A sphere at 120°C was being exposed to surrounding air at 30°C with convection coefficient of 33 W/m2K. Thermocouples were attached to the sphere on the surface, in its center, and in a random point inside the sphere. The thermocouples showed readings of approximately 100°C at 40s later. On the next day, a fan was switched on which provided an airstream of approximately 10 m/s surrounding the sphere. Analyze this situation to predict the time taken for the sphere to cool from 60°C to 40°C. The properties of the sphere material and air at the specified temperature are provided in Table 1 Table 1 Properties Air at 30°C Sphere material Density (kg/m³) Specific heat (J/kg.K) Kinematic viscosity (m2/s) 1.151 8000 1.007 x10 300 1.619 x10 Dynamic viscosity (N.s/m) Conductivity (W/m.K) 1.86 x105 0.0265 600 Prandtl Number 0.707 Note: Dynamic viscosity of air at 60°C is 2.002 x10 N.s/m2
A sphere at 120°C was being exposed to surrounding air at 30°C with convection coefficient of 33 W/m2K. Thermocouples were attached to the sphere on the surface, in its center, and in a random point inside the sphere. The thermocouples showed readings of approximately 100°C at 40s later. On the next day, a fan was switched on which provided an airstream of approximately 10 m/s surrounding the sphere. Analyze this situation to predict the time taken for the sphere to cool from 60°C to 40°C. The properties of the sphere material and air at the specified temperature are provided in Table 1 Table 1 Properties Air at 30°C Sphere material Density (kg/m³) Specific heat (J/kg.K) Kinematic viscosity (m2/s) 1.151 8000 1.007 x10 300 1.619 x10 Dynamic viscosity (N.s/m) Conductivity (W/m.K) 1.86 x105 0.0265 600 Prandtl Number 0.707 Note: Dynamic viscosity of air at 60°C is 2.002 x10 N.s/m2
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN:9781305387102
Author:Kreith, Frank; Manglik, Raj M.
Publisher:Kreith, Frank; Manglik, Raj M.
Chapter7: Forced Convection Inside Tubes And Ducts
Section: Chapter Questions
Problem 7.50P
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Question
![A sphere at 120°C was being exposed to surrounding air at 30°C with
convection coefficient of 33 W/m2K. Thermocouples were attached to the
sphere on the surface, in its center, and in a random point inside the sphere.
The thermocouples showed readings of approximately 100°C at 40s later. On
the next day, a fan was switched on which provided an airstream of
approximately 10 m/s surrounding the sphere. Analyze this situation to predict
the time taken for the sphere to cool from 60°C to 40°C. The properties of the
sphere material and air at the specified temperature are provided in Table 1
Table 1
Properties
Air at 30°C
Sphere material
Density (kg/m³)
Specific heat (J/kg.K)
Kinematic viscosity (m2/s)
1.151
8000
1.007 x10
300
1.619 x10
Dynamic viscosity (N.s/m)
Conductivity (W/m.K)
1.86 x105
0.0265
600
Prandtl Number
0.707
Note: Dynamic viscosity of air at 60°C is 2.002 x10 N.s/m2](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2F2319ecf4-add7-44c6-a774-3e942499a68f%2Fabd83b9d-bcdf-48a0-bf28-27df25334177%2Fgfqhhxo_processed.png&w=3840&q=75)
Transcribed Image Text:A sphere at 120°C was being exposed to surrounding air at 30°C with
convection coefficient of 33 W/m2K. Thermocouples were attached to the
sphere on the surface, in its center, and in a random point inside the sphere.
The thermocouples showed readings of approximately 100°C at 40s later. On
the next day, a fan was switched on which provided an airstream of
approximately 10 m/s surrounding the sphere. Analyze this situation to predict
the time taken for the sphere to cool from 60°C to 40°C. The properties of the
sphere material and air at the specified temperature are provided in Table 1
Table 1
Properties
Air at 30°C
Sphere material
Density (kg/m³)
Specific heat (J/kg.K)
Kinematic viscosity (m2/s)
1.151
8000
1.007 x10
300
1.619 x10
Dynamic viscosity (N.s/m)
Conductivity (W/m.K)
1.86 x105
0.0265
600
Prandtl Number
0.707
Note: Dynamic viscosity of air at 60°C is 2.002 x10 N.s/m2
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