In reply to P.J van Noorden's message of Thu, 7 Apr 2011 11:19:06 +0200: Hi, [snip] >Hello > >In figure 6 of the article >http://www.nyteknik.se/incoming/article3144960.ece/BINARY/Download+the+report+by+Kullander+and+Ess%C3%A9n+%28pdf%29 > > >it is stated that the waterflow is 6.47 l/ hour= about 2 ml/sec. This is >about the waterflow of a espressomachine. >When 4kW is added to such a waterflow the temperature would rise >instantaneously to 100 degr C. The curve in figure 6 would have to rise >vertically. >If only 400 Watts is added the waterflow the temp would rise 50 degr C in >temperature continously. > >The curve in figure 6 rises in about 3 minutes 30 degr C ( steepest part). >This would compare to a power of only a few watts.
If you just consider the water flow rate, then the graph makes no sense at all, since a constant flow rate with a constant power input of 300 W at the beginning should result in a flat line at about 58 ºC. However what we see is a rising line. The only conclusion I can come to is that you need to include the thermal mass of the device which is also being heated by the electric heater so that in the beginning the whole thing is heating up. The really interesting point is that the reaction appears to take off at precisely the point where the temperature of the device has reached the 58ºC which would be the constant water temperature point for heating by the electric heater alone (300 W can maintain a temp. differential of 40 ºC at that flow rate) . I can't but help find this strange, but perhaps there is a causal link between the two? Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/Project.html
