Heat Transfer Practice Test 9

1. The average drag coefficient for turbulent boundary layer flow past a thin plate is given by
C _f= 0.455/ (log ₁₀ R _el)^2.58
Where R _elis the Reynolds number based on plate length. A plate 50 cm wide and 5 m long is kept parallel to the flow of water with free stream velocity 3 m/s. Calculate the drag force on both sides of the plate. For water, kinematic viscosity = 0.01 stokes

73.38 N

83.38 N

53.38 N

63.38 N

2. A counter flow heat exchanger is used to col 2000 kg/hr of oil (c _p = 2.5 k J/kg K) from 105 degree Celsius to 30 degree Celsius by the use of water entering at 15 degree Celsius. If the overall heat transfer coefficient is expected to be 1.5 k W/m²K, find out the water flow rate. Presume that the exit temperature of the water is not to exceed 80 degree Celsius

1580.2 kg/hr

1480.2 kg/hr

1380.2 kg/hr

1680.2 kg/hr

3. What is the value of fouling factor for sea water?

0.0003-0.0004 m² K/W

0.0002-0.0003 m² K/W

0.0001-0.0002 m² K/W

0.0004-0.0005 m² K/W

4. Which is true for two dimensional boundary layer?

d u/d x - d v/d y = 0

d u/d x + d v/d y = 1

d u/d x - d v/d y = 1

d u/d x + d v/d y = 0

5. During test-run, air flows at 215 m/s velocity and 25 degree Celsius temperature past a smooth thin model airfoil which can be idealized as a flat plate. If the chord length of the airfoil is 15 cm, find drag per unit width. The relevant physical properties of air are
p = 1.82 kg/m³
v = 15.53 * 10 ^-6 m²/s

55.42 N per unit width

35.42 N per unit width

25.42 N per unit width

45.42 N per unit width

6. What is the symbol used for the coefficient of volumetric expansion?

7. For laminar film condensation on a vertical plate, the local heat transfer coefficient at the lower edge of the plate is given by

[k ³ p² g h _{f g}/4 δ l (t _sat – t _s)] ^0.5

[k ³ p² g h _{f g}/4 δ l (t _sat – t _s)] ^0.1

[k ³ p² g h _{f g}/4 δ l (t _sat – t _s)] ^0.25

[k ³ p² g h _{f g}/4 δ l (t _sat – t _s)] ^0.125

8. For laminar film condensation on a vertical plate, the mass flow rate of the condensate per unit depth of the film at any position x is given by

p g δ ³/ 3

p g δ ²/ 3

p g δ ³/ 3 σ

p g δ ²/ 3 σ

9. In how many categories heat exchangers are classified on the basis of direction of flow of fluids?

1 categories

2 categories

4 categories

3 categories

10. A small thermo-couple is positioned in a thermal boundary layer near a flat plate past which water flows at 30 degree Celsius and 0.15 m/s. The plate is heated to a surface temperature of 50 degree Celsius and at the location of the probe, the thickness of thermal boundary layer is 15 mm. If the temperature profile as measured by the probe is well-represented by
t – t _S/t _INFINITY– t _S = 1.5 (y/δ _t) – 0.5 (y/δ _t) ³
Determine the heat flux from plate to water

3266 W/m²

266 W/m²

1266 W/m²

2266 W/m²