A thermopane window consists of two pieces of glass 7 mm thick that enclose an air space 7 mm thick. The window separates room air at 20°C from outside ambient air at -10°C. The convection coefficient associated with the inner (room- side) surface is h= 10 W/m2. K. If the convection coefficient associated with the outer (ambient) air is h,= 80 W/m². K, what is the heat loss through a window that is 0.8 m long by 0.5 m wide? Neglect radiation, and assume the air enclosed between the panes to be stagnant. k, (glass) = 1.4 W/m.K, ka (air) = %3D 0.0245 W/m.K Window, 0.8 m x 0.5 m Glass FL+L+-L Air |I L= 0.007 m Air Teo =-10 °C ho = 80 W/m2-K Air Too.j = 20 °C h; = 10 W/m2•K %3D %3D

A thermopane window consists of two pieces of glass 7 mm thick that enclose an air space 7 mm thick. The window separates room air at 20°C from outside ambient air at -10°C. The convection coefficient associated with the inner (room- side) surface is h= 10 W/m2. K. If the convection coefficient associated with the outer (ambient) air is h,= 80 W/m². K, what is the heat loss through a window that is 0.8 m long by 0.5 m wide? Neglect radiation, and assume the air enclosed between the panes to be stagnant. k, (glass) = 1.4 W/m.K, ka (air) = %3D 0.0245 W/m.K Window, 0.8 m x 0.5 m Glass FL+L+-L Air |I L= 0.007 m Air Teo =-10 °C ho = 80 W/m2-K Air Too.j = 20 °C h; = 10 W/m2•K %3D %3D

Principles of Heat Transfer (Activate Learning with these NEW titles from Engineering!)

8th Edition

ISBN:9781305387102

Author:Kreith, Frank; Manglik, Raj M.

Publisher:Kreith, Frank; Manglik, Raj M.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.57P

See similar textbooks

Similar questions

2.3 The shield of a nuclear reactor is idealized by a large 25-cm-thick flat plate having a thermal conductivity of . Radiation from the interior of the reactor penetrates the shield and there produces heat generation that decreases exponentially from a value of at the inner surface to a value of at a distance of 12.5 cm from the interior surface. If the exterior surface is kept at 38°C by forced convection, determine the temperature at the inner surface of the field. Hint: First set up the differential equation for a system in which the heat generation rate varies according to .
1.4 To measure thermal conductivity, two similar 1-cm-thick specimens are placed in the apparatus shown in the accompanying sketch. Electric current is supplied to the guard heater, and a wattmeter shows that the power dissipation is 10 W. Thermocouples attached to the warmer and to the cooler surfaces show temperatures of 322 and 300 K, respectively. Calculate the thermal conductivity of the material at the mean temperature in W/m K. Problem 1.4
Question 1: A glass window of width W = 1 m and height H = 2m is 5 mm thick and has a thermal conductivity of kg =1.4 W/m.K. If the inner and outer surface temperatures of the glass are 15 °C and -20 C, respectively, on a cold winter day, what is the rate of heat loss through the glass? To reduce heat loss through windows, it is customary to use a double pane construction in which adjoining panes are separated by an air space. If the spacing is 10 mm and the glass surfaces in contact with the air have temperatures of (last two digit of your Registration number) °C and -15 °C, what is the rate of heat loss from a 1 mx2mwindow? The thermal conductivity of air is ka = 0.024 W/m.K.
Question 1: A glass window of width W = 1 m and height H = 2 m is 5 mm thick and has a thermal conductivity of kg =1.4 W/m.K. If the inner and outer surface temperatures of the glass are 15 oC and -20 oC, respectively, on a cold winter day, what is the rate of heat loss through the glass? To reduce heat loss through windows, it is customary to use a double pane construction in which adjoining panes are separated by an air space. If the spacing is 10 mm and the glass surfaces in contact with the air have temperatures of 20 oC and -15 oC, what is the rate of heat loss from a 1 m x 2 m window? The thermal conductivity of air is ka = 0.024 W/m.K.
A house located in the south of the country was built using windowsdoubles to reduce heat loss to the outside environment on very cold days. Consider that the house has 6 windows 80 cm high and 1.2 m wide, each consisting of 2 layers of glass (kv=1.4 W/(m.oC) 4 mm thick, separated from each other for a spacing of 10 mm filled with stagnant air (ka=0.024 W/(mK), we disregard natural convection effects) On a day when the interior of the house is kept at 22oC, with h=10 W/(m2. K) while the external environment is at 5oC with h=50 W/(m2.K), it is requested:(a) What is the rate of heat dissipation through the windows?(b) What are the temperatures on the glass surfaces inside and in theexterior of the house?(c) Which of the resistances is the limiting in the dissipation process ofheat?(d) Estimate the increase in dissipation rate if we consider that the natural air convection in the space between the windows is characterizedby a convective coefficient h=5 W/(m.K).(e) How the value obtained…
A 1 in. o.d. (outer diameter) tube reactor is insulated with a 3 inch layer of asbestos. If the temperature of the outer surface of the insulation is 100 °F and the rate of heat loss per foot of reactor length is 50 BTU/hr, what must the temperature of the inside of the reactor be? [for asbestos, k = 0.105 BTU/hr ft °F]
The rear window of an automobile is defogged by passing warm air over its inner surface. If the warm air is at T∞,i=40°C and the corresponding convection coefficient is hi=30 W/m2·K, what are the inner and outer surface temperatures, in °C, of 4-mm-thick window glass, if the outside ambient air temperature is T∞,o= -27.5°C and the associated convection coefficient is ho=65 W/m2·K? Evaluate the properties of the glass at 300 K. a. what is Ts, i in °C? b. what is Ts, o in °C?
1. A simple cavity wall consists of two brick layers separated by an air gap of 50 mm. If the inside air temperature is 20oC and the ambient outside temperature is 5 oC, calculate the heat flux through the wall. Bricks are 100 mm thick with thermal conductivity kbrick = 0.5 W/m K, hin = 10 W/m2 K, hout = 20 W/m2 K. The internal air cavity can be considered still (no convection) with kair = 0.015 W/m K. 2. On a day in winter, the outside air temperature drops to -5 oC and the outside convective heat transfer changes to hout = (2 x V) + 8.9 W/m2 K. If the outside wind speed gusts at 50 kph, calculate the change in heat flux for the wall in question 3.
A furnace wall consists of 200 mm of refractory fireclay brick, 100 mm of kaolin brick, and 6 mm of steel plate. The fire side of the refractory is at 1150°C and the outside of the steel is at 30°C. An accurate heat balance over the furnace shows the heat loss from the wall to be 300 W/m2. It is known that there may be thin layers of air between the layers of brick and steel. To how many millimeters of kaolin are these air layers equivalent? The thermal conductivities of the fireclay brick, the kaolin brick and the steel are 1.7, 0.17, 17, respectively
A 10.0-cm cube of stainless steel is initially at 500oC. It is suddenly immersed in a tank of oil maintained at 100oC. The convection coefficient is 1000 W/m2×oC. Calculate the temperature at the center of one face after 1 min.Data: stainless steel properties, k = 22 W/m×oC, r = 7,689 kg/m3, c = 460 J/kg×oC.
The rear window of an automobile is defogged by pass- ing warm air over its inner surface. (a) If the warm air is at T ,i 40 C and the correspond- ing convection coefficient is hi 30 W/m2 K, what are the inner and outer surface temperatures of 4-mm-thick window glass, if the outside ambient air temperature is T ,o 10 C and the associated con- vection coefficient is ho 65 W/m2 K? In practice T ,o and ho vary according to weather conditions and car speed. For values of ho 2, 65, and 100 W/m2 K, compute and plot the inner and outer surface temperatures as a function of T ,o for –30 T ,o 0 C.
3.6 Heat losses through windows in buildings are substantial. What would be the percentage reduction in heat loss that would be mitigated by replacing a window containing a single pane of glass with (a) double-pane low-E insulating glass or (b) a 3-inch-thick sheet of expanded polystyrene sheet? The quoted R values for these items are: • single pane of glass: 0.90 ft 2 hr ° F/Btu, • double pane of low-E insulating glass: 2.3 ft 2 hr ° F/Btu, • 1-inch-thick sheet of polystyrene sheet: 4.0 ft 2 hr ° F/Btu.