Timeline for Radiation emission and absorption
Current License: CC BY-SA 3.0
7 events
| when toggle format | what | by | license | comment | |
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| Jul 23, 2014 at 1:38 | comment | added | Kelvin S | Does your equation $$P_{net} = P_a - P_e = \epsilon\sigma T^4 - \alpha \epsilon_s \sigma T_s^4$$ allows heat flow from lower temperature to higher temperature? It seems it is possible that if $$\alpha \epsilon_s $$ is very small there exists a situation that even the surrounding temperature is higher than the object's temperature, energy still flows from the object to the surrounding. | |
| Jul 22, 2014 at 15:17 | comment | added | user3814483 | @KelvinS Which equation? Yours? Yours makes some assumptions, I believe. Look at the first two equations in my answer. They include information about the environment and the object. $\epsilon_s$ prescribes ability of surrounding to radiate. Since $\alpha \leq 1$, $P_a \leq P_s$. | |
| Jul 22, 2014 at 15:16 | history | edited | user3814483 | CC BY-SA 3.0 |
added 75 characters in body
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| Jul 22, 2014 at 14:38 | history | edited | user3814483 | CC BY-SA 3.0 |
added 20 characters in body
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| Jul 22, 2014 at 6:00 | comment | added | Kelvin S | The above equation assumes that the radiation absorption only depends on the surround temperature and the property of the absorbent. It doesn't include the ability of the surrounding to emit radiation. What am I missing? | |
| Jul 22, 2014 at 5:53 | comment | added | Kelvin S | The problem is, there still exist a situation that the emissivity of surrounding and the object are different. In the case that emissivity of the surrounding is smaller. Energy radiated from surrounding will be less than energy absorbed by the object if we use Pa=αϵsσTs^4 to calculate the absorption. Even you add a coefficient α the problem is not resolved. | |
| Jul 22, 2014 at 5:16 | history | answered | user3814483 | CC BY-SA 3.0 |