Chapter One 1 Thermalfluid sciences involve the transfer

Chapter One 1. Thermal-fluid sciences involve the transfer, transport, and conversion of energy, usually studied under the subcategories of thermodynamics, heat transfer, and fluid mechanics. 2. Thermal stems from the Greek word therme, which means heat.

Application (1): designing the radiator of a car involves the determination of the amount of energy transfer from a knowledge of the properties of the coolant using thermodynamics, the determination of the size and shape of the inner tubes and the outer fins using heat transfer, and the determination of the size and type of the water pump using fluid mechanics.

Application (2): The heart is constantly pumping blood to all parts of the human body, various energy conversions occur in trillions of body cells, and the body heat generated is constantly rejected to the environment.

• Thermodynamics can be defined as the science of energy. words therme (heat) and dynamis (power), the ability to cause changes. The change in the energy content of a system is equal to the difference between the energy input and the energy output, and the energy balance is expressed as Ein- Eout = ∆ E.

The first law of thermodynamics is simply an expression of the conservation of energy principle, and it states that energy is a thermodynamic property. The second law of thermodynamics states that energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy. For example, a cup of hot coffee left on a table eventually cools to room temperature, but a cup of cool coffee in the same room never gets hot by itself.

Heat Transfer deals with the determination of the rates and mechanism of energy being transferred. Energy that can be transferred from one system to another as a result of temperature difference. Thermodynamics deals with equilibrium states and changes from one equilibrium state to another. Heat transfer deals with systems that lack thermal equilibrium(nonequilibrium phenomenon), and tell us the rate and mechanism of heat been transferred.

• fluid mechanics is defined as the science that deals with the behavior of fluids at rest (fluid statics) or in motion (fluid dynamics). . A substance in the liquid or gas phase is referred to as a fluid. • Hydro-dynamics deals with liquid flows in pipes and open channels. Gas dynamics deals with flow of fluids that undergo significant density changes, such as the flow of gases through nozzles at high speeds. Aerodynamics deals with the flow of gases (especially air) over bodies such as aircraft, rockets.

• The normal component of a force acting on a surface per unit area is called the normal stress σ, and the tangential component of a force acting on a surface per unit area is called shear (or tangential) stress τ. In a fluid at rest, the normal stress is called pressure. Normal stress Shear stress

Unit Systems Any physical quantity characterized by dimensions called units. Primary dimensions: such as mass m, length L, time t, and temperature T Secondary dimensions: such as velocity, energy E, and volume V are expressed in terms of the primary dimensions.

Units are still in common use today: 1 - English system, which is also known as the United States Customary System (USCS), (12 in in 1 ft (foot), 16 oz in 1 lb (libra), 4 qt in 1 gal, etc. ). 2 - Metric SI (from Le Système International d’ Unités), which known as the International System. ( meter (m) for length, kilogram (kg) for mass, second (s) for time, degree Kelvin (°K) for temperature). • 1 lbm (pound mass) = 0. 45359 kg • ft = 0. 3048 m

• In SI, N (newton) force required to accelerate a mass of 1 kg at a rate of 1 m/s 2. In the English system, the force unit is the pound-force (lbf ) and is defined as the force required to accelerate a mass of 32. 174 lbm at a rate of 1 ft/s 2. That is, 1 N = 1 kg · m/s 2 1 lbf = 32. 174 lbm · ft/s 2 • Unlike mass, weight W is a force. It is the gravitational force applied to a body, and its magnitude is determined from Newton’s second law, W = mg = (N) • where m is the mass of the body, and g is the local gravitational acceleration (g is 9. 807 m/s 2 or 32. 174 ft/s 2 at sea level). • The specific weight γ and is determined from γ= ρg, where ρ is density.

Work : a form of energy, defined as force time distance; therefore, it has the unit “newton meter (N ·m), ” called a joule (J), 1 J = 1 N · m, for energy in SI is the kilojoule (1 k. J=103 J), . energy unit is the Btu (British thermal unit) = energy required to raise the temperature of 1 lbm of water a 68 F by 1 F. In the metric system, the amount of energy needed to raise the temperature of 1 g of water at 15 C by 1 C is defined as 1 calorie (cal), and 1 cal= 4. 1868 J. The magnitudes of the kilojoule and Btu are almost identical (1 Btu=1. 055 k. J).

• In engineering, all equations must be dimensionally homogeneous. That is, every term in an equation must have the same unit (apples and oranges do not add). E= 25 k. J + 7 k. J/kg • Obtaining Formulas from Unit Considerations: A tank is filled with oil whose density is ρ= 850 kg/m 3. If the volume of the tank is V=2 m 3, determine the amount of mass m in the tank. It is clear m = ρ. V = (850 kg/m 3) (2 m 3) =1700 kg

• An engineering device or process can be studied either experimentally (testing and taking measurements) or analytically (by analysis or calculations). • PROBLEM-SOLVING TECHNIQUE Step 1: Problem Statement Step 2: Schematic Step 3: Assumptions and Approximations Step 4: Physical Laws Step 5: Properties Step 6: Calculations Step 7: Reasoning, Verification, and Discussion • Engineering software packages available today are just tools, and tools have meaning only in the hands of masters.