Beatirg Systems 



As was mentioned in the sectica describing uses o* metal-hydride 

 storage, the heat needed to desorb hydrogen from the hydride can be 

 supplied by exhaust gases and cooling water if the hydrogen is used in a 

 combustion process; or it can be provided by burning some of the hydro- 

 gen. The following analyses consider only the thermodynamics of the 

 probless. The full design of heat exchangers has not been attempted ..ue 

 to the lack of information concerning the chemical interactions of the 

 hydrides with other metals, the density and thermal conductivity of civ 

 metal hydrides, and the necessary pressures and temperatures needed to 

 provide desirable kinetics of absorption and desorption. 



In considering using heat derived from the exhaust o'-ses and cool- 

 ing water, certain assumptions Bust be made. If the end use of the 

 hydrogen is in an internal combustion engine, a fair assumption is that 

 30Z of the energy derived from burning the hydrogen will be lost in the 

 exhaust gases and 302 will be lost through the cooling system. Repre- 

 sentative temperatures for these systems are 1,400 F at the exhaust 

 manifold and 180 F at the cooling water exit from the engine. 



Two methods of heating the hydride have been considered. In the 

 first, fluids are allovcd to blow over and around tubes containing the 

 hydrides to accomplish the heating and cooling requirements. In the 

 second, the tubes containing the hydrides are closely packed and hydro- 

 gen circulating through the hydrides perforas the heating and cooling 

 requirements . 



Figure 8 shows these concepts nore clearly. The first concept i= 

 shown in Figure 8a. The hydride Is scored in tubes (I) which provide a 

 containment capable of withstanding the pressures required during 

 absorption of the hydrogen. The tubes are closed at one end and open 

 at the other. The open ends are fixed to a tube plate (II). On the 

 other side of the tube plate a doted cavity (III), designed to withstand 

 the necessary pressures, provides a collection space for the hydrogen. 

 A valved tube passing through the dome provides the entrance and exit 

 port for the hydrogen. Hot gases or liquids can be passed through po_ts 

 (IV) in the thin shell surrounding the tubes. The hot gases or liquids 

 are then passed over and around the tubes in several passes guided by 

 baffles. The heat from the gases or liquids flow through the tubes to a 

 cooler hydride which upon absorption of the heat releases hydrogen. The 

 hydrogen then ic allowed to collect in the domed cavity at a pressure 

 slightly above atmospheric from which it is ejected into the engine. 



In the second concept (Figure 8b), the hydride is again contained 

 In tubes which provide the necessary pressure containment. In this 

 concept, however, i.^z fuoes are packed close together, thus reducing the 

 size of thf». hydride containment component. The heat transfer is accom- 

 plished by hydrogen which is pumpej through the hydride. Trie hydrogen 

 is heated or cooled in a heat exch u*.^er as the need .irises. During 

 times when hydrogen must be withdrawn ; roc, the hydride, heat is supplied 

 to the hydrogen--from the exhaust go .••: , ; •-■rhaps. Ti«?n the hot hydrogen 



35 



