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2017-06-21 daily note

1- I'm thinking about exergy, second law of thermodynamics, and of course reversibility. Few years ago (well, more than a few years) I was helping Maryam translating a biology paper (or a book chapter). The paper described the transport of nutrients and ions in from the blood stream into the human cells via the cell membrane and how important it is to have the right concentration of ions around this membrane (do not eat salt!). What mesmerized me at the time was the efficiency of this small unit. It could not really do much, but in combinations with millions of other cells (perhaps all as efficient), they can do all the amazing things that we do every day, with a low exergy loss, or, in other words with a high reversibility. This is something that is achieved over millions of years of evolution, although I'm not sure if reversibility has anything to do with survival or not.
When I look for irreversible processes, the first example that comes to my mind is war. It s large and fast, with many irreversible effects. A drone attack -justified or not- against a terrorist commander disguised among civilians suddenly kills the school children playing outside his house. This is highly irreversible. So is a process like insitu combustion for the extraction of oil (it burns lots of hydrocarbons to mobilize the rest). All the manmade irreversible processes that I can think of are large and fast. When you want the results overnight, you have destruct lots of exergy. Reversible processes are slow. We can make them fast by doing them in small scale. Millions of miniaturized fuel cells can be combined to do the job of a power plant. They can be stopped easily; a power plant cannot. It must go on and on because it is not easy to start it up. It's simply too big. A small unit? Not difficult to start up. I have to stop here, otherwise I cannot get anything done today.


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