Destabilization of Film Boiling Due to Arrival of a Pressure Shock—Part I: Experimental

Transient heat transfer from an electrically-heated 3 mm o.d. horizontal tube, initially in subcooled film boiling, was measured immediately after passage of a shock wave of 1–5 × 10⁵ N/m² over-pressure. The fluids tested were Freon-113 and 95 percent ethanol-5 percent water at initially 0.5–2 × 10⁵ N/m² at 22–24° C. Transient heat transfer rates, averaged over 0.5–1 ms after vapor film collapse, ranged up to 20 times the steady-state value. The maximum transient flux occurred at supercritical contact temperatures, with frequently a minimum in the range of contact temperatures between the homogeneous nucleation and the critical temperature. Photography at 5000 frames/s showed apparently complete vapor film collapse within one or two frames, followed by re-establishment of film boiling in ∼1 ms, and eventually nucleate boiling in ∼100 ms. The surface temperature which gave the highest peak transient flux shifted appreciably with increasing shock pressure, which indicates some compressibility even after “contact” was made. Implications for vapor explosions are discussed.