Heat transfer—A review of 2005 literature

Heat transfer - A review of 2000 literature

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Fouling Of Nuclear Steam Generators: Fundamental Studies, Operating Experience and Remedial Measures Using Chemical Additives

Characteristics of steam generator tube deposits in an operating pressurized water reactor

The deposition rate of colloidal magnetite particles was measured under both single-phase forced-convective and flow-boiling conditions. All measurements were made at alkaline pH where both the heat transfer surface and the surface of the magnetite particles appear to be negatively charged. For single-phase forced convection, the deposition rate constant is lower than the mass transfer coefficient for colloidal particles, and the difference is attributed to the force of repulsion between the negatively charged surfaces of the particle and substrate. The deposition rate measured under flow-boiling conditions is lower than that reported for the deposition of colloidal particles at neutral pH. The difference is, again, attributed to the force of repulsion between the particle and substrate. Particle removal rates were significantly lower than deposition rates; analysis using the theory of turbulent bursts suggests a removal efficiency of only 10−9% for each turbulent burst. The low removal efficiency is consistent with the particle diameter being significantly smaller than the thickness of the laminar sublayer in these tests.



On a mesure la vitesse de deposition de particules de magnetite colloidales dans des conditions de convection forcee et d'ebullition monophasique. Toutes les rnesures ont ete prises a un pH alcalin ou la surface de transfert de chaleur et la surface des particules de magnetite semblent chargees negativement. Pour la convection forcee monophasique, la constante de vitesse de deposition est inferieure au coefficient de transfert de matiere pour les particules colloidales, et la difference est attribuee a la force de repulsion entre les surfaces chargees negativement de la particule et du substrat. La vitesse de deaposition mesuree dans des conditions d'ebullition est inferieure a celle publiee pour la deposition des particules colloidales a pH neutre. La difference est, de nouveau, attribuee a la force de repulsion entre la particule et le substrat. Les vitesses de retrait des particules sont considerable-ment plus petites que les vitesses de deposition; l'analyse par la theorie des elatements turbulents suggere une efficacite de retrait de seutement 10−9% pour chaque elatement turbulent. La faible efficacite de retrait est consistante avec le diametre des particules qui est nettement plus petit que l'epaisseur de la sous-couche laminaire dans ces essais.

Deposition of magnetite particles from flowing suspensions under flow‐boiling and single‐phase forced‐convective heat transfer

Measurements were made of the thermal resistance of porous deposits of various thicknesses under both single-phase forced convection and flow-boiling conditions. Both synthetic deposits and deposits on tubes removed from operating steam generators were used in this investigation. The thermal resistance was modeled as the sum of two components: one associated with conduction through the porous deposit and a second associated with the effect of surface roughness. The conductive component of the thermal resistance was always positive, whereas surface roughness made a negative contribution to the thermal resistance, i.e., roughness enhanced the rate of heat transfer. Thermal conductivity of the porous deposits was higher for single-phase forced convection, whereas the effect of deposit roughness on thermal resistance was higher under flow-boiling conditions. The results are discussed in terms of the effect of composition, morphology, surface roughness, and the mode of heat transfer on the thermal resistance of porous deposit.



On a effectue des mesures de la resistance thermique de depǒts poreux de diverses epaisseurs dans des conditions de convection forcee monophasique et d'ecoulement bouillonant. A la fois des depǒts synthetiques et les depǒts des tubes venant de chaudieres a vapeur en fonctionnement ont ete utillses dans cette etude. La resistance thermique a ete modellsee comme etant la somme de deux composantes: l'une liee a la conduction dans le depǒt poreux, l'autre liee a l'effet de la rugoslte de surface. La composante conductive de la resistance thermique est toujours positive, tandis que la rugosite de surface apporte une contribution negative a la resistance thermique, c'est-a-dire que la rugosite ameliore la vitesse du transfert de chaleur. La conductivite thermique des depǒts poreux est plus grande pour la convection forcee monophasique, tandis que l'effet de la rugosite des depǒts sur la resistance thermique est plus grand dans des conditions d'ebullition de l'ecoulement. Les resultats sont analysees relativement a l'effet de la composition, de la morphologie, de la rugosite de surface et du mode de transfert de chaleur sur la resistance thermique du depǒt poreux.

Mike G. Brideau

Papers

Thermal resistance of steam‐generator tube deposits under single‐phase forced convection and flow‐boiling heat transfer