Investigation of flow boiling critical heat flux and heat transfer within a horizontally oriented channel with one-sided heating at three levels of subcooled inlet

The aim of this study is to investigate the impact heater orientation and inlet conditions on heat transfer mechanisms during flow boiling, inside horizontally oriented rectangular channel using PF-5060. The experimental setup allows both upward and downward-facing single-sided heating configurations. Various inlet mass flux are examined, along with different levels of inlet subcooling. The impact of gravity is studied using flow visualization. During downward facing heating, vapor accumulates along the copper heater wall due to buoyancy effects resulting in notably low CHF and heat transfer values. In contrast, with upward facing heating, buoyancy assists in extraction of vapor from the copper heater wall, facilitating increased liquid contact and higher CHF and heat transfer values. CHF values begin to converge at high inlet mass flux for both orientations, which can be attributed to inertia dominating gravity. Inlet subcooling also influences CHF, with highly subcooled conditions yielding higher CHF. The impact of orientation and subcooled inlet on CHF and heat transfer coefficients are captured. Experimental CHF data was used to validate the Hydrodynamic Instability-Based Model for CHF prediction demonstrating a Mean Absolute Error of 10.8%. Effectively considering gravity forces, heated wall orientation, and flow regimes, the model demonstrates a proficiency in its comprehensive approach.