5.67 A tile-iron consists of a massive plate maintainėd al150°C by an embedded electrical heater. The iron is placed in contact with a tile to soften the adhesive, allowing the tile to be easily lifted from the subflooring. The adhesive will soften sufficiently if heated above 50°C for at least 2 min, but its temperature should not exceed120°C to avoid deterioration of the adhesive. Assume the tile and sub floor to have an initial temperature of 25°C and to have equivalent thermophysical properties of k = 0.15 W/m · K and pc, = 1.5 x 10° J/m · K. (a) How long will it take a worker using the tile-iron to lift a tile? Will the adhesive temperature exceed120°C? (b) If the tile-iron has a square surface area 254 mm to the side, how much energy has been removed from it during the time it has taken to lift the tile?

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