in five of the 12 modules. This was observed as an excess electrical load 

 and, while none of the heating elements burned out, they were replaced 

 with new units, and precautionary venting was provided. None of the data 

 included in this report are of tests with defective wet insulation in 

 the heating elements. 



DISCUSSION OF RESULTS 



The entire point of the experiment was to validate the capability of 

 the module design to dissipate the required heat, measured electrically, 

 and to provide low temperatures at the locations of thermocouples Ml, 

 M2, and M3 ivhich are on the surface where they would be in intimate 

 contact with the cold junctions of the thermoelectric units in the actual 

 RTG. The results are tabulated in Tables 1 through 8. A run consisted 

 of adjusting the electrical input to the desired value and observing 

 temperature rise until the inner temperatures were stabilized. Because 

 of the rapid cooling of the seawater, the high thernal diffisivity of 

 the copper fins, and the small mass of the water-alcohol mixture contained 

 in the heat pipes, temperature stability was typically achieved in about 

 an hour from cold start-up and even more rapidly with minor adjustments 

 in power input. To insure stability, a typical run consisted of a 1-1/2 

 to 2-hour stabilization periou, followed by taking a single set of read- 

 ings. 



With the exception of failure of the C-rings containing the alcohol- 

 water mixture as discussed above, there were no observed irregularities 

 nor unexpected temperature anomalies. 



While the nominal required heat input to the 12-module experiment 

 was 28 kw total, some tests are for a higher power dissipation, 32 kw. 

 This is slightly over the design heat load, so that the maximum temper- 

 atures recorded are somewhat higher than the values which might be expected 

 in a newly fueled RTG deployed in deep-ocean water at, say, 40°F ambient 

 seawater temperature. The temperatures as recorded in the tank tests are 

 shown in Tables 4 and 5. 



An appreciation for the linearity of the metal temperature changes 

 with change in ambient seawater can be obtained from Table 6, which gives 

 both the temperatures of the lead-filled single module at two water 

 temperatures, and the differences. With a difference :"n water temperatures 

 of 35°F, no measured temperature differences greater than 48°F were 

 observed. The most important single temperature, because it is physically 

 closest to the base, is T6. For this location, dropping the water temper- 

 ature by 35°F caused a metal temperature drop of 43 F, a conservative 

 development in assessing the eventual consequence of immersing a full- 

 scale RTG in very cold, deep -ocean water. 



Summarizing the results shown in Tables 7 and 8,' there was no evidence 

 under any of the conditions of test of poor flow to and around the modules 

 which cause excessive temperatures or poor cooling. The effect on the 

 inside metal temperatures, those seen by the thermo-electric nodules, of 



