THERMODYNAMICS AND HEAT TRANSFER
COEFFICIENT OF PERFORMANCE OF A REFRIGERATOR – COP Ref = Heat removed from cold body/work supplied
COEFFICIENT OF THERMAL CONDUCTIVITY – The quantity of heat that will flow across a unit area in unit time if the temperature gradient across this area is unity.
COLD – A comparative lack of heat, indicating chillness.
COMPRESSED SOLID – is a solid at a temperature below its saturation temperature.
COMPRESSIBILITY FACTOR, Z – is the factor introduced to modify the ideal gas equation Pv = RT, and to describe the behaviour of a real gas. Z = Pv/RT.
CONDENSATE – The liquid formed by the condensation of a gaseous substance.
CONDENSATION – The change of state of a substance from the gaseous to the liquid form.
CONDENSING – The process of giving up latent heat of vapourization in order to liquefy a vapour.
CONDUCTION – Transfer of heat from one part of a material to another or to a material with which it is in contact.
CONDUCTIVITY – The relative value of a material, as compared with a standard, in affording a passage through itself or over its surface for heat.
CONSTANT VOLUME PROCESS – is one wherein a gas is heated (or cooled) in a fixed enclosed space (no change in volume occupied by the gas). There will be no workdone by the gas. The whole heat supplied will be stored in the form of internal energy.
CONSTANT PRESSURE PROCESS – Also called isobaric process. Heat supplied to a system exhibits as the change in enthalpy.
CONSTANT TEMPERATURE PROCESS – Also called isothermal process. There is no change in temperature and hence internal energy and enthalpy remain constant. Heat supplied = work done.
CONVECTION – Passage of heat from one point to another by means of a gravity fluid circulation due to changes in density resulting from picking up and giving up heat. Also transfer of heat to or from a fluid (liquid or gas) flowing over the surface of a body.
COSMIC RADIATION – Radiation of many sorts, but mostly atomic nuclei (protons) with very high energies, originating outside the earth’s atmosphere.
COUNTER FLOW HEAT EXCHANGER – A heat exchanger in which the warm substance flows in the opposite direction to the flow of the cool substance.
CRITICAL STATE OF A SUBSTANCE – is that state at which liquid and vapour coexist in equilibrium. At critical state, latent heat of evaporation becomes zero.
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CRITICAL PRESSURE – The critical pressure of a vapour is the pressure required to liquefy it at the critical temperature and is the highest pressure on the temperature -pressure graph for saturated vapour.
CRITICAL TEMPERATURE – Temperature of the vapour above which no pressure, however high, will produce liquefaction.
CRITICAL VELOCITY – The velocity above which fluid flow is turbulent.
CYCLIC PROCESS – is a process (or a series of processes) which returns the system to the state it was before the process began.
DALTON’S LAW OF PARTIAL PRESSURES – At a common temperature, a mixture of gases will exert on the sides of the vessel a total pressure equal to the sum of the pressures which each constituent would exert separately if it alone occupied the vessel.
DERIVED UNITS – are those derived from basic units, e.g., force, work, density etc.
DIMENSIONS – are the properties by which the physical quantity of an object may be described.
DRY BULB TEMPERATURE – The actual temperature of air, as opposed to wet bulb temperature.
DRY STEAM – Steam containing no moisture. It may be either saturated or superheated steam.
DRY SATURATED STEAM – Saturated steam, as generated from water, that contains no moisture in suspension.
EFFICIENCY – Ratio of the useful work performed by a prime mover to the energy expended. In other words the output divided by the input.
ENERGY – Stored work, that is the ability to do work.
ENTHALPY – Name given to the total heat in the fluid at any temperature.
ENTROPY TEMPERATURE DIAGRAM – In thermodynamics, the base of a heat diagram, the area of which is heat units and the altitude of which is absolute temperature.
EQUIVALENT EVAPORATION – Amount of water in kg. that would be evaporated from water at 100°C into steam at 100°C and 1.03 kscm, by the heat put into steam actually evaporated in one hour by 1 kg of fuel.
EVAPORATION – Process by which a liquid changes into a vapour as a result of absorbing heat.
EVAPORATIVE CONDENSER – Combines the principles of forced circulation convection currents with the ability of a vapourizing liquid to absorb heat.
EXTERNAL LATENT HEAT – When vapourization takes place, the amount of heat required because of the work in pushing back the atmosphere to make room for the steam.
EXTRINSIC PROPERTIES – Also called extensive properties, are those properties which are dependent on the mass of the system. Examples are volume, weight and total energy.
FACTOR OF EVAPORATION – A quantity which when multiplied by the amount of steam generated at a given pressure from water at a given temperature, gives the equivalent evaporation from and at 100°C.
FLOW WORK – The product PV (pressure and specific volume) represents flow work in a steady flow system.
FORCED CONVECTION – Circulation of the fluid is made positive by some mechanical means such as a pump for water or a fan for hot gases.
FORCED DRAFT COOLING TOWER – Cools water by mechanically forcing air through the water spray in the tower.
FREE EXPANSION – is a process wherein a fluid from a pressure chamber expands into a vacuum chamber through an orifice of large dimensions.
FREEZING POINT – The temperature at which water turns into ice (0°C at sea level).
FROM AND AT 100°C – In boiler operation, it is an evaporation that would be the equivalent of the actual evaporation when the feed water enters the boiler at 100°C and steam is formed at 100°C, at standard atmospheric pressure.
FROSTING EVAPORATORS – Those evaporators which always operate at temperature below 0°C.
FUNDAMENTAL DIMENSIONS – Internationally accepted units are time, length, mass, force and temperature.
GAUGE PRESSURE – Pressure above or below atmospheric pressure.
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GAY LUSSAC LAW – The volume of a gas will vary directly as the absolute temperature, if the pressure remains constant.
GASES – are substances in which the molecules move freely and exist in an unbound state. Gases can be compressed easily because of the large empty space available between the molecules.
HEAT – A form of energy and is due to the motion of the molecules of which all substances are composed. Unit of heat is kilocalorie.
HEAT OF COMPRESSION – Increase of temperature brought about by compression of air or air fuel mixture.
HEAT OF CONDENSATION – The heat that is removed per kilogram of vapour to cause it to condense. It has the same numerical value as the heat of vapourization.
HEAT ENGINE – It is an energy transformer. It transforms heat energy into mechanical energy and render the latter available for doing useful work.
HEAT PUMP – is a device which extracts heat from low temperature surroundings and sends it to a high temperature body, while operating in a cycle. Heat pump maintains a body or system at a temperature higher than the temperature of the surroundings, with the work supplied to it.
HEAT SINK – A means for disposing of unwanted heat, usually by using it to increase the temperature of water, which is then run to waste.
HEAT SOURCE – Supplier of heat to the working agent of a heat engine-a fraction of the heat supplied being changed into work.
HEAT TRANSFER – Movement of heat energy from one place to another (warmer to cooler portion).
HETEROGENEOUS SYSTEM – is a system which is made of more than one phase.
HOMOGENEOUS SYSTEM – is a system consisting of a single phase.
HYPERBOLIC PROCESS – is one in which a gas is heated in such a way that at any instant its pressure multiplied by its volume remains constant.
IDEAL GAS – is one which will obey all the gas laws, under all conditions of temperature and pressure. For an ideal gas, the internal energy and enthalpy are functions of temperature alone.
INDICATED HORSE POWER – The actual power developed or used within a cylinder as calculated from the indicator diagram.
INERT GAS – A gas which under normal conditions does not react with or combine with other substances for example, argon, helium, neon, krypton, xenon.
INTERNAL ENERGY – is the energy arising from the motion and from configuration of the internal particles (atoms and molecules). It is the energy stored in the gas and is used for raising its temperature. v = CvT.,
∆u = Cv (T2 – T1).
INTRINSIC PROPERTIES – also called intensive properties, are those properties which are independent of the mass of the system. Example are pressure, temperature and density.
ISENTROPIC PROCESS – which is called reversible adiabatic process is one in which no heat is supplied and work done is at the expense of internal energy. Law followed is Pvγ = constant.
ISOLATED SYSTEM – is a special case of the closed system which will not be influenced by the surrounding. In this system, no mass transfer, no energy transfer occur. Work and heat cannot cross the boundary of the system.
ISOTHERM – The line drawn through points or areas of similar temperature.
ISOTHERMAL EXPANSION or COMPRESSION – The expansion or compression of a gas at constant temperature, that is with the gas temperature remaining the same during the process.
JOULE’S LAW OF INTERNAL ENERGY – The internal energy of a given quantity of a gas depends only on the temperature of the gas. As temperature changes, the internal energy also changes.
KELVIN PLANK STATEMENT – It is impossible to construct an engine undergoing a cyclic process, which will convert all the heat supplied to it into an equivalent amount of work.
KILO PASCALS (kPa) – Measurement of pressure in the metric system 1 kilo pascal is approximately equal to 6.895 pounds per square inch.
KINETIC ENERGY – Energy due to momentum, that is the energy of a moving body, which is equivalent to saying, dynamic inertia. The kinetic energy of a moving body is the work which the body is capable of performing against a resistance before it is brought to rest, that is, it equals the work which has brought it from its state of rest to its actual velocity.
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LATENT HEAT – The quantity of heat required to change the state or condition under which a substance exists without changing its temperature.
LATENT HEAT OF FUSION – The amount of heat which must be added to one kilogram of material to change its state from a solid to a liquid or which must be subtracted from one kilogram of a liquid to change it to a solid.
LATENT HEAT (internal) – The amount of heat that the water will absorb (latent heat minus heat equivalent of work of evaporation), at the boiling point without a change in temperature.
LATENT HEAT OF VAPOURIZATION – Amount of heat to be added to (or subtracted from) one kilogram of the refrigerant to cause it to vapourize (or condense). Also, the amount of heat energy in a gas which is in addition to that found in the liquid at the same temperature.
LAW OF CONSERVATION OF ENERGY – States that energy can neither be created nor destroyed. However, it can be stored in various forms and can be transferred from one form to another. In other words, the total energy of a body or substance always remains constant.
LIQUIDS – are substances in which the molecules are loosely bounded. A definite volume is maintained by the bond forces, but can change the shape according to the shape of the container.
MATTER – General name for all material substances, gaseous, liquid or solid forming the earth and its surrounding atmosphere.
MEAN EFFECTIVE PRESSURE – The difference between the mean forward pressure and the mean back pressure acting on a moving piston during a cycle of operation.
MECHANICAL CYCLE – is one wherein during the various processes, the properties of the working fluid change.
MECHANICAL EFFICIENCY – Ratio of mechanical energy available at the brake or flywheel to the mechanical energy put into the moving mechanism at the piston of the engine.
MECHANICAL EQUIVALENT OF HEAT – 1 kcal is equal to 1427 Mtkg of mechanical energy.
MOLE OF GAS – Quantity of gas, the weight of which is equal to the molecular weight in pounds.
MOLAR HEAT – is the quantity of heat required to raise the temperature of one mole of a substance through one degree.
MOLLIER DIAGRAM – A graphical representation of the properties of a fluid in which enthalpy is plotted as abscissa and pressure as ordinate.
NATURAL CONVECTION – Circulation or the transfer of fluid due to a difference in density resulting from temperature changes.
NATURAL DRAFT COOLING TOWER – Cooling tower which cools water by moving air at low velocities through the tower, without the aid of any mechanical means.
NON FLOW PROCESS – It is the one in which there is no mass interaction across the system boundaries during the process. This occurs in a closed system.
NTP – The normal temperature and pressure refer to the conditions of temperature 0°C (273 K) and pressure of 760 mm of mercury.
OPEN SYSTEM – It has no closed boundary, but has one or more openings.
Fluid may enter or leave the system, it undergoes thermodynamic process, while moving through the system.
PARALLEL FLOW HEAT EXCHANGER – A heat exchanger in which the warm and cool fluids flow in the same direction but separated from one another.
PERFECT GAS – Gas which behaves in accordance with the gas law PV = MRT, where P-absolute pressure, V-volume, M-mass, T-absolute temperature and R-constant for the particular gas depending on its molecular weight.
PERPETUAL MOTION MACHINE OF FIRST KIND – is a machine which will give continoues work without taking any energy from other system or surrounding.
PERPETUAL MOTION MACHINE OF SECOND KIND – is a machine which abstracts heat continuously from a reservoir and converts it completely into work or 100% efficient engine.
PERPETUAL MOTION MACHINE OF THIRD KIND – is applied to devices that, once set in motion, continue in motion for an indefinitely long time without slowing down.
PHASE OF A SUBSTANCE – It refers to a quantity of matter which is homogeneous or uniform throughout its physical structure and chemical composition.
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PHASE DIAGRAM – is a pressure temperature diagram showing more than one of the saturation lines (liquid-vapour, liquid-solid, solid-vapour and other of a pure substance).
PATH FUNCTIONS – depend on which path is followed between the states 1 and 2. Examples are heat, work, internal energy and entropy.
POINT FUNCTIONS – are the properties of a system at a state.
POLYTROPIC PROCESS – follows the law Pvn = constant. In this process, heat is supplied in such a way there is some work done by the gas (i.e., during expansion) and there is also a change in internal energy.
PROCESS – It is the transformation of a system from one state to another.
PROPERTY OF A FLUID – is its characteristic such as pressure, volume, temperature, internal energy, enthalpy and entropy which are measurable directly or indirectly.
POTENTIAL ENERGY – Energy possessed by a substance by virtue of its position with respect to a datum.
POWER – The rate at which work is done, i.e., 1 HP = 4500 Mtkg/ minute.
PRESSURE – As defined by Rankine-A force of the nature or a thrust, distributed over a surface measured as kg/sqcm.
PURE SUBSTANCE – is any material of single chemical structure or of homogeneous and invariant chemical structure.
QUALITY OF STEAM – Refers indirectly the amount of water or unevaporated moisture in steam.
QUASI-STATIC PROCESS – is a process which is carried out in such a manner that at every instant the system departs only infinitesimally from the thermodynamic equilibrium state.
R – An experimentally determined constant which is equal to the mechanical work done by the expansion of unit weight of a perfect gas at a constant pressure while heat is added to increase its temperature through one degree.
RADIATION – Continuous form of interchange of heat energy from one body to another by means of electromagnetic waves without causing a change in the temperature of the medium between the two bodies involved. These energy waves may be reflected, penetrate the material or be absorbed.