研究目的
To investigate the effect of varying concentration of SiO2 nanoparticles and subcooling levels on single vapor bubble dynamics and associated heat transfer rates under nucleate pool boiling conditions.
研究成果
The study demonstrates that suspended SiO2 nanoparticles significantly alter bubble dynamics and heat transfer in nucleate pool boiling. Bubble diameter and aspect ratio decrease with increasing nanoparticle concentration and subcooling, while evaporative heat flux increases with concentration but decreases with subcooling. Natural convective heat flux decreases with nanoparticle concentration due to diffused thermal gradients but increases with subcooling. The rainbow schlieren technique effectively maps these phenomena, providing insights into the roles of Brownian motion and thermophoresis. Future work could explore higher concentrations, different nanoparticles, and multi-bubble systems.
研究不足
The study is limited to low concentrations of nanofluids (up to 0.01% V/V) and subcooling levels up to 9°C. The schlieren technique provides path-integrated data, requiring axisymmetric assumptions for inversion, which may not hold perfectly. Uncertainties in heat flux measurements are around 14-16% for natural convection and 2% for evaporation. The experiments focus on isolated single bubbles, which may not fully represent multi-bubble interactions in practical applications.
1：Experimental Design and Method Selection:
Single bubble-based nucleate pool boiling experiments were conducted using a specially designed boiling chamber with optical access. Rainbow schlieren deflectometry was employed for non-invasive, real-time mapping of bubble dynamics and temperature gradients. The technique relies on light deflection due to refractive index variations caused by temperature gradients, with a color filter used to quantify deflections.
2：Sample Selection and Data Sources:
Experiments were performed with de-ionized water and SiO2-water nanofluids at concentrations of 0.005% and 0.01% (V/V). Subcooling levels ranged from 0 to 9°C. Nanofluids were prepared by dispersing silica nanoparticles in water using an ultrasonicator for stability.
3：005% and 01% (V/V). Subcooling levels ranged from 0 to 9°C. Nanofluids were prepared by dispersing silica nanoparticles in water using an ultrasonicator for stability.
List of Experimental Equipment and Materials:
3. List of Experimental Equipment and Materials: Boiling chamber made of stainless steel with BK7 optical windows, borosilicate heater substrate coated with ITO film for resistive heating, DC power source (0-5 A, 0-32 V), K-type thermocouples, re?ux condenser, white light source (250 W), achromatic plano-convex lenses (collimating and de-collimating), color filter, high-speed color CMOS camera (IDT vision NX8S1 with Navitar 12x zoom lens), ultrasonicator, weighing balance (Citizon), and nanofluids prepared from Sigma Aldrich silica nanoparticles.
4：Experimental Procedures and Operational Workflow:
The bulk liquid was maintained at saturation temperature for degasification, then adjusted to desired subcooling. Single bubbles were generated by supplying constant heat flux (≈56 kW/m2). Schlieren images were recorded and analyzed to extract bubble dynamics parameters and temperature fields. Each experiment used a new clean heater substrate to avoid nanoparticle deposition effects.
5：Data Analysis Methods:
Schlieren images were converted from RGB to HSI space to obtain hue values. Calibration curves correlated hue to light deflections. Abel inversion was applied to retrieve refractive index fields, which were then converted to temperature distributions using empirical correlations. Heat transfer fluxes (natural convective and evaporative) were calculated based on temperature gradients and bubble dynamics.
独家科研数据包，助您复现前沿成果，加速创新突破
获取完整内容
