A carbon nanotube is suspended across a trench of width s = 5 μm that separates two islands, each at T ∞ = 300 K . A focused laser beam irradiates the nanotube at a distance ξ from the left island, delivering q = 10 μW of energy to the nanotube. The nanotube temperature is measured at the midpoint of the trench using a point probe. The measured nanotube temperature is T 1 = 324.5 K for ξ 1 = 1.5 μm and T 2 = 326.4 K for ξ 2 = 3.5 μm . Determine the two contact resistances, R t , c , L and R t , c , R at the left and right ends of the nanotube, respectively. The experiment is performed in a vacuum with T sur = 300 K . The nanotube thermal conductivity and diameter are ken k cn = 3100 W/m ⋅ K and D = 14 nm, respectively.
A carbon nanotube is suspended across a trench of width s = 5 μm that separates two islands, each at T ∞ = 300 K . A focused laser beam irradiates the nanotube at a distance ξ from the left island, delivering q = 10 μW of energy to the nanotube. The nanotube temperature is measured at the midpoint of the trench using a point probe. The measured nanotube temperature is T 1 = 324.5 K for ξ 1 = 1.5 μm and T 2 = 326.4 K for ξ 2 = 3.5 μm . Determine the two contact resistances, R t , c , L and R t , c , R at the left and right ends of the nanotube, respectively. The experiment is performed in a vacuum with T sur = 300 K . The nanotube thermal conductivity and diameter are ken k cn = 3100 W/m ⋅ K and D = 14 nm, respectively.
Solution Summary: The author explains the thermal conductivities for both the laser irradiation locations.
A carbon nanotube is suspended across a trench of width
s
=
5
μm
that separates two islands, each at
T
∞
=
300
K
.
A focused laser beam irradiates the nanotube at a distance
ξ
from the left island, delivering
q
=
10
μW
of energy to the nanotube. The nanotube temperature is measured at the midpoint of the trench using a point probe. The measured nanotube temperature is
T
1
=
324.5
K
for
ξ
1
=
1.5
μm
and
T
2
=
326.4
K
for
ξ
2
=
3.5
μm
.
Determine the two contact resistances,
R
t
,
c
,
L
and
R
t
,
c
,
R
at the left and right ends of the nanotube, respectively. The experiment is performed in a vacuum with
T
sur
=
300
K
.
The nanotube thermal conductivity and diameter are ken
k
cn
=
3100
W/m
⋅
K
and
D
=
14
nm,
respectively.
Q1: Determine the length, angle of contact, and width of a 9.75 mm thick
leather belt required to transmit 15 kW from a motor running at 900 r.p.m. The
diameter of the driving pulley of the motor is 300 mm. The driven pulley runs at
300 r.p.m. and the distance between the centers of two pulleys is 3 meters. The
density of the leather is 1000 kg/m³. The maximum allowable stress in the
leather is 2.5 MPa. The coefficient of friction between the leather and pulley is
0.3. Assume open belt drive.
5. A 15 kW and 1200 r.p.m. motor drives a compressor at 300 r.p.m. through a pair of spur gears having
20° stub teeth. The centre to centre distance between the shafts is 400 mm. The motor pinion is made
of forged steel having an allowable static stress as 210 MPa, while the gear is made of cast steel
having allowable static stress as 140 MPa. Assuming that the drive operates 8 to 10 hours per day
under light shock conditions, find from the standpoint of strength,
1. Module; 2. Face width and 3. Number of teeth and pitch circle diameter of each gear.
Check the gears thus designed from the consideration of wear. The surface endurance limit may be
taken as 700 MPa. [Ans. m = 6 mm; b= 60 mm; Tp=24; T=96; Dp = 144mm; DG = 576 mm]
4.
G
A micarta pinion rotating at 1200 r.p.m. is to transmit 1 kW to a cast iron gear at a speed of 192 r.p.m.
Assuming a starting overload of 20% and using 20° full depth involute teeth, determine the module,
number of teeth on the pinion and gear and face width. Take allowable static strength for micarta as 40
MPa and for cast iron as 53 MPa. Check the pair in wear.
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