The Experts below are selected from a list of 297 Experts worldwide ranked by ideXlab platform
G N Tiwari - One of the best experts on this subject based on the ideXlab platform.
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an overall exergy analysis of glass Tedlar photovoltaic thermal air collector incorporating thermoelectric cooler a comparative study using artificial neural networks
Energy Conversion and Management, 2019Co-Authors: Neha Dimri, Arvind Tiwari, G N TiwariAbstract:Abstract In this research, a three-layer feed-forward artificial neural network (ANN) model has been developed for glass-Tedlar photovoltaic thermal (PVT) air collector incorporating thermoelectric cooler (TEC). The ANN model is used for estimating the fluctuating outputs of the glass-Tedlar PVT-TEC air collector, i.e. thermal energy gain, electrical energy gain, overall thermal energy gain and overall exergy gain, as a result of intermittent and varying weather conditions. The traditional modelling techniques, used for predicting the output performances of a PVT system, rely on analysis of complex relationships between different components of PVT collector, solution of differential equations and several design parameters. ANN model, however, aids in approximating the outputs by learning through training examples and hence, does not involve complex analysis and calculations. The developed ANN model is based on global solar radiation, diffuse solar radiation and ambient temperature, as inputs. Further, the outputs of glass-Tedlar PVT-TEC air collector [Case I] are compared against glass-glass PVT-TEC air collector [Case II], using ANN model. The monthly and annual outputs of glass-Tedlar PVT-TEC air collector [Case I] have been estimated for New Delhi, India. Also, a comparison between the annual results of Case I and Case II, obtained using ANN model, has been presented.
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Analytical expression for electrical efficiency of PV/T hybrid air collector
Applied Energy, 2009Co-Authors: Swapnil Dubey, G.s. Sandhu, G N TiwariAbstract:The overall electrical efficiency of the photovoltaic (PV) module can be increased by reducing the temperature of the PV module by withdrawing the thermal energy associated with the PV module. In this communication an attempt has been made to develop analytical expression for electrical efficiency of PV module with and without flow as a function of climatic and design parameters. The four different configurations of PV modules are considered for the present study which are defined as; case A (Glass to glass PV module with duct), case B (Glass to glass PV module without duct), case C (Glass to Tedlar PV module with duct), case D (Glass to Tedlar PV module without duct). Further, experiments were carried out for all configurations under composite climate of New Delhi. It is found that the glass to glass PV modules with duct gives higher electrical efficiency as well as the higher outlet air temperature amongst the all four cases. The annual effect on electrical efficiency of glass to glass type PV module with and without duct is also evaluated. The annual average efficiency of glass to glass type PV module with and without duct is 10.41% and 9.75%, respectively.
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Energy and exergy analysis of photovoltaic/thermal integrated with a solar greenhouse
Energy and Buildings, 2008Co-Authors: Sujata Nayak, G N TiwariAbstract:Abstract In this paper, an attempt has been made to validate the thermal model with experimental results of a typical day August, 25, 2006 for clear weather condition of New Delhi. An energy and exergy analysis for the prediction of performance of a photovoltaic/thermal (PV/T) collector integrated with a greenhouse at I.I.T, Delhi, India has been carried out. The analysis is based on quasi-steady state condition. Experiments have been conducted extensively during period from June 2006 to May 2007, for annual performance. Numerical computation has been carried out for a typical day only for validation. It is observed that the theoretical value of solar cell, Tedlar back surface and greenhouse room air temperatures is approximately equivalent to the experimental values. The predicted and measured values of solar cell, Tedlar back surface and greenhouse air temperatures have been verified in terms of root mean square of percent deviation (7.05–17.58%) as well as correlation coefficient (0.95–0.97) and both exhibit fair agreement. Exergy analysis calculations of the PV/T integrated greenhouse system show an exergy efficiency level of approximately 4%.
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energy and exergy analysis of photovoltaic thermal integrated with a solar greenhouse
Energy and Buildings, 2008Co-Authors: Sujata Nayak, G N TiwariAbstract:Abstract In this paper, an attempt has been made to validate the thermal model with experimental results of a typical day August, 25, 2006 for clear weather condition of New Delhi. An energy and exergy analysis for the prediction of performance of a photovoltaic/thermal (PV/T) collector integrated with a greenhouse at I.I.T, Delhi, India has been carried out. The analysis is based on quasi-steady state condition. Experiments have been conducted extensively during period from June 2006 to May 2007, for annual performance. Numerical computation has been carried out for a typical day only for validation. It is observed that the theoretical value of solar cell, Tedlar back surface and greenhouse room air temperatures is approximately equivalent to the experimental values. The predicted and measured values of solar cell, Tedlar back surface and greenhouse air temperatures have been verified in terms of root mean square of percent deviation (7.05–17.58%) as well as correlation coefficient (0.95–0.97) and both exhibit fair agreement. Exergy analysis calculations of the PV/T integrated greenhouse system show an exergy efficiency level of approximately 4%.
Michael L Everett - One of the best experts on this subject based on the ideXlab platform.
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chemical alteration of poly vinyl fluoride Tedlar induced by exposure to vacuum ultraviolet radiation
Applied Surface Science, 2006Co-Authors: Michael L Everett, Gar B HoflundAbstract:Abstract In this study the chemical alteration of poly(vinyl fluoride) Tedlar® by vacuum ultraviolet radiation (VUV) (115–400 nm) has been examined using X-ray photoelectron spectroscopy (XPS). The initial F/C atom ratio of 0.34 decreases to 0.17 after a 2-h exposure. The F/C atom ratio is further reduced to a steady-state value of approximately 0.04 after a 24-h exposure. Similarly, the O/C atom ratio is reduced from 0.08 to 0.05 and then to 0.02 during these two exposures. As the F and O are removed by VUV exposure, the C concentration increases from 70.5 to 82.0 and then to 94.6 at.% thus forming a graphitic or amorphous carbon-like layer which erodes more slowly than the virgin Tedlar surface. Exposure of the VUV-damaged surface to O2 results in chemisorption of O, indicating that reactive sites are formed during the chemical erosion by VUV. Further exposure to VUV removes this chemisorbed oxygen but a subsequent exposure to air at atmospheric conditions causes a three-fold increase in O chemisorbed at the surface. Comparison of XPS data indicates that the mechanisms of chemical alteration by VUV radiation and hyperthermal (∼5 eV) atomic oxygen (AO) are similar.
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chemical alteration of poly vinyl fluoride Tedlar by hyperthermal atomic oxygen
Applied Surface Science, 2005Co-Authors: Gar B Hoflund, Michael L EverettAbstract:Abstract In this study the erosion of poly(vinyl fluoride) Tedlar by hyperthermal atomic oxygen (AO) has been examined using X-ray photoelectron spectroscopy (XPS). Initially the Tedlar film had F/C and O/C atom ratios of 0.45 and 0.11, which decrease to 0.018 and 0.04, respectively, after a 2-h exposure to a flux of 2 × 10 15 atoms/cm 2 s AO with an average kinetic energy of 5 eV. This exposure essentially produced a graphitic or amorphous carbon-like layer with a carbon content greater than 90 at.%. Longer AO exposures do not alter the composition of this layer significantly. Exposure to O 2 or air nearly doubles the oxygen content in the near-surface region. This is due to dissociative oxygen adsorption at reactive sites formed at the polymer surface during AO exposure. Further exposure to AO removes this chemisorbed oxygen.
Gar B Hoflund - One of the best experts on this subject based on the ideXlab platform.
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chemical alteration of poly vinyl fluoride Tedlar induced by exposure to vacuum ultraviolet radiation
Applied Surface Science, 2006Co-Authors: Michael L Everett, Gar B HoflundAbstract:Abstract In this study the chemical alteration of poly(vinyl fluoride) Tedlar® by vacuum ultraviolet radiation (VUV) (115–400 nm) has been examined using X-ray photoelectron spectroscopy (XPS). The initial F/C atom ratio of 0.34 decreases to 0.17 after a 2-h exposure. The F/C atom ratio is further reduced to a steady-state value of approximately 0.04 after a 24-h exposure. Similarly, the O/C atom ratio is reduced from 0.08 to 0.05 and then to 0.02 during these two exposures. As the F and O are removed by VUV exposure, the C concentration increases from 70.5 to 82.0 and then to 94.6 at.% thus forming a graphitic or amorphous carbon-like layer which erodes more slowly than the virgin Tedlar surface. Exposure of the VUV-damaged surface to O2 results in chemisorption of O, indicating that reactive sites are formed during the chemical erosion by VUV. Further exposure to VUV removes this chemisorbed oxygen but a subsequent exposure to air at atmospheric conditions causes a three-fold increase in O chemisorbed at the surface. Comparison of XPS data indicates that the mechanisms of chemical alteration by VUV radiation and hyperthermal (∼5 eV) atomic oxygen (AO) are similar.
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chemical alteration of poly vinyl fluoride Tedlar by hyperthermal atomic oxygen
Applied Surface Science, 2005Co-Authors: Gar B Hoflund, Michael L EverettAbstract:Abstract In this study the erosion of poly(vinyl fluoride) Tedlar by hyperthermal atomic oxygen (AO) has been examined using X-ray photoelectron spectroscopy (XPS). Initially the Tedlar film had F/C and O/C atom ratios of 0.45 and 0.11, which decrease to 0.018 and 0.04, respectively, after a 2-h exposure to a flux of 2 × 10 15 atoms/cm 2 s AO with an average kinetic energy of 5 eV. This exposure essentially produced a graphitic or amorphous carbon-like layer with a carbon content greater than 90 at.%. Longer AO exposures do not alter the composition of this layer significantly. Exposure to O 2 or air nearly doubles the oxygen content in the near-surface region. This is due to dissociative oxygen adsorption at reactive sites formed at the polymer surface during AO exposure. Further exposure to AO removes this chemisorbed oxygen.
Anton Amann - One of the best experts on this subject based on the ideXlab platform.
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stability of selected volatile breath constituents in Tedlar kynar and flexfilm sampling bags
Analyst, 2013Co-Authors: Pawel Mochalski, Anton Amann, Julian King, Karl UnterkoflerAbstract:The stability of 41 selected breath constituents in three types of polymer sampling bags, Tedlar, Kynar, and Flexfilm, was investigated using solid phase microextraction and gas chromatography mass spectrometry. The tested molecular species belong to different chemical classes (hydrocarbons, ketones, aldehydes, aromatics, sulphurs, esters, terpenes, etc.) and exhibit close-to-breath low ppb levels (3–12 ppb) with the exception of isoprene, acetone and acetonitrile (106 ppb, 760 ppb, 42 ppb respectively). Stability tests comprised the background emission of contaminants, recovery from dry samples, recovery from humid samples (RH 80% at 37 °C), influence of the bag's filling degree, and reusability. Findings yield evidence of the superiority of Tedlar bags over remaining polymers in terms of background emission, species stability (up to 7 days for dry samples), and reusability. Recoveries of species under study suffered from the presence of high amounts of water (losses up to 10%). However, only heavier volatiles, with molecular masses higher than 90, exhibited more pronounced losses (20–40%). The sample size (the degree of bag filling) was found to be one of the most important factors affecting the sample integrity. To sum up, it is recommended to store breath samples in pre-conditioned Tedlar bags up to 6 hours at the maximum possible filling volume. Among the remaining films, Kynar can be considered as an alternative to Tedlar; however, higher losses of compounds should be expected even within the first hours of storage. Due to the high background emission Flexfilm is not suitable for sampling and storage of samples for analyses aiming at volatiles at a low ppb level.
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Suitability of different polymer bags for storage of volatile sulphur compounds relevant to breath analysis
Journal of Chromatography B, 2008Co-Authors: Paweł Mochalski, Beata Wzorek, Ireneusz Śliwka, Anton AmannAbstract:Abstract Suitability of five polymer sampling containers (Nalophan, transparent Tedlar, black layered Tedlar, Teflon and FlexFoil) for sampling and storage of six relevant to breath analysis volatile sulphur compounds: H2S, MeSH, EtSH, COS, DMS and CS2 was studied using solid phase microextraction (SPME) and gas chromatography coupled with mass spectrometry (GC–MS). Investigations were made with respect to the several factors like: recovery, background, influence of light, ageing effect and matrix effects. Additionally, the optimal reusability conditions were established. Findings suggest analyzing the breath VSCs within 6 h after sampling. Flexfoil bags were found to be the best choice for the VSCs storage up to 24 h (recovery about 90% with the exception of DMS). For shorter storing times (6–8 h) transparent Tedlar is a good alternative for Flexfoil (losses up to 10%).
Jos?? Luis Cortina - One of the best experts on this subject based on the ideXlab platform.
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Analytical methodology for sampling and analysing eight siloxanes and trimethylsilanol in biogas from different wastewater treatment plants in Europe
Analytica Chimica Acta, 2014Co-Authors: J. Raich-montiu, C. Ribas-font, N. De Arespacochaga, E. Roig-torres, F. Broto-puig, Lynne Bouchy, Marion Crest, Jos?? Luis CortinaAbstract:Abstract Siloxanes and trimethylsilanol belong to a family of organic silicone compounds that are currently used extensively in industry. Those that are prone to volatilisation become minor compounds in biogas adversely affecting energetic applications. However, non-standard analytical methodologies are available to analyse biogas-based gaseous matrixes. To this end, different sampling techniques (adsorbent tubes, impingers and Tedlar bags) were compared using two different configurations: sampling directly from the biogas source or from a 200 L Tedlar bag filled with biogas and homogenised. No significant differences were apparent between the two sampling configurations. The adsorbent tubes performed better than the Tedlar bags and impingers, particularly for quantifying low concentrations. A method for the speciation of silicon compounds in biogas was developed using gas chromatography coupled with mass spectrometry working in dual scan/single ion monitoring mode. The optimised conditions could separate and quantify eight siloxane compounds (L 2 , L 3 , L 4 , L 5 , D 3 , D 4 , D 5 and D 6 ) and trimethylsilanol within fourteen minutes. Biogas from five waste water treatment plants located in Spain, France and England was sampled and analysed using the developed methodology. The siloxane concentrations in the biogas samples were influenced by the anaerobic digestion temperature, as well as the nature and composition of the sewage inlet. Siloxanes D 4 and D 5 were the most abundant, ranging in concentration from 1.5 to 10.1 and 10.8 to 124.0 mg Nm −3 , respectively, and exceeding the tolerance limit of most energy conversion systems.
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Analytical methodology for sampling and analysing eight siloxanes and trimethylsilanol in biogas from different wastewater treatment plants in europe
Analytica Chimica Acta, 2014Co-Authors: J. Raich-montiu, C. Ribas-font, N. De Arespacochaga, E. Roig-torres, F. Broto-puig, Lynne Bouchy, Marion Crest, Jos?? Luis CortinaAbstract:Siloxanes and trimethylsilanol belong to a family of organic silicone compounds that are currently used extensively in industry. Those that are prone to volatilisation become minor compounds in biogas adversely affecting energetic applications. However, non-standard analytical methodologies are available to analyse biogas-based gaseous matrixes. To this end, different sampling techniques (adsorbent tubes, impingers and Tedlar bags) were compared using two different configurations: sampling directly from the biogas source or from a 200L Tedlar bag filled with biogas and homogenised. No significant differences were apparent between the two sampling configurations. The adsorbent tubes performed better than the Tedlar bags and impingers, particularly for quantifying low concentrations. A method for the speciation of silicon compounds in biogas was developed using gas chromatography coupled with mass spectrometry working in dual scan/single ion monitoring mode. The optimised conditions could separate and quantify eight siloxane compounds (L2, L3, L4, L5, D3, D4, D5 and D6) and trimethylsilanol within fourteen minutes. Biogas from five waste water treatment plants located in Spain, France and England was sampled and analysed using the developed methodology. The siloxane concentrations in the biogas samples were influenced by the anaerobic digestion temperature, as well as the nature and composition of the sewage inlet. Siloxanes D4 and D5 were the most abundant, ranging in concentration from 1.5 to 10.1 and 10.8 to 124.0mgNm-3, respectively, and exceeding the tolerance limit of most energy conversion systems. © 2013 Elsevier B.V.
