The Experts below are selected from a list of 12855 Experts worldwide ranked by ideXlab platform
Mohammad Shakir Nasif - One of the best experts on this subject based on the ideXlab platform.
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Air to air fixed plate enthalpy heat exchanger, performance variation and energy analysis
Journal of Mechanical Science and Technology, 2013Co-Authors: Mohammad Shakir Nasif, Rafat Al-waked, Masud Behnia, Graham MorrisonAbstract:The thermal performance of a Z shape enthalpy heat exchanger utilising 70 gsm Kraft Paper as the heat and moisture transfer surface has been investigated. Effects of different inlet air humidity ratio conditions on the heat exchanger effectiveness and on the energy recovered by the heat exchanger have been the main focus of this investigation. A typical air conditioning cooling coil which incorporates an enthalpy heat exchanger has been modelled for tropical climate. Under test conditions, results have shown that latent effectiveness and the moisture resistance coefficient have strong dependency on the inlet air humidity ratio. Moreover, the latent effectiveness has been found to be strongly dependent on the moisture resistance coefficient rather than the convective mass transfer coefficient. Finally, annual energy analysis for Singapore weather conditions have also shown that energy recovered under variable inlet air conditions is 15% less than that recovered under constant inlet air conditions for the same heat exchanger.
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Modeling of Air to Air Enthalpy Heat Exchanger
Heat Transfer Engineering, 2012Co-Authors: Mohammad Shakir Nasif, Masud Behnia, Rafat Al-waked, Graham L. MorrisonAbstract:The thermal performance of a Z-shaped enthalpy heat exchanger utilizing 45-gsm Kraft Paper as the heat and moisture transfer surface for heating, ventilation, and air conditioning (HVAC) energy recovery is experimentally investigated through temperature and moisture content measurements. A mathematical model is developed and validated against the experimental results using the effectiveness-NTU method. In this model the Paper moisture transfer resistance is determined by Paper moisture permeability measurements. Results showed that the Paper moisture transfer resistance is not constant and varies with moisture gradient across the Paper. Furthermore, the model is used to predict the heat exchanger performance for different heat exchanger flow configurations. The results showed that higher effectiveness values are achieved when the heat exchanger flow path width is reduced. Temperature and moisture distribution in the heat exchanger is also studied using a computational fluid dynamics package (FLUENT). To m...
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membrane heat exchanger in hvac energy recovery systems systems energy analysis
Energy and Buildings, 2010Co-Authors: Graham L. Morrison, Rafat Alwaked, Mohammad Shakir Nasif, Masud BehniaAbstract:The thermal performance of an enthalpy/membrane heat exchanger is experimentally investigated. The heat exchanger utilizes a 60gsm Kraft Paper as the heat and moisture transfer surface for HVAC energy recovery. The heat exchanger sensible, latent and total effectiveness have been determined through temperature and moisture content measurements. The annual energy consumption of an air conditioner coupled with an enthalpy/membrane heat exchanger is also studied and compared with a conventional air conditioning cycle using in-house modified HPRate software. The heat exchanger effectiveness are used as thermal performance indicators and incorporated in the modified software. Energy analysis showed that an air conditioning system coupled with a membrane heat exchanger consumes less energy than a conventional air conditioning system in hot and humid climates where the latent load is high. It has been shown that in humid climate a saving of up to 8% in annual energy consumption can be achieved when membrane heat exchanger is used instead of a conventional HVAC system.
Jocelyn Jalbert - One of the best experts on this subject based on the ideXlab platform.
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kinetics of the production of chain end groups and methanol from the depolymerization of cellulose during the ageing of Paper oil systems part 3 extension of the study under temperature conditions over 120 c
Cellulose, 2015Co-Authors: Jocelyn Jalbert, Brigitte Morin, Esperanza Rodriguezcelis, Steve Duchesne, Mohamed Ryadi, Roland GilbertAbstract:To go further in our assessment of methanol for the monitoring of the cellulosic insulation condition in electrical transformers, two of the Paper/oil systems [one comprising a standard wood Kraft Paper and the other, a thermally-upgraded Kraft Paper (TU Paper)] discussed in Parts 1 and 2 (Gilbert et al. in Cellulose 16:327–338. doi: 10.1007/s10570-008-9261-1, 2009; Cellulose 17:253–269. doi: 10.1007/s10570-009-9365-2, 2010) were reinvestigated under accelerated ageing conditions (T between 130 and 210 °C). The experimental data were tracked by testing two mathematical models, one that takes into account the inhomogeneous nature of the polymer by decreasing with time a pseudo-zero rate constant by a first-order process and the other, by simultaneously operating a separate first-order law for the three main categories of 1,4-β-glycosidic bonds in the polymer structure. These additional results provide evidence that the degradation proceeds via a random opening of these bonds in both the amorphous and crystalline regions, with the influence of a pyrolysis-like mechanism even at relatively low temperatures. Very good dependence with the temperature (lnk vs 1/T) is noted for the rate constants of the production of chain-end groups and the formation of methanol, confirming the importance of carrying out the ageing tests beyond the LODP of the specimens (leveling-off value of the degree of polymerization). The grouping of some of these data with those published in Part 2 for an identical system reveals that the degradation is governed by a single reaction pattern over 70–210 °C. The Arrhenius law applied to this data grouping shows an activation energy of 95 ± 4 kJ mol−1 with a frequency factor (lnAa) of 22 ± 1 for the depolymerization, while for the formation of CH3OH, the respective values are 122 ± 6 kJ mol−1 and 33 ± 2. Finally, the kinetic parameters obtained under accelerated ageing conditions over 150–210 °C show that the stabilizing substances of the TU-Kraft Paper modify the bond opening mechanism by blocking the effect of the acid and water generated by the oil decomposition. When they are present in the fibrous structure, the activation energy of the reaction goes up to 148 ± 14 kJ mol−1 with a frequency factor of 33 ± 4 for the depolymerization and 133 ± 11 kJ mol−1 with a frequency factor of 33 ± 3 for the formation of CH3OH.
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Relationships between methanol marker and mechanical performance of electrical insulation Papers for power transformers under accelerated thermal aging
IEEE Transactions on Dielectrics and Electrical Insulation, 2015Co-Authors: Oscar H. Arroyo, Jocelyn Jalbert, Issouf Fofana, Mohamed RyadiAbstract:The mechanical performance of two commercial Papers used as solid insulation in power transformers, namely standard Kraft and a thermally upgraded Kraft Paper, were studied during accelerated aging in Luminol oil at 170 °C. The results show a relationship between the degree of polymerization and the mechanical properties measured by tensile testing. A linear relationship was found between the mechanical properties of Paper, the tensile index (Tidx), and the concentration of methanol present in the oil. The methanol chemical marker has been proven to be an accurate assessment tool for the aging of cellulosic Paper. The results show a promising tool for correlating the methanol concentration in oil, as an indirect indicator, with the mechanical performance of the Paper. This approach can be used to monitor the real state of the cellulose chains in the power transformer insulation Paper.
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identification of a chemical indicator of the rupture of 1 4 β glycosidic bonds of cellulose in an oil impregnated insulating Paper system
Cellulose, 2007Co-Authors: Jocelyn Jalbert, Roland Gilbert, Pierre Tetreault, Brigitte Morin, Denise LessarddezielAbstract:In this study, headspace gas chromatography/mass spectrometry has been used to assess the volatile by-products generated by the ageing of oil-impregnated Paper insulation of power transformers. Sealed-glass ampoules were used to age under oxidative conditions 0.5-g specimens of insulating Paper in 9 mL of inhibited mineral oil in a temperature range of 60–120 °C and moisture of 0.5, 1 and 2% (w/w). A linear relationship between one of the oil-soluble degradation by-products, i.e. methanol, and the number of ruptured 1,4-β-glycosidic bonds of cellulose, regardless of the type of Paper (ordinary Kraft or thermally-upgraded (TU) Kraft Paper), was established for the first time in this field. Ageing at 130 °C of model compounds of the Kraft Paper constituents (α-cellulose, hemicellulose and lignin) and two cellulosic breakdown by-products (D-(+)-glucose and 1,6-anhydro-β-d-glucopyranose) confirmed that the α-cellulose degradation was mostly responsible for the presence of this molecule in the system. Furthermore, additional 130 °C-tests with six different Papers and pressboard samples under a tight control of initial moisture indicated that at least one molecule of methanol is formed for each rupture of 1,4-β-glucosidic bond of the molecular chains. Stability tests showed that the ageing indicator is stable under the oxygen and temperature conditions of open-breathing transformers. The presence of methanol was detected in 94% of oil samples collected from over than 900 in-service pieces of equipment, confirming the potential for this application. Lastly, the tests have shown that oil-oxidation by-products and TU-nitrogenous agents modify the methanol partitioning coefficients in the Paper/oil/air system, which makes their study essential over a range of field conditions encountered by power transformers. Results are presented and discussed in comparison with 2-furfuraldehyde, which is the current reference in the domain.
Masud Behnia - One of the best experts on this subject based on the ideXlab platform.
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Air to air fixed plate enthalpy heat exchanger, performance variation and energy analysis
Journal of Mechanical Science and Technology, 2013Co-Authors: Mohammad Shakir Nasif, Rafat Al-waked, Masud Behnia, Graham MorrisonAbstract:The thermal performance of a Z shape enthalpy heat exchanger utilising 70 gsm Kraft Paper as the heat and moisture transfer surface has been investigated. Effects of different inlet air humidity ratio conditions on the heat exchanger effectiveness and on the energy recovered by the heat exchanger have been the main focus of this investigation. A typical air conditioning cooling coil which incorporates an enthalpy heat exchanger has been modelled for tropical climate. Under test conditions, results have shown that latent effectiveness and the moisture resistance coefficient have strong dependency on the inlet air humidity ratio. Moreover, the latent effectiveness has been found to be strongly dependent on the moisture resistance coefficient rather than the convective mass transfer coefficient. Finally, annual energy analysis for Singapore weather conditions have also shown that energy recovered under variable inlet air conditions is 15% less than that recovered under constant inlet air conditions for the same heat exchanger.
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Modeling of Air to Air Enthalpy Heat Exchanger
Heat Transfer Engineering, 2012Co-Authors: Mohammad Shakir Nasif, Masud Behnia, Rafat Al-waked, Graham L. MorrisonAbstract:The thermal performance of a Z-shaped enthalpy heat exchanger utilizing 45-gsm Kraft Paper as the heat and moisture transfer surface for heating, ventilation, and air conditioning (HVAC) energy recovery is experimentally investigated through temperature and moisture content measurements. A mathematical model is developed and validated against the experimental results using the effectiveness-NTU method. In this model the Paper moisture transfer resistance is determined by Paper moisture permeability measurements. Results showed that the Paper moisture transfer resistance is not constant and varies with moisture gradient across the Paper. Furthermore, the model is used to predict the heat exchanger performance for different heat exchanger flow configurations. The results showed that higher effectiveness values are achieved when the heat exchanger flow path width is reduced. Temperature and moisture distribution in the heat exchanger is also studied using a computational fluid dynamics package (FLUENT). To m...
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membrane heat exchanger in hvac energy recovery systems systems energy analysis
Energy and Buildings, 2010Co-Authors: Graham L. Morrison, Rafat Alwaked, Mohammad Shakir Nasif, Masud BehniaAbstract:The thermal performance of an enthalpy/membrane heat exchanger is experimentally investigated. The heat exchanger utilizes a 60gsm Kraft Paper as the heat and moisture transfer surface for HVAC energy recovery. The heat exchanger sensible, latent and total effectiveness have been determined through temperature and moisture content measurements. The annual energy consumption of an air conditioner coupled with an enthalpy/membrane heat exchanger is also studied and compared with a conventional air conditioning cycle using in-house modified HPRate software. The heat exchanger effectiveness are used as thermal performance indicators and incorporated in the modified software. Energy analysis showed that an air conditioning system coupled with a membrane heat exchanger consumes less energy than a conventional air conditioning system in hot and humid climates where the latent load is high. It has been shown that in humid climate a saving of up to 8% in annual energy consumption can be achieved when membrane heat exchanger is used instead of a conventional HVAC system.
Kevin S. Fancey - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation on performance of fabrics for indirect evaporative cooling applications
Building and Environment, 2016Co-Authors: Peng Xu, Xudong Zhao, Xiaoli Ma, Kevin S. FanceyAbstract:Indirect evaporative cooling, by using water evaporation to absorb heat to lower the air temperature without adding moisture, is an extremely low energy and environmentally friendly cooling principle. The properties of the wet channel surface in an indirect evaporating cooler, i.e. its moisture wicking ability, diffusivity and evaporation ability, can greatly affect cooling efficiency and performance. Irregular fibres help to divert moisture and enlarge the wetted area, thus promoting evaporation. A range of fabrics (textiles) weaved from various fibres were experimentally tested and compared to Kraft Paper, which has been conventionally used as a wet surface medium in evaporative coolers. It was found that most of the textile fabrics have superior properties in moisture wicking ability, diffusivity and evaporation ability. Compared with Kraft Paper, the wicking ability of some fabrics was found to be 171%–182% higher, the diffusion ability 298%–396% higher and evaporation ability 77%–93% higher. A general assessment concerning both the moisture transfer and mechanical properties found that two of the fabrics were most suitable for indirective evaporative cooling applications.
L E Lundgaard - One of the best experts on this subject based on the ideXlab platform.
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ageing of mineral oil impregnated cellulose by acid catalysis
IEEE Transactions on Dielectrics and Electrical Insulation, 2008Co-Authors: L E Lundgaard, W Hanse, S IngebrigtseAbstract:Acid catalyzed ageing of oil impregnated Kraft Paper has been studied experimentally. Five different carboxylic acids (formic, acetic, laevulinic, stearic and naphtenic acid) have been added to mineral oil to arrive at a neutralization value of 0.4 mg KOH/g. Thereafter, Kraft Paper of two different humidities has been allowed to equilibrate with the oil. The results show that the lower the molecular weight of the carboxylic acids is the more is absorbed by the Paper. Furthermore, a clear synergy for the Paper ageing rates between moisture and the lower molecular weight acids is found, while for the higher molecular weight acids almost no effects were found. It is concluded that present techniques for measuring acidity of oils do not reflect these detailed conditions. It is suggested to introduce a new measuring technique for neutralization value where water rinsing is used to identify the content of low molecular weight, water soluble acids.
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aging of Kraft Paper by acid catalyzed hydrolysis
International Conference on Dielectric Liquids, 2005Co-Authors: L E Lundgaard, D Linhjell, W Hansen, S Ingebrigtsen, M DahlundAbstract:Hydrolysis of transformer insulating Kraft Paper is experimentally investigated. Paper moisture content was varied and five different acids representative of what may be found in an aging transformer - were added to the oil. The low molecular weight acids were to a large degree absorbed by the Paper, contrary to the high molecular acids that remained in the oil. The three low molecular acids accelerated the aging of the Paper, and a clear synergy between these acids and water content was found. The high molecular acids did not influence the Paper aging significantly. The results support a theory explaining the hydrolysis as governed by acid catalysis. Examples from measurements on real transformers are shown. It is concluded that low molecular acids constitute an important aging factor for transformer windings and should be included in diagnostic schemes, and when estimating the pay-back from maintenance actions.
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dielectric response of oil impregnated Paper insulation variation with humidity and ageing level power transformer applications
Conference on Electrical Insulation and Dielectric Phenomena, 2004Co-Authors: D Linhjell, U. Gafvert, L E LundgaardAbstract:The dielectric response of oil-impregnated Kraft Paper with 3 initial humidity levels (0,17%, 1,75% and 3,5%) has been studied in the frequency range 0.1 mHz -1 kHz, before ageing at DP (degree of polymerisation) 1200 and after ageing to DP 900, 600 and 2-300, primarily to investigate if the method can be used for non-destructive characterization of the state of cellulose insulation in electrical power devices, e.g. transformers. Also, because ageing produces acids, known acids have been added to unaged Paper to investigate the influence on the dielectric response. Results indicate that the effect of ageing is small compared to the effect of moisture, but the loss peak of the humid samples become more prominent. Light acids (formic, acetic), which are absorbed in the Paper, have an effect on the dielectric response, similar to water.
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Dielectric response of oil-impregnated cellulose from 0.1 mHz to 3 MHz
IEEE International Conference on Dielectric Liquids 2005. ICDL 2005., 2024Co-Authors: D Linhjell, O. L. Hestad, U. Gafvert, L E LundgaardAbstract:Pressboard and Kraft Paper with and without moisture, with and without added acids have been tested with frequency domain spectroscopy up to 1 kHz. Kraft Paper with three moisture levels has also been tested at various ageing levels. Moisture and low-molecular carboxylic acids cause shifts in the permittivity vs. frequency curves. In addition, in Paper but not pressboard, moisture is associated with an extra relaxation in the low-frequency part. High-molecular carboxylic acids have little effect on the permittivity. The same is the case for reduction in chain length of the cellulose polymer. The method should be useful as a non-invasive field test method for destructive agents in transformers, but not for the ageing (chain scission) itself. The measurements up to 3 MHz are so far inconclusive, but have yielded a few results that blend in well with the measurements below 1 kHz.
