SCHOOL of ENGINEERING  

BENG2 APPLIED THERMODYNAMICS (THER 205)

Heat Transfer : 2-D Steady State Conduction

Use spreadsheet methods and the recommended mesh size

Click here to see spreadsheet. Click on page tabs to see solutions to individual questions.

1. A 2 m square chimney has a flue 0.8 m square. The internal and external surface temperatures are 225°C and 25°C respectively. Calculate the heat transfer rate per unit height if the thermal conductivity of brick is 0.9 W/mK. (mesh = 20cm) [1422 W/m]

2. In Q.1 halve your mesh size and compare results. [1385 W/m]

3. Repeat Q.1 with convection on the outside only: where h = 22.5 W/mK, where the air temperature is 20°C . (mesh = 10cm) [989 W/m]

4. Electrical heating elements are buried 50mm from the upper surface of a concrete slab 120mm thick, equi-spaced at 200mm intervals. Assuming the base of the concrete slab is perfectly insulated, determine the temperature distribution in the concrete slab. The heating cable temperature is 50°C. The air temperature is 19°C with an upper surface heat transfer coefficient of 20 W/m²K. Assume l _concrete = 1.37 W/mK.
Determine the average surface temperature, and hence determine the average heat transfer rate into the air per square meter of slab. (mesh = 10mm) [29.2°C, 204 W/m²]

5. An alloy bus bar is of right-angled section 50 mm by 50 mm by 10 mm thick. It carries a current of 27,850 amps. It is air cooled. The surface temperature on the outside of the angle section is 50°C and on the inside it is 65°C. The temperature at the ends is linear between the inside and outside. Determine the temperature distribution within the cross section, and also calculate the energy dissipated per meter length. (mesh = 2mm)
For the alloy: its thermal conductivity is 76.6 W/mK;
its electrical resistivity is 4 x 10^-8 ohm m. [34.47 kW/m]