Heat Production System 



The heat source, which weighs 10 pounds (4.5 kg), consists of a 

 series of cells (Figure 2) bolted (shorted) together. Twenty magnesium 

 anodes 5-7/8 x 7-3/8 x 1/8 inch thick (14.9 x 18.7 x 0.32 cm) and 21 

 steel cathodes 0.010 inch (0.026 cm) thick are spaced at an electrode 

 gap of 0.060 inch (0.152 cm). The electrode gap is fixed by copper 

 spacer washers that also serve as electrical current paths between 

 adjacent electrodes. Copper washers are used to minimize local reaction 

 on the anode.* 



With the above cell construction the starting power density in 

 140 F (60 C) electrolyte is approximately 1 W/in. 2 of magnesium surface 

 area (0.155 W/cm 2 ), which gives a total initial power for this cell of 

 1,800 watts. At the end of 8 hours, the power density decays to about 

 0.6 W/in. 2 (0.093 W/cm 2 ), which provides the required 1,000 watts. The 

 decay is primarily due to increased electrode gap resulting from anode 

 consumption. 



An important part of the heat production system is maintenance of 

 the electrolyte and disposal of reaction products. Hydrogen must be 

 continuously vented to prevent overpressurizing of the case. The 

 hydrogen vent system is designed to provide an electrolyte overpressure 

 of 1 psi (6.9 kPa) that is used to expel the spent electrolyte slurry at 

 a rate of 0.026 gal/min (100 ml/min) through the economizer. Since the 

 diver's orientation is constantly changing, the gas vents must be located 

 on all corners of the case. In this model, the hydrogen vents are 

 relief valves that are set at 1 psi (6.9 kPa) over ambient and are 

 equipped with neutrally buoyant rubber flapper valves (Figure 24). In 

 the presence of hydrogen, the flappers open, which allows the gas to 

 escape through the relief vaive. With water present, the flappers close 

 to prevent hot electrolyte from being expelled to the environment. 



A hydrogen-permeable membrane was explored for ventilating the 

 hydrogen. Nonwettable porous Teflons and other synthetic materials were 

 tested. The porous Teflon adequately vented the hydrogen with the 

 required overpressure in clean seawater, but it was subject to pore 

 clogging in the presence of magnesium hydroxide. Further investigation 

 is necessary to find a noncloggable hydrogen-permeable membrane. 



The economizer heat exchanger (Figure 25) is mounted within the two 

 thick sides of the heater case. The seawater /magnesium hydroxide 

 slurry passes through the copper tubing. The 0.18-inch (0.46-cm) 

 inside diameter and the 17- foot (5. 2- in.) length of the tubing were 

 sized to provide a continuous discharge of 9.5 cu in./min [(150 ml/min) 



Local reaction around similar steel washers causes the 

 anodes to prematurely corrode through, which separates 

 the main portion of the anode from the short circuit 

 paths. 



13 



