**3.2.1 Air-water fluid mixing test**

TPFIT code was applied to 2-channel air-water mixing tests (Yoshida, 2007). The dimension of calculated test channel is shown in Fig.10 (a). The test channel, which consists of two parallel subchannels with an 8×8 mm square cross section and the interconnection, is 220 mm long and air and water flow upwards in it. The interconnection's gap clearance, horizontal and vertical length are 1.0 mm, 5.0 mm and 20 mm respectively. An irregular mesh division in the Cartesian system was adopted and two subchannels and the interconnection were formed by using obstacles as shown in Fig.11. The total number of effective control volumes was 428,680 respectively. The fluid mixing was observed at interconnection in the experiments. A non-slip wall, constant exit pressure and constant inlet velocity were selected as boundary conditions for each subchannel. The time step was controlled with a typical safety factor of 0.2 to keep it lower than the limitation value given by the Courant condition and stability condition of the CSF model. Calculation conditions are shown in Table 3.

Development of Two-Phase Flow Correlation

and 0.094cc in the calculation.

interconnection.

each subchannel.

for Fluid Mixing Phenomena in Boiling Water Reactor 299

moved bubble volumes from Ch.1 to Ch.2 were estimated to be 0.087cc in the observation

Fig. 12. Observed and calculated slug behavior of air-water fluid mixing test around the

Fig. 13. Calculation meshes in channel cross section for steam-water fluid mixing test.

The TPFIT was applied to steam water fluid mixing test (Yoshida, 2007). Calculated test channels used in these simulations are shown in Fig.10 (b). The calculation conditions are shown in Table 4. An irregular mesh division in the Cartesian system was adopted and two subchannels and the interconnection were formed by using obstacles as shown in Fig.13. The total number of effective control volumes was 2,647,400 respectively. A non-slip wall, constant exit pressure, and constant inlet velocity were selected as boundary conditions for

**3.2.2 Steam-water fluid mixing under high pressure** 

Fig. 10. Calculated test channel.

Fig. 11. Calculation meshes in channel cross section for air-water fluid mixing test.


Table 3. Air-water flow calculation condition.

The slug behavior observed around the interconnection is shown in Fig.12 (a). Once the top of an ascending air slug in Ch.1 reaches the center height of the interconnection, part of it starts to be drawn toward Ch. 2. Then the tip of stretched part of the air slug flows into Ch.2 through the interconnection and is separated to form a single bubble. The calculated air slug behavior is shown in Fig.12 (b). As shown in Fig.12 (b), any intrusion of air into the interconnection as well as any separation of the air slug can be effectively calculated. The

Fig. 11. Calculation meshes in channel cross section for air-water fluid mixing test.

Water inlet velocity (m/s) Injected air volume (cc) Ch.1 Ch.2 Ch.1 Ch.2 0.26 0.26 1.27 1.50

The slug behavior observed around the interconnection is shown in Fig.12 (a). Once the top of an ascending air slug in Ch.1 reaches the center height of the interconnection, part of it starts to be drawn toward Ch. 2. Then the tip of stretched part of the air slug flows into Ch.2 through the interconnection and is separated to form a single bubble. The calculated air slug behavior is shown in Fig.12 (b). As shown in Fig.12 (b), any intrusion of air into the interconnection as well as any separation of the air slug can be effectively calculated. The

Fig. 10. Calculated test channel.

Table 3. Air-water flow calculation condition.

moved bubble volumes from Ch.1 to Ch.2 were estimated to be 0.087cc in the observation and 0.094cc in the calculation.

Fig. 12. Observed and calculated slug behavior of air-water fluid mixing test around the interconnection.
