Problem 4Emissivity/Absorptivity0.830.6་A white paint that can be used for passive radiative (b) 1cooling under the Sun. Provided the followingsimplified spectral absorptivity/emissivity plot (α)or &) on the right, calculate the net radiative heatflux qrad from a uniform-temperature paintedsurface at Ts=300 K. The Sun's irradiation on Earthis Gsun 1380 W/m² and its blackbody temperatureis Tsun = 5800 K. Ignore the radiation from theatmosphere (surroundings).0.20°35DOWavelength (um)

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Answered: Problem 4 Emissivity/Absorptivity 0.8…

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.

Chapter11: Heat Transfer By Radiation

Section: Chapter Questions

Problem 11.49P

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11.31 A large slab of steel 0.1 m thick contains a 0.1 -m-di- ameter circular hole whose axis is normal to the surface. Considering the sides of the hole to be black, specify the rate of radiative heat loss from the hole. The plate is at 811 K, and the surroundings are at 300 K.
11.68 Two infinitely large, black, plane surfaces are 0.3 m apart, and the space between them is filled by an isothermal gas mixture at 811 K and atmospheric pressure. The gas mixture consists of by volume. If one of the surfaces is maintained at 278 K and the other at 1390 K, calculate (a) the effective emissivity of the gas at its temperature, (b) the effective absorptivity of the gas to radiation from the 1390 K surface, (c) the effective absorptivity of the gas to radiation from the 278 K surface, and (d) the net rate of heat transfer to the gas per square meter of surface area.
1.26 Repeat Problem 1.25 but assume that the surface of the storage vessel has an absorbance (equal to the emittance) of 0.1. Then determine the rate of evaporation of the liquid oxygen in kilograms per second and pounds per hour, assuming that convection can be neglected. The heat of vaporization of oxygen at –183°C is .
An engineered passive radiative cooler coating is placed under the Sun. Provided the following simplified spectral emissivity/absorptivity plot below, calculate the total diffuse emissivity and absorptivity if its uniform surface temperature is a Ts=20°C. Assume the Sun's irradiation onk Earth is Gsun=1380 W/m2 and its blackbody temperature is Tsun= 5800K. Ignore the radiation from the atmosphere (surroundings).
Heat Transfer Question is image
The last portion asks you for "net radiant heat flux to the surface", meaning that positive net radiative heat flux means in and negative net radiative heat flux means out. This is opposite the typical sign convention - be aware of this
Please explain with steps.
A typical car's exterior consists of a thin layer of silica (SiO2) over an opaque painted metal panel. Silica is transparent in the visible wavelengths but offers high reflectance in the near- to mid- infrared wavelengths. The plot on the next page depicts the diffuse spectral reflectivity (pa) of the car's surface: Spectral reflectivity, P₂ 0.8 0.6 0.4 ལ 0.2 0 0.1 1 1 10 Wavelength, λ(μm) 100 If the car's exterior temperature is T₁ = 77°C, determine both the total absorptivity (a) and the total emissivity (a) of the silica-covered panel. Assume that the Sun's temperature is Tsun = 5800 K.
A drying oven consists of a long semicircular duct of diameter D=1 m. Materials to be dried cover the base of the oven while the wall is maintained at 1200 K. Length of the oven (into paper direction) is 1 m. Water coated material is maintained at 325 K. Assume both the wall and the material to be blackbodies. (1) What is heat transfer rate? (2) Given at temperature 325 K, water needs heat 2.378 × 106 J/kg in order to be dried (from liquid water to steam). How much water can be dried per second based on the heat transfer rate from (1)? T₁ = 1200 K T₂ = 325 K — D = 1 m D= m→
11.19 A long rod, with a diameter of 3 mm, is placed in a vacuum parallel to a large and flat heated surface. The other side of the rod is exposed to vacuum chamber walls at 300 K. Assume that the heated surface and the surface of the rod are both gray with equal emissivities of 0.7. The rod has a volumetric heat capacity of pc, = 6.7 × 106J m‍³ K¨¹. Calculate the heating rate of the rod at 335 K, 500 K, 700 K, and 800 K. Rod Heated surface at 830 K
A thin, disk-shaped silicon wafer of diameter D=20 cm on a production line must be maintained at a temperature of 100 deg C. The wafer loses heat to the room by convection and radiation from its upper surface, while heat is supplied at a constant flux from below. The surrounding air is at 20 deg C, while all surrounding surfaces (which can be treated as blackbodies) can be approximated to be isothermal at a temperature of 15 deg C. The wafer-to-air heat transfer coefficient is 30 W/m2-K and the emissivity of the wafer’s surface (which can be approximated to be gray) is 0.85. How much heat (in W) must be supplied to the wafer?
5. (25%) A frustum of a cone has its base heated as shown in Figure 2. The top surface is held at 1200K while the side is perfectly insulated. Surfaces 1, 2, and 3 are assumed gray and diffuse. What are the temperatures of surface 1 and 2? If the emissivity of surface 2 changes from 0,8 to 0.6, will the temperature of surface 2 change to different value? The radius of upper circle is 1 m and the radius of lower circle is 3 m. The height of frustum is 4 m. Surface 3 T= 1200K 8 = 0.8 Surface 1 Surface 2 q= 100W/m? 8 = 0.6 Perfectly insulated ɛ = 0.8

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