An opaque surface at 1000 K if its spectral emissivity is = 0.4, 0.7, and 0.3 for 0 < < 2 μm, 2μm = λ < 6 μm, and 6μm = λ < æ respectively. Determine the average emissivity of the surface Choose... Determine the emissive power of Choose... the surface →

An opaque surface at 1000 K if its spectral emissivity is = 0.4, 0.7, and 0.3 for 0 < < 2 μm, 2μm = λ < 6 μm, and 6μm = λ < æ respectively. Determine the average emissivity of the surface Choose... Determine the emissive power of Choose... the surface →

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.

Chapter1: Basic Modes Of Heat Transfer

Section: Chapter Questions

Problem 1.26P: 1.26 Repeat Problem 1.25 but assume that the surface of the storage vessel has an absorbance (equal...

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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 .
Two concentric spheres of diameter Dj = 0.8 mand D2 T1 = 400 K and T2 = 300 K. = 1.2 m are separated by an air space and have surface temperatures of (a) If the surfaces are black, what is the net rate of radiation exchange between the spheres, in W? 912 i (b) What is the net rate of radiation exchange between the surfaces if they are diffuse and gray with e = 0.5 and e2 = 0.05, in W? 912 i w (c) What is the net rate of radiation exchange if D2 is increased to 20 m, with &2 = 0.05, ɛ 1 = 0.5, and Di = 0.8 m, in W? 912 w = 1.0) and with ej = 0.5, D2 = 20 m, (d) What is the net rate of radiation exchange if the larger sphere behaves as a black body (82 and Di = 0.8 m, in W? 912 = i W
A 3-in-diameter cylindrical wire is coated in 3 inches of polyethylene insulation. The wire can be modeled as a grey body with an emissivity of .85. Due to the electrical resistance, the wire is at a temperature of 300 degrees Celsius. The insulation is also a great body with an emissivity of .95, at a temperature of 40 degrees Celsius. (Assume F12=1). What is the heat flux (W/m^2) of the energy going from the wire to the insulation?
A small sphere (emissivity =0.503 radius=r1) is located at the center of a spherical abestos shell ( thickness =1.74 cm, outer radius= r2; thermal conductivity of abestos is 0.090 J/ (sm c degrees) The thickness of the shell is small compared to the inner and outer radii of the shell. The temperature of the small sphere is 695 degrees Celsius while the temperature of the inner surface of the shell is 352 degrees Celsius, both temperatures remaining constant. Assuming that r2/r1 =8.75 and ignoring any air inside the shell, find the temperature in degrees Celsius of the outer surface of the shell.
1. Continuum wave equation. Show that for long wavelengths the equation of motion, d²u M s = dt² = C(us+1+ug-1-2u), reduces to the continuum elastic wave equation where v is the velocity of sound. d'u ôt² d²u əx²
Two concentric spheres of diameter Di = 0.7 mand D2 = 1.2 mare separated by an air space and have surface temperatures of T = 400 K and T, = 300 K. (a) If the surfaces are black, what is the net rate of radiation exchange between the spheres, in W? ৭12 = w (b) What is the net rate of radiation exchange between the surfaces if they are diffuse and gray with ɛi = 0.5 and e2 = 0.05, in W? 12 (c) What is the net rate of radiation exchange if D2 is increased to 20 m, with e2 = 0.05, e1 = 0.5, and Di = 0.7 m, in W? 912 = i (d) What is the net rate of radiation exchange if the larger sphere behaves as a black body (e2 = 1.0) and with e = 0.5, D2 = 20 m, and D1 = 0.7 m, in W? w 912 = Physical Properties Mathematical Functions
Two concentric spheres of diameter D = 0.9 m and D2 = 1.2 m are separated by an air space and have surface temperatures of T = 390 Kand T2 = 300 K. (a) If the surfaces are black, what is the net rate of radiation exchange between the spheres, in W? 912 = i w (b) What is the net rate of radiation exchange between the surfaces if they are diffuse and gray with ej = 0.5 and ez = 0.05, in W? 912 = W (c) What is the net rate of radiation exchange if D2 is increased to 20 m, with e, = 0.05, e = 0.5, and D = 0.9 m, in W? 912 = (d) What is the net rate of radiation exchange if the larger sphere behaves as a black body (82 = 1.0) and with e1 = 0.5, D2 = 20 m, and D, = 0.9 m, in W? 412 =
(a) Calculate the mass and linear absorption coefficients of air for Cr Ka radiation.Assume that air contains 80 percent nitrogen and 20 percent oxygen by weight and has adensity of1.29 x g/cm3. (b) Plot the transmission factor of air for Cr Ka radiationand a path length of 0 to 20 cm.Please use any table or data from the Elements of X-ray Diffraction by Cullity
Q4(a) Explain how the emissive power of real body is estimated. (b) A black body in vacuum emits maximum radiation at wavelength 0.6x10° m. Estimate the : (i) Surface temperature (ii)Monochromatic emissive power (iii)Total Emissive power. (c) A two layer wall is to be constructed having dimensions 2.5m (width ) by 3.5 m (height). The wall is constructed of one layer of common brick( k=0.72 W/m °C) of thickness 22 cm and one layer of cement(k=1.4 W/m °C) of thickness 6 cm. The inner surface of the wall is maintained at 25°C while the outer surface is exposed to outdoors at 11°C with a combined convection and radiation heat transfer cofficient of 20 W/m? °C. (1)Determine the rate of heat transfer through the wall. (ii)Estimate the temperature drops across the brick, cement and surface ambient air.
1. Consider a spaceship that has a volume V = 3000 m³, is effectively spherical in shape and has a density comparable to water (p = 1000 kg m-3). It absorbs CMB radiation (TCMB = 2.73K) and radiates its own radiation with a blackbody spectrum of T = 300K. What is its mass, radius and surface area? At what rate does it absorb energy from the CMB? (Hint: You can use the Stefan-Boltzmann law.) How many CMB photons are absorbed per а. b. с. second? d. At what rate does it emit energy through blackbody radiation? What is the net rate that the spaceship temperature would change if the spaceship has an е. effective heat capacity of pure water: C = 4200 J kg-1K-1 ?
A plate that is exposed to the outside environment at 30 ° C, gets airradiation of 2000 W / m2. The plate, which absorbs 80% of the irradiationand it has an emissivity of 0.5, it is always at a uniform temperature.An external air flow at 20 ° C and 15 W / m2-K go through the plate. Calculatethe temperature of the plate if it is in thermal equilibrium and insteady state conditions.
! Required information Irradiation on a semi-transparent medium is at a rate of 640 W/m². If 160 W/m² of the irradiation is reflected from the medium and 130 W/m² is transmitted through the medium, Determine the absorptivity of the medium. The absorptivity of the medium is 0.75 X