Heat Transfer - Introduction

Textbook

Heat and Mass Transfer: A Practical Approach

by

Yunus A. Çengel

McGraw-Hill, NY, 2007

CHAPTER 1

Basic Concepts of Thermodynamics and Heat Transfer

What is going on?

What do you feel when you enter a warm classroom? What happens to a cold canned drink or a hot cup of coffee left in a room? What do you feel when you jump into cold sea (from a hot beach)? Why do put on more clothing on a cold day?

Heat transfer

What is Heat Transfer ?

Heat :

It is the form of energy that can be transferred from one system to another as a result of temperature difference.

Heat Transfer :

It is the science that deals with the determination of the rates of such energy transfers.

Thermodynamics and Heat Transfer

They are called thermal sciences

What is the difference? Thermodynamics :

It concerns with the amount of heat transfer (between equilibrium states). Time independent Equilibrium phenomenon

Heat Transfer :

It deals with the rate of heat transfer. Time dependent processes Non-equilibrium phenomenon Driving force: temperature difference Thermodynamic principles alone are not enough for heat transfer analysis

The Difference between Heat Transfer & Thermodynamics

How long will it take to cool the coffee in a thermos bottle from 90oC to 70oC? Which one, heat transfer or thermodynamics, can answer this question?

Heat transfer can calculate the time needed

Some application areas of heat transfer

Heat and Other Forms of Energy

Forms of Energy :

Thermal Kinetic Electrical Chemical Mechanical Potential Magnetic Nuclear

Total Energy of a System (E) = Σ all energies

• Internal energy may be viewed as the sum of the kinetic and potential energies of the molecules. • The kinetic energy of the molecules is called sensible heat. • The internal energy associated with the phase of a system is called latent heat. • The internal energy associated with the atomic bonds in a molecule is called chemical (or bond) energy. •...