328 ENGINEERING EVALUATION 



The poor performance of the dehumidifiers was not anticipated, but is attributed largely to 

 inadequate cooling capacity. The specific heat of the Sealab II mixture of oxygen, helium, and 

 nitrogen at approximately seven atmospheres pressure is about 32 times that of air at sea 

 level (Appendix C). Hence, a much larger amount of heat must be removed from the Sealab II 

 mixture than from air at the same temperature to effect the same dehumidification. The fact 

 that the Sealab atmosphere was approximately six times as conductive as air tended to offset 

 this difficulty but could not remedy it altogether. Other factors such as film coefficients and 

 the dew point of the Sealab II atmosphere also tended to offset the specific -heat effect, but the 

 extent is not known. 



The relative humidity was reduced considerably by the use of an automatic coffee urn for 

 heating water for beverages rather than open pots. The radiant heaters in the entry area were 

 turned off at night to reduce evaporation of sea water. 



The atmospheric circulation and distribution system was not adequate and contributed to 

 the dehumidification problem. A higher flow rate and improved distribution of the atmosphere 

 would have lessened the buildup of humidity in the berthing and galley areas and would have 

 improved the evaporation of perspiration. Better moisture distribution should have permitted 

 more uniform and efficient operation of the dehumidifiers. 



The performance of the carbon dioxide filter was acceptable but was somewhat less than 

 satisfactory. Each set of lithium hydroxide canisters provided for only about 400 man-hours 

 of operation rather than the design figure of 540 man-hours (75 percent saturation). This limi- 

 tation aggravated an already severe handling and storage problem aboard Sealab II. A total of 

 291 canisters of LiOH (1700 pounds) were used for 427.5 man-days of operations. One pound 

 of LiOH should absorb one pound of CO 2. The average rate of production of CO 2 is approxi- 

 mately 0.10 pound per man hour, or 2.4 pounds per man day. Hence, the efficiency of absorp- 

 tion in the canisters was only 



428 man-days x 2.4 lb C02/day 

 100 ^ 1700 lb CO 2/1700 lb LiOH = 60 P^^^^^t. 



The charcoal filters seem to have operated satisfactorily, since objectionable odors were 

 not evident. These filters were well overdesigned by normal standards in order to provide for 

 such anticipated but unknown quantities as high humidity, LiOH dust, internally vented sanitary 

 systems, and contaminants from cooking at the high ambient pressures. 



Heating System — The heating system performed exceptionally well. As can be seen from 

 Table A4, the baseboard heaters and radiant heaters 1 and 2 could have been omitted without 

 affecting the comfort of the Sealab. The radiant deck heating proved ideal for Sealab and pro- 

 vided a comfortable atmosphere. Radiant heaters 3 and 4, installed in the entry area, were 

 used primarily for quick warmup after outside excursions. It should be noted that the total 

 average heat requirement for Sealab II, approximately 60,000 Btu, was somewhat higher than 

 indicated by heater operation, since essentially all electrical power except exterior lights (17 

 kw average) was realized as sensible heat inside Sealab. 



Breathing-Gas Systems — The automatic oxygen system performed well, except that the 

 solenoid valve chattered when the oxygen level fell just below the mean control level. This 

 difficulty occurred during the first team's stay and was remedied by deenergizing the system 

 until the oxygen level neared the lower control limit. At this point the system would be re- 

 energized and allowed to replenish the atmosphere with oxygen to the upper control limit. 

 Since the cycle time for this procedure was from one to two hours, it was not considered a 

 major problem. The malfunction seemed to be caused by a faulty relay in the control system. 



During the third team's stay the pressure reducer failed, causing oxygen to be dumped 

 overboard through the pressure-relief valve. Since the spare regulator furnished did not have 

 the proper connections, the automatic system was secured. Subsequent oxygen input was con- 

 trolled using the manual system. In addition, the emergency system was utilized to replace 

 the lost oxygen from the surface. 



