Measurements of pool boiling heat transfer from ceramic Y1Ba2Cu3O7-δ superconductors to liquid nitrogen

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