W A 30-cm-radius metallic sphere is having thermal conductivity of k = 100; , overall density of mk kg = 1500- and heat capacity of C₂ = 3000; . The sphere is initially at a uniform temperature of kgk T¡ = 20°C and is dropped into boiling water at T = 90°C. The convective heat transfer coefficient is assumed to be only h = 50- W m²K Jsing lump model, compute the temperature of the sphere after t = 1200 seconds. n solving this problem, please use and show the following steps (do not use EES) 1. Compute the volume and surface area of the sphere Vol = Vol 2. Compute the characteristic length Lc = As k 3. Compute the diffusivity a pCp h Lc k 5. Calculate the Fourier number Fo= (at)/Lc² 6. Calculate the excess temperature using 8 = exp(-Bi * Fo) T-Too 7. Compute the target temperature T using 8 = Ti-Too 4. Compute the Biot number Bi = ³ and A² = 4²

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)
8th Edition
ISBN:9781305387102
Author:Kreith, Frank; Manglik, Raj M.
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Chapter8: Natural Convection
Section: Chapter Questions
Problem 8.28P
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A 30-cm-radius metallic sphere is having thermal conductivity of k = 100. overall density of
W
7
mk
p = 1500-
kg
m²
and heat capacity of C₂ = 3000
The sphere is initially at a uniform temperature of
kgk
CO
T₁ = 20°C and is dropped into boiling water at T = 90°C. The convective heat transfer coefficient is
assumed to be only h = 50;
W
m²K
Using lump model, compute the temperature of the sphere after t = 1200 seconds.
In solving this problem, please use and show the following steps (do not use EES)
1. Compute the volume and surface area
2. Compute the characteristic length Lc
=
k
p Cp
h Lc
4. Compute the Biot number Bi
k
5. Calculate the Fourier number Fo= (at)/Lc²
6. Calculate the excess temperature using 0 = exp(-Bi * Fo)
T-Too
7. Compute the target temperature T using 0 =
Ti-Too
3. Compute the diffusivity a =
=
the sphere Vol
Vol
As
==
3
r³ and А¸ = 4πr²
Transcribed Image Text:A 30-cm-radius metallic sphere is having thermal conductivity of k = 100. overall density of W 7 mk p = 1500- kg m² and heat capacity of C₂ = 3000 The sphere is initially at a uniform temperature of kgk CO T₁ = 20°C and is dropped into boiling water at T = 90°C. The convective heat transfer coefficient is assumed to be only h = 50; W m²K Using lump model, compute the temperature of the sphere after t = 1200 seconds. In solving this problem, please use and show the following steps (do not use EES) 1. Compute the volume and surface area 2. Compute the characteristic length Lc = k p Cp h Lc 4. Compute the Biot number Bi k 5. Calculate the Fourier number Fo= (at)/Lc² 6. Calculate the excess temperature using 0 = exp(-Bi * Fo) T-Too 7. Compute the target temperature T using 0 = Ti-Too 3. Compute the diffusivity a = = the sphere Vol Vol As == 3 r³ and А¸ = 4πr²
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