FULL-SCALE PROTOTYPE EXPERIMENT 



! 



Following successful verification of the design to this point using 

 the single lead-filled module (which for purposes of this report is not 

 considered to be a valid experiment, but a design device), 12 full-scale 

 modules made of solid copper were fabricated (Figure 13). Details of 

 fabrication are shown in Figure 14. In effect, each of the 12 copper 

 modules is a small boiler or upper terminus of a heat pipe heated by 

 three electrical immersion heaters of 1,000 watts nominal rating each. 



To allow the use of fins of copper, the best material, and at the 

 same tiiae allow fabrication at reasonable cost, stubby rectangular fins 

 were used. Further, this was necessary to avoid interlocking of the 

 fins on the tight circle prescribed by the design; the loss of the extra 

 area had negligible effect on the base temperatures as will be shown 

 later. When the complete RTG is built, there may be a small advantage 

 in using the complex, higher fins--that is, longer in the radial direc- 

 tion, Figure 2. This would require either interlocking the fins or 

 increasing the diameter of the major circle on which the 12 modules are 

 mounted. A close-up view of the copper heat rejection modules is shown 

 in Figure 15, and an underwater view of the completed experiment with 

 instrumentation as tested in CEL's 60,000-gallon tank of seawater in 

 Figure 16. 



All temperatures were read from a manually balanced, direct reading 

 portable Leeds and Northrop potentiometer, with a rapid-response electronic 

 mil 1 aeter. The calibration allowed reading to within 1/2°F, and esti- 

 mating somewhat more closely. Thermocouple locations are shown in Figure 

 17. 



Tests of the full-scale device, Figures 11 and 16, were conducted 

 in ambient temperature water in the vertical position as shown and at 

 30 and 60 degrees from the vertical, without and with a protective shroud 

 which counted in the four 1/2-inch holes which can be seen adjacent 

 to the nodules, Figure 13. 



The very large volume of water in the tank made it impracticable 

 to reduce the ambient water temperature appreciably with ice without 

 incurring excessive cost and reducing the salinity. One loading of ice 

 was used, and the data are identified in the tabulation of results. The 

 freshwater tended to stratify on the surface as the ice melted because 

 of its lack of salinity. An effort was made to stir the water in the 

 tank, with uncertain results. The normal temperature gradient in the 

 tank from top to bottom was measured at about 2 F. 



The only irregularity in experimental procedure occurred when the 

 complete experiment was left in the seawater test tank over a weekend. 

 The single-module lead-filled prototype had as a precaution been vented 

 to avoid pressure build-up in the event of insufficient heat transfer. 

 Provision was made for venting on the full-scale experiment, but the 

 holes were plugged as a simplification, inasmuch as no pressure build- 

 up had been observed in the first prototype. Apparently a faulty 0-ring 

 sealing the water-alcohol mixture allowed leakage past the heater elements 



