# THERMODYNAMICS 05

version from 2018-03-28 12:39

## Section

Microscopicforms of energy are those related to the molecular structure of a system and the degree of the molecular activity, and they are independent of outside reference frames.
Mixing chamberis the section of a control volume where mixing process takes place for two or more streams of fluids. The mixing chamber does not have to be a distinct "chamber." Mixing chambers are sometimes classified as direct-contact heat exchangers.
Molar analysisis one way to describe the composition of a mixture that is accomplished by specifying the number of moles of each component.
Molar massM can simply be defined as the mass of one mole (also called a gram-mole, abbreviated gmol) of a substance in grams, or the mass of one kmol (also called a kilogram-mole, abbreviated kgmol) in kilograms. In English units, it is the mass of 1 lbmol in lbm. Notice that the molar mass of a substance has the same numerical value in both unit systems because of the way it is defined.
Mole fractionis the ratio of the number of moles of one component in a mixture to the total moles of the mixture. Note that for an ideal-gas mixture, the mole fraction, the pressure fraction, and the volume fraction of a component are identical.
Mollier diagramafter the German scientist R. Mollier (1863-1935), is the h-s diagram. The Mollier diagram is useful when solving isentropic, steady flow process problems dealing with nozzles, turbines, and compressors.
Motor efficiencyis the ratio of the mechanical energy output of a motor to the electrical energy input. The full-load motor efficiencies range from about 35 percent for small motors to over 96 percent for large high-efficiency motors.
Multistage compression refrigeration systemis a cascade refrigeration system where the fluid used throughout the cascade refrigeration system is the same, and the heat exchanger between the stages is replaced by a device that has better heat-transfer characteristics, a mixing chamber (called a flash chamber).
Multistage compression with intercoolingis a compression process where a gas is compressed in stages and cooled between each stage by passing it through a heat exchanger called an intercooler.
Multistage compression with intercoolingrequires the compression process in a compressor to be carried out in stages and to cool the gas in between each stage such that the work required to compress a gas between two specified pressures can be decreased.
Multistage expansion with reheatingrequires the expansion process in a turbine be carried out in stages and reheating the gas between the stages such that the work output of a turbine operating between two pressure levels can be increased.
Natural-draft cooling toweruses the naturally occurring density gradients between the inside air-water vapour mixture and the outside air which create an airflow from the bottom to the top of a wet cooling tower.
Natural gas is produced from gas wells or oil wells rich in natural gas. It is composed mainly of methane, but it also contains small amounts of ethane, propane, hydrogen, helium, carbon dioxide, nitrogen, hydrogen sulphate, and water vapour. It is stored either in the gas phase at pressures of 150 to 250 atm as CNG (compressed natural gas) or in the liquid phase at 162° C as LNG (liquefied natural gas).
Nonreacting gas mixtureis a mixture of gases not undergoing a chemical reaction and can be treated as a pure substance since it is usually a homogeneous mixture of different gases.
Normal shock waveis an abrupt change over a very thin section normal to the direction of flow in which the flow transitions from supersonic to subsonic flow. This abrupt change in the flow causes a sudden drop in velocity to subsonic levels and a sudden increase in pressure. Flow through the shock is highly irreversible, and thus it cannot be approximated as isentropic.
Nozzle is a device that increases the velocity of a fluid at the expense of decreasing pressure.
Nuclear energyis the tremendous amount of energy associated with the strong bonds within the nucleus of the atom itself.
Octane ratingof a fuel is a measure of the engine knock resistance of a fuel.
Open (or direct-contact) feedwater heaterbasically a mixing chamber, where the steam extracted from the turbine mixes with the feedwater exiting the pump. Ideally, the mixture leaves the heater as a saturated liquid at the heater pressure.
Open system or control volumeis any arbitrary region in space through which mass and energy can pass across the boundary.
Orsat gas analyzera commonly used device to analyze the composition of combustion gases. The amounts of carbon dioxide, carbon monoxide, and oxygen are measured on a percent by volume and are based on a dry analysis.
Osmotic pressurethe pressure difference across a semi permeable membrane that separates fresh water from the saline water under equilibrium conditions.
Osmotic rise is the vertical distance saline water would rise when separated from the fresh water by a membrane that is permeable to water molecules alone at equilibrium.
Overall efficiencyfor a power plant is the ratio of the net electrical power output to the rate of fuel energy input. Overall efficiencies are about 25 to 28 percent for gasoline automotive engines, 34 to 38 percent for diesel engines, and 40 to 60 percent for large power plants.
Partial derivativeis the change in a function that depends on two (or more) variables, such as z = z (x, y), when allowing one variable to change while holding the others constant and observing the change in the function as another variable is held constant. The variation of z(x, y) with x when y is held constant is called the partial derivative of z with respect to x.
Partial pressureof a component in a gas mixture is the product of the mole fraction and the mixture pressure. The partial pressure is identical to the component pressure for ideal gas mixtures.
Partial volumeof a component in a gas mixture is the product of the mole fraction and the mixture volume. The partial volume is identical to the component volume for ideal gas mixtures.
Path of a processis the series of states through which a system passes during a process.
Peltier effectis the cooling effect that occurs when a small current passes through the junction of two dissimilar wires. This effect forms the basis for thermoelectric refrigeration and is named in honour of Jean Charles Athanase Peltier, who discovered this phenomenon in 1834.
Percent deficiency of airis the deficiency of air expressed as a percent of stoichiometric air. For example, 90 percent theoretical air is equivalent to 10 percent deficiency of air.
Percent excess air or percent theoretical airis the amount of excess air usually expressed in terms of the stoichiometric air. For example, 50 percent excess air is equivalent to 150 percent theoretical air.
Perpetual-motion machineis any device that violates either the first or second law of thermodynamics.
Perpetual-motion machine of the first kind(PMM1) is a device that violates the first law of thermodynamics (by creating energy).
Perpetual-motion machine of the second kindPMM2) is a device that violates the second law of thermodynamics.
Phase diagramis the P-T diagram of a pure substance and shows all three phases separated from each other by the sublimation line, vaporization line, and melting line.
Phase equilibriuma system involves two phases is established when the mass of each phase reaches an equilibrium level and stays there.
Phase equilibriumthe condition that the two phases of a pure substance are in equilibrium when each phase has the same value of specific Gibbs function. Also, at the triple point (the state at which all three phases coexist in equilibrium), the specific Gibbs function of each one of the three phases is equal.
Piezoelectric (or press-electric) effectthe emergence of an electric potential in a crystalline substance when subjected to mechanical pressure. This phenomenon, first discovered by brothers Pierre and Jacques Curie in 1880, forms the basis for the widely used >strain-gage pressure transducers.
Polytropic processis a process in which pressure and volume are often related by PVn= C, where n and C/ are constants, during expansion and compression processes of real gases.
Potential energyPE is the energy that a system possesses as a result of its elevation in a gravitational field and is expressed as PE = mgz.
Pound-force (lbf)the English system, is the force unit defined as the force required to accelerate a mass of 32.174 lbm (1 slug) at a rate of 1 ft/s2.
Pressure fraction of a gas component in a gas mixture is the ratio of the component pressure to the mixture pressure. Note that for an ideal-gas mixture, the mole fraction, the pressure fraction, and the volume fraction of a component are identical.
Pressure ratioIs the ratio of final to initial pressures during a compression process.
Pressure recovery factora measure of a diffuser's ability to increase the pressure of the fluid, is expressed in terms of the ratio of the actual stagnation pressure of a fluid at the diffuser exit relative to the maximum possible stagnation pressure.
Pressure rise coefficient,a measure of a diffuser's ability to increase the pressure of the fluid, is defined as the ratio of the actual pressure rise in the diffuser to the pressure rise that would be realized if the process were isentropic.
Pressure transducersare made of semiconductor materials such as silicon and convert the pressure effect to an electrical effect such as a change in voltage, resistance, or capacitance. Pressure transducers are smaller and faster, and they are more sensitive, reliable, and precise than their mechanical counterparts.
Primary or fundamental dimensionssuch as mass m, length L, time t, and temperature T, are the basis for the derivation of secondary dimensions.
Principle of corresponding statesis the fact that compressibility factor Z for all gases is approximately the same at the same reduced pressure and temperature.
Processis any change that a system undergoes from one equilibrium state to another. To describe a process completely, one should specify the initial and final states of the process, as well as the path it follows, and the interactions with the surroundings.
Process heatis required energy input in the form of heat for many industrial processes. The process heat is often obtained as heat transfer from high-pressure, high-temperature steam. Some industries that rely heavily on process heat are chemical, pulp and paper, oil production and refining, steel making, food processing, and textile industries.
Productsthe components that exist after the reaction in a combustion process.
Propertyany characteristic of a system. Some familiar properties are pressure P, temperature T, volume V, and mass m. The list can be extended to include less familiar ones such as viscosity, thermal conductivity, modulus of elasticity, thermal expansion coefficient, electric resistivity, and even velocity and elevation.
Propulsive efficiencyof an aircraft turbojet engine is the ratio of the power produced to propel the aircraft and the thermal energy of the fuel released during the combustion process.
Propulsive poweris the power developed from the thrust of the aircraft gas turbines and is the propulsive force (thrust) times the distance this force acts on the aircraft per unit time, that is, the thrust times the aircraft velocity.
Pseudo-reduced specific volumeis used with the generalized compressibility chart to determine the third property when P and v, or T and v, are given instead of P and T.
Psychrometric chartpresents the properties of atmospheric air at a specified pressure and two independent intensive properties. The psychrometric chart is a plot of absolute humidity versus dry-bulb temperature and shows lines of constant relative humidity, wet-bulb temperature, specific volume, and enthalpy for the atmospheric air.
Pumpis a device that increases the pressure of liquids very much as compressors increase the pressure of gases.
Pure substancea substance that has a fixed chemical composition throughout.
P-v-T surfaceis a three-dimensional surface in space which represents the P-v-T behaviour of a substance. All states along the path of a quasi-equilibrium process lie on the P-v-T surface since such a process must pass through equilibrium states. The single-phase regions appear as curved surfaces on the P-v-T surface, and the two-phase regions as surfaces perpendicular to the P-T plane.
Quasi-static, or quasi-equilibrium, processis a process which proceeds in such a manner that the system remains infinitesimally close to an equilibrium state at all times. A quasi-equilibrium process can be viewed as a sufficiently slow process that allows the system to adjust itself internally so that properties in one part of the system do not change any faster than those at other parts.
Radiationis the transfer of energy due to the emission of electromagnetic waves (or photons).
Ramjet engineis a properly shaped duct with no compressor or turbine, and is sometimes used for high-speed propulsion of missiles and aircraft. The pressure rise in the engine is provided by the ram effect of the incoming high-speed air being rammed against a barrier. Therefore, a ramjet engine needs to be brought to a sufficiently high speed by an external source before it can be fired.
Rankine cycle with reheatis a modification of the Rankine cycle in which the steam is expanded in the turbine in two stages and reheated in between. Reheating is a practical solution to the excessive moisture problem in the lower-pressure stages of turbines, and it is used frequently in modern steam power plants.
Rankine scale The temperature unit on this scale is the rankine, which is designated by R.
Raoult's lawapplies to a gas-liquid mixture when a gas is highly soluble in a liquid (such as ammonia in water) and relates the mole fractions of the species of a two-phase mixture in the liquid and gas phases in an approximate manner.
Rayleigh lineis the locus of all states for frictionless flow in a constant-area duct with heat transfer plotted on a T-s diagram.
Reactantsare the components that exist before the reaction in a combustion process.
Reciprocity relationshows that the inverse of a partial derivative is equal to its reciprocal.