Chemodynamic Cycles

The ribbon dips into seawater on one side, and dips into freshwater on the other side. The ribbon can take up only freshwater, but not the salt. With the movement the ribbon stretches and contracts due to the different swelling in the seawater and in the freshwater. The ribbon stretches in freshwater and contracts in seawater. A machine, which exemplifies such a process, is shown in Fig. 9.7. 

We idealize the steps We identify the chemical potential of the water in the volume as fi. As in other cycle processes we index 1 for the lower and 2 for the higher chemical potential. We do that here exceptionally. Otherwise, the index is always used in order to designate the material concerned. 

We could point out the essential steps in another way, if we consider a ribbon with a weight hanging on the lower end. It is then immersed in the freshwater. Then we change the weight and dive into seawater. Then we change again the weight 

In the /u. — n diagram again a rectangle results. Altogether the seawater is diluted by freshwater, and some power energy is generated. If we dilute the seawater by simply pouring in freshwater, then only the entropy of the system would increase. With the machine, the dilution becomes possible only under achievement of power work. As a result of the different tension at both rollers different torques arise codl and the system delivers mechanical work. In principle, the chemodynamic process dilutes the seawater. The dilution does not take place now simply via the addition of freshwater into the seawater, but that process uses the dilution work. By the way, the reversal of the process effects the production of freshwater. 

We examine the energetic situation now more exactly. The energy of the ribbon can be written down as 

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The advantage of this treatment is that the total mol numbers are constant. We can then easily deal this reaction as a chemodynamic cycle. If in a combustion process the mol numbers are changing, then it is more advantageous to use the masses instead of the mol numbers. In the view of a chemodynamic cycle a combustion engine is still a four-stroke engine, but the meaning of the individual processes is different in comparison to those what a technician would explain ... 

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