# THERMODYNAMICS 01

version from 2018-03-28 10:33

## Section

Question Answer
Absolute entropyis entropy calculated relative to the absolute reference point determined by the third law of thermodynamics.
Absolute or specific humidity (also called humidity ratio) is the mass of water vapour present in a unit mass of dry air; that is, it is the ratio of the mass of water vapour to the mass of dry air in atmospheric air.
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.
Absorption refrigeration systems involve the absorption of a refrigerant by a transport medium. The most widely used absorption refrigeration system is the ammonia-water system, where ammonia (NH3) serves as the refrigerant and water (H2O) as the transport medium. Absorption refrigeration systems are economically attractive when there is a source of inexpensive heat energy at a temperature of 100 to 200 °C. Some examples of inexpensive heat energy sources include geothermal energy, solar energy, and waste heat from cogeneration or process steam plants, and even natural gas when it is available at a relatively low price.
Adiabatic flame or adiabatic combustion temperature is the maximum temperature the products of combustion will reach in the limiting case of no heat loss to the surroundings during the combustion process. The adiabatic flame temperature attains its maximum value when complete combustion occurs with the theoretical amount of air.
Adiabatic process is a process during which there is no heat transfer. The word adiabatic comes from the Greek word adiabatos, which means not to be passed.
Adiabatic saturation process is the process in which a steady stream of unsaturated air of unknown specific humidity is passed through a long insulated channel that contains a pool of water. As the air flows over the water, some water will evaporate and mix with the airstream. The moisture content of air will increase during this process, and its temperature will decrease, since part of the latent heat of vaporization of the water that evaporates will come from the air. If the channel is long enough, the airstream will exit as saturated air (100 percent relative humidity) at the exit temperature.
Adiabatic saturation temperature is the exit temperature that air attains in the adiabatic saturation process.
Afterburner is a section added between the turbine and the nozzle of an aircraft turbine engine where additional fuel is injected into the oxygen-rich combustion gases leaving the turbine. As a result of this added energy, the exhaust gases leave at a higher velocity, providing extra thrust for short takeoffs or combat conditions.
Air conditioners are refrigerators whose refrigerated space is a room or a building instead of the food compartment.
Air-fuel ratio AF is a frequently used quantity in the analysis of combustion processes to quantify the amounts of fuel and air. It is usually expressed on a mass basis and is defined as the ratio of the mass of air to the mass of fuel for a combustion process.
Air-source heat pumps use the cold outside air as the heat source in winter.
Air-standard cycle is a cycle for which the air-standard assumptions are applicable.
Amagat's law of additive volumesThe volume of a gas mixture is equal to the sum of the volumes each gas would occupy if it existed alone at the mixture temperature and pressure.
Annual fuel utilization efficiency, or AFUE accounts for the combustion efficiency as well as other losses such as heat losses to unheated areas and start-up and cool-down losses in buildings.
Apparent (or average) molar mass of a mixture can be expressed as the sum of the products of the mole fraction and molar mass of each component in the mixture.
Atmospheric air is the air in the atmosphere, which normally contains some water vapour (or moisture).
Auto ignition is the premature ignition of the fuel produces an audible noise, which is called engine knock.
Average (or apparent) gas constant of a mixture is the universal gas constant divided by the apparent molar mass of the mixture.
Back pressure is the pressure applied at the nozzle discharge region.
Back work ratio is the ratio of the compressor work to the turbine work in gas-turbine power plants.
Bar is the unit of pressure equal to 105 Pascal.
Barometer is a device that measures the atmospheric pressure; thus, the atmospheric pressure is often referred to as the barometric pressure.
Beattie-Bridgeman equation of state is one of the best known and is a reasonably accurate equation of state.
Benedict-Webb-Rubin equation of state is one of the more recent and very accurate equations of state.
Bernoulli's equation is a form of the conservation of momentum principle for steady-flow control volumes.
Binary vapour cycle is a vapour cycle in which the condenser of the high-temperature cycle (also called the topping cycle) serves as the boiler of the low-temperature cycle (also called the bottoming cycle). That is, the heat output of the high-temperature cycle is used as the heat input to the low-temperature one.
Boiler is basically a large heat exchanger where the heat originating from combustion gases, nuclear reactors, or other sources is transferred to the water essentially at constant pressure.
Bore is the diameter of a piston.
Bottom dead center (BDC) is the position of the piston when it forms the largest volume in the cylinder.
Bottoming cycle is a power cycle operating at low average temperatures that receives heat from a power cycle operating at higher average temperatures.
Boundary is the real or imaginary surface that separates the system from its surroundings. The boundary of a system can be fixed or movable.
Boundary work(PdV work) is the work associated with the expansion or compression of a gas in a piston-cylinder device. Boundary work is the area under the process curve on a P-V diagram equal, in magnitude, to the work done during a quasi-equilibrium expansion or compression process of a closed system.
Bourdon tube , 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.
Brayton cycle with regenerationis the Brayton cycle modified with a regenerator, a counter flow heat exchanger, to allow the transfer of heat to the high pressure air leaving the compressor from the high-temperature exhaust gas leaving the turbine.
British thermal unit(Btu) is the energy unit in the English system needed to raise the temperature of 1 lbm of water at 68 °F by 1°F.
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.
Carnot cyclewas first proposed in 1824 by French engineer Sadi Carnot, is composed of four reversible processes-two isothermal and two adiabatic, and can be executed either in a closed or a steady-flow system.
Carnot efficiencyis the highest efficiency a heat engine operating between the two thermal energy reservoirs at temperatures TL and TH can have, hth, rev = 1 - TL / TH.
Carnot heat engine is the theoretical heat engine that operates on the Carnot cycle.
Carnot heat pumpis a heat pump that operates on the reversed Carnot cycle. When operating between the two thermal energy reservoirs at temperatures TL and TH the Carnot heat pump can have a coefficient of performance of COPHP, rev = 1/ (1- TL / TH) = TH /( TH - TL).
Carnot heat pump is a heat pump that operates on the reversed Carnot cycle.
Carnot refrigerator is a refrigerator that operates on the reversed Carnot cycle. When operating between the two thermal energy reservoirs at temperatures TL and TH the Carnot refrigerator can have a coefficient of performance of COPR, rev = 1/ (TH / TL - 1) = TL /( TH - TL).
Cascade refrigeration cyclesperform the refrigeration process in stages, that is, to have two or more refrigeration cycles that operate in series.
Celsius scale 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.
Chemical energyis the internal energy associated with the atomic bonds in a molecule.
Chemical equilibriumis established in a system when its chemical composition does not change with time.
Chemical equilibrium reactionsare chemical reactions in which the reactants are depleted at exactly the same rate as they are replenished from the products by the reverse reaction. At equilibrium the reaction proceeds in both directions at the same rate.
Chemically correct amount of airis the stoichiometric or theoretical air, or 100 percent theoretical air.
Chemical potential is the change in the Gibbs function of the mixture in a specified phase when a unit amount of a given component of the mixture in the same phase is added as pressure and temperature and the amounts of all other components are held constant. The chemical potential of a component of an ideal gas mixture depends on the mole fraction of the components as well as the mixture temperature and pressure, and is independent of the identity of the other constituent gases.
Choked flow occurs in a nozzle when the mass flow reaches a maximum value for the minimum flow area. This happens when the flow properties are those required to increase the fluid velocity to the velocity of sound at the minimum flow area location.
Clapeyron-Clausius equationis used to determine the variation of saturation pressure with temperature.
Clapeyron equation relates the enthalpy change associated with a phase change (such as the enthalpy of vaporization hfg) from knowledge of P, v, and T data alone.
Classical thermodynamicsis the macroscopic approach to the study of thermodynamics that does not require knowledge of the behaviour of individual particles.
Clausius inequalityis expressed as the cyclic integral of Q/T is always less than or equal to zero. This inequality is valid for all cycles, reversible or irreversible.
Clausius statement of the second law is expressed as follows: It is impossible to construct a device that operates in a cycle and produces no effect other than the transfer of heat from a lower-temperature body to a higher-temperature body.
Clearance volumeis the minimum volume formed in the cylinder when the piston is at top dead center.
Closed feedwater heater is a feedwater heater in which heat is transferred from the extracted steam to the feedwater without any mixing taking place. The two streams are typically not at the same pressures, since they do not mix. In an ideal closed feedwater heater, the feedwater is heated to the exit temperature of the extracted steam, which ideally leaves the heater as a saturated liquid at the extraction pressure. In actual power plants, the feedwater leaves the heater below the exit temperature of the extracted steam because a temperature difference of at least a few degrees is required for any effective heat transfer to take place.