use in cold water can be designed to 

 minimize moisture condensation by in- 

 corporating thermal insulation or by 

 heating of the cannister. 



A variety of absorbent-bed configu- 

 rations are in use, and none seem to 

 have advantages that make them uni- 

 versally applicable. The principal de- 

 sign requirements are to provide an 

 adequate amount of absorbent, very 

 uniform distribution of gas flow 

 through the absorbent bed, and suffi- 

 cient time for the absorption reactions 

 to occur. 



The total weight of the absorbent 

 can be selected on the basis of the 

 total weight of carbon dioxide to be 

 absorbed. The volume of a tightly 

 packed absorbent bed will then de- 

 pend upon the absorbent density, and 

 the residence time will be the same for 

 any configuration of this volume. 



The pressure drop through an ab- 

 sorbent bed will depend upon the relor 

 tion of flow cross section and bed 

 depth for a fixed bed volume. A large 

 cross section and small depth will 

 result in low pressure drop. However, 

 flow distribution over the cross section 

 depends upon uniformity of pressure 

 drop, and may be difficult to control 

 if the bed is too thin. This difficulty 

 can be minimized by using a perfo- 

 rated plate at the inlet of the bed to 

 provide controlled pressure drop and 

 flow distribution. 



If bed volume is selected on the 

 basis of absorbent weight, then the 

 residence time of gas in the bed will be 

 proportional to the rate of ventilation 

 through the absorber. As a general 

 rule the volume flow rate through the 

 scrubber should be the same at all 

 depths, matching respiratory volume 

 characteristics." 



Reference (6) did not discuss potassium 

 superoxide as a carbon dioxide absorbent, 

 but Presti et al. (9) provided the results of a 

 design, development and testing program of 

 commercially available KOj for submersible 

 life support. The All Ocean Industries vehi- 

 cle is the only one known to use KO2 al- 



though its application vi^as tested and found 

 successful by the General Dynamics investi- 

 gators for STAR III. Mentioned earlier was 

 the ability of KOj to both supply oxygen and 

 absorb carbon dioxide. In brief, when cabin 

 air passes through the KOj bed the moisture 

 in the air reacts with the KOj to produce 

 oxygen and potassium hydroxide (KOH). The 

 KOH, a strong alkali, then absorbs carbon 

 dioxide. 



According to the authors, a KOj system 

 offers the following advantages: 



— It weighs less and occupies a smaller 

 volume 



— It costs less to operate 



— Stored properly, it has an indefinite shelf 

 life 



— It removes water from the atmosphere 



— Its color change (canary-to-white) can be 

 used as a depletion indicator 



— It will remove odors and trace contami- 

 nants and kill micro-organisms. 



On the other hand, Presti and his co-inves- 

 tigators admit to several disadvantages of 

 KO^: 



— An initial over production of oxygen can 

 occur 



— Caking or "mushing" and subsequent 

 plugging of the KOj bed can take place 



— KOj emits an irritating dust 



— It is a strong oxidizer and therefore 

 must be handled and used with care 



— It reacts very readily with water to pro- 

 duce oxygen and heat; with sufficient 

 heat, combustible materials can ignite. 



The authors, however, describe design and 

 handling methods to overcome the disadvan- 

 tages and offer test results to show KOj's 

 practical application in small submersibles. 



Another system, using a molecular sieve 

 solid absorbent which can be regenerated, is 

 planned for use in a submersible under con- 

 struction by Messrs. P. Dostal and J. Hair of 

 Alvin, Texas. In a personal communication 

 Mr. Dostal sketched the system shown in 

 Figure 9.6 and cautioned that it is only in the 

 design stage and, because of its complexity, 

 its use is speculative. The philosophy leading 

 to this system and its operation is described 

 by Mr. Dostal as follows: 



^'Originally, we had planned to use 



LiOH in the scrubber, which was caus- 



424 



