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A smart surface that is a TiO 2 -coated surface (TCS) is a hydrophobic surface initially, but becomes a hydrophilic surface when heated. Therefore, such a surface can be used to enhance both boiling heat transfer (BHT) and critical heat flux (CHF) in pool boiling. In the present study, the time effect of the wetting transition of TCS was focused on. The CHF on TCS was enhanced more when the holding time of the heat flux in high-temperature regime was increased. By observing changes in contact angles on TCS through heat treatment in air, it was found that the wetting transition was affected not only by the temperature, but also by the time. Thus, a variation of the receding contact angle was correlated in the form of an exponential function. The suggested empirical correlation includes temperature and time, and it describes the transition of the receding contact angle. The correlation was also used to predict the CHF on TCS in pool boiling. As a result, CHFs on TCS could be explained using the correlation. [ABSTRACT FROM AUTHOR]

We report nucleate pool boiling experiments using reduced graphene oxide (RGO) colloidal suspensions on a silicon dioxide plate surface, in order to describe a kind of quasi-transition boiling phenomenon, whereby the wall temperature gradually increased as a function of time without a rapid increase in temperature at the critical heat flux (CHF). Under boiling conditions, the RGO flakes formed a three-dimensional (3D) graphene structure at the surface, so that the RGO colloidal suspension exhibited a larger boiling heat transfer coefficient and larger CHF with the quasi-transition boiling phenomenon than when the working fluid was deionized water. To evaluate the effect of the heat flux conditions on the phenomenon, various heat fluxes were investigated, and the transient behavior of the boiling heat transfer characteristics was observed. We found that the rate of change of the wall temperature in the quasi-transition boiling regime was proportional to the heat flux, even if the higher heat flux was applied following the onset of the increase in the wall temperature. [ABSTRACT FROM AUTHOR]

Abstracts An experimental study was carried out to measure the boiling heat transfer and critical heat flux on serpentine-pattern thin film heater having a 120 nm thick platinum under pool boiling. Pool boiling critical heat flux experiments were performed using plain heater, 2-serpentine, 4-serpentine, and 6-serpentine pattern thin film heater. From the experimental results, it is found that the measured boiling heat transfer performance and critical heat flux are dependent of serpentine pattern, however critical heat flux is independent of the number of serpentine pattern. Measured data of critical heat flux are compared with classical model of critical heat flux, and degradation phenomena of boiling heat transfer and critical heat flux on serpentine-pattern thin film heater under pool boiling analyzed in this work. [ABSTRACT FROM AUTHOR]

The graphene has been interested world-widely for the superb mechanical and electrical properties. Among them, the thermal conductivity of graphene was often reported as the 500–5000 W/mK. We tried to apply the graphene to the thermal application of boiling heat transfer through the graphene coating. The graphene was used for the reduced graphene oxide flakes in water (RGO colloid). The RGO colloid boiling on silicon-dioxide heater (substrate) showed both the boiling heat transfer and the critical heat flux enhancement as 65% and 70%, respectively. After RGO colloid boiling, the base graphene layer (BGL) with 10–100 nm thickness below the self-assembled foam-like graphene (SFG) was observed. In order to confirm the effect of BGL on the enhanced boiling performance, the only water boiling on an artificial graphene multilayers (RGO film) coated heater was conducted, and shows the similar result with the RGO colloid boiling. [ABSTRACT FROM AUTHOR]