In reply to Alberto De Souza's message of Sat, 21 Mar 2015 12:46:16 -0400: Hi, [snip] >To be sure about the resistance, one needs to measure the voltage and the >current at regular intervals. Direct measurement of current (series >ammeter) and voltage are desirable and easy to do precisely today with >affordable equiment. To avoid doubts about when we have excess heat, two >reactors should be run together with the heater coils in series - one with >fuel and one empty. This way we are absolutely sure we have the same >current. To obtain the resistance of each heater coil, one needs only to >measure the voltage on their terminals. With this setup, we have all we >need to measure precisely the input power of each reactor. Assuming that >the resistance of the coils are the same (easy to achieve: make the two >coils with the same amount of wire; temperature is not much relevant for >the value of resistance since heater wires have about the same resistance >for the range of temperatures of interest; see >http://kanthal.com/en/products/material-datasheets/wire/resistance-heating-wire-and-resistance-wire/kanthal-a-1/), >it is easy to spot excess heat if we have a large COP (> 2). > >Alberto.
If the objective is to compare the temperatures, then one has to ensure that the input _power_ to both coils is identical. It is not enough to just _measure_ the input power. It needs to be _actively controlled_ to ensure that it is identical. Since P=I^2*R, if the resistance changes, then the current needs to change too, in order to maintain constant power. If the coils are in series, and they have different resistances, then they must have different powers, since the current through both is identical. Ergo, they can't be placed in series. They also can't be placed in parallel, since identical voltage over both would ensure a larger current through the coil with lowest resistance. In short each coil needs to be powered and controlled independently, and power consumption of each measured and logged to prove that the power consumption in both remains the same. Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/project.html
