# example 3-2 - Example 3-2 An electric resistance heater is...

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Example 3-2 An electric resistance heater is inserted in a well-insulated tank of water. The heater has a resistance of 6 and is subjected to an applied voltage of 120 V. The water is initially at 70°F and has a volume of 7.8 ft 3 . How long will it be before the water temperature is 90°F? Solution: Choose the water and the heater to be the system under study. (Exclude the walls of the tank). From the first law, K EP EUQW ∆+ ∆=− There are no changes in kinetic or potential energy and the tank is well-insulated, so UW ∆= () 21 Wm c TT =− mV ρ = Include only the mass of water, assuming the mass of the heater to be small in comparison. The density of water can be obtained from EES, assuming atmospheric pressure,

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## This note was uploaded on 04/06/2009 for the course ENGR 2250 taught by Professor Borca-tasciuc during the Spring '08 term at Rensselaer Polytechnic Institute.

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example 3-2 - Example 3-2 An electric resistance heater is...

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