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A 10-mm-thick workpiece, initially at 25°C, is to be annealed at a temperature above 725°C for a period of at least 5 minutes and then cooled. The workpiece is opaque and diffuse, and the spectral distribution of its emissivity is shown schematically. Heating is effected in a large furnace with walls and circulating air at 750°C and a convection coefficient of 120 W/m².K. The thermophysical properties of the workpiece are p = 2700 kg/m³, c = 885 J/kg-K, and k = 165 W/m.K. Assume that ₁ = 0.3 and ₂ = 0.8. α = 82 i &₁ (a) Calculate the emissivity and the absorptivity of the workpiece when it is placed in the furnace at its initial temperature of 25°C. 8 = 2.5 λ (um) (b) Determine the net heat flux into the workpiece for this initial condition, in kW/m². What is the corresponding rate of change in

A 10-mm-thick workpiece, initially at 25°C, is to be annealed at a temperature above 725°C for a period of at least 5 minutes and then cooled. The workpiece is opaque and diffuse, and the spectral distribution of its emissivity is shown schematically. Heating is effected in a large furnace with walls and circulating air at 750°C and a convection coefficient of 120 W/m².K. The thermophysical properties of the workpiece are p = 2700 kg/m³, c = 885 J/kg-K, and k = 165 W/m.K. Assume that ₁ = 0.3 and ₂ = 0.8. α = 82 i &₁ (a) Calculate the emissivity and the absorptivity of the workpiece when it is placed in the furnace at its initial temperature of 25°C. 8 = 2.5 λ (um) (b) Determine the net heat flux into the workpiece for this initial condition, in kW/m². What is the corresponding rate of change in

Elements Of Electromagnetics
Elements Of Electromagnetics
7th Edition
ISBN:9780190698614
Author:Sadiku, Matthew N. O.
Publisher:Sadiku, Matthew N. O.
ChapterMA: Math Assessment
Section: Chapter Questions
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Keep in mind that both the bottom and top surfaces of the workpiece are exposed to radiation and convection. The workpiece is suspended in air in the furnace.

A 10-mm-thick workpiece, initially at 25°C, is to be annealed at a temperature above 725°C for a period of at least 5 minutes and then cooled. The workpiece is opaque and diffuse, and the spectral distribution of its emissivity is shown schematically. Heating is effected in a large furnace with walls and circulating air at 750°C and a convection coefficient of 120 W/m².K. The thermophysical properties of the workpiece are p = 2700 kg/m³, c = 885 J/kg-K, and k = 165 W/m.K. Assume that ₁ = 0.3 and ₂ = 0.8. ε = α = i dT/dt = (a) Calculate the emissivity and the absorptivity of the workpiece when it is placed in the furnace at its initial temperature of 25°C. Ya i 82 i &1 (b) Determine the net heat flux into the workpiece for this initial condition, in kW/m². What is the corresponding rate of change in temperature, dT / dt, for the workpiece, in K/s? qnet.in 2.5 kW/m² λ (um) K/s
Transcribed Image Text:A 10-mm-thick workpiece, initially at 25°C, is to be annealed at a temperature above 725°C for a period of at least 5 minutes and then cooled. The workpiece is opaque and diffuse, and the spectral distribution of its emissivity is shown schematically. Heating is effected in a large furnace with walls and circulating air at 750°C and a convection coefficient of 120 W/m².K. The thermophysical properties of the workpiece are p = 2700 kg/m³, c = 885 J/kg-K, and k = 165 W/m.K. Assume that ₁ = 0.3 and ₂ = 0.8. ε = α = i dT/dt = (a) Calculate the emissivity and the absorptivity of the workpiece when it is placed in the furnace at its initial temperature of 25°C. Ya i 82 i &1 (b) Determine the net heat flux into the workpiece for this initial condition, in kW/m². What is the corresponding rate of change in temperature, dT / dt, for the workpiece, in K/s? qnet.in 2.5 kW/m² λ (um) K/s
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