由於具有高能量密度及環保無污染的特性，氫氣已成為未來能源系統中最具有潛力的能量載體之一，但是在儲存與運輸上仍有許多需要克服的問題。在操作條件及安全性的考量下，金屬氫化物是一個相當適合作為氫氣儲存與運輸的方法，也有許多研究團隊與學者投入新材料的開發與系統最佳化的研究。由於金屬氫化物的吸放氫行為是一伴隨複雜熱質傳與吸放熱的可逆化學反應，所以操作條件的控制與整體系統設計皆會影響其供應氫氣的特性。本論文整合現有理論基礎，建立了金屬氫化物(LaNi5)的吸放氫行為計算模型並與其他學者所發表的實驗數據進行驗證，進而探討系統設計與操作參數對系統性能之影響等重要研究課題。
本論文分為兩個主題，第一部份我們探討當金屬氫化物反應器的出口壓力為二階曲線下降時會如何影響氫氣釋放流率的平均值與穩定性。為此，我們建立一數學模型來計算裝載鑭化鎳合金之圓柱狀反應器內的釋氫反應動力式、質量守恆式、動量守恆式和能量守恆式。在固定初始及最終的出口壓力值下，降壓時間及初始降壓斜率為可控制的參數。經由有系統地分析後，我們發現在指定的降壓時間下增加初始降壓斜率會造成平均釋氫流率上升，並且存在一特定初始降壓斜率值會使釋氫流率變異數產生最小值。換言之，可藉由控制金屬氫化物反應器的出口壓力為手段來改善其釋氫行為以得到較穩定的流率，進而在整體氫能系統的流量控制元件設計上可得到一定程度的簡化。
於第二部分，我們探討在內部裝設有金屬發泡結構的金屬氫化物反應器中，其金屬發泡結構的體積比率(ϕ_mf)會對吸氫速率產生如何的影響。計算結果顯示若固定反應器內金屬氫化物的總量下，僅需很少的金屬發泡結構量即可有效地增強反應器內部熱傳的效果進而使充氫時間大大縮短。另一方面，在固定的反應器尺寸下，ϕ_mf值增加會占據更多反應器內空間而使金屬氫化物的量減少並使反應器的最大可儲氫量下降。換言之，在指定的儲氫量需求下，充氫所需時間會隨ϕ_mf值漸漸增加而減少，當到達「最佳ϕ_mf值」時可得到最短的充氫時間，之後繼續增加ϕ_mf值則會因金屬氫化物充填量不足(metal-hydride underpacking)的影響而使充氫時間劇烈增加。

Among all current options, hydrogen appears to be the most promising alternative to fossil fuels, because it has a high calorific value and is environmentally friendly. For safety and operability concerns, hydrogen storage in metal hydrides appears to be a more promising option at present. However, the hydriding and dehydriding processes of metal hydrides are rather complex since simultaneous heat and mass transfers take place with chemical reaction. Therefore, operating conditions and system design would affect the hydrogen supply characteristics directly. In this thesis, on the basis of an existing model, with realistic parameter values appropriate for the hydriding/dehydriding kinetics of LaNi5 (as a specific particular example), we examine several important issues in the design and optimization of metal hydride reactor (MHR).
Specifically, in the first part of this thesis, we examine how the temporal mean and steadiness of the hydrogen discharge rate of an MHR vary, when its exit pressure is deceased quadratically with time. To accomplish this task, the aforementioned mathematical model accounting for the hydrogen desorption kinetics of LaNi5 and the mass and energy balance in a cylindrical MHR is solved numerically. The initial and final exit pressures of the MHR are prescribed, whereas the “pressure drop time” (during which the exit pressure is decreasing) and the initial exit-pressure drop rate are the control parameters. Results of a systematic parameter study indicate that, for a given pressure drop time, increasing initial exit-pressure drop rate generally increases the mean hydrogen discharge rate, while there is a particular initial exit-pressure drop rate that minimizes the variance of the hydrogen discharge rate. The MHR exit-pressure variation therefore can be “optimized” to discharge hydrogen with maximized temporal steadiness. Some other strategies for MHR performance improvement also are discussed here.
In the second part of this thesis, we examine how the hydriding time of an MHR varies with the volume fraction, ϕ_mf, of a metal foam installed in the reactor. Technically, the aforementioned mathematical model accounting for the hydrogen absorption kinetics of LaNi5 and variable ϕ_mf is used to compute the heat and mass transport in a cylindrical MHR. We then demonstrate that, with a fixed amount of metal hydride powder sealed in the reactor, saving a relatively small fraction (say, 1%) of the MHR internal volume to accommodate a metal foam usually suffices to substantially facilitate heat removal from the reactor, thereby greatly shortening the MHR hydriding time. However, for a metal foam of fixed apparent size, increasing ϕ_mf would reduce the metal hydride content, and hence the maximum hydrogen storage capacity, of the MHR. Consequently, if a prescribed amount of hydrogen is to be stored in the MHR, the hydriding time would decrease with increasing ϕ_mf at first (due to heat conduction augmentation), reach a minimum at an “optimal” ϕ_mf value, and then increase drastically due to metal-hydride underpacking.

[1]U.S. Department of Energy. Fuel Cells&Infrastructure Technologies Program Multi-Year Research. Development and Demonstration Plan. URL: http://www1.eere.energy.gov/hydrogenandfuelcells/mypp/ (website contents access date: 2011/01).
[2]U.S. Department of Energy.URL: http://www.doe.gov/ (website contents access date: 2011/01).
[3]U.S. Department of Energy. Office of Basic Energy Sciences. Basic Research Needs for the Hydrogen Economy. URL: http://www.hydrogen.energy.
gov/pdfs/review04/4_science_stevens_04.pdf (website contents access date: 2011/01).
[4]U.S. Department of Energy. Development and Demonstration Plan. Hydrogen Program Posture Plan. URL: http://www.hydrogen.energy.gov
/pdfs/hydrogen_posture_plan.pdf (website contents access date: 2011/01).
[5]National Research Council and National Academy of Engineering. The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs. The National Academies Press, Washington, DC, 2004.
[6]MacDonald BD, Rowe AM. A thermally coupled metal hydride hydrogen storage and fuel cell system. Journal of Power Sources; 161(1): 346–355, 2006.
[7]Jiang Z, Dougal RA, Liu S, Gadre SA, Ebner AD, Ritter JA. Simulation of a thermally coupled metal-hydride hydrogen storage and fuel cell system. Journal of Power Sources; 142(1–2): 92–102, 2005.
[8]Wilson PR, Bowman Jr. RC, Mora JL, Reiter JW. Operation of a PEM fuel cell with LaNi4.8Sn0.2 hydride beds. Journal of Alloys and Compounds; 446–447: 676–680, 2007.
[9]Fronk MH, Wetter DL, Masten DA, Bosco AD. PEM fuel cell system solutions for transportation. SAE Paper; No. 2000–01–0373, 2000.
[10]Masten DA, Bosco AD. System design for vehicle applications: GM/Opel. Handbook of Fuel Cells—Fundamentals, Technology and Applications. Vielstich W, Gasteiger HA, and Lamm A eds., John Wiley & Sons, Hoboken, NJ; 4: 714–724, 2003.
[11]Komatubara T. A study for improving thermal effectiveness in automotive radiators. JSAE Rev;16(1):111, 1995.
[12]Goldstein RJ, Eckert ERG, Ibele WE, Patankar SV, Simon TW, Kuehn TH, Strykowski PJ, Tamma KK, Heberlein JVR, Davidson JH, Bischof J, Kulacki FA, Kortshagen U, Garrick S. Heat transfer - a review of 2001 literature. International Journal of Heat Mass Transfer; 46:1887–1992, 2003.
[13]Zhang J, Fisher TS, Ramachandran PV, Gore JP, Mudawar I. A review of heat transfer issues in hydrogen storage technologies. Journal of Heat Transfer; 127(12):1391–1399, 2005.
[14]Schlapbach L, Züttel A. Hydrogen-storage materials for mobile applications. Nature; 414(6861):353–358, 2001.
[15]Jung KS, Lee EY, Lee KS. Catalytic effects of metal oxide on hydrogen absorption of magnesium metal hydride. Journal of Alloys and Compounds; 421(1–2):179–184, 2006.
[16]Li L, Akiyama T, Yagi JI. Hydrogen storage alloy of Mg2NiH4 hydride produced by hydriding combustion synthesis from powder of mixture metal. Journal of Alloys and Compounds; 308: 98–103, 2008.
[17]Chen J, Kuriyama N, Takeshita HT, Tanaka H, Sakai T, Haruta M. Hydrogen storage alloys with PuNi3-type structure as metal hydride electrodes. Electrochemical and Solid-State Letters; 3(6):249–252, 2000.
[18]Wang X, Chen R, Chen C, Wang Q. Hydrogen storage properties of TixFe + y wt.% La and its use in metal hydride hydrogen compressor. Journal of Alloys and Compounds; 425(1–2):291–295, 2006.
[19]Sudhakar VA, Karl Johnson J, David SS. Identification of destabilized metal hydrides for hydrogen storage using first principles calculations. Journal of Physical Chemistry B; 110(17):8769–8776, 2006.

[20]Borislav B, Richard AB, Ankica M, Manfred S, Joachim T. Metal-doped sodium aluminium hydrides as potential new hydrogen storage materials. Journal of Alloys and Compounds; 302(1–2):36–58, 2000.
[21]Schwarz M, Haiduc A, Stil H, Paulus P, Geerlings H. The use of complex metal hydrides as hydrogen storage materials: Synthesis and XRD-studies of Ca(AlH4)2 and Mg(AlH4)2. Journal of Alloys and Compounds; 404–406:762–765, 2005.
[22]Züttel A. Materials for hydrogen storage. Materials Today; 6(9):24–33, 2003.

[23]Sakintuna B, Lamari-Darkrim F, Hirscher M. Metal hydride materials for solid hydrogen storage: A review. International Journal of Hydrogen Energy; 32(9):1121–1140, 2007.
[24]Seayad AM, Antonelli DM. Recent advances in hydrogen storage in metal-containing inorganic nanostructures and related materials. Advanced Materials; 16(9–10):765–777, 2004.
[25]Hirscher M, Becher M, Haluska M, Zeppelin FV, Chen X, Dettlaff-Weglikowska U, Roth S. Are carbon nanostructures an efficient hydrogen storage medium? Journal of Alloys and Compounds; 356–357:433–437, 2003.
[26]Oelerich W, Klassen T, Bormann R. Metal oxides as catalysts for improved hydrogen sorption in nanocrystalline Mg-based materials. Journal of Alloys and Compounds; 315(1–2):237–242, 2001.
[27]Orimo S, Fukunaga T, Majer G. Hydrogen desorption property of mechanically prepared nanostructured graphite. Journal of Applied Physics; 90(3):1545–1549, 2001.
[28]Kiyobayashi T, Komiyama K, Takeichi N, Tanaka H, Senoh H, Takeshita HT, Kuriyama N. Hydrogenation of nanostructured graphite by mechanical grinding under hydrogen atmosphere. Materials Science and Engineering B; 108(1–2):134–137, 2004.
[29]Wu CZ, Wang P, Yao X, Liu C, Chen DM, Lu GQ, Cheng HM. Effect of carbon/noncarbon addition on hydrogen storage behaviors of magnesium hydride. Journal of Alloys and Compounds; 414(1–2):259–264, 2006.
[30]Yao X, Wu CZ, Du A, Zou J, Zhu Z, Wang P, Cheng HM, Smith S, Lu GQ. Metallic and carbon nanotube-catalyzed coupling of hydrogenation in magnesium. Journal of the American Chemical Society; 129(50):15650–15654, 2007.
[31]Georgiadis MC, Kikkinides ES, Makridis SS, Kouramas K, Pistikopoulos EN. Design and optimization of advanced materials and processes for efficient hydrogen storage. Computers and Chemical Engineering; 33(5):1377–1390, 2009.
[32]Kim KJ, Montoya B, Razani A, Lee KH. Metal hydride compacts of improved thermal conductivity. International Journal of Hydrogen Energy; 26(6):609–613, 2001.
[33]Wakao S, Sekine M, Endo H, Ito T, Kanazawa H. A heat storage reactor for metal hydrides. Journal of the Less-Common Metals; 89(2):341–350, 1983.
[34]Kawamura M, Ono S, Mizuno Y. Dynamic characteristics of a hydride heat storage system. Journal of the Less-Common Metals; 89(2):365–372, 1983.
[35]Mat MD, Kaplan Y. Numerical study of hydrogen absorption in an Lm-Ni5 hydride reactor. International Journal of Hydrogen Energy; 26(9):957–963, 2001.
[36]Dogan A, Kaplan Y, Nejat Veziroglu T. Numerical investigation of heat and mass transfer in a metal hydride bed. Applied Mathematics and Computation; 150(1):169–180, 2004.
[37]Aldas K, Mat MD, Kaplan Y. A three-dimensional mathematical model for absorption in a metal hydride bed. International Journal of Hydrogen Energy; 27(10):1049–1056, 2002.
[38]Mat MD, Kaplan Y, Aldas K. Investigation of three-dimensional heat and mass transfer in a metal hydride reactor. International Journal of Energy Research; 26(11):973–986, 2002.
[39]Gadre SA, Ebner AD, Al-Muhtaseb SA, Ritter JA. Practical modeling of metal hydride hydrogen storage systems. Industrial and Engineering Chemistry Research; 42(8):1713–1722, 2003.
[40]Freni A, Cipitı` F, Cacciola G. Finite element-based simulation of a metal hydride-based hydrogen storage tank. International Journal of Hydrogen Energy; 34(20):8574–8582, 2009.
[41]Phate AK, Maiya MP, Murthy SS. Simulation of transient heat and mass transfer during hydrogen sorption in cylindrical metal hydride beds. International Journal of Hydrogen Energy; 32(12):1969–1981, 2007.
[42]Kaplan Y. Effect of design parameters on enhancement of hydrogen charging in metal hydride reactors. International Journal of Hydrogen Energy; 34(5):2288–2294, 2009.
[43]Askri F, Ben Salah M, Jemni A, Ben Nasrallah S. Optimization of hydrogen storage in metal-hydride tanks. International Journal of Hydrogen Energy; 34(2):897–905, 2009.
[44]Mellouli S, Askri F, Dhaou H, Jemni A, Ben Nasrallah S. Numerical study of heat exchanger effects on charge/discharge times of metal-hydrogen storage vessel. International Journal of Hydrogen Energy; 34(7):3005–3017, 2009.
[45]Demircan A, Demiralp M, Kaplan Y, Mat MD, Veziroglu TN. Experimental and theoretical analysis of hydrogen absorption in LaNi5-H2 reactors. International Journal of Hydrogen Energy; 30(13–14):1437–1446, 2005.
[46]Førde T, Næss E, Yartys VA. Modelling and experimental results of heat transfer in a metal hydride store during hydrogen charge and discharge. International Journal of Hydrogen Energy; 34(12):5121–5130, 2009.
[47]Gopal MR, Murthy SS. Prediction of heat and mass transfer in annular cylindrical metal hydride beds. International Journal of Hydrogen Energy; 17(10):795–805, 1992.
[48]Gopal MR, Murthy SS. Studies on heat and mass transfer in metal hydride beds. International Journal of Hydrogen Energy; 20(11):911–917, 1995.
[49]Ye J, Jiang L, Li Z, Liu X, Wang S, Li X. Numerical analysis of heat and mass transfer during absorption of hydrogen in metal hydride based hydrogen storage tanks, International Journal of Hydrogen Energy; 35(15):8216–8224, 2010.
[50]Georgiadis MC, Kikkinides ES, Makridis SS, Kouramas K, Pistikopoulos EN. Design and optimization of advanced materials and processes for efficient hydrogen storage. Computers and Chemical Engineering; 33(5):1077–1090, 2009.
[51]Kikkinides ES, Georgiadis MC, Stubos AK. On the optimization of hydrogen storage in metal hydride beds. International Journal of Hydrogen Energy; 31(6):737–751, 2006.
[52]Yang TS, Tsai ML, Ju DS. Effects of exit-pressure variation on the hydrogen supply characteristics of metal hydride reactors. International Journal of Hydrogen Energy; 35(16):8597–8608, 2010.
[53]Verga M, Armanasco F, Guardamagna C, Valli C, Bianchin A, Agresti F, Russo SL, Maddalena A, Principi G. Scaling up effects of Mg hydride in a temperature and pressure-controlled hydrogen storage device. International Journal of Hydrogen Energy; 34(10):4602–4610, 2009.
[54]Dehouche Z, Grimard N, Laurencelle F, Goyette J, Bose TK. Hydride alloys properties investigations for hydrogen sorption compressor. Journal of Alloys and Compounds; 399(1–2):224–236, 2005.
[55]Oi T, Maki K, Sakaki Y. Heat transfer characteristics of the metal hydride vessel based on the plate-fin type heat exchanger. Journal of Power Sources; 125(1):52–61, 2004.
[56]Chen Y, Sequeira CAC, Chen C, Wang X, Wang Q. Metal hydride beds and hydrogen supply tanks as minitype PEMFC hydrogen sources. International Journal of Hydrogen Energy; 28(3):329–333, 2003.
[57]MacDonald BD, Rowe AM. Impacts of external heat transfer enhancements on metal hydride storage tanks. International Journal of Hydrogen Energy; 31(12):1721–1731, 2006.
[58]Nagel M, Komazaki Y, Suda S. Effective thermal conductivity of a metal hydride bed augmented with a copper wire matrix. Journal of the less-common metals; 120(1):35–43, 1986.
[59]1.Kim KJ, Montoya B, Razani A, Lee K-H. Metal hydride compacts of improved thermal conductivity. International Journal of Hydrogen Energy; 26(6):609–613, 2001.
[60]Kim KJ, Lloyd G, Razani A, Feldman Jr. KT. Development of LaNi5/Cu/Sn metal hydride powder composites. Powder Technology; 99(1):40–45, 1998.
[61]Mellouli S, Askri F, Dhaou H, Jemni A, Ben Nasrallah S. A novel design of a heat exchanger for a metal-hydrogen reactor. International Journal of Hydrogen Energy; 32(15):3501–3507, 2007.
[62]Dhaou H, Souahlia A, Mellouli S, Askri F, Jemni A, Ben Nasrallah S. Experimental study of a metal hydride vessel based on a finned spiral heat exchanger. International Journal of Hydrogen Energy; 35(4):1674–1680, 2010.
[63]Yang F, Meng X, Deng J, Wang Y, Zhang Z. Identifying heat and mass transfer characteristics of metal hydride reactor during adsorption–Parameter analysis and numerical study. International Journal of Hydrogen Energy; 33(3):1014–1022, 2008.
[64]Matijasevic B, Banhart J. Improvement of aluminium foam technology by tailoring of blowing agent. Scripta Materialia; 54(4):503–508, 2006.
[65]Boomsma K, Poulikakos D, Zwick F. Metal foams as compact high performance heat exchangers. Mechanics of Materials; 35(12):1161–1176, 2003.
[66]Lu W, Zhao CY, Tassou SA. Thermal analysis on metal-foam filled heat exchangers. Part I: Metal-foam filled pipes. International Journal of Heat and Mass Transfer; 49(15–16):2751–2761, 2006.
[67]Bhattacharya A, Calmidi VV, Mahajan RL. Thermophysical properties of high porosity metal foams. International Journal of Heat and Mass Transfer; 45(5):1017–1031, 2002.
[68]Leong KC, Jin LW. Effect of oscillatory frequency on heat transfer in metal foam heat sinks of various pore densities. International Journal of Heat and Mass Transfer; 49(3–4):671–681, 2006.
[69]Laurencelle F, Goyette J. Simulation of heat transfer in a metal hydride reactor with aluminium foam. International Journal of Hydrogen Energy; 32(14):2957–2964, 2007.
[70]Mayer U, Groll M, Supper W. Heat and mass transfer in metal hydride reaction beds: Experimental and theoretical results. Journal of the Less-Common Metals; 131(1–2):235–244, 1987.
[71]Choi H, Mills AF. Heat and mass transfer in metal hydride beds for heat pump applications. International Journal of Heat and Mass Transfer; 33(6):1281–1288, 1990.
[72]Jemni A, Ben Nasrallah S. Study of two-dimensional heat and mass transfer during absorption in a metal-hydrogen reactor. International Journal of Hydrogen Energy; 20(1):43–52, 1995.
[73]Jemni A, Ben Nasrallah S. Study of two-dimensional heat and mass transfer during desorption in a metal-hydrogen reactor. International Journal of Hydrogen Energy; 20(11):881–891, 1995.
[74]Ben Nasrallah S, Jemni A. Heat and mass transfer models in metal-hydrogen reactor. International Journal of Hydrogen Energy; 22(1):67–76, 1997.
[75]Nakagawa T, Inomata A, Aoki H, Miura T. Numerical analysis of heat and mass transfer characteristics in the metal hydride bed. International Journal of Hydrogen Energy; 25(4):339–350, 2000.
[76]Jemni A, Ben Nasrallah S, Lamloumi J. Experimental and theoretical study of a metal-hydrogen reactor. International Journal of Hydrogen Energy; 24(7):631–644, 1999.
[77]Askri F, Jemni A, Ben Nasrallah S. Study of two-dimensional and dynamic heat and mass transfer in a metal-hydrogen reactor. International Journal of Hydrogen Energy; 28(5):537–557, 2003.
[78]Askri F, Jemni A, Ben Nasrallah S. Prediction of transient heat and mass transfer in a closed metal-hydrogen reactor. International Journal of Hydrogen Energy; 29(2):195–208, 2004.
[79]Askri F, Jemni A, Ben Nasrallah S. Dynamic behavior of metal-hydrogen reactor during hydriding process. International Journal of Hydrogen Energy; 29(6):635–647, 2004.
[80]Mellouli S, Dhaou H, Askri F, Jemni A, Ben Nasrallah S. Hydrogen storage in metal hydride tanks equipped with metal foam heat exchanger. International Journal of Hydrogen Energy; 34(23):9393–9401, 2009.
[81]ERG Materials and Aerospace Corporation. Duocel Aluminum Foam, URL: http://www.ergaerospace.com/literature/erg_duocel.pdf (website contents access date: 2011/01).
[82]Yartys’ VA, Burnasheva VV, Semenenko KN, Fadeeva NV, Solov’ev SP. Crystal chemistry of RT5H(D)x, RT2H(D)x and RT3H(D)x hydrides based on intermetallic compounds of CaCu5, MgCu2, MgZn2 and PuNi3 structure types. International Journal of Hydrogen Energy; 7(12):957–965, 1982.
[83]Kaplan Y, Veziroglu TN. Mathematical modelling of hydrogen storage in a LaNi5 hydride bed. International Journal of Energy Research; 27(11):1027–1038, 2003.
[84]Munson BR, Young DF, Okiishi TH. Fundamentals of fluid mechanics. New York: Wiley; 5th edn, 2006.
[85]Dhaou H, Askri F, Ben Salah M, Jemni A, Ben Nasrallah S, Lamloumi J. Measurement and modelling of kinetics of hydrogen sorption by LaNi5 and two related pseudobinary compounds. International Journal of Hydrogen Energy; 32(5):576–587, 2007.
[86]Ju DS. Effects of release-pressure control on the hydrogen supply characteristics of metal hydride reactors. Master’s thesis, Department of Mechanical Enginering, National Cheng Kung University (in Chinese), 2008.
[87]Wang F, Tarabara VV. Permeability of fiber-filled porous media: Kozeny-Carman-Ethier modeling approach, Environmental Engineering Science; 26(6):1149–1155, 2009.
[88]Kaviany M. Principles of Heat Transfer in Porous Media. New York: Springer; 2nd edn, 1999.
[89]Chen YC. Effects of Structural Design on the Expansion Deformation in LaNi5 Hydride Storage Vessels. Master’s thesis, Department of Mechanical Engineering , National Central University, 2010.