Hydrodynamic and Thermal Analyses of Pool Boiling Data Obtained from Experiments Performed on Flat Horizontal Heaters with Conventional and Nano-Structured Surfaces
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Pool boiling phenomena on different types of heater configurations have been explored in the heat transfer literature. Pool boiling experiments on heaters with nanostructured surfaces have gained popularity in contemporary literature for microchip cooling application. The thermal management challenges for cooling of electronic chips have become more acute with decrease in the size for these microchips with concomitant increase in device density and heat flux. Pool boiling is expected to provide appropriate technology solutions to meet these challenges for high heat flux cooling at low temperature differentials. In this study, results obtained from pool boiling experiments were analyzed. The experiments were performed using heaters with plain surfaces (copper and silicon) and nanostructured surfaces (Anodic Aluminum Oxide/AAO). In these experiments, high speed digital image acquisition apparatus was used to record bubble dynamics (nucleation, growth and departure) for both nucleate and film boiling regimes. The videos were used to obtain the bubble diameter at departure, bubble growth rates (bubble height as a function of time) and bubble departure frequency. The objective of these experiments was to explore the change in bubble dynamics for different heater configurations in order to ascertain their role in the observed changes in the values of pool boiling heat flux as a function of wall superheat (i.e., from the boiling curves obtained in these experiments). These experiments were performed for saturated boiling conditions as well as for liquid subcooling of 5 °C and 10 °C. The test fluid was PF-5060 (Manufacturer: 3M Corp.). The experimental apparatus utilized in this study consisted of a visualization chamber, cartridge heaters, power supply, high speed digital data acquisition system and chiller unit. Temperature nanosensors (Thin Film Thermocouples/ TFT) as well as wire bead thermocouples were used for measurement of wall superheat. Micro/ nano-fabrication techniques were utilized in this study for realizing the test surfaces integrated with temperature nanosensors. The data gleaned from these experiments were compiled to obtain a correlation for the optimal heat transfer for different heater surface configurations. Literature review was also performed in this study to compare the experimental results with correlations for bubble dynamics available in the literature. The experimental results for bubble dynamics show that while silicon and copper surfaces have similar values for bubble departure diameter, the variability in the bubble departure frequency values for copper heater experiments were larger than that of silicon heaters. This trend is potentially due to large variation in surface roughness on copper heaters compared to that of silicon wafers (which are single crystal silicon substrates and therefore are atomically smooth at the commencement of the experiments). Heaters with nanostructured surfaces (e.g., for AAO heaters) were observed to yield smaller bubble departure diameters and higher bubble departure frequencies.
Critical Heat Flux
Roy, Ronita (2017). Hydrodynamic and Thermal Analyses of Pool Boiling Data Obtained from Experiments Performed on Flat Horizontal Heaters with Conventional and Nano-Structured Surfaces. Master's thesis, Texas A & M University. Available electronically from