First and Second Laws of Thermodynamics and Their Applications - Assignment Example

Energy Transfer and Thermodynamics Demonstrate an understanding of the first and second laws of thermodynamics and their applications. First Law of Thermodynamics: Energy can be changed from one form to another, but it cannot be created or destroyed. The total amount of energy and matter in the Universe remains constant, merely changing from one form to another. The First Law of Thermodynamics (Conservation) states that energy is always conserved, it cannot be created or destroyed. In essence, energy can be converted from one form into another. Click here for another page (developed by Dr. John Pratte, Clayton State Univ., GA) covering thermodynamics. The Second Law of Thermodynamics states that "in all energy exchanges, if no energy enters or leaves the system, the potential energy of the state will always be less than that of the initial state." This is also commonly referred to as entropy. A watch spring-driven watch will run until the potential energy in the spring is converted, and not again until energy is reapplied to the spring to rewind it. A car that has run out of gas will not run again until you walk 10 miles to a gas station and refuel the car. Once the potential energy locked in carbohydrates is converted into kinetic energy (energy in use or motion), the organism will get no more until energy is input again. In the process of energy transfer, some energy will dissipate as heat. Entropy is a measure of disorder: cells are NOT disordered and so have low entropy. The flow of energy maintains order and life. Entropy wins when organisms cease to take in energy and die. Appraise the elementary concepts in combustion: types of combustion, heat of combustion, combustion temperature and chemical equilibrium. The investigation of the students preconceptions brought up several hints to tie up to. Together with the predictions of the experts the aim is to find guidelines for the work with elementary school students where their special pre-knowledge is to be considered and included into the didactic requirements given by the experts. The method of Concept Mapping will form the promoter for learning concepts more efficient and therefore more lasting. The combination of all three parts of the study as well as the guidelines for the Didactical Structuration are still in process and therefore can not be further explicated Here. In a homogeneous mixture with an equivalence ratio, of the actual fuel-air ratio to the stoichiometric fuel-air ratio) In 1.0, the flame speed is normally of the order of 40 cm/s. However In a spark-ignition engine the maximum flame speed is obtained when (f) is between 1.1 and 1.2, i.e., when the mixture is slightly richer in stoichiometric. If the equivalence ratio is outside this range the flame speed drop* rapidly to a low value. When the flame speed drops to a very low value, the heat loss from the combustion zone becomes equal to 11 in amount of heat-release due to combustion and the flame gets extinguished. Therefore, it is quite preferable to operate the engine within an equivalence ratio of 1.1 to 1.2 for proper combustion. However, by introducing turbulence and incorporating proper air movement, 1.1 in flame speed can be increased in mixtures outside the above range. 4. Demonstrate an understanding of the behaviour and properties of external flows. The flame front is a narrow zone separating the fresh mixture of the combustion products. The velocity with which the flame front moves, with respect to the unburned mixture in a direction normal to its surface is called the normal flame velocity. Define the four laws of thermodynamics using words, diagrams and equations where appropriate. The First Law of Thermodynamics The first law of thermodynamics centralizes, generally, on the existence of the property of energy. It states: "For any process involving only the displacement of a mass between specified levels in a gravity field and no externalities to the system, the magnitude of that mass is fixed by the end states of the system and is independent of the details of the process. The second law of thermodynamics focuses mainly on the equilibrium states of systems and processes that associate these states with others. The word equilibrium signifies that with time the state of a system will remain unchanged while being isolated from any other systems that may be found in an environment. It states: "Among all the allowed states of a system with specific values of energy, constraints, and numbers of particles, one and only one is a stable equilibrium state." Other hypotheses have been inferred from this law. The third law of thermodynamics remarks that absolute zero cannot be obtained easily by any procedure. It is only possible to approach absolute zero, but impossible to reach it. This law also defines the term zero entropy by stating that all bodies at absolute zero would have the same entropy. The most commonly proposed Fourth Law is the Onsager reciprocal relations, which give a quantitative relation between the parameters of a system in which heat and matter are simultaneously flowing. Other tentative fourth law statements are attempts to apply thermodynamics to evolution. In the late 19th century, thermodynamicist Ludwig Boltzmann argued that the fundamental object of contention in the life-struggle in the evolution of the organic world is 'available energy'. Another example is the maximum power principle as put forward initially by biologist Alfred Lotka in his 1922 article Contributions to the Energetics of Evolution Most variations of hypothetical fourth laws (or principles) have to do with the environmental sciences, biological evolution, or galactic phenomena. What is entropy? Explain what happens to the motion of water molecules when ice melts into water? What happens to the entropy in this situation? entropy is a measure of the disorder of a system. The concept of entropy is particularly notable as it is applied across physics, information theory and mathematics. In a thermodynamic system, a "universe" consisting of "surroundings" and "systems" and made up of quantities of matter, its pressure differences, density differences, and temperature differences all tend to equalize over time - simply because equilibrium state has higher probability (more possible combinations of microstates) than any other - see statistical mechanics. In the ice melting example, the difference in temperature between a warm room (the surroundings) and cold glass of ice and water (the system and not part of the room), begins to be equalized as portions of the heat energy from the warm surroundings spread out to the cooler system of ice and water. Calculate ΔS for the following reaction, using the information in a Table of Thermochemical Data, and state whether entropy increases (becomes more random) or decreases (becomes less random)? Based on entropy changes, do you predict a spontaneous reaction? 2 NO(g) + O2(g) →N2O4(g) To derive a generalized entropy balanced equation, we start with the general balance equation for the change in any extensive quantity Θ in a thermodynamic system, a quantity that may be either conserved, such as energy, or non-conserved, such as entropy. The basic generic balance expression states that dΘ/dt, i.e. the rate of change of Θ in the system, equals the rate at which Θ enters the system at the boundaries, minus the rate at which Θ leaves the system across the system boundaries, plus the rate at which Θ is generated within the system. Using this generic balance equation, with respect to the rate of change with time of the extensive quantity entropy S, the entropy balance equation for an open thermodynamic system is: where = the net rate of entropy flow due to the flows of mass into and out of the system (where = entropy per unit mass). = the rate of entropy flow due to the flow of heat across the system boundary. = the rate of internal generation of entropy within the system. Note, also, that if there are multiple heat flows, the term is to be replaced by where is the heat flow and Tj is the temperature at the jth heat flow port into the system. These questions test your understanding of temperature measurements and temperature scales. What is absolute zero on the Kelivin, Celsius, Fahrenheit and Rankine scales? Kelvin Celsius Fahrenheit Absolute zero (precisely, by definition) 0 K −273.15 °C −459.67 °F Melting point of ice (approximate) 273.15 K 0 °C 32 °F Water's triple point (precisely, by definition) 273.16 K 0.01 °C 32.018 °F Water's boiling point at 1 atm (101.325 kPa) (approximate: see Boiling point) 373.1339 K 99.9839 °C 211.9710 °F The boiling point of water if 100°C what is this in Kelvins? 373.15° The temperature of a system rises by 30°C during a heating process. Express this rise in temperature in Kelvins. from Celsius to Celsius Fahrenheit [°F] = [°C] × 9⁄5 + 32 [°C] = ([°F] − 32) × 5⁄9 Kelvin [K] = [°C] + 273.15 [°C] = [K] − 273.15 Rankine [°R] = ([°C] + 273.15) × 9⁄5 [°C] = ([°R] − 491.67) × 5⁄9 For temperature intervals rather than specific temperatures, 1 °C = 1 K = 1.8 °F = 1.8 °R Comparisons among various temperature scales This is put simply by illustrating that while 10 °C and 20 °C have the same interval difference as 20 °C and 30 °C the temperature 20 °C is not twice the air heat energy as 10 °C. As this example shows degrees Celsius is a useful interval measurement does not possess the characteristics of ratio measures like weight or distance The temperature of a system rises by 60°F during a heating process. Express this rise in temperature in R, K and °C. from Celsius to Celsius Fahrenheit [°F] = [°C] × 9⁄5 + 32 [°C] = ([°F] − 32) × 5⁄9 Kelvin [K] = [°C] + 273.15 [°C] = [K] − 273.15 Rankine [°R] = ([°C] + 273.15) × 9⁄5 [°C] = ([°R] − 491.67) × 5⁄9 For temperature intervals rather than specific temperatures, 1 °C = 1 K = 1.8 °F = 1.8 °R Comparisons among various temperature scales How is work related to equilibrium? Work refers to forms of energy transfer which can be accounted for in terms of changes in the macroscopic physical variables of the system, for example energy which goes into expanding the volume of a system against an external pressure, by driving a piston-head out of a cylinder against an external force. This is in contrast to heat energy, which is carried into or out of the system in the form of transfers in the microscopic thermal motions of particles. The concept of thermodynamic work is slightly more general than that of mechanical work because it includes other types of energy transfers as well. The electrical work required to move a charge against an external electrical field can be measured, as can the work required to move heat against a temperature gradient. An extremely important fact to understand is that thermodynamic work need not have any mechanical component to be considered such. Give examples of equilibrium state, steady state and uniform. In thermodynamics, a thermodynamic system is said to be in thermodynamic equilibrium when it is in thermal equilibrium, mechanical equilibrium, and chemical equilibrium. The local state of a system at thermodynamic equilibrium is determined by the values of its intensive parameters, as pressure, temperature, etc. Specifically, thermodynamic equilibrium is characterized by the minimum of a thermodynamic potential, such as the Helmholtz free energy, i.e. systems at constant temperature and volume. State whether the following are open or closed systems, give reasons for your answer. Rechargeable battery,-Open Household refrigerator,-open Radiator.-Closed An open system is a state of a system, in which a system continuously interacts with its environment. Open systems are those that maintain their state and exhibit the characteristics of openness previously mentioned. Open systems contrast with closed systems. Systems are rarely ever either open or closed but open to some and closed to other influences. Basic characteristics of an open system are environment, input, throughput and output. And some control systems with feedback. What is the difference between a gas, a liquid and a solid? The particles (ions, atoms or molecules) are packed closely together. The forces between particles are strong enough so that the particles cannot move freely but can only vibrate. As a result, a solid has a stable, definite shape, and a definite volume. Solids can only change their shape by force, as when broken or cut. The volume is definite if the temperature and pressure are constant. When a solid is heated above its melting point, it becomes liquid. Intermolecular (or interatomic or interionic) forces are still important, but the molecules have enough energy to move relative to each other and the structure is mobile. This means that the shape of a liquid is not definite but is determined by its container. The volume is usually greater than that of the corresponding solid, with the noteworthy exception of water, H2O. In a gas, the molecules have still more energy, so that the effect of intermolecular forces is small (or zero for an ideal gas), and the molecules are far apart from each other and can move around quickly. A gas has no definite shape or volume, but occupies the entire container in which it is confined. What does thermodynamics tell us with regards to heat transfer? Heat transfer is the transition of thermal energy or simply heat from a hotter object to a cooler object ("object" in this sense designating a complex collection of particles which is capable of storing energy in many different ways). When an object or fluid is at a different temperature than its surroundings or another object, transfer of thermal energy, also knownas heat transfer, or heat exchange, occurs in such a way that the body and thesurroundingsreach thermal equilibrium. Explain the difference between internal energy (u) and enthalpy (h). In thermodynamics and molecular chemistry, the enthalpy (denoted as H, h, or rarely as χ) is a quotient or description of thermodynamic potential of a system, which can be used to calculate the heat transfer during a quasistatic process taking place in a closed thermodynamic system under constant pressure. In thermodynamics, the internal energy of a thermodynamic system, or a body with well-defined boundaries, denoted by U, or sometimes E, is the total of the kinetic energy due to the motion of molecules (translational, rotational, vibrational) and the potential energy associated with the vibrational and electric energy of atoms within molecules or crystals The mass flow rate is 4kg/s, the heat of combustion for C3H8 is 46450kJ/kg. Determine the heat release rate. = where: = mass flow rate ρ = density v = velocity A = flow area This is equivalent to multiplying the volume flow rate by the density. = where: ρ = density Q = volume flow rate The symbol for mass flow rate is Newton's notation for a derivative: What is Fourier’s Law? What is thermal conductivity? Compare the values of thermal conductivity of metals, insulating materials and gases. What does Fourier's law have a minus sign? The law of Heat Conduction, also known as Fourier's law, states that the time rate of heat transfer through a material is proportional to the negative gradient in the temperature and to the area at right angles, to that gradient, through which the heat is flowing. We can state this law in two equivalent forms: the integral form, in which we look at the amount of energy flowing into or out of a body as a whole, and the differential form, in which we look at the flows or fluxes of energy locally. Given a real function f(x), its Fourier transform has the following properties. where F * is the complex conjugate of F. Centrosymmetric points (k, − k) are called Friedel's pairs. The squared amplitude ( | F | 2) is centrosymmetric: The phase φ of F is antisymmetric: . Explain the Stefen-Boltzman Law. What is emissivity? What role does the view factor play in determining the rate of heat transfer? What is a blackbody? The Stefan–Boltzmann law, also known as Stefan's law, states that the total energy radiated per unit surface area of a black body in unit time (known variously as the black-body irradiance, energy flux density, radiant flux, or the emissive power), j, is directly proportional to the fourth power of the black body's thermodynamic temperature T (also called absolute temperature Explain the Newton’s Law of Cooling. What is the heat transfer coefficient? What is the Nusselt number? What are the two types of convection? A related principle, Newton's law of cooling, states that the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings, or environment. The law is Q = Thermal energy in Joules h = Heat transfer coefficient A = Surface area of the heat being transferred T0 = Temperature of the object's surface Tenv = Temperature of the environment Define heat of combustion, heat release rate and combustion reaction giving appropriate equations. Explain the different types of combustion and definitions of the following: Specific heat capacity, latent heat, calorimetry, combustion temperature and chemical equilibrium. The heat of combustion (ΔHc0) is the energy released as heat when one mol of a compound undergoes complete combustion with oxygen. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat. It may be expressed with the quantities: energy/mole of fuel (J/mol) energy/mass of fuel energy/volume of fuel The heat of combustion is traditionally measured with a bomb calorimeter. It may also be calculated as the difference between the heat of formation (ΔfH0) of the products and reactants. What is the efficiency of an engine that produces 150J of work from 212J of energy? Energy conversion efficiency is the ratio between the useful output of an energy conversion machine and the input, in energy terms. The useful output may be electric power, mechanical work, or heat. Energy conversion efficiency is not defined uniquely, but instead depends on the usefulness of the output. All or part of the heat produced from burning a fuel may become rejected waste heat if, for example, work is the desired output from a thermodynamic cycle. =1.41 A Styrofoam cup (of negligible heat capacity) contains 150g of water at 10°C. If you add 100g of water at a temperature of 85°C what is the final temperature of the mixture after it has been thoroughly mixed? 80°C A closed Styrofoam cup, which is 6 mm thick and has a surface area of 390 cm2, contains 550 ml of hot coffee at 850C. The air outside the cup remains at a constant temperature of 210C. Assuming that the coffee has a mass of 0.6 kg, and that the specific heat capacity is the same as that of water, determine The initial rate of heat flow through the Styrofoam (in SI units), And the time required for the coffee to cool from 850C to 700C. Define flame? Describe the different types of flames and whether they are laminar or turbulent.? The flame front is a narrow zone separating the fresh mixture of the combustion products. The velocity with which the flame front moves, with respect to the unburned mixture in a direction normal to its surface is called the normal flame velocity. Define fluid. What is the viscosity of a fluid? A fluid is defined as a substance that continually deforms (flows) under an applied shear stress. All liquids and all gases are fluids. Fluids are a subset of the phases of matter and include liquids, gases, plasmas and, to some extent, plastic solids. Is air a compressible fluid or an incompressible fluid? How about water? Explain your answer. yes. In fluid dynamics, air or fluid refers to forces that oppose the relative motion of an object through a fluid (a liquid or gas). Drag forces act in a direction opposite to the oncoming flow velocity A concrete slab has a length of 24 m at -8 ºC on a winter's day. What is the change in length from winter to summer, when the temperature is 35 ºC? The linear expansion coefficient of concrete is 1 X 10-5 ºC-1. In mathematics, one can consider the scaling properties of a function or curve f(x) under rescalings of the variable x. That is, one is interested in the shape of f(λx) for some scale factor λ, which can be taken to be a length or size rescaling. The requirement for f(x) to be invariant under all rescalings is usually taken to be f(x) = λ − Δf(λx) for some choice of exponent Δ, and for all dilations λ. Examples of scale-invariant functions are the monomials f(x) = xn, for which one has Δ = n, in that clearly f(λx) = (λx)n = λnf(x). An example of a scale-invariant curve is the logarithmic spiral, a kind of curve that often appears in nature. In polar coordinates (r, θ) the spiral can be written as Change of length is 20 m at -8 ºC A box is pushed 5m across a room with a force of 30N. What is the work done and how much energy is used? (1 mark) =150 A piece of aluminium siding is 12.45 meters long on a cold winter's day, -18°C. How much longer is it on a very hot summer's day, 37°C? 15m Define boundary layers. Draw a velocity profile for a fluid in a pipe showing both laminar and turbulent flow. In physics and fluid mechanics, a boundary layer is that layer of fluid in the immediate vicinity of a bounding surface. In the Earth's atmosphere, the planetary boundary layer is the air layer near the ground affected by diurnal heat, moisture or momentum transfer to or from the surface. On an aircraft wing the boundary layer is the part of the flow close to the wing. The boundary layer effect occurs at the field region in which all changes occur in the flow pattern where u and v are the velocity components, ρ is the density, p is the pressure, and ν is the kinematic viscosity of the fluid at a point. References 1. Clark, John, O.E. (2004). The Essential Dictionary of Science. Barnes & Noble Books. ISBN 0-7607-4616-8.  2. Clausius, Ruldolf (1850). On the Motive Power of Heat, and on the Laws which can be deduced from it for the Theory of Heat. Poggendorff's Annalen der Physick, LXXIX (Dover Reprint). ISBN 0-486-59065-8.  3. Van Ness, H.C. (1969). Understanding Thermodynamics. Dover Publications, Inc.. ISBN 0-486-63277-6.  4. Dugdale, J.S. (1998). Entropy and its Physical Meaning. Taylor and Francis. ISBN 0-7484-0569-0.  Read More