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Analysis of entropy generation due to natural convection in rhombic enclosures / R. Anandalakshmi in Industrial & engineering chemistry research, Vol. 50 N° 23 (Décembre 2011) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 50 N° 23 (Décembre 2011) . - pp. 13169–13189 Titre : Analysis of entropy generation due to natural convection in rhombic enclosures Type de document : texte imprimé Auteurs : R. Anandalakshmi, Auteur ; Tanmay Basak, Auteur Année de publication : 2012 Article en page(s) : pp. 13169–13189 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Entropy  generation Résumé : One way of increasing the energy efficiency in thermal processing of materials is to reduce exergy losses due to irreversibilities, measured as “entropy generation”. In this study, an analysis of entropy generation during natural convection in rhombic enclosures with various inclination angles (φ = 30°, 45°, and 75°) has been carried out for the efficient thermal processing of various fluids (Prandtl numbers of Pr = 0.015, 0.7, 7.2, and 1000) in a range of Rayleigh numbers (Ra = 103–105). The enclosure is bounded by an adiabatic top wall, cold side walls, and an isothermally (case 1) and nonisothermally (case 2) heated bottom wall. Isotherms (θ), streamlines (ψ), and entropy generation contours due to heat transfer (Sθ) and fluid friction irreversibility (Sψ) are analyzed for both cases. At low Rayleigh number (Ra = 103), the entropy generation in the cavity is dominated by Sθ for all φ, irrespective of Pr. As Ra increases to 105, the fluid flow intensifies and Sψ also increases for all φ, irrespective of Pr. The total entropy generation (Stotal), average Bejan number (Beav), and average heat-transfer rate (Nub) are plotted for Rayleigh number ranges of 103 ≤ Ra ≤ 105. The total entropy generation (Stotal) is found to be low for φ = 30° and high for φ = 75° for all Pr values at Ra = 105. Analysis of variations of Beav with Ra for high-Pr fluids indicates that Sψ contributes significantly for increase in Stotal. It is also found that the largest heat-transfer rate (Nub) corresponds to minimum entropy generation (Stotal) for φ = 30° cavities at Ra = 105 with all Pr in case 1. The nonisothermal heating strategy (case 2) is energy efficient, because of its lower Stotal value, corresponding to low Nub, which is due to a lesser heating effect than case 1 for all φ. Overall, rhombic cavities with φ = 30° may be the optimal geometrical design for thermal processing of all types of fluids (Pr = 0.015, 0.7, 7.2, and 1000), irrespective of the heating strategy. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie200184y [article] Analysis of entropy generation due to natural convection in rhombic enclosures [texte imprimé] / R. Anandalakshmi, Auteur ; Tanmay Basak, Auteur . - 2012 . - pp. 13169–13189. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 50 N° 23 (Décembre 2011) . - pp. 13169–13189 Mots-clés : Entropy  generation Résumé : One way of increasing the energy efficiency in thermal processing of materials is to reduce exergy losses due to irreversibilities, measured as “entropy generation”. In this study, an analysis of entropy generation during natural convection in rhombic enclosures with various inclination angles (φ = 30°, 45°, and 75°) has been carried out for the efficient thermal processing of various fluids (Prandtl numbers of Pr = 0.015, 0.7, 7.2, and 1000) in a range of Rayleigh numbers (Ra = 103–105). The enclosure is bounded by an adiabatic top wall, cold side walls, and an isothermally (case 1) and nonisothermally (case 2) heated bottom wall. Isotherms (θ), streamlines (ψ), and entropy generation contours due to heat transfer (Sθ) and fluid friction irreversibility (Sψ) are analyzed for both cases. At low Rayleigh number (Ra = 103), the entropy generation in the cavity is dominated by Sθ for all φ, irrespective of Pr. As Ra increases to 105, the fluid flow intensifies and Sψ also increases for all φ, irrespective of Pr. The total entropy generation (Stotal), average Bejan number (Beav), and average heat-transfer rate (Nub) are plotted for Rayleigh number ranges of 103 ≤ Ra ≤ 105. The total entropy generation (Stotal) is found to be low for φ = 30° and high for φ = 75° for all Pr values at Ra = 105. Analysis of variations of Beav with Ra for high-Pr fluids indicates that Sψ contributes significantly for increase in Stotal. It is also found that the largest heat-transfer rate (Nub) corresponds to minimum entropy generation (Stotal) for φ = 30° cavities at Ra = 105 with all Pr in case 1. The nonisothermal heating strategy (case 2) is energy efficient, because of its lower Stotal value, corresponding to low Nub, which is due to a lesser heating effect than case 1 for all φ. Overall, rhombic cavities with φ = 30° may be the optimal geometrical design for thermal processing of all types of fluids (Pr = 0.015, 0.7, 7.2, and 1000), irrespective of the heating strategy. DEWEY : 660 ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie200184y

Analysis of entropy generation minimization during natural convection in trapezoidal enclosures of various angles with linearly heated side wall (s) / Tanmay Basak in Industrial & engineering chemistry research, Vol. 51 N° 10 (Mars 2012) 

Public ISBD [article]  in Industrial & engineering chemistry research > Vol. 51 N° 10 (Mars 2012) . - pp. 4069–4089 Titre : Analysis of entropy generation minimization during natural convection in trapezoidal enclosures of various angles with linearly heated side wall (s) Type de document : texte imprimé Auteurs : Tanmay Basak, Auteur ; Pushpendra Kumar, Auteur ; R. Anandalakshmi, Auteur Année de publication : 2012 Article en page(s) : pp. 4069–4089 Note générale : Chimie industrielle Langues : Anglais (eng) Mots-clés : Entropy  Trapezoidal Résumé : Entropy generation during natural convection in trapezoidal enclosures with various inclination angles (φ), φ = 45°, 60°, and 90° for uniformly heated bottom wall and insulated top wall with linearly heated side walls (case 1) or linearly heated left wall with cold right wall (case 2) have been investigated numerically using penalty finite element method. Parametric studies for the wide range of Rayleigh numbers (Ra = 103–105) and Prandtl numbers (Pr = 0.015–1000) have been performed. Symmetry in flow pattern is observed for case 1. During the conduction regime at low Ra (Ra = 103), the entropy generation in the cavity is dominated by heat transfer irreversibility for all Pr. The strength of fluid flow increases with Ra and that leads to an increase in thermal energy transport due to enhanced convection at Ra = 105. Consequently, the entropy generation due to heat transfer (Sθ) and fluid friction (Sψ) also increases with Ra for all Pr. The comparison of magnitudes of Sθ and Sψ indicates that maximum entropy generation due to heat transfer (Sθ,max) and fluid friction (Sψ,max) is lower for case 1 and higher for case 2. It is found that Sθ,max occurs at the top portion of side walls in case 1, whereas Sθ,max occurs at a hot–cold junction due to a high thermal gradient in case 2. The total entropy generation, Stotal is found to be smaller in case 1 and larger in case 2 for all Pr at Ra = 105. It is observed that Sψ,max occurs at the top wall in both heating situations for Pr = 0.015 and Ra = 105. It is also found that, Sψ,max is observed near side walls in case 1, whereas that is observed near the right cold wall in case 2 for Pr = 0.7 and 1000 at Ra = 105. The total entropy generation (Stotal) is larger for φ = 45° in both heating cases at high Pr (Pr = 1000). The total entropy generation (Stotal) also increases with Pr due to an increase in Sψ with Pr. It is found that, high heat transfer rate (Nub) and minimum entropy generation (Stotal) occur for square cavities at Ra = 105 for all Pr in case 1. It is observed that Stotal is smaller for case 1 compared to case 2, even though high Nub is observed at case 2 for all φs. The inclination angle (φ) has almost identical effect on entropy production rate for 45° ≤ φ ≤ 60° within the entire range of Pr at all Ra. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie201107f [article] Analysis of entropy generation minimization during natural convection in trapezoidal enclosures of various angles with linearly heated side wall (s) [texte imprimé] / Tanmay Basak, Auteur ; Pushpendra Kumar, Auteur ; R. Anandalakshmi, Auteur . - 2012 . - pp. 4069–4089. Chimie industrielle Langues : Anglais (eng) in Industrial & engineering chemistry research > Vol. 51 N° 10 (Mars 2012) . - pp. 4069–4089 Mots-clés : Entropy  Trapezoidal Résumé : Entropy generation during natural convection in trapezoidal enclosures with various inclination angles (φ), φ = 45°, 60°, and 90° for uniformly heated bottom wall and insulated top wall with linearly heated side walls (case 1) or linearly heated left wall with cold right wall (case 2) have been investigated numerically using penalty finite element method. Parametric studies for the wide range of Rayleigh numbers (Ra = 103–105) and Prandtl numbers (Pr = 0.015–1000) have been performed. Symmetry in flow pattern is observed for case 1. During the conduction regime at low Ra (Ra = 103), the entropy generation in the cavity is dominated by heat transfer irreversibility for all Pr. The strength of fluid flow increases with Ra and that leads to an increase in thermal energy transport due to enhanced convection at Ra = 105. Consequently, the entropy generation due to heat transfer (Sθ) and fluid friction (Sψ) also increases with Ra for all Pr. The comparison of magnitudes of Sθ and Sψ indicates that maximum entropy generation due to heat transfer (Sθ,max) and fluid friction (Sψ,max) is lower for case 1 and higher for case 2. It is found that Sθ,max occurs at the top portion of side walls in case 1, whereas Sθ,max occurs at a hot–cold junction due to a high thermal gradient in case 2. The total entropy generation, Stotal is found to be smaller in case 1 and larger in case 2 for all Pr at Ra = 105. It is observed that Sψ,max occurs at the top wall in both heating situations for Pr = 0.015 and Ra = 105. It is also found that, Sψ,max is observed near side walls in case 1, whereas that is observed near the right cold wall in case 2 for Pr = 0.7 and 1000 at Ra = 105. The total entropy generation (Stotal) is larger for φ = 45° in both heating cases at high Pr (Pr = 1000). The total entropy generation (Stotal) also increases with Pr due to an increase in Sψ with Pr. It is found that, high heat transfer rate (Nub) and minimum entropy generation (Stotal) occur for square cavities at Ra = 105 for all Pr in case 1. It is observed that Stotal is smaller for case 1 compared to case 2, even though high Nub is observed at case 2 for all φs. The inclination angle (φ) has almost identical effect on entropy production rate for 45° ≤ φ ≤ 60° within the entire range of Pr at all Ra. ISSN : 0888-5885 En ligne : http://pubs.acs.org/doi/abs/10.1021/ie201107f