Blackbody Rooftop Homework | Emissivity 0.9, Absorbtivity 0.8

  • Thread starter Thread starter gfd43tg
  • Start date Start date
  • Tags Tags
    Blackbody
Click For Summary
SUMMARY

The discussion focuses on calculating the equilibrium temperature of a black rooftop with an emissivity of 0.9 and absorbtivity of 0.8, subjected to solar radiation of 300 BTU/hr ft². Given the ambient temperature of 68 °F and negligible wind, the equilibrium temperature can be determined using the conduction/convection rate equation q/A = 0.38 (ΔT)¹²⁵. Additionally, the fraction of heat lost to radiation from the roof is analyzed, considering an effective sky temperature of -10 °F.

PREREQUISITES
  • Understanding of thermal radiation principles
  • Familiarity with emissivity and absorbtivity concepts
  • Knowledge of heat transfer equations, specifically conduction and convection
  • Proficiency in using mathematical tools like WolframAlpha for solving equations
NEXT STEPS
  • Research the principles of thermal radiation and emissivity
  • Learn about the calculation of equilibrium temperature in heat transfer scenarios
  • Explore the impact of wind velocity on heat loss from surfaces
  • Investigate advanced heat transfer equations and their applications in building design
USEFUL FOR

Students in engineering or physics, building designers, and professionals involved in thermal management and energy efficiency in buildings will benefit from this discussion.

gfd43tg
Gold Member
Messages
949
Reaction score
48

Homework Statement


The black roof of a building has an emissivity of 0.9 and an absorbtivity of 0.8 for solar radiation. The sun beats down at midday with an intensity of 300 BTU / hr ft2.

a) If the temperature of the air and the surroundings is 68 °F, if the wind velocity is negligible, and if no heat penetrates the roof, what is the equilibrium temperature of the roof ? For the rate of conduction / convection use q/A = 0.38 (T) 1.25, where T is the temperature drop between the roof and air in degrees F.

b) What fraction of the heat from the roof is lost to radiation.


Homework Equations





The Attempt at a Solution


For this problem, assume the effective sky temperature on that day is -10F. also, the "rate of conduction / convection" just means the overall rate of conduction + convection away from the roof.

I am wondering if I approached this correctly. I used wolframalpha to solve the equation.
 

Attachments

Physics news on Phys.org
Solved disregard
 

Similar threads

How Hot Should the Radiant Heat Lamp Be to Maintain Pizza at 250 F?
  • · Replies 3 ·
Replies
3
Views
2K
Filament radiation in light bulb
  • · Replies 1 ·
Replies
1
Views
3K
Graduate Average temperature in a greenhouse
  • · Replies 2 ·
Replies
2
Views
2K
Thermal Resistance due to Convection Heat Transfer
  • · Replies 4 ·
Replies
4
Views
4K
Where Should Radiation Be Considered in Heat Transfer Through a Wall?
  • · Replies 3 ·
Replies
3
Views
3K
How Does Wind Speed Affect Perceived Temperature and Heat Transfer?
  • · Replies 3 ·
Replies
3
Views
3K
Radiation/convection heat transfer problem. (Thermodynamics)
  • · Replies 1 ·
Replies
1
Views
6K
Simplified Air-Conditioning Calculations
  • · Replies 1 ·
Replies
1
Views
2K
Convection and Radiation in an Electrically Heated Cylinder
  • · Replies 1 ·
Replies
1
Views
2K
Graduate Emissivity & internal blackbody
  • · Replies 18 ·
Replies
18
Views
3K