NGHIEN CUTU - TRAO Ddi
NGHIEN CIJU THLTC NGHIEM DAC TINH LAM VIEC CCiA BO THU NANG LU'CXNG MAT TRCXI
D i DUN NU'QC NONG TAI VIET NAM
EXPERIMENTAL STUDY OF WORKING CHARACTERISTICS OF A SOLAR COLLECTOR TO HEAT V^ATER IN VIETNAM
Nguyin Quoc Uy', Nguyen Nguyen An^ Ta Van Chirong^
'Khoa Cong nghe Nang lugng, Truong Dai hpc Dien luc
^Vien Khoa hpc va Cdng nghe Nhiet - L^nh, Trudng Dai hpc Bach Khoa Hd Npi
TOM TAX
Bdi bdo trinh bdy ket qud nghien euu thuc nghiem ve dac tinh lam viec cua mpt he thong dun nuac nong bdng ndng lucmg mat trai dat tQi thdnh phd Nha Trang, tinh Khdnh Hoa. Muc dich cua nghien euu Id cung cdp cho nguai dpc so lieu danh gid hieu sudt tai thuc dia ctia mpt mdu bp thu ndng luang mat trai kieu ong thuy tinh chan khong dang su diing a Viet Nam. Kit qud nghien cint cho thay hieu sudt tht^c te do duac nho hon so v&i cdc kit qud da duac cong bo doi v&i bp thu ciing loai. Trong gi&i han thuc nghiem, hieu sudt Ion nhdt do duac la 43,85% vd nho nhdt Id 26,78%, trong khi hieu sudt cong bo tuang img la 61,71%o vd 54,16%.
Tn khoa: Bp thu ndng lupng mat trai ong thuy tinh chan khong; Hieu sudt nhiet.
ABSTRACT
This article presents the results of experimental study on characteristics of a solar water heating system that is located in Nha Trang City, Khanh Hoa Province. The aim of this study is to provide figures to evaluate performance of a solar collector, that's used in Viet Nam. The test results revealed that measured performances are smaller than the results were announced for the same class of vacuum glass tube solar collector. In range of experiment, the maximum performance is 43,85% and minimum performance is 26,78%, while results, that were announced are 61,71% and 54,16%, corresponding.
Keywords: Evacuated tube solar collector; Thermal performance. ^
ISSN 0866 - 7056
TAP CHf CO KHf V I £ T NAM, 86 7 nam 2015 www.cokhivietnam.vn
NGHIEN ClJfU - TRAO DOI
l.DATVANDE
Nang lugng mat trdi (NLMT) ngdy cang trd nen huu ich vd khd dung trong nhieu linh v\rc. Xet rieng Imh vyc dun nude ndng, NLMT ciing da c6 sy tang trudng nhanh chdng trong nhiing nam gin ddy. Su tang trudng ndy chinh la dpng luc thiic diy qua trinh nghien ciiu vd sdn xuit cdc he thing thilt bi sii dung nhiet mat trdi. Trong cdc he thdng nay, bp thu NLMT la bp phdn quan trpng nhit, cd dnh hudng quyet dinh din hieu qud cua toan he thdng. Khi tinh todn thiet ke cung nhu tinh toan kiem tra su boat dpng cua cac hS thong thiet bi dun nude ndng bang NLMT thi viec xac dinh hieu suit bp thu la yeu cau bat budc.
6 trong nude, cho den nay, da cd mot sd tac gid quan tam nghien ciiu ve hieu suat cua cdc bp thu NLMT. Tac gia Nguyen Qudn [1] de xuit phuong phdp thuc nghiem de nghien ciiu xac dinh cdc thong sd dac trung cua bd thu kieu tam phang. Tdc gid Hd Dang Trung [2], nghien ciiu thuc nghiem hieu qua ciia bp thu NLMT kieu hop phang mong c6 canh ben trong. Nhdm tdc gid Le Chi Hiep, Hodng An Quoc, Hoang Duong Hiing da chi t^o, thu nghiem, ddnh gid hiSu suit, khd nang cap nhi^t, xay dung phdn mem xac dinh hieu sudt cua cdc bd thu NLMT kieu ong thuy tmh chan khong su dung ong nhiet [3], [4], [5].
Tren the gidi, thai gian gan ddy, da cd nhilu tdc gid nghifin ciiu, danh gid hieu suit bg thu ca bdng ly thuyet Ian thuc nghiem. Mpt sd nghien ciiu dien hinh nhu I. Budihardjo vd G.L. Morrison [7] ddnh gia hieu suat cac thiet bi dun nude ndng bang NLMT bang each do thuc nghiSm tr6n hai he thong thiet hi dung bd thu tdm phang va bp thu ong thiiy tinh chdn khong su d\mg tim phan xa dat tai Sydney, Australia.
Phdn tich bang thuc nghiem hieu suit nhiet ciia cdc bp thu NLMT kieu tam phang vd kieu dng
thuy tinh chan khong d^t tai Dai hpc Padova, Y duoc thuc hien boi E. Zambolin va D. Del Col [8]. Tin-Tai Chow va cdc cdng su [9], danh gid hieu suit ciia cac he thdng dun nude ndng bang NLMT kiln dng thiiy tmh chdn khong vd kieu dng thuy tinh chan khdng cd sii dung dng nhi|t bing mo phong sd va bang thirc nghiem d Hong Kong. Xinyu Zhang va cac cdng su [10], kilm tra bing thuc nghiem hieu suit ciia hem 1000 he thdng thilt bi dun nude ndng gia dung bang NLMT kilu dng thiiy tinh chdn khdng theo cdc tieu chudn ciia Trung Quoc.
Viec nghien ciiu, ddnh gid hieu sudt bp thu NLMT da vd vin dupe nhilu tac gia quan tam thirc hien. Cac cong ty sdn xuit dng thiiy tinh chan khdng ciing nhu cac cdng ty sdn xudt thilt hi dun nude ndng bang NLMT, khi dua san phim ra thi trudng thuong cd cdng bo mot so dac tinh ky thuat cua chiing, trong dd cd hieu suit. Tuy nhien, cau hdi dat ra la: Vdi mpt he thong dun nude ndng bang NLMT cu the d Yiet Nam dat tai mgt dia diem nhdt dinh thi hieu sudt ctia nd se nhu the ndo, cd gidng vdi cdng bd cua nhd san xuit hay khdng? Vi the, viec xay dung dudng hieu sudt ciia mot he thdng bang thuc nghiem trong dieu kien Viet Nam la viec lam can thiet dl cd dinh hudng ban diu cho viec tmh toan thiet ke va tinh toan kiem tra cac h? thdng dun nude ndng bang NLMT, dong thai ciing de so sdnh, danh gid su sai lech giua cong bo ciia nha sdn xudt va thuc tl sii dung.
2. PHirONG PHAP XAC DINH HIEU SUAT BANG THV'C NGHIEM
Hieu suat bd thu NLMT ciing gidng nhu cdc khdi niem hieu suit noi chung, dugc xdc dinh bang ti sd giiia phdn nang lupng huu ich thu dupe so vdi tdng nang lugng dua din bd thu;
Qu (1)
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NGHIEN CUTU - TRAO eOl
Nang lupmg huu ich cua bd thu (cong suat nhiet ciia bp thu) dupe xdc dinh bang hieu ciia biic xji nhiet ma bg thu hdp thu dugc va tdng ton thdt nhipt tu bd thu ra moi trudng. Do nhiet dp cua bg thu 1dm hem nhi?t dp mdi trudng nen ludn cd s\r truyen nhi§t b i n g d i i luu va biic xa tii bp thu ra mdi trucmg xung quanh. Vi vay, tdng ton that nhiet ndy cd t h i dugc tinh bang tich ciia h$ so ton that nhift toan phin cua bp thu vdi chSnh l?ch giua nhiet dg trung binh b l mat bp thu vd nhiet do mdi trudng. Vi thi cdng suit nhiet ciia bd thu dugc xac dinh nhu sau [6]:
Q,=Ac-S~Ac-U^-{t^-t,) (2)
Tuy nhien, theo [1], [6] vi nhiet dp trung binh cua be mat bp thu khd do hoac khd xac dinh bang giai tich n6n de thuan tien ban, ngudi ta dua ra h? sd lay nhiet FR la ti sd giira nang lugng huu ich thuc ciia bg thu va nang lugng huu ich cue d^i dat duge khi todn bd b l mat h i p thu ciia bd thu cd nhiet dp ddng deu vd bang nhiet dp nude di vdo bp thu (tucmg ducmg vdi hieu sudt cua thiet bi trao ddi nhift truyen thdng):
'"•Cpjtfo-lfi)
Ac-[GjiTa)-Ui,itji-t,] (3)
7 = F j , ( r a ) - F j , U i .'fi-
bien dgc lap: T G-r
(cdn dugc gpi la chenh lech nhiet dp don vi). <3 che dp on dinh, neu xem cdc thanh p h a n f ^ , ( z ' a ) , Ui\a hang sd thi hieu sudt la ham bac nhdt vd diem cat true tung chinh Id tich s6 F g -(ror), dat dugc khi bg thu khdng cd ton that nhiet (nhiet dp nude di vao bp thu bing nhiet dp mdi trudng), con thanh phinFj^ Uilk do doc ciia dudng hieu suat. c a c dai lugng nay cdn dugc gpi la thdng sd dac trung hay dac tinh cua bp thu. Thirc chat cdc dai lupng nay khdng phai hang sd nen cdc diem thuc nghiem (gia tri hieu sudt tdc thai) se khong n i m tren 1 dudng thang ma phan bo rdi rac. Khi coi he sd ton thdt nhiet toan phdn U^ phu thugc nhiet dp theo quan he bac nhat thi cd the bieu dien hieu suat theo ham bac hai cua T*:
' 7 - ' 7 o - « i -
•{r-r
(6)De tinh todn hieu sudt ttieo cdng thiic (6) thi cdn xdc dmh cac he sd TJQ , a^, a^- Dieu ndy se dugc thuc hien bang each hdi quy cdc diem do thuc nghiem hieu suat tiic thai tren do thi. Cdc gid tri thuc nghiem hieu sudt tiic thoi dugc tmh theo cdng thiic (7):
Tu do, xac dinh cdng suat bp thu theo he sd liy nhiet vd nhiet dp nude vdo:
Qu=Ac -Fji [GJ • ( r « ) - ( 7 i -{tji -tj\ (4) Hi$u suit bg thu vi th6 se dugc bieu dien d dang khac:
'"•Cp-jt/o-tfl)
(7)
Tren co sd cdng thiic (7), thdng qua thuc nghiem do luu lupng nude, nhiet dp nude vao va ra khdi bp thu, tong xa tren mat phang bd thu thi se xdc dinh dupe hieu sudt tiic thoi cua bg thu.
(5)
Nhu vay, hi^u sudt bp thu la ham so ciia
ISSN 0866 - 7056
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NGHIEN CUrU-TRAODOl
3. M 6 T A H$ T H 6 N G T H I E T B | T H V C NGHIjM
" ^ I tuan
• (w) Luu lupng ke hodn Nude nong
sudyng © Cam biln nhi^t dg
Nuoc lanfa bo sung Hinh 1: Sa ^ nguyen ly he thong thiet bf thuc nghifm
Hp thdng dun nude ndng bdng NLMT nghien ciiu cr day dugc ciu thanh tix 27 bg thu kieu ong thiiy tinh chdn khdng l o ^ cdng n g h i ^ , dugc chia lam 2 nhanh vdi sd lugng b$ thu trong mdi nhanh tuong ling Id 18 vd 9. Nude nong tii hai nhdnh nay dugc dua v l binh chiia cd thi tich 30 m^. Khi khdng CO hue X9 m^t trdi ho^ic khi biic x^ m^it trdi khong du thi se dung kit hgp vdi bom nhiet d l dun nude ndng. So do nguyen ly h^ thong va b l tri thilt bi dugc thi hipn nhu tren hinh 1 va hinh 2.
[ • [ • b t=
U>^£UBB.UkW>• M ^ n s BlLIUtW
Hinh 2: Sa do bd tri bg thu cua h^ thong
ISSN 0866-7056
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NGHIEN CljrU-TRAOD6l
Cac d|c tinh ky thuat co ban cua he thdng bp thu NLMT dugc trinh bay trong bang I.
Bdng 1. Thong so ca bdn cm he thdng bp thu NLMT
T T 1 2 3 4 5 6
Thong so ky thuSt So luong bo thu
Ki£u bo thu: KiSu xuong ca
So lugfng 6ng thuy tinh chan khong trong 1 bo thu Kich thuoc ong thuy tinh (duong kinh trong/ngoai/chi§u dai) Goc nghieng cua bp thu
Goc vT do lap dat bo thu
Giitrj 27 50 47/58/1800 mm
P = 20'' 9 = 12°
Cac dac tinh ky thuat ciia thiet bi do dugc mo ta trong bang 2.
Bdng 2. Dgc tinh ky thuat cua thiet bi do TT
1 2 3 4
Lo^i thiit bi Do nhiet do PtIOO Do nhiet do PtlOO
DoBXMT Do luu lupng nuoc
KyUSu
(
tr(Mi)Gg
Pham vi do {K100"C (>+100»C (H1800W/m^
0*999,99999 m=/h
Sai so
±0,5
±0,5
±5%
CCX1,0
Chuc nang Do nhi$t dp moi trudng
Ek) nhi€t dd nu6c Do cuong dp BXMT Do Itm luong nuoc sii dyng Cdc thiSt bi do dugc kSt noi vdi he thong
tu ghi so lieu cho phep ghi nhan sir thay ddi cua cac thdng sd 1dm viec vdi tan suat lOs/lan. He thong tu ghi dung cdng nghe AD converter va Digital logger tich hgp trong PLC. Cac bp AD converter dugc lua chpn Id 3 md-dun md rgng cd ky hieu DVP-04AD de dang tich hgp vdi md-dun vi xu ly cd ky hieu DVP-14SS2, tit ca do hang Delta sdn xuat. Mec ket noi giiia cdc md-dun dugc thgc hien hoan todn tu dpng thong qua cac BUS kit ndi tieu chuan do hang Delta thiet Idp. Tren co sd cdc ket ndi ndy, md-dun vi xu ly DVP-14SS2 cd thi viia dilu khien toan bp he thdng vua giam sat su thay ddi cua tat cd cae kenh dii lieu Analog do cdc md-dun md rpng DVP-04AD cung cap. Ngoai viec trang bi cac md-dim dl do va xu ly sd lieu nhu da neu, trong he thing cdn sii dung mdn hinh cdm iing HMI (model AS57-BSTD) cd tich hgp chiic nang tu dpng ghi tit ca cdc sd lieu do dugc ra cac phuang
tien ky thuat so thdng d\mg nhu die nhd SD hay USB.
4. KET QUA VA THAO LUAN
Thdng qua thuc nghiem, chiing tdi da xac dinh dugc cac gia tri hi€u suat tiic thdi d nhieu thoi diem do khac nhau trong thang 3/2014. Cac ket qua nay dugc trinh bay tdm tit tren do thi
hinh 1
O.OlS 0.030 0.045 0.060 0.075
Hinh 3: Ehtang cong hieu sudt cda bg thu xdc dinh bdng thuc nghi$m
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NGHIEN CLUU-TRAO Ddi
Bang viec h6i quy cac gia tri do thvtc nghiem, ta CO cong thiic tinh hieu suat ciia bg thu;
^ I
(8)Theo quy luat thdng thuong, khi dd chenh nhiet dp giiia nude vao vd moi trudng tang len hoac cudng dp biic xa gidm xudng, tiic Id chenh lech nhiet dp don vi J = 'fi- tang thi hieu suat bp thu phdi giam. Tuy nhien, cdng thiic (8) lai cd he so cua phan bac nhat khdng mang ddu dm nhu thuong le nen cd mot sd trudng hgp hieu suit tang khi T* tang. Gidi thich su bdt thuong nay la do he thing dun nude ndng 6 ddy cd su' dung bom nhiet d l duy tri nhiet dp nude ndng trong binh chiia nen cd thi vdo cdc thoi dilm dd {t^ -^^)tang nhung G^ lai ciing tMig lam cho ton thit nhi6t todn phin U^ cua bp thu gidm di.
So sanh dudng hieu suit xdc dinh dupe bang thuc nghiem vdi cdc dudng hieu suit chuin da dugc cdng bd [6] thi hien tren hinh 4.
Ducmg hieu suit bp thu dugc xdc djnh ' bing thyc nghiem cd dp d i e khd gidng vdi dudng hieu suat chuan cdng bd cua bp thu kilu 6ng thiiy tinh chdn khong, tuy nhien nd n i m phia dudi, tiic Id gia tri hieu sudt thuc nghiem nho horn. So sanh cu the sai leeh tuyet ddi giua hieu suit do thuc nghipm va hifu sudt chudn cdng b l ciia bp thu ong thuy tinh chan khong d m^t s l vj tri dugc trinh bay trong bang 3.
Bdng 3. So sdnh sai lech
^ 0 . 7 S 0.6
0.4 0 3 0 2 0.1 0
-•-:.^
= i = L _
-%;-
, 1
I i
• - - - ^ • ^ _
"^ ! 1
_ ^ -' '-;:
0.03 0.045 T--(tjrlJ/Gr
0 06 0-075 [m^.KAV]
TT 1 2 3 4 5 6 7 8 9 10
^ '[ Or )
0.01815 0.02010 0.02224 0.02605 0.03282 0.03926 0.04700 0.05708 0.06891 0.07640
Hieu suat do
0.4385 0.4383 0.4377 0.4354 0.4277 0.4161 0.3966 0.3622 0.3089 0.2678
HiSu sudt chuan 0.6171 0.6151 0.6127 0.6085 0.6007 0.5930 0.5832 0.5697 0.5529 0.5416
Sai l^ch tuyp doi 0.1786 0.1768 0.1750 0.1731 0.1730 0.1769 0.1866 0.2075 0.2440 0.2738 Hi§u suat do thuc te nhd hon hieu sudt da dugc cong bd, ngodi viec cd thi do chit lupng dng thuy tinh khong gidng nhu loai chuin, cdn cd the do viee ket ndi cdc bp thu trong he thing chua ddm bdo duge su ddng d i u v l luu lupng nude qua timg bp thu, nen d cae bd thu cd luu lupng nho hon se cd hieu suit thip han.
5. KET LUAN Hinh 4: So sdnh dudng hiiu sudt thuc nghiem vai
cdc duang hieu sudt dd duac cong bd
Bq thu khongco vo hoc; ^ ^^* ^^^ ^^ ^^Y ^^B dupc dudng hieu Bp thu ong thuy tinh chdn khong, ^^^^ ^d thu NLMT kieu dng thuy tinh chdn Bd thu tdm phang khong co Idp hdp thu chgn loc; khdng tuan hodn cudng biic cd kich thudc dng
Dudng thiic nghiim; 47/58/1800 mm tren co sd so lieu thuc nghiSm B6 thu tdm phang. vdi he thing thilt bi dat tai thdnh phd Nha Trang,
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NGHIEN Cljru-TRAO Ddi tinh Khanh Hoa. Cac sd lieu thu thap dugc tii he thing thilt bi thue nghiem dam bao dp chmh xac yen cau trong thuc te ky thuat, la co sd tham khdo dinh hudng cho viec tinh todn thilt ke hoac tinh toan Idem tra cac he thdng dun nude ndng bang NLMT kilu tuong tu. Trong tuong lai, de cung cdp nguon dii lieu tham khao phong phu hon, chiing toi se tiln hanh lam thuc nghiem va xdc dinh hieu suat cua cac bg thu su dung dng thuy tmh chdn khdng cd kich thudc khac hien cd tren thi trudng vd lap dat 6 mpt so dia phuong khac nira.
Dua tren npi dung bdi bdo, cd the xay dung phuong phdp ddnh gid he thing tuong tu dp dung cho bat ky san pham dun nuoc ndng bdng NLMT ndo tai Viet Nam, phii hgp vdi tinh hinh th\rc tl thi trudng, trang thiet bi ky thuat, khd nang tai chinh,... cua chiing ta.
Nghien ciiu dnh hudng ciia su che khuat giiia cac Ing, each kit ndi giiia cac bd thu hay luu lugng ddng chdy den hieu suat chung cua toan bp he thdng la cac hudng nghien ciru tiep theo ciia nhdm nghien cuu.<*
Bdng cdc ky hieu su dung trong bdi:
K y Y n ^ u a
hieu '
Ac iDien tich b l mat bg thu Cp ;Nhiet Himg naag cua midic
Don vi m2 J/(kgK) Fs {He so lay nhiet ciia bp tiiu
i>^ng suat hCtc xa toan phdn
GT •
: tren mat pdiang bg &u _ :Luu higng midc qua bp Ihu Q, ;C&ig suat nhiet cua bg thu
^Biic xa duac h i p tim tren I S -
jn^ bg tim troog 1 giay
W/m2 kg/s
W W/m2
K y !
Y nghia hieu
ta Miiet do mdi trudng (if iNhiet do nuoc vao bg thu tfo Nhiet dp nude xa khdi bg tim
[Nhiet do trung Innh b l mat bo '"• ilhu
^He so t6a Ihit nhiet 1x)an pli3n t/i : " •
ictiabplbu
Don vj
°C
»C
»c
»c
W/(m2X) Tj iHieu s u ^ bo Ihu
(zK^ ;Tich so tray&biap thu
Ngay nhan bai: 18/6/2015 Ngay phan bien; 19/7/2015
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NGHIEN cut) - TRAO D 6 I
Tai liSu tham khao:
[1]. Nguyen Quan (1998); Phuangphdp thuc nghiem xdc dinh cdc dac tinh bp thu ndng lupng mat trai. Tap chi Khoa hgc va Cong nghe nhift, sl 6/98, trang 9-11.
[2]. Ha Dang Tmng (2002); Nghiin euu hieu qud cua bg thu ndng lupng mat trdi kieu hpp phang mong co canh bin trong; Tap chi Khoa hgc va Cdng nghe Nhiet, s l 11/2002, trang 16-19.
[3]. Hoang An Quoc, Le Chi Hi?p, Hoang Duong Hiing, 2007; Che tao vd thu nghiim ong nhiet mat trdi loai chdn khong trong diiu kien He? A'am; T^p chi Khoa hgc va Cong nghe Nhiet, so 74*3/2007, trang 8-11.
[4]. Le Chi Hiep, Hoang An Qu6c, Hoang Ducmg Hiing (2009); Ddnh gid khd nang cdp nhiet cua cdc Collector mat trdi kiiu ong nhiet; T?ip chi Khoa hpc va Cong nghe Nhift, s6 87*05/2009, trang 5-7.
[5], Hoang An Quic, Le Chi Hi?p, Hoang Duong Hung (2010); Xdy d^mgphdn mem tinh todn cdc thdng so dgc trung cua bp thu ndng lugng mat trdi kiiu dng nhiet; Tap chi Khoa hpc va Cong nghf Nhiet, s6 91*01/2010, trang 19-22.
[6]. John A. Duffie and William A. Beckman, 2006. Solar Engineering of Thermal Processes, Third Edition.
John Willey & Sons.
[7]. I. Budihardjo, G.L. Morrison, 2009. Performance of water-in-glass evacuated tube solar water heaters.
Solar Energy 83 (2009) 49-56.
[8]. E. Zambolin, D. Del Col, 2010. Experimental analysis of thermal performance of flat plate and evacuated tube solar collectors in stationary standard and daily conditions. Solar Energy 84 (2010) 1382-1396.
[9]. Tin-Tai Chow, et al., 2011. Performance evaluation of evacuated tube solar domestic hot water systems in Hong Kong. Energy and Buildings 43 (2011) 3467-3474.
[10]. Xmyu Zhang, et al., 2013. Experimental investigation of the higher coefficient of thermal performance for water-in-glass evacuated tube solar water heaters in China. Energy Conversion and Management 78
(2014)386-392.
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