The heat transfer surface for ultraviolet experiments is coated by a TiO 2 thin film by
a sputtering process in Kyushu University. The surface for γ-ray experiments is
polished with #400 emery paper and then heated in air at 200
C for 1 h. After the
thermal oxidation of the copper surface, it is irradiated in the
60 Co facility where the
integrated dose is 220 kGy. The irradiation conditions for heat-transfer experiments
are summarized in Table 10.1.
10.3.2 Results and Discussion
Measured boiling curves with and without ultraviolet irradiation are shown in
Fig. 10.6. Calculated lines denote existing correlations for nucleate boiling [12–14]
and critical heat flux [15, 16]. As shown in this figure, the boiling curve after
irradiation moves to the higher wall superheated side in the nucleate boiling region,
which may be caused by inactivation of nucleation sites on the heat transfer surface
resulting from hydrophilicity. In this experiment the maximum heat flux after the
Fig. 10.5 Schematic of experimental apparatus
Table 10.1 Irradiation
conditions
Irradiation source
Ultraviolet
γ-ray
Surface material
TiO 2
Copper oxide
Irradiation condition
3 mW/cm
2
, 30 min
220 kGy
100
D. Ito et al.