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23) 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/m² .º C. Estimate the time required to cool the aluminum to 90 °C, using the lumped- capacity method.

23) 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/m² .º C. Estimate the time required to cool the aluminum to 90 °C, using the lumped- capacity method.

Elements Of Electromagnetics
Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
ChapterMA: Math Assessment
Section: Chapter Questions
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Solve only Q3 please
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 = 2Nux=L = 0.664Re,5 Pr0.334 For Aluminum take density=2787 kg/m³, thermal conductivity (k) =216 W/m.K, specific heat(c)=800 J/kg.K
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 = 2Nux=L = 0.664Re,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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