ENG. SAMRA ESSALAIMEH PHILADELPHIA UNIVERSITY 2 ND SEMESTER Thermo-Fluid

Introduction and Overview INTRODUCTION TO THERMAL-FLUID SCIENCES:

Cont.

THERMODYNAMICS Thermodynamics: The science of energy. Energy: The ability to cause changes. The name thermodynamics stems from the Greek words therme (heat) and dynamis (power). Conservation of energy principle: During an interaction, energy can change from one form to another but the total amount of energy remains constant. Energy cannot be created or destroyed. The first law of thermodynamics: An expression of the conservation of energy principle. The first law asserts that energy is a thermodynamic property. Energy cannot be created or destroyed; it can only change forms (the first law).

The second law of thermodynamics: It asserts that energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy. Classical thermodynamics: A macroscopic approach to the study of thermodynamics that does not require a knowledge of the behavior of individual particles. It provides a direct and easy way to the solution of engineering problems and it is used in this text. Statistical thermodynamics: A microscopic approach, based on the average behavior of large groups of individual particles. It is used in this text only in the supporting role. Cont.

HEAT TRANSFER In heat transfer, we are primarily interested in heat, which is the form of energy that can be transferred from one system to another as a result of temperature difference. The science that deals with the determination of the rates of such energy transfers is heat transfer. In engineering, we are often interested in the rate of heat transfer, which is the topic of the science of heat transfer. Thermodynamics deals with equilibrium states and changes from one equilibrium state to another. Heat transfer, on the other hand, deals with systems that lack thermal equilibrium, and thus it is a nonequilibrium phenomenon.

The first law requires that the rate of energy transfer into a system be equal to the rate of increase of the energy of that system. The second law requires that heat be transferred in the direction of decreasing temperature. The basic requirement for heat transfer is the presence of a temperature difference. Cont.

FLUID MECHANICS Mechanics is the oldest physical science that deals with both stationary and moving bodies under the influence of forces. Statics: The branch of mechanics that deals with bodies at rest. Dynamics: the branch that deals with bodies in motion. fluid mechanics: the science that deals with the behavior of fluids at rest (fluid statics) or in motion (fluid dynamics), and the interaction of fluids with solids or other fluids at the boundaries.

Stress: force per unit area, and is determined by dividing the force by the area upon which it acts. normal stress: The normal component of a force acting on a surface per unit area. shear stress: the tangential component of a force acting on a surface per unit area. Pressure: In a fluid at rest, the normal stress. Cont.

DIMENSIONS AND UNITS Any physical quantity can be characterized by dimensions. The magnitudes assigned to the dimensions are called units. Some basic dimensions such as mass m, length L, time t, and temperature T are selected as primary or fundamental dimensions, while others such as velocity V, energy E, and volume V are expressed in terms of the primary dimensions and are called secondary dimensions, or derived dimensions. Metric SI system: A simple and logical system based on a decimal relationship between the various units. English system: It has no apparent systematic numerical base, and various units in this system are related to each other rather arbitrarily.

Some SI and English Units Work = Force  Distance 1 J = 1 N∙m 1 cal = J 1 Btu = kJ

Cont. W weight m mass g gravitational acceleration A body weighing 60 kgf on earth will weigh only 10 kgf on the moon. The relative magnitudes of the force units newton (N), kilogram-force (kgf), and pound-force (lbf). The weight of a unit mass at sea level.