TAP CHi KHOA HOC & CONG N ( ; H E CAC TRI ONG D\l IIQC K\ THU.AT * SO 9
DETERMINE THE CONVECTIVE HEAT TRANSFER COEFFICIENT INSIDE BOILING SECTION OF VERTICAL GRAVITY HEAT PIPE XAC DINH HE SO TRAO DOI NHIET DOI LUU BEN TRONG PHAN SOI
CUA ONG NHIET TRONG TRUONG T H A N G DU'NG
Nguyen Nguyen An, Le Kieu Hiep Trudng Dai hoc Bdch khoa Hd Ndi Din Toa soan 28-0K20I3, chdp nhdn ddng 25-12-2013
TOM TAT
Bai bao de cap den van de xay dwng mo hinh loan hoc cua qua tnnh soi tren mang ben trong ong nhiet trong trwdng co be mat nhan, dat thang dirng. Trong mo hinh nay, sw anh hwang cua irng suit trwcrt tren be mat phan pha din he so trao dot nhiet doi Iwu trong qua trinh soi tren mang se dwac xem xet va danh gia Viec kit hgp 2 qua tnnh soi tren mang va soi ngap cho phep dua ra mot phwang phap ly thuySt xac dmh he so trao doi nhiet ddi Iwu trung binh cua toan bo phin soi Cac kit qua tinh toan dwa tren mo hinh toan hoc dwac xay dwng eo do sai lech chip nhan dwgc so vdi cae eong thirc thuc nghiem dang dwo'c sir dung pho bien hien nay. Day la tien de cho viec nang cao do chinh xac trong tinh toan, thiet ke ong nhiet loai nay.
Jir khoa: Soi ngap, sdi tren mang, ong nhiet.
ABSTRACT
The adicle presents the development of a mathematical model of the film boiling process inside the vedical gravity heat pipe with smooth sudace In this model, the influence of intedacial shear stress between liquid film and vapor flow to convective heat transfer coefficient in the film boiling process will be considered and evaluated. The combination of the flooded and film boiling processes allows to develop a theoretical method to determine the average convective heat transfer coefficient of the boiling section. The calculated results based on this mathematical model have acceptable deviation from the correlation which is widely used today This is a prerequisite for improving the accuracy of the calculation and design for gravity heat pipe
Keywords,' film boiling, flooded boiling, heat pipe Cdc ky hieu sir dung Irong bdi hdo t: Nhiet dp, ["C]
u Toe do, [m/s]
p: Do nhdi dgng luc hgc, [Ns/m^]
8: Do ddy mdng chat Idng, [m]
x: Uhg sudt trugt, p^l/m']
a- He sd trao doi nhiet ddi luu, [W/m^K]
F: Luu luang mdi chat tren Im chieu ngang, [kg/ms]
hfgi Nhiet dn chuyen pha long - hoi, [J/kg]
Re: Tieu chuan Reynold C|,: Nhiet dung rieng ddng dp [J/kgK]
L: Chieu dai vimg sdi [m]
Cdc ky hieu chdn
i: VI tri phdn pha s: bao hda 1: long p: sdi ngdp
\: hai f: sdi tren mang
Ong nhiet la mdt phan tu truyen nhiet cd kha nang truyen di mgt nhiet lupng ldn vdi mot do chenh nhiet do nhd. 6 phdn soi ciia dng nhiet, mdi chdt nhan nhiet va chuyen tir pha long thdnh pha hai. Moi chat chuyen ddng sang phdn ngung do chenh lech dp suat va sau khi nhd m6t lugng nhiet, moi chat dugc ngung tu lai tai ddy. Chdt long ngung tii dugc dua ve phan sdi dudi tdc dgng ciia ngoai luc ma cu th^ la luc trgng trudng ddi vdi dng nhiet trgng trudng Vdn de xdc dinh chinh xac he sd toa nhiet ddi luu khi soi va ngung ben trong dng nhiet la dieu kien tien quyet de ndng cao do tin cdy cua viec tinh toan. thilt kl dng nhiet [1],[2]. Nam 1962, cdng thuc thuc nghiem xac dinh he sd trao ddi nhiet dii luu khi sdi trong dng nhiet ldn ddu tien da dugc de xudt bdi W.M. Rohsenow. Den ndm 1979, Imura dd dira ra mdt cdng thirc thuc nghiem khde cd do
TAP C H I K H O \ HOC & CONG NGHE C \C TRUCfNG DAI HQC K\ THCAT • SO 98-2014 Gs.2 Luu lugng khi \ j hoa tron CO, H2, Thanh phan phan tram theo the tich khf CN: Ndng do khi Nztrong cbai mau CH4 CO, H3, CHjtrong khi san pham C,r„ \ 6 n g do khi san pham sau hoa Iron
TAI LIEU THAIVI KHAO
I Hoang-Luong Pham. Promoting an efficient and clean use of biomass fuels for energy production in Vietnam, The final project report submitted to VLIR-HUT Research Council, April 2007.
2. Nguyen Due Cirdng. Hien trang cac d u an dien sinh khoi tai Viet Nam. Ky yeu Hgi ihdo ve co- che khuyin khich phdt trien dien sinh khdi. ndng lugng tic xie U rdc thdi, Hd Ndi, thdng 5/2013.
3 Ajay Kumar. David D. Jones and Milford A, Hanna. Thermochemical Biomass Gasification. A Review of the Current Status of the Technology, Energies 2 (2009), pp. 556-581.
4. Bhattacharya, S . C , San Shwe Hla and Hoang-Luong Pham. A study on a multi-stage hybrid gasifier-engine system. Biomass and Bioenergy,1\ (2001), pp 4 4 5 - 4 6 0 .
5. K. jaojaruek S. Jarungthammachote, Maria K. B. Gratuito, H. Wongsuwan, S. Homhual Experimental study of wood downdraft gasification for an improved producer gas quality through an innovative two-stage air and premixed air/gas supply approach. Bioresource Technology 102 (2011). pp. 4834-4840.
6. I.-S. Antonopoulos, A . Karagiannidis, L. Elefsiniotis, G. Perkoulidis, A. Gkouletsos. Development of an innovative3-stagesteady-bedgasifier for municipal solid waste and biomass. Fuel Processing Technology, 92 (201 1), pp 2389-2396.
7. Nhuchhen Daya and P Abdul Salam. Experimental study on two-stage air supply downdraft gasifier and dual fuel engine system. Biomass Conversion and Biorefinery , 2, 2012, pp 159-168.
8. Pham Hoang Luang, Nguyen Tien C u a n g vd Vdn Dinh San Thg. Nghien cuu thuc nghiem anh hudng cua che do van hanh den vdi qud irinh khi hoa than ciii tren he thdng khi hda kieu cung chieu cdng sudt nhd. Bao cac tiln dd Nhiem vu KHCN Nghi Dinh Thu. Bp KHCN, thang 5. 2013. 85 trang.
9. Van Dinh Son Tho. Vo Cao Hong Thu, Nguyen Tien Cuong and Pham Hoang Luong.
Characterization of Vietnam biomass fuel properties and investigation of their combustion behavior.
Journal of Science and Technology of Vietnam Technological Universities, No 87, 2012, pp 47-51
Dia chi lien hi--. Pham Hoang Luong - Tel: 04,3868.0406, email: [email protected],vn Vien tien tien khoa hgc va cong nghe, Trudng Dai hoc Bach Khoa Ha Ndi.
Sd 1, Dai Cd Viet, Hai Ba Trung. Ha Noi
TAP CHI KHOA HOC & CONG NGllg CAC TRUONG DAI HQC K\ THI f 1 * SO 9]
DETERMINE THE CONVECTIVE HEAT TRANSFER COEFFICIENT INSIDE BOILING SECTION OF VERTICAL GRAVITY HEAT PIPE XAC DINH HE SO TRAO DOI NHIET DOI LUU BEN TRONG PHAN SOI
CUA ONG NHIET TRONG TRUING T H A N G DU'NG Nguyen Nguyen An, Le Kieu Hiep
Trudng Dai hgc Bdch khoa Hd Ndi Din Tda soan 28-01-2013. cbdp nhan ddng 25-12-2013
TOM TAT
Bai bao di cap den vin de xay du-ng mo hinh loan hoc cua qua trinh sol tren mdng ben trong ong nhiet trong trirang co be mat nhin, d§t thing dirng. Trong mo hinh nay, sw anh hwang cua irng suit trwat tren be mat phan pha den he so trao dot nhiet doi Iwu trong qua trinh soi tren mang se dwgc xem xet va danh gia Viec kit hgp 2 qua trinh soi tren mang va soi ngap cho phep dwa ra mot phwang phap ly thuyet xae dmh he so trao ddi nhiet ddi Iwu trung binh cua toan bg phan soi Cac kit qua tinh toan dwa tren md hinh toan hoc dwac xay dwng eo dg sai lech chip nhan dwgc so vdi cac eong thirc thi/c nghiem dang dirge sir dung pho bien hien nay. Day la tien de cho viec nang cao do chinh xac trong tinh toan, thiet ke ong nhiet loai nay.
Tir khda Sdi ngap, sdi tren mang, ong nhiet.
ABSTRACT
The adicle presents the development of a mathematical model of the film boiling process inside the vedical gravity heat pipe with smooth sudace In this model, the influence of intedacial shear stress between liquid film and vapor flow to convective heat transfer coeffieient in the film boiling process will be considered and evaluated. The combination of the flooded and film boiling processes allows to develop a theoretical method to determine the average convective heat transfer coefficient of the boiling section. The calculated results based on this mathematical model have acceptable deviation from the correlation which is widely used today. This is a prerequisite for improving the accuracy of the calculation and design for gravity heat pipe
Keywords: film boiling, flooded boiling, heat pipe Cdc k}' hieu sir dung trong hdi hdo t: Nhiet do, ["C]
u: Tdc dp, [m/s]
p: Do nhdt dgng luc hgc, [Ns/m^]
5: Dp day mdng chdt long, [m]
T: Uhg suat trugt, [N/m']
a: He sd trao ddi nhiet ddi luu, [W/in-K]
F: Luu lugng mdi chdt Iren Im chieu ngang, [kg/ms]
hfg: Nhiet an chuyen pha Idng - hai, [J/kg]
Re: Tieu chudn Reynold Cp: Nhiel dung rieng dang dp [J/kgK]
L: Chieu ddi viing sdi [m]
Cdc ky hieu chdn
i: vi Iri phan pha s: bao hda I: Idng p: soi ng^p v: hai f: sdi tren mang
I. MO DAU
Ong nhiet la mgt phdn tu truyen nhiet ed kha nang truyen di mdt nhiet lugng Idn vdi mgt do chenh nhiet do nho. 6 phdn sol cua dng nhiet.
moi chat nhan nhiet va chuyen tir pha long thdnh pha hai. Mdi chat chuyen ddng sang phan ngirng do chenh lech dp sudt va sau khi nha mgt lugng nhiet, mdi chdt dugc ngirng tu lai tai day. Chdt long ngung tu dugc dua ve phan soi dudi tac dgng ciia ngoai luc ma cu the la luc trgng trudng doi vdi dng nhiet trgng trudng. Vdn de xdc dinh chinh xdc he sd tda nhiet ddi luu khi sdi va ngung ben trong dng nhiet la dieu kien tien quyel de ndng cao do tin cay cua viec tinh todn, thiet ke 6ng nhiet [1],[2]. Nam 1962. cong thirc thuc nghiem xdc djnh he so trao ddi nhiet ddi luu khi soi trong dng nhiet lan dau tien da dugc de xudt bdi W.M. Rohsenow. Den ndm 1979. Imura dd dua ra mgt cdng thirc thuc nghiem khac co do
TAP CHi KHOA HOC & CONG NGHE CAC TRL'OTVG DAI HQC KV T i n \ r • SO 98-2014 Trong dd:
-«,('.-o
c,
c, =
Pl(Pi-P,)s 4 f tPhuong trinh (11) cho phep xac dinh quan be gida chieu ddy mdng chdt long d va tga do x, lay dgc theo chieu chuyen ddng ciia mang chdt long vd cd goc dugc tinh tir diem bdt ddu cua phan soi, trong vung soi tren mdng. Khi xae dinh dugc chieu ddy mdng chdt long, he sd trao ddi nhiet ddi luu khi sdi trSn mang dugc tinh theo cdng thirc:
at-h/S (12) He so trao ddi nhiet doi luu trung binh tren
doan ong co hien tugng sdi tren mang dugc xac djnh theo cdng thiic sau:
(13) L,
C"''^
2.2. Mo hinh toan hgc ciia qua tnnh sdi ngdp 0' phan ddy ong nhiet
He so trao doi nhiet ciia qua trinh sdi ngap dugc xdc djnh theo cdc cdng thuc thuc nghiem
khac nhau. Cdc cdng thuc na\ c6 the lim thdy trong cdc sd tay tra cuu. Trong nghien ciru nay, de dan gidn. ta su dung cdng thirc thirc nghiem cua M.A. Mikheev [6]:
, ^ „ j = 4 6 . A / " V ° ' (14) trong dd,
+ p la dp sudt mdi chat khi sdi, [bar]
+ A/ ^ /„ - /, Id do qua nhiet, ['^C]
2.3. Ung dung phuong pMp so giai mo hinh toan cua qua trinh sdi tren m^ng b£n trong dng nhilt trgng tru-dng
He phirong trinh (7), (8), (9), (I i) cho phep xdc dinh dugc chieu ddy mdng chdt long lai mdt vi tri x bdt kj. Qua dd, giiip xdc dinh dirge he sd trao ddi nhiet doi luu a^rtgi vi tri x bat ky va he so trao doi nhiel ddi luu trung binh ai tren loan bd chieu dai phan sdi tren mang, xi. cua ong nhiet. He phuang trinh ndy se dugc giai theo luu dd thudt todn dugc dl xudt trong bdi bdo va trinh bdy tren hinb 3 vdi £, la dd chinh xac yeu cdu (i^
= 10-").
Xac amh u„ n theo phuo'ng trinh (8),(9)
Xac dmh u,, t, theo phifong innh (5), (6)
I Xac dinh T, I31 \ = \r Iheo (9) j I Tinh Q,j, - h,, T, nd, I
ci,j, Iheo (I j ) j
' Giai phuong trinh (10) Xi
I dinh5n 't;„'(Qpb/a„b-:.U,V4)/(7[d,)
( End ; i__End j
Hinh 3. Liru dd ihudl todn xdc dmh chieu ddy Hinh 4. Lim dd ihudl todn xdc dinh chiiu ddi cu mdng chdl long lgi vi tri x vimg sdi tren mdng
70
TAP cm KHOA UQV & CONG N<;HE CAC TRl'ONG DAI HOC KY Till .AT * .SO 98 - 2014 0 che do dn dinh, su lien he gifla viing sdi
ngap va viing sdi tren mdng dugc the hien qua phuang trinh cdn bdng chdt. Theo do. lugng chdt long td viing soi tren mang di vao vung sdi ngap se can bdng lugng hai dugc sinh ra trong viing sdi ngdp. Thudt todn lap trinh bdy tren hinb 4 se giup xac djnh chieu dai vung sdi tren mdng ndy.
3. KET QUA VA THAO LUAN De danh gid dd chinh xdc ciia m6 hinh todn, ta se tien hdnh so sdnh cdc ket qua thu dugc vdi cac ket qua tinh todn lu cac cong ihirc ly thuyet va thgc nghiem hien cd.
Xet phdn soi cua mdt dng nhiet trgng irudng, ddi ddng cd chilu dai la I in. dudng kinh trong 0,01 m,su dung mdi chat la nude. Gia thiet nhiet do hoi bdo hoa vd nhiet dg vdch 6ng tuang irng la 100°C va 1 lO^C. Chilu daymang nude di ra khdi vung doan nhiet dugc Idy ban ddu Id S^ =0,00012 m.Su dung cac Ihudl toan dd trinh bdy d tren, ta xac djnh dugc chieu ddi viing soi tren mang va viing soi ngdp tuang ung la
X/ ^ 0,5497 m vd x^ -0,4503 m. Su thay d6i cua chieu ddy mdng nude trong viing sdi tren mang dugc the hien trong hinh 5.
Hinh 5. Phdn bd chieu ddy mdng nude Irong vii sdi tren mdng
,inh 6. Su thay ddi he sd trao ddi nhiet doi luu theo chieu dai phdn .sdi
Ket hgp vdi md hinh sdi ngap, suthay doi cua he sd tda nhiet ddi luu tren toan bp chieu dai vLlng soi dugc the hien trong hinh 6. Trong viing sdi tren mdng, M sd trao d6i nhiet ddi luu tdng ddn theo chieu dai vimg soi va dat gia tri ldn nhdt tai vj tri chuyen tiep gida viing sdi tren mdng vd soi ngap do chieu day mang nude gidm ddn. Bat dau tir vj tri ndy, qud trinh soi ngdp diin ra dan den he so trao doi nhiet ddi luu gidm manh.
Diem khac biet ciia mo hinh todn hgc md bai bao da xay dung so vdi mdt sd cdng thirc thuc nghiem hien co la kha ndng ddnh gid dugc dnh hudng ciia chieu dai viing soi ngap va viing soi tren mdng den he so trao ddi nhiet doi liru trung binh trong phan soi.
De danh gid do chinh xdc ciia md hinh, kit qua tinh loan he sd trao ddi nhiet doi luu trung binh cho lodn bd phdn sdi theo cong thuc thuc nghiem ciia Imura cho trudng hgp lugng nap nho
[7] dd dugc sir dung. Cdng thuc thuc nghiem ciia Imura duac viet nhu sau:
«:„-0,32.-
Irong dd: P^„,,, = \bar la ap suat khi quyen.
Bdng 1 - He sd Irau doi nhiel ddi luu trung hinh cho lodn hd phdn sdi tinh Iheo ind hinh ciia bdi bdo vd cdng thiec thuc nghiem ciia Imura
Chieu ddy mdng nude, S„ [m]
0,00010 0,00011 0,00012 0,00013
He so trao cloi nhiel ilSilim. [W/nrKI Imura
9924,7 Mo hinh
bai bao 9729,6 9353,4 8801,8 8048,1
Chenh inch, [%]
-1.97 -5.76 -11.31 -18.91
TAP CHi KHOA HOC & CONG NGHE CAC TRU•6^'G DAI HOC KV THl'AT * S6 98 - 2014 N h u dugc trinh bay tren bang 1, chenh chieu day mang soi cung nhu he so trao doi nhiet lech giua k i t qud tinh toan he sd trao doi nhiet d6i luu trung binh cho toan bo phdn s6i la khong d6i lim trung binh theo m o binh ciia bai bao va nhd va da dugc ke d i n trong md hinb ciia bai bao.
cong thii'c thuc nghiem cua Imura cho vdi cac ^ ^^j LUAN trudng hap S^, - 0,00010 m vd ^„ = 0,00011 m
i a n l u ' a t l a - l , 9 7 % , v a - 5 , 6 7 % . C b e n h l e c h n a y l a ^ Viec ket hop md binh toan hgc cua qua do mo hinh ciia bdi bao da ke den anh budng ciia trinh trao d6i nhiet khi soi tren mang vd s6i ngdp : ,Tr . ; 1 -1 .. . !••,.- trone nhan soi cua ong nhiet trong truang flat iing suat truol, dan den chieu day mang soi tang ''^"& i"'""' ","' '',"'' ^ • -, f . . . ^ , .•
,, ^ , , , • *;, , - . . * ; • , . I.- u dunii cho phep xac dmh duoc be so trao doi nhiet Ien vd he sd trao doi nbiet doi luu trung binh ". ° ,\^. K. --"- , u ' - ' i u- u- • .. • _ 1 , • • ' ; * - I- u •.- • I, d6i uu kbi soi vai anh h u a n g khong nho cua gidm dl. Cung can luu y a day la hai truong hgp ^lui iuu ^ ^ . , . - x , % , : • , •-, , .1 , ^ . , I ^ . , I l u a n e nao Ket nua so sanh he so trao doi nhiet vira de cap duac tinh cho truong hgp luang nap ' " y ' ^ "^P" '^^'•, " " - 1 , - u • i • i •'
u- • u- 1 r - u . i , " • / : o / ^ s ^ - u ^ t i , - . , ,tA doi UU trung bmh tmh theo iTio hmh CLia bai bao nho va chenh lech khong qua 6% dd cho thay dg _ _ , . , , • - • , u • * . ; . , . . , , . * ' A^^. i/i,; va cong thuc thuc nghiem cua Imura, hien dang tin cay cua mo hmh tmh toan duoc xay dung. Khi va t u t, , • . , . ? • . , , ' ^ luang nap tiing Ien n h u trong 2 truong hop con '^''"''"^f P'?° " ' = " t.°T"^"."P'""'"f " » lai, t h j hien t i l n bang 1, chenh lech gitta Mt qua " ' " I 1 'fa.'^hothay m o h m h d u o c x a y . d t m g t r o n g tinh t o i n theo n,6 h i ^ cua bai bao va theo cong ba' bao <tu dp ttn cay de su d , „ g tro,,g cac tuth thuc thuc nghiem ctia Imura Ien toi -18,91 %. ">»" ^y * " ? ' Bay chtnh la t,en de cho v,ec xay DiJu nay cho thSy anh huong c^a luong nap den ^ung mo h,nh toan hpc hoan chuih cua ong nh.et
trgng trudng.
TAI LIED THAIVI K H A O
I Bin Hai, Trdn Van Vang, Ong nhiet, Nha xudt ban Khoa hpc Ky thudt. Ha Npi (2009).
2. D.A. Reay, P.A. Kew, Heat pipes, Elsevier (2006)
3. N g u y l n Nguyen An, Le K i l u Hiep, Xay dung mo hinh todn hoc cho phdn ngung ciia ong nhiet trgng trudng. Tap chi Cdng nghe Nhiet, S6 98 , Trang 15-18 Ha Ngi (2011)
4. B. Jiao, L.M. Qiu, X.B. Zhang, Y. Zhang, Investigation on the effect of filling ratio on the steady- state heat transfer performance of a vertical two-phase closed thermosyphon. Applied Thermal Engineering, Volume 28, Issues 11-12, Pages 1417-1426(2008)
J. Gung-Huei Chou, Jyb-Chen Chen, A general modeling for heat transfer during reflux condensation inside vertical tubes surrounded by isothermal fluid. International Journal of Heat and Mass Transfer, Volume 42, Issue 12, Pages 2299-2311 (1999)
u. Dang Quoc Phu, Tran Van Phu, Tran The San, Truyen nhiet, Nha xuat ban Gido due. Ha Ngi, 1999 7. S.H. Noie, Heat transfer characteristics of a two-phase closed thermosyphon. Applied Thermal
Engineering, Volume 25, Issue 4, Pages 495-506 (2005)
8 S. Mostafa Ghiaasiaan, Two-Phase Flow, Boiling and Condensation in conventional and miniature systems, Cambridge University Press (2008)
Le Kieu Hiep - Tel: 0982592378 - E-mail: [email protected] Trudng Dai hgc Bach khoa Ha Noi
S6 I - Dai Cd Viet - Hai Ba Trung - Ha Npi
