Question A small sphere of reference-grade iron with a specific heat of 447 J/kg.K and a mass of 0.515 kg is suddenly immersed in a water-ice mixture. Fine thermocouple wires suspend the sphere, and the temperature is observed to change from 15 to 14 0C in 6.35s. The experiment is repeated with a metallic sphere of the same diameter, but of unknown composition with a mass of 1.263 kg. If the same observed temperature change occurs in 4.59s, what is the specific heat of the unknown material?
Second question
An uninsulated steam pipe passes through a room in which the air and walls are at 25 0C. The outside diameter of the pipe is 70 mm and its surface temperature and emissivity are 200 0C and 0.8 respectively. What are the surface emissive power and irradiation? If the coefficient associated with free convection heat transfer from the surface to the air is 15W/m2.K. What is the rate of heat loss from the pipe? And the facilities manager wants you to recommend methods for reducing the heat loss to the room, and two options are proposed. The first option would restrict air movement around the outer surface of the pipe and thereby reducing the convection coefficient by a factor of two. The second option would coat the outer surface of the pipe with low emissivity (0.4) paint. Which of the foregoing options would you recommend?
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