Radiation Heat Transfer Understand how heat transfers without contact through electromagnetic waves!This section focuses on radiation concepts, Stefan–Boltzmann law, emissivity, and black-body behavior. Perfect for mechanical engineering students learning how energy is emitted, absorbed, and exchanged between surfaces in thermal systems. 1 / 20 In radiation heat transfer, the primary mode of energy transmission is Electromagnetic Waves Molecular Collision Conduction Convection Currents Radiation transmits energy via electromagnetic waves, independent of medium 2 / 20 Surfaces with high absorptivity also have Low Emissivity High Reflectivity High Emissivity Low Reflectivity As per Kirchhoff’s law, good absorbers are good emitters 3 / 20 The total emissive power of a black body at 300 K is proportional to (300)⁴ (300)³ (300)² (300) Emissive power is proportional to the fourth power of absolute temperature 4 / 20 The unit of Stefan–Boltzmann constant is W/m·K W/m²·K J/m³·K W/m²·K⁴ It represents the proportionality constant in the Stefan–Boltzmann equation. 5 / 20 Radiation shape factor between a surface and itself is Zero One Infinity Depends On Area A surface cannot radiate energy to itself, hence its view factor is zero. 6 / 20 The emissivity of polished aluminum is Low High Equal To 1 Greater Than 1 Polished metals reflect most radiation, so emissivity is low. 7 / 20 A surface which absorbs all incident radiation is called Black Body White Body Opaque Body Gray Body A black body absorbs 100% of radiation falling on it. 8 / 20 The net radiation heat exchange between two parallel plates is proportional to T₁ - T₂ T₁² - T₂² T₁³ - T₂³ T₁⁴ - T₂⁴ According to Stefan–Boltzmann law, heat transfer varies with the difference of fourth powers of temperatures. 9 / 20 Radiation exchange between two bodies depends mainly on Density Specific Heat Pressure View Factor The view factor (or shape factor) indicates the fraction of energy leaving one surface that strikes another. 10 / 20 A Gray body is defined as one which Reflects All Radiation Absorbs All Incident Radiation Has Constant Emissivity For All Wavelengths Has Zero Absorptivity Gray bodies have same emissivity for all wavelengths but less than unity. 11 / 20 The radiosity of a surface includes Emitted And Reflected Energy Only Emitted Energy Only Reflected Energy Absorbed Energy Radiosity is the total radiation leaving a surface, both emitted and reflected. 12 / 20 The sun’s radiation reaches the earth mainly by Radiation Convection Conduction Reflection Space has no medium, so radiation is the only mode of heat transfer. 13 / 20 The wavelength corresponding to maximum emissive power is given by Kirchhoff’s Law Newton’s Cooling Law Pascal’s Law Wien’s Law Wien’s law relates peak wavelength to absolute temperature (λₘ·T = constant). 14 / 20 Radiation intensity depends on Specific Heat Temperature And Nature Of Surface Thickness Of Material Velocity Of Fluid Smooth, polished, and lighter surfaces emit less radiation than rough or dark ones. 15 / 20 The absorptivity and emissivity of a body are equal according to Planck’s Law Newton’s Law Kirchhoff’s Law Stefan–Boltzmann Law Kirchhoff’s law states that good absorbers are also good emitters at the same temperature. 16 / 20 A perfect reflector has emissivity equal to 1 0.9 0.5 0 Reflectors emit no radiation; thus, emissivity is zero. 17 / 20 The emissivity of a perfect black body is 1 0 Between 0 And 1 Greater Than 1 A black body emits maximum possible radiation, hence emissivity = 1. 18 / 20 The unit of emissive power is J/kg·K W/m²·K W/m² W/m·K It represents energy emitted per unit area per second. 19 / 20 The energy radiated per unit area is governed by Fourier’s Law Newton’s Law Pascal’s Law Stefan–Boltzmann Law The Stefan–Boltzmann law states that radiated energy is proportional to the fourth power of absolute temperature. 20 / 20 Heat transfer by radiation requires No Medium A Solid Medium A Liquid Medium A Gas Medium Radiation can occur even in a vacuum, unlike conduction and convection. Your score isThe average score is 0% 0% Restart quiz
