A household oven door of 0.6-m height and 0.7-m width reaches an average surface temperature of...
A household oven door of 0.6-m height and 0.7-m width reaches an average surface temperature of 32°C during operation. The temperature of ambient air is 22°C. Assuming the door has an emissivity of 0.8 and the surroundings are also at 22°C, determine the heat transfer by free convection and the heat transfer by radiation.
1) What is the volumetric thermal expansion coefficient of air at the film temperature outside the oven door, in 1/K?
2) What is the Rayleigh number outside the oven door?
3) What is the free convection Nusselt number?
4) What is the free convection heat transfer coefficient, in W/m2·K?
5) What is the heat transfer by free convection, in W?
6) What is the heat transfer by radiation, in W?
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A household oven door of 0.6-m height and 0.7-m width reaches an
average surface temperature of...
The interior surface of an oven of internal dimensions 1mx1mx1m has an emissivity of 0.8, and is maintained at a uniform temperature of 500 K. The oven is placed in a very large room where th...
The interior surface of an oven of internal dimensions 1mx1mx1m has an emissivity of 0.8, and is maintained at a uniform temperature of 500 K. The oven is placed in a very large room where the ambient temperature is 300K. On the front wall of the oven is a square opening of dimensions 100mmx 100mm. To reduce the heat loss through the opening, a thin metallic plate is used to cover the opening. The emissivity of the cover plate surface...
The interior surface of an oven of internal dimensions 1mx1mx1m has an is maintained at a uniform...
The interior surface of an oven of internal dimensions 1mx1mx1m has an is maintained at a uniform temperature of 500 K. The oven is placed in a very large room the ambient temperature is 300K. On the front wall of the oven is a square opening of dimensions ce of an o where 00mm. To reduce the heat loss through the opening, a thin metallic plate is used to cover the opening. The emissivity of the cover plate surface facing...
Problem 2 (50 Points A flat, isothermal vertical heating panel, 0.5 m wide by 1 m...
Problem 2 (50 Points A flat, isothermal vertical heating panel, 0.5 m wide by 1 m high is mounted inside a large room. The surface of the panel has an emissivity of 0.90 and is maintained at 400 K If the walls and air of the room are at 300 K, calculate: a) The Rayleigh number of the free convection boundary layer. b) Selecting a suitable equation for Nusselt number, calculate the heat transfer coefficient of the flow c) The...
III. A composite walled window separates oven cavity from room air. The composite is to consist...
III. A composite walled window separates oven cavity from room air. The composite is to consist of two high temperature plastics of thickness L. = 2L. and thermal conductivities k = 0.15 W/(m·K) and k, = 0.08 W/( m K). During the self-cleaning process, the oven w and oven air temperatures are at 400°C, while the room air temperature is at 25°C. The insid convection coefficient, outside convection coefficient, and radiation heat transfer coefficient to be confused with Stefan Boltzmann...
Problem #3 (30 point): A glass-door fire-screen has a height of 0.8 m and a width...
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3. A small cylindrical filament is heated in a large combination convection-radiation oven. The filament has...
3. A small cylindrical filament is heated in a large combination convection-radiation oven. The filament has a diameter D= 50 mm and length L= 1 m. During the process, the oven wall temperature is fixed at Tsur=800 K, and the hot air is blowing with a temperature T.= 500 K and an average heat transfer coefficient h=50 W/m²K. Assuming the filament surface is opaque and diffuse, and it has a spectral emissivity as shown below: (25 pts) The oven walls behave...
Problem 3 (20p) During a winter day, the window of a patio door with a height of 1.8 m and width ...
Problem 3 (20p) During a winter day, the window of a patio door with a height of 1.8 m and width of 1.0 m has a uniform temperature of 0°C. T through the window due surface is 0.94. Hint: Use the correlation relation developed by Churchill and Chu: he room wall and air temperatures are 15°C. Estimate the heat loss to free convection and radiation. Assume the emissivity of the glass Nu = 0.825 + 1 +(0.492/Pr)9/16j8/27
Problem 3 (20p)...
(13) A brewery fermentation tank 12 m in diameter is situated in a room, which has...
(13) A brewery fermentation tank 12 m in diameter is situated in a room, which has a temperature of 15°C. The tank is constructed of 10-mm welded steel plate with 12-mm glass lining. The temperature at the inner surface of the glass lining is 50°C. Assume that the convective resistance offered by the air film on the outside of the tank equals the combined resistance of the glass and steel. The thermal conductivity of glass is 0.80 W/mK and that...
hair dryer may be idealized as a circular duct through which a small fan draws ambient...
hair dryer may be idealized as a circular duct through which a
small fan draws ambient air and within which the air is heated as
it flows over a coiled electric resistance wire.
(1) If a dryer is designed to operate with an electric power
consumption of Pelec= 1500 W and to heat air from an ambient
temperature of Ti= 20°C to a discharge temperature of To= 45°C, at
what volumetric flow rate ∀˙ should the fan operate? Heat loss...
A rod of 10-mm diameter and 250-mm length has one end maintained at 100°C
A rod of 10-mm diameter and 250-mm length has one end maintained at 100°C. The surface of the rod experiences free convection with the ambient air at 25°C and a convection coefficient that depends on the difference between the temperature of the surface and the ambient air. Specifically, the coefficient is prescribed by a correlation of the form, hfc = 2.89[0.6 +0.624(T - T∞)1/6]2, where the units are hfc (W/m².K) and T (K). The surface of the rod has an...
The interior surface of an oven of internal dimensions 1mx1mx1m has an emissivity of 0.8, and is maintained at a uniform temperature of 500 K. The oven is placed in a very large room where the ambient temperature is 300K. On the front wall of the oven is a square opening of dimensions 100mmx 100mm. To reduce the heat loss through the opening, a thin metallic plate is used to cover the opening. The emissivity of the cover plate surface...
The interior surface of an oven of internal dimensions 1mx1mx1m has an is maintained at a uniform temperature of 500 K. The oven is placed in a very large room the ambient temperature is 300K. On the front wall of the oven is a square opening of dimensions ce of an o where 00mm. To reduce the heat loss through the opening, a thin metallic plate is used to cover the opening. The emissivity of the cover plate surface facing...
Problem 2 (50 Points A flat, isothermal vertical heating panel, 0.5 m wide by 1 m high is mounted inside a large room. The surface of the panel has an emissivity of 0.90 and is maintained at 400 K If the walls and air of the room are at 300 K, calculate: a) The Rayleigh number of the free convection boundary layer. b) Selecting a suitable equation for Nusselt number, calculate the heat transfer coefficient of the flow c) The...
III. A composite walled window separates oven cavity from room air. The composite is to consist of two high temperature plastics of thickness L. = 2L. and thermal conductivities k = 0.15 W/(m·K) and k, = 0.08 W/( m K). During the self-cleaning process, the oven w and oven air temperatures are at 400°C, while the room air temperature is at 25°C. The insid convection coefficient, outside convection coefficient, and radiation heat transfer coefficient to be confused with Stefan Boltzmann...
Problem #3 (30 point): A glass-door fire-screen has a height of 0.8 m and a width of 1.1 m and a temperature of 280°C. The room temperature is 24°C. (a) Estimate the convection heat transfer from the fireplace to the room. Use Churchill and Chu correlation. Is the flow laminar or turbulent. (b) Calculate also the radiation heat transfer from the fire-screen to the room. Assume, emissivity of fire-screen, E: 0.95. Assume, for air at T-425 K: v= 29.4x10m/s, k...
3. A small cylindrical filament is heated in a large combination convection-radiation oven. The filament has a diameter D= 50 mm and length L= 1 m. During the process, the oven wall temperature is fixed at Tsur=800 K, and the hot air is blowing with a temperature T.= 500 K and an average heat transfer coefficient h=50 W/m²K. Assuming the filament surface is opaque and diffuse, and it has a spectral emissivity as shown below: (25 pts) The oven walls behave...
Problem 3 (20p) During a winter day, the window of a patio door with a height of 1.8 m and width of 1.0 m has a uniform temperature of 0°C. T through the window due surface is 0.94. Hint: Use the correlation relation developed by Churchill and Chu: he room wall and air temperatures are 15°C. Estimate the heat loss to free convection and radiation. Assume the emissivity of the glass Nu = 0.825 + 1 +(0.492/Pr)9/16j8/27
Problem 3 (20p)...
(13) A brewery fermentation tank 12 m in diameter is situated in a room, which has a temperature of 15°C. The tank is constructed of 10-mm welded steel plate with 12-mm glass lining. The temperature at the inner surface of the glass lining is 50°C. Assume that the convective resistance offered by the air film on the outside of the tank equals the combined resistance of the glass and steel. The thermal conductivity of glass is 0.80 W/mK and that...
hair dryer may be idealized as a circular duct through which a
small fan draws ambient air and within which the air is heated as
it flows over a coiled electric resistance wire.
(1) If a dryer is designed to operate with an electric power
consumption of Pelec= 1500 W and to heat air from an ambient
temperature of Ti= 20°C to a discharge temperature of To= 45°C, at
what volumetric flow rate ∀˙ should the fan operate? Heat loss...
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