HEAT-TRANSFER CHARACTERISTICS FROM A PLANE SURFACE TO A SATURATED HE-II BATH

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.