1: A horizontal, opaque flat surface at a steady-state temperature of 77C is exposed to an...
1: A horizontal, opaque flat surface at a steady-state temperature of 77C is exposed to an airflow having a freestream temperature of 27C with a velocity of 15 m/s, and a length of 1 m along the flow direction. The emissive power of the surface is 628 W/m2 , the irradiation from surroundingsis 1380 W/m2 , and the reflectivity is ?=0.40. (a) Determine the absorptivity (?) of the surface. Ans: 0.6 (b) Determine the net radiation heat transfer rate for this surface. Is this heat transfer to the surface or from the surface? Ans: -200 W/m2 (c) Determine the combined heat transfer rate for the surface (radiation+convection). Is this heat transfer to the surface or from the surface?
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1: A horizontal, opaque flat surface at a steady-state
temperature of 77C is exposed to an...
2. (25 Pts) A horizontal, opaque surface at a steady- state temperature of 77°C. The emissive...
2. (25 Pts) A horizontal, opaque surface at a steady- state temperature of 77°C. The emissive power of the surface is 628W/m2, the irradiation is 1380 W/ m2, and the absorptivity is 0.40. a) (5 Pts) determine the reflectivity of the surface. b) (5 Pts) Determine the radiosity of the surface Determine the net radiation heat transfer rate for this surface. (Indicate whether this heat transfer is to the surface or from the surface.) d) (5 Pts) Calculate the emissivity...
A small object with an opaque, diffuse surface at a temperature of 500 K is suspended...
A small object with an opaque, diffuse surface at a temperature
of 500 K is suspended in a large furnace with walls at 2000 K.
Assume that the walls of the furnace provide a diffuse irradiation
to the object at a blackbody temperature equal to the furnace wall
temperature. The object’s surface has a spectral hemispherical
emissivity and absorptivity as given below. (a) Determine the total
emissivity and total absorptivity of the object’s surface. Partial
Ans: ?=0.021 (b) Evaluate the...
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...
please show me how I can finds the answers of these two examples Example 1: Design of a Solar Heater (Black bodies: no convection) A square flat plate collector is exposed to solar radiation from...
please show me how I can finds the answers of these two
examples
Example 1: Design of a Solar Heater (Black bodies: no convection) A square flat plate collector is exposed to solar radiation from both the sides. The exposed surface of the plate has an absorptivity of 1.0 for solar radiation. On a clear summer day on the earth's surface the solar radiation flux is approximately 1140 W/m2 and the surrounding air temperature is 25oC. Determine the surface temperature?...
A flat plate is maintained at 400 degrees C and it is well insulated around the...
A flat plate is maintained at 400 degrees C and it is well insulated around the sides and bottom. The plate experiences 800 w/m^2 of irradiation from its surroundings. The surrounding air is at 40 degrees C. The surrounding 40C air provides a convection coefficient of 15 w/m^2K. The plate surface has an emissivity of 0.9 and an absorptivity (for all irradiation) of 0.7. What is the net heat transfer.
Problem 1. (25%) The temperature on the inside surface of a CYLINDRICAL tank is T.(11) =...
Problem 1. (25%) The temperature on the inside surface of a CYLINDRICAL tank is T.(11) = 100°C under steady state conditions. The temperature outside the tank, T2(2), needs to be determined. The inner radius is 1 m and the outer radius is 1.3 m, and the tank material has a conductivity of k = 15 W/m. K. ONLY CONVECTION on the outer surface has to be considered. The ambient temperature is To = 25°C and the convection heat transfer coefficient...
The solar radiation incident on the outside surface of an aluminum shading device is 1300 W/m2...
The solar radiation incident on the outside surface of an aluminum shading device is 1300 W/m2 . Aluminum absorbs 10% of the incident solar energy, and dissipates it by convection from the back surface and by combined convection and radiation from the outside surface. The convection heat transfer coefficient is 10 W/m2 ·K for both surfaces, and the ambient/surrounding temperature can be taken 20 °C for both convection and radiation. Assuming that the aluminum shade has a uniform temperature, determine...
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...
An aluminum plate with a thickness of L=5 mm is mounted in a horizontal position, and...
An aluminum plate with a thickness of L=5 mm is mounted in a horizontal position, and its bottom surface is well insulated. A special, thin coating (with emissivity and solar absorptivity of 0.25) is applied to the top surface. The density ρ and specific heat c of aluminum are known to be 2700 kg/m3 and 900 J/kg · K, respectively. Consider conditions for which the plate is initially at a temperature of ??????=25 °C and its top surface is suddenly...
2. (25 Pts) A horizontal, opaque surface at a steady- state temperature of 77°C. The emissive power of the surface is 628W/m2, the irradiation is 1380 W/ m2, and the absorptivity is 0.40. a) (5 Pts) determine the reflectivity of the surface. b) (5 Pts) Determine the radiosity of the surface Determine the net radiation heat transfer rate for this surface. (Indicate whether this heat transfer is to the surface or from the surface.) d) (5 Pts) Calculate the emissivity...
A small object with an opaque, diffuse surface at a temperature
of 500 K is suspended in a large furnace with walls at 2000 K.
Assume that the walls of the furnace provide a diffuse irradiation
to the object at a blackbody temperature equal to the furnace wall
temperature. The object’s surface has a spectral hemispherical
emissivity and absorptivity as given below. (a) Determine the total
emissivity and total absorptivity of the object’s surface. Partial
Ans: ?=0.021 (b) Evaluate the...
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)...
please show me how I can finds the answers of these two
examples
Example 1: Design of a Solar Heater (Black bodies: no convection) A square flat plate collector is exposed to solar radiation from both the sides. The exposed surface of the plate has an absorptivity of 1.0 for solar radiation. On a clear summer day on the earth's surface the solar radiation flux is approximately 1140 W/m2 and the surrounding air temperature is 25oC. Determine the surface temperature?...
Problem 1. (25%) The temperature on the inside surface of a CYLINDRICAL tank is T.(11) = 100°C under steady state conditions. The temperature outside the tank, T2(2), needs to be determined. The inner radius is 1 m and the outer radius is 1.3 m, and the tank material has a conductivity of k = 15 W/m. K. ONLY CONVECTION on the outer surface has to be considered. The ambient temperature is To = 25°C and the convection heat transfer coefficient...
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