David Roberson <dlrober...@aol.com> wrote:
> .91 grams/second x 2260 joules/gram = 2056.6 watts. Water all assumed to > be vapor which is not being conservative. > You forgot to add the heat required to go from tap water temp to boiling, 267 J. (29.8 C - 24.5 C + .8 C) = 6.1 C Measured at time of water collection with > correction factor included. > No, this was 12 minutes after he began collecting the water. > The maximum power available is approximately 2056.6 watts versus a reading > of 4538.644 watts. This is far too much to neglect. Please explain how > the small error expected could allow this? > Possible sources of error: 1. As noted, the measurements were 12 min. apart. The power was fluctuating rapidly when this occurred, as you see in the graphs. Both answers might be right. 2. It is difficult to measure this flow rate with precision using Lewan's method. He had to make sure the hose was full before he started, and then let it dribble out into the collection flask. He measured 328 g in 360 seconds. It could easily have been more. Granted it might have been less, too, but I suppose it was more. A few bubbles in the hose or unexpectedly high back pressure from holding up the hose will retard the flow. Not much will make it go faster. That is my experience with hoses of this dimension and ornamental pond pumps, in my 200 L outdoor pond. You can retard the flow easily with those things. Just look at 'em cross-eyed. You can measure it three times and get three different answers. The flow rate from the tap, on the other hand, is extremely reliable and predictable. I have measured that often and found remarkably small differences. It has way more pressure behind it. If the flow was higher, that would bring it closer in line to the cooling loop measurement. I am not suggesting that either method constitutes ideal calorimetry! But measuring the condensate is a rough-and-ready approximation at best. The cooling loop flow method is better. I would trust it more no matter where the thermocouples are placed. I am not saying that Lewan's measurement of the flow is useless. But I expect it is an approximation. - Jed
