Liquid oxygen, which has a boiling into of 90 K and a latent heat of vaporization of 214 kJ/kg, is stored in a spherical container whose outer surface is of 500-mm diameter and at a temperature of − 10 ° C . The container is housed in a laboratory whose air and walls are at 25°C. (a) If the surface emissivity is 0.20 and the heat transfer coefficient associated with free convection at the outer surface of the container is 10 W / m 2 ⋅ K , what is the rate, in kg/s. at which oxygen vapor must be vented from the system? (b) Moisture in the ambient air will result in frost formation on the container, causing the surface emissivity to increase. Assuming the surface temperature and convection coefficient to remain at − 10 ° C and 10 W / m 2 ⋅ K , respectively, compute the oxygen evaporation rate (kg/s) as a function of surface emissivity over the range 0.2 ≤ ∈ ≤ 0.94 .
Liquid oxygen, which has a boiling into of 90 K and a latent heat of vaporization of 214 kJ/kg, is stored in a spherical container whose outer surface is of 500-mm diameter and at a temperature of − 10 ° C . The container is housed in a laboratory whose air and walls are at 25°C. (a) If the surface emissivity is 0.20 and the heat transfer coefficient associated with free convection at the outer surface of the container is 10 W / m 2 ⋅ K , what is the rate, in kg/s. at which oxygen vapor must be vented from the system? (b) Moisture in the ambient air will result in frost formation on the container, causing the surface emissivity to increase. Assuming the surface temperature and convection coefficient to remain at − 10 ° C and 10 W / m 2 ⋅ K , respectively, compute the oxygen evaporation rate (kg/s) as a function of surface emissivity over the range 0.2 ≤ ∈ ≤ 0.94 .
Solution Summary: The author explains the evaporation rate in kg/s at which oxygen vapor must be vented from the system.
Liquid oxygen, which has a boiling into of 90 K and a latent heat of vaporization of 214 kJ/kg, is stored in a spherical container whose outer surface is of 500-mm diameter and at a temperature of
−
10
°
C
. The container is housed in a laboratory whose air and walls are at 25°C. (a) If the surface emissivity is 0.20 and the heat transfer coefficient associated with free convection at the outer surface of the container is
10
W
/
m
2
⋅
K
, what is the rate, in kg/s. at which oxygen vapor must be vented from the system? (b) Moisture in the ambient air will result in frost formation on the container, causing the surface emissivity to increase. Assuming the surface temperature and convection coefficient to remain at
−
10
°
C
and
10
W
/
m
2
⋅
K
, respectively, compute the oxygen evaporation rate (kg/s) as a function of surface emissivity over the range
0.2
≤
∈
≤
0.94
.
An aluminum alloy (2024) plate, heated to a uniform temperature of Ti = 231°C, is allowed to cool while vertically suspended in a room where the ambient air and surroundings are both at 28°C. The plate is 0.4 m square with a thickness of 17 mm and an emissivity of 0.31.
(a) Develop an expression for the time rate of change of the plate temperature, assuming the temperature to be uniform at any time.
(b)Determine the initial rate of cooling (K/s) when the plate temperature is Ti °C.
The production line of a special biscuit at 30 ̊C and 1 atm has a 0.8 X 0.8 (m) square plate. One side of the plate is maintained at a temperature of 100 ̊C, while the other side is insulated.
Determine the rate of heat transfer from the plate by natural convection if the plate (i) Is horizontal with the hot surface facing down; (ii) Is horizontal with the hot surface facing up;
Data: The properties of air at the film temperature are: thermal conductivity, k= 0.0279 W/m.k); kinematic viscosity= 1.815 x 10-5 m2/s; Pr = 0.709
Question No. 1
Gaseous carbon dioxide at 1 atm and 300°C is flowing inside a horizontal pipe that has 5.3 cm
ID and 6.0 cm OD. The flow velocity of carbon dioxide is 15 m/s. The outside surface of the
pipe is exposed to the atmospheric air that has temperature of 40°C. Considering free convection
conditions at the outer pipe surface and assuming pipe wall temperature as 200°C, calculate the
inside overall heat transfer coefficient, outside heat transfer coefficient, and overall heat transfer
coefficient based on the inside surface of the pipe.
Warning: Calculate both the inside and the outside heat transfer coefficients only using the
respective correlations and ignore radiation effects.
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