- -.-'- -— .'.---"r,,,.. 



filled with helium under the same conditions [2].* The metabolic heat 

 generated varies with individual activity level and physical condition 

 and ranges from near zero for inactive divers to as much as 500 watts 

 for sustained heavy work periods. To insure adequate heat would be 

 available to maintain thermal balance under extreme conditions, an 

 initial program goal of 2,000 watts was selected as the heater output. 



Heating is required both for tethered and self-contained divers. 

 The present method for heating the tethered diver is to supply hot water 

 via an umbilical hose from the support platform (surface ship, PTC, 

 etc). The hot water is flushed over the diver's body under his diving 

 suit and then exhausted directly to the surrounding environment. In 

 this case, the physical size and weight of the heat source is not 

 critical, since it is not carried by the diver. However, because of 

 both the high heat losses in hoses and the open-circuit design, the 

 system is grossly inefficient. In addition, the hot water umbilical 

 greatly restricts the diver's mobility. 



For the free- swimming diver, thermal protection is not easily 

 provided. Since the heat source must be carried on his person, it must 

 be lightweight and compact and not impair his mobility. In addition it 

 must be simple, safe, and reliable. 



In the past, several methods of providing heat for free- swimming 

 divers have been investigated [3-11]. The resulting systems have 

 exhibited several disadvantages: batteries are heavy, bulky, expensive, 

 and short-lived; nuclear sources can be used by the diver only for short 

 durations because of radiation exposure, and the radiation shielding and 

 thermal safety devices make the nuclear heater bulky and complicated; 

 and most thermochemical heat sources employ axotic reactants and involve 

 high operating temperatures and complicated control systems. 



A compact, lightweight, high-energy density, easily controlled, 

 reliable, safe heat source that can be integrated with closed-circuit 

 hot water suits is vitally needed. To this end, CEL has been investi- 

 gating the development of a heater that utilizes the reaction of a 

 magnesium alloy with seawater to produce heat. 



HEAT SOURCE DEVELOPMENT 



Background 



The oxidation reaction of magnesium was chosen for the heat source, 

 because it is simple, reliable, compact, and inexpensive, and has a 

 comparatively high-energy density. A comparison of the CEL-developed 



Ongoing research being conducted at NCSL in thermal 

 protection suits is expected to produce significant 

 improvements in this area. 



