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7. Consider a car in a parking lot. The wall temperature of the parking lot (Tsur) is 68 °C. The ...
5 The roof of a car in a parking lot absorbs a solar radiant flux of...
5 The roof of a car in a parking lot absorbs a solar radiant flux of 800 W/m2 and the underside is perfectly insulated. The convection coefficient between the roof and the ambient air is 12 W/m2.K. (a) Neglecting radiation exchange with the surroundings, calculate the temperature of the roof under steady state conditions if the ambient air temperature is 20°C. (b) For the same ambient air temperature, calculate the temperature of the roof if its surface emissivity is 0.8.
A 50 mm x 45 mm x 20 mm cell phone charger has a surface temperature...
A 50 mm x 45 mm x 20 mm cell phone charger has a surface temperature of T,-330C when plugged into an electrical wall outlet but not in use. The surface of the charger is of emissivity ε = 0.92 and is subject to a free convection heat transfer coefficient of h 4.5 W/m2, K. The room air and wall temperatures are T.-220C and Tsur-200C, respectively Tsur w 20 mm L = 50 mm Wall ir Charger T, h
11 We often see frost on a windshield of car at a clear cold night. A...
11 We often see frost on a windshield of car at a clear cold night. A thin layer of water formed from moist ar dew point) on a windshield of a car in a parking lot is exposed to a clear sky at -17°C. The ambient air temperature and convection coefficient are 5°C and 10 W/m2.K. Assume that the emissivity of the thin layer of water is 0.9. Explain how frost can be formed even the ambient air temperature of...
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...
1. Consider an opaque, horizontal square plate (Im by 1m) with an electrical heater on its backside. The front side is exposed to ambient quiescent air that is at 20° C, solar irradiation (from...
1. Consider an opaque, horizontal square plate (Im by 1m) with an electrical heater on its backside. The front side is exposed to ambient quiescent air that is at 20° C, solar irradiation (from sun at 5800° K) of 600 W/m2, and an effective sky temperature of -40° C. The plate surface temperature is kept at Ts 60 C (at steady state condition). Calculate natural convection heat transfer coefficient from the plate. (10 points) What is the electrical power (W/m2)...
A wall panel is insulated on the back and exposed to solar radiation on the front...
A wall panel is insulated on the back and exposed to solar radiation on the front surface. The exposed surface of the plate has an absorptivity α = 0.8 for radiation (i.e. 80% of radiant energy is absorbed). Solar radiation arrives to the panel at a rate of 1 kW⁄m2. The panel emissivity ϵ = 1 and the surrounding air temperature is 25°C. a. If we assume radiation is the only mechanism of heat transfer, in this scenario determine the...
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...
Q1) Inner surface of a side wall is used for heating of ambient-room air as shown...
Q1) Inner surface of a side wall is used for heating of ambient-room air as shown below. There is an electrical heater with 10 W/m2 heat flux generation between a layer of insulation and 2 cm thick marble exposed to ambient-room air at T-20 °C with h-20 W/m2K. k-0.04 W/mK Marble with a thickness of 2 cm Ts= 10 ℃ outside Ambient-room air at To Electrical heating layer (negligible thickness) of temperature T-? Insulation with a thickness of 5 cm...
Homework 7 heat transfer 2018-20 1) A horizontal tube of 12.5-mm dimeter with an outer srface temperature of 240°C is placed in a room with an air temperature of 20°C. Estimate the heat transfer rate...
Homework 7 heat transfer 2018-20 1) A horizontal tube of 12.5-mm dimeter with an outer srface temperature of 240°C is placed in a room with an air temperature of 20°C. Estimate the heat transfer rate per unit length of the tube due to free convection. 2) Air at -10°C flows at 10 m/s over the roof plate of two 5m length rooms whose air is at Too-200C. The roof plate is 0.20-m thick concrete (k = 0.6 w/ m. K)....
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...
5 The roof of a car in a parking lot absorbs a solar radiant flux of 800 W/m2 and the underside is perfectly insulated. The convection coefficient between the roof and the ambient air is 12 W/m2.K. (a) Neglecting radiation exchange with the surroundings, calculate the temperature of the roof under steady state conditions if the ambient air temperature is 20°C. (b) For the same ambient air temperature, calculate the temperature of the roof if its surface emissivity is 0.8.
A 50 mm x 45 mm x 20 mm cell phone charger has a surface temperature of T,-330C when plugged into an electrical wall outlet but not in use. The surface of the charger is of emissivity ε = 0.92 and is subject to a free convection heat transfer coefficient of h 4.5 W/m2, K. The room air and wall temperatures are T.-220C and Tsur-200C, respectively Tsur w 20 mm L = 50 mm Wall ir Charger T, h
11 We often see frost on a windshield of car at a clear cold night. A thin layer of water formed from moist ar dew point) on a windshield of a car in a parking lot is exposed to a clear sky at -17°C. The ambient air temperature and convection coefficient are 5°C and 10 W/m2.K. Assume that the emissivity of the thin layer of water is 0.9. Explain how frost can be formed even the ambient air temperature of...
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...
1. Consider an opaque, horizontal square plate (Im by 1m) with an electrical heater on its backside. The front side is exposed to ambient quiescent air that is at 20° C, solar irradiation (from sun at 5800° K) of 600 W/m2, and an effective sky temperature of -40° C. The plate surface temperature is kept at Ts 60 C (at steady state condition). Calculate natural convection heat transfer coefficient from the plate. (10 points) What is the electrical power (W/m2)...
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...
Q1) Inner surface of a side wall is used for heating of ambient-room air as shown below. There is an electrical heater with 10 W/m2 heat flux generation between a layer of insulation and 2 cm thick marble exposed to ambient-room air at T-20 °C with h-20 W/m2K. k-0.04 W/mK Marble with a thickness of 2 cm Ts= 10 ℃ outside Ambient-room air at To Electrical heating layer (negligible thickness) of temperature T-? Insulation with a thickness of 5 cm...
Homework 7 heat transfer 2018-20 1) A horizontal tube of 12.5-mm dimeter with an outer srface temperature of 240°C is placed in a room with an air temperature of 20°C. Estimate the heat transfer rate per unit length of the tube due to free convection. 2) Air at -10°C flows at 10 m/s over the roof plate of two 5m length rooms whose air is at Too-200C. The roof plate is 0.20-m thick concrete (k = 0.6 w/ m. K)....
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...
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