Oddball theoretical question - ammonia absorption

[hephaestus]

G'day all,

Wanted to bounce something off the experts... Came to mind while talking to an aussie company who sells solar refridgerators; while reading about the Vtwin compressor retrofits...

Would it not be useful to run an ammonia absorption coil on a sterling engine? Same principles as the sterling - except the output is in cooling... Already applying heat to one end of the engine; and wanting more cooling on the other...

http://en.wikipedia.org/wiki/Absorption_refrigerator

I'm no expert - I'm just muddling through the designs you guys are doing seeing what I can come up with for my needs; but it seems to me it'd be a good fit...

[Ferraccio]

The work of Stirling, as all heat engines, is linked to the temperature difference between hot spot and cold spot; is important as well the mass of the working fluid.
Raising the temperature can easily get the point fall in the use of special materials, high costs.
Lower to the temperature to near ambient can be achieved with good heat extraction systems from cold spot.

You can certainly use a cooling circuit to lower the temp. of the cold spot more, but we are sure that the Stirling engine produces enough energy to run the refrigeration compressor?
The ammonia compression is a really heavy work of pneumatic pumping, and in not many high efficiency.

[hephaestus]

ammonia absorption systems have no compressor... Sealed system, heat one end, get cold out the other... (RV fridges are the most common variation) Also refered to as an einstein fridge, amongst many other names...

good explanation:

But there is a second type of ammonia refrigerator that makes use of an absorption cycle—ammonia dissolves extremely well in cool water but not so well in hot water. In an absorption cycle refrigerator, a concentrated solution of ammonia in water is heated in a boiler until most of the ammonia is driven out of the water as a high-pressure gas. This hot, dense ammonia gas then enters a condenser, where it gives up heat to its surroundings and becomes a cooler liquid. The liquid ammonia then enters a low-pressure evaporator, where it evaporates into a cold gas. This evaporation process draws heat out the evaporator and refrigerates everything nearby. Finally, the ammonia gas must be returned to the boiler to begin the process again. That return step makes use of the absorption process, in which the ammonia gas is allowed to dissolve in relatively pure, cool water. The gas dissolves easily in this water and thus maintains the low pressure needed for evaporation to continue in the evaporator. The now concentrated ammonia solution flows to the boiler where the ammonia is driven back out of the water and everything repeats.

[vile_fly]

Well, the real question is, how rapidly can adsorption remove the heat from a stirling engine? I am not sure of how to scale an adsorption system to fit a specific size stirling engine. What BTU rating are the average RV fridges? All the ones I have seen were old and only reached 45-50 deg F. I imagine if it were coupled with a stirling engine, it would make a nice cryocooler. I just don't have an idea of what the average efficiency of such a system is.

[hephaestus]

That's beyond my knowledge, I know my rv fridge freezes the whole fridge up solid if I crank it up (3cuft)... The aussie designed solar fridges we're planning to buy (3 way, 12v, solar heater, LPG) are supposed to be way more advanced than the RV fridges and they're full size fridges; designed to run primarily off solar heating.

Might have to see if that manufacturer can provide some design info; it's got to be out there; even if google isn't popping it up quickly... the ammonia absorption systems are coming back into vogue with these green houses / off grid homes... They're using them for everything from fridges to central a/c... And we know some of these guys are rednecks like me who'll DIY at all costs...

I found some info on rebuilding the RV fridge cooling systems including recharging the system; so it'd seem DIY'able...

[Ferraccio]

Is evident that I do not have enough knowledge in description of ammonia absorbtion cycle, ...and overall in English language.
But you are sure that you do not need power to pump (excuse me: not to compress) fluid and actionate a fan that remove heat?
May be that all power made from Stirling engine is necessary for actionate the absorption cycle, or quite, or instead ..even.
The answer is in the balance of numbers,

Good however the idea to consider two systems: the Stirling that produces waste heat, and the absorbtion cooling that utilize waste heat.

If there isn't a fresh substantial power output, .... in losses, frictions, air turbolences and so on,...may you have only a production of heat.

[Ferraccio]

Each cooling system does not produce cold: By means of an external job moves heat from one point to another, to effect the movement a place become colder.
Has to to be removed much more heat than the moved one, you've to consider losses to effect the own efficiency of the system.

[hephaestus]

What can google translate do? :)

Ma c'è un secondo tipo di frigorifero ammoniaca che fa uso di un ciclo di assorbimento e ammoniaca si scioglie molto bene in acqua fredda, ma non così bene in acqua calda. In un ciclo frigorifero ad assorbimento, una soluzione concentrata di ammoniaca in acqua è riscaldata in una caldaia fino a quando la maggior parte dell'ammoniaca è spinta fuori dall'acqua come un gas ad alta pressione. Questa calda, gas di ammoniaca denso entra poi in un condensatore, dove cede calore all'ambiente circostante e diventa un liquido di raffreddamento. L'ammoniaca liquida entra poi in un evaporatore a bassa pressione, dove evapora in un gas freddo. Questo processo di evaporazione attira il calore e l'evaporatore refrigera tutto nelle vicinanze. Infine, il gas di ammoniaca deve essere restituito alla caldaia per iniziare il processo di nuovo. Questo passo ritorno fa uso del processo di assorbimento, in cui è consentito il gas di ammoniaca a dissolversi in relativamente pura, acqua fresca. Il gas si scioglie facilmente in acqua e mantiene quindi la bassa pressione necessaria per l'evaporazione di continuare nell'evaporatore. L'ora soluzione concentrata di ammoniaca flussi alla caldaia dove è guidato l'ammoniaca indietro fuori dall'acqua e si ripete tutto.

The ammonia absorption systems I'm familiar with have no moving parts or pumps, just a heat source... Minor exception, the big fridges we're looking at use some small fans for circulation.

[Ferraccio]

Grazie per la traduzione!!, ora ho compreso, grazie!! E' un sistema di raffreddamento che utilizza la circolazione spontanea di ammoniaca invece di quella di acqua.
Buoni vantaggi: il cambiamento di stato (evaporazione) del fluido (assorbimento di calore) a bassa pressione.
Svantaggi: la complessità (tipo di fluido, dimensioni) dell'apparato, il contenuto termico del fluido.

Thanks for the translation!, now I understand, thanks! It 's a cooling system that uses the spontaneous circulation of ammonia rather than water.
Good advantages: the change of state (evaporation) of the fluid (heat absorption) at low pressure.
Disadvantages: complexity (fluid type, size of apparatus) to remove the necessary heat.

[Murph]

Why use an ammonia absorbtion cooler to run a Stirling engine, when you can just use a gas expansion engine, e.g. "steam engine", in place of the gas expansion valve in the cooler line?

[Ferraccio]

I fear that in order to simplify the system, starting from the cold part simply ubmerged in a bucket of water, we end up building a ton of equipment to get 100 watts.

[hephaestus]

Sometimes a bucket of water isn't appropriate...

Really we're talking a pressurized loop of tubing with a resevoir in it... Not a huge refrigeration system...

ubiquitous rv fridge 'buisness end' :


A bucket of water works in a hobby application, but sometimes going into a more utilitarian application - it's not so workable...

[Ian S C]

One contributor to Model Engineer mag had a problem, his gas container was freezing up, and the cooling water was too hot, so he put thegas cylinder in the water container, and the motor took off. Ian S C

[Yuvan]

Mysore Ammonia was the first in India to start a Cylinder Filling Plant for Ammonia in 1979 and in 1984 was the first to start a Liquor Ammonia Manufacturing Plant in India. With a Long-Term outlook focused on Service, Quality and Safety, in the Ammonia Industry, Mysore Ammonia is known for Transparency in their interactions and good HR practices. Only Indian Company sourcing Ammonia from the overseas besides India, and also the only Indian company with Manufacturing Plants and tie-ups for Production of Ammonia overseas, Mysore Ammonia is highly reputed in the industry for their Supply-Chain Management also. They follow their commitment to provide solutions as per customer needs and deliver where the Customers needs the Product; when they need it, and with consistent Quality & Quantity standards.

http://www.mysoreammonia.com/aboutus/am ... orters.htm

[Ian S C]

After I built my Ross Yoke ALPHA motor, I coupled it to my horizontal BETA motor via belt and pulleys, and after 20 minutes the temperature of the hot cap on the ALPHA motor dropped 40*C, from + 20*C to - 20*C, the motor driving produces about 5 Watts at the crankshaft. If a jacket of some sort was place around the hot cap and a loop of metal tube to and from that filled with a refrigerant (even saline) a refrigeration system could be made. More power, more cold.

Ian S C
The ALPHA as it was at the top, and below is the BETA motor, based on Dyna a design by James G. Risso

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