(See related pages)
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| Absolute pressure | is the actual pressure at a given position and it is measured relative to absolute vacuum (i.e., absolute zero pressure). Throughout this text, the pressure P will denote absolute pressure unless specified otherwise. |
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| Bar | is the unit of pressure equal to 105 pascal. |
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| Barometer | is a device that measures the atmospheric pressure; thus, the atmospheric pressure is often referred to as the barometric pressure. |
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| Boundary | is the real or imaginary surface that separates the system from its surroundings. The boundary of a system can be fixed or movable. |
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| Bourdon tube | named after the French inventor Eugene Bourdon, is a type of commonly used mechanical pressure measurement device which consists of a hollow metal tube bent like a hook whose end is closed and connected to a dial indicator needle. |
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| British thermal unit BTU | the energy unit in the English system, representing the energy needed to raise the temperature of 1 lbm of water at 68 °F by 1 °F. |
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| Calorie (cal) | is the amount of energy in the metric system needed to raise the temperature of 1 g of water at 15 °C by 1°C. |
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| Celsius scale | (formerly called the centigrade scale; in 1948 it was renamed after the Swedish astronomer A. Celsius, 1701-1744, who devised it) is the temperature scale used in the SI system. On the Celsius scale, the ice and steam points are assigned the values of 0 and 100 °C, respectively. |
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| Chemical equilibrium | is established in a system when its chemical composition does not change with time. |
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| Classical thermodynamics | is the macroscopic approach to the study of thermodynamics that does not require knowledge of the behavior of individual particles. |
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| Closed system | consists of a fixed amount of mass, and no mass can cross its boundary. But energy, in the form of heat or work, can cross the boundary. |
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| Conservation of energy principle | states that during an interaction, energy can change from one form to another but the total amount of energy remains constant. That is, energy cannot be created or destroyed. |
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| Constant-volume gas thermometer | measures the temperature on the ideal-gas temperature scale using a rigid vessel filled with a gas, usually hydrogen or helium, at low pressure. The temperature of a gas of fixed volume varies linearly with pressure at sufficiently low pressures. |
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| Continuum | is a view of mass as continuous, homogeneous matter with no holes. Matter is made up of atoms that are widely spaced in the gas phase. Yet it is very convenient to disregard the atomic nature of a substance. The continuum idealization allows us to treat properties as point functions, and to assume the properties to vary continually in space with no jump discontinuities. This idealization is valid as long as the size of the system we deal with is large relative to the space between the molecules. This is the case in practically all problems, except some specialized ones. |
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| Control mass | (see closed system). |
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| Control surface | is the boundary of a control volume, and it can be real or imaginary. |
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| Control volume | (also see open system) is any arbitrary region in space through which mass and energy can pass across the boundary. Most control volumes have fixed boundaries and thus do not involve any moving boundaries. A control volume may also involve heat and work interactions just as a closed system, in addition to mass interaction. |
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| Cycle | is a process, or series of processes, that allows a system to undergo state changes and returns the system to the initial state at the end of the process. That is, for a cycle the initial and final states are identical. |
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| Density | is defined as mass per unit volume. |
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| Derived dimensions | (see secondary dimensions). |
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| Dimensionally homogeneous | means that every term in an equation must have the same unit. To make sure that all terms in an engineering equation have the same units is the simplest error check one can perform. |
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| Dimensions | are any physical characterizations of a quantity. |
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| English system, | which is also known as the United States Customary System (USCS), has the respective units the pound-mass (lbm), foot (ft), and second (s). The pound symbol lb is actually the abbreviation of libra, which was the ancient Roman unit of weight. |
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| Equilibrium | implies a state of balance. In an equilibrium state there are no unbalanced potentials (or driving forces) within the system. A system in equilibrium experiences no changes when it is isolated from its surroundings. |
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| Extensive properties | are those whose values depend on the size-or extent-of the system. Mass m, volume V, and total energy E are some examples of extensive properties. |
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| Fahrenheit scale | (named after the German instrument maker G. Fahrenheit, 1686-1736) is the temperature scale in the English system. On the Fahrenheit scale, the ice and steam points are assigned 32 and 212 °F. |
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| First law of thermodynamics | is simply an expression of the conservation of energy principle, and it asserts that energy is a thermodynamic property. |
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| Fundamental dimensions | (see primary dimensions). |
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| Gage pressure | is the difference between the absolute pressure and the local atmospheric pressure. |
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| Gravitational acceleration | g is 9.807 m/s2 at sea level and varies by less than 1 percent up to 30,000 m. Therefore, g can be assumed to be constant at 9.81 m/s2. |
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| Heat transfer | is defined as the form of energy that is transferred between two systems (or a system and its surroundings) by virtue of a temperature difference. |
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| Ideal gas temperature scale | is a temperature scale that turns out to be identical to the Kelvin scale. The temperatures on this scale are measured using a constant-volume gas thermometer, which is basically a rigid vessel filled with a gas, usually hydrogen or helium, at low pressure. The temperature of a gas is proportional to its pressure at constant volume. |
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| Incompressible substances | such as liquids and solids, have densities that have negligible variation with pressure. |
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| Independent properties | exist when one property can be varied while another property is held constant. |
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| Intensive properties | are those that are independent of the size of a system, such as temperature, pressure, and density. |
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| Iso-prefix | is often used to designate a process for which a particular property remains constant. |
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| Isobaric process | is a process during which the pressure P remains constant. |
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| Isochoric process | (isometric process) is a process during which the specific volume v remains constant. |
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| Isolated system | is a closed system in which energy is not allowed to cross the boundary. |
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| Isometric process | (see isochoric process). |
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| Isothermal process | is a process during which the temperature T remains constant. |
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| Joule (J) | is a unit of energy and has the unit "newton-meter (N·m)." |
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| Kelvin scale | is the thermodynamic temperature scale in the SI and is named after Lord Kelvin (1824-1907). The temperature unit on this scale is the kelvin, which is designated by K (not ° K; the degree symbol was officially dropped from kelvin in 1967). The lowest temperature on the Kelvin scale is 0 K. |
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| kelvin | is the temperature unit of the Kelvin scale in the SI. |
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| Kilojoule (1 kJ) | is 1000 joules. |
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| Kilopascal (kPa) | is the unit of pressure equal to 1000 pascal or 1000 N/m2. |
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| Manometer | is a device based on the principle that an elevation change of Δz of a fluid corresponds to a pressure change of ΔP/ ρg, which suggests that a fluid column can be used to measure pressure differences. The manometer is commonly used to measure small and moderate pressure differences. |
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| Mechanical equilibrium | is related to pressure, and a system is in mechanical equilibrium if there is no change in pressure at any point of the system with time. |
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| Megapascal (MPa) | is the unit of pressure equal to 106 pascal. |
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| Metric SI | (from Le Système International d' Unités), which is also known as the International System, is based on six fundamental dimensions. Their units, adopted in 1954 at the Tenth General Conference of Weights and Measures, are: meter (m) for length, kilogram (kg) for mass, second (s) for time, ampere (A) for electric current, degree Kelvin (K) for temperature, candela (cd) for luminous intensity (amount of light), and mole (mol) for the amount of matter. |
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| Newton (N) | in SI, is the force unit defined as the force required to accelerate a mass of 1 kg at a rate of 1 m/s2. |
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| Open system | is any arbitrary region in space through which mass and energy can pass across the boundary. |
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| Pascal (Pa) | is the unit of pressure defined as newtons per square meter (N/m2 ). |
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| Pascal's law | allows us to "jump" from one fluid column to the next in manometers without worrying about pressure change as long as we don't jump over a different fluid, and the fluid is at rest. |
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| Pascal's principle | after Blaise Pascal (1623-1662), states that the consequence of the pressure in a fluid remaining constant in the horizontal direction is that the pressure applied to a confined fluid increases the pressure throughout by the same amount. |
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| Path of a process | is the series of states through which a system passes during a process. |
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| Phase equilibrium | when a system involves two phases is established when the mass of each phase reaches an equilibrium level and stays there. |
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| Primary dimensions | are the basic dimensions such as mass m, length L, time t, and temperature T. |
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| Piezoelectric effect | is the emergence of an electric potential in a crystalline substance when subjected to mechanical pressure, and this phenomenon forms the basis for the widely used strain-gage pressure transducers. |
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| Piezoelectric transducers | also called solid-state pressure transducers, work on the principle that an electric potential is generated in a crystalline substance when it is subjected to mechanical pressure. This phenomenon, first discovered by brothers Pierre and Jacques Curie in 1880, is called the piezoelectric (or press-electric) effect. Piezoelectric pressure transducers have a much faster frequency response compared to the diaphragm units and are very suitable for high-pressure applications, but they are generally not as sensitive as the diaphragm-type transducers. |
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| Pound-force lbf | in 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. |
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| Pressure | is defined as the force exerted by a fluid per unit area. |
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| Pressure transducers | are 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. |
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| Primary or fundamental dimensions, | such as mass m, length L, time t, and temperature T, are the basis for the derivation of secondary dimensions. |
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| Problem-solving technique | is a step-by-step approach to problem solving discussed in Chapter 1. |
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| Process | is 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. |
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| Property | is any 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. |
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| Quasi-equilibrium process | (see quasi-static process). |
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| Quasi-static, or quasi-equilibrium, process | is 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. |
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| Rankine | is the temperature unit for the Rankine scale in the English system. |
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| Rankine scale | named after William Rankine (1820-1872), is the thermodynamic temperature scale in the English system. The temperature unit on this scale is the rankine, which is designated by R. |
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| Rarefied gas flow theory | applies to a substance in which the mean free path of its molecules is large compared to the characteristic length of the systems such that the impact of individual molecules should be considered, and the substance cannot be modeled as a continuum. |
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| Relative density | (see specific gravity) |
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| Secondary dimensions, or derived dimensions | such as velocity, energy E, and volume V, are expressed in terms of the primary dimensions. |
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| Secondary units | are expressed in terms of the primary units. |
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| Second law of thermodynamics | asserts that energy has quality as well as quantity, and actual processes occur in the direction of decreasing quality of energy. |
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| Simple compressible system | is a system in which there is the absence of electrical, magnetic, gravitational, motion, and surface tension effects. These effects are due to external force fields and are negligible for most engineering problems. |
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| Specific gravity, or relative density | is defined as the ratio of the density of a substance to the density of some standard substance at a specified temperature (usually water at 4°C, for which the density is 1000 kg/m3). |
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| Specific properties | are extensive properties per unit mass. Some examples of specific properties are specific volume (v=V/m) and specific total energy (e= E/m). |
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| Specific volume | is the reciprocal of density and is defined as the volume per unit mass. |
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| Specific weight | w is the weight of a unit volume of a substance and is determined from the product of the local acceleration of gravity and the substance density. |
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| State | is the condition of a system not undergoing any change gives a set of properties that completely describes the condition of that system. At this point, all the properties can be measured or calculated throughout the entire system. |
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| State postulate | specifies the number of properties required to fix the state of a system: The state of a simple compressible system is completely specified by two independent, intensive properties. |
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| Statistical thermodynamics | an approach to thermodynamics more elaborate than classical thermodynamics, is based on the average behavior of large groups of individual particles. |
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| Steady | implies no change with time. The opposite of steady is unsteady, or transient. |
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| Steady-flow devices | operate for long periods of time under the same conditions. |
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| Steady-flow process | is defined as a process during which a fluid flows through a control volume steadily. That is, the fluid properties can change from point to point within the control volume, but at any fixed point they remain the same during the entire process. |
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| Strain-gage pressure transducer Surrounding | is the mass or region outside the thermodynamic system. |
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| Thermal equilibrium | means that the temperature is the same throughout the entire system. |
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| Thermodynamic equilibrium | is a condition of a system in which all the relevant types of equilibrium are satisfied. |
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| Thermodynamics | can be defined as the science of energy. Energy can be viewed as the ability to cause changes. The name thermodynamics stems from the Greek words therme (heat) and dynamis (power), which is most descriptive of the early efforts to convert heat into power. Today the same name is broadly interpreted to include all aspects of energy and energy transformations, including power production, refrigeration, and relationships among the properties of matter. |
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| Thermodynamic system or simply a system | is defined as a quantity of matter or a region in space chosen for study. |
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| Thermodynamic temperature scale | is a temperature scale that is independent of the properties of any substance or substances. |
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| Units | are the arbitrary magnitudes assigned to the dimensions. |
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| Unity conversion ratios | are ratios of units that are based on the definitions of the units in question that are identically equal to 1, are unitless, and can be inserted into any calculation to properly convert units. |
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| Vacuum pressure | is the pressure below atmospheric pressure and is measured by a vacuum gage that indicates the difference between the atmospheric pressure and the absolute pressure. |
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| Weight | is the gravitational force applied to a body, and its magnitude is determined from Newton's second law. |
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| Zeroth law of thermodynamics | states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. By replacing the third body with a thermometer, the zeroth law can be restated as two bodies are in thermal equilibrium if both have the same temperature reading even if they are not in contact. |