MEASUREMENTS OF POOL BOILING HEAT-TRANSFER FROM CERAMIC Y1BA2CU3O7-DELTA SUPERCONDUCTORS TO LIQUID-NITROGEN

We present measurements of pool boiling heat transfer from ceramic Y1Ba2Cu3O7-delta to liquid nitrogen in the range of heat flux density up to q(e) = 35 W cm-2. Along the convective pool boiling regime, a linear relationship between the interface overtemperature, T(w), and q(e) has been observed, with a value of the heat transfer coefficient h = 1.3 W cm-2 K-1. In the nucleate regime, the q(e) dependence on T(w) follows quite well a power law, with an exponent close to 0.7. In the low heat flux regime (q(e) less than or similar to 5 W cm-2), the heat transfer curve shows a double hysteresis, which seems to be closely related to the porosity of the samples.