This dissertation investigates the critical heat flux (CHF) behavior of chromium-coated zirconium tubes under low-pressure forced-convection boiling in a vertical annular geometry. Experiments were conducted at three pressure levels (120, 200, and 300 kPa), three mass flux levels (400, 500, and 600 kgm^(-2) s^(-1)), and multiple inlet temperature conditions (64–91 °C).
Two independently fabricated but compositionally identical samples were tested to evaluate experimental reproducibility and sample-to-sample variability. In addition to smooth reference surfaces, controlled mechanical surface modifications (150-, 80-, and 40-grit treatments) were applied to assess the influence of surface morphology on CHF behavior.
Results demonstrate that CHF increases systematically with pressure, mass flux, and inlet subcooling, consistent with classical hydrodynamic scaling behavior for annular flow. Roughness-induced enhancement remained moderate (typically ≤10%) and exhibited pressure dependence, with the strongest effects observed at intermediate pressure.
Dimensionless analysis using Reynolds, Boiling, Jakob, and Weber numbers confirms that all smooth and roughened data collapse within the same scaling envelope, indicating preservation of the dominant annular film dryout mechanism. Sample-to-sample deviations remain within 1–7% under most conditions and are comparable to experimental repeatability scatter, confirming robust reproducibility of the dataset.
The results indicate that surface morphology modifies the absolute CHF value, while the underlying hydrodynamic scaling remains governed by liquid film stability controlled by flow inertia. The work provides a systematically controlled CHF dataset for chromium-coated zirconium under low-pressure annular flow boiling and contributes to improved understanding of surface effects within hydrodynamically dominated boiling systems.