ABSTRACT
Forced convective and pool boiling heat transfer from a small thin film square heaters on a glass plate has been investigated using various sizes of heaters (20×20μm to 5×5mm), which are cooled by FX3250 saturated liquid in a narrow channel or in a pool. In addition to the measurement of heater temperature, boiling behavior was observed by a high-speed video camera which was synchronized with the measurement of temperature fluctuation. In the case of larger heaters, heat transfer characteristics in nucleate boiling region are similar to those for conventional wide heating surface, and transition to film boiling occurs with moderate temperature increase. The transition occurs at a larger heat flux for larger flow rate. With the decrease of heater size the heat flux increases due to the effect of substrate heat conduction, and the heat transfer characteristics approaches those for pure substrate conduction. Further, in the case of smaller heaters, only one bubble is nucleated periodically, and the heater temperature fluctuates corresponding to the bubble growth and departure. The heater temperature reaches minima just at the moments of bubble detachment from the surface. In addition, under certain conditions, a large bubble is formed which fills the channel and reduces the heat transfer. The effect of flow velocity on the boiling behavior was also observed.
