ME2320_CHAPTERI

# ME2320_CHAPTERI - CH. I ME232 Thermo I Introduction and...

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CH. I ME232 Thermo I Introduction and basic concepts 1 INTRODUCTION AND BASIC CONCEPTS 1. THERMODYNAMICS AND ENERGY Thermodynamics is defined as the science of energy. The word thermodynamics comes from the Greek words: Therme b Heat and Dynamis b Power. The study of the energy contained in a system and its ability to produce work is ruled by some scientific laws: - Conservation of Energy Principle . The energy can change from one form to another but the total amount of energy remains constant. (Energy cannot be created nor destroyed). In general, the change in the energy content of a body or any other system is equal to the difference between the energy input and the energy output, and the energy balance is expressed as E in – E out = E The study of the energy contained by a system is made through two laws: First Law of Thermodynamics. The first law of thermodynamics is an expression for the conservation of energy principle. Second Law of Thermodynamics. The second law of thermodynamics predicts the direction in which energy flows as well as the quality of that energy. The science of thermodynamics is used to analyze, study, and design a large number of devices such as refrigerators, boilers, pumps, automotive engines, power plants, etc. 2. DIMENSIONS AND UNITS Physical quantities are characterized by dimensions and the magnitudes assigned to the dimensions are called units . Reference A: PE = 0 units KE = 10 units B: PE = 4 units KE = 6 units Figure 1.1 Principle of conservation of energy.

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CH. I ME232 Thermo I Introduction and basic concepts 2 Table 1.1. Fundamental and Derived Dimensions Fundamental Dimensions Derived Dimensions Mass (m) Velocity (V=L/t) Time (t) Acceleration (a=L/t 2 ) Length (L) Surface (A = L 2 ) Temperature (T) Volume (V = L 3 ) Force (F = m a) Work (W = F L) Power (P = W/t) Systems of Units . The English and the International systems are the two most common and used systems of units. The English system of units is also know as United States Customary System (USCS) Table 1.2. Units in the English and SI Systems English System Dimension International System (SI) ft Length Meter (m) lb m Mass Kilogram (kg) Second (s) Time Second (s) Degree Rankine (R) Temperature Degree Kelvin (K) The SI is a system based on a decimal relationship between units and the prefixes used to abbreviate the some quantities are shown in Table 1.3 Table 1.3. Standard prefixes in SI units Multiple Prefix 10 12 tera, T 10 9 giga, G 10 6 mega, M 10 3 kilo, k 10 2 hecto, h 10 1 deka, da 10 -1 deci, d 10 -2 centi, c 10 -3 mili, m 10 -6 micro, μ 10 -9 nano, n 10 -12 pico, p Most of the equivalencies between units in the English and SI systems can be derived from mass and length equivalencies: 1 lbm = 0.45359 kg 1 ft = 0.3048 m
CH. I ME232 Thermo I Introduction and basic concepts 3 In the English system the force is considered to be a fundamental dimension and therefore is assigned a non-derived unit. However, to avoid confusion we will follow SI system and consider force as a derived unit. Thus, from Newton’s second law

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## This note was uploaded on 04/07/2008 for the course ME 232 taught by Professor Monefort during the Spring '08 term at Western Michigan.

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ME2320_CHAPTERI - CH. I ME232 Thermo I Introduction and...

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