Boy, copper is a joy to work with. Takahashi and others use it in calorimeters. I can see why.
In my experience steel pipes are equally stable but nothing conducts like copper. I did a quick test. Summary: with insulated thermocouples, the pipe is 1°C cooler than the water coming out of it. Almost smack on 1°C. When I remove the insulation, the pipe surface registers between 2.4 and 4.0°C cooler than the water during a 5 min. MIN/MAX test. The readings are much more stable than with the braided metal. Here is the log, with some explanation in square brackets: Dec. 8, 2011 8:26 PM Attach T1 with adhesive tape, T2 9 cm below. [No Band Aids or string in attempt to make "tent effect"] Ambient 19°C [red liquid thermometer] T1 21.2, T2 20.7, T1-T2 0.5 A large bias remains several minutes. Adjust OFFSET. T1-T2 0.0 ... 0.1 T1 20.5, T2 20.5 8:35 T1-T2 0.3 ... 0.2 T1 20.4, T2 20.6 Hot water full on 8:37 T1 53°C, Water 56°C [red liquid thermometer] 8:38 Reduce water flow a little to keep from knocking around thermometer. Water 58°C T1 57.3, T2 57.3, T1-T2 0.1 ... 0.2 [OFFSET holding up well at higher temperatures] 8:40 Note water heater is running. Water 59°C, T1 58.0°C, T2 58.0°C, T1-T2 0.0°C [Uncanny!] Ambient 20°C Begin T1 MIN/MAX 8:42 T1 58.5, Water ~59.5 [approximate with red liquid thermometer] 8:45 T1 59.5, Water 60 8:46 End T1 MIN/MAX: MAX 59.8, MIN 58.1, Delta T 1.8 8:47 T1 60.0, T2 60.1, T1-T2 0.0 [instantaneous, but not quite] Water 61 STOP FLOW Remove insulation T1 falls off pipe, so move to cup of water in sink with red liquid thermometer 8:50 RESTART flow of hot water 8:52 Ambient 20 Water 62 [red liquid thermometer] T1 62.4 [now in cup in sink] T2 59.4 T1-T2 3.1 ... 3.4 8:53 Begin T1-T2 MIN/MAX [To measure difference between pipe and liquid temperature without insulation] 8:58 End T1-T2 MIN/MAX MAX 4.0, MIN 2.4, Delta T 1.6 STOP WATER T1 62.0 T2 58.1 END
