Comparison between two solar tower receivers of different geometry

Transcription

1 Reve des Energes Renovelables Vol. 20 N 4 (2017) Comparson beween wo solar ower recevers of dfferen geomery M. Hazmone 1.2 *, B. Aor 2, M.M. Hada 1 and A. Male 1 1 Cenre de Développemen des Energes Renovelables, CDER B.P. 62 Roe de l'observaore, Bozaréah, Alger, Algera 2 Laboraore de Bomécanqe Applqé e Bomaéra, LABAB Ecole Naonale Polyechnqe d'oran, Oran, Algera (reç le 10 Décembre accepé le 20 Décembre 2017) Absrac - Ths sdy presens a comparson beween wo solar power ower recevers. Selecng he opmm locaon of hosands of helosas, he mos profable ower hegh, recever sze and geomerc shape remans a challenge. In or case, we are neresed n he geomerc shape of he recever. Two solar recevers conneced n seres and he oher n parallel wh dfferen cross-secons and dencal nernal srface areas were sded. We performed a comparson o fnd he rgh ppe connecon ha gves s he good hermal capacy and solar ower effcency. The hea ransfer flds sed are waer vapor and molen sals (NaNO3-NaNO2 - KNO3/NaNO3 - KNO3/LF - NaF - BeF2), he sofware sed for hs sdy s ANSYS CFX wh an nsrcred grd wh cells and sandard (-) rblen model and he flow of hea mposed on he recever bes 0.5 MW. We have been assmed ha hea ransfer occrs only by condcon and convecon. The smlaon resls show he nflence of parameers on he emperare feld beween he np and op of he recever. The nmercal smlaon was done by he ANSYS CFX calclaon sofware and sng a Z620 Worsaon compng machne. The obecve of hs wor s o defne he performance geomery for recevers n solar owers. Résmé - Cee éde présene ne comparason enre de récepers de ors d'énerge solare. En chosssan l'emplacemen opmal de mllers d'hélosas, la haer de la or la pls renable, la alle d réceper e la forme géomérqe resen n déf. Dans nore cas, nos nos néressons à la forme géomérqe d réceper. De récepers solares connecés en sére e l'are en parallèle avec des secons ransversales dfférenes e des srfaces nernes denqes on éé édés. Nos avons effecé ne comparason por rover la bonne conneon de ya q nos donne la bonne capacé hermqe e l'effcacé de la or solare. Les fldes caloporers lsés son la vaper d'ea e les sels fonds (NaNO3-NaNO2 - KNO3 / NaNO3 - KNO3 / LF - NaF - BeF2), le logcel lsé dans cee éde es l'ansys CFX avec ne grlle non srcrée de cellles e modèle rblen sandard (-) e le fl de chaler mposé a bes récepers 0.5 MW. Nos avons spposé qe le ransfer de chaler se prod nqemen par condcon e convecon. Les réslas de la smlaon monren l'nflence des paramères sr le champ de empérare enre l'enrée e la sore d réceper. La smlaon nmérqe es réalsée par le logcel de calcl Ansys CFX e à l'ade de la machne nformaqe Z620 Worsaon. L'obecf de ce raval es de défnr ne géomére performane por les récepers dans les ors solares. Keywords: 3D-smlaon - Solar power ower - Solar recevers - Flow - Hea ransfer. 1. INTRODUCTION Recenly, he ses of solar concenraon echnologes has regsered a bg developmen. In 2013, regsered GW as an eploed power amon, GW as ne realzaon program and GW as annonced solar energy program n USA. Where he crescen dnes solar energy proec and cenral of Ivanpah represen one of bg * m.hazmone@cder.dz 713

2 714 M. Hazmone e al. nvesmen n solar energy n In Chna, bg CSP proecs of 17 GW of prodcon capacy are n realzaon. The generaon of energy by sng he echnology solar power ower has a consdered advanages compared by he oher echnologes. Ths echnology ses consder nmber of moble mrrors (helosas) for reaches he hgh emperares nder hgh concenraon of he solar radaon on recever a op of ower as presened n fgre 1. These mrrors have he same focal pon a he recever. Where he energy of solar rays convered o he hea energy ha sed o feed he rbne relaed by elecrcal generaor o prodce he elecrcy. The effcency of hs sysem relaed by varos desgn parameers and consrans. Serval wors have been done n he am o deermne he bes seleced desgn parameers nder consrans o reach he mamm solar colleced energy. X e al. [3] appled he seady hea and mass ransfer models of he poros meda on solar recevers, also hey analyze he ypcal nflences of he porosy, average parcle dameer, ar nle velocy, and hcness on he emperare dsrbon. Dfferen desgns of recever are es sch s cavy recever s ypes. Ths desgns developed o redce he losses n refleced radaon and ncrease he effcency. In echncal desgns, radave losses are evenally redced o he same order of magnde as he convecve losses [4]. The compley of analyses and he mporan nvesmen n hs feld psh s o se he effcen pacages and mehods o sdy and o predc he losses n appled echnologes. In hs cone, CFD analyss mehods represen one of he bes mehod sed acally. In hs case, n ams o mnmze he hermal losses by ncreases he aac srface, Garbrech e al. [7] nvesgaed a new desgn solar cenral recever by nrodcng of heagonal pyramd shapes, whch are srrond he helosa feld he resls gave a decreases of 1.3 % of he reflecon radaon losses wh hermal effcency of 91.2%. Crocer e al. [6] fond ha conercrren flow seemed o lead o he mos effcen recepor. b hese earler sdes laced some physcs, sch as he effecs of he wndow and re solar rradaon from he helosa feld, and were. Lmed o sragh cylndrcal geomery. In hs wor, we es a recever of a solar ower wh wo dfferen geomeres wh dfferen parameers sch as he flow of hea, hea ransfer flds, and he speed of he enry of he calorfc flds. Fg. 1: Solar power ower

3 Comparson beween wo solar ower recevers of dfferen geomery GEOMETRY DETAILS AND MESHING Ansys CFX sofware (Verson 13) was sed n hs sdy. The geomery of recever s obaned by Ansys Worbench. I have D 2.2 cm of he recever dameer seleced. Wh lengh of L 100 cm and hegh of H 100 cm, (fgre 2 and 3). A non-nform grd sysem s sed o dscreze he governng eqaons, as shown n fgre 4 and 5. In addon, dfferen ess were carred o o sdy he mesh sensvy as shown n Table 1. The bes resls regsered by meshng of erahedral cells for a recever conneced n seres. Ths he meshng by erahedral cells for a recever conneced n parallel. Fg. 2: Fld flow recever conneced n seres Fg. 3: Fld flow recever conneced n parallel Table 1: Meshng resls for boh recevers Case Nmber of nodes (n seres) Nmber of nodes (n parallel) Fg. 4: Mesh of he recever conneced n seres Fg. 5: Mesh of he recever conneced n parallel

4 M. Hazmone e al MATHEMATICAL MODEL Based on he fndamenal eqaons of mass conservaon, momenm, and energy. The seady sae s epressed by: Conny 0 l (1) Momenm ' ' l l g p (2) Energy ' ' p p T C T C 1 T (3) 4. TURBULENCE Afer he ole of he ppe, he change n flow drecon creaed he rblence flow ha have he sgnfcanly nflence on hea ransfer. As nown, he rblence modelng s so necessary n smlaon wors. In he case, he model s sed wh nrodcng he wall fncon n am o analyss he flow near wall. The bondary layer s no resolved by he mesh. The mplemenaon mehod of he model n Ansys CFX 13 was done based on Lander e al. [80] wors and Ansys docmenaon. In am o analyze near he oled, he rblen nec energy ( ) and he dsspaon of he rblen nec energy ( ) are obaned from her ranspor eqaons. Trblen nec energy ( ) G P (4) Dsspaon of he rblen nec energy ( ) c G c P c (5)

5 Comparson beween wo solar ower recevers of dfferen geomery RESULTS AND DISCUSSION In hs sdy, he fl dsrbon s esmaed by assmng ha he solar rays have a normal ncdence from pncal sorce. An energec modelng have been esablshed o deermne he emperare dsrbon n all ransversal ppe secons of he recevers. In all cases, he hea flow eqaon s sed for dfferen emperare vales beween he nle and ole secon, gven by: 4 4 ma 4 mn 4 Tmn T T Q (6) T In addon, he obaned resls of boh solar recevers geomeres (seral and parallel conneced) was compared. The nal and lm condons was oen he n boh sdy case. 5.1 Dsrbon of emperare In order o nvesgae he effec of fl on he solar recevers, nmercal smlaons were performed sng he same confgraons and he same fld. The same nal and bondary condons have been appled for boh sded cases. An nle emperare of 503 K and molen sals (HTF) wh flow speeds of 0.5 m/s have nvesgaed. The obaned resl are presened n fgre 6 and 7. For hese parclar recevers desgn, can be seen ha he srface emperares obaned for he case of he recever conneced n seres are very hgh compared o ha of he parallel conneced recever. In addon, he dfference n emperare beween he wo recevers n 161 C. Ths dfference can be sfed by he fac ha he crclaon of he hea ransfer fld n he case of a recever conneced n seres s very easy compared o ha of he recever conneced n parallel becase he flow does no fnd geomerc obsacles creaed by he connecon n parallel. Frhermore, he fgres (6) and (7) also shows ha he emperare of solar radaon can reach 565 C as mamm vale. Whch represens he mamm emperare operaon of he solar radaon ncden on he recever. (a) solar recever n seres (b) solar recever n parallel Fg. 6: Temperare dsrbon on he be srfaces of he wo ypes recevers

6 718 M. Hazmone e al. (a) Solar recever conneced n seres (b) Solar recever conneced n parallel Fg. 7: The emperare dsrbon a he op of he recever 5.2 Inflence of he speed of he hea ransfer fld on he hermal ransfer Fg. 8: Inflence of he speed of he hea ransfer fld on he op emperare {Recever conneced n seres} Fg. 9: Inflence of he speed of he hea ransfer fld on he Temperare {recever conneced n parallel} I shold be noed ha, n he solar ower, we are neresed o ensre a hgher emperare a he op of he recever o allow he rbne roaon whch gves mechancal energy o he generaor. In hs comparave sdy beween he boh recevers {conneced n seres and n parallel}, we were fond ha he op emperares of he recever conneced n seres are very hgh hen ha of he recever conneced n parallel, despe he change n speed of he hea ransfer fld beween m/s and 1 m/s. Fgres 8 and 9 show respecvely he Q evolon along he lengh of he boh recevers conneced n seres and n parallel. I can be observed ha he velocy of he hea ransfer fld clearly nflences he effcency of he recever. Indeed, he emperare crve always reaches an elevaon a he op of he recever conneced n seres whle, n he case of he recever conneced n parallel he emperare reaches s mamm vales a he mddle regon and a low emperare a he op of he recever.

7 Comparson beween wo solar ower recevers of dfferen geomery Inflence of he hea ransfer fld on he hermal ransfer Fg. 10: Inflence of he hea ransfer fld on he op emperare {recever conneced n seres} Fg. 11: Inflence of he hea ransfer fld on he op emperare {recever conneced n parallel} The sed hea fld nflences drecly on he effcency of solar ower. Tha relaed by he hermal and chemcal proprees and hs ressance a hgh emperares vales. The sals s prodced by sng he hea echanger. The seam prodced feeds a rbne copled by an elecrc generaor. The ses of molen sals s relaed by her hgher emperare as he maor advanage. Tha allows o prodce he seam nder pressre and mprove he global performance. The consderaon of he coolan effec on lqd, for ypes of flds have been esed sch s {NaNO 3 -NaNO 2 -KNO 3 / NaNO 3 -KNO 3 / LF-NaF-BeF 2 and waer}. The fgre (10) and (11) llsraes he obaned nmercal resls of seral and parallel conneced recever respecvely. The bes resls s he resls regsred by sng he hea fld (NaNO 3 -NaNO 2 -KNO 3 ). 6. CONCLUSION CFD smlaon was carred o o nvesgae hea loss of cenral ower solar recever. Egh (08) dfferen cases coverng wo dfferen shapes of recever from flly eernal o fll cavy ype, for dfferen fld veloces ( m/s; 0.1 m/s; 0.5 m/s; and 1 m/s), were consdered for he smlaon and for ypes of fld (NaNO 3 - NaNO 2 - KNO 3 / NaNO 3 - KNO 3 / LF - NaF - BeF 2 and waer). The ocome of he smlaon was hen correlaed o fnd a smplfed model for predcng he hea loss. Accordng o or bblographc sdy on he wor of researchers and academcs on he feld of he solar recpen, and accordng o he nmercal resls obaned from he calclaon sofware Ansys CFX. We noe ha he hea ransfer fld adeqae o he ransfer of hea whn he recever for he power plans s he molen sals of ype (NaNO 3 - NaNO 2 - KNO 3 ) and he geomery whch gves s a good yeld and a hgh emperare a he op of he recever s conneced n seres.

8 720 M. Hazmone e al. NOMENCLATURE 3D, Three-Dmensonal HTF, Hea ransfer fld CFD, Compaonal Fld Dynamcs SPT, Solar power ower, Trblence model T, The mean emperare, K ', Insan flcaon of -velocy drecon, m/s T, Flcaon of emperare, K c and c, are coeffcens 3 2 P, Generaon of he rblen nec energy, Dsspaon of he nec energy D, Hegh, cm L, Lengh, cm, Inle velocy, m/s, Knec energy, Vscosy, g/m.s, Toal G, Generaon of rblen nec energy de o he boyancy force and, Trblen Prandl nmber c p, Specfc hea, J/g.K, Dsspaon of he rblen nec energy and, h and h elemens H, Dameer, cm T, Temperare of fld, K g, Gravy, m/s p, Pressre, Pa, Sysem coordnae (, y, z, y,z) REFERENCES [1] O. Behar, K. Khellaf, and K. Mohammed, 'A Revew of Sdes on Cenral Recever Solar Thermal Power Plans', Renewable and Ssanable Energy Revews, Vol. 23, pp , [2] Repor IRENA, 'Concenrang Solar Power. Cos Analyss Seres', In: Renewable Energy Technologes, Power Secor, Vol. 1, N 2/5, [3] C. X, Zh. Song, Le. Chen, Y. Zhen, 'Nmercal Invesgaon on Poros Meda Hea Transfer n a Solar Tower Recever', Renewable Energy, Vol. 36, N 3, pp , [4] R.K. McMorde, 'Convecon Hea-Loss From a Cavy Recever', Jornal of Solar Energy Engneerng-Transacons of he ASME, Vol. 106, N 1, pp , [5] J.B. Fang, J.J. We, X.W. Dong and Y.S. Wang, 'Thermal Performance Smlaon of a Solar Cavy Recever Under Wndy Condons', Solar Energy, Vol. 85, N 1, pp , [6] A. Crocer and F.J. Mller, 'Copled Fld Flow and Radaon Modelng of a Cylndrcal Small Parcle Solar Recever', In: Proceedngs of he ASME, 6 h Inernaonal Conference on Energy Ssanably, ES Fel Cell , San Dego, CA, <hp://proceedngs.asmedgalcollecon.asme.org/proceedng.asp?arcled= >. [7] O. Garbrech, F. Al-Sba, R. Kneer and K. Weghard, 'CFD-Smlaon of a New Recever Desgn for a Molen Sal Solar Power Tower', Solar Energy. Vol. 90, pp , [8] Scenfc Repor, 'ANSYS', ANSYS, Inc. FLUENT 12.0 Theory Gde, [9] N.Z. Ince and B.E. Lander, 'On he Compaon of Boyancy Drven Trblen Flows n Recanglar Enclosres', Inernaonal Jornal of Hea and Fld Flow, Vol. 10, pp , 1989.