Upper limit of forced boiling with an impinging jet. Challenge to achieve critical heat flux beyond 200 MW/m2 with highly subcooled liquid

Critical heat flux (CHF) has been measured on a small rectangular heated surface of L=5 and 10 mm in length and W=4 and 6 mm in width with an impinging jet of highly subcooled water to achieve an ultra high critical heat flux. The experiments were carried out at jet velocities of u=5-60 m/s, system pressures of P=0.1-1 MPa and degree of subcooling of ΔTsub=80-170 K. The effect of heater thickness appeared below 0.3 mm and the CHF reduces with decrease in the thickness. Characteristics of the CHF for the longer heated surface L=10 mm agreed well with an existing correlation within ±20%. The maximum CHF of 212 MW/m2 was recorded at P=0.5 MPa, u=35 m/s and ΔTsub=151 K. Then, the maximum CHF at atmospheric pressure can approach to 48% of the ultimate maximum heat flux qmax,max proposed by Gambill and Lienhard who evaluated it from the mean velocity of molecular dynamics. (author)