Defkalion's demonstration wasn't bad. Any demonstration is tough. Something always goes wrong. It wasn't bad, but it could have been better. I have done demonstrations and I have taught and given lectures so let me offer a few suggestions based on this experience.
Practice, practice, practice. Rehearse beforehand. Be sure you can comfortably complete the presentation in the time allotted. This was their biggest failing. Set up your props beforehand. As I explain below, in this case I would have put a black drop cloth on the wall and brought in a meter stick, a weight scale, and a bucket of water with a thermometer in it. Make yourself clear. Get to the point and stick to it. You need not write out every word, but it is a good idea to write down your talking points in the order you intend to present them. Here is the sort of thing I would have said: ". . . The inlet temperature is 21°C, the outlet is 115°C. Here on the screen we are computing enthalpy by the heat capacity of water. We ignore the heat of vaporization. However, at this outlet temperature we know the water has vaporized. Let's prove that. Let's take the outlet tube from the sink and hold it up next to this black drop cloth. [Holding meter stick next to plume.] As you see the plume of steam is around 80 cm long. The first 20 cm are invisible, which means the steam is dry. Now let us show that our flowmeter is correct and the water is flowing at 500 mL per minute. We will also show that the steam has about 1130 kJ of enthalpy per minute. We have placed this bucket on the weight scale. As you see it has 20 kg of water in it, and the water temperature is 21°C. Now were going to submerge the hose under the water for about a minute and see how much water condenses and how much the entire mass of water heats up. Starting NOW. [Splash! 'Buku buku buku' as bubbles say in Japanese] [A minute later] Okay we removed the hose after one minute three seconds. The weight of water has increased by 460 g. Some of the steam escaped from the water but most of it condensed. We see that the temperature has risen to 31°C . . ." And so forth. Prepare your tables and spreadsheets beforehand so you can describe results smoothly without stopping to do a lot of arithmetic. You need not state that the heat of vaporization is 2260 kJ per kilogram. The viewer can look that up later on. You need not explain that the bucket when empty weighs 820 g. The viewer knows about how much a plastic bucket weighs, and can see you have taken that into account. Skip the details; get to the point. As I said before, you demonstrate every key point twice, by two different methods. Ideally, one method relies upon precision instruments and the second method depends on first principles that are easily understood and easily measured, even if they are somewhat crude. The two methods must be completely different so that a single artifact cannot cause both to be wrong. People sometimes say that in a lecture you should tell the audience what you're going to say; tell them what you have to say; and then tell them what you just told them. I think this is going too far, but it does not hurt to repeat your key points at least once. I assume the people at Defkalion are doing similar demonstrations for potential customers and investors. So I think they should polish up the presentation and make it more convincing. - Jed
