A bar of aluminum is placed in a large bath of ice and water (see Figure). Curre

Question

A bar of aluminum is placed in a large bath of ice and water (see Figure). Current is passed through the bar until, at steady-state, there is a power dissipation of 1000W. A thermocouple on the surface of the aluminum reads 640K. Film boiling is occurring at the interface with a subsequent, noisy collapse of the bubbles. What is the entropy change of the bar, water-ice, and the universe during 2 min of operation for this highly irreversible operation? Assume that there is ice remaining at the end of the 2 minutes. State any assumptions.

Explanation / Answer

as the ice is remaining , that implies there is no temperature change in ice -water mixture.

initiallytemperture of Al bar = 273 k

change in entropy of bar = -Q* (1/t1-1/t2) = 1000*120( 1/273 - 1/640) = 252.06 J/K

change in entropy of water-ice = 1000*120/273= 439.56 J/K

delta S universe = -(252.06+439.56) = -691.62 J/K

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