CRITICAL HEAT-FLUX OF COUNTER-FLOW BOILING IN A UNIFORMLY HEATED VERTICAL TUBE WITH A CLOSED BOTTOM

An experimental study is carried out on the critical heat flux (CHF) of counter-flow boiling in a uniformly heated vertical tube which is open to an upper, large liquid reservior and closed at the bottom end. CHF characteristics which are quite different from those of CHF in the ordinary boiling system are revealed, particularly the matters such as the location to initiate CHF in the tube, a noticeable time-lag and a subsequent period for falling of local wall temperature just before the onset of CHF, and the complicated and comparatively slow variation of local wall temperature after the onset of CHF. Then a physical model capable of explaining such peculiar phenomena through the behavior of vapor and liquid in a heated tube is discussed.