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2. (25 Pts) A horizontal, opaque surface at a steady- state temperature of 77°C. The emissive...
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...
A horizontal plate made of an opaque material is subjected to an irradiation of 5200 W...
A horizontal plate made of an opaque material is subjected to an irradiation of 5200 W m2 on its upper surface. The edges and lower surface are well insulated. The upper surface of the plate is maintained at a steady temperature of 480 K. The plate has a total hemispherical absorptivity of 0.45. The spectral emissivity function of the plate material is given as f ι-05, 0 λ 3μm; ε,-07, 3μm1S 15 00, Find (a) the total ollowS: hemispherical 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)...
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 average temperature of the surface of the Earth is approximately 14◦C. What would the steady-state...
The average temperature of the surface of the Earth is approximately 14◦C. What would the steady-state temperature of the Earth be if there were no greenhouse effect — i.e. if the emissivity of the earth was independent of wavelength? Give your answer in ◦C. Note that the radius of the Earth is 6.38 106 m, and the intensity of sunlight at the Earth’s location is 1366 W/m2. Hint, how much power from the sun would strike a plate with the...
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...
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...
(a) Schematically draw the spectral emissive power of two blackbodies with the temperature of 2400 K...
(a) Schematically draw the spectral emissive power of two blackbodies with the temperature of 2400 K and 300 K (ie. EBA versus λ). What are the wavelengths at the maximum spectral emissive power? (5 pts) (b) A thin-walled plate separates the interior of a large furnace from surroundings at 300 K. The plate is fabricated from a ceramic material for which diffuse surface behavior may be assumed and the exterior surface is air-cooled. With the furnace operating at 2400 K...
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...
A horizontal plate made of an opaque material is subjected to an irradiation of 5200 W m2 on its upper surface. The edges and lower surface are well insulated. The upper surface of the plate is maintained at a steady temperature of 480 K. The plate has a total hemispherical absorptivity of 0.45. The spectral emissivity function of the plate material is given as f ι-05, 0 λ 3μm; ε,-07, 3μm1S 15 00, Find (a) the total ollowS: hemispherical 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)...
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)....
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...
(a) Schematically draw the spectral emissive power of two blackbodies with the temperature of 2400 K and 300 K (ie. EBA versus λ). What are the wavelengths at the maximum spectral emissive power? (5 pts) (b) A thin-walled plate separates the interior of a large furnace from surroundings at 300 K. The plate is fabricated from a ceramic material for which diffuse surface behavior may be assumed and the exterior surface is air-cooled. With the furnace operating at 2400 K...
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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