Manipulating thin film boiling to achieve record-breaking high heat flux

Thin film boiling (TFB) is an intensive phase change heat transfer mode and therefore is highly expected to cope with those urgent heat dissipation requirements of chips and electronic devices. Theoretically, the upper limit of critical heat flux (CHF) for TFB can be 5000 W/cm2. However, the highest CHF of TFB reported in the literature is 1230 W/cm2. To fill the gap, research efforts were made on both the experimental sample and the experimental procedure. The unilateral fixation of the experimental samples was upgraded to bilateral fixation so as to improve the pressure-bearing capacity of the samples. TFB experiments under constant driving pressure difference proved that bilateral fixation indeed helped samples to withstand higher liquid pressure and consequently contributed to improved heat flux, but the measured CHF was only around 1400 W/cm². It was attributed to the inherent operating procedures of the constant driving pressure mode that when the liquid pressure was relatively high, the sample was under extreme mechanical condition at the very beginning of the experiment, therefore was fragile and would probably break before achieve the theoretical CHF for that pressure. Accordingly, two alternative liquid pressure and heating power variation approaches for manipulating TFB were proposed and applied. In the asynchronous variation approach, the liquid pressure was increased in a stepping mode, with pressure difference of several hundred Pa between two steps. For each pressure step, the heating power increased until approaching the theoretical CHF of that pressure. Therefore, it is analogous to automatic transmission (AT) with finite gear ratios. In the simultaneous variation approach, the liquid pressure and heating power were varied with smaller step and higher frequency. Consequently, the ultimate situation is the simultaneous variation of liquid pressure and heating power, which is analogous to continuously variable transmission (CVT). In these ways, the experimental samples stayed in a relatively relaxed state and the achieved CHF results were notably improved to the range of 1500 to 2000 W/cm2, and a record-breaking high CHF of 2074 W/cm2 was also obtained.