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Thread: heat exchanger exergy analysis

  1. #1 heat exchanger exergy analysis 
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    hey!

    does anyone know if there are any good articles about exergy analysis and exergy efficiencies of finned tube heat exchangers (for heating and sensible and latent cooling of air with water)? or any other articles which are not strictly related to this topic but could be useful?

    thanks


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  3. #2  
    Ascended Member Ascended's Avatar
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    zdej likes this.
    “The whole problem with the world is that fools and fanatics are always so certain of themselves, and wiser people so full of doubts.”

    Bertrand Russell
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  4. #3  
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    thanks for links, but i already have effectivness-NTU calculation so I am searching for articles regarding exergy analsys of heat exchangers...
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  5. #4  
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    the problem which i am having looks like this:

    in one of the cases air (mass flow of air: m,a=0,71 kg/s) is entering the heat exchanger with temperature T,aIN=21C and relative humidity RH,aIN=57%, air is cooled to the state where it has temperature T,aOUT=19C and RH,aOUT=64%. Water entering the heat exchanger has T,wIN=7C and on the outlet T,wOUT=14,91C, mass flow of water is 0,043 kg/s.

    for exergy calculation:
    air inlet entalpy and entropy h,aIN=43,55 kJ/kg and s,aIN=0,1552 kJ/kgK. Air inlet conditions are the same as dead end state conditions. Air outlet enthalpy and entropy are h,aOUT=41,50 kJ/kg and s,aOUT=0,1487 kJ/kgK.
    water enthalpy and entropy: h,wIN=29,52 kJ/kg; s,wIN=0,1064 kJ/kgK; h,wOUT=62,68 kJ/kgK;s,wOUT=0,2231 kJ/kgK. Water enthalpy and entropy at dead end state (21C): h,w0=88,18 kJ/kg and s,w0=0,3107 kJ/kgK.

    calculated exergies, air: ex,aIN=0 kj/kg;(ex,aIN*m,a): Ex,aIN=0 kW, ex,aOUT=0,1330 kJ/kg, Ex,aOUT=0,0944 kW
    calculated exergies, water: ex,wIN=1,4348 kJ/kg, Ex,wIN=0,0627, ex,wOUT=0,2675 kJ/kg, Ex,wOUT=0,0117 kW

    if i calculate second law efficiency ( outlet exergies/inlet exergies), i get efficiency: 1,69 !?

    i do not know where could be a mistake... enthalpy and entropy values seems to be correct... any ideas?

    Thanks alot!
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  6. #5  
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    i just want to add this:

    problem seems to appear when dead end state temperature is not the highest (or the lowest) temperature appearing in process...
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