COMBINED HEAT AND SOLUTE TRANSPORT MODEL IN POROUS DEPOSITS WITH CHIMNEYS

The existence of a wick-boiling mechanism has been postulated as being the dominant heat transfer mode for nuclear fuel pins covered with porous deposits in boiling water reactors and at specific locations of pressurized water reactors as well. Although wick boiling is a very efficient heat transfer process, it can lead to the accumulation of potentially large concentrations of soluble species close to the evaporative surfaces; this perturbs the heat transfer process by elevating the boiling point. A two-dimensional model involving a system of coupled heat, momentum, and mass transport relations that require simultaneous treatment has been developed and solved by an iterative approach. When properly accounting for the interdependence between heat and mass transfers, higher evaporative-surface temperatures and lower solute concentration factors are obtained, in agreement with experimental observations. The model also predicts that the wall superheat is insensitive to bulk coolant subcooling, which is also in agreement with experimental observations.