[1–3], whereas a solid target such as tungsten or tantalum should be also developed
for a water-cooled ADS neutron source [4, 5].
High-energy radiation affects the surface wettability and boiling heat transfer of
the solid target. Wettability on a solid surface can be changed by using ultraviolet
radiation or γ-rays, and recently the authors have found that the surface wettability
can be also changed by proton-beam irradiation [6]. Applying the wettability
change resulting from ultraviolet irradiation to titanium dioxide (TiO 2 ), heat transfer research has been carried out to evaluate the wettability effect [7]. In addition,
radiation-induced surface activation (RISA) enhances the surface wettability by
irradiating a metal oxide layer with γ-rays. Takamasa et al. [8] have applied RISA
to heat-transfer experiments and reported that boiling heat transfer could be
enhanced by changing the wettability of the heating surface. However, there has
been no research to investigate surface wettability effect on boiling heat transfer at a
solid target cooling system, where microbubble emission boiling (MEB) [9] might
occur. MEB can take place when the heat transfer area is small (about 1 cm
2 ) with
subcooling conditions. In the target cooling system, the target should be cooled by
subcooled water, and the heat-transfer area can be small when the proton beam is
focused to a small area. Thus, MEB should be investigated for thermal hydraulic
design and safety analysis of the solid target system, and also the effect of
wettability on boiling heat transfer should be studied.
The purpose of this study is to investigate wettability change by ultraviolet,
γ-ray, and proton beam and to study the wettability effect on subcooled boiling heat
transfer with a small heat-transfer area, and finally to obtain knowledge on the heattransfer mechanism of the MEB phenomena.
10.2 Surface Wettability Change by Irradiation
10.2.1 Sample and Irradiation Facility
To investigate surface wettability change by irradiation, samples are irradiated by
using an ultraviolet lamp, a
60 Co γ-ray source, and a proton accelerator. In this
study, a TiO 2 sample, which is a typical photocatalyst [10], is used to compare the
irradiation effects of ultraviolet, γ-ray, and proton beam. TiO 2 is prepared through
anodizing a 0.1-mm-thick titanium plate [11]. Details of the experimental procedure with TiO 2 samples and irradiation facilities are described as follows.
10.2.1.1 Ultraviolet
Ultraviolet irradiates TiO 2 by using a commercial UV lamp. Irradiation intensity is
measured by an ultraviolet meter and is controlled by changing the distance
between the lamp and the sample. The intensity is varied at a range from 0.01
96
D. Ito et al.
for a water-cooled ADS neutron source [4, 5].
High-energy radiation affects the surface wettability and boiling heat transfer of
the solid target. Wettability on a solid surface can be changed by using ultraviolet
radiation or γ-rays, and recently the authors have found that the surface wettability
can be also changed by proton-beam irradiation [6]. Applying the wettability
change resulting from ultraviolet irradiation to titanium dioxide (TiO 2 ), heat transfer research has been carried out to evaluate the wettability effect [7]. In addition,
radiation-induced surface activation (RISA) enhances the surface wettability by
irradiating a metal oxide layer with γ-rays. Takamasa et al. [8] have applied RISA
to heat-transfer experiments and reported that boiling heat transfer could be
enhanced by changing the wettability of the heating surface. However, there has
been no research to investigate surface wettability effect on boiling heat transfer at a
solid target cooling system, where microbubble emission boiling (MEB) [9] might
occur. MEB can take place when the heat transfer area is small (about 1 cm
2 ) with
subcooling conditions. In the target cooling system, the target should be cooled by
subcooled water, and the heat-transfer area can be small when the proton beam is
focused to a small area. Thus, MEB should be investigated for thermal hydraulic
design and safety analysis of the solid target system, and also the effect of
wettability on boiling heat transfer should be studied.
The purpose of this study is to investigate wettability change by ultraviolet,
γ-ray, and proton beam and to study the wettability effect on subcooled boiling heat
transfer with a small heat-transfer area, and finally to obtain knowledge on the heattransfer mechanism of the MEB phenomena.
10.2 Surface Wettability Change by Irradiation
10.2.1 Sample and Irradiation Facility
To investigate surface wettability change by irradiation, samples are irradiated by
using an ultraviolet lamp, a
60 Co γ-ray source, and a proton accelerator. In this
study, a TiO 2 sample, which is a typical photocatalyst [10], is used to compare the
irradiation effects of ultraviolet, γ-ray, and proton beam. TiO 2 is prepared through
anodizing a 0.1-mm-thick titanium plate [11]. Details of the experimental procedure with TiO 2 samples and irradiation facilities are described as follows.
10.2.1.1 Ultraviolet
Ultraviolet irradiates TiO 2 by using a commercial UV lamp. Irradiation intensity is
measured by an ultraviolet meter and is controlled by changing the distance
between the lamp and the sample. The intensity is varied at a range from 0.01
96
D. Ito et al.