Abstract
To clarify the heat transfer mechanisms in microgravity nucleate boling, the experiment was conducted by the use of NASDA TR-IA No. 5 rocket. Detailed heat transfer data and values of liquid film thickness underneath a growing bubble on the surface were otained from a transparent heating surface on which electorodes of the sensors are coated directly. The degree of subcooling of ethanol as test liquid and the heat flux supplied were varied in the wide range under the constant liquid temperature. The following was obtained. i) In the coalesced bubble region, the heat transfer is dominated by the behavior of microlayers underneath primary bubbles which are just generated at the base of the coalesced one. ii) Marked heat transfer enhancement is observed at moderate heat flux under the saturated liquid condition, but it changes easily to the deterioration when the dry patches are extended in the microlayers of enlarged area. iii) In the subcooled boiling, the steady bubble behavior and heat transfer are possible in microgravity by the balance of evaporating and consensing rates. iv) In saturated boiling, the reduction of heat flux supplied results in the deactivation of nucleation site in the liquid film underneath a large coalesced bubble contacting to the heating surface.
