Effect of entropy on Process equipment design

[Buchi]

Hi Guys,

Can someone help explain to me, in simple terms, the effect of entropy on process equipment design.

thanks

Buchi

 

[sailoday28]

The net effect on the overall process is an increase in entropy.

 

[davefitz]

Entropy is a measure of energy that is available to do work. Such energy has more value than energy that is not available for work. By configuring the process so as to minimize the increase in entropy, you conserve the energy that is available to do work,or you do more work while consuming the same amount of energy. In our market economy, this should also be consistent with minimizing the fuel and electrical consumption of the plant for a given amount of product output from the plant.

Entropy increases when heat is transferred across a large temperature difference, or when a pure substance is mixed with other substances to form a mixture, or when a high pressure gas is throttled across an orifice without doing work.

In a simplistic summary, one should configure the process so that heat is transferred across temperature drops that are minimized ( of course this means much more surface areas is needed), and large pressure drops should be accoplished across turbines or pelton wheels instead of acorss orifices or valves ( and this means a higher capital cost for the rotating machinery).

Breaking down the entire process into individual sub-proceses and calculating each sub process's entropy increase should give the analyst a clue as to where the greates potential for cycle efficiency can be found.

 

[epoisses]

In other words.......
When you do the dishes, you start with the not-so-dirty items (the glasses). Gradually you move on to the dirtier things. The dirtiest ones (the horrible frying pan) usually need a two-stage treatment with intermediate replacement of the dishwater.

 

[SmartEngineer]

Entropy is usually seen in expander/compressor equipment wherein assumptions are made for calculations of performance of the machine. This is the only application I have seen before but in static equipment or even pumps the entropy term is not considered in the design.

Just a quick question:
Can you specify your question as we made very generic that you would not get good answers I guess!!

Cheers

 

[davefitz]

The use of entropy in the calc for turbines is a traditional application, but the concepts and theory asociated with entropy ( or exergy or available energy) are much more broad based than just turbines.

Overseas engineers have striven to improve the efficiency of other processes to reduce fuel consumptio and reduce specifc emissions. Some newer terms that are associated with entropy are pinch technology and exergy analysis, and some notable process improvements assocated with those are the use of binary fluids for refrigeration ( Kalina cycles, LNG chillers, modern refrigeration cycles) , and heat exchanger optimization.

 

[JStephen]

Buchi, entropy is not a simple concept, process equipment is not simple equipment, and there's simply no way to really answer the question in ways you might like. You might be a bit more specific with your question. Are you just curious, writing a term paper, wondering why the heck you're studying the topic, or what?

Just in general, engineers don't sit around worrying about entropy a lot in a direct way. But entropy ideas are behind a lot of other work that is done.