A study of bubble behaviors in the volumetrically heated packed bed

Highlights: • Electromagnetic induction heating method was used to heat packed bed. • The bubble behaviors in volumetrically heated packed bed was studied firstly. • There was "regrowth phenomenon" in the packed bed. • Structures of contact corner had great impacts on the bubble behaviors. - Abstract: The volumetrically heated packed bed has been widely utilized in modern industry, however, no research on the bubble behaviors in forced convection subcooled boiling was studied. To study the bubble behaviors in the volumetrically heated packed bed, here electromagnetic induction heating method was used to heat oxidized carbon steel balls adopted to stack packed bed, while water was utilized as the refrigerant in the experiment. Bubble behaviors were observed by a high speed camera for particle diameter varying from 8 mm to 12 mm, mass flux varying from 29.3 kg m⁻² s⁻¹ to 84.2 kg m⁻² s⁻¹, heat flux varying from 14.5 kW m⁻² to 50 kW m⁻², inlet pressure varying from 0.116 MPa to 0.125 MPa, inlet subcooling varying from 7 k to 9.2 k and porosity = 0.39. Obtained flow visualization images were analyzed. The experimental results indicated that the bubbles were blocked by steel balls and easily attached to the surface of balls, then slipped along the surface of steel balls. There was "regrowth phenomenon" in the packed bed and generated bubbles repeated growth several times in the lifetime. The nucleate boiling was firstly observed in the contact surface. Structures of contact surface had great impacts on the bubble shapes, departure diameter and frequency.