Presentation on theme: "MEL140 Lectures 1 & 2. Course outline TopicNumber of Lectures Introduction and basic concepts2 Energy, energy transfer and the first law of thermodynamics2."— Presentation transcript:
MEL140 Lectures 1 & 2
Course outline TopicNumber of Lectures Introduction and basic concepts2 Energy, energy transfer and the first law of thermodynamics2 Properties of pure substances3 Energy analysis of closed systems3 Mass and Energy analysis of open systems5 The second Law of thermodynamics6 Entropy and the second law5 Exergy or Available Energy4 Thermodynamic property relations4 Air standard cycles2 Vapor power cycles4 Refrigeration cycles2 Total42
Course outline (contd.) Evaluation policy: Minor 1: 20 Minor 2: 20 Major: 40 Projects and assignments: 20 Textbook: Cengel, Y.A., and Boles, M.A., Thermodynamics an Engineering Approach, Tata McGraw-Hill., New York, 7 th Edition. References: Moran, M.J., and Shapiro, H.N., Fundamentals of Engineering Thermodynamics, John Wiley, New York, Sixth edition. P. K. Nag, Engineering Thermodynamics, Tata Mcgraw-Hill, Attendance Policy: 75% and above with or without medical certificate. Only IIT Delhi medical certificate can be used for application for Re-minor. Audit Criteria: B and above, with same attendance policy.
What is thermodynamics? Study of energy transformations and its effects on matter. Although thermodynamics is applicable to any kind of energy transformation historically, concepts and rules of thermodynamics evolved from attempts to understand how energy from “hot” bodies could be harnessed for useful purposes. Hence, “heat” plays an important role. “Effects on matter” how the “condition” of a given amount of matter changes as energy is transferred into or out of it is also an important aspect of thermodynamics.
System and surroundings System: a region chosen for thermodynamic analysis Surroundings: The part of the universe other than the system Boundary: The real or imaginary surface separating the system from its surroundings.
Types of system Closed system: energy but no mass crosses its boundary. –Everyday examples: cup of tea with air-tight lid; pressure-cooker before its first whistle. Open system: mass and energy both cross its boundary. –Everyday examples: open cup of hot tea; pressure-cooker after its first whistle; car; hair (blow) dryer; human body (see pic). heat
Types of system (continued) Isolated system: neither energy nor mass crosses its boundary. Everyday example: a perfect thermos flask Conceptual example: –Universe (system + surroundings)
Nerdy (engineering) examples of open systems Boiler burns fossil fuels to produce steam for a power plant. Keep and eye on what (energy/mass) crosses which part of the boundary. The boiler is designed to operate “on and on”. Air being drawn and compressed into a tank using a motor-plus-compressor set (mass enters as air through the boundary shown; electrical energy from the electricity mains enters the boundary shown). This system does not operate “on and on”; once charged a valve at the entry to the tank (not shown) is closed and the “compressed air” is reserved for later use such as pumping bicycle tyres.
Alert: Alternative and confusing engineering terminology The term “control volume” is commonly used as an alternative terminology for “open system”; but occasionally for “system”. Here, control means “kontrol”, which is German for “accounting”; Tip: forget the English usage of control, please. The word system is occasionally used to imply a closed system.
Pure substance A pure substance has the same chemical composition throughout. Are the following pure substances: –Ice –A mixture of water and water vapor –Air –Oil in contact with water –A gaseous mixture containing N 2,O 2,H 2 O, CO 2 obtained from burning kerosene –Liquid air in contact with gaseous air –Sea Ice in contact with sea water Alert: in chemistry a pure substance is defined such that it consists of one component (chemical species) and therefore must be “non-mixture”. We follow a different definition (see above) in engineering thermodynamics.
Phases Solid LiquidGas A region within matter with distinct molecular arrangement that is homogeneous throughout that region which is separated from other regions (if any) by distinct boundary surfaces. Physical properties (like density and refractive index) of each phase is different; macroscopically these properties “jump” across certain boundary surfaces known as “phase boundaries”. The three principal phases:
How many phases in? 1.Ice 2.A mixture of water and water vapor 3.Air 4.Oil in contact with water 5.A gaseous mixture containing N 2,O 2,H 2 O, CO 2 obtained from burning kerosene 6.Liquid air in contact with gaseous air 7.Sea Ice in contact with sea water Ans. (1) 1, (2) 2,(3) 1, (4) 2, (5) 1, (6) 2 (7) 2