Introduction to Mechanical Engineering Lecture Slides 1 & 2 PDF

Introduction to Mechanical Engineering Lecture slides 1 and 2 Mechanical Engineering’s contribution to society The Automobile The development and commercialization of the automobile were judged as the profession’s most significant achievement in the twentieth century. Two factors responsi...

Introduction to Mechanical Engineering Lecture slides 1 and 2 Mechanical Engineering’s contribution to society The Automobile The development and commercialization of the automobile were judged as the profession’s most significant achievement in the twentieth century. Two factors responsible for the growth of automotive technology have been high-power, lightweight engines and efficient processes for mass manufacturing. In addition to engine improvements, competition in the automobile market has led to advances in the areas of safety, fuel economy, comfort, and emission control. Some of the newer technologies include hybrid gas-electric vehicles, antilock brakes, run-flat tires, air bags, widespread use of composite materials, computer control of fuel- injection systems, satellite-based navigation systems, variable valve timing, and fuel cells. Mechanical Engineering’s contribution to society The Airplane The development of the airplane and related technologies for safe powered flight were recognized by the American Society of Mechanical Engineers as a key achievement. Mechanical engineers contributed to nearly every aspect of aviation technology. Advancements include vectored turbofan engines, vertical takeoffs and landings, and lightweight materials like titanium alloys and graphite-fiber-reinforced composites. Mechanical Engineering’s contribution to society Power Generation One aspect of mechanical engineering involves designing machinery that can convert energy from one form to another. Abundant and inexpensive energy is recognized as an important factor behind economic growth and prosperity, and the generation of electrical power is recognized as having improved the standard of living for billions of people across the globe. In the twentieth century, entire societies changed as electricity was produced and routed to homes, businesses, and factories. Mechanical engineers are credited with having developed efficient technologies to convert various forms of stored energy into electricity. Advanced power-generation technologies include solar, ocean, and wind power systems. Mechanical Engineering’s contribution to society Air Conditioning and Refrigeration Mechanical engineers invented efficient air conditioning and refrigeration technologies. Today, these systems not only ensure safety and comfort but also preserve food and medical supplies. Mechanical Engineering’s contribution to society Computer-Aided Engineering (CAE) The term 'computer-aided engineering' (CAE) refers to a wide range of automation technologies in mechanical engineering, encompassing the use of computers for calculations, simulations, and machine control. CAE tools were instrumental in developing the Boeing 777, which was designed without traditional drafting techniques. Mechanical Engineering’s contribution to society Codes and Standards Codes and standards ensure that engineered products are compatible with one another. They are necessary for specifying physical characteristics of mechanical parts, and have become increasingly important in global trade. Standards are developed through consensus among governments, industry groups, and professional societies. Mechanical Engineering’s contribution to society Mass production Mechanical engineers play a crucial role in mass production by designing and optimizing machinery, tools, and manufacturing processes. Their innovations improve efficiency, reduce costs, and ensure product consistency, enabling large- scale production at higher speeds and lower defects. IBM Model 350 Disk File The world's first hard disk drive, the IBM Model 350 Disk File, appeared in 1956, with fifty 24″ disks holding up to 5MB of data. Mechanical engineers contributed to miniaturizing integrated circuits and creating advanced manufacturing methods. Today's processors contain billions of transistors, with mechanical engineers designing machinery for producing integrated circuits at nanometer scales. Mechanical Engineering’s contribution to society Agricultural Mechanization Mechanical engineers have developed technologies to improve significantly the efficiency in the agricultural industry. Automation began with the introduction of powered tractors in 1916 and the development of the combine, simplifying grain harvesting. Research is underway to develop machines to harvest fields autonomously using advanced machinery, GPS technology, and intelligent guidance. Other advances include improved weather observation, high-capacity irrigation pumps, automated milking machines, and digital management of crops. Current trend - Interdisciplinary engineering Fundamental Concepts and Definitions THERMODYNAMICS:  It is the science of the relations between heat, Work and the properties of the systems.  How to adopt these interactions to our benefit? Thermodynamics enables us to answer this question.  Examples If we like to  Rise the temperature of water in kettle  Burn some fuel in the combustion chamber of an aero engine to propel an aircraft.  Cool our room on a hot humid day.  Heat up our room on a cold winter night.  Have our vanilla chocolate ice cream. What is the smallest amount of electricity/fuel we can get away with?  Examples On the other hand we burn,  Some coal/gas in a power plant to generate electricity.  Petrol in a car engine. What is the largest energy we can get out of these efforts? Thermodynamics allows us to answer some of these questions  Definitions  In our study of thermodynamics, we will choose a small part of the universe to which we will apply the laws of thermodynamics. We call this subset a SYSTEM.  The system is a macroscopically identifiable collection of matter on which we focus our attention (eg: the water kettle or the aircraft engine).  Definitions  The rest of the universe outside the system close enough to the system to have some perceptible effect on the system is called the surroundings.  The surfaces which separates the system from the surroundings are called the boundaries as shown in fig below (eg: walls of the kettle, the housing of the engine). System Boundary Surroundings  Types of System  Closed system - in which no mass is permitted to cross the system boundary i.e. we would always consider a system of constant mass.We do permit heat and work to enter or leave but not mass. Boundary Heat/work Out system Heat/work in No mass entry or exit  Open system- in which we permit mass to cross the system boundary in either direction (from the system to surroundings or vice versa). In analysing open systems, we typically look at a specified region of space, and observe what happens at the boundaries of that region. Most of the engineering devices are open system. Boundary Heat/work Mass Out out System Heat/work Mass in In  Isolated System - in which there is no interaction between system and the surroundings. It is of fixed mass and energy, and hence there is no mass and energy transfer across the system boundary. System Surroundings  Choice of the System and Boundaries Are at Our Convenience  We must choose the system for each and every problem we work on, so as to obtain best possible information on how it behaves.  In some cases the choice of the system will be obvious and in some cases not so obvious.  Choice of the System and Boundaries Are at Our Convenience (contd…)  The boundaries may be real physical surfaces or they may be imaginary for the convenience of analysis. eg: If the air in this room is the system,the floor,ceiling and walls constitutes real boundaries.the plane at the open doorway constitutes an imaginary boundary.  Choice of the System and Boundaries Are at Our Convenience (contd…)  The boundaries may be at rest or in motion. eg: If we choose a system that has a certain defined quantity of mass (such as gas contained in a piston cylinder device) the boundaries must move in such way that they always enclose that particular quantity of mass if it changes shape or moves from one place to another.  Macroscopic and Microscopic Approaches Behavior of matter can be studied by these two approaches. In macroscopic approach, certain quantity of matter is considered,without a concern on the events occurring at the molecular level. These effects can be perceived by human senses or measured by instruments.  eg: pressure, temperature  Microscopic Approach In microscopic approach, the effect of molecular motion is Considered. eg: At microscopic level the pressure of a gas is not constant, the temperature of a gas is a function of the velocity of molecules. Most microscopic properties cannot be measured with common instruments nor can be perceived by human senses  Property It is some characteristic of the system to which some physically meaningful numbers can be assigned without knowing the history behind it. These are macroscopic in nature. Invariably the properties must enable us to identify the system. eg: Anand weighs 72 kg and is 1.75 m tall. We are not concerned how he got to that stage. We are not interested what he ate!!.  Examples (contd...) We must choose the most appropriate set of properties.  For example: Anand weighing 72 kg and being 1.75 m tall may be a useful way of identification for police purposes.  If he has to work in a company you would say Anand graduated from IIT, Chennai in 2020 in mechanical engineering.  Anand hails from Mangalore. He has a sister and his father is a poet. He is singer. ---If you are looking at him as a bridegroom!!  Examples (contd…) All of them are properties of Anand. But you pick and choose a set of his traits which describe him best for a given situation. Similarly, among various properties by which a definition of a thermodynamic system is possible, a situation might warrant giving the smallest number of properties which describe the system best.  Categories of Properties Extensive property: whose value depends on the size or extent of the system (upper case letters as the symbols). eg: Volume, Mass (V,M). If mass is increased, the value of extensive property also increases. Intensive property: whose value is independent of the size or extent of the system. eg: pressure, temperature (p, T).  Property (contd..) Specific property:  It is the value of an extensive property per unit mass of system. (lower case letters as symbols) eg: specific volume, density (v, ).  It is a special case of an intensive property.  Most widely referred properties in thermodynamics:  Pressure; Volume; Temperature; Entropy; Enthalpy; Internal energy  State and Phase  State: It is the condition of a system as defined by the values of all its properties. It gives a complete description of the system. Any operation in which one or more properties of a system change is called a change of state.  Phase: It is a quantity of mass that is homogeneous throughout in chemical composition and physical structure. e.g. solid, liquid, vapour, gas. Phase consisting of more than one phase is known as heterogenous system.  Path And Process The succession of states passed through during a change of state is called the path of the system. A system is said to go through a process if it goes through a series of changes in state. Consequently: A system may undergo changes in some or all of its properties. A process can be construed to be the locus of changes of state  Quasi-static Processes The processes can be restrained or unrestrained We need restrained processes in practice. A quasi-static process is one in which  The deviation from thermodynamic equilibrium is infinitesimal.  All states of the system passes through are equilibrium states. Gas  Quasi-static Processes (contd…) If we remove the weights slowly one by one the pressure of the gas will displace the piston gradually. It is quasistatic. On the other hand if we remove all the weights at once the piston will be kicked up by the gas pressure.(This is unrestrained expansion) but we don’t consider that the work is done - because it is not in a sustained manner In both cases the systems have undergone a change of state. Another eg: if a person climbs down a ladder from roof to ground, it is a quasistatic process. On the other hand if he jumps then it is not a quasistatic process.  Equilibrium State A system is said to be in an equilibrium state if its properties will not change without some perceivable effect in the surroundings. Equilibrium generally requires all properties to be uniform throughout the system. There are mechanical, thermal, phase, and chemical equilibria  Types of Equilibrium Between the system and surroundings, if there is no difference in Pressure Mechanical equilibrium Potential Electrical equilibrium Concentration of species Species equilibrium Temperature Thermal equilibrium No interactions between them occur. They are said to be in equilibrium. Thermodynamic equilibrium implies all those together. A system in thermodynamic equilibrium does not deliver anything.  We Concentrate On Two Categories Of Heat And Work  Thermodynamic definition of work: Positive work is done by a system when the sole effect external to the system could be reduced to the rise of a weight.  Thermodynamic definition of heat: It is the energy in transition between the system and the surroundings by virtue of the difference in temperature.  Traits of Engineers  All our efforts are oriented towards how We require a to convert heat to work or vice versa: combination of processes. Heat to work Thermal power plant Sustainability is ensured from a cycle Work to heat Refrigeration A system is said to have gone through a cycle if the initial state has been regained after a series of processes  Sign Conventions  Work done BY the system is +ve  Obviously work done ON the system is –ve  Heat given TO the system is +ve  Obviously Heat rejected by the system is -ve W W -VE +VE Q Q -VE +VE  Displacement work (pdV work) p p p Cross sectional area=A 1 2 dl v  If the piston moves through a finite distance (say 1-2), then work done has to be evaluated by integrating W=pdV  Discussion on Work Calculation The system (shown by the dotted line) has gone through a change of state from 1 to 2.We need to 1 2 know how the pressure and volume change. p Possibilities:  Pressure might have remained constant v or  It might have undergone a change as per a relation p (V) or p 2  The volume might have remained constant In general the area under the process on p-V plane gives the work 1 v