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Thermal Performance (thermal + performance)

Distribution by Scientific Domains

Engineering	71%
Polymers and Materials Science	15%
4 Other Domains	14%

Selected Abstracts

Thermal performance of juvenile Atlantic Salmon, Salmo salar L.

FUNCTIONAL ECOLOGY, Issue 6 2001
B. JONSSON
Summary 1,Experimental data for maximum growth and food consumption of Atlantic Salmon (Salmo salar L.) parr from five Norwegian rivers situated between 59 and 70°N were analysed and modelled. The growth and feeding models were also applied to groups of Atlantic Salmon growing and feeding at rates below the maximum. The data were fitted to the Ratkowsky model, originally developed for bacterial growth. 2,The rates of growth and food consumption varied significantly among populations but the variation appeared unrelated to thermal conditions in the river of population origins. No correlation was found between the thermal conditions and limits for growth, thermal growth optima or maximum growth, and hypotheses of population-specific thermal adaptation were not supported. Estimated optimum temperatures for growth were between 16 and 20 °C. 3, Model parameter estimates differed among growth-groups in that maximum growth and the performance breadth decreased from fast to slow growing individuals. The optimum temperature for growth did not change with growth rate. 4, The model for food consumption (expressed in energy terms) peaked at 19,21 °C, which is only slightly higher than the optimal temperature for growth. Growth appeared directly related to food consumption. Consumption was initiated ,2 °C below the lower temperature for growth and terminated ,1·5 °C above the upper critical temperature for growth. Model parameter estimates for consumption differed among growth-groups in a manner similar to the growth models. 5,By combining the growth and consumption models, growth efficiencies were estimated. The maximum efficiencies were high, 42,58%, and higher in rivers offering hostile than benign feeding and growth opportunities. [source]

Thermal performance of aluminium-foam CPU heat exchangers

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2006
H. Mahdi
Abstract This study investigates the performance of existing central processing unit (CPU) heat exchangers and compares it with aluminium-foam heat exchangers in natural convection using an industrial set-up. Kapton flexible heaters are used to replicate the heat produced by a computer's CPU. A number of thermocouples are connected between the heater and the heat sink being used to measure the component's temperature. The thermocouples are also connected to a data-acquisition card to collect the data using LabVIEW program. The values obtained for traditional heat exchangers are compared to published data to validate experiments and set-up. The validated set-up was then utilized to test the aluminium-foam heat exchangers and compare its performance to that of common heat sinks. It is found that thermal resistance is reduced more than 70% by employing aluminium-foam CPU heat exchangers. The results demonstrate that this material provides an advantage on thermal dissipation under natural convection over most available technologies, as it considerably increases the surface-area-to-volume ratio. Furthermore, the aluminium-foam heat exchangers reduce the overall weight. Copyright © 2005 John wiley & Sons, Ltd. [source]

Thermal performance of the exhausting and the semi-exhausting triple-glazed airflow windows

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2006
Moo-Hyun Kim
Abstract The thermal performance of the airflow window systems was studied numerically using the finite-volume method. Effort was directed towards the reduction in space cooling load for the exhausting and the semi-exhausting triple-glazed airflow windows. The effects of various parameters such as exhausting airflow rate, solar insolation, and aspect ratio were presented. Some qualitative and quantitative comparisons between two systems were made. It was disclosed that the space-heat gain was considerably reduced by increasing the exhausting airflow rate, and the decrease in the space-heat gain of the semi-exhausting airflow window was larger than that of the exhausting airflow window by about 10 W throughout most of the Re range (except the range of near Re = 0) of this numerical work. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Thermal performance of a packed bed reactor for a high-temperature chemical heat pump

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 7 2001
Yukitaka Kato
Abstract The thermal performance of a chemical heat pump that uses the reaction system of calcium oxide/lead oxide/carbon dioxide, which is developed for utilization of high-temperature heat above 800°C, is studied experimentally. The thermal performance of a packed-bed reactor of a calcium oxide/carbon dioxide reaction system, which stores and transforms a high-temperature heat source in the heat pump operation, is examined under various heat pump operation conditions. The energy analysis based on the experiment shows that it is possible to utilize high-temperature heat with this heat pump. This heat pump can store heat above 850°C and then transform it into a heat above 900°C under an approximate atmospheric pressure. An applied system that combines the heat pump and a high-temperature process is proposed for high-efficiency heat utilization. The scale of the heat pump in the combined system is estimated from the experimental results. Copyright © 2001 John Wiley & Sons, Ltd. [source]

Thermal performance in three different low-cost dwellings for the tropical climate of Brazil

BAUPHYSIK, Issue 1 2008
Marlon Leão Msc.
The aim of this project was to analyze the thermal performance of passive low-cost housing in half-humid tropical climate. The houses are located in Cuiabá-MT (15.5° southern latitude), one of the hottest cities in Brazil. The data about the typology of the houses were obtained from three representative construction systems; wood, masonry, and prefabricated. The measurements had been carried out through a year, during 20 consecutive days of each season and were evaluated by three distinct methodologies: (1) analyses of previous recommendations of the construction where the envelope materials were compared with the Brazilian standard NBR 15220-3/ 2005, (2) frequency, through dry bulb temperature with values of 18 °C and 29 °C, and (3) performance, by analysis of comfort levels and bioclimatic strategies processed by Analysis Bio 2.1.2 program in accordance to the adapted Bioclimatic Chart of Givoni for developing countries. Thermisches Verhalten dreier kostengünstiger Wohnhaustypen im tropischen Klima Brasiliens. Ziel des Projektes war, das thermische Verhalten kostengünstiger Passivwohnhäuser im halbfeuchten tropischen Klima zu untersuchen. Die Häuser befinden sich in Cuiabá-MT (15.5° südlicher Breite), eine der heißesten Städte Brasiliens. Die Daten über die Typologie der Häuser wurden von drei repräsentativen Bauweisen gewonnen: Holz, Mauerwerk und Massivbauweise. Die Messungen wurden innerhalb eines Jahres während jeweils 20 aufeinanderfolgenden Tagen in den vier Jahreszeiten durchgeführt und nach drei Kriterien ausgewertet: (1) Untersuchung der Konstruktionsempfehlungen und Vergleich der Außenwandkonstruktion mit der brasilianischen Norm NBR 15220-3/2005, (2) Häufigkeitsverteilung der Temperaturwerte 18 °C und 29 °C, sowie (3) thermisches Verhalten mit Untersuchung der Behaglichkeit und eines bioklimatischen Konzepts mit Hilfe der Software Analysis Bio 2.1.2 in Übereinstimmung mit dem darin verwendeten Bioklimatischen Diagramm für Entwicklungsländer nach Givoni. [source]

Effect of internal cooling/heating coil on adsorption/regeneration of solid desiccant tray for controlling air humidity

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 11 2008
B. N. Hung
Abstract Thermal performances of solid desiccant tray having internal cooling/heating coil for air humidity adsorption and desiccant regeneration are investigated. Three units of desiccant tray each of 48,cm,×,48,cm cross-sectional area and 2.5,cm thickness filled with silica gel are tested in a wind tunnel. For adsorption process, an air stream is flowing through the desiccant trays and the air humidity is captured by the silica gel. Approximately 10,40% of air humidity could be adsorbed more in case of the internal cooling. Besides, the outlet air temperature increases only slightly. In regeneration process, a hot air stream is used to repel the moisture in the silica gel. With the internal heating, the regeneration time is shorter compared with that without internal water heating. In addition, a correlation for calculating the adsorption/regeneration performance of the silica gel trays is developed and the results from the model agree well with the experimental data. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Thermal performance analysis of a tube finned surface

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2002
Kadir Bilen
Abstract The present work submits an experimental work on the heat transfer and friction loss characteristic, employing a tube finned heating surface kept at a constant temperature in a rectangular channel. The tube fins attached on the surface (o.d.=29 mm) were arranged as either in-line or staggered. The parameters for the study were Reynolds number (3700,30 000), depending on hydraulic diameter, the distance between the tube fins in the flow direction (Sy/D=1.72,3.45) and the fin arrangement. The change in the Nusselt number with these parameters was determined. For both tube fin arrangements, it was observed that increasing Reynolds number increased Nusselt number, and maximum heat transfer occurred at Sy/D=2.59. Thermal performances for both arrangements were also determined and compared with respect to heat transfer from the same surface without fins. With staggered array, a heat transfer enhancement up to 25 per cent for Sy/D=3.45 in staggered array was achieved in constant pumping power. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Convective heat transfer and pressure drop of annular tubes with three different internal longitudinal fins

HEAT TRANSFER - ASIAN RESEARCH (FORMERLY HEAT TRANSFER-JAPANESE RESEARCH), Issue 1 2008
Lin Tian
Abstract Pressure drop and heat transfer characteristics of air in three annular tubes with different internal longitudinal fins were investigated experimentally at uniform wall heat flux. The tested tubes have a double-pipe structure with the inner blocked tube as an insertion. Three different kinds of fins, plain rectangle fin, plain rectangle fin with periodical ridges and wave-like fin, were located peripherally in the annulus. The friction factor and Nusselt number can be corrected by a power-law correction in the Reynolds number range tested. It was found that the tube with periodical ridges on the plain fin or with wave-like fin could augment heat transfer; however, the pressure drop was increased simultaneously. In order to evaluate the comprehensive heat transfer characteristics of the tested tubes, two criteria for evaluating the comprehensive thermal performance of tested tubes were adopted. They are: 1) evaluating the comprehensive heat transfer performance under three conditions: identical mass flow, identical pumping power, and identical pressure drop; 2) the second law of thermodynamics, i.e., the entropy generation. According to the two different evaluating methods, it was found that the tube with wave-like fins provided the most excellent comprehensive heat transfer performance among the three tubes, especially when it was used under higher Reynolds number conditions. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(1): 29,40, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20186 [source]

Performance of a modified direct expansion A/C unit

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2010
Esmail M. A. Mokheimer
Abstract This technical note communicates the thermal performance of a modified ten-Ton Refrigerant Direct Expansion (10-TR DX) air conditioning unit into a chiller under actual operating conditions. The modified unit achieved higher COP and cooling capacity compared with conventional DX. The increase in the unit cooling capacity is basically attributed to the enhanced heat transfer coefficient of the Plate-and-Frame Heat Exchanger evaporator. Copyright © 2009 John Wiley & Sons, Ltd. [source]

A simplified method for modelling the effect of blinds on window thermal performance

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 7 2006
D. Naylor
Abstract An approximate method is presented for predicting the effect of a louvered blind on the centre-glass thermal performance of a fenestration. The method combines a one-dimensional heat transfer model with data from a numerical simulation of the window and blind. Sample results for a blind mounted on the indoor surface of a window show the effect of blind slat angle on heat transmission. Both summer and winter conditions are considered. The results show that a louvered blind can improve the U -value of a standard double-glazed window by up to 37%. Also, the radiation heat exchange with the room can be dramatically reduced (by up to 60%), which will improve the level of occupant comfort. However, there was found to be a trade-off between U -value and occupant comfort; placing the blind closer to the window improves the U -value, but increases the radiation heat exchange with the room. The predictions from the present simplified method compare well with results from a full two-dimensional computational fluid dynamics solution of the conjugate blind/window interaction. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Thermodynamic study of wet cooling tower performance

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 6 2006
V. D. Papaefthimiou
Abstract An analytical model was developed to describe thermodynamically the water evaporation process inside a counter-flow wet cooling tower, where the air stream is in direct contact with the falling water, based on the implementation of the energy and mass balance between air and water stream describing thus, the rate of change of air temperature, humidity ratio, water temperature and evaporated water mass along tower height. The reliability of model predictions was ensured by comparisons made with pertinent experimental data, which were obtained from the literature. The paper elaborated the effect of atmospheric conditions, water mass flow rate and water inlet temperature on the variation of the thermodynamic properties of moist air inside the cooling tower and on its thermal performance characteristics. The analysis of the theoretical results revealed that the thermal performance of the cooling tower is sensitive to the degree of saturation of inlet air. Hence, the cooling capacity of the cooling tower increases with decreasing inlet air wet bulb temperature whereas the overall water temperature fall is curtailed with increasing water to air mass ratio. The change of inlet water temperature does not affect seriously the thermal behaviour of the cooling tower. Copyright © 2005 John Wiley & Sons, Ltd. [source]

The impact of fouling on performance evaluation of evaporative coolers and condensers

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2005
Bilal A. Qureshi
Abstract Fouling of evaporative cooler and condenser tubes is one of the most important factors affecting their thermal performance, which reduces effectiveness and heat transfer capability with time. In this paper, the experimental data on fouling reported in the literature are used to develop a fouling model for this class of heat exchangers. The model predicts the decrease in heat transfer rate with the growth of fouling. A detailed model of evaporative coolers and condensers, in conjunction with the fouling model, is used to study the effect of fouling on the thermal performance of these heat exchangers at different air inlet wet bulb temperatures. The results demonstrate that fouling of tubes reduces gains in performance resulting from decreasing values of air inlet wet bulb temperature. It is found that the maximum decrease in effectiveness due to fouling is about 55 and 78% for the evaporative coolers and condensers, respectively, investigated in this study. For the evaporative cooler, the value of process fluid outlet temperature Tp,out varies by 0.66% only at the clean condition for the ambient wet bulb temperatures considered. Copyright © 2005 John Wiley & Sons, Ltd. [source]

The performance of natural draft dry cooling towers under crosswind: CFD study

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2004
Rafat Al-Waked
Abstract The thermal performance of a natural draft dry cooling tower (NDDCT) under a crosswind has been investigated using a general-purpose CFD code. A three-dimensional study using the standard k,, turbulence model to simulate airflow in and around an NDDCT has been conducted. A parametric study has been carried out to examine the effect of crosswind velocity profile and air dry-bulb temperature on the thermal performance of an NDDCT. Two approaches have been considered in this study to quantify the crosswind effect. Firstly, simulations have been conducted at the nominal conditions and crosswind effect has been represented by thermal effectiveness parameter. Secondly, the ejected heat from the NDDCT has been maintained at a constant value (285 MW) and the crosswind effect has been represented by the change in the cooling tower approach parameter. After quantifying the effect of the crosswind on the thermal performance, windbreak walls have been introduced as a means of reducing this effect. The results in this paper show the importance of considering the crosswind velocity profile. Moreover, the introduction of windbreak walls has indicated an improvement in reducing the thermal performance losses due to the crosswind. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Simulation of an integrated PCM,wallboard system

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2003
J.-S. Kim
Abstract Heat transfer barriers and other practical difficulties do currently hamper the development and application of (phase change materials) PCM,wallboard systems. In this study thermal performance of randomly mixed PCM and laminated PCM,wallboard systems have been numerically evaluated and results compared. The laminated system displayed up to 50% increment in heat flux enhancement and about 18% increase in heat transfer rates. Consequently, the laminated PCM,wallboard system has greater potential for heating and cooling application in buildings than the randomly mixed system. Experimental validation and investigation into manufacturing techniques are however needed to establish the commercial viability. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Simplification of analytical models and incorporation with CFD for the performance predication of closed-wet cooling towers

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 13 2002
Ala Hasan
Abstract Simplified analytical models are developed for evaluating the thermal performance of closed-wet cooling towers (CWCTs) for use with chilled ceilings in cooling of buildings. Two methods of simplification are used with regard to the temperature of spray water inside the tower. The results obtained from these models for a prototype cooling tower are very close to experimental measurements. The thermal performance of the cooling tower is evaluated under nominal conditions. The results show that the maximum difference in the calculated cooling water heat or air sensible heat between the two simplified methods and a general computational model is less than 3%. The analytical model distribution of the sensible heat along the tower is then incorporated with computational fluid dynamics (CFD) to assess the thermal performance of the tower. It is found that CFD results agree well with the analytical results when the air flow is simulated with air supply from the bottom of the tower, which represents a uniform air flow. CFD shows the importance of the uniform distribution of air and spray water to achieve optimum design. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Performance analysis of a solar cooker in Turkey

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 2 2002
Galip Oturanç
Abstract A box-type solar cooker is designed and its thermal performance is analysed experimentally. The cooker tracks the sun in two axes, altitude and sun azimuth, by hand control for hourly periods. The experimental results show that the tested cooker may be assumed suitable in some cooking processes for specific country conditions. Copyright © 2002 John Wiley & Sons, Ltd. [source]

Thermal analysis of multi-finger GaInP collector-up heterojunction bipolar transistors with miniature heat-dissipation packaging structures

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 1 2010
Pei-Hsuan Lee
Abstract We build up a finite element modeling (FEM) approach to analyze the thermal performance of collector-up (C-up) heterojunction bipolar transistor (HBTs) with a heat-dissipation via configuration. Highly compact heat-dissipation packaging structures of GaInP/GaAs C-up HBTs have been designed and evaluated systematically. In this work, we devise the 2-D and 3-D models to simulate the actual devices and to investigate the temperature distribution behavior. Results from 2-D model indicate that the large heat-dissipation via configuration can be further reduced by 29% to meet the requirement of HBT-based small high-power amplifiers (HPAs) for the cellular phones. Furthermore, the demonstrated results show that the maximum temperature within the collector calculated from 3-D model is lower than that from 2-D model. In the 3-D analysis, it is revealed that the configuration can be reduced by 32%. Therefore, thinning the heat-dissipation via constructed underneath the GaInP/GaAs C-up HBT should be helpful for miniaturization of HBT-based HPAs in future mobile communication systems. Copyright © 2009 John Wiley & Sons, Ltd. [source]

A fast power loss calculation method for long real time thermal simulation of IGBT modules for a three-phase inverter system

INTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 1 2006
Z. Zhou
Abstract A fast power losses calculation method for long real time thermal simulation of IGBT module for a three-phase inverter system is presented in this paper. The speed-up is obtained by simplifying the representation of the three-phase inverter at the system modelling stage. This allows the inverter system to be simulated predicting the effective voltages and currents whilst using large time-step. An average power losses is calculated during each clock period, using a pre-defined look-up table, which stores the switching and on-state losses generated by either direct measurement or automatically based upon compact models for the semiconductor devices. This simulation methodology brings together accurate models of the electrical systems performance, state of the art-device compact models and a realistic simulation of the thermal performance in a usable period of CPU time and is suitable for a long real time thermal simulation of inverter power devices with arbitrary load. Thermal simulation results show that with the same IGBT characteristics applied, the proposed model can give the almost same thermal performance compared to the full physically based device modelling approach. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Stability and optimum polymerized condition of polysiloxane,polyacrylate core/shell polymer

ADVANCES IN POLYMER TECHNOLOGY, Issue 3 2010
Chengyue Ge
Abstract The stable emulsion of core/shell latex with little coagulum (no more than 0.5% in quality relative to total monomers) has been prepared at low temperature with potassium-persulfate (KPS), sodium formaldehyde sulfoxylate (SFS), and 2,2,-azobis(2-(2-imidazolin-2-yl)propane)dihydrochloride (VA-044) as composite initiators by staged emulsion polymerization. Reactive surfactants were used to significantly improve the stability of emulsion. More interestingly, reverse core/shell structure was investigated when the organic silicon was added in the late period of polymerization. The effects of the emulsifier, initiators, dosage of organic silicon, and monomer's content on conversion and graft efficiency were studied in detail. Moreover, the stability of emulsion was investigated by the values of zeta potential (,) and coagulum. More importantly, the thermal performance and stability of PSI/PA composite latex was studied by the glass transition temperature (Tg). The results showed that there are appropriate values for all factors to obtain high conversion, graft efficiency, and excellent stability: The dosage of surfactant was about 0.44 g, the dosage of VA-044 was about 1000 mg kg,1, the dosage of organic silicon was about 15%, and the monomer's content was about 30%. In addition, the introduction of organic silicon improved the Tg. © 2010 Wiley Periodicals, Inc. Adv Polym Techn 29:161,172, 2010; View this article online at wileyonlinelibrary. DOI 10.1002/adv.20182 [source]

Thermal tolerance and geographical range size in the Agabus brunneus group of European diving beetles (Coleoptera: Dytiscidae)

JOURNAL OF BIOGEOGRAPHY, Issue 2 2008
P. Calosi
Abstract Aim, Within clades, most taxa are rare, whilst few are common, a general pattern for which the causes remain poorly understood. Here we investigate the relationship between thermal performance (tolerance and acclimation ability) and the size of a species' geographical range for an assemblage of four ecologically similar European diving beetles (the Agabus brunneus group) to examine whether thermal physiology relates to latitudinal range extent, and whether Brown's hypothesis and the environmental variability hypothesis apply to these taxa. Location, Europe. Methods, In order to determine the species tolerances to either low or high temperatures we measured the lethal thermal limits of adults, previously acclimated at one of two temperatures, by means of thermal ramping experiments (± 1°C min,1). These measures of upper and lower thermal tolerances (UTT and LTT respectively) were then used to estimate each species' thermal tolerance range, as total thermal tolerance polygons and marginal UTT and LTT thermal polygons. Results, Overall, widespread species have higher UTTs and lower LTTs than restricted ones. Mean upper lethal limits of the Agabus brunneus group (43 to 46°C), are similar to those of insects living at similar latitudes, whilst mean lower lethal limits (,6 to ,9°C) are relatively high, suggesting that this group is not particularly cold-hardy compared with other mid-temperate-latitude insects. Widespread species possess the largest thermal tolerance ranges and have a relatively symmetrical tolerance to both high and low temperatures, when compared with range-restricted relatives. Over the temperature range employed, adults did not acclimate to either high or low temperatures, contrasting with many insect groups, and suggesting that physiological plasticity has a limited role in shaping distribution. Main conclusions, Absolute thermal niche appears to be a good predictor of latitudinal range, supporting both Brown's hypothesis and the environmental variability hypothesis. Restricted-range species may be more susceptible to the direct effect of climate change than widespread species, notwithstanding the possibility that even ,thermally-hardy', widespread species may be influenced by the indirect effects of climate change such as reduction in habitat availability in Mediterranean areas. [source]

Temperature-Gradient Effects in Thermal Barrier Coatings: An Investigation Through Modeling, High Heat Flux Test, and Embedded Sensor

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2010
Yang Tan
The harsh thermal environment in gas turbines, including elevated temperatures and high heat fluxes, induces significant thermal gradients in ceramic thermal barrier coatings (TBCs), which are used to protect metallic components. However, the thermal conductivity of plasma-sprayed TBC increases with exposure at high temperatures mainly due to sintering phenomena and possible phase transformation, resulting in coating performance degradation and potential thermal runaway issues. An analytical thermal model and experimentally obtained coating thermal conductivity data are used to determine the coating through-thickness temperature profile and effective thermal conductivity under gradient conditions at high temperatures. High heat flux tests are then performed on TBCs to evaluate coating thermal behavior under temperature gradients close to service conditions. Coating internal temperature during the tests was also measured by thermally sprayed embedded thermocouples within the top coat. This combined approach provides a sintering map with a new model and allows for the assessment of temperature-gradient effects on the thermal performance of plasma-sprayed TBCs. [source]

Effectual dispersion of carbon nanofibers in polyetherimide composites and their mechanical and tribological properties

POLYMER ENGINEERING & SCIENCE, Issue 10 2010
Bin Li
The use of proliferation of nanotechnology in commercial applications is driving requirements for minimal chemical processing and simple processes in industry. Carbon nanofiber (CNF) products possess very high purity levels without the need of purification processing before use and are in growing demand for this quality. Polyetherimide (PEI) has excellent mechanical and thermal performance, but its high viscosity makes its nanocomposites processing very challenging. In this study, a facile melt-mixing method was used to fabricate PEI nanocomposites with as received and physically treated CNFs. The dispersion of CNFs was characterized by scanning electron microscopy, transmitted optical microscopy, and electrometer with large-area electrodes. The results showed that the facile and powerful melt-mixing method is effective in homogeneously dispersing CNFs in the PEI matrix. The flexural and tribological characteristics were investigated and the formation of spatial networks of CNFs and weak interfacial bonding were considered as competitive factors to enhanced flexural properties. The composites with 1.0 wt% CNFs showed flexural strength and toughness increased by more than 50 and 550%, respectively, but showed very high wear rate comparable with that of pure PEI. The length of the CNFs also exerted great influences on both mechanical and tribological behaviors. POLYM. ENG. SCI., 50:1914,1922, 2010. © 2010 Society of Plastics Engineers [source]

Simultaneously improving the toughness, flexural modulus and thermal performance of isotactic polypropylene by ,-, crystalline transition and inorganic whisker reinforcement

POLYMER ENGINEERING & SCIENCE, Issue 2 2010
Yewen Cao
Magnesium salt (M-HOS) whisker and ,-nucleating agent were introduced into polypropylene and their effects on the crystalline structures, morphologies, mechanical properties, and thermal resistance of polypropylene (PP) were investigated. The results of wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), and polar optical microscopy (POM) examinations suggested that the presence of the whisker did not cause any negative effect on the occurrence of ,-modification, and ,-phase became absolutely dominant form in ,-nucleated samples. The mechanical and thermal properties tests demonstrated that there is an excellent synergy between the ,-nucleating agent and the whisker. For PP composite containing 0.1 wt% of the ,-nucleating agent and 10 wt% of the whiskers, the Izod notched impact strength, elongation at break, flexural modulus, and heat deflection temperature were increased by 108, 194, 31, and 40%, respectively, compared with those of neat PP. By combining the toughening effect of ,,, transition with the reinforcing effect of the whisker, simultaneous improvement in toughness, flexural modulus, and thermal performance of PP was successfully achieved. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers [source]

Thermal performance in three different low-cost dwellings for the tropical climate of Brazil

Analytical Model for Predicting Thermal Bridge Effects due to Vacuum Insulation Panel Barrier Envelopes,

BAUPHYSIK, Issue 1 2008
Martin Tenpierik ir. arch.
Because of a necessity for sustainability and thus for a reduction of the amount of primary energy generated with fossil fuels, vacuum insulation panels (VIP) have recently caught the attention of practitioners in the building industry. The reduction of layer thickness may be considered among the most promising features for large-scale application of VIPs in buildings. The high barrier laminate (or casing) with relatively high thermal conductivity envelops the core material, thus introducing a thermal bridge at the panel edges and corners. Especially for barrier laminates containing ,thick' metal foils, the thermal bridge effect needs to be considered thoughtfully. In this contribution analytical models are presented which on the one hand allow rapid estimation of the VIP's overall thermal performance and on the other hand show the influence of material and geometric parameters on this performance. The analytical models are validated through numerical simulations. Rechenmodell zur Vorhersage von Wärmebrückeneffekten an der Hülle aus Hochbarrierefolien von Vakuum-Isolations-Paneelen (VIP). Aufgrund der Notwendigkeit von nachhaltigem Bauen und Energieeinsparung wird zunehmend der Einsatz von Vakuum-Isolations-Paneelen (VIP) zur Wärmedämmung im Bauwesen erwogen, insbesondere ist damit die erhebliche Reduzierung der Wärmedämmschichtdicke möglich. Die Umhüllung aus Hochbarrierefolien erfordert allerdings die Berücksichtigung der Wärmebrückenwirkung. Der vorliegende Beitrag stellt Berechnungsmodelle vor, welche einerseits die schnelle Abschätzung des thermischen Verhaltens von VIP-Elementen ermöglichen und andererseits den Einfluss der Geometrie und Konstruktion der Elemente aufzeigen. Die Berechnungsmodelle wurden anhand von Simulationen validiert. [source]

Energy scavenging for energy efficiency in networks and applications

BELL LABS TECHNICAL JOURNAL, Issue 2 2010
Kyoung Joon Kim
Telecommunication networks will play a huge part in enabling eco-sustainability of human activity; one of the first steps towards this is to dramatically increase network energy efficiency. In this paper we present two novel approaches for energy scavenging in networks. One involves thermal energy scavenging for improving wireless base station energy efficiency, and the other involves mechanical energy scavenging for powering sensors in sensor networks, for machine-to-machine (M2M) communications, and for smart grid applications. Power amplifier (PA) transistors in base stations waste 30 percent of the total energy used in a wireless access network (WAN) as heat to the environment. We propose a thermoelectric energy recovery module (TERM) to recover electricity from the waste heat of PA transistors. A fully coupled thermoelectric (TE) model, combining thermoelectricity and heat transfer physics, is developed to explore the power generation performance and efficiency as well as the thermal performance of the TERM. The TE model is comprehensively used to determine optimized pellet geometries for power generation and efficiency as a function of PA transistor heat dissipation, heat sink performance, and load resistance. Maximum power generation and efficiency for various parametric conditions are also explored. Untapped kinetic energy is almost everywhere in the form of vibrations. This energy can be converted into electrical energy by means of transducers to power wireless sensors and mobile electronics in the range of microwatts to a few milliwatts. However, many problems limit the efficiency of current harvesting generators: narrow bandwidth, low power density, micro-electro-mechanical system (MEMS) scaling, and inconsistency of vibrating sources. We explore energy scavenger designs based on multiple-mass systems to increase harvesting efficiency. A theoretical and experimental study of two degrees-of-freedom (2-DOF) vibration-powered generators is presented. Both electromagnetic and piezoelectric conversion methods are modeled by using a general approach. Experimental results for the multi-resonant system are in agreement with the analytical predictions and demonstrate significantly better performance in terms of maximum power density per total mass and a wider bandwidth compared to single DOF (1-DOF) generators. © 2010 Alcatel-Lucent. [source]

Simulation of a new concept of an indirect solar dryer equipped with offset rectangular plate fin absorber-plate

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 4 2005
S. Youcef-Ali
Abstract A simulation code was developed to predict the indirect solar dryer performance of the thin beds of discs of potato, subjected to time-varying air conditions. Two mathematical models are developed separately; the first allows the determination of the thermal performances of the solar collector with offset rectangular plate fin absorber-plate and the second, allows to determine the kinetics of drying for the data input of the air at the exit of the collector. The latter takes into account calorific losses through the walls of the dryer and shrinkage of discs. Experimental results of the solar dryer thermal performances, using sunlight in Valenciennes (in the North of France), will be compared with the results obtained by the theoretical model suggested. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Structural characterization of silica modified polyimide membranes

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 1 2006
Mehtap Safak Boroglu
Abstract Polyimide and hybrid polyimide-siloxane were synthesized by polycondensation, imidization, and sol-gel reaction. The polyimides were prepared from pyromellitic dianhydride (PMDA) and 4,4-oxydianiline (ODA) in N -methyl-2-pyrollidone (NMP). Trimethoxyvinyl silane (TMVS) was used as a source of silica. Their surface morphologies, structures and thermal performances were determined using scanning electron microscopy (SEM), infrared spectroscopy (IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that the silica particles were finely and rather homogeneously dispersed in polymers. The glass transition temperature (Tg) of hybrid membrane materials increased with the increasing silica content. TGA analysis showed that polyimides were thermally stable with silica. Modified polyimide-siloxane films, thermal characteristics were found to be better than the polyimide films without silica. Copyright © 2006 John Wiley & Sons, Ltd. [source]