BME Notes Unit 1 PDF

**LAW'S OF THERMODYNAMICS** **Zeroth law of thermodynamics** It was 1935, when Ralph Fowler was reading a book and he came upon one text -- "Every physical quantity must be measurable in some numeric terms". No one was knowing about the term "*temperature*" before 1935. The main thing, all the thr...

**LAW'S OF THERMODYNAMICS** **Zeroth law of thermodynamics** It was 1935, when Ralph Fowler was reading a book and he came upon one text -- "Every physical quantity must be measurable in some numeric terms". No one was knowing about the term "*temperature*" before 1935. The main thing, all the three laws of thermodynamics (first, second and third law) were already discovered before 1935.  In 1935, Fowler discovered the title "Zeroth law of thermodynamics" and thermal equilibrium. Fowler realized that this phenomenon of thermal equilibrium is very important and it should be discussed before the first law of thermodynamics as this law shows the presence of one important property "Temperature". But already so many books were published with the first law, second law and third law. Now changing the number of these three laws can create a lot of confusion. Thus he was forced to adopt the number "zero" for his law. This is the reason why this law is called the zeroth law of thermodynamics. 1. [Second law of thermodynamics for heat engine](https://lawofthermodynamicsinfo.com/what-is-second-law-of-thermodynamics/) (Kelvin Planck's statement) 2. [Second law of thermodynamics for heat pump/refrigerator](https://lawofthermodynamicsinfo.com/what-is-second-law-of-thermodynamics/) (Clausius's statement) **Heat Engines** **Introduction** - Once man discovered the use of heat in the form of fire, it was just a step to formulate the energy interactions. With this, human beings started to use heat energy for cooking, warming up living spaces, drying and so on. - Further, due to the development of civilization and increase in population, man had to move from one place to another. Animals were used in transportation between the 4^th^ and 5^th^ centuries BC, and spread to Europe and other countries in the 5^th^ century BC and China in about 1200 BC. - Gradually, man replaced the animals with motive power that was used in transportation. The use of power vehicles began in the late 18th century, with the creation of the steam engine. The invention of Otto (1876) and Diesel (1892) cycles in the 19th century transformed the method of propulsion from steam to petroleum fuel. - **ENGINE:** Engine is a device which converts one form of Energy into another form - **HEAT ENGINE:** Heat engine is a device which transforms the chemical energy of a fuel into thermal energy and utilizes this thermal energy to perform useful work. Thus, thermal energy is converted to mechanical energy in a heat engine. - Heat engines can be broadly classified into two categories: a. Internal Combustion Engines (IC Engines) b. External Combustion Engines (EC Engines) c. 1. Classification of heat engines i. Rotary engines ii. Reciprocating engines Comparison of I.C. Engines and E.C. Engines -- -- -- -- -- -- -- -- Basic components and terminology of IC engines - Even though reciprocating internal combustion engines look quite simple, they are highly complex machines. There are many components which have to perform their functions effectively to produce output power. - There are two types of engines, viz., spark-ignition (SI) and compression-ignition (Cl) engine. 1. Engine Components Cylinder block - The cylinder block is the main supporting structure for the various components. The cylinder of a multicylinder engine are cast as a single unit, called cylinder block. The cylinder head is mounted on the cylinder block. The cylinder head and cylinder block are provided with water jackets in the case of water cooling or with cooling fins in the case of air cooling. b. Cylinder - As the name implies it is a cylindrical vessel or space in which the piston makes a reciprocating motion. The varying volume created in the cylinder during the operation of the engine is filled with the working fluid and subjected to different thermodynamic processes. The cylinder is supported in the cylinder block. c. Piston - It is a cylindrical component fitted into the cylinder forming the moving boundary of the combustion system. It fits perfectly (snugly) into the cylinder providing a gas-tight space with the piston rings and the lubricant. It forms the first link in transmitting the gas forces to the output shaft. d. Combustion chamber - The space enclosed in the upper part of the cylinder, by the cylinder head and the piston top during the combustion process, is called the combustion chamber. The combustion of fuel and the consequent release of thermal energy results in the building up of pressure in this part of the cylinder. e. Inlet manifold - The pipe which connects the intake system to the inlet valve of the engine and through which air or air-fuel mixture is drawn into the cylinder is called the inlet manifold. f. Exhaust manifold - The pipe which connects the exhaust system to the exhaust valve of the engine and through which the products of combustion escape into the atmosphere is called the exhaust manifold. g. Inlet and Exhaust valves - Valves are commonly mushroom shaped poppet type. They are provided either on the cylinder head or on the side of the cylinder for regulating the charge coming into the cylinder (inlet valve) and for discharging the products of combustion (exhaust valve) from the cylinder. h. Spark Plug - It is a component to initiate the combustion process in Spark- Ignition (SI) engines and is usually located on the cylinder head. i. Connecting Rod - It interconnects the piston and the crankshaft and transmits the gas forces from the piston to the crankshaft. The two ends of the connecting rod are called as small end and the big end. Small end is connected to the piston by gudgeon pin and the big end is connected to the crankshaft by crankpin. j. Crankshaft - It converts the reciprocating motion of the piston into useful rotary motion of the output shaft. In the crankshaft of a single cylinder engine there are a pair of crank arms Piston rings - Piston rings, fitted into the slots around the piston, provide a tight seal between the piston and the cylinder wall thus preventing leakage of combustion gases. l. Gudgeon pin - It links the small end of the connecting rod and the piston. m. Camshaft - The camshaft (not shown in the figure) and its associated parts control the opening and closing of the two valves. The associated parts are push rods, rocker arms, valve springs and tappets. This shaft also provides the drive to the ignition system. The camshaft is driven by the crankshaft through timing gears. n. Cams - These are made as integral parts of the camshaft and are so designed to open the valves at the correct timing and to keep them open for the necessary duration. o. Flywheel - The net torque imparted to the crankshaft during one complete cycle of operation of the engine fluctuates causing a change in the angular velocity of the shaft. In order to achieve a uniform torque an inertia mass in the form of a wheel is attached to the output shaft and this wheel is called the flywheel. p. Carburetor - Carburetor is used in petrol engine for proper mixing of air and petrol. q. Fuel pump - Fuel pump is used in diesel engine for increasing pressure and controlling the quantity of fuel supplied to the injector. r. Fuel injector - Fuel injector is used to inject diesel fuel in the form of fine atomized spray under pressure at the end of compression stroke. 2. Terminologies used in IC engine - **Cylinder Bore (d):** The nominal inner diameter of the working cylinder is called the cylinder bore and is designated by the letter d and is usually expressed in millimeter (mm). - **Piston Area (A):** The area of a circle of diameter equal to the cylinder bore is called the piston area and is designated by the letter A and is usually expressed in square centimeter (cm^2^). - **Stroke (L):** It is the linear distance traveled by the piston when it moves from one end of the cylinder to the other end. It is equal to twice the radius of the crank. It is designated by the letter L and is expressed usually in millimeter (mm). - **Stroke to Bore Ratio (L/d):** L / d ratio is an important parameter in classifying the size of the engine. - If d \< L, it is called under-square engine. - If d = L, it is called square engine. - If d \> L, it is called over-square engine. - Dead Centre: - **Displacement or Swept Volume (Vs)**: The volume displaced by the piston in one stroke is known as stroke volume or swept volume. It is expressed in terms of cubic centimeter (cc) and given by 𝑉~𝑠~ - **Cubic Capacity or Engine Capacity:** The displacement volume of a cylinder multiplied by number of cylinders in an engine will give the cubic capacity or the engine capacity. For example, if there are K cylinders in an engine, then - **Clearance Volume (Vc):** It is the volume contained between the piston top and cylinder head when the piston is at top or inner dead center. - **Compression Ratio (r):** The ratio of total cylinder volume to clearance volume is called the compression ratio (r) of the engine. 𝑟 = ∴ 𝑟 = - **Piston speed (V~p~):** It is average speed of piston. It is equal to 2LN, where N is speed of crank shaft in rev/sec. 𝑉~𝑝~ 2. Working of Four Stroke Spark-Ignition Engine - In a four-stroke engine, the cycle of operations is completed in four strokes of the piston or two revolutions of the crankshaft. - During the four strokes, there are five events to be completed, viz., suction, compression, combustion, expansion and exhaust. Each stroke consists of 180° of crankshaft rotation and hence a four-stroke cycle is completed through 720° of crank rotation. - The cycle of operation for an ideal four-stroke SI engine consists of the following four strokes: (i) suction or intake stroke; (ii) compression stroke; (iii) expansion or power stroke and (iv) exhaust stroke. - The details of various processes of a four-stroke spark-ignition engine with overhead valves are shown in Fig. 1.4 (a-d). When the engine completes all the five events under ideal cycle mode, the pressure-volume (p-V) diagram will be as shown in Fig.1.5. a. **Suction or Intake Stroke:** Suction stroke 0→1 (Fig.1.5) starts when the piston is at the top dead centre and about to move - Due to the suction created by the motion of the piston towards the bottom dead centre, the charge consisting of fuel-air mixture is drawn into the cylinder. When the piston reaches the bottom dead centre the suction b. **Compression Stroke:** The charge taken into the cylinder during the suction stroke is compressed by the return stroke of the piston 1→2, (Fig.1.5). During this stroke both inlet and exhaust valves are in closed position, Fig. 1.4(b). - The mixture which fills the entire cylinder volume is now compressed into the clearance volume. At the end of the compression stroke the mixture is ignited with the help of a spark plug located on the cylinder head. - In ideal engines it is assumed that burning takes place instantaneously when the piston is at the top dead centre and hence the burning process can be approximated as heat addition at constant volume. - During the burning process the chemical energy of the fuel is converted into heat energy producing a temperature rise of about 2000 °C (process 2→3), Fig.1.5. The pressure at the end of the combustion process is considerably increased due to the heat release from the fuel. c. **Expansion or Power Stroke:** The high pressure of the burnt gases forces the piston towards the BDC, (stroke 3→4) Fig.1.5. Both the valves are in closed position, Fig. 1.4(c). Of the four-strokes only during this stroke power is produced. Both pressure and temperature decrease during expansion. d. **Exhaust Stroke:** At the end of the expansion stroke the exhaust valve opens instantaneously and the inlet valve remains closed, Fig. 1.4(d). The pressure falls to atmospheric level a part of the burnt gases escape. The piston starts moving from the bottom dead centre to top dead centre (stroke 5→0), Fig.1.5 and sweeps the burnt gases out from the cylinder almost at atmospheric pressure. The exhaust valve closes when the piston reaches TDC. - At the end of the exhaust stroke and some residual gases trapped in the clearance volume remain in the cylinder. These residual gases mix with the fresh charge coming in during the following cycle, forming its working fluid. - Each cylinder of a four-stroke engine completes the above four operations in two engine revolutions, first revolution of the crankshaft occurs during the suction and compression strokes and the second revolution during the power and exhaust strokes. - Thus for one complete cycle there is only one power stroke while the crankshaft makes two revolutions. For getting higher output from the engine the heat addition (process 2→3) should be as high as possible and the heat rejection (process 3→4) should be as small as possible. Hence, one should be careful in drawing the ideal p - V diagram (Fig.1.5), which should represent the processes correctly. 3. Working of Four Stroke Compression-Ignition Engine - The four-stroke Cl engine is similar to the four-stroke SI engine but it operates at a much higher compression ratio. The compression ratio of an SI engine is between 6 and 10 while for a Cl engine it is from 16 to 20. - In the Cl engine during suction stroke, air, instead of a fuel-air mixture, is inducted. Due to higher compression ratios employed, the temperature at the end of the compression stroke is sufficiently high to self-ignite the fuel which is injected into the combustion chamber. - In Cl engines, a high pressure fuel pump and an injector are provided to inject the fuel into the combustion chamber. The carburetor and ignition system necessary in the SI engine are not required in the Cl engine. - The ideal sequence of operations for the four-stroke Cl engine as shown in Fig. 1.6 is as follows: a. **Suction Stroke:** In the suction stroke piston moves from TDC to BDC. Air alone is inducted during the suction stroke. During this stroke inlet valve is open and exhaust valve is closed, Fig.1.6 (a). b. **Compression Stroke:** In this stroke piston moves from BDC to TDC. Air inducted during the suction stroke is compressed into the c. **Expansion Stroke:** Fuel injection starts nearly at the end of the compression stroke. The rate of injection is such that combustion maintains the pressure constant in spite of the piston movement on its expansion stroke increasing the volume. Heat is assumed to have been d. **Exhaust Stroke:** The piston travelling from BDC to TDC pushes out the products of combustion. The exhaust valve is open and the intake valve is closed during this stroke, Fig. 1.6 (d). The ideal p - V diagram is shown in Fig. 1.7. - Due to higher pressures in the cycle of operations the Cl engine has to be sturdier than a SI engine for the same output. This results in a Cl engine being heavier than the SI engine. However, it has a higher thermal efficiency on account of the high compression ratio (of about 18 as against about 8 in SI engines) used. 4. Comparison of SI and Cl Engines - The detailed comparison of SI and CI engine is given in table 1.2 -- -- -- -- -- -- +-----------------------+-----------------------+-----------------------+ | | | Self-ignition occurs | | | | d u e to high | | | | | | | | temperature of air | | | | because of the high | | | | compression. Ignition | | | | system and spark plug | | | | are not necessary. | +=======================+=======================+=======================+ | | | 16 to 20. Upper limit | | | | is limited by weight | | | | increase of the | | | | engine. | +-----------------------+-----------------------+-----------------------+ | | | Due to heavy weight | | | | and also due to | | | | heterogeneous | | | | combustion, they are | | | | low speed engines. | +-----------------------+-----------------------+-----------------------+ | | | Because of higher CR, | | | | the maximum value of | | | | thermal efficiency | | | | that can be obtained | | | | is higher. | +-----------------------+-----------------------+-----------------------+ | | | Heavier due to | | | | comparatively higher | | | | peak pressures. | +-----------------------+-----------------------+-----------------------+ 5. Two-Stroke Engine - In two-stroke engines the cycle is completed in one revolution of the crankshaft. The main difference between two-stroke and four-stroke engines is in the method of filling the fresh charge and removing the burnt gases from the cylinder. - In the four-stroke engine these operations are performed by the engine piston during the suction and exhaust strokes respectively. - In a two- stroke engine, the filling process is accomplished by the charge compressed in crankcase or by a blower. The induction of the compressed charge moves out the product of combustion through exhaust ports. Therefore, no separate piston strokes are required for these two operations. - Two strokes are sufficient to complete the cycle, one for compressing the fresh charge and the other for expansion or power stroke. It is to be noted that the effective stroke is reduced. - Figure 1.8 shows one of the simplest two-stroke engines, viz., the crankcase scavenged engine. Figure 1.9 shows the ideal p - V diagram of such an engine. - The air-fuel charge is inducted into the crankcase through the spring loaded inlet valve when the pressure in the crankcase is reduced due to upward motion of the piston during compression stroke. After the compression and ignition, expansion takes place in the usual way. - During the expansion stroke the charge in the crankcase is compressed. Near the end of the expansion stroke, the piston uncovers the exhaust ports and the cylinder pressure drops to atmospheric pressure as the combustion products leave the cylinder. - Further movement of the piston uncovers the transfer ports, permitting the slightly compressed charge in the crankcase to enter the engine cylinder. - The piston top usually has a projection to deflect the fresh charge towards the top of the cylinder preventing the flow through the exhaust ports. This serves the double purpose of scavenging the combustion products from the upper part of the cylinder and preventing the fresh charge from flowing out directly through the exhaust ports. - The same objective can be achieved without piston deflector by proper shaping of the transfer port. During the upward 6. IC engine Classification - I.C. Engines may be classified according to, a. Type of the fuel used as : 1. Petrol engine (2) Diesel engine b. Nature of thermodynamic cycle as : 2. Otto cycle engine (2) Diesel cycle engine c. Number of strokes per cycle as : 3. Four stroke engine (2) Two stroke engine d. Method of ignition as : 4. Spark ignition engine (S.I. engine) 5. Compression ignition engine (C.I. engine) e. Method of cooling as : 6. Air cooled engine (2) Water cooled engine f. Speed of the engine as : 7. Low speed (2) Medium speed g. Number of cylinder as : 8. Single cylinder engine (2) Multi cylinder engine h. Position of the cylinder as : 9. Inline engines (2) V -- engines 7. Application of IC Engines - The most important application of IC engines is in transport on land, sea and air. Other applications include industrial power plants and as prime movers for electric generators. Table 1.3 gives, in a nutshell, the applications of both IC and EC engines. -- -- -- -- -- -- -- -- Engine Performance Parameters Indicated Power 2 2. Brake power - It is the power available at engine crank shaft for doing useful work. It is also known as engine output power***.*** It is measured by dynamometer. *B*.*P*.  [2 *NT*] 3. Indicated Thermal Efficiency (*ith* ) - Indicated thermal efficiency is the ratio of energy in the indicated power, ip, to the input fuel energy in appropriate units. *ith*  4. Brake Thermal Efficiency (*~bth~* ) - Brake thermal efficiency is the ratio of power available at crank shaft, bp, to the input fuel energy in appropriate units. *bth*  5. Mechanical Efficiency (*m* ) - Mechanical efficiency is defined as the ratio of brake power (delivered power) to the indicated power (power provided to the piston).   *bp*  *bp* (1.4) Volumetric Efficiency (*v* ) - Volumetric efficiency indicates the breathing ability of the engine. It is to be noted that the utilization of the air is that determines the power output of the engine. Intake system must be designed in such a way that the engine must be able to take in as much air as possible. - Volumetric efficiency is defined as the ratio of actual volume flow rate of air into the intake system to the rate at which the volume is displaced by the system. 7. Air standard efficiency - It is the efficiency of the thermodynamic cycle of the engine. - For petrol engine, - For diesel engine, 1 *r*  1    1 *air* 8. Relative Efficiency or Efficiency Ratio - Relative efficiency or efficiency ratio is the ratio of thermal efficiency of an actual cycle to that of the ideal cycle. The efficiency ratio is a very useful criterion which indicates the degree of development of the engine. *rel* (1.9) Specific output - The specific output of the engine is defined as the power output per unit area. *A* 10. Specific fuel consumption - Specific fuel consumption (SFC) is defined as the amount of fuel consumed by an engine for one unit of power production. SFC is used to express the fuel efficiency of an I.C. engine. *B*.*P*. - Thermal energy is the major source of power generation in India. More than 60% of electric power is produced by steam plants in India. India has large deposit of coal (about 170 billion tonnes), 5^th^ largest in world. Indian coals are classified as A-G grade coals. - In Steam power plants, the heat of combustion of fossil fuels is utilized by the boilers to raise steam at high pressure and temperature. The steam so produced is used in driving the steam turbines or sometimes steam engines couples to generators and thus in generating electrical energy. - Steam turbines or steam engines used in steam power plants not only act as prime movers but also as drives for auxiliary equipment, such as pumps, stokers fans etc. - Steam power plants may be installed either to generate electrical energy only or generate electrical energy along with generation of steam for industrial purposes such as in paper mills, textile mills, sugar mills and refineries, chemical works, plastic manufacture, food manufacture etc. - The steam for process purposes is extracted from a certain section of turbine and the remaining steam is allowed to expand in the turbine. Alternatively the exhaust steam may be used for process purposes. - Thermal stations can be private industrial plants and central station. - Less initial cost as compared to other generating stations. - It requires less land as compared to hydro power plant. - The fuel (i.e. coal) is cheaper. - The cost of generation is lesser than that of diesel power plants. - It pollutes the atmosphere due to the production of large amount of smoke. This is one of the causes of global warming. - The overall efficiency of a thermal power station is low (less than 30%). - Requires long time for errection and put into action. - Costlier in operating in comparison with that of Hydro and Nuclear power plants. - Requirement of water in huge quantity. {#section-1} {#section-2}  {#section-3} ======================= {#section-4} {#section-5} {#section-6} {#section-7} {#section-8} {#section-9} {#section-10} {#section-11} {#section-12} {#section-13} {#section-14} {#section-15} {#section-16} {#section-17} {#section-18} {#section-19} {#section-20} {#section-21} {#section-22} {#section-23} {#section-24} {#section-25} {#section-26} {#section-27} {#section-28} {#section-29} {#section-30} {#section-31} {#section-32} {#section-33} {#section-34} {#section-35} {#section-36} {#section-37} {#section-38} {#section-39} **Major Components of a Thermal Power Plant** ============================================= - **Coal Handling Plant** - Pulverizing Plant ================= - Draft or Draught fan - Boiler ====== - Ash Handling Plant - Turbine and Generator ===================== - Condenser - Cooling Tower And Ponds ======================= - Feed Water Heater - Economiser ========== - **Super heater and Reheater** - **Air pre heater** ================== - **Alternator with Exciter** - **Protection and control equipment** ==================================== - **Instrumentation** **BOILER** ========== 1. Vertical tube boiler 2. Horizontal tube boiler A fire tube boiler is simple , compact and rugged in construction. Its initial cost is low. Figure : Fire Tube Boiler ========================= **Water Tube Boilers** ====================== 1. Vertical tube boiler 2. Horizontal tube boiler 3. Inclined tube boiler  Figure :Water tube boiler Figure: Superheaters ====================  **ECONOMIZER** ============== **AIR PREHEATERS** ================== - Plate type - Tubular type - Regenerative type **STEAM TURBINES** ================== 1. Impulse turbine and 2)Reaction Turbine In this turbine there are alternate rows of moving and fixed blades. The moving blades are mounted on the shaft and fixed blades are fixed to the casing of the turbine. A set of fixed nozzle is provided and steam is passed through these nozzles. The P.E in steam due to pressure and internal energy is converted to K.E. The steam comes out of the nozzles with very high velocity and impinges on the rotor blades. The direction of steam flow changes without changing its pressure. Thus due to the change in momentum the turbine rotor starts rotating. **Reaction Turbine:** ===================== Reaction turbine have no nozzles. These two have alternate rows of moving and fixed blades. The moving blades are mounted on shaft, while fixed blades are fixed in casing of turbine. When high pressure steam passes through fixed blades, then steam pressure drops down and velocity of steam increases. As steam passes over moving blades, the steam expands and imparts energy, resulting in reduction in pressure and velocity of steam. **Note**:Turbines used in thermal power stations are Impuse, Reaction or combined. Generally multistage turbines are used. H.P steam after doing work in the H.P stage passes over l.P stage. more works extracted thereby, with consequent increase in thermal efficiency. **CONDENSERS** {#section-40} **COOLING TOWERS AND SPRAY PONDS** ================================== Condensers need huge quantity of water to condense the steam. Water is led into the plants by means of circulating water pumps and after passing through the condenser is discharged back into the river. If such a source is not available closed cooling water circuit is used where the warm water coming out of the condenser is cooled and reused. In such cases ponds and cooling towers are used where the water loses heat to the atmosphere.  Figure : Cooling Tower ====================== **ELECTROSTATIC PRECIPITATORS** =============================== An electrostatic precipitator (ESP), or electrostatic air cleaner is a particulate collection device that removes particles from a flowing gas (such as air) using the force of an induced electrostatic charge. - *Charging* - *collecting.* - *removing* Every particle either has or can be given a charge---positive or negative. we impart a negative charge to all the particles in a gas stream in ESP. Then a grounded plate having a positive charge is set up. The negatively charged particle would migrate to the grounded collection plate and be captured. The particles would quickly collect on the plate, creating a dust layer. The dust layer would accumulate until we removed it. The structural design and operation of the discharge electrodes (rigid-frame, wires or plate) and collection electrodes. - tubular type ESP - plate type ESP - The method of charging - single-stage ESP - two-stage ESP - The temperature of operation - cold-side ESP - hot-side ESP - The method of particle removal from collection surfaces - wet ESP - Dry ESP