Impact of Thermal Shock on Fouling of Various Structured Tubes During Pool Boiling of CaSO4 Solutions

Abstract

Crystallization fouling during nucleate pool boiling is characterized with relatively rapid formation of a hard and brittle deposit layer. In this study, the impact of thermal shock is experimentally investigated on cleaning of various tubes when subjected to fouling of CaSO4 solutions. The heat transfer tubes included stainless-steel plain and finned tubes with fin densities of 19 and 40 fins per inch. The tubes were used during pool boiling for heat fluxes ranging from 80 to 300 kW/m2. The thermal shock is applied by the sudden decrease or increase in heat flux for approximately 30 s after the fouling layer is formed. In terms of cleaning, the experimental results showed far better performance for the plain tube. During the sudden change in heat flux the whole fouling layer cracked and peeled off, receiving again almost initial clean heat transfer performance. Contrariwise, the results for the finned tubes showed that the fouling layer was only affected marginally by the thermal shock.