Heat transfer from a plane surface to a saturated He II bath is studie
d up to and beyond the critical heat flux density q inducing film boi
ling. The experiments were performed with two similar test cells, deno
ted 1 and 2. Test cell 2 consists mainly of four OFHC copper rods heat
ed at their top extremity and equipped each with three calibrated carb
on resistors for in situ measurement of the thermal conductivity k(Cu)
(T). Three of these test specimens are equipped with specially develop
ed surface thermometers. The measured Kapitza conductance at high heat
flux (q less than or equal to 5 x 10(4) W m(-2)) as well as k(Cu) ver
sus T data (temperature range 2-6 K) presents a good reproducibility b
etween the four samples tested. The heat transfer characteristics were
recorded at T-bath = 1.8 K for different immersion depths H-0 of the
heat transfer surface and the results are discussed. We also report on
the experimental q versus H-0 data. These data measured on both test
specimens either equipped or not equipped with surface thermometers,
show a strong dependence of q on the sample surface cooling condition
s. (C) 1997 Elsevier Science Ltd.