SCHOOL of ENGINEERING  

BENG2 APPLIED THERMODYNAMICS (THER 205)

Heat Transfer : Heat Exchangers - Fins

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1. Central heating panel radiator fins have dimensions approximately as shown to the right.
If the material is steel ( l = 49 W/mK) and the mean surface heat transfer coefficient by natural convection is 5 W/m²K, determine the fin efficiency. [61%]

2. A metal bar simulating a gas turbine blade is 102 mm long. It has a cross section area of 1.93 cm², and a perimeter of 76mm. Gas at 815°C flows over the bar, one end of which is maintained at 483°C by root cooling. Assuming the gas-to-surface heat transfer coefficient is 284 W/m²K and the conductivity of the blade material is 26 W/mK, find the heat transfer rate at the root. [109 W]

3. The inner surface of a 10mm thick aluminium wall is maintained at 120°C. Air at 15°C flows over the outside of the wall giving rise to a surface heat transfer coefficient of
57 W/m²K. Compare the heat transfer rates on the basis of one fin pitch by 1m width, when:-

(a) it has no fins, and

(b) it has rectangular fins 50mm long by 4mm thick pitched 18mm apart.

Find also the fin tip temperature for case ‘a’ above.

For aluminium, l = 225 W/mK. [107.5 W, 626 W, 105.3°C]

4. In attempt to increase the cooling from a glass vessel the base area is approximately trebled by making the base with fins as shown below. Air is blown over the base giving rise to a heat transfer surface coefficient of 26 W/m²K. The thermal conductivity of glass is 1.27 W/mK. Determine the area weighted fin efficiency. Comment on the attempt. [52%]

Fin width = 150mm