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Ind. Eng. Chem. Res. 1997, 36, 3920-3926
Absorption of Hydrogen in LaNi4.75Al0.25/n-Octane Slurries Kwang J. Kim† and K. Thomas Feldman, Jr. Thermal Electric Devices, Inc., Albuquerque, New Mexico 87101
George Lloyd and Arsalan Razani* Mechanical Engineering Department, The University of New Mexico, Albuquerque, New Mexico 87131
The absorption kinetics of hydrogen into a LaNi4.75Al0.25/n-octane slurry was investigated in a stirred reactor. The rate-determining step was hydrogen absorption into the liquid n-octane phase in agreement with the model proposed by Reilly and Johnson (J. Less-Common Met. 1984, 104, 175). The activation energy was found to be approximately 8.4 kJ/mol of H2. Although the activation energies for hydrogen absorption into various slurry combinations are quite scattered, the data reported here indicate that the overall kinetics is sufficient for many practical applications. Introduction Metal hydrides have been considered for use in hydrogen recovery units, hydrogen storage beds, heat pumps, and thermal compressors for cryocoolers (Sheridan et al., 1983; Nichols, 1991; Ron et al., 1992; Groll, 1993; Suda, 1993; Flanagan, 1994; Gopal and Murthy, 1995; Bhandari et al., 1995; Lloyd et al., 1995a,b; 1996; 1997; Kim et al., 1997a; Feldman et al., 1996). Despite intrinsically rapid kinetics, an inherent problem with metal hydrides is the fact that they decrepitate into micron-sized powders after several absorption/desorption cycles. The thermal conductivity of such powder beds is small (0.1 < keff < 1 W/m‚K; Ron et al., 1992) and is a substantial resistance for heat transfer. The result is that powder beds show very poor absorption characteristics. One way of resolving this problem is to suspend metal hydride powders in a fluid phase (inert liquids), forming slurries so as to utilize the convective heat transfer enhancement (Smith and Waring, 1939; Bowman and Sirovich, 1979; Reilly and Johnson, 1984, 1988; Johnson and Reilly, 1986; Ptasinski and van Swaaig, 1986; Reilly et al., 1987, 1989; Gamo et al., 1987; Zwart et al., 1989; Holstvoogd et al., 1989; Bjurstro¨m, 1991; Tinge, 1993; Kim et al., 1997b). This approach minimizes temperature gradients within the slurry reactor and allows rapid heat transfer. Additionally, such slurries are pumpable and can minimize the problems associated with powder migrations within the systems. A disadvantage is that the inert liquid brings additional masstransfer resistances between the gas and solid phases (Tung et al., 1986; Snijder et al., 1993; Kim et al., 1997c). Table 1 summarizes the previous efforts on metal hydride slurries. In a metal hydride slurry, as diagrammed in Figure 1, the following mass-transfer steps may be involved for absorption (Reilly and Johnson, 1984; Snijder et al., 1993; Kim et al., 1997c): Step 1. Absorption from the hydrogen gas phase into the liquid at the gas/liquid interface; H2(gas) f H2(liquid). * Corresponding author. Telephone: (505) 277-6251. Fax: (505) 277-1571. E-mail:
[email protected]. † Present address: Mechanical Engineering Department, The University of New Mexico, Albuquerque, New Mexico 87131. Telephone: (505) 277-1335. Fax: (505) 277-1335. E-mail:
[email protected]. S0888-5885(97)00094-8 CCC: $14.00
Step 2. Diffusion in the liquid phase from the gas/ liquid interface into the bulk liquid. Step 3. Diffusion from the bulk liquid to the external surface of the hydride particle and dissociation on the solid surface; H2(liquid) f 2H (solid surface). Step 4. Internal diffusion inside the hydride particle. Step 5. Hydriding reaction within the hydride particle; 2H + (2/x)M f (2/x)MHx (R f β phase). In the hydrogen gas phase, there will be essentially no resistance. In the slurry, the inert liquid introduces additional mass-transfer resistances, resulting in a decrease in the overall hydrogen absorption. Optimization of slurry reactors requires knowledge of the overall mass-transfer resistance as well as the rate-limiting step. The authors are not aware of kinetic studies reported for the hydrogen/n-octane/LaNi4.75Al0.25 system which would be useful for many practical applications. The major objective of this paper is to investigate this slurry system containing hydrogen in the gas phase as a reactant, n-octane in the liquid phase as an inert, and LaNi4.75Al0.25 in the solid phase as a reactant. Experimental Apparatus Figure 2 shows the experimental apparatus built for the hydrogen absorption experiment. It consists of a slurry reactor, a hydrogen tank, and a data acquisition system. The slurry reactor has a volume of 177.0 cm3 and is equipped with a magnetically driven stirrer. Details of construction of the slurry reactor are also provided in Figure 2. The stirrer has six flat blades located near the midpoint of the slurry. The stirrer shaft is magnetically coupled to a variable-speed dc motor whose rotating speed is controlled by an inline voltage regulator and measured by a precision tachometer. The hydrogen tank is made of stainless steel with a known volume, is equipped with a pressure regulator, and was leak-tested. Two pressure transducers are utilized, one at the hydrogen tank and the other at the slurry reactor. The quantity of hydrogen absorbed is determined from the pressure drop of the hydrogen tank. A data acquisition system with LabView software (National Instruments, 1995) is used to measure pressures and temperatures. A SCXI-1300 terminal block along with a SCXI-1100 mutiplexer attached to a SCXI1000 chassis communicates with a NBMIO-16 AD board on a Power Mac 6100/66. Technical data for the measurements is provided in Table 2. © 1997 American Chemical Society
Ind. Eng. Chem. Res., Vol. 36, No. 9, 1997 3921 Table 1. Previous Efforts on Metal Hydride Slurries publication
work
findings
The first order was found to be the best for the rate equation. The rate-limiting step is the absorption of hydrogen in the liquid with the activation energy of 11.0 ( 1.0 kJ/mol of H2. Johnson and Isothermal absorption kinetics of The rate-limiting steps are the absorption of hydrogen in Reilly, 1986 LaNi5Hx/n-octane and LaNi4.7Al0.3Hx/n-undecane the liquid phase. The activation energy of 11.5 ( 1.1 and systems were investigated. 5.7 ( 0.7 kJ/mol of H2 was found for LaNi4.7Al0.3Hx/n-undecane and LaNi5Hx/n-octane systems, respectively. Ptasinski and Hydrogen absorption experiments were performed They reported that LaNi5 particles enhanced the rate van Swaaij, 1986 on a LaNi5/silicone oil system. of absorption depending upon the temperature up to 2 times. Tung et al., 1986 Isothermal kinetic measurements were performed At a high stirring speed of 2000 rpm, hydrogen absorption on the absorption ofhydrogen into a was completed within 1 min. The importance of the LaNi5/n-undecane system. adsorption of n-undecane molecules on the LaNi5 surface was addressed. Reilly et al., 1987 With the presence of CH4 in the gas phase, The system behaves similarly to those studied in the isothermal absorption kinetics of a absence of CH4 with the activation energies of 9.3 ( 0.5 LaNi5Hx/n-undecane system was studied. and 5.5 ( 0.9 kJ/mol of H2 for CH4 pressures at 0.4 and 2.53 atm, respectively. Gamo et al., 1987 Isothermal absorption kinetics of a LaNi5Hx/water The absorption rates of hydrogen into pure water system was investigated. and the aqueous surfactant solution obeyed the first order with the respective activation energies of 15.4 ( 1.4 and 11.9 ( 1.4 kJ/mol of H2. Reilly and Summarized metal hydride slury systems. Johnson, 1988 Reilly et al., 1989 The isothermal kinetics of the desorption of the The shrinking-core model well-describes the kinetics hydrogen (β f R phase) from LaNi5Hx were where the rate-limiting process exists in the solid phase. investigated for both n-undecane and n-octane systems. Zwart et al., 1989 The hydrogen purification process, based on the The metal hydride slurry process is an attractive metal hydride slurry, was investigated. alternative to the present pressure-swing adsorption (PSA) and membrane separation techniques (MST). Holstvoogd Absorption of hydrogen in metal hydride slurries The hydrogen absorption process is described in terms et al., 1989 (LaNi5/silicone oil) was investigated in a of mass-transfer resistances in series. High absorption continuous process. rates were achieved by the selected valve-tray column. Bjurstro¨m, 1989 Metal hydride slurries were considered as It may be feasible to obtain a temperature lift of 80 °C. absorbent fluids for use in heat pumps. It has been pointd out that the absorption resistance in the liquid phase dominates the process kinetics. Tinge, 1993 The chemical purification process, based upon the The use of metal hydride slurry for hydrogen purification metal hydride slurry, was considered. may be attractive due to higher selectivity than those of PSA and MST. Snijder et al., 1993 The kinetics of hydrogen absorption and The absorption in a slurry is limited by a surface desorption in LaNi5/cyclohexane, chemisorption process. Larger molecules show lower LaNi5/ethanol, LaNi4.9Al0.1/cyclohexane, and absorption rates due to a higher surface coverage. LaNi4.8Al0.2/cyclohexane systems have been Higher aluminum contents attribute to an increase investigated. in the absorption rate. Kim et al., 1997b Compressor-driven metal hydride heat pumps Optimum operating conditions were found. High hydride were theoretically investigated. loadings and effective heat exchange between the hydride streams are crucial to achieve high efficiency of the system. Kim et al., 1997c Thermodynamic analysis on the heat-driven metal Thermodynamic analysis indicates that metal hydride hydride heat pumps was performed. Also, slurry heat pumps can achieve high performance. hydrogen absorption in LaNi4.75Al0.25/n-octane A packed-bed absorber shows a rapid hydrogen was performed with a packed-bed absorber. absorption into the metal hydride slurry. Reilly and Johnson, 1984
Isothermal absorption kinetics of a LaNi5Hx/n-undecane system was investigated.
quently 10 absorption/desorption cycles at a pressure of 13.6 atm of hydrogen. n-Octane (purity greater than 99%, Aldrich) was used as the inert liquid without further treatments. High-purity hydrogen (>99.999%, Air-Products) was used. Figure 1. Metal hydride slurry system.
Results and Discussion
The rare-earth intermetallic hydride, LaNi4.75Al0.25, was used throughout this study (purchased from Japan Metal Chemical Co.; purity greater than 99.9%). The relevant properties of LaNi4.75Al0.25 (Diaz et al., 1979) are the van’t Hoff equation, which refers to the absorption plateau pressure of the hydride, of ln PH2 ) -34 700/RTK + 110/R (PH2 units in atm and TK units in Kelvin; R is the gas constant) and a hydrogen uptake capacity of 0.84 wt %. The activation procedure involved 12 h of vacuum bakeout at 373 K and subse-
Hydrogen/n-Octane System. First, the kinetics of hydrogen absorption into n-octane in the absence of LaNi4.75Al0.25 was investigated. Since the liquid phase is important for the mass transfer, the reaction rate is dependent on any factors that influence the liquid mixing and/or interfacial area (i.e., the stirring speed, the reactor geometry, and the stirrer geometry). It is reasonable to conclude that first order is the best fit to describe the observed kinetics, similar to the hydrogen/ n-undecane system (Reilly and Johnson, 1984). Then,
3922 Ind. Eng. Chem. Res., Vol. 36, No. 9, 1997
Figure 4. Dynamic behavior of hydrogen absorption: ln[fe/(fe f)] vs t (P ) 13.6 atm, φ ) 1000 rpm, n-octane only).
Figure 2. Experimental apparatus built for hydrogen absorption.
Figure 5. Experimental results: kL vs 1/TK (P ) 13.6 atm, n-octane only).
TK, with xL units in mole fraction). Integration of eq 1 produces
ln[fe/(fe - f)] ) kLt
Figure 3. Measured hydrogen solubilities in n-octane. Table 2. Technical Data for the Measurements error temperature pressure stirring speed
(0.1 at 25 °C (0.05 atm (0-20.4 atm) (0.09 atm (0-34.0 atm) (10 rpm at 1000 rpm
source manufacturer manufacturer uncertainty analysis
the rate of hydrogen absorption, RH2(t), can be described as
RH2(t) ) kL[fe - f(t)]
(1)
where kL, fe, and f(t) are the rate constant, the equilibrium concentration of absorbed hydrogen in the liquid, and the concentration of absorbed hydrogen in the liquid at time t, respectively. The equilibrium concentration of absorbed hydrogen, fe, was obtained directly from the measured values of hydrogen solubility, xL, as shown in Figure 3 (least-squares fit: ln xL) -2.6925 - 626.9/
(2)
Figure 4 shows the dynamic behavior of hydrogen absorption based upon eq 2: using a stirring speed of 1000 rpm, absorber pressure of 13.6 atm, and slurry temperatures of 25, 40, and 55 °C, respectively. As can be seen, the hydrogen absorption rate is rapid and is completed within 15 s. Nearly linear behavior between ln[fe/(fe - f)] and t is obtained with an induction time of approximately 1-2 s. As expected, the absorption rate increases with the temperature. Figure 5 shows that the resulting values of kL (approximated from the data in Figure 4) versus 1/TK are assumed to obey an Arrhenius relationship,
kL ) AL exp(-EL/RTK)
(3)
where AL and EL are the frequency factor and the apparent activation energy for gas absorption, respectively. By calculating the slopes and intercepts for different stirring speeds, the activation energy for hydrogen absorption into n-octane, EL, was found to be 8.1 ( 0.9 kJ/mol of H2 with frequency factors, AL, of 6.9, 5.6, and 4.3 for stirring speeds, φ, of 1150, 1000, and 850 rpm, respectively. In Figure 6, data shown in Figure 5 is replotted in terms of kL vs φ (showing the effect of stirring speed on
Ind. Eng. Chem. Res., Vol. 36, No. 9, 1997 3923
Figure 8. Effect of hydrogen pressure on the rate of hydrogen absorption.
Figure 6. Experimental results: kL vs φ (P ) 13.6 atm, n-octane only).
Figure 9. Effect of stirring speed on the rate of hydrogen absorption.
Figure 7. Comparisons between measured and fitted values of KL (n-octane only, P ) 13.6 atm, 850 < φ < 1150 rpm, 25 < T < 55 °C).
the rate constant). It appears that if the intersect is chosen by linear extrapolation, there would be a critical stirring speed for hydrogen absorption, φ0, of approximately 245 rpm. Similar behavior has been reported by others (Tung et al., 1986; Mehta and Sharma, 1971). An increase of kL with temperature shows the effects on the activation energy, EL. The following equation can represent these findings as
kL ) K1eK2TK(φ - 245)
(4)
where fitted values of K1 and K2 are 1.558 × and 9.768 × 10-3, respectively. Figure 7 shows comparisons between measured and fitted values of kL. Hydrogen/n-Octane/LaNi4.75Al0.25 System. Figures 8-10 show the effects of hydrogen pressure, stirring speed, and temperature on the rate of hydrogen absorption in the form of the conversion factor, Cf, vs time, t. Note that the particle loading (RS ) mass of LaNi4.75Al0.25/mass of n-octane) for all experiments was held at 0.23. Conversion factors were calculated from the pressure drop of the hydrogen tank, dPH2/dt, and 10-5
Figure 10. Effect of temperature on the rate of hydrogen absorption.
the total hydrogen uptake capacity, nH2, of LaNi4.75Al0.25 as
Cf ) nH2(t)/nH2
(5)
where nH2(t) is the amount of hydrogen absorbed at time t. An increase in hydrogen pressure makes the overall driving potential larger, giving off a faster conversion as shown in Figure 8. The effect of stirring speed may be attributed to steps 2 and 3 discussed before. In all these cases 80% of hydrogen absorption occurs within
3924 Ind. Eng. Chem. Res., Vol. 36, No. 9, 1997 Table 3. Activation Energies, ES, for Hydrogen Absorption into Metal Hydride Slurry Systems publication
slurry system
Reilly and Johnson, 1984
LaNi5/n-undecane
Johnson and Reilly, 1986
LaNi4.7Al0.3/n-undecane LaNi5/n-octane
Tung et al., 1986
LaNi5/n-undecane
Reilly et al., 1987 Gamo et al., 1987
LaNi5/n-undecane/CH4 in the gas phase LaNi5/water
Holstvoogd et al., 1989
LaNi5/silicone oil
Snijder et al., 1993
(i) LaNi5/cyclohexane (ii) LaNi4.9Al0.1/cyclohexane (iii) LaNi4.8Al0.2/cyclohexane (iv) LaNi5/ethanol LaNi4.75Al0.25/n-octane
this work
experimental conditions
reactor with a six-blade stirrer, 12.1 < PH2 < 15.5 atm, RS ∼ 0.23, 850 < φ < 1150 rpm
a reasonable amount of time of approximately 120 s. This is important for practical consideration. Figure 9 indicates that the resistances associated with these steps can be reduced by raising the stirring speed. No attempts were made to increase the stirring speed beyond 1150 rpm. In Figure 10 the effect of temperature on the hydrogen absorption is shown. There are two dependent variables with respect to temperature; the rate constant for slurry, kS, and the plateau pressure, PP. As the temperature increases, Pp should increase, resulting in a decrease in the overall driving potential. At the same time, kS should increase. Then, a complicated behavior may be expected. But the present results show that the temperature effect on kS is dominant since the Pp of LaNi4.75Al0.25 is quite low within the operating range. Based on the model proposed by Reilly and Johnson (1984), the rate of hydrogen absorption into the slurry can be written as
RH2(t) ) kS[f(t) - fpt]
(6)
where kS, f(t), and fpt are the overall rate constant for the slurry system, the concentration of absorbed hydrogen in the liquid at time t, and the concentration of hydrogen at equilibrium with a plateau pressure of LaNi4.75Al0.25, respectively. Using the Arrehnius relationship, kS is
kS ) AS exp(-ES/RTK)
(7)
where AS and ES are the frequency factor and the activation energy for hydrogen absorption into the slurry system, respectively. From a rearrangement of eq 1, f(t) becomes
f(t) ) fe -
RH2(t) kL
kS )
f(t) - fpt
11.0 11.5 5.7 42.2-47.2 9.3 at 5 mol %, 5.5 at 25 mol % 15.4, 11.9 with surfactants 32.0 (i) 10.7 (ii) 10.7 (iii) 10.2 (iv) 14.5 8.4
Figure 11. Experimental results: kS vs 1/TK (P ) 13.6 atm, LaNi4.75Al0.25/n-octane only).
A series of experiments were conducted to evaluate values of Es and As for the LaNi4.75Al0.25/n-octane system. Within the operating range of pressure (12.1 < PH2 < 15.5 atm) Henry’s law was used to calculate the values of fe based upon the measured hydrogen solubility data, shown in Figure 3 (Kim et al., 1997d). Results are provided in Figure 11 as kS plotted vs 1/TK. Assuming a linear relationship between kS and 1/TK, the values are calculated to be ES of 8.4 ( 1.4 kJ/mol of H2 with frequency factors, AS, of 6.4, 5.2, and 4.0 for the stirring speeds, φ, of 1150, 1000, and 850 rpm, respectively. These values correspond to nearly the same ones as for EL. In other words, EL and ES are essentially the same but with slightly smaller values of AS than those of AL. This implies the absorption resistance dominates. To see this more clearly, eliminating f(t) from eq 6 with eq 8 yields
(8) RH2(t) )
A combination of eqs 6 and 7 gives the following equation:
RH2(t)
ES, kJ/mol of H2
reactor with a magnetic stirrer, PH2 ∼ 10 atm, 0.08 < RS < 0.38, φ ∼ 600 rpm reactor with a magnetic stirrer, PH2 ∼ 10 atm, RS ∼ 0.27, φ ∼ 600 rpm reactor with a magnetic stirrer, PH2 ∼ 10 atm, RS ∼ 0.14, φ ∼ 400 rpm reactor with a six-blade impellor, PH2 ∼ 11 atm, 0.07 < RS < 0.27, φ ∼ 2000 rpm reactor with a magnetic stirrer, PH2 ∼ 8 atm, RS ∼ 0.09, φ ∼ 600 rpm reactor with a magnetic stirrer, PH2 ∼ 10 atm, RS ∼ 0.06, φ ∼ 600 rpm reactor with a turbine, 5 < PH2 < 20 atm, 0.07 < RS < 0.35, φ e 1500 rpm reactor with a two-blade propeller or six-blade turbine 8 < PH2 < 16 atm, 0.08 < RS < 0.15, 800 < φ < 2000 rpm
kS(fe - fpt) 1 + kS/kL
The results allow the simplification of kS ∼ kL (see Figures 5 and 11):
RH2(t) ) kS(fe - fpt)/2 ) AS exp(-ES/RTK)
(10)
(11)
(9) Equation 11 expresses that the hydrogen absorption in
Ind. Eng. Chem. Res., Vol. 36, No. 9, 1997 3925
go to Dr. C. Stein of Thermal Electric Devices, Inc., for fruitful discussions on the research. Nomenclature
Figure 12. Experimental results: kS vs φ (P ) 13.6 atm, LaNi4.75Al0.25/n-octane only).
the slurry is essentially related to the mass-transfer driving potential of fe - fpt with the rate constant of kS/ 2. Figure 12 shows the effect of stirring speed on the rate constant, kS. It appears that the intercept would be a critical stirring speed, φ0, of approximately 150 rpm, slightly smaller than that without LaNi4.75Al0.25. This is somewhat contradictory to previous observations (φ0 ∼ 250 rpm without LaNi4.75Al0.25). No attempts were made to study the stirring speed at less than 850 rpm, since experience indicates that reasonable values of kS begin at 200 ( 100 rpm. In Table 3 the reported activation energies of various metal hydride slurry systems are compiled. Note that experimental conditions are somewhat different and results are scattered. Concluding Remarks A stirred reactor was designed and fabricated to study the hydrogen absorption kinetics in a LaNi4.75Al0.25/noctane system under experimental conditions: 12.1 < PH2 < 15.5 atm, RS ∼ 0.23, and 850 < φ < 1150. The results were used to estimate the activation energy for hydrogen absorption. The major conclusions of this study are as follows: (a) The activation energy for hydrogen absorption was found to be 8.4 kJ/mol of H2. (b) The absorption resistance in the liquid phase was found to be the rate-determining step. The data support the liquid phase resistance model proposed by Reilly and Johnson (1984). (c) A faster stirring speed leads to a higher rate constant with a critical value of approximately 200 rpm. (d) In general, the overall kinetics seems sufficient enough for many practical applications. (e) Further studies could include a wider spectrum of metal hydride/liquid pairs for testing so as to further understand the nature of the liquid-solid mass-transfer resistance. Acknowledgment The authors thank the grant from the U.S./DOE under Contract No. DE-FG05-94ER81890. Special thanks
AL ) frequency factor, liquid AS ) frequency factor, slurry CF ) conversion factor defined in Eq. (5) EL ) activation energy for hydrogen absorption, liquid ES ) activation energy for hydrogen absorption, slurry f ) concentration of absorbed hydrogen in the liquid fe ) equilibrium concentration of absorbed hydrogen in the liquid fpt ) concentration of hydrogen at equilibrium with a plateau pressure of LaNi4.75Al0.25 kL ) rate constant, liquid kS ) rate constant, slurry K1 ) constant defined in eq 4 K2 ) constant defined in eq 4 nH2 ) hydrogen uptake capacity R ) gas constant RH2 ) rate of hydrogen absorption PH2 ) hydrogen pressure, atm t ) time TK ) temperature, K xL ) hydrogen solubility Greek Symbols φ ) rotating speed φ0 ) critical rotating speed
Literature Cited Bhandari, P.; Rodriguez, J.; Bard, S.; Wade, L. Dynamic Simulation of a Periodic 10K Sorption Cryocooler. Cryocoolers 8; Ross, G. R., Jr., Ed.; Plenum Press: New York, 1995. Bjurstro¨m, H. Slurries as Absorbent Fluids. Proceedings of International Absorption Heat Pump Conference ‘91, Tokyo, Japan, 1991; p 171. Bowman, W. H.; Sirovich, B. E. Moving Bed Hydride/Dehydride System. U.S. Patent 4,178,987, 1979. Diaz, H.; Percheron-Guegan, A.; Achard, J. C. Thermodynamic and Structual Properties of LaNi5-yAly, Compounds and Their Related Hydride. Int. J. Hydrogen Energy 1979, 4 (5), 445. Feldman, K. T., Jr.; Kim, K. J.; Way, T.; Lloyd, G. M.; Razani, A. Compressor Driven Metal Hydride Heat Pumps. Proceedings of International Absorption Heat Pumps Conference ‘96, Montreal, Canada, 1996; p 497. Flanagan, T. B. Metal Hydrides: Fundamentals and Applications. Lecture Notes, University of Vermont, 1994. Gamo, T.; Johnson, J. R.; Reilly, J. J. The Kinetics of the Absorption of Hydrogen by LaNi5Hx Suspended in Aqueous Solutions. J. Less-Common Met. 1987, 131, 81. Gopal, M. R.; Murthy, S. S. Performance of a Metal Hydride Cooling System. Int. J. Ref. 1995, 18 (6), 413. Groll, M. Reaction Beds for Dry Sorption Machines. Heat Recovery Syst. CHP 1993, 13 (4), 341. Holstvoogd, R. D.; van Swaaij, W. P. M.; Versteeg, G. F.; Snijder, E. D. Continuous Absorption of Hydrogen in Metal Hydride Slurries. Z. Phys. Chem. (Neue Folge) 1989, 164S, 1429. Johnson, J. R.; Reilly, J. J. Kinetics of Hydrogen Absorption by Metal Hydride Suspensions: The Systems LaNi5Hx/n-octane and LaNi4.7Al0.3Hx/n-undecane. Z. Phys. Chem. (Neue Folge) 1986, 147S, 901. Kim, K. J.; Feldman, K. T., Jr.; Lloyd, G. M.; Razani, A. Compressor Driven Metal Hydride Heat Pumps. Appl. Thermal Eng. 1997a, 17 (6), 551. Kim, K. J.; Feldman, K. T., Jr.; Razani, A. Cooling Power and Efficiency Diagram for Compressor-Driven Metal Hydride Slurry Air-Conditioners. EnergysInt. J. 1997b, 22 (8), 787. Kim, K. J.; Feldman, K. T., Jr.; Razani, A. Heat Driven Metal Hydride Slurry Heat Pumps. Int. J. Ref. 1997c, in press. Kim, K. J.; Way, T.; Feldman, K. T., Jr.; Razani, A. Solubility of Hydrogen in Octane, 1-Octanol, and Squalane. J. Chem. Eng. Data 1997d, 42 (1), 214.
3926 Ind. Eng. Chem. Res., Vol. 36, No. 9, 1997 Lloyd, G. M.; Razani, A.; Feldman, K. T., Jr. Fundamental Issues Involved in a Theoretical Description of the Heat and Hydrogen Transfer Occurring in Coupled Porous Metal Hydride Reactors. Proceedings of ASME International Mechanical Engineering Congress and Exposition, San Francisco, CA, 1995a; HTD-321/ FED-233, p 671. Lloyd, G. M.; Razani, A.; Feldman, K. T., Jr. Design of Absorption Hydride Heat pump: Use of 1-D Model Focusing Media Development and Refinement. Proceedings of ASME International Mechanical Engineering Congress and Exposition, San Francisco, CA, 1995b; AES-34, p 205. Lloyd, G. M.; Razani, A.; Feldman, K. T., Jr. Computational Study of a MmNi4.15Fe0.85 Compressor-Driven Metal Hydride Refrigerator. Proceedings of International Absorption Heat Pumps Conference ‘96, Montreal, Canada, 1996; p 513. Lloyd, G. M.; Razani, A.; Kim, K. J.; Feldman, K. T., Jr.; Way, T. R. Cooling Power/Efficiency Diagram for a Compressor-Driven Metal Hydride Heat Pump. ASHRAE Trans. 1997, 103 (1), PH97-1-3. Mehta, V. D.; Sharma, M. M. Mass Transfer in Mechanically Agitated Gas-Liquid Contactors. Chem. Eng. Sci. 1971, 26, 461. National Instruments. LabView for Macintosh; National Instruments: Austin, TX, 1995. Nichols, G. S. Flow in a Metal Hydride Chromatographic Column. J. Less-Common Met. 1991, 172-174, 1338. Ptasinski, K. J.; van Swaaij, W. P. M. Gas Absorption into Slurry: Rate Enhancement by Fine Insoluble Solid Reactant. Chem. Eng. Sci. 1986, 41 (7), 1943. Reilly, J. J.; Johnson, J. R. The Kinetics of the Absorption of Hydrogen by LaNi5Hx-n-Undecane Suspensions. J. Less-Common Met. 1984, 104, 175. Reilly, J. J.; Johnson, J. R. Metal Hydride Slurries. Proceedings of International Workshop on Metal Hydrides for Hydrogen Storage, Purification and Thermodynamic Devices, 1988; p 54. Reilly, J. J.; Johnson, J. R.; Gamo, T. The Effect of Methane on the Rate of Hydrogen Absorption by LaNi5Hx in Liquid Suspension. J. Less-Common Met. 1987, 131, 41.
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Received for review January 31, 1997 Revised manuscript received June 6, 1997 Accepted June 12, 1997X IE970094U
X Abstract published in Advance ACS Abstracts, August 15, 1997.
