Company LOGO THERMODYNAMICS The Frs Law and Oher Basc Conceps (par ) Deparmen of Chemcal Engneerng, Semarang Sae Unversy Dhon Harano S.T., M.T., M.Sc.
Have you ever cooked? Equlbrum
Equlbrum (con.) Equlbrum s a word denong a sac condon, he absence of change In hermodynamcs, means no only he absence of change bu also he absence of any endency oward on macroscopc scale Oher defnon, equlbrum s sac condon n whch no changes occur n he macroscopc properes of a sysem wh me. Bu, n mcroscopc properes, he condon s no sac Equlbrum condon all forces n exac balance kondensor hea
Equlbrum (con.) A B Vapor phase Lqud phase Lqud phase = 0 mnue (n a ceran A composon mxures, P, and T) = C mnues (n a ceran B composon mxures, P, and T) Condon : Macroscopc no changes, sac Mcroscopc changes, no sac
Phase Rule When wo nensve hermodynamc properes are se a defne values, he sae of a pure homogeneous flud s fxed. In conras, when wo phases are n equlbrum, he sae of he sysem s fxed when only a sngle propery s specfed 0.35 kpa 373.5 K Changng emperaure wll also change he pressure f vapor-lqud are n equlbrum A mxure of seam + lqud waer n equlbrum
Le s check ou n HYSYS Phase Rule (con.) Go o flud packages Choose H O as seleced componen Choose Peng-Robnson as propery package Choose maeral sream Go o smulaon envronmen
Le s check ou n HYSYS Phase Rule (con.) Se emperaure o 00 o C Se pressure o 0.35 kpa Go o composon, hen fll H O mole fracon wh, hen OK Take bass molar flow kgmole/h
Le s check ou n HYSYS Phase Rule (con.) Wh se he emperaure and pressure, HYSYS auomacally change he vapor phase o be, means he waer n vapor phase
Phase Rule (con.) Cook waer unl bolng pon n mounan When he waer bol Pressure less han am (0.3 kpa) Temperaure also less han 00 o C Wha happen when you bol waer n hgh area such as mounan whch he pressure s less han am (0.3 kpa)
Phase Rule (con.) Cook waer unl bolng pon n deep blue sea T (K) When he waer bol Pressure more han am (0.3 kpa) Temperaure also ncrease o more han 00 o C Tugas HYSYS : Cek campuran eanol ()+ ar () konsenras mol fracon 0- dengan ncremen 0. (0,0., 0, ds.) Vapor fracon = Pada P = am Bagamana perubahan emperaur, Bua grafknya (mole fracon eanol vs emperaure) Wha happen when you bol waer n hgh pressure area wh pressure more han am (0.3 kpa) x
Degree of freedom of he sysem F N N : number of chemcal speces F : degree of freedom ph : phase Phase Rule (con.) For any sysem a equlbrum, he number of ndependen varables ha mus be arbrarly o esablsh s nensve sae s gven by he phase-rule The phase-rule s nensve propery Example : Varous phase can coexs, mus be n equlbrum Three-phase sysem a equlbrum s a sauraed aqueous soluon a s bolng pon wh excess sal crysals presen. N = 3 (hree phase) are crysallne sal, he sauraed aqueous soluon = (wo chemcal speces) are waer and sal So, degree of freedom F 3
Degree of freedom of he sysem Phase Rule (con.) The nensve sae of a sysem a equlbrum s esablshed when s emperaure, pressure, and he composon of all phase are fxed The phase rule gves he number of varables from hs se whch mus be arbrarly specfed o fx all remanng phase-rule varables The mnmum degree of freeedom for any sysem s zero When F = 0 The sysem s nvaran Equaon becomes N Value of ph s he maxmum number of phase whch can coexs a equlbrum for a sysem conanng N chemcal speces
Degree of freedom of he sysem Phase Rule (con.) For example : The rple pon of waer where lqud, vapor, and he common from ce exs ogeher n equlbrum a 73.6 K (0.0 o C) and 0.006 bar Any change from hese condon causes a leas one phase o dssapear N 3 phase lqud Waer a 0.0 o C 0.006 bar ce vapor
Phase Rule (con.) How many degrees of freedom has each of he followng sysem : a) Lqud waer n equlbrum wh s vapor b) Lqud waer n equlbrum wh a mxure of waer vapor and nrogen c) A lqud soluon of alcohol n waer n equlbrum wh s vapor Answer : a) F N In fac, emperaure or pressure bu no boh may be specfed for a sysem of waer n equlbrum wh s vapor b) c) F N The addon of an ner gas o a sysem of waer n equlbrum wh s vapor changes he characersc of he sysem. Temperaure and pressure maybe ndependly vared F N The phase-rule varables are emperaure, pressure, and he phase composon Fxng he mole fracon of waer n lqud phase auomacally fxes he mole fracon of he alcohol
The Reversble Process A process s reversble when s drecon can be reversed a any pon by an nfnesmal change n exernal condons.
The Reversble Process (con.) When heaed, CaCO 3 decompossed forms CaO and CO When wegh s ncreased, CO pressure s ncreased and CO combnes wh CaO o form CaCO 3 allowng he wegh o fall slowly
The Reversble Process (con.) Summary : A reversble process has he followng condon :. Is frconless. Is never more han dfferenally removed from equlbrum 3. Traverses a successon of equlbrum saes 4. Is drven by forces whose mbalance s dfferenal n magnude 5. Can be reversed a any pon by a dfferenal change n exernal condons 6. When reversed, reraces s forward pah, and resores he nal sae of sysem and surroundngs
Mechancally reversble The Reversble Process (con.) W V V P dv Example : A horzonal pson/cylnder arrangemen s placed n a consan-emperaure bah. The pson sldes n he cylnder wh neglgble frcon, and an exernal force holds n place agans an nal gas pressure of 4 bar. The nal gas volume s 0.003 m 3. The exernal force on he pson s reduced gradually and he gas expands sohermally as s volume doubles. If he volume of he gas s relaed o s pressure so ha he produc PV s consan, wha s he work done by he gas n movng he exernal force? How much work would be done f he exernal force were suddenly reduced o half s nal value nsead of beng gradually reduced?
The Reversble Process (con.) Soluon : The process s mechancally reversble If PV = k, hen P=k/V W V k W PV V V P dv 0.03m 3 PV k ; V V V dv V 0.06 m (4. 0 4000ln 9 Fnal pressure : 5 V k ln V 3 )(0.03) J 4000 J k 4000 P 700000 Pa 7bar V 0.06
The Reversble Process (con.) Soluon : In he second case, a half of he nal force has been removed The gas under goes a sudden expanson agans a consan force equvalen o pressure of 7 bar. Thus V s he same as before and he ne work accomplshed equals he equvalen exernal pressure mes he volume change. 5 W (7.0 )(0.06 0.03) 000 J Ths second case s rreversble, and compared wh reversble one he effcency s effcency 000 9 0.7 or 7.%
Consan V and Consan P Process Energy balance for a homogeneous closed sysem of n moles : d( nu) dq dw Work n mechancally reversble : dw Pd (nv ) Combne hs wo equaon, yeld : d( nu) dq Pd ( nv ) General frs-law equaon for mechancally reversble and closed sysem
Consan V (volume) Process In consan oal volume process, he work s 0, hus he equaon wll be : dq d( nu ) Q n U Thus for a mechancally reversble, consan-volume, closed-sysem process, he hea ransferred s equal o he nernal-energy change of he sysem.
Consan P (Pressure) Process Arrange he equaon below o solve dq : d( nu) dq Pd ( nv ) yeld, dq d( nu) Pd ( nv ) For consan pressure dq d( nu) Pd ( nv) d[ n( U PV )] Where U + PV s he defnon of enhalpy H U PV The equaon become dq d( nh ) Q n H Thus for a mechancally reversble, consan-pressure, closed-sysem process, he hea ransferred s equal o he enhalpy change of he sysem.
Enhalpy Un of enhalpy (H) : energy per mole or un mass Enhalpy s sae funcon due o U, V, and P are sae funcon Enhalp s nensve propery dh H du d( PV ) U ( PV ) These equaon apply o a un mass or a mole of subsance
Hea Capacy Hea has relaon wh s effec on he obec Ths s he orgn of he dea ha a body has capacy The smaller he emperaure change n a body caused by he ransfer of a gven quany of hea, he greaer s capacy C dq dt In fac, here are knd of hea capaces are n common use for homogeneous fluds. Boh are sae funcon There are :. Hea capacy a consan volume (Cv). Hea capacy a consan pressure (Cp)
Hea Capacy a consan volume (Cv) T T V V V V dt C U dt C du T Q C For mechancally reversble a consan volume process T T C V dt n U n Q
Hea Capacy a consan pressure (Cp) T T P P P P dt C H dt C dh T H C For mechancally reversble a consan pressure process : T T C P dt n H n Q
Open Sysem Energy Balance Q m sysem W Frs Law: E(sysem) + E(surroundng) = 0 Per un mass conanng energy: U u zg Toal energy carred ou: m U u zg
Open Sysem Energy Balance d mu d Energy n he sysem can change due o accumulaon or loss : Thus: W Q g z u U m g z u U m d mu d (npu) (oupu)
Open Sysem Energy Balance Work: caused by flud pushng n and ou or pson (W f ) and shaf work (W s ) W f W s W f m PV m PV W npu oupu s W PV m m PV Q g z u U m g z u U m d mu d Remember: PV U H
Open Sysem Energy Balance s W Q g z u H m g z u H m d mu d npu oupu In general: Seady sae: one nle and oule sream: 0 d mu d m m m W s Q z g u H m W s Q z g u H Rae of energy Rae of energy per un mass or mole
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