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INTRODUCTION 



Under the sponsorship of the Naval Sea Systems Command, the Civil 

 Engineering Laboratory (CEL) has been engaged in the development of an 

 experimental diver heater. The project objective is to develop a 

 compact, portable, self-contained energy source capable of supplying 

 heated water to a closed-loop circulation garment worn by the diver. 

 Circulation garments and associated thermal protection gear are under 

 development at the Naval Coastal Systems Laboratory (NCSL), Panama City, 

 Florida. Basic requirements for the heater include operation in 28 F 

 (-2°C) seawater at depths of 1,000 feet (305 m) for up to 8 hours without 

 replenishment. Experimental models of 8- and 16-kWh (28.8- and 57.6-MJ) 

 capacity were developed and laboratory tested. In addition the 8-k.Wh 

 (28.8-MJ) unit was successfully diver-tested, proving the feasibility of 

 the magnesium/seawater heat source. 



BACKGROUND 



Divers exposed to cold water for extended periods of time require 

 thermal protection equipment to maintain acceptable physiological 

 conditions and operational effectiveness. The overall heating problem 

 is that of maintaining the diver's normal thermal balance. The amount 

 of heat required varies with environmental factors, such as water 

 depth, breathing gas type, water temperature, and duration of exposure, 

 and with individual factors, such as physical condition, metabolic rate, 

 and activity level. Thermal balance can be expressed by the simplified 

 equation: 



Heat Replacement = Respiratory heat loss + diving suit loss 

 - metabolic heat generated 



Respiratory losses are due to involuntary heating of inspired gas to 

 body temperature prior to expiration. The amount can be up to about 500 

 watts [1] depending upon the specific heat, density, volume, and tempera- 

 ture of the inspired gas. Diving suit losses vary with depth, type of 

 suit, suit material, and water temperature. The values range from 3,000 

 watts for the standard 3/8-inch (9.5-mm) thick neoprene wet suit [19 ft^ 

 (1.75m*) surface area] at 1,000-foot (305-m) depth with a skin-to-seawater 

 temperature difference of 50°F (28°C), to 1,000 watts for a dry suit 



