Hopper cooling

Hopper cooling is a simple form of water cooling used for small stationary engines. The defining feature of hopper cooling, amongst other water-cooled engines, is that there is no radiator. Cooling water is heated by the engine and evaporates from the surface of the hopper as steam.

Internal combustion engines are inefficient and so require cooling to dispose of the waste heat they generate when running. Water-cooled engines remove this heat from around the cylinder head by surrounding it with a water jacket.

In most familiar engines, this water is circulated from the hot parts of the engine to a radiator, where it gives up its heat to the air. In these early and low powered engines with hopper cooling, there is little circulation. Water is instead slowly boiled off, the heat of vaporisation needed to boil the water coming from the engine heat. The loss of heat with this departing water vapour is enough to cool the engine.

As the heat of vaporisation (energy needed to vaporise water) is much larger than the specific heat capacity (energy to raise the temperature of water by one degree), relatively little water is required to replace that lost by evaporation. A typical small engine would consume a few bucketfuls in a working day.

${\displaystyle {\frac {(2260{\text{J}}{\text{g}}^{-1}/4.1813{\text{J}}{\text{g}}^{-1}{\text{K}}^{-1})}{(100{\text{°C}}-20{\text{°C}})}}\approx 7}$

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