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**To**:**"NFC list" <nfc at actwin_com>****Subject**:**NFC: How to determine heat transfer****From**:**"Andrew S Dalton" <ASDALTON at prodigy_net>**- Date: Sun, 10 Jan 1999 13:20:45 -0500

1. The easy way. Most native fish tanks don't have a heater, but you probably have a powerhead or submersible filter that will inevitably add heat to the water. Determine the power consumption in watts. Then measure the temperature of the water and the ambient air. Q = power consumption in watts T = water temperature Ta = ambient air temperature Since Q = UA*(T - Ta), UA = Q/(T - Ta) The units of UA will be watts/deg C if you measured the temperatures in deg C, and watts/deg F if you measured the temperatures in deg F. If you want the power units in Btu/hr, multiply by 3.41. Some precautions: Since this method assumes that the powerhead is the only source of heat in the aquarium, it won't work if the tank lights have been on for more than a few minutes. It also won't work if the tank is not covered to prevent evaporation. In other words, the aquarium must be in a steady state where the only significant source of heat gain is the powerhead, and the only significant source of heat loss is directly through the walls of the tank. Also, if you use the same thermometer for the water and air, make sure that the thermometer is completely dry when you take the air temperature. 2. The hard (but probably more accurate) way. This method measures the temperature change over time when an aquarium starts out significantly warmer or cooler than the ambient air. It requires all of the precautions that I mentioned for the "easy" method. It also requires that you have _no_ internal heat sources, so you can't use a powerhead to circulate the water. Use an airstone, and adjust the air flow in order to match the intensity of water circulation that you will use during the tank's normal operation. For this experiment, you will need a clock or stopwatch and two accurate thermometers--one for the water and one for the ambient air. Make a table arranged in the following way: Time (t) Ambient temp. (Ta) Water temp. (T) You can record either the clock time or elapsed time (with the first measurement being taken at t = 0), but the elapsed time is what will actually be used in the calculations. The equation to use is V*d*Cp*ln((T0 - Ta)/(T - Ta)) = UA*t. V = volume of aquarium d = density of water = 8.35 lb/gal or 1000 g/L Cp = heat capacity of water = 1 Btu/lb/deg F or 1 cal/g/deg C = 4.134 J/g/deg C T0 = water temperature at first measurement (t = 0) t = elapsed time since first measurement Strictly speaking, Ta needs to be constant, but you can just use an average as long as Ta doesn't vary too much over time. Make a graph with the quantity V*d*Cp*ln((T0 - Ta)/(T - Ta)) on the y-axis and t on the x-axis. The result will be a line passing through the origin with a slope of UA. ------------------------------------------------------------ [\ Andrew Dalton [\[\ [\ [\ [\[\[\[\ [\ [\ [\[\ [\[\ [\ [\ [\ [\ [\[\[\[\[\[\[\[\ [\ [\ [\[\ [\[\ [\ [\ [\ [\ [\[\[\[\ [\[\[\[\ [\ [\ [\ [\ [\[\ [\[\ [\[\ [\[\ [\ [\ [\ [\ [\ [\ [\ [\ [\[\[\[\[\[\[\[\[\[\[\[\[\[\[\[\ ------------------------------------------------------------

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