A novel infrared recycler has been proposed for reclaiming the millions of kilograms of waste plastics produced by the dismantling and shredding of auto motive vehicles following their retirement. To address the problem of sorting mixed plastics into components such as polypropylene and polycarbonate, a washed stream of the mixed plastics is routed to an infrared heating system, where it is dried and subsequently heated to a temperature for which one of the components begins to soften, while the others remain rigid. The mixed stream is then routed through steel rollers, to which the softened plastic sticks and is removed from the stream. Heating of the stream is then continued to facilitate removal of a second component, and the heating/removal process is repeated until all of the components are separated. Consider the initial drying stage for a system comprised of a cylindrical heater aligned coaxially with a rotating drum of diameter D d = 1 m . Shortly after entering the drum, wet plastic pellets may be assumed to fully cover the bottom semicylindrical section and to remain at a temperature of T p = 325 K during the drying process. The surface area of the pellets may be assumed to correspond to that of the semicylinder and to have an emissivity of ε p = 0.95 . (a) If the flow of dry air through the drum maintains a convection mass transfer coefficient of 0.024 m/s on the surface of the pellets, what is the evaporation rate per unit length of the drum? (b) Neglecting convection heal transfer, determine the temperature T h that must be maintained by a heater of diameter D h = 0.10 m and emissivity ε h = 0.8 to sustain the foregoing evaporation rate. What is the corresponding value of the temperature T d for the top surface of the drum? The outer surface of the drum is well insulated, and its length-to-diameter ratio is large. As applied to the top ( d ) or bottom ( p ) surface of the drum, the view factor of an infinitely long semicylinder to itself, in the presence of a concentric, coaxial cylinder, may be expressed as F i i = 1 − 2 π { [ 1 − ( D h / D d ) 2 ] 1 / 2 + ( D h / D d ) sin − 1 ( D h / D d ) }
A novel infrared recycler has been proposed for reclaiming the millions of kilograms of waste plastics produced by the dismantling and shredding of auto motive vehicles following their retirement. To address the problem of sorting mixed plastics into components such as polypropylene and polycarbonate, a washed stream of the mixed plastics is routed to an infrared heating system, where it is dried and subsequently heated to a temperature for which one of the components begins to soften, while the others remain rigid. The mixed stream is then routed through steel rollers, to which the softened plastic sticks and is removed from the stream. Heating of the stream is then continued to facilitate removal of a second component, and the heating/removal process is repeated until all of the components are separated. Consider the initial drying stage for a system comprised of a cylindrical heater aligned coaxially with a rotating drum of diameter D d = 1 m . Shortly after entering the drum, wet plastic pellets may be assumed to fully cover the bottom semicylindrical section and to remain at a temperature of T p = 325 K during the drying process. The surface area of the pellets may be assumed to correspond to that of the semicylinder and to have an emissivity of ε p = 0.95 . (a) If the flow of dry air through the drum maintains a convection mass transfer coefficient of 0.024 m/s on the surface of the pellets, what is the evaporation rate per unit length of the drum? (b) Neglecting convection heal transfer, determine the temperature T h that must be maintained by a heater of diameter D h = 0.10 m and emissivity ε h = 0.8 to sustain the foregoing evaporation rate. What is the corresponding value of the temperature T d for the top surface of the drum? The outer surface of the drum is well insulated, and its length-to-diameter ratio is large. As applied to the top ( d ) or bottom ( p ) surface of the drum, the view factor of an infinitely long semicylinder to itself, in the presence of a concentric, coaxial cylinder, may be expressed as F i i = 1 − 2 π { [ 1 − ( D h / D d ) 2 ] 1 / 2 + ( D h / D d ) sin − 1 ( D h / D d ) }
Solution Summary: The following assumptions is to be made while solving the problem: flow conditions are steady, heat transfer from the drum is negligible.
A novel infrared recycler has been proposed for reclaiming the millions of kilograms of waste plastics produced by the dismantling and shredding of auto motive vehicles following their retirement. To address the problem of sorting mixed plastics into components such as polypropylene and polycarbonate, a washed stream of the mixed plastics is routed to an infrared heating system, where it is dried and subsequently heated to a temperature for which one of the components begins to soften, while the others remain rigid. The mixed stream is then routed through steel rollers, to which the softened plastic sticks and is removed from the stream. Heating of the stream is then continued to facilitate removal of a second component, and the heating/removal process is repeated until all of the components are separated. Consider the initial drying stage for a system comprised of a cylindrical heater aligned coaxially with a rotating drum of diameter
D
d
=
1
m
. Shortly after entering the drum, wet plastic pellets may be assumed to fully cover the bottom semicylindrical section and to remain at a temperature of
T
p
=
325
K
during the drying process. The surface area of the pellets may be assumed to correspond to that of the semicylinder and to have an emissivity of
ε
p
=
0.95
. (a) If the flow of dry air through the drum maintains a convection mass transfer coefficient of 0.024 m/s on the surface of the pellets, what is the evaporation rate per unit length of the drum? (b) Neglecting convection heal transfer, determine the temperature Ththat must be maintained by a heater of diameter
D
h
=
0.10
m
and emissivity
ε
h
=
0.8
to sustain the foregoing evaporation rate. What is the corresponding value of the temperature Tdfor the top surface of the drum? The outer surface of the drum is well insulated, and its length-to-diameter ratio is large. As applied to the top (d) or bottom (p) surface of the drum, the view factor of an infinitely long semicylinder to itself, in the presence of a concentric, coaxial cylinder, may be expressed as
F
i
i
=
1
−
2
π
{
[
1
−
(
D
h
/
D
d
)
2
]
1
/
2
+
(
D
h
/
D
d
)
sin
−
1
(
D
h
/
D
d
)
}
Net movement of mass from one location, usually meaning stream, phase, fraction, or component, to another. Mass transfer occurs in many processes, such as absorption, evaporation, drying, precipitation, membrane filtration, and distillation.
A manufacturing facility located at 32° N latitude has a glazing area of 60 m² facing west that consists of
double pane windows made of clear glass (SHGC = 0.766). To reduce the solar heat gain in summer, a
reflective film that will reduce the SHGC to 0.35 is considered. The cooling season consists of June, July,
August, and September, and the heating season, October through April. The average daily solar heat fluxes
incident on the west side at this latitude are 2.35, 3.03, 3.62, 4.00, 4.20, 4.24, 4.16, 3.93, 3.48, 2.94, 2.33,
and 2.07 kWh/day · m² for January through December, respectively. Also, the unit costs of electricity and
natural gas are $0.09/kWh and $0.45/therm., respectively. If the coefficient of performance of the cooling
system is 3.2 and the efficiency of the furnace is 0.90, determine the net annual cost savings due to installing
reflective coating on the windows. Also, determine the simple payback period if the installation cost of
reflective film is $20/m².
Answers:…
What is the actual wavelength and velocity of a near-infrared beam 1l = 0.901 mm2 of light modulated at a frequency of 330 MHz through an atmosphere with a dry bulb temperature, T, of 26°C; a relative humidity, h, of 75%; and an atmospheric pressure of 893 hPa?
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Principles of Heat Transfer (Activate Learning wi...Mechanical EngineeringISBN:9781305387102Author:Kreith, Frank; Manglik, Raj M.Publisher:Cengage Learning