A phenomenological study on effects leading to the departure from nucleate boiling in subcooled flow boiling

A study on the mechanisms triggering the departure from nucleate boiling in subcooled vertical flow boiling using a complementary experimental approach

“…25 Hz [27]. In the wakes of these agglomerations, movement of fresh liquid towards the heater surface could be visualized using PIV as shown in [27]. Below the coalesced vapor structure, single vapor bubbles could be observed as well, moving at high velocities.…”

“…It could be observed that the vapor behavior was highly periodic, with larger agglomerations appearing at roughly constant frequencies of approx. 25 Hz [27]. In the wakes of these agglomerations, movement of fresh liquid towards the heater surface could be visualized using PIV as shown in [27].…”

“…The heater surface temperature was extrapolated for each of the three rows of thermocouples using a polynomial extrapolation. Particle Image Velocimetry (PIV) was done both in cold flow to define the flow characteristics [25] as well as in nucleate and film boiling [27]. A time averaged setup was used for the flow characterization, while a high-speed approach was used for the boiling studies.…”

“…Furthermore, as this is true for all conducted experiments, it does not affect the comparability of the results within this study. High-speed photography and shadowgraphy were applied using a Photron Fastcam SA5 highspeed camera as described in [27] using a back-lit setup. Recording rates were typically at 2000 fps for the images shown here.…”

“…It could be observed that the scatter within the results was typically less than AE1% at steady state conditions and a deviation of less than AE2% was observed within repeated experiments. A more thorough discussion on the used processing steps is given by the authors in [27]. However, due to the depth integrating nature of the technique it has to be noted that the measured void fractions can only serve as qualitative information to gain insight on the general vapor behavior and to compare different thermohydraulic parameters and setups.…”