PPT NITTTR

1. National Institute of Technical Teacher‘s Training & Research, Bhopal Modes Of Heat Transfer

2. Contents • Introduction • Heat transfer • Modes of heat transfer • Fourier’s law • Newton’s law of cooling • Stefan-Boltzmann law • Conclusion • Home assignment

3. Session outcomes The students will be able to: • Understanding of mode of heat transfer such as conduction, convection and radiation process. • Use of governing equations for conduction, convection and radiation process.

4. Heat Transfer Heat:  Heat is the form of energy that transfers due to the temperature differences between the system and surroundings. Heat transfer: Exchange of heat (energy) between hot and cold bodies. Heat transfer Hot body 700 K Cold body 300 K

5. Modes of heat transfer

7. Conduction: Transfer of heat through a material due to vibration of molecules. • Fourier’s law governs the conduction. • Convection: Transfer of heat due to random molecular motion and by the bulk motion of the fluid. • Newton’s law of cooling governs the convection. • Radiation: Heat transfer in the form of electromagnetic waves. • Stefan-Boltzmann law governs the radiation.

8. Example of modes of heat transfer

9. Fourier’s law • Rate of heat transfer is directly proportional to the temperature difference, directly proportional to area and inversely proportional to thickness. Q = -KA(dT/dx) Where, “Q” is rate of heat transfer (W) “K” is thermal conductivity of material (W/(m.K)) “A” is area of conduction (m2) “T” is temperature, Kelvin (K) “x” is thickness of heat transfer (m)

10. Newton’s law of cooling • Rate of heat transfer by convection between a solid body and the surrounding fluid is directly proportional to the temperature difference between them and is also directly proportional to area of exposure between the body and fluid. • Q ∝ A, Q ∝ ΔT • Q ∝ A. ΔT • Q = h.A.ΔT Where, “Q” is rate of heat transfer (W) “h” is convective heat transfer coefficient (W/m2.K) “A” is area of heat transfer (m2) “ΔT” is temperature difference between body (K)

11. Stefan-Boltzmann Law • The radiation energy emitted from the surface of black body per unit time and per unit area is directly proportional to the fourth power of absolute temperature. • Eb α T4 • Eb α σ.T4 ,W/m2 • Eb α σ.A.T4 , W Where, “σ” is stefen-Boltzmann constant = 5.67 x 10-8 W/(m2.k4) “A” is area of heat transfer (m2) “T” is absolute temperature (K)

12. Conclusion • Conduction is most dominant in solid. • Convection is most dominant in liquid. • Radiation does not require any medium.

13. Home Assignment • What are different type of mode of heat transfer? • If thickness of slab is increases then rate of heat transfer decreases?(true/false) • In boiling of milk which mode of heat transfer dominates?