# THERMODYNAMICS 07

version from 2018-03-28 13:36

## Section

Tds relationsrelate the Tds product to other thermodynamic properties. The first Gibbs relation is Tds = du + Pdv. The second Gibbs relation is Tds = dh - vdP.
Therm of natural gas is an amount of energy equal to 29.3 kWh.
Thermal efficiencyis a measure of the performance of a heat engine and is the fraction of the heat input to the heat engine that is converted to net work output.
Thermal efficiency is the ratio of the net work produced by a heat engine to the total heat input, hth = Wnet/Qin.
Thermal efficiency of a heat engineis the fraction of the thermal energy supplied to a heat engine that is converted to work.
Thermal efficiencyof a power plantis defined as the ratio of the shaft work output of the turbine to the heat input to the working fluid.
Thermal energyis the sensible and latent forms of internal energy.
Thermal energy reservoiror just a reservoir is a hypothetical body with a relatively large thermal energy capacity (mass specific heat) that can supply or absorb finite amounts of heat without undergoing any change in temperature.
Thermal equilibriummeans that the temperature is the same throughout the entire system.
Thermodynamic equilibriumis a condition of a system in which all the relevant types of equilibrium are satisfied.
Thermodynamicscan 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.
Thermodynamic systemor simply a system, is defined as a quantity of matter or a region in space chosen for study.
Thermodynamic temperaturescale is a temperature scale that is independent of the properties of the substances that are used to measure temperature. This temperature scale is called the Kelvin scale, and the temperatures on this scale are called absolute temperatures. On the Kelvin scale, the temperature ratios depend on the ratios of heat transfer between a reversible heat engine and the reservoirs and are independent of the physical properties of any substance.
Thermodynamic temperature scaleis a temperature scale that is independent of the properties of any substance or substances.
Thermoelectric refrigeratoris a refrigerator using electric energy to directly produce cooling without involving any refrigerants and moving parts.
Third law of thermodynamicsstates that the entropy of a pure crystalline substance at absolute zero temperature is zero.
Throatof a converging-diverging nozzle is located at smallest flow area.
Thrustis the unbalanced force developed in a turbojet engine that is caused by the difference in the momentum of the low-velocity air entering the engine and the high-velocity exhaust gases leaving the engine, and it is determined from Newton's second law.
Top dead center(TDC) is the position of the piston when it forms the smallest volume in the cylinder.
Total energyE of a system is the sum of the numerous forms of energy such as thermal, mechanical, kinetic, potential, electric, magnetic, chemical, and nuclear, and their constituents. The total energy of a system on a unit mass basis is denoted bye and is defined as E/m.
Total energy of a flowing fluidis the sum of the enthalpy, kinetic, and potential energies of the flowing fluid.
Totally reversible process,or simply reversible process, involves no irreversibilities within the system or its surroundings. A totally reversible process involves no heat transfer through a finite temperature difference, no non-quasi-equilibrium changes, and no friction or other dissipative effects.
Transsonic flowoccurs when a flow has a Mach number M @1.
Trapis a device that allows condensed steam to be routed to another heater or to the condenser. A trap allows the liquid to be throttled to a lower-pressure region but traps the vapour. The enthalpy of steam remains constant during this throttling process.
Triple lineis the locus of the conditions where all three phases of a pure substance coexist in equilibrium. The states on the triple line of a substance have the same pressure and temperature but different specific volumes.
Triple pointof water is the state at which all three phases of water coexist in equilibrium.
Turbineis a device that produces shaft work due to a decrease of enthalpy, kinetic, and potential energies of a flowing fluid.
Topping cycleis a power cycle operating at high average temperatures that rejects heat to a power cycle operating at lower average temperatures.
Throttling valvesare any kind of flow-restricting devices that cause a significant pressure drop in the fluid. Some familiar examples are ordinary adjustable valves, capillary tubes, and porous plugs.
Turboprop engineuses propellers powered by the aircraft turbine to produce the aircraft propulsive power.
Two-stroke enginesexecute the entire cycle in just two strokes: the power stroke and the compression stroke.
Uniformimplies no change with location over a specified region.
Uniform-flow processinvolves the following idealization: The fluid flow at any inlet or exit is uniform and steady, and thus the fluid properties do not change with time or position over the cross section of an inlet or exit. If they do change with time, the fluid properties are averaged and treated as constants for the entire process.
Unitsare the arbitrary magnitudes assigned to the dimensions.
Universal gas constantRu is the same for all substances and its value is 8.314 kJ/kmol·K and 1.986 Btu/lbmol·R.
Unsteady-flowor transient-flow, processes are processes that involve changes within a control volume with time.
Useful workWuis the difference between the actual work W and the surroundings work Wsurr.
Useful work potentialis the maximum possible work that a system will deliver as it undergoes a reversible process from the specified initial state to the state of its environment, that is, the dead state.
Utilization factoris a measure of the energy transferred to the steam in the boiler of a steam power plant that is utilized as either process heat or electric power. Thus the utilization factor is defined for a cogeneration plant as the ratio of the sum of the net work output and the process heat to the total heat input.
Vacuum cooling is a way to cool a substance by reducing the pressure of the sealed cooling chamber to the saturation pressure at the desired low temperature and evaporating some water from the products to be cooled. The heat of vaporization during evaporation is absorbed from the products, which lowers the product temperature.
Vacuum freezingis the application of vacuum cooling when the pressure (actually, the vapour pressure) in the vacuum chamber is dropped below 0.6 kPa, the saturation pressure of water at 0°C.
Vacuum pressureis the pressure below atmospheric pressure and is measured by a vacuum gage that indicates the difference between the atmospheric pressure and the absolute pressure.
van't Hoff equationis the expression of the variation of the equilibrium constant with temperature in terms of the enthalpy of reaction at temperature T.
van der Waals equation of stateis one of the earliest attempts to correct the ideal gas equation for real gas behaviour.
Vapourimplies a gas that is not far from a state of condensation.
Compression-compression refrigeration cycleis the most frequently used refrigeration cycle and involves four main components: a compressor, a condenser, an expansion valve, and an evaporator.
Vaporization lineseparates the liquid and vapour regions on the phase diagram.
Vapour pressure is usually considered to be the partial pressure of water vapour in atmospheric air.
Velocity coefficienta parameter that is used to express the performance of a nozzle, is defined as the ratio of the actual velocity at nozzle exit to the velocity at nozzle exit for isentropic flow from the same inlet state to the same exit pressure.
Velocity of sound (or the sonic velocity)is the velocity at which an infinitesimally small pressure wave travels through a medium.
Virial equations of stateis an equation of state of a substance expressed in a series form as P = RT/v + a(T)/v2 + b(T)/v3 + c(T)/v4 + d(T)/v5 +...where the coefficients a(T ), b(T ), c(T ), and so on, are functions of temperature alone and are called virial coefficients.
Volume expansivity(also called the coefficient of volumetric expansion) relates how volume changes when temperature changes when pressure is held constant.
Volume flow rateis the volume of the fluid flowing through a cross section per unit time.
Volume fractionof a gas component in a gas mixture is the ratio of the component volume to the mixture volume. Note that for an ideal-gas mixture, the mole fraction, the pressure fraction, and the volume fraction of a component are identical.
Waste heatis energy that must be dissipated to the atmosphere from a process such as the heat transferred from condensing steam in the condenser of a steam power plant.
Weightis the gravitational force applied to a body, and its magnitude is determined from Newton's second law.
Wet-bulb temperatureis temperature measured by using a thermometer whose bulb is covered with a cotton wick saturated with water and blowing air over the wick.
Wet cooling toweris essentially a semi enclosed evaporative cooler.
Wilson lineis the locus of points where condensation will take place regardless of the initial temperature and pressure as steam flows through a high-velocity nozzle. The Wilson line is often approximated by the 4 percent moisture line on the h-s diagram for steam. Therefore, steam flowing through a high-velocity nozzle is assumed to begin condensation when the 4 percent moisture line is crossed.
Workwhich is a form of energy, can simply be defined as force times distance.
Workis the energy transfer associated with a force acting through a distance.
Working fluidis the fluid to and from which heat and work is transferred while undergoing a cycle in heat engines and other cyclic devices.
Zeroth law of thermodynamicsstates 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.