Question

4. A 2-m-long, 0.3-cm-diameter electrical wire extends across a room at 15°C. Heat is generated in the wire as a result of resistance heating, and the surface temperature of the wire is measured to be 152 °C in steady operation. Also, the voltage drop and electric current through the wire are measured to be 60 V and 1.5 A, respectively. Disregarding any heat transfer by radiation, determine the convection heat transfer coefficient for heat transfer between the outer surface of the wire and the air in the room. Ans. 34.9 W/m²·K. The temperatures on the faces of a plane wall 15 cm thick are 375 and 85 °C. The wall is constructed of a special glass with the following properties: k = 0.78 W/m·°C, ρ = 2700 kg/m³, cP = 0.84 kJ/kg·°C. What is the heat flow through the wall at steady-state conditions? 6. A 50-cm-diameter pipeline in the Arctic carries hot oil at 30 °C and is exposed to a surrounding temperature of -20 °C. A special powder insulation 5 cm thick surrounds the pipe and has a thermal conductivity of 7 mW/m·°C. The convection heat-transfer coefficient on the outside of the pipe is 9 W/m²·°C. Estimate the energy loss from the pipe per meter of length.

          4. A 2-m-long, 0.3-cm-diameter electrical wire extends across a room at 15°C. Heat is generated in the wire as a result of resistance heating, and the surface temperature of the wire is measured to be 152 °C in steady operation. Also, the voltage drop and electric current through the wire are measured to be 60 V and 1.5 A, respectively. Disregarding any heat transfer by radiation, determine the convection heat transfer coefficient for heat transfer between the outer surface of the wire and the air in the room. Ans. 34.9 W/m²·K.
The temperatures on the faces of a plane wall 15 cm thick are 375 and 85 °C. The wall is constructed of a special glass with the following properties: k = 0.78 W/m·°C, ρ = 2700 kg/m³, cP = 0.84 kJ/kg·°C. What is the heat flow through the wall at steady-state conditions?
6. A 50-cm-diameter pipeline in the Arctic carries hot oil at 30 °C and is exposed to a surrounding temperature of -20 °C. A special powder insulation 5 cm thick surrounds the pipe and has a thermal conductivity of 7 mW/m·°C. The convection heat-transfer coefficient on the outside of the pipe is 9 W/m²·°C. Estimate the energy loss from the pipe per meter of length.

Added by Donna L.

Question

Please give Ace some feedback