Third year 32 Lectures

Lectures of Heat Transfer

Heat Transfer Rate Processes

Mode Conduction Convection Radiation Transfer Mechanism Diffusion of energy due to random molecular motion Diffusion of energy due to random molecular motion plus bulk motion Energy transfer by electromagnetic waves Rate of heat transfer (W)

q = - kA

dT dx

q = h A(Ts-T∞) q = σ ε A(Ts4-Tsur4)

By Mr. Amjed Ahmed Ali

Syllabus of Heat Transfer (English),

(2 hours/ week, Applied 2 hours /week) 1.Heat transfer by conduction, convection and radiation 2.One-dimensional steady state conduction 3.Systems with conduction-convection 4.Radial systems(cylinder and sphere) 4. Overall heat transfer coefficient 5. Critical thickness of the insulator 6. Heat source systems 7. Extended Surface (Fins) 8. Resistance to heat contact 9. Unsteady state conduction • Complete heat capacity system • Limited conditions of convection • Application and Hessler's diagrams 11. Multi-dimensions systems 12. Principles of heat transfer by convection 13. Boundary layer for laminar and turbulent flow 14. Thermal boundary layer for laminar and turbulent flow 15. Analogy between fluid friction and heat transfer 16. Experimental relations of heat transfer by forced convection inside pipes 17. Flow through cylindrical and spherical bodies 18. Flow through bundle of tubes 19. Heat exchangers Scaling Mean logarithmic difference of temperature NTU method 20. Heat transfer by radiation 21. Properties of radiation 22. Body in thermal radiation 23. Relation between coefficient and the body 24. Heal exchange between non-black bodies 25. Radiation barriers Hours 2 2 2 2 2 2 2 2 2 2 2 2 2 2 1 2 2 2 2 2 2 4 1 1 2 1 2 2 2 2 2

Ch 1: Introdaction

3rd Year College of Technical

Chapter Oneِ Introduction

Introduction

A consider the cooling of a hot steal rod which is water Thermodynamics may be used to predict the temperature of the rod-water combination. It will not tell takes to reach this equilibrium condition. Heat Transfer predict the temperature of the rod and the water as a function of time. place in a cold final equilibrium us how long it may be used to

1.1 Definition:

ﺗﻌﺎرﻳﻒ ﻣﻬﻤﺔ

Heat: is the energy transit as a result of the temperature difference. Heat transfer: is that science which seeks to predict the energy transfer that may take place between material bodes as a result of a temperature difference. Thermodynamics: is the state science of energy, the transformation of energy and the change in the state of matter. (Thermodynamics can be able to determination of heat and work requirements for chemical and physical process and the equilibrium conditions). Heat flux: heat transfer flow in the direction per unit area (q”). Steady state: Temperature is very does not very with time (dT/dt) =0. Unsteady state: temperature is depending on time.

1.2 Modes of Heat Transfer

أﻧﻤﺎط اﻧﺘﻘﺎل اﻟﺤﺮارة

The engineering area frequently referred to as thermal science includes thermodynamics and heat transfer. The role of heat transfer is to supplement thermodynamic analyses, which consider only systems in equilibrium, with additional laws that allow prediction of time rates of energy transfer. These supplemental laws are based upon the three fundamental modes of heat transfer conduction, convection, and radiation.

1.3 A Conduction Heat Transfer

Conduction may be viewed as the transfer of energy from the more energetic to the less energetic particles of a substance due to interactions between the particles. A temperature gradient within a homogeneous substance results in an energy transfer rate within the medium which can be calculated by Fourier's law dT q = -kA (1.1) dx Where q is the heat transfer rate (W or J/s) and k thermal conductivity (W/m K) is an experimental constant for the medium involved, and it may depend upon other properties, such as temperature and pressure.

dT dx...