The Experts below are selected from a list of 255 Experts worldwide ranked by ideXlab platform
K. C. Sood - One of the best experts on this subject based on the ideXlab platform.
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Dispersive effects and Correction Term in two-mode phonon conduction model for Ge
Journal of Physics and Chemistry of Solids, 2003Co-Authors: B.k. Singh, V. J. Menon, K. C. SoodAbstract:Abstract A complete analysis of the phonon conductivity κ , still lacking in the literature, is presented in the two-mode conduction model for Germanium. First a method is derived from which the Correction Term κ c of the Callaway model is separated into its longitudinal and transverse parts and then the effects of strong phonon dispersion and the role of longitudinal and transverse phonons on κ c are studied. For this purpose we have also proposed some new empirical expressions for the three phonon relaxation rates τ 3ph −1 's which are valid in the entire temperature range. This improvised model, when applied simultaneously to the phonon conductivity data of both normal and enriched Ge, yields some new results. These are (i) κ c neglected by the earlier workers in the two-mode phonon conduction model, gives a substantial contribution beyond the conductivity maximum and (ii) the longitudinal phonons are the major carriers of heat at high temperature.
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Effects of dispersion, Correction Term, and isotopes on the thermal conductivity of LiF crystal
Physical Review B, 2003Co-Authors: B.k. Singh, V. J. Menon, K. C. SoodAbstract:We have adapted the Callaway-Holland model so that the dispersive effect and Correction Term ${\ensuremath{\kappa}}_{c}$ can be included in the theoretical analysis of the lattice thermal conductivity of LiF over the temperature range 1\char21{}300 K, for varying concentration of the isotopic content ${}^{7}\mathrm{Li}.$ Some different empirical expressions for different three-phonon relaxation rates ${\ensuremath{\tau}}_{3\mathrm{ph}}^{\ensuremath{-}1}$ for the entire temperature range have been proposed. Anisotropic and dispersive point defect scattering relaxation rate for LiF is also introduced. Our main findings are as follows: ${\ensuremath{\kappa}}_{c}$ even for moderate isotopic concentration of ${}^{7}\mathrm{Li}$ in LiF gives sizable contribution at temperatures where ${\ensuremath{\tau}}_{3\mathrm{ph}}^{\ensuremath{-}1}$ umklapp U processes dominate, which was considered to be negligible by earlier workers; contribution of longitudinal phonons is substantial beyond the conductivity maximum; theoretical value of the isotope scattering parameter ${A}_{1}$ has to be increased only by 1.8\char21{}1.9 times in going from 50.8% to 97.2% of ${}^{7}\mathrm{Li}$ content as against 5 times increase taken by Callaway and Baeyer; and in conformity with Callaway's findings the presence of small chemical impurities has to be assumed to explain the phonon-conductivity data of the isotopically pure sample ${(}^{7}\mathrm{Li}99.99%)$ of LiF. Theoretically justified parameters are used to obtain excellent agreement with the results reported by Thacher as well as by Berman and Brock.
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Correction Term in total phonon conductivity
Indian Journal of Pure & Applied Physics, 2003Co-Authors: B.k. Singh, V. J. Menon, K. C. SoodAbstract:In Holland's two-mode thermal conduction theory, the Correction Term K c (which represents the effect of momentum conserving normal processes in the Callaway model) was treated under certain limitations. To be specific, (i) his starting expression of K c had an unwarranted temperature-dependent coefficient, (ii) the Taylor expansion of integrand was not quite satisfactory, and (iii) use of the same functional form of the three phonon normal process relaxation rate at low and high frequencies was not justified. These deficiencies were overcome by starting with the correct expression of K c , doing a careful Taylor expansion and also incorporating the umklapp processes, apart from the normal ones. The relative importance of K c is illustrated numerically for Si and LiF.
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Longitudinal and transverse parts of the Correction Term in the Callaway model for phonon conductivity
Journal of Physics: Condensed Matter, 1993Co-Authors: K. C. SoodAbstract:The Correction Term in the Callaway model for phonon conductivity is separated into its longitudinal and transverse parts in the presence of phonon dispersion. This will provide, for the first time, a realistic opportunity to speak about the total individual contribution of the phonons, of different polarizations, to the total phonon conductivity.
A. H. Awad - One of the best experts on this subject based on the ideXlab platform.
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The Correction Term in a dislocation containing lattice
1992Co-Authors: A. H. AwadAbstract:The Correction Term of a sample having dislocation (strain field as well as core) has been studied at low temperatures on the basis of the Callaway integral as well as in the frame of the generalized Callaway integral. Assuming four types of the scattering mechanisms, viz. boundary, dislocation, point defect and three phonon, analytical expressions for the Correction Term are given under two different conditions. The expressions derived give results in agreement with the findings of previous works.
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Contribution to the lattice thermal conductivity due to the three phonon normal processes in the presence of core dislocations in the frame of the Callaway integral
Acta Physica Hungarica, 1990Co-Authors: A. H. AwadAbstract:The contribution of the Correction Term due to the three phonon normal processes has been studied for a sample having core dislocation in the frame of Callaway integral by obtaining an analytical expression for it. To test the applicability of the expression obtained, the contribution of the Correction Term toward total phonon conductivity has been calculated in the temperature range of 0.2–5 K owing to which a negligible contribution has been found.
S. Franchini - One of the best experts on this subject based on the ideXlab platform.
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Estimation of the Correction Term of pitot tube measurements in unsteady (gusty) flows
Flow Measurement and Instrumentation, 2015Co-Authors: Sreenadh Chevula, Angel Sanz-andrés, S. FranchiniAbstract:Abstract In rough environments (train’s underbody, wind carrying sand etc.), the only feasible means of measuring flow speed is with a Pitot tube. Unsteady (gusty) flow effects can cause large errors in flow speed measurements. In this short communication work, an attempt has been made to identify these errors. Based on potential flow theory, a Term that takes into account the unsteady effects has been proposed to correct the Pitot tube measurements in unsteady (gusty) flow conditions. Experiments have been performed in an open circuit-closed test-section, low-speed wind tunnel, designed and built at the Instituto de Microgravedad “Ignacio Da Riva” of the Universidad Politecnica de Madrid (IDR/UPM). Different types of Pitot tubes have been used to check the validity of the Correction Term proposed. It has been shown that the distance between the total and static pressure taps has a major influence on the Pitot tube Correction Term.
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Estimation of the Correction Term of pitot tube measurements in unsteady (gusty) flows
Flow Measurement and Instrumentation, 2015Co-Authors: Sreenadh Chevula, Angel Sanz-andrés, S. FranchiniAbstract:In rough environments (train's underbody, wind carrying sand etc.), the only feasible means of measuring flow speed is with a Pitot tube. Unsteady (gusty) flow effects can cause large errors in flow speed measurements. In this short communication work, an attempt has been made to identify these errors. Based on potential flow theory, a Term that takes into account the unsteady effects has been proposed to correct the Pitot tube measurements in unsteady (gusty) flow conditions. Experiments have been performed in an open circuit-closed test-section, low-speed wind tunnel, designed and built at the Instituto de Microgravedad "Ignacio Da Riva" of the Universidad Politécnica de Madrid (IDR/UPM). Different types of Pitot tubes have been used to check the validity of the Correction Term proposed. It has been shown that the distance between the total and static pressure taps has a major influence on the Pitot tube Correction Term.
B.k. Singh - One of the best experts on this subject based on the ideXlab platform.
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Dispersive effects and Correction Term in two-mode phonon conduction model for Ge
Journal of Physics and Chemistry of Solids, 2003Co-Authors: B.k. Singh, V. J. Menon, K. C. SoodAbstract:Abstract A complete analysis of the phonon conductivity κ , still lacking in the literature, is presented in the two-mode conduction model for Germanium. First a method is derived from which the Correction Term κ c of the Callaway model is separated into its longitudinal and transverse parts and then the effects of strong phonon dispersion and the role of longitudinal and transverse phonons on κ c are studied. For this purpose we have also proposed some new empirical expressions for the three phonon relaxation rates τ 3ph −1 's which are valid in the entire temperature range. This improvised model, when applied simultaneously to the phonon conductivity data of both normal and enriched Ge, yields some new results. These are (i) κ c neglected by the earlier workers in the two-mode phonon conduction model, gives a substantial contribution beyond the conductivity maximum and (ii) the longitudinal phonons are the major carriers of heat at high temperature.
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Effects of dispersion, Correction Term, and isotopes on the thermal conductivity of LiF crystal
Physical Review B, 2003Co-Authors: B.k. Singh, V. J. Menon, K. C. SoodAbstract:We have adapted the Callaway-Holland model so that the dispersive effect and Correction Term ${\ensuremath{\kappa}}_{c}$ can be included in the theoretical analysis of the lattice thermal conductivity of LiF over the temperature range 1\char21{}300 K, for varying concentration of the isotopic content ${}^{7}\mathrm{Li}.$ Some different empirical expressions for different three-phonon relaxation rates ${\ensuremath{\tau}}_{3\mathrm{ph}}^{\ensuremath{-}1}$ for the entire temperature range have been proposed. Anisotropic and dispersive point defect scattering relaxation rate for LiF is also introduced. Our main findings are as follows: ${\ensuremath{\kappa}}_{c}$ even for moderate isotopic concentration of ${}^{7}\mathrm{Li}$ in LiF gives sizable contribution at temperatures where ${\ensuremath{\tau}}_{3\mathrm{ph}}^{\ensuremath{-}1}$ umklapp U processes dominate, which was considered to be negligible by earlier workers; contribution of longitudinal phonons is substantial beyond the conductivity maximum; theoretical value of the isotope scattering parameter ${A}_{1}$ has to be increased only by 1.8\char21{}1.9 times in going from 50.8% to 97.2% of ${}^{7}\mathrm{Li}$ content as against 5 times increase taken by Callaway and Baeyer; and in conformity with Callaway's findings the presence of small chemical impurities has to be assumed to explain the phonon-conductivity data of the isotopically pure sample ${(}^{7}\mathrm{Li}99.99%)$ of LiF. Theoretically justified parameters are used to obtain excellent agreement with the results reported by Thacher as well as by Berman and Brock.
-
Correction Term in total phonon conductivity
Indian Journal of Pure & Applied Physics, 2003Co-Authors: B.k. Singh, V. J. Menon, K. C. SoodAbstract:In Holland's two-mode thermal conduction theory, the Correction Term K c (which represents the effect of momentum conserving normal processes in the Callaway model) was treated under certain limitations. To be specific, (i) his starting expression of K c had an unwarranted temperature-dependent coefficient, (ii) the Taylor expansion of integrand was not quite satisfactory, and (iii) use of the same functional form of the three phonon normal process relaxation rate at low and high frequencies was not justified. These deficiencies were overcome by starting with the correct expression of K c , doing a careful Taylor expansion and also incorporating the umklapp processes, apart from the normal ones. The relative importance of K c is illustrated numerically for Si and LiF.
Sreenadh Chevula - One of the best experts on this subject based on the ideXlab platform.
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Estimation of the Correction Term of pitot tube measurements in unsteady (gusty) flows
Flow Measurement and Instrumentation, 2015Co-Authors: Sreenadh Chevula, Angel Sanz-andrés, S. FranchiniAbstract:Abstract In rough environments (train’s underbody, wind carrying sand etc.), the only feasible means of measuring flow speed is with a Pitot tube. Unsteady (gusty) flow effects can cause large errors in flow speed measurements. In this short communication work, an attempt has been made to identify these errors. Based on potential flow theory, a Term that takes into account the unsteady effects has been proposed to correct the Pitot tube measurements in unsteady (gusty) flow conditions. Experiments have been performed in an open circuit-closed test-section, low-speed wind tunnel, designed and built at the Instituto de Microgravedad “Ignacio Da Riva” of the Universidad Politecnica de Madrid (IDR/UPM). Different types of Pitot tubes have been used to check the validity of the Correction Term proposed. It has been shown that the distance between the total and static pressure taps has a major influence on the Pitot tube Correction Term.
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Estimation of the Correction Term of pitot tube measurements in unsteady (gusty) flows
Flow Measurement and Instrumentation, 2015Co-Authors: Sreenadh Chevula, Angel Sanz-andrés, S. FranchiniAbstract:In rough environments (train's underbody, wind carrying sand etc.), the only feasible means of measuring flow speed is with a Pitot tube. Unsteady (gusty) flow effects can cause large errors in flow speed measurements. In this short communication work, an attempt has been made to identify these errors. Based on potential flow theory, a Term that takes into account the unsteady effects has been proposed to correct the Pitot tube measurements in unsteady (gusty) flow conditions. Experiments have been performed in an open circuit-closed test-section, low-speed wind tunnel, designed and built at the Instituto de Microgravedad "Ignacio Da Riva" of the Universidad Politécnica de Madrid (IDR/UPM). Different types of Pitot tubes have been used to check the validity of the Correction Term proposed. It has been shown that the distance between the total and static pressure taps has a major influence on the Pitot tube Correction Term.
