ASSIGNMENT 4 BMM3513_1415/2

FACULTY OF MECHANICAL ENGINEERING

BMM3513 HEAT TRANSFER

Assignment 4 (CO4)

NAME MATRIC NO.

1. Why did we define the blackbody radiation function? What does it represent? For what is it used?

2. Define the total and spectral blackbody emissive powers. How are they related to each other? How do

they differ?

3. Consider two identical bodies, one at 1000 K and the other at 1500 K. Which body emits more

radiation in the shorter-wavelength region? Which body emits more radiation at a wavelength of

20m?

4. The temperature of the filament of an incandescent lightbulb is 3200 K. Treating the filament as a

blackbody, determine the fraction of the radiant energy emitted by the filament that falls in the visible

range. Also, determine the wavelength at which the emission of radiation from the filament peaks.

5. Consider a 20-cm X 20-cm X 20-cm cubical body at 1000 K suspended in the air. Assuming the body

closely approximates a blackbody, determine (a) the rate at which the cube emits radiation energy, in

W, and (b) the spectral blackbody emissive power at a wavelength of 4 m.

6. Daylight and candlelight may be approximated as a blackbody at the effective surface temperatures of

5800 K and 1800 K, respectively. Determine the radiation energy (in W/m2) emitted by both lighting

sources (daylight and candlelight) within the visible light region (0.4 to 0.76 m)

7. A small surface area A1 = 3 cm2 emits radiation as a blackbody with total emissive power of Eb= 5.67

X 104 W/m

2. Part of the radiation emitted by A1 strikes another small surface of area A2 = 8 cm

2

oriented as shown in Figure 7. Determine the rate at which radiation emitted by A1 strikes A2, and the

irradiation on A2.

Figure 7

8. A small surface area of A1 = 3 cm2 emits radiation as a blackbody and part of the radiation emitted by

A1 strikes another small surface area A2 = 8 cm2 oriented as shown in Figure 7. If the rate at which

radiation emitted by A1 that strikes A2 is measured to be 274 X 10-6

W, determine the intensity of the

radiation emitted by A1 and the temperature of A1.

/100 UMP