Icy Ball
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Cold side ball on left, hot side ball on right.
The Icy Ball was the name given to an early refrigerator designed by Powell Crosley Jr, somewhere between 1928 and 1938. It was unusual in design in that it did not require the use of electricity for cooling. It instead ran on kerosene, or other heat sources (even a wood stove would work) and allowed rural areas without the luxury of electricity to utilize the benefits of refrigeration.
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[edit] Operation
The Crosley Icy Ball was an example of a gas-absorption refrigerator, as are used in RVs. Unlike an RV fridge, the Icy Ball was not a continuous cycle, but rather a batch cycle design. The entire refrigeration "mechanism" (not a typical mechanism, because it had no moving parts at all) was removed from the refrigerator cabinet, and regenerated each day.
An understanding of the distinguishing features of absorbtion refrigeration is needed to understand how the Icy Ball worked: All refrigeration systems rely on the reduction of pressure to cause liquid refrigerant to evaporate, This partial vacuum must be sustained or cooling action will cease. Mechanical refrigeration systems (the most common type) use the suction side of their compressor to provide this partial vacuum. Absorption refrigerators instead use the affinity of a sorbent material (water in this case) to absorb the refrigerant vapor (ammonia in this case). Though probably the most common, this so called "ammonia cycle" is not the only possible sorbtion refrigeration scheme. It is actually possible to use water as a refrigerant, and e.g. zeolite or glycol as an absorber. In order to maintain refrigeration the absorber must be either periodically (batch systems) or continuously regenerated.
In the simplistic description, the Icy Ball "mechanism" consists of two hollow balls, with an inverted U shaped pipe connecting them. The chest style cabinet is made so that the U tube passes through a slot in the upper wall, leaving one ball inside (cold side) and the other ball outside. (hot-side) Upon completion of regeneration, the cold-side ball contains liquid ammonia, at near anhydrous (no water content) strength. The hot-side ball contains nearly pure water. The tube between the balls, and the space above the liquid contains mostly ammonia vapor, and a small amount of water vapor. The liquid water in the hot-side ball absorbs the ammonia vapor, lowering the pressure. This causes the liquid ammonia to evaporate. The evaporation of the liquid ammonia provides a powerful cooling effect, lowering the temperature of the cold-side ball to around 19 °F (−7 °C), sufficient to freeze ice.
By this action, heat is moved from the cold-side ball to the hot-side ball, Therefore the hot-side ball becomes warm. This is undesirable, as the effectiveness of the water as an adsorber is reduced with temperature. The hot-side ball was therefore equipped with (somewhat crude) cooling fins, allowing it to be convection cooled by room air.
Eventually all of the ammonia in the cold-side ball evaporates, leaving a near saturated water/ammonia solution in the hot-side ball. (similar to, but stronger than household cleaning ammonia) At this point the refrigerator stops working, and must be regenerated.
Regeneration is accomplished by heating the hot-side ball. The ammonia adsorbing capacity of water is temperature dependent. As the temperature increases, the ammonia desorbs from the water. A second requirement for regeneration is that the cold side ball must be kept reasonably cool, so that the ammonia vapor desorbed from the water will condense into the liquid ammonia needed for refrigeration. This was traditionally accomplished by immersing the cold-side ball in a tub, or bucket of water.
The actual construction of the Icy-ball is slightly more complex than described above. Several features were incorporated to improve the efficiency (bubbling the ammonia vapor through the water) and to minimize the amount of water transferred to the cold-side ball during the regeneration cycle (trapping structures).
Additionally, the cold-side ball had a tube into which a special ice-cube tray could be placed - the forerunner of the "freezing compartment) in more modern refrigerators.
[edit] History
While the Crosley Icy ball refrigerator has gone the way of the buggy whip, absorption cycle refrigeration is still with us. In addition to RV applications, ammonia cycle refrigerators are still used in undeveloped countries. These are also batch-cycle devices, but incorporate various condensers, check valves, integral kerosene burner, etc, so that the dissassembly and tub of water required to regenerate the Icy Ball are no longer needed. Ammonia refrigeration is also used in large industrial applications, where it's efficiency more than compensates for the higher initial cost, and associated risk. Though it was once fairly popular for home air conditioning, concerns related to ammonia leakage have caused mechanical refrigeration to dominate that market.
