Experimental investigation of hematite particulate deposition under sub-cooled boiling conditions

In order to establish a relationship between the phenomenon of boiling and deposition of suspended particulate (crud) on the boiling surfaces examination of experimental data has been done to determine the validity of existing models and to propose some modifications. Examination of the boiling process becomes more complicated when accompanied with flow. Thus only pool boiling experiments are considered. in which a confined heat source in a large coolant tank with Iron (III) Oxide particles suspended in an aqueous coolant medium. Results are obtained for different process conditions to establish the individual effect of each process condition. Parameters varied are heat flux, subcooling level and pH. These observations are important to show the applicability of different models, including hydrophobicity and micro-layer evaporation, in different situations. When subcooling is high or heat flux is low, bubble residence time is very long and contributes to deposition around the bubble nucleation site. This can be attributed due to the hydrophobicity of metallic particles which move towards bubble interfaces and collect around the nucleation site on boiling surfaces. The electric charge on suspended particles is related to pH of the aqueous medium, which affects the deposition amount by varying the charges between particle and substrate, from being opposite to the same. (authors)