3:10< Back1. Ch. 8An 8-m-long, uninsulated square duct of cross section 0.2 m x0.2 m and relative roughness 10³ passes through the atticspace of a house. Hot air enters the duct at 1 atm and 80°C ata volume flow rate of 0.15 m³/s. The duct surface is nearlyisothermal at 60°C. Determine the rate of heat loss from theduct to the attic space and the pressure difference between theinlet and outlet sections of the duct. Evaluate air properties ata bulk mean temperature of 80°C. Is this a good assumption?(Use the Moody chart if you need a friction factor.)Water2. Ch 8Liquid water flows at a mass flow rate of 0.7 kg/s through aconcentric annulus tube with the inlet and outlet meantemperatures of 20°C and 80°C, respectively. The concentricannulus tube has inner and outer diameters of 10 mm and 100mm, respectively. The inner tube wall is maintained with aconstant surface temperature of 120°C, while the outer tubesurface is insulated. Determine the length of the concentricannulus tube.-HW_CH8_CH9.docxFIGURE P9-95Dashboard9-95 Flat-plate solar collectors are often tilted up toward the sun in order to intercept a greater amount of direct solar radiation. The tiltangle from the horizontal also affects the rate of heat loss from the collector. Consider a 1.5-m-high and 3-m-wide solar collector that istilted at an angle from the horizontal. The back side of the absorber is heavily insulated. The absorber plate and the glass cover, whichare spaced 2.5 cm from each other, are maintained at temperatures of 80°C and 40°C, respectively. Determine the rate of heat loss fromthe absorber plate by natural convection for 80°, 30°, and 90°.188SolarradiationCalendar80°C40°COuter cover at TInsulation9-103 PD A hot liquid (c₂=950 J/kg-K) flows at a flow rate of 0.005 kg/s inside a tube with a diameter of 25 mm. At the tube exit, theliquid temperature decreases by 8°C from its temperature at the inlet. The hot liquid causes the tube surface temperature to be 120°C. Toprevent thermal burn hazards, the tube is enclosed in a concentric outer cover 5 cm in diameter. Determine whether the outer covertemperature is below 45°C to prevent thermal burns to human skin. Evaluate the properties of air in the concentric enclosure at 80°C andI atm pressure. Is this a good assumption?To DoInsulationGlasscoverAirspaceAbsorberplate3TD,D254NotificationsInbox5

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An 8-m-long, uninsulated square duct of cross section 0.2 m x 0.2 m and relative roughness 10³ passes through the attic space of a house. Hot air enters the duct at 1 atm and 80°C at a volume flow rate of 0.15 m³/s. The duct surface is nearly isothermal at 60°C. Determine the rate of heat loss from the duct to the attic space and the pressure difference between the inlet and outlet sections of the duct. Evaluate air properties at a bulk mean temperature of 80°C. Is this a good assumption? (Use the Moody chart if you need a friction factor.)

An 8-m-long, uninsulated square duct of cross section 0.2 m x 0.2 m and relative roughness 10³ passes through the attic space of a house. Hot air enters the duct at 1 atm and 80°C at a volume flow rate of 0.15 m³/s. The duct surface is nearly isothermal at 60°C. Determine the rate of heat loss from the duct to the attic space and the pressure difference between the inlet and outlet sections of the duct. Evaluate air properties at a bulk mean temperature of 80°C. Is this a good assumption? (Use the Moody chart if you need a friction factor.)

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

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Question

3:10
< Back
1. Ch. 8
An 8-m-long, uninsulated square duct of cross section 0.2 m x
0.2 m and relative roughness 10³ passes through the attic
space of a house. Hot air enters the duct at 1 atm and 80°C at
a volume flow rate of 0.15 m³/s. The duct surface is nearly
isothermal at 60°C. Determine the rate of heat loss from the
duct to the attic space and the pressure difference between the
inlet and outlet sections of the duct. Evaluate air properties at
a bulk mean temperature of 80°C. Is this a good assumption?
(Use the Moody chart if you need a friction factor.)
Water
2. Ch 8
Liquid water flows at a mass flow rate of 0.7 kg/s through a
concentric annulus tube with the inlet and outlet mean
temperatures of 20°C and 80°C, respectively. The concentric
annulus tube has inner and outer diameters of 10 mm and 100
mm, respectively. The inner tube wall is maintained with a
constant surface temperature of 120°C, while the outer tube
surface is insulated. Determine the length of the concentric
annulus tube.
-
HW_CH8_CH9.docx
FIGURE P9-95
Dashboard
9-95 Flat-plate solar collectors are often tilted up toward the sun in order to intercept a greater amount of direct solar radiation. The tilt
angle from the horizontal also affects the rate of heat loss from the collector. Consider a 1.5-m-high and 3-m-wide solar collector that is
tilted at an angle from the horizontal. The back side of the absorber is heavily insulated. The absorber plate and the glass cover, which
are spaced 2.5 cm from each other, are maintained at temperatures of 80°C and 40°C, respectively. Determine the rate of heat loss from
the absorber plate by natural convection for 80°, 30°, and 90°.
188
Solar
radiation
Calendar
80°C
40°C
Outer cover at T
Insulation
9-103 PD A hot liquid (c₂=950 J/kg-K) flows at a flow rate of 0.005 kg/s inside a tube with a diameter of 25 mm. At the tube exit, the
liquid temperature decreases by 8°C from its temperature at the inlet. The hot liquid causes the tube surface temperature to be 120°C. To
prevent thermal burn hazards, the tube is enclosed in a concentric outer cover 5 cm in diameter. Determine whether the outer cover
temperature is below 45°C to prevent thermal burns to human skin. Evaluate the properties of air in the concentric enclosure at 80°C and
I atm pressure. Is this a good assumption?
To Do
Insulation
Glass
cover
Airspace
Absorber
plate
3
TD,
D
254
Notifications
Inbox
5

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Hot air flows with a mass flow rate m = 0.09 kg/s through an uninsulated sheet metal duct of diameter D = 0.15 m, which is in the crawlspace of a house. The hot air enters at 110°C and, after a distance of L 5 m, cools to 80°C. The heat transfer coefficient between the duct surface and the ambient air at To 0°C is known to be h, = 9 W / m²K. (a) Calculate the heat loss from the duct over the length L. (b) Determine the heat flux and the surface temperature at x = L. (c) Determine the heat flux and the surface temperature at x = 0. Assume, for air at Tm 368 K: c, 1011 J/kg.K; for air at Tm.L = 353 K: k= 0.030 W/m.K, u = 209x10' N.s/m2, Pr = 0.70%; for air at Tm,0 = 383 K: k = 0.033 W/m.K, u=223x10" N.s/m2, Pr = 0.69. Show all calculations. Cold Air Hot air in -L-
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