimental and numerical investigation of tube bank heat exchanger thermofluids

Heat exchangers are extensively used in engineering applications, such as for the thermal management of electronic cabinets. Although computational fluid dynamics (CFD) has the potential to provide a more accurate assessment of exchanger thermal performance than empirically-based software, CFD-based parametric analysis of a wide range of exchanger geometries and Reynolds numbers can be computationally prohibitive. This paper proposes and assesses the effectiveness of a dual design strategy, which combines empirical and numerical analyses of heat exchanger thermofluid performance. Empirical analysis serves to provide initial design specifications, while performance is optimized using CFD. The test vehicle consists of a staggered tube bank heat exchanger arrangement (St = Sl = 3.0). Good agreement is obtained between the empirical relationships developed by Martin [ 1 ] for heat transfer and Gaddis and Gnielinski [2] for pressure drop, and corresponding CFD predictions for Reynolds numbers varying from 1,749 to 17,491. Numerical flow field predictions are found to be accurately predicted relative to particle image velocimetry (PIV) measurements for a Reynolds number of 700. This study therefore provides a degree of confidence in using empirical correlations to undertake an initial sizing of tube bank heat exchanger design, to be refined for application specific environments using CFD analysis.

Numerical Investigation of the Effect of Fuel Recycling on the Susceptibility of a Direct Internal Methane Reforming SOFC to Carbon Deposition

There is considerable interest in developing solid oxide fuel cell (SOFCs) systems capable of operating directly on methane via direct internal reforming (DIR). However, a major barrier to DIR is the susceptibility of current state-of-the-art nickel based anodes to carbon deposition, particularly at low fuel humidification levels. Overcoming these difficulties will require improved anode designs and identification of suitable operating conditions. In this study, the potential effectiveness of partial fuel recycling in mitigating the risks of carbon deposits is investigated in a planar DIR-SOFC operated on humidified methane at inlet steam-to-carbon ratios (S:Cs) of 0.1 to 1. This is achieved using a detailed computational fluid dynamics (CFD) model which couples momentum, heat, mass and charge transport with electrochemical and chemical reactions. The model thermodynamically predicts the spatial extent of carbon deposits by accounting for both the cracking and Boudouard reactions, for several fuel humidification and recycling conditions. At temperatures close to 1173 K and for inlet fuel S:Cs of 0.5 to 1, 50% (mass %) fuel recycling is found to be an effective strategy against carbon deposition. For lower recycling ratios at the same fuel compositions, or lower S:C ratios (regardless of the recycling ratio), fuel recycling reduces the risk of coking, but does not eliminate it. The results suggest that partial fuel recycling could contribute to extend the operational range of DIR-SOFCs to lower S:C ratios (0.5 to 1.0) than typically considered, with reduced risks of carbon deposition, while reducing system cost and complexity in terms of steam production. For dry or weakly humidified fuels, additional mitigation strategies would be required.Copyright

The Effect of Electrostatic Discharge on Electrical Overstress Susceptibility in a Gallium Arsenide MESFET-Based Device

The electrostatic discharge (ESD) and electrical overstress (EOS) susceptibility of gallium arsenide (GaAs) MESFET microwave monolithic integrated circuits is investigated using a combination of threshold ESD/EOS tests, ESD step stress tests, and multiple low-level ESD stresses of constant magnitude less than the hard failure threshold voltage. The ESD stresses applied were based on standard ESD test models. Multiple low-level ESD stresses produced no stress hardening or weakening effect on the hard ESD failure threshold voltage of the device and no detectable degradation in electrical performance. However, such stresses were found to increase the device susceptibility to subsequent EOS failure, suggesting that low-level ESD stresses can latently damage GaAs MESFET-based devices. EOS susceptibility did not recover with annealing. The failure signatures suggest that the hard failure mechanisms caused by EOS following the application of low-level ESD stresses are dependent on the amplitude of the pre-ESD stress and that field failures may be caused by successive ESD and EOS stresses. The findings indicate the need for dual ESD and EOS protection in the GaAs MESFET component studied and suggest that the relationship between ESD and EOS susceptibility may need to be considered for other semiconductor technologies.

Enhancement of flat-type solar photovoltaics power generation in harsh environmental conditions

Interest in solar energy has dramatically increased in recent years in the Middle East. However, despite high solar irradiance levels, harsh climatic conditions adversely affect the performance of solar photovoltaics (PVs) in the Persian Gulf. The objective of this study is to characterize the performance characteristics of PV systems utilizing either sun tracking or active cooling to increase electrical power output relative to stationary, passive cooling operation in such climatic conditions. This is achieved using dedicated experimental test facilities, that permit simultaneous PV performance characterization of sun-tracked and water-cooled configurations. Sun tracking is found to increase the daily yield of passively cooled PV modules by approximately 40% in summer months relative to stationary operation, with the largest power output gains occurring from approximately 30 minutes after sunrise to 90 minutes before solar noon, and from 90 minutes after solar noon to 30 minutes before sunset. Continuous water-cooling, with water at ambient air temperature (i.e., 35°C to 40°C), is found to increase PV module daily energy yield by approximately 15% relative to passively cooled operation in stationary conditions in summer, with the highest energy gains occurring two hours either side of solar noon. Peak electrical power output can be further increased by approximately 0.5 W for every °C reduction in water temperature below ambient air temperature, from 35°C to 2°C. Time- and temperature-relay actuated dynamic water-cooling is also investigated to reduce water consumption relative to continuous cooling. The use of a time relay-actuated five seconds-on, two-minute off cooling sequence is found to generate the same energy gain as for continuous water cooling, while requiring only 4% of continuous water consumption. This is attributed to the evaporative cooling effect caused by vaporization of a remaining thin film of water on the module surface during the off-period of the cooling cycle.

Air cooled heat sink design optimization in free convection

The optimization of heat sink performance is becoming ever more critical in passively air-cooled applications. In this paper, an overview of analytical, semi-empirical and Computational Fluid Dynamics (CFD)-based methodologies for air-cooled heat sink design optimization in free convection is presented. The advantages and potential limitations of these design techniques are summarized. A multi-faceted heat sink design strategy is advocated, which combines the analysis techniques presented with experimentation. The need to incorporate sustainability and formal optimization in the design process is highlighted.