A wooden sphere of diameter 5 cm is initially at a uniform temperature of 21 °C. Its surface temperature is suddenly raised to 83 °C. The thermal conductivity and thermal diffusivity of the wood are 0.15 W/m K and 0.82 x 10-7 m^2/s, respectively.  a) Calculate the temperature 2 cm beneath the surface of the sphere 30 min after the sudden increase in temperature. b) Calculate the energy gained by the sphere during this time.

Elements Of Electromagnetics
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A wooden sphere of diameter 5 cm is initially at a uniform temperature of 21 °C. Its surface
temperature is suddenly raised to 83 °C. The thermal conductivity and thermal diffusivity of
the wood are 0.15 W/m K and 0.82 x 10-7 m^2/s, respectively. 

a) Calculate the temperature 2 cm beneath the surface of the sphere 30 min after the sudden increase in temperature.

b) Calculate the energy gained by the sphere during this time. 

T(0,1)-T,
T-T,
0.8
0.7
0.6
1.0
20.9
Q(oc)
1.0
0.01
0.007
0.005
0.004
0.003
0.002
0.5
0.4
0.3
0.2
0.001
0.5
0.4
0.1
0.07
0.05
0.04
0.03
0.02
1.0
T(r.1)-T, 0.9
T(0.1)-T,
0.3
0.2
0.1
0
0.5 1.0
0
10-5
0.8 0.4
0.7 0.5
0.6
0.6
0.5
0.4 0.7
0.3 0.8
0.2 0.9
0.1
1.0
0
0.01
Bi=
r/R=0.2
THAN
aR
T
15 2.0
10-4
0.1
2.5 3 4 5 6 7 8 9 10
1.0
Bi= 0.001
0.002-
0.005.
0.01-
10-3
Bi=
02-
0.02
0.05
10 Bi 100
20
10-2 10-1
30 40
1
70
10
103
104
Bf Fo=to²/kpc
Figure 3- Dimensionless Transient Temperatures and Heat Transfer for a Sphere
Bi=
DR
noi
110 130 170 210
Fo-tk
pcR²
102
250
Transcribed Image Text:T(0,1)-T, T-T, 0.8 0.7 0.6 1.0 20.9 Q(oc) 1.0 0.01 0.007 0.005 0.004 0.003 0.002 0.5 0.4 0.3 0.2 0.001 0.5 0.4 0.1 0.07 0.05 0.04 0.03 0.02 1.0 T(r.1)-T, 0.9 T(0.1)-T, 0.3 0.2 0.1 0 0.5 1.0 0 10-5 0.8 0.4 0.7 0.5 0.6 0.6 0.5 0.4 0.7 0.3 0.8 0.2 0.9 0.1 1.0 0 0.01 Bi= r/R=0.2 THAN aR T 15 2.0 10-4 0.1 2.5 3 4 5 6 7 8 9 10 1.0 Bi= 0.001 0.002- 0.005. 0.01- 10-3 Bi= 02- 0.02 0.05 10 Bi 100 20 10-2 10-1 30 40 1 70 10 103 104 Bf Fo=to²/kpc Figure 3- Dimensionless Transient Temperatures and Heat Transfer for a Sphere Bi= DR noi 110 130 170 210 Fo-tk pcR² 102 250
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