Concept explainers
Consider an opaque horizontal plate that is well insulated on its back side. The irradiation on the plate is
The value of emissivity, absorptivity and the radiosity of the plate.
The value of the net heat transfer rate per unit area.
Answer to Problem 12.1P
The value of emissivity is,
The value of absorptivity is,
The value of radiosity is,
The value of the net heat transfer rate per unit area is,
Explanation of Solution
Given:
The irradiation on the plate is,
The reflected irradiation is,
The emissive power of any surface,
The temperature of the plate,
The temperature of the air over the plate
Calculation:
The energy balance equation as per the incident radiation on a surface is,
Where,
For an opaque surface transmissivity,
Now the equation (1) become as,
The emissive power of a black surface,
Where,
The Stefan Boltzmann constant,
Emissivity
Mathematically,
Reflectivity
Mathematically,
Absorptivity
From equation (2), absorptivity will be calculated as,
Radiosity
The net heat transfer rate per unit area is calculated as:
Therefore, the value of the net heat transfer rate per unit area is,
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Fundamentals of Heat and Mass Transfer
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