Thermodynamic analysis of the actual air cycle refrigeration system

Transcription

1 Availabl onlin at Systms Enginring Prodia (2) Intrnational Confrn on Ris and Enginring Managmnt (REM) hrmodynami analysis of th atual air yl rfrigration systm Liu Shngjun a,b, Zhang Zhnying a,b, *, ian Lili a Hbi Unitd Univrsity, angshan 69, China b Earthqua nginring rsarh ntr of Hbi Provin, angshan 69, China angshan Collg, angshan 6, China Abstrat h thrmodynami analysis of th atual air yl rfrigration is rformd. h rsults show that, th fators on th rforman of th atual yl inlud th rssur ratio, th isntroi ffiinis of th rotors, woring tmratur and t.; thr is an otimal rssur ratio for th atual yl; th rfrigrator an b usd for air onditioning nar th otimal rssur ratio. hos fators ar imortant for nginring dsign. 2 Publishd by Elsvir B.V. On ass undr CC BY-NC-ND lins. Sltion and/or r-rviw undr rsonsibility of th Organising Committ of h Intrnational Confrn of Ris and Enginring Managmnt. Kywords : thrmodynami analysis; air yl rfrigration systm; rssur ratio; inginring dsign; sntroi ffiiny. Introdution From an nvironmnt oint of viw air is on of th most intrsting woring fluids for hat ums and rfrigration mahins. [] Air is vrywhr availabl and totally fr. Using air as rfrigrant has normous advantags ovr onvntional rfrigrants, many of whih hav harmful nvironmntal ffts, ar toxi or ar flammabl. Air yl systms hav various advantags inluding inhrnt high rliability and as of maintnan and thy avoid roblms assoiatd with otntial futur lgislation rstriting th us of HFCs. Laag is also not a roblm with air yl systms thy do not aus nvironmntally harmful missions and thir fft on systm rforman an b minimizd by having automati air to-u systms. [2] Howvr, th gnral ida is that air yls suffr from low nrgy ffiiny, and whih has rvntd thir us in onvntional rfrigration. oday s highly ffiint turbo mahinry, whih was not availabl to arly air yl systms, has nhand th rforman of th air-yl. [] Rntly, with CFCs and HCFCs roblm boming rssing issus, air, as a natural rfrigrant, has bn attrating mor and mor attntion. 2. hrmodynami analysis of air-yl rfrigration h orating yl usd with air as a woring fluid is th rvrs Joul or Brayton yl, whih is shown in * Corrsonding author. l.: addrss: zzying@26.om Publishd by Elsvir B.V. On ass undr CC BY-NC-ND lins. Sltion and/or r-rviw undr rsonsibility of th Organising Committ of h Intrnational Confrn of Ris and Enginring Managmnt. doi:.6/j.sro.2.8.9

2 Liu Shngjun t al. / Systms Enginring Prodia (2) 2 6 Figur. h yl onsists of four rosss: air is omrssd in th omrssor ausing its rssur and tmratur to inras(-2); th air is oold by transfrring hat to a ooling mdium in th high-rssur xhangr(2-); th air is xandd in th xandr, doing wor on th surroundings and ausing its tmratur to dras(-4); th rsulting old air is usd to rovid ooling(4-). Hat out wor inut omrssor Hat in (ooling) Fig. Shmati diagram of th air yl xandr t q P P Fig.2 -s diagram of th air yl h thortial yl is ditd on -s (tmratur -sifi ntroy) diagram in Figur 2 as h thortial offiint of rforman () of this yl is dfind as 4 ( 2 ) ( 4 ) 2 ( / ) Howvr, th atual omrssion rosss for most omrssors and th atual xansion rosss for most xandrs ar irrvrsibl olytroi rosss. And thr ar tmratur diffrn and rssur losss in th atual hat transfr ross. hs fators ma th rforman of th atual yl diffrnt from th thortial on. h analysis of th atual yl is basd on th following assumtions: h air is an idal gas. hr ar no rssur losss in th hat xhangrs. h tmratur diffrn in th atual hat transfr ross is tan into aount in th xit tmratur of hat xhangrs. hn th atual yl is ditd on a -s (tmratur -sifi ntroy) diagram in Figur 2 as -2s--4s-. For simliity, th ovrall isntroi ffiiny, whih is a widly usd ffiiny indx for rfrigration omrssors and xandrs, is usd to modl th omrssor and th xandr for th yl. h atual wor r g of air inut to th omrssor for th ross -2 is alulatd as, w = ( 2a - t s () (2) whr is th isntroi ffiiny for th omrssor. h atual wor dvlod r g of air for th xansion ross -4 is givn by, w = = ( - 4a whr is th isntroi ffiiny for th xandr. Nt wor inut to th air yl rfrigration systm is alulatd as w =w -w = ( 2a - )/ - ( - 4a Nt rfrigrating fft r g of air is givn by, q =h -h 4s = ( - 4s ) () (5) (4)

3 4 Liu Shngjun t al. / Systms Enginring Prodia (2) 2 6 h offiint of rforman () of this yl an b alulatd as q w ( ( 2a ) 4s ) ( 4a ) h rlationshi btwn tmratur and rssur for isntroi omrssion ross 2- is 4 a For th isntroi xansion ross -4, h rlationshi btwn tmratur and rssur is 2 a Whr, rrsnt air rssur at inlt and outlt of turbin rstivly, is th ratio of sifi hat at onstant rssur to sifi hat at onstant volum. If,, and,, and rssur ratio ar nown valus, 4s an b dtrmind by using Eqs.() as 4s= -( - 4a ) using Eqs.(6)-(9), of this yl an b alulatd as ( ( ) ) / ( ) (6) (7) (8) (9) So th fators that may influn th of this rfrigrating systm inlud th rssur ratio, th ffiinis of th omrssor and xandr, and th outlt tmraturs of th hat xhangrs.. Rsults and disussion h influn of th rssur ratio on th yl for = = = =.85 is rsntd in Fig.. It is sn that th of th thortial yl dros raidly with th inras of th rssur ratio. Howvr, it is also notd from Fig. that thr xists an otimal rssur ratio ot whih givs a maximum for th atual yl. As th rssur ratio is inrasd, th inrass raidly whn th rssur ratio is lss than ot but drass rlativly slowly whn th rssur ratio is gratr than ot. Morovr, it is vidnt from Fig. that th of th thortial yl is far biggr than that of th atual yl. hrfor, in ordr to imrov th yl rforman, w should try to ma th atual yl los to th thortial on t a /K Fig. Variation of and 4 along with th hang of rssur ratio

4 Liu Shngjun t al. / Systms Enginring Prodia (2) Fig. 4 and Fig. 5 show th fft of th isntroi ffiiny for th omrssor and th isntroi ffiiny for th xandr on th for = = at various rssur ratios rstivly. h inrass raidly as th isntroi ffiiny for th omrssor and th isntroi ffiiny for th xandr is inrasd. h fft of th isntroi ffiiny for th xandr is sn to b rlativly imortant as omard with th isntroi ffiiny for th omrssor =.9 =.8 =.7 = =.9 =.8 =.7 = Fig.4 Imat of on th of th yl Fig.5 Imat of on th of th yl h influn of th inlt tmratur of th omrssor and th xandr on th for = =.85at various rssur ratios is rsntd in Fig. 6 and Fig. 7 rstivly. h is sn to inras gradually with th inras of th inlt tmratur of th omrssor but dro gradually with th inras of th inlt tmratur of th xandr. h fft of th inlt tmratur is sn to b rlativly small as omard with th disussd rssur ratio and th isntroi ffiiny for th omrssor and xandr. h biggr is th rssur ratio, th smallr is th influn = K =298 K =29 K =288 K =8 K = K =8 K =2 K Fig.6 Imat of on th of th yl Fig.7 Imat of on th of th yl 4. Conluding rmars In this ar, a thrmodynami yl analysis of air-yl rfrigration systm has bn rsntd. It is shown that for an atual air yl thr xists an otimal rssur ratio that givs a maximum, whih is diffrnt from th thortial yl. h analysis rvals that th of th atual air yl mainly dnds on th rssur ratio, th isntroi ffiiny of th omrssor and xandr, and th inlt tmratur of th omrssor and xandr. Among ths aramtrs, th isntroi ffiinis of th rotors (th omrssor and th xandr) ar mor influntial, sially th isntroi ffiiny of th xandr.

5 6 Liu Shngjun t al. / Systms Enginring Prodia (2) 2 6 Anowldgmnts h authors anowldg th suort by th Natural Sin Foundation of Hbi Unitd Univrsity (No.z88). Rfrns. Vrshoor MJE, ditor. Guidlins for th aliation and dsign of air yl systms for hating, vntilating and air onditioning in buildings. Aldoorn, h Nthrlands: NOMEP;2. 2. D J G Butlr. Using air for ooling. Building Rsarh Establishmnt Ltd, 2.. Sn S.W., Doran W.J, Artt D.W. Prforman analysis of a fasibl air-yl rfrigration systm for road transort. Intrnational Journal of Rfrigration 25, 28(5): 8 88.