Investigation On Heat Transfer And Calcium Carbonate Scale Formation During Nucleate Pool Boiling

Heat transfer and scale formation characteristics during nucleate pool boiling has been experimentally investigated and theoretically analyzed in this paper. The main work is as follows:The method of applying limiting diffusion current technology (LDCT) with heat transfer measuring simultaneously has been used to study the interfacial vaporization heat sink effect and hysteresis during nucleate pool boiling, and the spreading process of boiling nuclei on the heat transfer surface in boiling incipience. The results reveal that heat transfer during nucleate boiling is mostly contributed by the interfacial vaporization heat sink effect and convection, the contribution of interfacial vaporization heat sink effect to heat transfer increases with increasing heat flux or system pressure. The heat transfer mechanism has been analyzed by the interaction of fundamental processes contained in nucleate pool boiling. The heating methods have evident effects on hysteresis. Hysteresis occurs under the condition of increasing the heat flux with constant pressure, while TD hysteresis (Temperature Deviation) occurs when decreasing the heat flux. The results also revel that the interfacial vaporization heat sink effect enhances during boiling incipience, when the formation of boiling nuclei is a gradual process. The boiling hysteresis mechanism has been analyzed on the base of the interfacial vaporization heat sink effect and the change in activation way of boiling nuclei.The characteristics of CaCO₃ scale formation on a horizontal round heat transfer surface has been investigated systematically through dynamic thermal resistance experiments which reveal the effects of heat flux, solution concentration and solution bulk temperature on fouling resistance. The experiments of CaCO₃ scale formation were also carried out on a hydrophobic Cu-F₈₂₆₁ surface and a hydrophilic Cu surface. The experiments results and theoretical analysis both reveal the antifouling characteristic of Cu-F₈₂₆₁ surface. Study of CaCO₃ scale formation during subcooled nucleate pool boiling shows that the change trend of heat transfer coefficient is the same with which during saturated nucleate pool boiling, while the values of heat transfer coefficient and fouling rate are less than that of saturated nucleate pool boiling. The negative fouling resistance phenomenon has been found in boiling incipience and the mechanism is analyzed. Two different scale formation mechanism during nucleate boiling is further analyzed. The effect mechanism of scale formation on nucleate boiling heat transfer has been further analyzed on the base of the interaction between scale formation and bubble...