THERMAL AND FLOW VISUALIZATION OF SUBMERGED JET IMPINGEMENT BOILING WITH FC-72

Dielectric fluids like FC-72 have been popularly used as electronic coolants owing to their chemical inertness and low saturation temperatures at atmospheric pressure. This work visualizes the heat transfer characteristics of FC-72 during submerged jet impingement boiling on a silicon surface heated by means of a thin film serpentine heater. Infrared thermography is used to obtain quantitative thermal maps of the boiling process from beneath the surface. Simultaneous high-speed visualization is used to record the corresponding bubble dynamics on the top surface. Experiments for two jet Reynolds numbers are compared with pool boiling under saturated conditions at a fixed surface to nozzle diameter ratio. Area-averaged temperatures evaluated from the thermal maps are used to describe the boiling trends for increasing and decreasing heat flux. Wall superheat required for phase-change varies randomly with increasing jet Reynolds numbers. Incipience overshoot as high as similar to 21 degrees C is observed and visually documented for the lower jet flow rate. Radial temperature profiles along the surface indicate that locally overshoots may vary significantly (similar to 8-21 degrees C) for conditions with extremely high incipient superheats.