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  1. #1
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    absorption cycle with low generator temperature ?



    I am IT engineer not a refrigeration expert, pardon my basic question.

    Would a NH3 or other absorption cycle work with a generator temperature of say 30C, and condenser temperature of 10C by maintaining correct pressure level.

    Most of the technical papers I read on the internet, talk about requirement of 80C+ temperature for generator and 25-30C for condenser. This would make sense if one has access to hot water source like geo thermal, or any other free heat source. But if I have access to low temperature cool water of 10C, and relatively stable heat source of 25C+ (say atmospheric temperature), can a absorption refrigeration system be designed to harvest that energy. One of the main objective is to have very low electrical energy input, so compression system may not work out. The second objective is to have a -3C or lower evaporator temperature to make salty ice and store it, and use it when the cold water source is not available. If at all its possible, what major issues to keep in mind.

    I guess even the standard off the shelf absorption systems can be made to use 30C heat, by first passing it through a heat pump to increase that temperature to 80C+. But that additional stage also need lot of electricity.

    Any suggestion to effectively harvest this low temperature source would be of great help.



  2. #2
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    Re: absorption cycle with low generator temperature ?

    What would be minimum pressure difference needed between generator and absorber to operate absorption cycle ?

    By looking at Enthalpy-Concentration Diagram for Aqua-Ammonia provided at ashrae. Looks like I can get vapor pressure difference of 380kpa. By having a Tgen of 80F and Tabs of 50F or lower, max concentration at generator at 60% W/W of ammonia.

    If the pressure difference is say 350kpa and condenser output is at 50F, can the evaporator temperature difference be below 32F ?

  3. #3
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    Re: absorption cycle with low generator temperature ?

    Quote Originally Posted by rnrajan View Post
    What would be minimum pressure difference needed between generator and absorber to operate absorption cycle ?

    By looking at Enthalpy-Concentration Diagram for Aqua-Ammonia provided at ashrae. Looks like I can get vapor pressure difference of 380kpa. By having a Tgen of 80F and Tabs of 50F or lower, max concentration at generator at 60% W/W of ammonia.

    If the pressure difference is say 350kpa and condenser output is at 50F, can the evaporator temperature difference be below 32F ?
    I guess I would also need a low enough temperature to condense the NH3 gas at low pressure generated at 80F. For 5.5bar, this would be 44F or I would have to bump up the sol concentration to 65% and get a 620kpa at generator and still can use 50F temperature at condenser.
    Last edited by rnrajan; 02-05-2016 at 08:33 AM.

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