EXPERIMENTAL HEATER DEVELOPMENT 



To demonstrate the feasibility of using the magnesium- iron couple 

 as a self-contained heat source, two experimental heater models were 

 developed. A 16-kW-hr model (Figure 21) was designed to provide 2,000 

 watts for 8 hours. The second unit, an 8-kW-hr model (Figure 22), 

 was designed to provide 1,000 watts also for 8 hours. The discussion 

 below refers in detail only to the 8-kW-hr heater, since it was developed 

 last and incorporates improvements over the 16-kW-hr heater. However, 

 important differences between them are discussed. 



Operation 



The magnesium-iron dual-plate cell is contained in the insulated 

 case shown schematically in Figure 23. The heater is activated by 

 flooding the case with seawater. Heat, hydrogen gas, and magnesium 

 hydroxide are produced by the reaction. A heat exchanger immersed in 

 t&e electrolyte transfers the generated heat to a second fluid that is 

 circulated to the diver. Hydrogen gas is continuously vented through a 

 valve that maintains a small overpressure within the case. This pres- 

 sure drives a small amount of the slurry out through an economizer heat 

 exchanger. Fresh seawater is pumped counterf low through the economizer 

 to recover the heat from expelled hot slurry. The slurry and seawater 

 exchange maintains the electrolyte pH and density relatively constant. 



Heater Case 



The heater case provides thermal insulation, neutral buoyancy, 

 and protection for the heater components. It is constructed of syntac- 

 tic foam sandwiched between inner and outer fiberglass shells. The foam 

 provides buoyancy and thermal insulation, while the fiberglass provides 

 mechanical strength. Overall wall thickness for the case is 5/8 inch 

 ran two sides and top and 3/4 inch on the two remaining sides. Heat 

 loss through the case walls with a 106 F (59 C) temperature differential 

 was found to be approximately 90 watts. 



The case is built in two separate sections (Figure 22). The upper 

 case contains the heat source, electrolyte, electrolyte/suit-water heat 

 exchanger, hydrogen vent valves, and an economizer heat exchanger. The 

 lower case houses the pumps, motors, monitoring electronics, and inter- 

 connecting plumbing. The upper case is sealed, while the lower case is 

 free- f lood ing . 



The seal between the upper case and the environment is an 0-ring 

 placed against a flat rubber gasket. Sealing pressure is provided by 

 six plastic cam latches. The overall outer dimensions for the 8-kW-hr 

 case are 8 x 8-1/2 x 14-1/2 inches (20 x 22 x 37 cm). The case weighs 

 11 pounds (5 kg). The 16-kW-hr heater measures 7-1/4 x 7-1/2 x 21-3/4 

 inches (18 x 19 x 55 cm). 





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