A cold air chamber is proposed for quenching steel ball bearings of diameter D = 0.2 m and initial temperature T i = 400 ° C . Air in the chamber is maintained at − 15 ° C by a refrigeration system, and the steel balls pass through the chamber on a conveyor belt. Optimum bearing production requires that 70 % of the initial thermal energy content of the ball above − 15 ° C be removed. Radiation effects may be neglected, and the convection heat transfer coefficient within the chamber is 1000 W/m 2 ⋅ K . Estimate the residence time of the balls within the chamber, and recommend a drive velocity of the conveyor. The following properties may be used for the steel: k = 50 W/m ⋅ K, α = 2 × 10 − 5 m 2 /s, and c = 450 J / k g ⋅ K .
A cold air chamber is proposed for quenching steel ball bearings of diameter D = 0.2 m and initial temperature T i = 400 ° C . Air in the chamber is maintained at − 15 ° C by a refrigeration system, and the steel balls pass through the chamber on a conveyor belt. Optimum bearing production requires that 70 % of the initial thermal energy content of the ball above − 15 ° C be removed. Radiation effects may be neglected, and the convection heat transfer coefficient within the chamber is 1000 W/m 2 ⋅ K . Estimate the residence time of the balls within the chamber, and recommend a drive velocity of the conveyor. The following properties may be used for the steel: k = 50 W/m ⋅ K, α = 2 × 10 − 5 m 2 /s, and c = 450 J / k g ⋅ K .
Solution Summary: The author describes the time required by the steel balls to stay in the chamber and recommend a drive velocity for the conveyer belt.
A cold air chamber is proposed for quenching steel ball bearings of diameter
D
=
0.2
m
and initial temperature
T
i
=
400
°
C
.
Air in the chamber is maintained at
−
15
°
C
by a refrigeration system, and the steel balls pass through the chamber on a conveyor belt. Optimum bearing production requires that
70
%
of the initial thermal energy content of the ball above
−
15
°
C
be removed. Radiation effects may be neglected, and the convection heat transfer coefficient within the chamber is
1000
W/m
2
⋅
K
.
Estimate the residence time of the balls within the chamber, and recommend a drive velocity of the conveyor. The following properties may be used for the steel:
k
=
50
W/m
⋅
K,
α
=
2
×
10
−
5
m
2
/s,
and
c
=
450
J
/
k
g
⋅
K
.
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a) Find the temperature (°C) and power rating (kW) of the heater coil.
b) Find the boiling point of the water in the tank under these conditions, and the time required to bring the water to this temperature.
c) Find the proportion of water…
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1. Calculate the thickness of the insulating brick layer.
2. If the common brick is 9 in, calculate the exit temperature.
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