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186 S. Takahashi et ai

(D For the beam chamber side Q,/2 = h x A x AT

Q i    :    reąuired power for bakeout    (W)

Q₂    :    heat generated during NEG activation (W)

v    :    water velocity    (cm/s)

N    :    number of cooling channels    (—)

p : density (at 150°C)    = 0.916 kg/cnrⁱ

k : conversion factor    = 4.33 J/gK

A    :    heat transfer area    (cm²)

h    :    heat transfer coefficient    (W/cm²-°C)

= 0.023 (Re)^{0 S}(Pr)^{0 4} x )Jd AT: temperaturę differrence between heated water and channel’s wali of a chamber (°C) A : thermal conductivity (at 150°C)

= 0.587 kcal/m-hr-°C Pr : Plandtl number (at 150°C) = 1.15

The calculations give 7'₁ = 141.6°C and T_;J=145.3°C for y = 1.5 m/s and T'₂ = 150°C (see Fig. 2). As a result, AT’s for the pumping and beam chamber side are 0.30°C and 1.59°C, respectively. This means that the temperaturę of the chamber wali is almost the same as that of heated water. Thus the maximum thermal gradients of the chamber for the longitudinal direction and the transverse direction are 8.4°C/30m and 3.7°C, respectively. A total pressure loss for a system of one celi is about 1.01 kg/cm², and a reąuired flow is approximately 1000 Uh.

Figurę 3 shows a rough layout of a unit of HBS. At first, sińce the vapor pressure of water at 150°C

Thcrmo cou^ 'Tl    Ta cooiing

- ■    of rftaram chimbfr

Fig. 3. Diagram of the Heated Water Bakeout System.

is about 5.9 kg/cm²-G, the hydraulic pressure of hot water should be increased up to about 7 kg/ cm²-G. After that, to increase the temperaturę up to about 150°C, the water is transferred to the heater by a pump. A heat exchanger is used when the heater is overheated or in case of emergency. The heater power and the cooling valve will be adjusted to keep the temperaturę T, at a predeter-mined value.

We are planning to test and evaluate the performance of HBS, using a 5 m prototype straight chamber (Fig. 1).

References

1) H. Sakamoto, T. Bizen, S. Yokouchi, Y. Morimoto, T. Nishidono, Y.P. Lee, and S.H. Be: RIKEN Accel. Próg. Rep.. 23, 145 (1989).