Heat Transfer Quiz-1

For a cylinder of radius 10 mm the temperature distribution in radial direction is given by T = 2r 2 – 4r + 5 where r (in m) is measured from centre. The cylinder is placed in ambient at 20°C and heat transfer coefficient of 8.49 W/m2K. If the thermal conductivity of cylinder is 30 W/mK. The wall temperature of cylinder is

30°C

18°C

34°C

29°C

A wall of 0.5 m thickness is to be constructed from a material which has an average thermal conductivity of 1.4 W/mK. The wall is to be insulated with a material having an average thermal conductivity of 0.35 W/mK so that the heat loss per square metre will not exceed 1450 W. Assuming that the inner and outer surface temperature are 1200°C and 15°C respectively. The thickness of insulation required is _____metre.

0.16

0.20

0.24

0.28

One end of a thermally black metallic rod of length 10 cm is inserted in a furnace whose temperature is 827°C. The curved surface of the rod is insulated. The room temperature is 27°C. When the steady state is attained the temperature of the other end of rod is 702°C. The thermal conductivity of the rod is ______ W/mK.

44.32

40.62

54.28

56.27

A counter flow heat exchanger is employed to cool 0.55 kg/s (cp = 2.45 kJ/kg-K) of oil from 115°C to 40°C by the use of water. The inlet and outlet temperature of cooling water (cp = 4.18 kJ/kg-K) are 15°C and 75°C, respectively. The effectiveness of the heat exchanger is

0.80

0.25

0.52

0.75

An enclosure 1 × 2 × 4 consists of three surfaces. Flat surface at the bottom 1 × 2, A1 = 2 m2, flat surface at the top 1 × 2 m, A2 = 2 m2 and all vertical surfaces taken together A3 = 24 m2. All the surfaces are flat and A1 is parallel to A2. Shape factor F1–2 = 0.035. The ratio of F13 and F3–2 will be

1.89

1.05

1.19

0.89