Purdue e-pubs. Purdue University. Shigeru Koyama Kyushu University. Ryuichiro Yonemoto Hitachi Appliances

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1 Purdue Unversty Purdue e-pubs Internatonal Refrgeraton and r Condtonng Conference School of Mechancal Engneerng 006 Expermental Study on Condensaton of Pure Refrgerants n Horzontal Mcro-n Tube Proposal of Correlatons for Heat Transfer Coeffcent and rctonal Pressure Drop Shgeru Koyama Kyushu Unversty Ryuchro Yonemoto Htach pplances ollow ths and addtonal works at: Koyama, Shgeru and Yonemoto, Ryuchro, "Expermental Study on Condensaton of Pure Refrgerants n Horzontal Mcro-n Tube Proposal of Correlatons for Heat Transfer Coeffcent and rctonal Pressure Drop " (006). Internatonal Refrgeraton and r Condtonng Conference. Paper Ths document has been made avalable through Purdue e-pubs, a servce of the Purdue Unversty brares. Please contact epubs@purdue.edu for addtonal nformaton. Complete proceedngs may be acqured n prnt and on CD-ROM drectly from the Ray W. Herrck aboratores at Herrck/Events/orderlt.html

2 R33, Page Expermental Study on Condensaton of Pure Refrgerants n Horzontal Mcro-n Tube -Proposal of Correlatons for Heat Transfer Coeffcent and rctonal Pressure drop- Shgeru KOYM and *Ryuchro YONEMOTO Interdscplnary Graduate School of Engneerng Scences, Kyushu Unversty 6-, Kasuga-kohen, Kasuga-sh, ukuoka , Japan Phone: , ax: , E-mal: koyama@cm.kyushu-u.ac.jp Shmzu r Condtonng Works, Htach pplances, Inc. Muramatsu, Shmzu-ku, Shzuoka-sh, Shzuoka ,Japan Phone: , ax: E-mal: ryuchro.yonemoto.aa@htach.com BSTRCT Ths paper deals wth the condensaton heat transfer and pressure drop of pure refrgerant n mcro-fn tubes. The correlatons for heat transfer and frctonal pressure drop are proposed usng expermental data for mcro-fn tubes wth dfferent fn dmensons, where test refrgerants were pure refrgerants R, R3 and R34a. The proposed correlatons are developed based on the correlaton for vod fracton mcro-fn tube and the correlaton for pressure drop of sngle phase flow n mcro-fn tube. The predcted results show good agreement wth expermental results wthn the devaton of about 30 % for both condensaton heat transfer and pressure drop. Expermental results were also compared wth prevous correlatons proposed for mcro-fn tube.. INTRODUCTION Mcro-fn tubes are wdely used n heat pump and refrgeraton systems, and the mprovement n heat transfer performance of mcro-fn tubes are stll requred n order to make these systems hghly effcent and compact. In a vewpont of optmzng heat exchangers n these systems, proposng correlatons of heat transfer and pressure drop of refrgerant n mcro-fn tube are effectve. Therefore, many researchers have nvestgated the condensaton and flow bolng of refrgerants nsde many knds of mcro-fn tubes. or the condensaton, Cavalln et al. (99), Kedzersk-Goncalves (997), Yu-Koyama (998), Shkazono et al. (998) and Goto et al. (003) proposed correlatons for the condensaton heat transfer and/or frctonal pressure drop of refrgerant n mcro-fn tube. However, there are stll unsolved problems as, () The vod fracton n mcro-fn tube was estmated usng the vod fracton correlaton proposed for smooth tube n many cases. () Many correlatons for frctonal pressure drop n mcro-fn tube were developed based on the correlatons proposed for smooth tube such as the Colburn equaton, the Blasus equaton. (3) Many correlatons for heat transfer n mcro-fn tube were developed modfyng the correlatons proposed for smooth tube. In the present study, the heat-transfer correlaton proposed by Yu-Koyama s modfed usng correlatons for vod fracton and frcton coeffcent, whch are developed for mcro-fn tube. correlaton for frctonal pressure drop s also proposed. To propose these correlatons, expermental data obtaned by the present authors, Myara (003) and Haraguch (994) are used. Internatonal Refrgeraton and r Condtonng Conference at Purdue, July 7-0, 006

3 R33, Page. TESTED MICRO-IN TUBES. Specfcaton of Tested Mcro-fn Tubes Tables (a), (b) and (c) show the specfcaton of mcro-fn tubes tested by the present authors, Myara and Haraguch, respectvely. In the table, do s the outer dameter, d s the mean dameter whch s the dameter of smooth tube havng the same nner cross-secton area as that of mcro-fn tube, P s the fn ptch, h s the fn heght, γ s the vertex angle of fn, β s the helx angle of fns, n s the number of fns, and η s the enlargement rato of heat transfer surface. Expermental data for mcro-fn tubes lsted n Table are used to develop the correlatons for condensaton heat transfer coeffcent and frctonal pressure drop of refrgerant n mcro-fn tube.. Expermental pparatus The expermental apparatus used by the present authors s a forced crculaton loop by an ol-free lqud pump. The test secton to measure the heat transfer and pressure drop characterstcs n mcro-fn tube s nstalled n the loop. The superheated vapor s suppled to the test secton and condensed n t. The test secton s a 4.4 long double-tube heat exchanger, where the refrgerant flows nsde an nner tube, whle coolng water flows counter-currently n the annulus. The annulus s dvded nto 7 subsectons to measure the local heat transfer rate, refrgerant temperature and refrgerant pressure. The effectve heat transfer length of the frst to sxth subsectons s m long, whle that of the seventh subsecton s 64 m long. The physcal quanttes measured n the present study are as follows: () flow rates of the refrgerant and coolng water, () refrgerant temperature and pressure at the both ends of each subsecton, (3) wall temperature of the nner tube at the central poston of each subsecton, and (4) coolng water temperature at the both ends of each subsecton. Myara and Haraguch used the expermental apparatuses smlar to the present one, and measured the local heat transfer and pressure drop characterstcs of refrgerants n mcro-fn tubes. Table shows ther expermental condtons along wth present expermental condton. Tested refrgerants are R34a, R and R3. 3. CORRETION O RICTION PRESSURE DROP d o Table Dmensons of Mcro-fn Tube. (a) Present data d p h γ β n g η d o (b) Reference: Myara's data d p h γ β n g η (c) Reference: Haraguch's data d p h γ β n g d o η Table Expermental condtons. (a) Present data Tube Type Helcal mcro-fn tube Refrgerant R34a P n (MPa).. G (kg/(m s)) T n ( o C) 46 (b) Myara's data Tube Type Helcal mcro-fn tube Refrgerant R P n (MPa).-.94 G (kg/(m s)) T n ( o C) 30-0 (c) Haraguch's data Tube Type Helcal mcro-fn tube Refrgerant R R34a R3 P n (MPa) G (kg/(m s)) T n ( o C) Internatonal Refrgeraton and r Condtonng Conference at Purdue, July 7-0, 006

4 R33, Page 3 3. Data Reducton for rctonal Pressure Drop To obtan the fractonal pressure drop through each subsecton, the pressure drop due to momentum change, ΔP estmated from the followng equaton ΔP M G x = Δ ξρ G ( x) ( ) ξ ρ where G s the mass velocty, x s the vapor qualty, ρ s the densty, ξ s the vod fracton, and subscrpts and denote vapor and lqud, respectvely. The vod fracton ξ n mcro-fn tube s estmated by the followng correlaton of Koyama et al. (00), whch was proposed based on the expermental data on the vod fracton n mcro-fn tube. 8 00( ρv ρl ξ = 0. 8 ξ 9 x ) ξ () Smth In the above equaton, ξ Smth s the Smth correlaton (97), and ξ Homo s the vod fracton of homogeneous two phase flow. rctonal pressure drop through each subsecton, Δ, s calculated from the measured statc pressure drop, ΔP, and the pressure drop due to momentum change, ΔP M, as ΔP P T M Homo M, s = ΔP ΔP (3) 3. Correlaton for rctonal Pressure Drop In the present study the frctonal pressure drop s attempted to be correlated by the ockhart-martnell parameters as ΔP ΔP x ρ μ Φ =, Χ tt = Δz Δz x (4), () ρ μ where Δ z s the axal length between the neghborng pressure ports, ( Δ P Δz) s the pressure drop when only the vapor component flows n tube, and μ s the vscosty. The value of ( Δ P Δz) n equaton (4) s defned as where the frcton coeffcent, Φ (-) 0 f Φ v =.0. (r 0 ) (χ tt ) :r =3.0 [-] :r =8.0 [-] ΔP G x = f Δz d ρ 9, s estmated by the Carnavos correlaton proposed for sngle phase flow nsde Present data R34a P=.(MPa) P=.(MPa) G = 00 (kg/(m s)) G = 300 (kg/(m s)) G = 400 (kg/(m s)) G = 40 (kg/(m s)) G = 00 (kg/(m s)) Φ (-) 0 G=0(kg/(m s)) G=00(kg/(m s)) G=300(kg/(m s)) Φ v =.0. (r 0 ) (χ tt ) :r =3.0 [-] :r =8.0 [-] R R34a R3 Haraguch data () T (6) χ tt (-) (a) Present data g. Relaton between Φ and χ tt χ tt (-) (b) Haraguch s data Internatonal Refrgeraton and r Condtonng Conference at Purdue, July 7-0, 006

5 R33, Page 4 low-fn and mcro-fn tubes (980). The followng correlaton s obtaned based on the present expermental data. where r s the roude number defned as where g s the gravty acceleraton. 0 Φ =. r Χ tt ( ρ ρ ) r = G g d ρ (8) g. shows the comparson between the expermental data and the correlaton expressed by equaton (7), where gs. (a) and (b) llustrate the present results and Haraguch s results, respectvely. Equaton (7) correlates the present data well, whle t does not predcts Haraguch s data well. Haraguch s data are scattered over wde area on the graph. Ths suggests that errors of hs measurement n pressure drop are relatvely large. Therefore, hs data were not referred when equaton (7) was obtaned. 4. CORRETION O HET TRNSER COEICIENT 4. Data Reducton for Heat Transfer Coeffcent The heat transfer rate n each subsecton, Q, s calculated as Q = W C c Pc ΔT where Wc and C Pc are the mass flow rate and the specfc sobarc heat of coolng water, and Δ Tc s the temperature change of coolng water n each subsecton. The heat transfer coeffcent, α, and the sselt number,, are defned as α Q = π d η Δz T T, α d = (0), () λ H ( ) sat w where η s the area enlargement rato, Δ z H s the effectv e heat transfer length, T sat s the saturaton temperature, and T w s the nner wall temperature. T sat s obtaned from the measured statc pressure usng the equaton of thermodynamc state, and T w s estmated from the measured outer wall temperature usng the radal heat conducton equaton n the tube wall. The vapor qualty, x, s also calculated from the energy conservaton equaton n each subsecton. c 4. Correlaton for Heat Transfer Coeffcent Yu-Koyama (998) proposed the correlaton for heat transfer coeffcent n mcro-fn tube, whch s functonally expressed by the combnaton of the forced and natural convecton condensaton terms as m m ( ) m = () where s the forced convecton condensaton term, N s the natural convecton condensaton term, and m s the exponent. In ther correlaton, the vod fracton n mcro-fn tube s estmated usng the vod fracton correlaton proposed for smooth tube, and the correlaton for frctonal pressure drop used n calculaton of s based on the Colburn equaton for smooth tube. Therefore, n the present study, the Yu-Koyama correlaton s modfed based on the vod fracton correlaton proposed for mcro-fn tube and the correlaton for frctonal pressure drop expressed by equaton (7). rom the turbulent lqud flm theory, the forced convectve condensaton term s expressed as N * = Re T Pr ( 3) * where Re s the lqud R eynolds number, Pr s the lqud Prandtl number, T s the dmensonless temperature dfference between the vapor-lqud nterface and the tube wall, and ther defntons are shown as (7) (9) Internatonal Refrgeraton and r Condtonng Conference at Purdue, July 7-0, 006

6 * ρ τ w ρ d Re =, μ The wall shear stress τ w n equatons (4) and () can be expressed as w T τ = Φ τ w ρ ( Tsat Tw ) ( η π d Δz ) H R33, Page ρ Cp = (4), () Q f G x ρ Substtutng equatons (4), () and (6) nto equaton (3), the followng equaton s obtaned. where Re s the lqud Reynolds number defned as = f (6) ρ x Pr Re Φ (7) ρ x T Re ( x) μ = G (8) d On the other hand, the natural convectve condensaton term, N = G ( η, Bo) N Ga Pr H ( ξ ) Ph, s assumed to be expressed as where Bo, Ga and Ph are the Bond number, the Galleo number and the phase change number, respectvely, whch are defned as Bo 3 = ( P t) d g ( ρ ρ ) σ, Ga = g ρ d μ, Ph = C P ( Tsat Tw ) h 4 (9) Δ (0), (), () where P s the ptch of mcro-fn, t s the wdth of mcro-fn tp, σ s the surface tenson, and Δ s the latent ( ) heat. In equaton (9), G η, Bo s the functon expresses effects of area enlargement and surface tenson of lqud n groove between mcro-fns, and H ( ξ ) s the functon whch expresses effect of thck lqud flm flowng at the bottom of tube. To obtan the optmum correlaton for heat transfer coeffcent n mcro-fn tube, addtonal assumptons are ntroduced as () unctons of Φ and f n equaton (7) are gven by equaton (7) and the Carnavos correlaton, respectvely. nct H ξ n equaton (9) s the same as that of smooth tube, that s, () u on ( ) exp 000 R34a P=. G = 00 G = 300 G = 400 G = 40 G = 00 P : (MPa) G : (kg/(m s)) P=. p ex 000 R P=.~.94 (MPa) G=00~400 (kg/(m s)) G = 00 : G = 300 : G = 400 : h y 00 30% -30% 00 30% -30% cal cal (a) Present data g. Comparson of exp and cal (b) Myara s data Internatonal Refrgeraton and r Condtonng Conference at Purdue, July 7-0, 006

7 Table 3 Devatons between exp and cal R33, Page 6 Expermental Data Source Myara Haraguch Present study Overall mber of orgnal data Resdual Er Er B Er Er B Er Er B Er Er B Present eqn Cavalln et al Kedzersk-Goncalves Yu-Koyama Shkazono et al Goto et al Er = n n k = cal, k cal, k exp, k where n s number of expermental data., Er B = n n k= BS ( ξ ) ξ 0 ( ξ ) ( ) cal, k cal, k exp, k { 8.9 } ξ ( ξ ) H = (3) Therefore, the parameter / T n equaton (7) and the functon G η,bo n equaton (9) should be determned together wth the exponent m n equaton (),. Usng the expermental data of present study, Myara and Haraguch, optmum value of exponent m, optmum functons of Pr / T and G ( η,bo ) are determned by the tral and error. The results are as follows. Pr ( ) m =, Pr. 0 η =, G (, ) T Re Bo η.98 Bo = (4), (), (6) The fnal correlaton for condensaton heat transfer coef fcent n the mcro-fn tubes s summarzed as where =. f ( ) ρ x Φ Re Pr, ρ x = (7) N N ( ) H ξ =.98 η Bo Ga Pr Ph (8), (9) g. shows the comparson of expermental data and predcted values usng the present correlaton (equaton (7)), where gs. (a) and (b) llustrate results of the present data and Myara s data, respectvely. In both fgures, most of expermental data agree well wth predcted values wthn the devaton of 30 %. Table 3 shows the devaton between expermental data and predcted values usng the present and the prevous correlatons. Er and Er B values of the present correlaton are the smallest among correlatons n Table 3.. CONCUSIONS New correlatons for the condensaton heat transfer coeffcent and frctonal pressure drop of refrgerant condensng n mcro-fn tube are developed usng expermental data obtaned by the present authors, Myara and Haraguch. () The correlaton for frctonal pressure drop s developed usng the vod fracton correlaton n mcro-fn tube and the Carnavos correlaton. () The correlaton for heat transfer coeffcent s developed by modfyng the Yu-Koyama correlaton. MIN NOMENCTURE Bo Bond number Subscrpts d verage nner dameter of tes t Mcro-fn tube (m) c Water Internatonal Refrgeraton and r Condtonng Conference at Purdue, July 7-0, 006

8 R33, Page 7 d o Outer dameter of test Mcro-fn tube (m) cal Calculaton f rcton coeffcent exp Experment r roude number orced convecton G Refrgerant mass velocty (kg m - s - ) n Inlet g Gravtatonal acceleraton (m/s ) qud Ga Galleo number N Natural convecton h n heght (m) out Outlet n mber of groov es sat Saturaton g P p sselt number apor Pressure (Pa) w Insde surface wall n Ptch (m) wo Outsde surface wall Ph Phase change number Pr Prandtl number Q Heat transfer rate of each test secton (W) Re Reynolds number T Temperature (K or o C) t n tp wdth (m) x apor qualty W Mass flow rate (kg/h) α Heat transfer coef fcent (W m K - ) β Spral angle (rad) γ ertex angle of fn (rad) η Enlargement rato of hea t transfer surface area λ Thermal conductvt y (W m K μ Dynamc vscosty (kg m - s - ) ξ od fracton ρ Densty (kg m -3 ) σ Surface tenson (N m - ) Χ tt ockhart-martnell s pa rameter Δz H Effectve heat transf er length of subsecton (m) Δz xal length b etween neghborng pressure ports (m) Two-phase mu ltpler factor Φ - ) REERENCES Carnavos, T.C., 980, Heat transfer performance of nternal fnned tubes n turbulent flow, Heat Transfer Engneerng, ol., No. 4, p Cavall n,., Dorett,., Nlammstener,N., ongo,g.., Rosseto,., 99, Condensaton of new refrgerants nsde smoot h and enhanced tubes, Proceedngs9th Internatonal Congress of refrgeraton,ol. 4, p Got o, M., Inoue, N., Yonemoto, R., Condensaton heat transfer of R40 nsde nternally grooved horzontal tubes, 003, I nternatonal Journal of refrgeraton, ol. 6, p Haraguch, H., 994, Doctor theses, Condensaton of pure refrgerants n horzont al smooth and mcrofn tubes, Kyus hu unversty (n Japanese). Kedzersk,M.., Goncalves,J.M., 997, Horzontal convectve condensaton of alternatve refrgerants wthn a Mcro-fn tube, NISTIR 609, US Department of commerce, p. -8. Koy ama, S., Chen, S., Ktano, R., Kuwahara, K., 00, Expermental study on vod fracton of two-phase flow Internatonal Refrgeraton and r Condtonng Conference at Purdue, July 7-0, 006

9 R33, Page 8 nsde a mcro-fn tube, The Reports of Insttute for advanced Materal Study, Kyushu Unversty, ol., No., p ockhart, Martnell, 949, Proposed correlaton of data for sothermal two-phase, two-component flow n ppes, Che m. Eng. Prog., ol. 4, No., p Myara,., 003, Prvate communcaton. Shkazono, N., Itoh, M., Uchda,M., ukushma,t., Hatada,T., Predctve equaton proposal for condensaton heat transfer coeffcent of pure refrgerants n horz ontal mcro-fn tubes, 998, Trans. JSME, vol. 64, No. 67, p (n Japanese). Smth, S.., 97, od fractons n two-phase flow: correlaton based upon an equal velocty heat model, Heat and lud low, ol., No., p Yu, J., Koyama, S., 998, Condensaton heat transfer of pure refrgerants n mcrofn tubes, Proceedngs Internatonal Refrgeraton Conference at Purdue, p CKNOWEDGEMENT The authors acknowledge gratefully Professor ko Myara of Saga Unversty n provdng hs very useful expermental data. Internatonal Refrgeraton and r Condtonng Conference at Purdue, July 7-0, 006