Q3) A sphere of aluminum has a diameter of 5 cm is initially at a temperature of 200 °C is suddenly immersed in a fluid at 40 °c. The convection heat-transfer coefficient is 100 W/m? .° C. Estimate the time required to cool the aluminum to 90 °C, using the lumped- capacity method.
Q3) A sphere of aluminum has a diameter of 5 cm is initially at a temperature of 200 °C is suddenly immersed in a fluid at 40 °c. The convection heat-transfer coefficient is 100 W/m? .° C. Estimate the time required to cool the aluminum to 90 °C, using the lumped- capacity method.
Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
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Author:Kreith, Frank; Manglik, Raj M.
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Chapter2: Steady Heat Conduction
Section: Chapter Questions
Problem 2.30P: 2.30 An electrical heater capable of generating 10,000 W is to be designed. The heating element is...
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![Q1) A laser slab with thermal conductivity of 5 W/m. K, thickness of 2 cm, has a uniform heat
generation of 4x105 W/m ³ due to uniform pumping assume the convection heat transfer from
the slab is 100 W/m?.C. if the environmental temperature is 15 ° C What is the surface
temperature of the slab also find the temperature at the center of the slab?
Q2) A semi-infinite solid of aluminum at an initial temperature of 20 °C is suddenly imposed
to surface temperature of 90 °C. Calculate the temperature at a depth of 1 cm after 1.8 s.
Q3) A sphere of aluminum has a diameter of 5 cm is initially at a temperature of 200 °C is
suddenly immersed in a fluid at 40 °C. The convection heat-transfer coefficient is
100 W/m? .° C. Estimate the time required to cool the aluminum to 90 °C, using the lumped-
capacity method.
Q4) Air at 1 atm and 20 °C flows across a large concrete surface 4 m wide and length of 2 m
and is maintained at 60°C The flow velocity is 0.1 m /s. Calculate the convection heat loss
from the surface. For air take [u=1.906×10 5 kg/m.s, k=0.0281 W/m •C, Pr=0.7, R=287 J/kg.K]
Assume
Nuį = 2NU×=L = 0.664RE9.5 Pr0.334
For Aluminum take density=2787 kg/m³, thermal conductivity (k) =216 W/m.K, specific
heat(c)=800 J/kg.K](/v2/_next/image?url=https%3A%2F%2Fcontent.bartleby.com%2Fqna-images%2Fquestion%2Fe225ebec-0b2b-406c-8027-6f440426eccd%2Ff8c91548-6ab3-42a0-83b1-9be918d5ec76%2F1w4z1ew_processed.png&w=3840&q=75)
Transcribed Image Text:Q1) A laser slab with thermal conductivity of 5 W/m. K, thickness of 2 cm, has a uniform heat
generation of 4x105 W/m ³ due to uniform pumping assume the convection heat transfer from
the slab is 100 W/m?.C. if the environmental temperature is 15 ° C What is the surface
temperature of the slab also find the temperature at the center of the slab?
Q2) A semi-infinite solid of aluminum at an initial temperature of 20 °C is suddenly imposed
to surface temperature of 90 °C. Calculate the temperature at a depth of 1 cm after 1.8 s.
Q3) A sphere of aluminum has a diameter of 5 cm is initially at a temperature of 200 °C is
suddenly immersed in a fluid at 40 °C. The convection heat-transfer coefficient is
100 W/m? .° C. Estimate the time required to cool the aluminum to 90 °C, using the lumped-
capacity method.
Q4) Air at 1 atm and 20 °C flows across a large concrete surface 4 m wide and length of 2 m
and is maintained at 60°C The flow velocity is 0.1 m /s. Calculate the convection heat loss
from the surface. For air take [u=1.906×10 5 kg/m.s, k=0.0281 W/m •C, Pr=0.7, R=287 J/kg.K]
Assume
Nuį = 2NU×=L = 0.664RE9.5 Pr0.334
For Aluminum take density=2787 kg/m³, thermal conductivity (k) =216 W/m.K, specific
heat(c)=800 J/kg.K
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