Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 27Citation - Scopus: 28Effects of Wall-Located Heat Barrier on Conjugate Conduction/Natural- Convection Heat Transfer and Fluid Flow in Enclosures(Taylor and Francis Ltd., 2008) Hakyemez, Erinç; Mobedi, Moghtada; Öztop, Hakan FehmiThe effects of a heat barrier, located in the ceiling wall of an enclosure, on conjugate conduction/natural convection are investigated numerically. The vertical walls of the enclosure are differentially heated and the horizontal walls are adiabatic. Heatline technique is used to visualize heat transport. The variations of average Nusselt number, dimensionless heat transfer rate through the ceiling wall, and dimensionless overall heat transfer rate are studied. Calculations are performed for different Rayleigh numbers (10 3≤ Ra ≤ 10 6), thermal conductivity ratios (1 ≤ K ≤ 100), dimensionless locations of the heat barrier (0 < X h < 1),and two dimensionless ceiling wall thicknesses (D = 0.05 and D = 0.20). For high thermal conductivity ratio (K = 100), the heat barrier considerably reduces the dimensionless overall heat transfer rate. The effect of the heat barrier on dimensionless heat transfer rate through the enclosure increases as the Rayleigh number decreases. For low Rayleigh number (i.e., Ra = 10 3), a location exists in the ceiling wall for which the dimensionless overall heat transfer rate is minimum.Article Citation - WoS: 4Citation - Scopus: 3Evaluation of the Effectiveness of the Bulk Thermal Stresses for Kraft Recovery Boiler Fireside Deposit Cleaning(Tappi Press, 2006) Özcan, Selçuk; Tran, HonghiRemoval of fireside deposits from the heat transfer tubes in kraft recovery boilers is carried out by sootblowing and occasionally "chill-and- blow" practices. During chill-and-blow, black liquor flow is reduced to rapidly cool the deposits.Thermal stresses generated in the deposit as a result of thermal shock can effectively weaken the deposit, facilitating its cleaning. For this study, we investigated the mechanical weakening effect of thermal stresses generated by the transient temperature gradients. We quantified the mechanical weakening effect due to thermal shock by measuring the decrease in biaxial flexure strength of a preheated sodium chloride disk at various quenching times and surface heat transfer coefficients. We observed that the mechanical weakening occured by transient thermal stresses as well as crack propagation. Approximately 35% loss in biaxial flexure strength could be achieved at heat transfer coefficients above 3.3·103 W/m 2K, and at quenching durations above 40 s.