For testing the scaling laws, a two-phase natural circulation loop as shown in Fig. 11 was constructed. The loop was made of 50 mm NB (2” Sch 80) pipes except for the separator which is 150 mm NB (6” Sch 120) pipe. The separated steam is condensed and the condensate is returned to the separator. The vertical heater is direct electrically heated with a high current source. The loop was extensively instrumented to measure temperature, pressure, differential pressure, level and flow rate. Further details of the loop are available in Naveen et al. (2000). Prior to the actual experiments, pressure drop across one pipe segment was measured under forced flow conditions. This gave the following equation for the friction factor

f = 0.05042/Re003768 (38)

FIG. 11. Experimental two-phase FIG. 12. Steady state flow in a two-phase natural natural circulation loop. circulation loop.