Pub Date : 2001-11-11DOI: 10.1115/imece2001/htd-24272
M. Mench, Z. H. Wang, K. Bhatia, C. Wang
Recently, there has been increased interest in the development of a small-sized direct methanol fuel cell (DMFC) for low-power applications. In this paper, the design of a self-activated DMFC stack is presented. Gravitational and capillary forces feed the anode side liquid methanol solution. On the cathode side, air is supplied by thermal and solutal buoyancy forces. Based upon experimental results for a larger test cell, and calculated flow velocities for the small-cell design, the fuel and oxidizer supply rates should be adequate for acceptable performance. The entire DMFC is therefore a pump-less operation and self-activated by electrochemical reactions. At 1 cm3 total volume, the DMFC is expected to provide a power density around 1 W/cm3, with a range of output of 10V, 0.1A to 1 V, 1A depending on the arrangement of individual cell connections.
{"title":"Design of a Micro Direct Methanol Fuel Cell (μDMFC)","authors":"M. Mench, Z. H. Wang, K. Bhatia, C. Wang","doi":"10.1115/imece2001/htd-24272","DOIUrl":"https://doi.org/10.1115/imece2001/htd-24272","url":null,"abstract":"\u0000 Recently, there has been increased interest in the development of a small-sized direct methanol fuel cell (DMFC) for low-power applications. In this paper, the design of a self-activated DMFC stack is presented. Gravitational and capillary forces feed the anode side liquid methanol solution. On the cathode side, air is supplied by thermal and solutal buoyancy forces. Based upon experimental results for a larger test cell, and calculated flow velocities for the small-cell design, the fuel and oxidizer supply rates should be adequate for acceptable performance. The entire DMFC is therefore a pump-less operation and self-activated by electrochemical reactions. At 1 cm3 total volume, the DMFC is expected to provide a power density around 1 W/cm3, with a range of output of 10V, 0.1A to 1 V, 1A depending on the arrangement of individual cell connections.","PeriodicalId":426926,"journal":{"name":"Heat Transfer: Volume 4 — Combustion and Energy Systems","volume":"492 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132019104","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-11-11DOI: 10.1115/imece2001/htd-24239
L. Oravecz-Simpkins, I. Wichman
A Hele-Shaw apparatus that produced spreading diffusion flames in the near extinction limit was designed and constructed. A scaling analysis was used to determine the maximum test section height for which effects of gravity could be neglected. Preliminary results showed that this apparatus could be used to produce flame instabilities which resemble drop tower test results from NASA [1,2] and other diffusion flame instability studies [3,4,5,6]. Therefore, the Hele-Shaw apparatus is useful for studying flames in a simulated low gravity environment. Additional unstable behaviors seen in the device, such as flame pulsing and spreading blue cusps, not in the NASA testing further supported the need for investigations during longer microgravity times on the International Space Station. The initial testing was only used to gain an observable region of unstable flames. Further studies will be directed at explaining and quantifying specific behaviors with test conditions.
{"title":"Production of Diffusion Flames in the Near Extinction Limit Regime Using a Hele-Shaw Apparatus in a Simulated Low Gravity Environment","authors":"L. Oravecz-Simpkins, I. Wichman","doi":"10.1115/imece2001/htd-24239","DOIUrl":"https://doi.org/10.1115/imece2001/htd-24239","url":null,"abstract":"\u0000 A Hele-Shaw apparatus that produced spreading diffusion flames in the near extinction limit was designed and constructed. A scaling analysis was used to determine the maximum test section height for which effects of gravity could be neglected. Preliminary results showed that this apparatus could be used to produce flame instabilities which resemble drop tower test results from NASA [1,2] and other diffusion flame instability studies [3,4,5,6]. Therefore, the Hele-Shaw apparatus is useful for studying flames in a simulated low gravity environment. Additional unstable behaviors seen in the device, such as flame pulsing and spreading blue cusps, not in the NASA testing further supported the need for investigations during longer microgravity times on the International Space Station. The initial testing was only used to gain an observable region of unstable flames. Further studies will be directed at explaining and quantifying specific behaviors with test conditions.","PeriodicalId":426926,"journal":{"name":"Heat Transfer: Volume 4 — Combustion and Energy Systems","volume":"2 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"132744810","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-11-11DOI: 10.1115/imece2001/htd-24232
A. Nieckele, M. Naccache, Marcos S. P. Gomes, J. Carneiro, R. Serfaty
In this work an evaluation of different combustion models for predicting oxygen enriched combustion processes was performed. Two types of models were selected. The first one was a generalized finite rate model, in which the conservation equation for the mass concentration was solved, for all species present in the process. In this modeling approach, three different reaction rate expressions were considered. The second case was based on the PDF formulation, which consisted in solving the conservation equations for the mass fraction and its variance. In this second approach the species distributions were determined by assuming two different shapes for the probability density functions. The mass, momentum, energy and species or mass fraction conservation equations were numerically solved by a finite volume formulation. The two-equation κ-ε turbulence model was selected for solving the turbulent problem. Radiation was taken into account by the discrete transfer radiation model. After solution, the temperature and species concentration fields were compared with available experimental data. Although the PDF formulation involved the solution of a smaller number of equations, therefore consuming less computer time, the performance of the generalized finite rate model was superior in the present test cases.
{"title":"Models Evaluations of Combustion Process in a Cylindrical Furnace","authors":"A. Nieckele, M. Naccache, Marcos S. P. Gomes, J. Carneiro, R. Serfaty","doi":"10.1115/imece2001/htd-24232","DOIUrl":"https://doi.org/10.1115/imece2001/htd-24232","url":null,"abstract":"\u0000 In this work an evaluation of different combustion models for predicting oxygen enriched combustion processes was performed. Two types of models were selected. The first one was a generalized finite rate model, in which the conservation equation for the mass concentration was solved, for all species present in the process. In this modeling approach, three different reaction rate expressions were considered. The second case was based on the PDF formulation, which consisted in solving the conservation equations for the mass fraction and its variance. In this second approach the species distributions were determined by assuming two different shapes for the probability density functions. The mass, momentum, energy and species or mass fraction conservation equations were numerically solved by a finite volume formulation. The two-equation κ-ε turbulence model was selected for solving the turbulent problem. Radiation was taken into account by the discrete transfer radiation model. After solution, the temperature and species concentration fields were compared with available experimental data. Although the PDF formulation involved the solution of a smaller number of equations, therefore consuming less computer time, the performance of the generalized finite rate model was superior in the present test cases.","PeriodicalId":426926,"journal":{"name":"Heat Transfer: Volume 4 — Combustion and Energy Systems","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"129398620","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-11-11DOI: 10.1115/imece2001/htd-24278
K. Ng, JinBao Wang, H. Xue
To develop effective heat exchangers for miniature and micro Joule-Thomson (J-T) cooling system, the performance of a recuperative heat exchanger is analyzed and evaluated. The evaluation is based on a theoretical model of the Hampson-type counter-flow heat exchanger. The effect of the pressure and temperature-dependent properties and longitudinal heat conduction are considered. The results of the numerical simulation are validated with the corresponding experimental measurements. The performance of the heat exchanger on effectiveness, flow and various heat conduction losses as well as liquefied yield fraction are analyzed and discussed. The simulation model provides a useful tool for miniature J-T cooler design.
{"title":"Modeling of Recuperative Heat Exchanger in a Joule-Thomson Cooler","authors":"K. Ng, JinBao Wang, H. Xue","doi":"10.1115/imece2001/htd-24278","DOIUrl":"https://doi.org/10.1115/imece2001/htd-24278","url":null,"abstract":"\u0000 To develop effective heat exchangers for miniature and micro Joule-Thomson (J-T) cooling system, the performance of a recuperative heat exchanger is analyzed and evaluated. The evaluation is based on a theoretical model of the Hampson-type counter-flow heat exchanger. The effect of the pressure and temperature-dependent properties and longitudinal heat conduction are considered. The results of the numerical simulation are validated with the corresponding experimental measurements. The performance of the heat exchanger on effectiveness, flow and various heat conduction losses as well as liquefied yield fraction are analyzed and discussed. The simulation model provides a useful tool for miniature J-T cooler design.","PeriodicalId":426926,"journal":{"name":"Heat Transfer: Volume 4 — Combustion and Energy Systems","volume":"20 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127996398","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-11-11DOI: 10.1115/imece2001/htd-24248
S. Kearney
Infrared radiation spectra from a 1-m diameter, JP-8-fueled, liquid pool fire in nominally quiescent surroundings have been acquired using a novel IR spectrometer. Data were acquired at a rate of 390 spectra/sec allowing for a time-resolved description of the radiation from the fully turbulent fire plume. Results are discussed in terms of an effective homogeneous pathlength and both gray and nongray spectral models, of which the gray model surprisingly fits the data in the soot-dominated regions of the spectrum more effectively. The results from the gray model are used to provide statistical descriptions of the heat transfer from the fire plume in terms of probability density functions (PDFs) of the effective fire temperature and emissivity.
{"title":"Temporally Resolved Radiation Spectra From a Sooting, Turbulent Pool Fire","authors":"S. Kearney","doi":"10.1115/imece2001/htd-24248","DOIUrl":"https://doi.org/10.1115/imece2001/htd-24248","url":null,"abstract":"\u0000 Infrared radiation spectra from a 1-m diameter, JP-8-fueled, liquid pool fire in nominally quiescent surroundings have been acquired using a novel IR spectrometer. Data were acquired at a rate of 390 spectra/sec allowing for a time-resolved description of the radiation from the fully turbulent fire plume. Results are discussed in terms of an effective homogeneous pathlength and both gray and nongray spectral models, of which the gray model surprisingly fits the data in the soot-dominated regions of the spectrum more effectively. The results from the gray model are used to provide statistical descriptions of the heat transfer from the fire plume in terms of probability density functions (PDFs) of the effective fire temperature and emissivity.","PeriodicalId":426926,"journal":{"name":"Heat Transfer: Volume 4 — Combustion and Energy Systems","volume":"18 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127337164","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The effect of inverter ripple current on fuel cell stack performance and stack lifetime remains uncertain. This paper provides a first attempt to examine the impact of inverter load dynamics on the fuel cell. Since reactant utilization is known to impact the mechanical state of a fuel cell, it is suggested that the varying reactant conditions surrounding the cell govern, at least in part, the lifetime of the cells. This paper investigates these conditions through the use of a dynamic model for the bulk conditions within the stack, as well as a one-dimensional model for the detailed mass transport occurring within the electrode of a cell. These two independent modeling approaches help to verify their respective numerical procedures. In this work, the inverter load is imposed as a boundary condition to the models. Results show the transient behavior of the reactant concentrations within the stack, and of the mass diffusion within the electrode under inverter loads with frequencies between 30 Hz and 1250 Hz.
{"title":"Analysis for the Effect of Inverter Ripple Current on Fuel Cell Operating Condition","authors":"R. Gemmen","doi":"10.1115/1.1567307","DOIUrl":"https://doi.org/10.1115/1.1567307","url":null,"abstract":"\u0000 The effect of inverter ripple current on fuel cell stack performance and stack lifetime remains uncertain. This paper provides a first attempt to examine the impact of inverter load dynamics on the fuel cell. Since reactant utilization is known to impact the mechanical state of a fuel cell, it is suggested that the varying reactant conditions surrounding the cell govern, at least in part, the lifetime of the cells. This paper investigates these conditions through the use of a dynamic model for the bulk conditions within the stack, as well as a one-dimensional model for the detailed mass transport occurring within the electrode of a cell. These two independent modeling approaches help to verify their respective numerical procedures. In this work, the inverter load is imposed as a boundary condition to the models. Results show the transient behavior of the reactant concentrations within the stack, and of the mass diffusion within the electrode under inverter loads with frequencies between 30 Hz and 1250 Hz.","PeriodicalId":426926,"journal":{"name":"Heat Transfer: Volume 4 — Combustion and Energy Systems","volume":"4 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"121886831","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Understanding of heat transfer in glass foams and the development of theoretical tools for predicting heat transfer properties of glass foams is critical to improving the efficiency of glass manufacturing. In this paper, combined radiation and conduction heat transfer in a semitransparent glass foam layer is analyzed. The foam layer is bounded by hot combustion gases on top and glass melt on bottom. Heat transfer is assumed to be one-dimensional perpendicular to the plane-parallel foam layer. A previously developed model is used to calculate effective extinction coefficients and scattering phase function of the foam layer using a void size distribution and assuming all voids to be spherical. These radiation properties are then used along with a Schuster-Schwarzchild two flux approximation to solve the radiative transfer equation (RTE). A method for obtaining the effective thermal conductivity of the foam layer is also presented. The RTE and the energy conservation equations are simultaneously solved using a numerical iteration procedure. The effect of foam thickness and bubble size on the temperature distribution in the foam layer is studied.
{"title":"Combined Radiation and Conduction in Glass Foams","authors":"M. J. Varady, A. Fedorov","doi":"10.1115/1.1513579","DOIUrl":"https://doi.org/10.1115/1.1513579","url":null,"abstract":"\u0000 Understanding of heat transfer in glass foams and the development of theoretical tools for predicting heat transfer properties of glass foams is critical to improving the efficiency of glass manufacturing. In this paper, combined radiation and conduction heat transfer in a semitransparent glass foam layer is analyzed. The foam layer is bounded by hot combustion gases on top and glass melt on bottom. Heat transfer is assumed to be one-dimensional perpendicular to the plane-parallel foam layer. A previously developed model is used to calculate effective extinction coefficients and scattering phase function of the foam layer using a void size distribution and assuming all voids to be spherical. These radiation properties are then used along with a Schuster-Schwarzchild two flux approximation to solve the radiative transfer equation (RTE). A method for obtaining the effective thermal conductivity of the foam layer is also presented. The RTE and the energy conservation equations are simultaneously solved using a numerical iteration procedure. The effect of foam thickness and bubble size on the temperature distribution in the foam layer is studied.","PeriodicalId":426926,"journal":{"name":"Heat Transfer: Volume 4 — Combustion and Energy Systems","volume":"15 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"127403383","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-11-11DOI: 10.1115/imece2001/htd-24257
Matt O’ Donnell, S. Acharya
This work summarizes efforts to determine the accuracy and performance characteristics of a new and novel laser diagnostic to measure instantaneous, in flight, droplet temperatures. The instrument uses the location of the rainbow peak to deduce the refractive index of the droplet, which in turn is related to the droplet temperature. Preliminary experiments were undertaken in order to understand the fundamental operating principles and limitations of the instrument. These experiments measured the temperature of an isothermal, single stream of monodisperse droplets. These measurements indicate that the mean refractive index can be measured with a standard deviation as low as 0.0001m. Once the operation of the refractometer was proved under isothermal conditions, the measurement of droplet temperatures in a swirl-stabilized combustor was performed. These measurements indicate that the strength of the rainbow signal is significantly hampered by the noise induced by the flame. Preliminary temperature measurements with the combustor equipped with 45° vanes showed relatively constant radial temperature profiles (∼55–60°C) at locations less than 2 inches from the nozzle exit. A detailed examination of the temperature correlation with velocity and diameter revealed that larger and faster moving droplets dominate the distributions. Thus, the smaller droplets that are suspected of having the highest temperatures are inadequately represented in the mean droplet temperature.
{"title":"Simultaneous Measurements of Droplet Size, Temperature, and Velocity Using an Integrated Phase-Doppler/Rainbow Thermometer","authors":"Matt O’ Donnell, S. Acharya","doi":"10.1115/imece2001/htd-24257","DOIUrl":"https://doi.org/10.1115/imece2001/htd-24257","url":null,"abstract":"\u0000 This work summarizes efforts to determine the accuracy and performance characteristics of a new and novel laser diagnostic to measure instantaneous, in flight, droplet temperatures. The instrument uses the location of the rainbow peak to deduce the refractive index of the droplet, which in turn is related to the droplet temperature. Preliminary experiments were undertaken in order to understand the fundamental operating principles and limitations of the instrument. These experiments measured the temperature of an isothermal, single stream of monodisperse droplets. These measurements indicate that the mean refractive index can be measured with a standard deviation as low as 0.0001m.\u0000 Once the operation of the refractometer was proved under isothermal conditions, the measurement of droplet temperatures in a swirl-stabilized combustor was performed. These measurements indicate that the strength of the rainbow signal is significantly hampered by the noise induced by the flame. Preliminary temperature measurements with the combustor equipped with 45° vanes showed relatively constant radial temperature profiles (∼55–60°C) at locations less than 2 inches from the nozzle exit. A detailed examination of the temperature correlation with velocity and diameter revealed that larger and faster moving droplets dominate the distributions. Thus, the smaller droplets that are suspected of having the highest temperatures are inadequately represented in the mean droplet temperature.","PeriodicalId":426926,"journal":{"name":"Heat Transfer: Volume 4 — Combustion and Energy Systems","volume":"95 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"131876673","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-11-11DOI: 10.1115/imece2001/htd-24258
S. Torii, S. Chan, T. Yano
The present study deals with the augmentation of the turbulent shear effect on transport in turbulent jet diffusion flames due to the presence of air-suction flow and the possibility of extending the flame blow-off limits through augmentation. The experimental apparatus employed here comprises a fuel nozzle placed at the center of a concentric annulus with an outer cylinder encompassing the nozzle. The fuel jet is allowed to eject upwards and turbulent jet diffusion flames are formed by igniting the jet, then by increasing the volume flow rate of the fuel. The annular counterflow technique was employed to augment the turbulent shear effect. It is found that (1) the augmentation of turbulent shear effect exerted on the shear layer formed between the jet flames and the opposed flow of air causes an increase in temperature of the cold fuel gas at the flame center and an extension of flame blowoff limits; (2) flame lift-off heights are suppressed; (3) the lift-off propensity of the diffusion flame is alleviated by such augmentation.
{"title":"Transport in Turbulent Jet Diffusion Flames With Annular Counterflow","authors":"S. Torii, S. Chan, T. Yano","doi":"10.1115/imece2001/htd-24258","DOIUrl":"https://doi.org/10.1115/imece2001/htd-24258","url":null,"abstract":"\u0000 The present study deals with the augmentation of the turbulent shear effect on transport in turbulent jet diffusion flames due to the presence of air-suction flow and the possibility of extending the flame blow-off limits through augmentation. The experimental apparatus employed here comprises a fuel nozzle placed at the center of a concentric annulus with an outer cylinder encompassing the nozzle. The fuel jet is allowed to eject upwards and turbulent jet diffusion flames are formed by igniting the jet, then by increasing the volume flow rate of the fuel. The annular counterflow technique was employed to augment the turbulent shear effect. It is found that (1) the augmentation of turbulent shear effect exerted on the shear layer formed between the jet flames and the opposed flow of air causes an increase in temperature of the cold fuel gas at the flame center and an extension of flame blowoff limits; (2) flame lift-off heights are suppressed; (3) the lift-off propensity of the diffusion flame is alleviated by such augmentation.","PeriodicalId":426926,"journal":{"name":"Heat Transfer: Volume 4 — Combustion and Energy Systems","volume":"31 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"133098471","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2001-11-11DOI: 10.1115/imece2001/htd-24260
V. Travkin, I. Catton
Conventional reasoning and established procedures for measurement of heat and charge conductivities at the continuum micrometer scale, or higher scales, results in a number of variables and physical entities being the subject of measurement. These variables themselves are not point values if to define them with the lower scale concepts. When the media overall properties are sought, their dependence on lower (smaller) scale physical phenomena and their mathematical descriptions need to be considered and incorporated into the higher (larger) scale description and mathematical modeling. This is not a new problem. How to treat or solve multi-scale problems is the issue. Effective scaled heat and charge conductivity are studied for a morphologically simple 1D layered heterostructure with the number of components being n ≥ 2, the effective scaled heat and charge conductivities. It is a two-scale media with the lower scale physics of energy and charge carriers being described by commonly used models. A continuum ↔ continuum description of ηm ↔ μm transport of electron-phonon energy fields, as well as the electromagnetic and temperature fields for ηm scale coupled with the microscale (μm) mathematical models are studied. The medium is heterogeneous because it has multiple phases, volumetric phases 1, 2, 3 .... and (n+m) phases that are the interfaces between volumetric phases. The fundamental peculiarities of interface transport and hierarchical mathematical coupling bring together issues that have never actually been addressed correctly. It is shown that accurate accounting for scale interactions and, as is inevitable in scaled problems, application of fundamental theorems to a scaled description of the Laplace and ▽ operators bring to the upper scales completely different mathematical governing equations and models. We have conducted and report some preliminary quantitative assessment of the differences between the static upper scale and transient nanoscale transport coefficients and show how the lattice morphology and its irregularities influence the effective conductivities.
{"title":"Heat and Charge Conductivities in Superlattices: Two-Scale Measuring and Modeling","authors":"V. Travkin, I. Catton","doi":"10.1115/imece2001/htd-24260","DOIUrl":"https://doi.org/10.1115/imece2001/htd-24260","url":null,"abstract":"\u0000 Conventional reasoning and established procedures for measurement of heat and charge conductivities at the continuum micrometer scale, or higher scales, results in a number of variables and physical entities being the subject of measurement. These variables themselves are not point values if to define them with the lower scale concepts. When the media overall properties are sought, their dependence on lower (smaller) scale physical phenomena and their mathematical descriptions need to be considered and incorporated into the higher (larger) scale description and mathematical modeling. This is not a new problem. How to treat or solve multi-scale problems is the issue. Effective scaled heat and charge conductivity are studied for a morphologically simple 1D layered heterostructure with the number of components being n ≥ 2, the effective scaled heat and charge conductivities. It is a two-scale media with the lower scale physics of energy and charge carriers being described by commonly used models. A continuum ↔ continuum description of ηm ↔ μm transport of electron-phonon energy fields, as well as the electromagnetic and temperature fields for ηm scale coupled with the microscale (μm) mathematical models are studied. The medium is heterogeneous because it has multiple phases, volumetric phases 1, 2, 3 .... and (n+m) phases that are the interfaces between volumetric phases. The fundamental peculiarities of interface transport and hierarchical mathematical coupling bring together issues that have never actually been addressed correctly. It is shown that accurate accounting for scale interactions and, as is inevitable in scaled problems, application of fundamental theorems to a scaled description of the Laplace and ▽ operators bring to the upper scales completely different mathematical governing equations and models. We have conducted and report some preliminary quantitative assessment of the differences between the static upper scale and transient nanoscale transport coefficients and show how the lattice morphology and its irregularities influence the effective conductivities.","PeriodicalId":426926,"journal":{"name":"Heat Transfer: Volume 4 — Combustion and Energy Systems","volume":"51 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2001-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"122855509","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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