Jsjsyensk nshjsjsdndjjs kskuabmsjjsjsnsjjsj

Heat transfer

1. HEAT TRANSFER INTRODUCTION 2. COMPARISION B/W HEAT TRANSFER AND THERMODYNAMICS 3. MODES OF HEAT TRANSFER 4. LAWS OF HEAT TRANSFER

2. What is Heat Transfer? “Energy in transit due to temperature difference.” Thermodynamics tells us: • how much heat is transferred ( dQ ) • how much work is done ( dW ) • final state of the system Heat transfer tells us: • how (with what modes) dQ is transferred • at what rate dQ is transferred • temperature distribution inside the body HEAT TRANSFER THERMODYNAMICS Complementary

3. MODES: Conduction Needs matter Molecular phenomenon (diffusion process) Without bulk motion of matter Convection Heat carried away by bulk motion of fluid Needs fluid matter Radiation Does not needs matter Transmission of energy by electromagnetic waves

4. LAWS GOVERNING HEAT TRANSFER FUNDAMENTAL LAWS: Laws of Thermodynamics 1 st Law of Thermodynamics : ∫ dQ = ∫ dW 2 nd Law of Thermodynamics : Q flow naturally from on body to another at a lower temperature but opp. Not possible without assistance. Newton's 2 nd Law of Motion : used to find the fluid flow parameters Law of Conservation of Mass : used to find the fluid flow parameters Experimental Laws: Fourier’s Laws of Heat conduction Newton's Law of cooling Stefan Boltzmann Law

5. CONDUCTION Transfer of heat from one part of the substance to another part of the same substance or to another in physical contact with it. Mechanisms: (a) by lattice vibration (b) By transport of free electrons

6. ASSIGNMENT

7. CONVECTION “Transfer of Heat within a fluid by mixing one portion of fluid with another”. Newton's Law of Cooling : Rate of HT is directly proportional to temperature difference b/w the surface and fluid, i.e., Q = h .A.(T-t) Where, Q = rate of HT A = Area exposed to HT, m 2 T = surface temperature, K or °C t= fluid temperature, K or °C h = Coefficient of convective HT, h= Q/A(T-t) Unit of h: W/ m 2 °C

8. May occur with phase change (boiling, condensation) Heat transfer coefficient (not a property) depends on geometry ,nature of flow, thermodynamics properties etc.

9. RADIATION Heat Transfer by electromagnetic waves or photons Stefan Boltzmann Law : emissive power of black body is directly proportional to forth power of absolute temperature, i.e., Q= F σ A (T₁⁴-T₂⁴) Where, F = 1…black body enclosed by other surface F= emissivity ( ε )…non black body enclosed by other surface A = Area, m 2 σ = Stefan Boltzmann constant = 5.67×10ˉ⁸ W/ m 2 K⁴ T₁ ,T₂ = Temperatures, K or °C

10. Assignment-2 Q1. Explain the laws governing Conduction, Convection, Radiation? Q2. Discuss the Fourier Laws of heat conduction? Also give the assumption for heat transfer? Submission on 03/02/2012