MEASUREMENTS OF POOL BOILING HEAT-TRANSFER FROM CERAMIC Y1BA2CU3O7-DELTA WITH DIFFERENT COATING TO LIQUID-NITROGEN

We present measurements of pool boiling heat transfer from ceramic Y1B a2Cu3O7-delta (YBCO) samples to liquid nitrogen for low heat flux dens ities, q(e), up to 9 W/cm(2). To analyze the influence of the surface treatment on the heat transfer characteristics, some of the samples we re coated with a Ag film that closes most of the microchannels at the surface. We observed that the heat transfer process is less effective for the coated samples, so circulating fluid within the superficial mi crochannels may have a non negligible role in the refrigeration mechan ism of these materials.