A cylindrical electrical heating element is used to heat up a baking oven. The heating element bears a voltage of 120 V/m, and has an electrical resistance of 1000 Ω/m. A ceramic pipe of inside radius rin = 2 mm, and outside radius rout = 5 mm encases the heating element. Thermal conductivity of the ceramic is k = 0.2 W/m-K. Given that the oven air temperature is T∞ = 180oC and convection coefficient h = 10 W/m2-K, find the temperature on the inside of the ceramic pipe

The front window of an automobile has a thickness of 4 mm and is defrosted by the passage of a stream of hot air through the inner surface. The thermal conductivity of glass is around 0.78 W/(m oC). Assume the ambient air temperature is -10°C and the external convection coefficient is 65W/(m2 K). If the hot air blowing to defog the glass internally is at 40 ºC and the internal convection coefficient corresponds to 30 W/(m2 K), the internal surface temperatures will be _____________. However, if the car accelerates and maintains high speed, the external convection coefficient should _____________  [increase or decrease?] and if the condition is maintained long enough the temperature of the inner surface of the glass should _____________  [increase or decrease?].

Consider modeling a temperature sensor as a sphere having a thermal conductivity of 91 W/m-K, a density of 8900 kg/m³, and a specific heat of 444 J/kg-K. The sensor is in an environment where the heat transfer coefficient is 100 W/m²-K. Determine the maximum allowable diameter of the sensor if the 90% response time to a step-change in the fluid temperature, T∞, must be: • 10 second • 1 second . 0.01 second

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