An immersible heater coil is to be designed to heat an insulated container with

Question

An immersible heater coil is to be designed to heat an insulated container with 4 liters of distilled water from 20 degrees to 50 degrees C in less than 30 minutes.

a) How much energy must be input to heat the water to this temperature?

b) To heat the water, what minimum power must be supplied?

c) If a 12 volt power supply is to be used, what minimum current must low in the heating coil?

d) what is the resistance of the heating coil? Is this a maximum or minimum resistance to heat the water in 30 minutes or less?

Explanation / Answer

a)

Q = m c deltaT = 4*4186*(50-20) = 502320 J

b)

P = Q/t = 502320/(30*60) = 279 W

c)

I = P/V = 279.067/12 = 23.3 A

d)

P = V^2/R

==> R = V^2/P = 12*12/279.067 = 0.516 ohms

R is maximum

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