The Experts below are selected from a list of 96 Experts worldwide ranked by ideXlab platform
Attakorn Asanakham - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of a single stage heat pump performance by figure of merit (FOM)
Energy Reports, 2020Co-Authors: Chan Oussa Suong, Attakorn AsanakhamAbstract:Abstract This paper proposes a quick method to investigate coefficient of performance (COP) of vapor compression heat pump from a Dimensionless Term, Figure of Merit (FOM), which covers refrigerant properties and operating temperatures as F O M = J a 0 . 1 . T c − T e v T c . Twelve pure refrigerants including low global warming and natural refrigerants were studied. It could be seen that FOM could be used to screen out the refrigerants those give high COP at the same operating temperature. Lower the FOM gave higher the COP. Two empirical correlations for heating and cooling applications were developed to predict the COP from the FOM. The results of the COPs from the model agreed very well with the available experimental data from the literatures of which the performance calculated from enthalpies of the working fluids.
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Performance analysis of low temperature organic Rankine cycle with zeotropic refrigerant by Figure of Merit (FOM)
Energy, 2016Co-Authors: Thoranis Deethayat, Attakorn Asanakham, Tanongkiat KiatsiriroatAbstract:This paper proposed a Dimensionless Term, the “Figure of Merit” (FOM), to investigate the thermal performance of a low temperature, organic Rankine cycle using six zeotropic mixtures (R245fa/R152a, R245fa/R227ea, R245fa/R236ea, R245ca/R152a, R245ca/R227ea and R245ca/R236ea) as working fluids. An empirical correlation was developed to estimate the cycle efficiency from the FOM for all working fluids at condensing temperatures of 25–40 °C and evaporating temperatures of 80–130 °C. The model results fit very well with both the experimental data and that from other researchers.
Piotr J. Franaszczuk - One of the best experts on this subject based on the ideXlab platform.
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Resonance Analysis as a Tool for Characterizing Functional Division of Layer 5 Pyramidal Neurons
Frontiers Media S.A., 2018Co-Authors: Melvin A. Felton, David L. Boothe, Kelvin S. Oie, Piotr J. FranaszczukAbstract:Evidence suggests that layer 5 pyramidal neurons can be divided into functional zones with unique afferent connectivity and membrane characteristics that allow for post-synaptic integration of feedforward and feedback inputs. To assess the existence of these zones and their interaction, we characterized the resonance properties of a biophysically-realistic compartmental model of a neocortical layer 5 pyramidal neuron. Consistent with recently published theoretical and empirical findings, our model was configured to have a “hot zone” in distal apical dendrite and apical tuft where both high- and low-threshold Ca2+ ionic conductances had densities 1–2 orders of magnitude higher than anywhere else in the apical dendrite. We simulated injection of broad spectrum sinusoidal currents with linearly increasing frequency to calculate the input impedance of individual compartments, the transfer impedance between the soma and key compartments within the dendritic tree, and a Dimensionless Term we introduce called resonance quality. We show that input resonance analysis distinguished at least four distinct zones within the model based on properties of their frequency preferences: basal dendrite which displayed little resonance; soma/proximal apical dendrite which displayed resonance at 5–23 Hz, strongest at 5–10 Hz and hyperpolarized/resting membrane potentials; distal apical dendrite which displayed resonance at 8–19 Hz, strongest at 10 Hz and depolarized membrane potentials; and apical tuft which displayed a weak resonance largely between 8 and 10 Hz across a wide range of membrane potentials. Transfer resonance analysis revealed that changes in subthreshold electrical coupling were found to modulate the transfer resonant frequency of signals transmitted from distal apical dendrite and apical tuft to the soma, which would impact the frequencies that individual neurons are expected to respond to and reinforce. Furthermore, eliminating the hot zone was found to reduce amplification of resonance within the model, which contributes to reduced excitability when perisomatic and distal apical regions receive coincident stimulating current injections. These results indicate that the interactions between different functional zones should be considered in a more complete understanding of neuronal integration. Resonance analysis may therefore be a useful tool for assessing the integration of inputs across the entire neuronal membrane
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Data_Sheet_2_Resonance Analysis as a Tool for Characterizing Functional Division of Layer 5 Pyramidal Neurons.XLSX
2018Co-Authors: Melvin A. Felton, David L. Boothe, Kelvin S. Oie, Piotr J. FranaszczukAbstract:Evidence suggests that layer 5 pyramidal neurons can be divided into functional zones with unique afferent connectivity and membrane characteristics that allow for post-synaptic integration of feedforward and feedback inputs. To assess the existence of these zones and their interaction, we characterized the resonance properties of a biophysically-realistic compartmental model of a neocortical layer 5 pyramidal neuron. Consistent with recently published theoretical and empirical findings, our model was configured to have a “hot zone” in distal apical dendrite and apical tuft where both high- and low-threshold Ca2+ ionic conductances had densities 1–2 orders of magnitude higher than anywhere else in the apical dendrite. We simulated injection of broad spectrum sinusoidal currents with linearly increasing frequency to calculate the input impedance of individual compartments, the transfer impedance between the soma and key compartments within the dendritic tree, and a Dimensionless Term we introduce called resonance quality. We show that input resonance analysis distinguished at least four distinct zones within the model based on properties of their frequency preferences: basal dendrite which displayed little resonance; soma/proximal apical dendrite which displayed resonance at 5–23 Hz, strongest at 5–10 Hz and hyperpolarized/resting membrane potentials; distal apical dendrite which displayed resonance at 8–19 Hz, strongest at 10 Hz and depolarized membrane potentials; and apical tuft which displayed a weak resonance largely between 8 and 10 Hz across a wide range of membrane potentials. Transfer resonance analysis revealed that changes in subthreshold electrical coupling were found to modulate the transfer resonant frequency of signals transmitted from distal apical dendrite and apical tuft to the soma, which would impact the frequencies that individual neurons are expected to respond to and reinforce. Furthermore, eliminating the hot zone was found to reduce amplification of resonance within the model, which contributes to reduced excitability when perisomatic and distal apical regions receive coincident stimulating current injections. These results indicate that the interactions between different functional zones should be considered in a more complete understanding of neuronal integration. Resonance analysis may therefore be a useful tool for assessing the integration of inputs across the entire neuronal membrane.
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Data_Sheet_1_Resonance Analysis as a Tool for Characterizing Functional Division of Layer 5 Pyramidal Neurons.DOCX
2018Co-Authors: Melvin A. Felton, David L. Boothe, Kelvin S. Oie, Piotr J. FranaszczukAbstract:Evidence suggests that layer 5 pyramidal neurons can be divided into functional zones with unique afferent connectivity and membrane characteristics that allow for post-synaptic integration of feedforward and feedback inputs. To assess the existence of these zones and their interaction, we characterized the resonance properties of a biophysically-realistic compartmental model of a neocortical layer 5 pyramidal neuron. Consistent with recently published theoretical and empirical findings, our model was configured to have a “hot zone” in distal apical dendrite and apical tuft where both high- and low-threshold Ca2+ ionic conductances had densities 1–2 orders of magnitude higher than anywhere else in the apical dendrite. We simulated injection of broad spectrum sinusoidal currents with linearly increasing frequency to calculate the input impedance of individual compartments, the transfer impedance between the soma and key compartments within the dendritic tree, and a Dimensionless Term we introduce called resonance quality. We show that input resonance analysis distinguished at least four distinct zones within the model based on properties of their frequency preferences: basal dendrite which displayed little resonance; soma/proximal apical dendrite which displayed resonance at 5–23 Hz, strongest at 5–10 Hz and hyperpolarized/resting membrane potentials; distal apical dendrite which displayed resonance at 8–19 Hz, strongest at 10 Hz and depolarized membrane potentials; and apical tuft which displayed a weak resonance largely between 8 and 10 Hz across a wide range of membrane potentials. Transfer resonance analysis revealed that changes in subthreshold electrical coupling were found to modulate the transfer resonant frequency of signals transmitted from distal apical dendrite and apical tuft to the soma, which would impact the frequencies that individual neurons are expected to respond to and reinforce. Furthermore, eliminating the hot zone was found to reduce amplification of resonance within the model, which contributes to reduced excitability when perisomatic and distal apical regions receive coincident stimulating current injections. These results indicate that the interactions between different functional zones should be considered in a more complete understanding of neuronal integration. Resonance analysis may therefore be a useful tool for assessing the integration of inputs across the entire neuronal membrane.
Chan Oussa Suong - One of the best experts on this subject based on the ideXlab platform.
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Evaluation of a single stage heat pump performance by figure of merit (FOM)
Energy Reports, 2020Co-Authors: Chan Oussa Suong, Attakorn AsanakhamAbstract:Abstract This paper proposes a quick method to investigate coefficient of performance (COP) of vapor compression heat pump from a Dimensionless Term, Figure of Merit (FOM), which covers refrigerant properties and operating temperatures as F O M = J a 0 . 1 . T c − T e v T c . Twelve pure refrigerants including low global warming and natural refrigerants were studied. It could be seen that FOM could be used to screen out the refrigerants those give high COP at the same operating temperature. Lower the FOM gave higher the COP. Two empirical correlations for heating and cooling applications were developed to predict the COP from the FOM. The results of the COPs from the model agreed very well with the available experimental data from the literatures of which the performance calculated from enthalpies of the working fluids.
Harold Dean Brannon - One of the best experts on this subject based on the ideXlab platform.
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Hydraulic Fracturing Treatment Design Considerations for Effective Proppant Pillar Construction
Day 1 Mon September 26 2016, 2016Co-Authors: Ahmed M. Gomaa, Scott G. Nelson, Harold Gene Hudson, Harold Dean BrannonAbstract:Abstract As an alternative to conventional proppant pack placement, propped pillar-fracturing promises more effective and conductive fractures that enable hydrocarbons to flow through open channels. Recent experimental and numerical studies confirmed that viscous fingering phenomena can be used to develop a proppant pillar-fracture type placement: High-viscosity, proppant-laden fluid can be placed, and then a low-viscosity clean fluid is pumped to carve pathways through the proppant-laden fluid in a dynamic, continuous process. However, the created channel pattern was found to be significantly dependent on fracture geometry and treatment design parameters such as injection rate, fluid pulsing time, and fluid viscosity ratio. The objective of this study is to extend the numerical investigation and normalize it to develop a treatment design methodology for constructing proppant pillars throughout the created fracture. A computational fluid dynamics (CFD) model was constructed using commercial CFD software, simulating the flow of fluids inside the fracture and the resulting proppant pillar generation. The study focused on the effects of surface injection rate (1 to 40 bpm/cluster), pulsing time (5 sec to 5 min), and viscosity ratio (from 2 to 20) between the two injected fluids to develop correlations between these parameters and the created fracture geometry. Based on numerical results, the viscosity ratio chosen to achieve the proppant pillars allows the use of conventional crosslinked fluid without a hindered settling agent. In these designs the settling of proppant into pillars can be made to occur after the end of the stimulation treatment. Controlled settling of proppant from a crosslinked proppant-laden slurry allows channel formation and creates wider propped fracture-width pillars as compared to current industry pillar-fracturing treatment techniques. The optimum channel pattern has small channel sizes, remains open under closure stress, creates more channels throughout the entire fracture area and maintains good communication between unpropped areas. A new Dimensionless Term, Dimensionless Stage Volume (VSD), is presented to describe the channel pattern inside the fracture. Smaller VSD numbers resulted in smaller and more distributed channels. Therefore, it is highly recommended to select and design a proppant pillar-fracture treatment to achieve the lowest VSD possible and create the optimal channel pattern.
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Treatment Design Considerations for Effective Proppant Pillar Construction
Day 1 Wed August 24 2016, 2016Co-Authors: Scott G. Nelson, Ahmed M. Gomaa, Harold Gene Hudson, Harold Dean BrannonAbstract:Abstract As an alternative to conventional proppant pack placement, propped pillar-fracturing promises more effective and conductive fractures by enabling hydrocarbons to flow through open channels. Recent experimental and numerical studies confirmed that viscous fingering phenomena can be used to develop a proppant pillar-fracture type placement: High-viscosity, proppant-laden fluid is placed, and then a low-viscosity clean fluid is pumped to carve pathways through the proppant-laden fluid in a dynamic, continuous process. However, the created channel pattern was found to be significantly dependent on fracture geometry and treatment design parameters such as injection rate, fluid pulsing time, and fluid viscosity ratio. The objective of this study is to extend the numerical investigation and normalize it to develop a treatment design methodology for constructing proppant pillars throughout the created fracture. A computational fluid dynamics (CFD) model was constructed using commercial CFD software, simulating the flow of fluids inside the fracture and the resulting proppant pillar generation. The study focused on the effects of surface injection rate, pulsing time, and viscosity ratio between the two injected fluids, to develop correlations between all these parameters and the created fracture geometry. Based on numerical results, the viscosity ratio chosen to achieve the proppant pillars allows for the use of conventional crosslinked fluid without the need for a hindered settling agent. The optimum channel pattern has small channel sizes, remains open under closure stress, creates more channels distributed throughout the entire fracture area, and maintains good communication between unpropped areas. A new Dimensionless Term, Dimensionless Stage Volume (VSD), is presented to describe the channel pattern inside the fracture. The settling of proppant occurs after the pumping of the job has ended, and prior to fracture closure, yielding wider pillar widths compared to current pillar-fracturing treatment techniques. A combination of conventional proppant and ultra-lightweight proppant can be continuously pumped as part of the treatment schedule. The application of lightweight buoyant proppant positioned within the created channels supports and braces against possible fracture closure between proppant pillars.
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Improving Fracture Conductivity by Developing and Optimizing Channels within the Fracture Geometry: CFD Study
Day 2 Thu February 25 2016, 2016Co-Authors: Ahmed M. Gomaa, Scott G. Nelson, Harold Gene Hudson, Harold Dean BrannonAbstract:Abstract A conventional proppant pack can lose up to 99% of its conductivity due to gel damage, fines migration, multiphase flow, and non-Darcy flow. Consequently, pillar fracturing was developed to generate highly conductive paths for hydrocarbon flow. This paper describes experimental results and numerical models of a new method of generating stable proppant pillars. The proposed treatment method depends on fingering phenomena observed when a less-viscous fluid, which does not carry proppant, is injected to displace a more-viscous fluid that carries proppant. The low-viscosity fluid channels through the high-viscosity fluid and creates isolated proppant pillars. This method promises to reduce proppant costs, pumping horsepower, and gel damage, when compared to conventional treatments. A computational fluid dynamics (CFD) model using commercial CFD software was constructed to simulate the fluid flow inside a full-scale fracture dimensions. The objective of this study was to further evaluate the treatment design parameters during the generation of stable pillar-propped fractures. This study focused on gravity effects on the created channels' characteristics. The study also performed detailed investigation of the channel pattern as a function of treatment design (injection rate (1 to 120 bpm), and pulse stage time (5 seconds to 5 minutes), viscosity ratio (2 to 200)), and fracture geometry (width and height). Finally, horizontal proppant covering efficiency was calculated. Numerical modeling results confirmed that the gravity effect can be minimized either by increasing the injected fluid viscosity or by increasing the fluid injection rate. A strong linear relation was found between the minimum required viscosity to eliminate gravity effect and the density ratio between the two injected fluids. As an example, for a fracture width of 0.2 in. and injection rate of 4 bpm, the minimum viscosity needed to eliminate the gravity effect was 50 cP, 150 cP and 300 cP for density ratios (ρR) of 1.05, 1.25 and 1.5, respectively. The optimum channel pattern has small channel sizes, remain opened under closure stress, more channels throughout the entire fracture area and good communication between unpropped areas. Increasing fracture height or width during injection shifted the created channel pattern toward an optimum shape. Reducing the injection rate and/or stage pulse time moved the created channel pattern toward an optimum shape. A new Dimensionless Term, Dimensionless Stage Volume (VSD), is presented to describe the channel pattern inside the fracture. Smaller the VSD number resulted in the smaller and more distributed channels. Therefore, it is highly recommended to select and design a proppant pillar fracture treatment to achieve the lowest VSD possible and create the optimal channel pattern. For each viscosity ratio, the horizontal proppant coverage efficiency was independent of the VSD. However, a power-law relationship was defined between the horizontal proppant coverage efficiency and viscosity ratio between the two injected fluids. Finally, data and results obtained in this paper can be used as guideline to design, develop and optimize the channel fracturing treatment.
Jozsef Rabai - One of the best experts on this subject based on the ideXlab platform.
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an improved design of fluorophilic molecules prediction of the ln p fluorous partition coefficient fluorophilicity using 3d qsar descriptors and neural networks
Journal of Fluorine Chemistry, 2001Co-Authors: Laszlo Kiss, Istvan Kovesdi, Jozsef RabaiAbstract:Abstract A combination of 3D QSAR molecular descriptors and artificial neural networks have been used to predict fluorophilicities, the natural logarithm of the perfluoro(methylcyclohexane)/toluene partition coefficients, for a wide range of partially fluorinated organic compounds. The average error of the predictions was less than twice the 0.2 experimental error. Multiple linear regression proved to be much less efficient. To better characterise the fluorous partition phenomenon, specific fluorophilicity was defined as the product of fluorophilicity and of the ratio of the van der Waals volumes of the expelled fluorous solvent and the entering solute molecules. This Dimensionless Term correlates well in a compound family with the calculated Hildebrand parameters of the fluorous molecules. The trifluoromethyl group was found highly effective for increasing the fluorous phase affinities of model compounds when used in combination with longer perfluoroalkyl groups.