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

Measurements were made of the thermal resistance of porous deposits of vari ous thicknesses under both single-phase forced convection and flow-bailing conditions. Both synthetic deposits and deposits on tubes removed from oper ating steam generators were used in this investigation. The thermal resista nce was modeled as the sum of two components: one associated with conductio n through the porous deposit and a second associated with the effect of sur face roughness. The conductive component of the thermal resistance was alwa ys positive, whereas surface roughness made a negative contribution to the thermal resistance; i.e., roughness enhanced the rate of heat transfer. The rmal conductivity of the porous deposits was higher for single-phase forced convection, whereas the effect of deposit roughness on thermal resistance was higher under flaw-boiling conditions. The results are discussed in term s of the effect of composition, morphology, surface roughness, and the mode of heat transfer on the thermal resistance of porous deposit.