ON THE BUBBLE DYNAMICS UNDER AN IMPINGING FREE PLANAR JET

摘要

A new scenario identification procedure (SIP) is proposed for the bubble growth termination during subcooled flow boiling under an impinging free planar jet. Two mechanisms are considered in the proposed SIP: 1) the thermal equilibrium between the bubble and the surrounding fluid and the heater surface, and 2) the dynamic equilibrium of the acting forces on the growing bubble. The scenario of bubble growth termination and the bubble maximum diameter under specific impingement conditions are attributed to the earlier of the two equilibrium conditions. Depending on the controlling mechanisms, a bubble will collapse at its nucleation site if the thermal equilibrium precedes the dynamic equilibrium or it will depart and slide along the heated surface otherwise. The proposed SIP has been validated using experimental data obtained from the high speed imaging of the subcooled flow boiling on a horizontal surface under various conditions of free planar jet impingement. The jet velocity was varied from 0.4 m/s to 1.7 m/s. The degree of water subcooling was varied from 10 deg C to 28 deg C. The surface superheat was varied from 0 to 30 deg C along a span of the heated surface from the stagnation down to ten jet widths. The validation process showed that the proposed SIP is not only capable of capturing the right growth termination scenario but it can also predict; reasonably, the maximum bubble diameter.