WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition 3 CHAPTER The First Law of Thermodynamics: Closed Systems

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary The first law of thermodynamics is essentially an expression of the conservation of energy principle. Energy can cross the boundaries of a closed system in the form of heat or work. If the energy transfer across the boundaries of a closed system is due to a temperature difference, it is heat; otherwise, it is work. 3-22

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary Heat is transferred in three ways: conduction, convection, and radiation. › Conduction is the transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles. › Convection is the mode of energy transfer between a solid surface and the adjacent liquid or gas that is in motion, and it involves the combined effects of conduction and fluid motion. › Radiation is the energy emitted by matter in the form of electromagnetic waves (or photons) as a result of the changes in the electronic configurations of the atoms or molecules. 3-23

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary The three modes of heat transfer are expressed as: 3-24

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Various forms of work are expressed as follows: › Electrical work: (kJ) › Boundary work: (kJ) › Gravitational work (=DPE): (kJ) › Acceleration work (=DKE): (kJ) › Shaft work: (kJ) › Spring work: (kJ) Chapter Summary 3-25

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary For the ploytropic process (Pv n = constant) of real gases, the boundary work can be expressed as: 3-26

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary The energy balance for any system undergoing any process can be expressed as: 3-27

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary The energy balances for any system undergoing any process can be expressed in the rate form as: 3-28

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary Taking heat transfer to the system and work done by the system to be positive quantities, the energy balance for a closed system can also be expressed as: where: 3-29

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary For a constant-pressure process,. Thus 3-30

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary The amount of energy needed to raise the temperature of a unit of mass of a substance by one degree is called the specific heat at constant volume C v for a constant-volume process and the specific heat at constant pressure C p for a constant pressure process. They are defined as: 3-31

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary For ideal gases u, h, C v, and C p are functions of temperature alone. The  u and  h of ideal gases can be expressed as: 3-32

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary For ideal gases C v, and C p are related by: 3-33

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary The specific heat ratio k is defined as: 3-34

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary For incompressible substances (liquids and solids), both the constant-pressure and constant- volume specific heats are identical and denoted by C: 3-35

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary The u and  h of incompressible substances are given by 3-36

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Chapter Summary The refrigeration and freezing of foods is a major application area of thermodynamics. 3-37

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Heat Transfer 3-1 (Fig. 3-3)

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Adiabatic Process (Fig. 3-4) 3-2

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Convection: Heat Transfer (Fig. 3-8) 3-3

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Convection: Cooling (Fig. 3-9) 3-4

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Radiation (Fig. 3-10) 3-5

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Heat and Work (Fig. 3-15) 3-6

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Path Functions (Fig. 3-16) 3-7

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Boundary Work (Fig. 3-27) 3-8

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Net Work per Cycle (Fig. 3-29) 3-9

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Schematic/Diagram for Ex. 3-8 (Fig. 3-31) 3-10

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Schematic/Diagram for Ex. 3-9 (Fig. 3-32) 3-11

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Schematic/Diagram for the Polytropic Process (Fig. 3-33) 3-12

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Schematic/Diagram for Ex (Fig. 3-43) 3-13

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Stretching a Liquid Film (Fig. 3-45) 3-14

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition System Energy Change (Fig. 3-52) 3-15

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Energy Change for a Cycle (Fig. 3-54) 3-16

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Closed-Systems, First-Law (Fig. 3-55) 3-17

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Formal Definitions of C v and C p (Fig. 3-72) 3-18

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Specific Heats for Some Gases (Fig. 3-76) 3-19

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Three Ways to Calculate ²u 3-20 (Fig. 3-80)

WCB/McGraw-Hill © The McGraw-Hill Companies, Inc.,1998 Thermodynamics Çengel Boles Third Edition Typical Freezing Curve (food) (Fig. 3-91) 3-21