About 25 years ago, a colleague of mine had a sign in his office: "Sometimes you just have to shoot the engineer and start production", which summarized his obvious contempt for engineers and their theories. It also applies to what I am about to say.
waterless condenser, shown on the right. It is just a standard condenser, but instead of being connected to a water line or circulating pump, it is filled with ethylene glycol and a short span of tubing connects the two outlets. It is a simple, reusable setup that avoids either the waste of clean water or the complications of a circulating pump.
Being formally educated as a chemical engineer, my engineering sensibilities are seriously suffering from looking at this.
A condenser is an apparatus for heat transfer and little more, with the heat going from the hot solvent through the glass and then into the fluid. And so I will analyze this from a heat transfer viewpoint. First, the direction of the fluid flow is entirely wrong. The hottest solvent fumes will be at the bottom of the condenser and so the ethylene glycol will be heated there more than further above. The heated ethylene glycol will be less dense, so it will rise and set up a flow that is clockwise in the illustration above. Unfortunately, that means that the ethylene glycol will be moving in the same direction as the solvent - parallel flow. It is a basic principle in junior level heat transfer textbooks that counter flow (i.e., the solvent and the heat transfer fluid moving in opposite directions) is much more effective for heat transfer than parallel flow - you have a larger average temperature difference in counter flow. When there is flowing water in a condenser, it should be set up for counter flow, entering at the downstream point and exiting upstream.
Further, the hot ethylene glycol has very few chances to cool. Normally the heat in the condensing fluid is either dumped down the drain or removed in a cooling section of the circulating pump, but in this case, the heat has to transfer through the rubber tubing to the air. Unfortunately, rubber tubing is a poor heat conductor; copper tubing would be simple to rig up, be much more durable and much more effective at transferring heat to the air.
And yet the blessedly simple design works and works well according to data in the paper. So much for engineering theory. Which way to the firing squad?