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Ambient air at 20 degree Celsius flows past a flat plate with a sharp leading edge at 3 m/s. The plate is heated uniformly throughout its entire length and is maintained at a surface temperature of 40 degree Celsius. Calculate the distance from the leading edge at which the flow in the boundary layer changes from laminar to turbulent conditions. Assume that transition occurs at a critical Reynolds number of 500000
A
4.67 m
B
3.67 m
C
2.67 m
D
1.67 m
Correct Answer:
2.67 m
Re = x U INFINITY/v.
Ambient air at 20 degree Celsius flows past a flat plate with a sharp leading edge at 3 m/s. The plate is heated uniformly throughout its entire length and is maintained at a surface temperature of 40 degree Celsius. Calculate the thickness of the hydrodynamic boundary layer. Assume that transition occurs at a critical Reynolds number of 500000
A
16.5 mm
B
17.5 mm
C
18.5 mm
D
19.5 mm
Ambient air at 20 degree Celsius flows past a flat plate with a sharp leading edge at 3 m/s. The plate is heated uniformly throughout its entire length and is maintained at a surface temperature of 40 degree Celsius. Calculate the thickness of the thermal boundary layer. Assume that transition occurs at a critical Reynolds number of 500000
A
19.23 mm
B
18.23 mm
C
17.23 mm
D
16.23 mm
Ambient air at 20 degree Celsius flows past a flat plate with a sharp leading edge at 3 m/s. The plate is heated uniformly throughout its entire length and is maintained at a surface temperature of 40 degree Celsius. Calculate the local convective heat transfer coefficient. Assume that transition occurs at a critical Reynolds number of 500000
A
4.519 k J/m2 hr degree
B
5.519 k J/m2 hr degree
C
6.519 k J/m2 hr degree
D
7.519 k J/m2 hr degree
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
A
266 W/m2
B
1266 W/m2
C
2266 W/m2
D
3266 W/m2
The boundary layer thickness at a distance of l m from the leading edge of a flat plate, kept at zero angle of incidence to the flow direction, is O.l cm. The velocity outside the boundary layer is 25 ml sec. The boundary layer thickness at a distance of 4 m is (Assume that boundary layer is entirely laminar)
A
0.40 cm
B
0.20 cm
C
0.10 cm
D
0.05 cm
The rear window of an automobile is made of thick glass i.e. AB = 5 mm and thermal conductivity is 0.8 W/m degree. To defrost this window, a thin transparent film type heating element has been fixed to its inner surface. For the conditions given below, determine the electric power that must be provided per unit area of window if a temperature 5 degree Celsius is maintained at its outer surface. Interior air temperature and the corresponding surface coefficient are 20 degree Celsius and 12 W/m2 degree. Surrounding air temperature and the corresponding surface coefficient are – 15 degree Celsius and 70 W/m2 degree. Electric heater provides uniform heat flux
A
232.5 /m2
B
1232.5 /m2
C
2232.5 /m2
D
3232.5 /m2
Air at 25 degree Celsius flows over a flat surface with a sharp leading edge at 1.5 m/s. Find the boundary layer thickness at 0.5 from the leading edge. For air at 25 degree Celsius, kinematic viscosity = 15.53* 10n -6 m2/s
A
4.1376 cm
B
3.1376 cm
C
2.1376 cm
D
1.1376 cm
Air at 20 degree Celsius flows over a flat plate maintained at 75 degree Celsius. Measurements shows that temperature at a distance of 0.5 mm from the surface of plate is 50 degree Celsius. Presuming thermal conductivity of air is 0.0266 W/m K, estimate the value of local heat transfer coefficient
A
23.18 W/m 2 K
B
24.18 W/m 2 K
C
25.18 W/m 2 K
D
26.18 W/m 2 K
Air at 25 degree Celsius flows over a flat surface with a sharp leading edge at 1.5 m/s. Find the value of Reynolds number. For air at 25 degree Celsius, kinematic viscosity = 15.53* 10n -6 m2/s
A
38694
B
12846
C
48294
D
76386
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 is 15 mm. The probe is well-represented by t – t S/t INFINITY – t S = 1.5 (y/δ) – 0.5 (y/δ) 3 Determine the heat transfer coefficient
A
33.3 W/m2 K
B
43.3 W/m2 K
C
53.3 W/m2 K
D
63.3 W/m2 K