A vertical slab of Wood’s metal is joined to a substrate onone surface and is incited as it is uniformly irradiated by alaser source on the opposite surface. The metal is initiallyat its fusion temperature of T f = 72 ° C , and the melt runsoff by gravity as soon as it is formed. The absorptivity ofthe metal to the laser radiation is α 1 = 0.4 , and its latentheat of fusion is h s f = 33 kJ/kg . (a) Neglecting heat transfer from the irradiated surfaceby convection or radiation exchange with thesurroundings, determine the instantaneous rate ofmelting in Kg/s ⋅ m 2 if the laser irradiation is 5 kW / m 2 .How much material is removed if irradiation is maintained for a period of 2 s? (b) Allowing for convection to ambient air, with T ∞ = 20 ° C and h = 15 W/m 2 ⋅ K , and radiationexchange with large surroundings ( ∈ = 0.4 , T s u r = 20 ° C ) , determine the instantaneous rate of melting during irradiation.
A vertical slab of Wood’s metal is joined to a substrate onone surface and is incited as it is uniformly irradiated by alaser source on the opposite surface. The metal is initiallyat its fusion temperature of T f = 72 ° C , and the melt runsoff by gravity as soon as it is formed. The absorptivity ofthe metal to the laser radiation is α 1 = 0.4 , and its latentheat of fusion is h s f = 33 kJ/kg . (a) Neglecting heat transfer from the irradiated surfaceby convection or radiation exchange with thesurroundings, determine the instantaneous rate ofmelting in Kg/s ⋅ m 2 if the laser irradiation is 5 kW / m 2 .How much material is removed if irradiation is maintained for a period of 2 s? (b) Allowing for convection to ambient air, with T ∞ = 20 ° C and h = 15 W/m 2 ⋅ K , and radiationexchange with large surroundings ( ∈ = 0.4 , T s u r = 20 ° C ) , determine the instantaneous rate of melting during irradiation.
Solution Summary: The author explains the instantaneous rate of melting and the amount of material removed.
A vertical slab of Wood’s metal is joined to a substrate onone surface and is incited as it is uniformly irradiated by alaser source on the opposite surface. The metal is initiallyat its fusion temperature of
T
f
=
72
°
C
, and the melt runsoff by gravity as soon as it is formed. The absorptivity ofthe metal to the laser radiation is
α
1
=
0.4
, and its latentheat of fusion is
h
s
f
=
33
kJ/kg
. (a) Neglecting heat transfer from the irradiated surfaceby convection or radiation exchange with thesurroundings, determine the instantaneous rate ofmelting in
Kg/s
⋅
m
2
if the laser irradiation is
5 kW
/
m
2
.How much material is removed if irradiation is maintained for a period of 2 s? (b) Allowing for convection to ambient air, with
T
∞
=
20
°
C
and
h
=
15
W/m
2
⋅
K
, and radiationexchange with large surroundings
(
∈
=
0.4
,
T
s
u
r
=
20
°
C
)
, determine the instantaneous rate of melting during irradiation.
The basal metabolic rate isthe rate at which energy is produced in the body when a person is at rest.A 75 kg (165 lb) person of height 1.83 m (6 ft) has a body surface areaof approximately 2.0 m2. (a) What is the net amount of heat this personcould radiate per second into a room at 18°C (about 65°F) if his skin’ssurface temperature is 30°C? (At such temperatures, nearly all the heatis infrared radiation, for which the body’s emissivity is 1.0, regardless ofthe amount of pigment.) (b) Normally, 80% of the energy produced bymetabolism goes into heat, while the rest goes into things like pumpingblood and repairing cells. Also normally, a person at rest can get rid ofthis excess heat just through radiation. Use your answer to part (a) to findthis person’s basal metabolic rate.
Two concentric spheres of diameters D1 = 0.3 m andD2 = 0.4 m are maintained at uniform temperatures T1 = 700 Kand T2 = 500 K and have emissivities «1 = 0.5 and «2 = 0.7,respectively. Determine the net rate of radiation heat transferbetween the two spheres. Also, determine the convection heattransfer coefficient at the outer surface if both the surroundingmedium and the surrounding surfaces are at 30°C. Assume theemissivity of the outer surface is 0.35.
The temperature of a hot gas stream flowing in a duct (90cm) length and (30cm) diameter is to be measured by using a spherical thermocouple junction (2mm) in diameter placed at the center of the duct. The duct wall is at (30 ° C) and the gas stream is at (110 ° C). If the heat is being transferred to the thermocouple at the rate of (560 W / m²) from the gas, and both the thermocouple and the duct are considered black, what will be the reading of the thermocouple?
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