venient X-ray viewing of boiling and condensing flow patterns. The X-ray apparatus could scan the loop from the boiler inlet through the condenser exit.

As indicated in figure 5, a closed-circuit television monitor was used with the X-ray system. A remote control arrangement was used to scan and select views of the loop. The television monitor served as a guide. The X-ray system included an electronic image amplifier and a motion picture attachment.

Details of Construction

The details of the boiler, superheater, and vapor throttle construction are described in the following paragraphs. In designing these components, particular attention was paid to making them easy to view with the X-ray system.

The boiler-superheater component consisted of a single length of tube with a 1/4-inch (0.63-cm) outside diameter and a 0.020-inch (0.05-cm) wall thickness. The boiler-superheater tube was 115 inches (292 cm) long and had a swaged helical groove along its entire length. The first 90 inches (228 cm) constituted the boiler. The superheater was a curved section beginning a few inches beyond the boiler outlet (figs. 1 and 2).

Typical helically swaged boiler sections are shown in figure 6. The pitch of the helix was 1/8 inch (0.32 cm), and the inside diameter of the groove was slightly greater

than 1/8 inch (0.32 cm). After swaging, the depth of the groove in the first 12 inches (31 cm) of the boiler was about 0. 03 inch (0.08 cm), and thereafter the depth of the groove was about 0.02 inch (0.05 cm). This change in depth and character of the groove is seen by comparing figures 6(b) and (c), and it may have been a factor affecting the flow pattern observed in this region.

The inlet of the boiler contained a 6-inch- (15-cm-) long, 1/8-inch- (0.32-cm-) diameter cylindrical insert. The insert fit tightly inside the swaged boiler tube (fig. 7) so that a helical channel was formed.

The boiler had three independently heated zones. The preheater and superheater were also independently heated. Electrical resistance heater elements were used to heat each of the five separately heated zones from the preheater through the superheater (fig. 1). Each heater element was made of strips of a nickel-chromium alloy ribbon. Each strip was formed into a half cylinder, and the half cylinders were clamped around the loop tube, as shown in figure 8. Alumina spacer rings were used to separate these tubular heater elements from the loop tube. Several layers of thermal insulation of quartz fiber and ceramic were applied over the heaters. Additional layers of quartzfiber blanket insulation were added over those shown in figure 8.

Figure 8. Cutaway mockup of insulation and electric heater element used to heat loop boiler-superheater.

The vapor throttle was a metallic, weld-sealed needle valve. The inlet tube extended into the expansion chamber so that the throttling orifice was surrounded with an expansion space (fig. 9(a)). As seen in figure 9(b), the throttle configuration permitted an X-ray silhouette of inner parts surrounding the orifice. Sufficiently dense fluids (i.e., liquid carryover and droplets) could be observed flowing through the throttle. The throttle was thoroughly covered with a thick layer of quartz-fiber insulation and was heated only