Thermo Lesson 2 Notes PDF

LESSON 2 What is Kinetic Energy, (KE)? a scalar quantity [The value of work (W) depends on the details of the interactions taking place between the system and surroundings...

LESSON 2 What is Kinetic Energy, (KE)? a scalar quantity [The value of work (W) depends on the details of the interactions taking place between the system and surroundings during a process and not just the initial and final states of the system] [Work is not a property of the system or What is Potential Energy, (PE)? the surroundings.] What is Work? What is Power? Work = Force (distance) The rate of energy transfer by work is called POWER and is denoted by W ( with “dot”, to indicate a time rate). [ Energy and Work have the same units.] What is Conservation of Energy? [In THERMODYNAMICS, the concept of energy is broadened to account for other observed changes, and the principle of conservation of energy is extended to include a wide variety of ways in which What is Quasiequilibrium Process (or systems interact with their surroundings] Quasistatic) Process? departure from thermodynamic equilibrium What is Work, (W)? is at most infinitesimal The work done by, or on, a system evaluated in terms of macroscopically observable forces and displacements is What is a Polytropic Process? A quasiequilibrium process described by [Work is done by a system on its surroundings if the sole effect on where n is a constant everything external to the system could have been the raising of a weight.] What is Change in the total energy of a What is Heat flux, (q) ? system? the heat transfer rate per unit of system surface area. What is Internal Inergy, (U)? where A represents the area on the extensive property of the system boundary of the system where heat transfer occurs Units for the heat flux: What is Energy Transfer by Heat? When a gas in a rigid container interacts with a hot plate, the energy of the gas is increased even though no work is done. What is Adiabatic Process? without heat transfer. [If a system undergoes a process involving no heat transfer with its surroundings, that process is called an adiabatic process.] What is Heat, (Q)? Three basic transfer mechanisms: amount of energy transferred across 1. Conduction the boundary of a system in a heat 2. Convection interaction with the system’s surroundings 3. Thermal radiation What is Conduction? Energy transfer can take place in solids, liquids, and gases. [The value of a heat transfer depends on the details of a process and not Transfer of energy from the more just the end states.] energetic particles of a substance to adjacent particles that are less energetic [Heat is not a property] due to interactions between particles. Follows Fourier’s law What is Net rate of heat transfer, (Q)? that the rate of heat transfer across any plane normal to the x direction, dT/dx proportional to the wall area, A, and the temperature gradient in the x direction, dT/dx: What is Fourier’s law? [ In general, the net rate of energy transfer by thermal radiation between two surfaces rate of heat transfer across any plane involves relationships among the properties normal to the x direction, dT/dx proportional of the surfaces, their orientations with to the wall area, A, and the temperature respect to each other, the extent to which gradient in the x direction, dT/dx: the intervening medium scatters, emits, and absorbs thermal radiation, and other factors.] The net rate of radiant exchange between the smaller surface, whose area is A and emissivity is ε, and the larger surroundings is: [Substances with large values of thermal conductivity such as copper are good conductors, and those with Small conductivities (cork and polystyrene foam) are good insulators.] What is Radiation? What is Convection? Thermal radiation is emitted by matter as a energy transfer between a solid surface result of changes in the electronic at a temperature Tb and an adjacent gas configurations of the atoms or molecules or liquid at another temperature Tf. It plays within it. a prominent role in the performance of many devices of practical interest. Energy is transported by electromagnetic waves (or photons). The rate of energy transfer from the surface Requires no intervening medium to to the air can be quantified by the following propagate and can even take place in a empirical expression which follows vacuum. NEWTON’S LAW OF COOLING: [Solid surfaces, gases, and liquids all emit, absorb, and transmit thermal radiation to varying degrees.] [The heat transfer coefficient is not a thermodynamic property.] What is Stefan–Boltzmann Law Radiation Equation? [It is an empirical parameter that incorporates into the heat transfer shows that the thermal radiation is relationship the nature of the flow pattern associated with the fourth power of the near the surface, the fluid properties, and absolute temperature of the surface, Tb. the geometry.] Comparison of Heat and Work Heat and work are both transient phenomena. Where: Systems never possess heat or work, Emissivity (ε) - property of the surface that but either or both cross the system indicates how effectively boundary when a system undergoes a the surface radiates (0≤ ε ≤ 1.0) change of state.  Both heat and work are boundary phenomena. Both are observed only at the boundary of the system, and both represent energy crossing the boundary. Both heat and work are path functions and inexact differentials. What is the First Law of Thermodynamics? application of the conservation of energy principle to heat and thermodynamic processes: [“The change in internal energy of a system is equal to the heat added to the system minus the work done by the system.”] Energy Balance symbols differential form instantaneous time rate form rate form