A Thermopane window consists of two 3-mm-thick pane of glass separated by a stagnant air space of thickness 6 mm. The convection heat transfer coefficients for the inside and outside air are hi = 5 W/m2·K and ho = 50 W/m2·K, respectively. The inside and outside air temperatures are Ti = 25°C and To = 0°C, respectively. a) Determine the heat flux through the Thermopane window. b) Compare the above result to the same environment around a single-pane glass window of thickness L = 12 mm.

A Thermopane window consists of two 3-mm-thick pane of glass separated by a stagnant air space of thickness 6 mm. The convection heat transfer coefficients for the inside and outside air are hi = 5 W/m2·K and ho = 50 W/m2·K, respectively. The inside and outside air temperatures are Ti = 25°C and To = 0°C, respectively. a) Determine the heat flux through the Thermopane window. b) Compare the above result to the same environment around a single-pane glass window of thickness L = 12 mm.

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 1.19P: 1.19 A cryogenic fluid is stored in a 0.3-m-diameter spherical container is still air. If the...

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1.1 On a cold winter day, the outer surface of a 0.2-m-thick concrete wall of a warehouse is exposed to temperature of –5°C, while the inner surface is kept at 20°C. The thermal conductivity of the concrete is 1.2 W/m K. Determine the heat loss through the wall, which is 10-m long and 3-m high. Problem 1.1
3.16 A large, 2.54-cm.-thick copper plate is placed between two air streams. The heat transfer coefficient on one side is and on the other side is . If the temperature of both streams is suddenly changed from 38°C to 93°C, determine how long it takes for the copper plate to reach a temperature of 82°C.
An electrical transmission line of 1.2-cm diameter carries a current of 200 amps and has a resistance of 310-4 ohm per meter of length. If the air around this line is at v, determine the surface temperature on a windy day, assuming a wind blows across the line at 33 km/h.
2.9 In a large chemical factory, hot gases at 2273 K are cooled by a liquid at 373 K with gas-side and liquid-side convection heat transfer coefficients of 50 and , respectively. The wall that separates the gas and liquid streams is composed of a 2-cm thick oxide layer on the gas side and a 4-cm thick slab of stainless steel on the liquid side. There is a contact resistance between the oxide layer and the steel of . Determine the rate of heat loss from hot gases through the composite wall to the liquid.
The air-conditioning system in a Chevrolet van for use in desert climates is to be sized. The system is to maintain an interior temperature of 20C when the van travels at 100 km/h through dry air at 30C at night. If the top of the van is idealized as a flat plate 6 m long and 2 m wide and the sides as flat plates 3 m tall and 6 m long, estimate the rate at which heat must be removed from the interior to maintain the specified
An electronic device that internally generates 600 mW of heat has a maximum permissible operating temperature of 70C. It is to be cooled in 25C air by attaching aluminum fins with a total surface area of 12cm2. The convection heat transfer coefficient between the fins and the air is 20W/m2K. Estimate the operating temperature when the fins are attached in such a way that (a) there is a contact resistance of approximately 50 K/W between the surface of the device and the fin array and (b) there is no contact resistance (in this case, the construction of the device is more expensive). Comment on the design options.
1.19 A cryogenic fluid is stored in a 0.3-m-diameter spherical container is still air. If the convection heat transfer coefficient between the outer surface of the container and the air is 6.8 , the temperature of the air is 27°C, and the temperature of the surface of the sphere is –183°C, determine the rate of heat transfer by convection.
1. (a) Consider a room with a 1.8-m-high and 2.0-m-wide double-pane window consisting of two 4-mm-thick layers of glass separated by a 10-mm-wide stagnant air space. The convection heat transfer coefficients on the inner and outer surfaces of the window are 12 W/m2 K and 25 W/m2 K, respectively, while the average thermal conductivity of glass is 0.78 W/m K; and the air, 0.026 W/m K. If the room is maintained at 22 oC, the outside temperature is -4 oC and heat transfer due to radiation can be neglected, determine: (i) Draw the sketch and thermal resistance network; (ii) the total thermal resistance; (iii) the steady rate of heat transfer through this double-pane window; (iv) the temperature of the inner surface of the window.…
In a multilayered rectangular wall, the thermal resistance of the first layer is 0.005 °C/W, the resistance of the second layer is 0.2° C/W, and for the third layer it is 0.1 ° C/W. The overall temperature gradient in the multilayered wall from one side to another is 70° C. a. Determine the heat flux through the wall. b. If the thermal resistance of the second layer is doubled to 0.4° C/W, what will be its influence in % on the heat flux, assuming the temperature gradient remains the same?
Question 3: A house has a composite wall of wood, fiberglass insulation, and plaster board, as indicated in the sketch. On a cold winter day the convection heat transfer coefficients are ho 60 W/m2 K and hi 30 W/m2 K. The total wall surface area is 350 m2. (a)Determine the total heat loss through the wall. (b) If the wind were blowing violently, raising ho to 300 W/m2 K, determine the percentage increase in the heat loss.
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.
The 4-mm-thick rear window of an automobile is defogged by passing warm air over its inner surface. Warm air temperature is at T,1 = 40C and corresponding convection coefficient is h1 =30 W/(m2·K). Outer ambient temperature T,2 = 5C and corresponding convection coefficient is h2 = 70 W/(m2·K). The size of the window is 0.5 m (height)  1.5 m (width). A. Draw two thermal circuits (one based on heat rate and one based on heat flux) considering the convection occurring over inner and outer surfaces and the conduction through the window. Show the equations for the thermal resistances in the circuits.B. Determine the total thermal resistance based on heat flux in m2K/W andoverall heat transfer coefficient U in W/m2K. Find the thermal conductivity of glass (sodalime at 300K)C. Determine the inner and outer temperatures of the glass (that are Ts,1 and Ts,2 shown above).