The scaling laws presented in section 3 are tested against experimental data for both steady state and stability behaviour.

5.1. Steady state behaviour of single-phase natural circulation

The steady state scaling laws were tested with data obtained from simple low pressure and high pressure loops. The data included both in-house experimental data and those compiled from literature.

5.1.1. In-house data

For testing of the scaling laws, experiments were carried out in three uniform diameter rectangular loops with horizontal heater and horizontal cooler (Vijayan et al. (1992)). These loops (see Fig. 3) had the same length and height but different internal diameters. These experiments helped to establish the adequacy of Grm/NG as the scaling parameter for the steady state flow as the data from the three loops could be expressed in the form of Eq. (14) with the same value of C and r. Subsequently, experiments were conducted to study the effect of the orientation of the heater and the cooler as different types of nuclear reactors have different orientations of the heat source (core) and the heat sink (steam generator). For example, PHWRs have horizontal core and vertical steam generators, PWRs have vertical

core and vertical steam generators and WWERs have vertical core and horizontal steam generators. In view of this, the heater and cooler orientations studied included the horizontal heater horizontal cooler (HHHC), horizontal heater vertical cooler (HHVC), Vertical heater horizontal cooler (VHHC) and vertical heater vertical cooler (VHVC). Further details of the experimental loop (see Fig. 4) and data generated can be obtained from Bade (2000) and Vijayan et al. (2000). The steady state data collected for different orientations of the heater and cooler are plotted without and with consideration of local pressure losses in Figs. 5a and b respectively. The experimental data is observed to be very close to the theoretical correlations for all orientations of the heater and cooler confirming the validity of the correlations (15) and (16). Considering the local pressure losses improves the agreement with the theoretical correlations (see Fig. 5b).

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FIG. 3. (left) Uniform diameter loops with different external diameters & identical lengths. FIG. 4. (right) Experimental loop to study the effect of orientation.

Subsequent to this, experiments were carried out in the high pressure nonuniform diameter figure-of-eight loop FISBE (Facility for the Integral System Behaviour Experiments, see Fig. 6), which simulates the Narora Atomic Power Station. Steady state data from FISBE are compared with the present correlation in Fig. 7, which shows good agreement. It may be noted that for these tests the loop was an all pipe loop with a tubular heater section, a single U-tube steam generator and pumps replaced by pipe sections. Since the SG used only one U — tube, more than 95% of the loop hydraulic resistance was due to this. Although the loop had several elbows, bends, Tees and other fittings, these were mainly concentrated in the large diameter pipe sections. Hence the contribution of the local pressure losses to the total hydraulic resistance became negligible giving good agreement with the turbulent flow correlation.