Thermodynamic chemical heat pump

The use of AB5 hydrides as chemically or thermally driven heat pumps is intriguing (6). Since two different AB5 alloys are involved, the relationship between their respective hydrogen decomposition pressures, as a function of temperature, is the key parameter that determines the thermodynamics of heat pump action. 

Figure 3. Three examples of chemical heat pump thermodynamic relationships...

Metal hydrides that have a linear dependence of In P vs 1/T can be used in chemical heat pump systems. General equations were developed to relate the thermodynamic variables of the hydrides to the chemical heat pump operating temperatures. A series of hydrides with variable thermodynamic properties were prepared from alloys of composition LaNi5-x Alx (x = 0-1.5). 

Orgaz, E., Dantzer, P. (1987) Thermodynamics of the hydride chemical heat pump III. Considerations for multistage operation, J. Less-Common Met., 131, 385-398. 

CC12FCC1F2. These compounds are non-toxic and non-flammable, and their thermodynamic properties are ideally suited for the compression/ expansion cycle in cooling and heat pump appliances. However, CFCs are chemically very inert, so when they are vented into the atmosphere, they do not react with atmospheric constituents. They diffuse unscathed first into the troposphere, then penetrate slowly into the stratosphere. There, the solar UV radiation photodissociates these compounds, liberating free chlorine atoms (the C-Cl bond is weaker than the C-F bond). The chlorine atoms react with atmospheric O3 to form chlorine oxide, which in turn reacts with atmospheric atomic oxygen regenerating chlorine atoms ... 

In spite of heat being continuously dissipated, the system is in a stationary state both dynamically and thermodynamically. From a thermodynamical point of view, the stationary state is maintained because by energy constantly pumped into the system by adding new molecules into the high concentration compartment and removing them from the low concentration one. Finally, due to the constant molecule flow and heat dissipation, the achieved stationary state is not compatible with chemical equilibrium. 

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