Note for Basics of Mechanical Engineering - BME By Jyotirmayee Reddy

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Introduction to Mechanical Engineering Module 1 DO NOT SKIP ANY TOPIC IN THIS NOTE MODULE I THERMODYNAMICS 1.1 INTRODUCTION Thermodynamics deals with the change of one form of energy to another form. Thermodynamics emerged primarily during the nineteenth century. The fundamental concepts of thermodynamics consider the problem of conversion of heat into mechanical work and vice versa, which inspired the great "Industrial Revolution". Thermodynamics can be defined as the science of energy and its effect on the physical properties of substances. The name thermodynamics was formed from the Greek words therme (heat) and dynamics (power). Thermodynamics is a branch of Physics that deals with the relationship among heat, work and properties of system which are in equilibrium with one another. Thermodynamic System: Certain quantity of matter or region in space which is under thermodynamic study or analysis is called as a thermodynamic system. Let us say for example we are studying the engine of the vehicle, in this case engine is called as the system. Similarly, the other examples of system can be complete refrigerator, air-conditioner, washing machine, .IN heat exchange, a utensil with hot water etc. Surroundings: Everything external to the system is called surroundings. System boundary: Interface separating system and surroundings. Boundaries can also be fixed or moveable (e.g. a piston). Page |1 VISAT

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Introduction to Mechanical Engineering Module 1 Universe: Combination of system and surroundings. Types of Thermodynamic Systems There are three mains types of system: open system, closed system and isolated system. Open system: The system in which the transfer of mass as well as energy can take place across its boundary is called as an open system. Our previous example of engine is an open system. In this case we provide fuel to engine and it produces power which is given out, thus there is exchange of mass as well as energy. The engine also emits heat which is exchanged with the surroundings. The other example of open system is boiling water in an open vessel, where transfer of heat as well as mass in the form of steam takes place between the vessel and surrounding. When studying and analysing devices such as engines, turbines as a whole… it is often useful to define the boundary of the system to be an identifiable volume with a continuous flow of working fluid in to and out of the system. This is termed a control volume. A control volume is said to be enclosed by a control surface. Page |2 VISAT

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Introduction to Mechanical Engineering Module 1 Closed system: The system in which the transfer of energy takes place across its boundary with the surrounding, but no transfer of mass takes place is called as closed system. The closed system is fixed mass system. An example is the water being heated in the closed vessel, where water will get heated but its mass will remain same. In the case of a closed system, in which the mass of matter inside the system remains constant, the control volume is referred to as control mass. Isolated system: The system in which neither the transfer of mass nor that of energy takes place across its boundary with the surroundings is called as isolated system. Here there will neither transfer of mass nor that of energy. Hot water, coffee or tea kept in the thermos flask is closed system. However, if we pour this fluid in a cup, it becomes an open system. Page |3 VISAT

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Introduction to Mechanical Engineering Module 1 1.2 MICROSCOPIC & MACROSCOPIC VIEW POINTS IN THERMODYNAMICS The behaviour of matter can be studied at two levels a) Microscopic and b) Macroscopic Macroscopic Approach 1. Microscopic Approach Also called Classical Thermodynamics Also called Statistical Thermodynamics In this approach, a certain quantity of 2. matter is considered, without taking in In this approach, events occurring at to account the events occurring at the the molecular level is considered. molecular level. 3. 4. 5. Does not require the knowledge of Does require the knowledge of behaviour of individual particles behaviour of individual particles (molecule/atoms etc…) (molecule/atoms etc…) Macroscopic effects could be easily Microscopic effects could be easily analysed by human sense. analysed by human sense. Example: A moving car, A rolling Example: Individual molecules present stone etc… in air 1.3 THERMODYNAMIC PROPERTY A property is any measurable characteristic of a system. The common properties include: pressure (P), temperature (T), volume (V), velocity (v), mass (m), enthalpy (H), entropy (S). Properties can be intensive or extensive. Intensive properties are those whose values are independent of the mass possessed by the system, such as pressure, temperature, and velocity. Extensive properties are those whose values are dependent of the mass possessed by the system, such as volume, enthalpy, and entropy 1.4 STATE, PATH & PROCESS When all the properties of a system has definite value at a particular instant, then the system is said to exist in a state at that instant. At a given state all the properties of the system have definite values. If the value of even one property changes, the state of the system changes. Page |4 VISAT