Ice Engine

Technical terms sometimes confuse the average person. Consider the phrases "flashlight battery" and "flashlight cell". The average person may use them interchangeably, but technically a battery is a group of cells, and so a cell cannot actually be a battery.

In the present case, there are the words "engine" and "motor" to talk about. Technically, an engine is a device that converts untamed energy into tamed energy (of any form, but usually motion). A motor is merely a device that uses tamed energy to create motion. A windmill qualifies as an "engine", but a gasoline engine should not be called a "motor".

Sometimes motors can be modified to become engines, however. In the present example, see the link about the "bent axis pump". It happens that if fluid is pressured into it, it can act as a motor. And this Idea is about how to turn that motor into an engine.

Once upon a time I saw a short video in which a hollow iron sphere about the size of a baseball (the shell was maybe half a centimeter thick) was filled with water, and then sealed and placed in a container of "dry ice" (frozen carbon dioxide). As you might expect, since dry ice is very cold, the water in the sphere turned to ice. You might not expect the sphere to explode with enough force to embed shards of itself in the walls 3 meters away, but it did.

When water freezes, it expands. Ice occupies about 10% greater volume than the original unfrozen water, and freezing water will exert tremendous force, in expanding that 10%. This is the force that we will tame in the engine described here.

The Ice Engine does all of its power-generating while at the fixed temperature of Zero Degrees Celsius, the freezing/melting point of water. Nevertheless, it qualifies as a "heat engine" because significant amounts of heat need to be added and removed from it, while it operates. Those two statements are NOT a contradiction. The key fact that elminates the contradiction is this: WHILE water freezes or melts, its temperature does not change; all the heat that is either removed or added is directly due to the work involved in the freezing or melting process. This energy is technically known as the "heat of fusion" (having absolutely nothing to do with nuclear fusion), because when individual items (like water molecules) become solidly linked together (as during freezing), it can be said that they have become "fused" together.

So, AT the freezing point of water, a bunch of heat gets added to make ice melt, and a bunch of heat must be removed to make water freeze. Only after all of the substance has completed this "phase change" (from the solid phase to the liquid phase, or vice-versa) can its temperature begin to rise or fall, from the freezing/melting point.

Constructing an Ice Engine is simple enough. We need a set of containers of water, all at the same temperature of Zero Degrees Celsius. Each container holds a different mixture of water and ice (slush, that is); one is all water and one is all ice.

Next, we open up the end of the bent-axis pump, where we can see different distances from that end to the tops of the pistons in the cylinders. In the shortest distance we put pure water, and in the longest distance (it should be 10% longer than the shortest distance, of course) we put solid ice. The mixtures go in the intermediary-distance cylinders, carefully matching the space available with the water/ice ratio. It happens that the exact same WEIGHT (or mass) of water should be placed in each cylinder.

The end of the pump is now completely sealed (we don't want any air at all in those cylinders!); no H2O ever needs to be added or removed from any of the cylinders. At the "swash plate", the tilted disc that the pistons are attached to, we may need to make some modifications. A sharp tilt is required for this type of pump to work as a motor, but here we are starting with about a 10% tilt, thanks to the amounts of H2O that were added to the cylinders. However, we can take advantage of the fact that we know that when water freezes, it will exert enormous force, so we can add some levers in this area, one for each piston, to exchange force to obtain distance, and convert the slight tilt into a sharp tilt for the swash plate.

Finally, we add some heating and some cooling apparatus around the assembly of piston cylinders. Based on the direction we want this engine to rotate, we want to add heat as the piston goes into the cylinder (ice melts and volume decreases), and we want to remove heat to make the piston go out of the cylinder (water freezes and volume increases).

It will probably rotate rather slowly. We may want this engine to be rather large, with more than a hundred cylinders, because of the time it can take for water to melt or freeze. Nevertheless, the Ice Engine will also produce tremendous torque, guaranteed.