What is The zeroth law of thermodynamics
The zeroth law of thermodynamics states that that if two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other. Two Two systems are said to be in the relation relation of thermal equilibrium if they are linked by a wall permeable only to heat, and do not change over time.[1] s a convenience of language, systems are sometimes also said to be in a relation of thermal equilibrium if they are not linked so as to be able to transfer heat to each other, but would not do so if they were connected by a wall permeable only to heat. Thermal equilibrium between two systems is a transitive relation. The physical meaning of the law was e!pressed by "a!well in the words# $ll heat is of the same kind$.[%] &or this reason, another statement of the law is $ll diathermal walls are equivalent$.['] The law is important for the mathematical formulation of thermodynamics, thermodynamics, which needs the assertion that the relation of thermal equilibrium is an equivalence relation. This information is needed for a mathematical de(nition of temperature that will agree with the physical e!istence of valid thermometers.[)] (b)Dene the The rst law of thermodynamics
The (rst law of thermodynamics is a version of the law of conservation conservation of energy, adapted for thermodynamic systems. The law of conservation of energy states that the total energy of an isolated system is constant* energy can be transformed from one form to another, but cannot be created or destroyed. The (rst law is often formulated by stating that the change in the internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work done by the system on its surroundings. +quivalently, perpetual motion machines of the (rst kind are impossible. Conceptually revised statement, according to the mechanical approach
The revised statement of the (rst law postulates that a change in the internal energy of a system due to any arbitrary process, that takes the system from a given initial thermodynamic state to a given (nal equilibrium thermodynamic state, can be determined through the physical e!istence, for those given states, of a reference process that occurs purely through stages of adiabatic work. The revised statement is then
&or a closed system, in any arbitrary process of interest that takes it from an initial to a (nal state of internal thermodynamic equilibrium, the change of internal energy is the same as that for a reference adiabatic work process that links those two states. This is so regardless of the path of the process of interest, and regardless of whether it is an adiabatic or a non adiabatic process. The reference adiabatic work process may be chosen arbitrarily from amongst the class of all such processes. This statement is much less close to the empirical basis than are the original statements,[1)] but is often regarded as conceptually parsimonious in that it rests only on the concepts of adiabatic work and of nonadiabatic processes, not on the concepts of transfer of energy as heat and of empirical temperature that are presupposed by the original statements. -argely through the inuence of "a! /orn, it is often regarded as theoretically preferable because of this conceptual parsimony. /orn particularly observes that the revised approach avoids thinking in terms of what he calls the $imported engineering$ concept of heat engines.[10]
(c)The Carnot cycle
The arnot cycle is a theoretical thermodynamic cycle proposed by 2icolas -3onard 4adi arnot in 15%) and e!panded upon by others in the 15'0s and 15)0s. 6t provides an upper limit on the e7ciency that any classical thermodynamic cycle can achieve during the conversion of thermal energy into work, or conversely, the e7ciency of a refrigeration system in creating a temperature di8erence 9e.g. refrigeration: by the application of work to the system. 6t is not an actual thermodynamic cycle but is a theoretical construct.
+very single thermodynamic system e!ists in a particular state. ;hen a system is taken through a series of di8erent states and (nally returned to its initial state, a thermodynamic cycle is said to have occurred. 6n the process of going through this cycle, the system may perform work on its surroundings, thereby acting as a heat engine. system undergoing a arnot cycle is called a arnot heat engine, although such a $perfect$ engine is only a theoretical construct and cannot be built in practice.[1]
The arnot cycle when acting as a heat engine consists of the following steps#
1 and of entropy ?=elta 4@>A1BTA1 from the high temperature reservoir.
6sentropic 9reversible adiabatic: e!pansion of the gas 9isentropic work output:. &or this step 9% to ' on &igure 1, / to in &igure %: the mechanisms of the engine are assumed to be thermally insulated, thus they neither gain nor lose heat. The gas continues to e!pand, doing work on the surroundings, and losing an equivalent amount of internal energy. The gas e!pansion causes it to cool to the $cold$ temperature, T%. The entropy remains unchanged. % and of entropy ?=elta 4@>A%BTA% to ow out of the gas to the low temperature reservoir. 9This is the same amount of entropy absorbed in step 1, as can be seen from the lausius inequality.:
6sentropic compression of the gas 9isentropic work input:. 9) to 1 on &igure 1, = to on &igure %: Dnce again the mechanisms of the engine are assumed to be thermally insulated. =uring this step, the surroundings do work on the gas, increasing its internal energy and compressing it, causing the temperature to rise to T1. The entropy remains unchanged. t this point the gas is in the same state as at the start of step 1.
(d) oyle!s law
/oyleEs law 9sometimes referred to as the /oyleF"ariotte law, or "ariotteEs law[1]: is an e!perimental gas law which describes how the pressure of a gas tends to decrease as the volume of a gas increases. modern statement of /oyleEs law is
The absolute pressure e!erted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system.[%][']
"athematically, /oyleEs law can be stated as
where G is the pressure of the gas, H is the volume of the gas, and k is a constant.
The equation states that product of pressure and volume is a constant for a given mass of con(ned gas as long as the temperature is constant. &or comparing the same substance under two di8erent sets of condition, the law can be usefully e!pressed as
The equation shows that, as volume increases, the pressure of the gas
decreases in proportion. 4imilarly, as volume decreases, the pressure of the gas increases. The law was named after chemist and physicist
(f) Charles!s law
harlesEs law 9also known as the law of volumes: is an e!perimental gas law which describes how gases tend to e!pand when heated. modern statement of harlesEs law is# ;hen the pressure on a sample of a dry gas is held constant, the Jelvin temperature and the volume will be directly related.[1] this directly proportional relationship can be written as#
where# H is the volume of the gas T is the temperature of the gas 9measured in Jelvin:. k is a constant. This law describes how a gas e!pands as the temperature increases* conversely, a decrease in temperature will lead to a decrease in volume. &or comparing the same substance under two di8erent sets of conditions, the law can be written as#
The equation shows that, as absolute temperature increases, the volume of the gas also increases in proportion.
(g)The "elvin#$lanc% statement
The JelvinFGlanck statement 9or the heat engine statement: of the second law of thermodynamics states that it is impossible to devise a cyclically
operating device, the sole e8ect of which is to absorb energy in the form of heat from a single thermal reservoir and to deliver an equivalent amount of work.[1] This implies that it is impossible to build a heat engine that has 100K thermal e7ciency.[%]
The second law of thermodynamics states that in every real process the sum of the entropies of all participating bodies is increased. 6n the idealized limiting case of a reversible process, this sum remains unchanged. The increase in entropy accounts for the irreversibility of natural processes, and the asymmetry between future and past.
;hile often applied to more general processes, the law technically pertains to an event in which bodies initially in thermodynamic equilibrium are put into contact and allowed to come to a new equilibrium. This equilibration process involves the spread, dispersal, or dissipation[1] of matter or energy and results in an increase of entropy.
The second law is an empirical (nding that has been accepted as an a!iom of thermodynamic theory. 4tatistical thermodynamics, classical or quantum, e!plains the microscopic origin of the law.
The second law has been e!pressed in many ways. 6ts (rst formulation is credited to the &rench scientist 4adi arnot in 15%) 9see Timeline of thermodynamics:.
Clausius statement
The Lerman scientist
Neat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time.['M]
The statement by lausius uses the concept of Epassage of heatE. s is usual in thermodynamic discussions, this means Enet transfer of energy as heatE, and does not refer to contributory transfers one way and the other.
Neat cannot spontaneously ow from cold regions to hot regions without e!ternal work being performed on the system, which is evident from ordinary e!perience of refrigeration, for e!ample. 6n a refrigerator, heat ows from cold to hot, but only when forced by an e!ternal agent, the refrigeration system. "elvin statement
-ord Jelvin e!pressed the second law as
6t is impossible, by means of inanimate material agency, to derive mechanical e8ect from any portion of matter by cooling it below the temperature of the coldest of the surrounding obCects.['I]
(h) &n air compressor
n air compressor is a device that converts power 9using an electric motor, diesel or gasoline engine, etc.: into potential energy stored in pressurized air 9i.e., compressed air:. /y one of several methods, an air compressor forces more and more air into a storage tank, increasing the pressure. ;hen tank pressure reaches its upper limit the air compressor shuts o8. The compressed air, then, is held in the tank until called into use. The energy contained in the compressed air can be used for a variety of applications, utilizing the kinetic energy of the air as it is released and the tank depressurizes. ;hen tank pressure reaches its lower limit, the air compressor turns on again and re pressurizes the tank. There are numerous methods of air compression, divided into either positive displacement or negativedisplacement types.[1][%]
ccording to the pressure delivered
•
•
•
-owpressure air compressors 9-Gs:, which have a discharge pressure of 1M0 psi or less "ediumpressure compressors, which have a discharge pressure of 1M1 psi to 1,000 psi Nighpressure air compressors 9NGs:, which have a discharge pressure above 1,000 psi
9O: To produce 100K dry steam in an boiler and keep the steam dry throughout the piping system is in general not possible. =roplets of water will escape from the boiler surface due to turbulence and splashing when bubbles of steam break through the water surface. The steam leaving the boiler space will contain a mi!ture of water droplets and steam.
6n addition heat loss in the pipe lines condensates parts of the steam to droplets of water.
4team produced in a boiler where the heat is supplied to the water and where the steam is in contact with the water surface of the boiler contains appro!imately MK water by mass. =ryness fraction of ;et 4team
6f the water content in the steam is MK by mass, then the steam is said to be OMK dry with a dryness fraction 0.OM.
=ryness fraction can be e!pressed#
P @ ws B 9ww Q ws:
91:
where
P @ dryness fraction
ww @ mass of water 9kg, lb:
ws @ mass of steam 9kg, lb:
+nthalpy of ;et 4team
ctual enthalpy of wet steam can be calculated with the dryness fraction P and the speci(c enthalpy hs of $dry$ steam picked from steam tables. ;et steam will always have lower usable heat energy than $dry$ steam.
ht @ hs P Q 91 P : hw
9%:
where
ht @ enthalpy of wet steam 9kRBkg, /tuBlb:
hs @ enthalpy of $dry$ steam 9kRBkg, /tuBlb:
hw @ enthalpy of saturated water or condensate 9kRBkg, /tuBlb:
4peci(c Holume of ;et 4team
The droplets of water in wet steam occupies a negligible space in the steam
and the speci(c volume of wet steam will be reduced by the dryness fraction.
vt @ vs P
9':
where
vt @ speci(c volume of wet steam 9m'Bkg, ft'Blb:
vs @ speci(c volume of the dry steam 9m'Bkg, ft'Blb:
