Performance calculation of single effect absorption heat pump using LiBr + LiNO3 + H2O as working fluid

In order to check the theoretical performance of the new working fluid LiBr + LiNO₃+H₂O (mole ratio of LiBr and LiNO₃ = 4:1), the theoretical coefficients of performance (COP) of this working fluid and LiBr + H₂O were calculated at various operating conditions. The improvement of crystallization problem was also checked. This proposed working fluid was proved to increase the COP by about 5% than LiBr + H₂O. The cooling water through absorber and evaporator was heated to higher temperature by this new working fluid. LiBr + LiNO₃ + H₂O was found to be an alternative to the conventional LiBr + H₂O with higher COP and less corrosivity.     

Experimental study of heat and mass transfer on an absorber with several enhancement tubes

An experimental study of the absorption process of water vapor into a lithium bromide solution was performed. For the purpose of the development of a high-performance absorption chiller/heater utilizing a lithium bromide solution as the working fluid, it is the most effective way to improve the performance of the absorber with the largest heat transfer area of the four heat exchangers. This paper considers a bare tube, bumping bare tube, floral tube, and twisted floral tube for the absorber of an absorption chiller/heater. The floral and twisted floral tubes have about 40% higher heat and mass transfer performance than the bare tube conventionally used in an absorber. Therefore, floral and twisted floral tubes are expected to realize high heat and mass transfer performance. © 1999 Scripta Technica, Heat Trans Asian Res, 28(8): 664–674, 1999     

Modeling and performance analysis of an absorption chiller with a microchannel membrane‐based absorber using LiBr‐H2O,LiCl‐H2O,and LiNO3‐NH3

In order to develop compact absorption refrigeration cycles driven by low heat sources, the simulated performance of a microchannel absorber of 5‐cm length and 9.5 cm³ in volume provided with a porous membrane is presented for 3 different solution‐refrigerant pairs: LiBr‐H₂O, LiCl‐H₂O, and LiNO₃‐NH₃. The high absorption rates calculated for the 3 solutions lead to large cooling effect to absorber volume ratios: 625 kW/m³ for the LiNO₃‐NH₃, 552 kW/m³ for the LiBr‐H₂O, and 318 kW/m³ for the LiCl‐H₂O solutions given the studied geometry. The performance of a complete absorption system is also analyzed varying the solution concentration, condensation temperature, and desorption temperature. The LiNO₃‐NH₃ and the LiBr‐H₂O solutions provide the largest cooling effects. The LiNO₃‐NH₃ can work at a lower temperature of the heating source, in comparison with the one needed in a LiBr‐H₂O system. The lowest cooling effect and coefficient of performance are found for the LiCl‐H₂O solution, but this mixture allows the use of lower temperature heating sources (below 70°C). These results can be used for the selection of the most suitable solution for a given cooling duty, depending on the available heat source and condensation temperature.     

2LiH + M (M = Mg, Ti): New concept of negative electrode for rechargeable lithium-ion batteries

xLiH + M composites, where M = Mg or Ti, are suggested as new candidates for negative electrode for Li-ion batteries. For this purpose, the xLiH + M electrode is prepared using the mechanochemical reaction: MH_x + xLi → xLiH + M or by simply grinding a xLiH + M mixture. The most promising electrochemical behaviour is obtained with the (2LiH + Mg) composite prepared via a mechanochemical reaction between MgH₂ and metallic Li leading to a very divided composite in which Mg crystallites of 20 nm size are embedded in a LiH matrix. Reversible capacities of 1064 mAh g⁻¹ (three times as much as the one of graphite) and 600 mAh g⁻¹ are reached for these phase mixtures after 1 and 28 h of grinding in vertical and planetary mill, respectively. The (2LiH + Ti) mixture prepared via the mechanochemical reaction between TiH₂ and Li exhibits a reversible capacity of 428 mAh g⁻¹. From X-ray diffraction measurements, the performances of the electrodes are attributed to the electrochemical conversion reaction: M + xLiH ↔ MH_x + xLi⁺ + xe⁻ (M = Mg, Ti) followed for M = Mg by an alloying process where M reacts with lithium ions to form Mg_1−xLi_x alloys.     

Initialization of a methane-fueled single-chamber solid-oxide fuel cell with NiO + SDC anode and BSCF + SDC cathode

The initialization of an anode-supported single-chamber solid-oxide fuel cell, with NiO + Sm_0.2Ce_0.8O_1.9 anode and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ + Sm_0.2Ce_0.8O_1.9 cathode, was investigated. The initialization process had significant impact on the observed performance of the fuel cell. The in situ reduction of the anode by a methane–air mixture failed. Although pure methane did reduce the nickel oxide, it also resulted in severe carbon coking over the anode and serious distortion of the fuel cell. In situ initialization by hydrogen led to simultaneous reduction of both the anode and cathode; however, the cell still delivered a maximum power density of ∼350 mW cm⁻², attributed to the re-formation of the BSCF phase under the methane–air atmosphere at high temperatures. The ex situ reduction method appeared to be the most promising. The activated fuel cell showed a peak power density of ∼570 mW cm⁻² at a furnace temperature of 600 °C, with the main polarization resistance contributed from the electrolyte.     

Structural and thermal properties of boron nanoparticles synthesized from B2O3 + 3Mg + kNaCl mixture

Amorphous boron nanoparticles were synthesized by heating a B₂O₃ + 3 Mg + kNaCl (k is the number of moles of NaCl) exothermic mixture in a laboratory oven at 800 °C under argon flow. NaCl was used as inert material to decrease the maximum combustion temperature of the reaction mixture when it was self-ignited after the melting of Mg at 650 °C. The size of the boron nanoparticles extracted from the final product by acid leaching ranged between 30 and 300 nm for k values ranging from 1 to 5. Moreover, increasing the value of k from 1 to 5 resulted in an increase in the specific surface area of the nanoparticles from 40 to 74 m² g⁻¹. However, at k = 10, a decrease in the specific surface area to 47.56 m² g⁻¹ was recorded due to incomplete reduction of B₂O₃. The ignition point of boron nanoparticles in air as estimated using a thermocouple was approximately 300 °C. Digital camera recording of the combustion process of boron nanoparticles in air revealed that the burning speed of the nanoparticles increased significantly from 0.3 to 15 cm/s when k increased from 1 to 5.     

Study of the H + O + M reaction forming OH: Kinetics of OH chemiluminescence in hydrogen combustion systems

The temporal variation of OH^∗ (A²Σ⁺) chemiluminescence in hydrogen oxidation chemistry has been studied in a shock tube behind reflected shock waves at temperatures of 1400-3300 K and at a pressure of 1 bar. The aim of the present work is to obtain a validated reaction scheme to describe OH^∗ formation in the H₂/O₂ system. Temporal OH^∗ emission profiles and ignition delay times for lean and stoichiometric H₂/O₂ mixtures diluted in 97-98% argon were obtained from the shock-tube experiments. Based on a literature review for the hydrogen combustion system, the key reaction considered was H + O + M = OH^∗ + M (R1). The temperature dependence of the measured peak OH^∗ emission from the shock tube and the peak OH^∗ concentration from a homogeneous closed reactor model are compared. Based on these results a reaction rate coefficient of k₁ = (1.5 ± 0.4) × 10¹³ exp(−25 kJ mol⁻¹/RT) cm⁶ mol⁻² s⁻¹ was found for the forward reaction (R1) which is slightly higher than the rate coefficient suggested by Hidaka et al. (1982). The comparison of measured and simulated absolute concentrations shows good agreement. Additionally, a one-dimensional laminar premixed low-pressure flame calculation was performed for where absolute OH^∗ concentration measurements have been reported by Smith et al. (2005). The absolute peak OH^∗ concentration is fairly well reproduced if the above mentioned rate coefficient is used in the simulation.     

Solar absorption cooling plant in Seville

A solar/gas cooling plant at the Engineering School of Seville (Spain) was tested during the period 2008-2009. The system is composed of a double-effect LiBr + water absorption chiller of 174 kW nominal cooling capacity, powered by: (1) a pressurized hot water flow delivered by mean of a 352 m² solar field of a linear concentrating Fresnel collector and (2) a direct-fired natural gas burner. The objective of the project is to indentify design improvements for future plants and to serve as a guideline. We focused our attention on the solar collector size and dirtiness, climatology, piping heat losses, operation control and coupling between solar collector and chiller. The daily average Fresnel collector efficiency was 0.35 with a maximum of 0.4. The absorption chiller operated with a daily average coefficient of performance of 1.1-1.25, where the solar energy represented the 75% of generator’s total heat input, and the solar cooling ratio (quotient between useful cooling and insolation incident on the solar field) was 0.44.     

The effects of ball milling and nanometric nickel additive on the hydrogen desorption from lithium borohydride and manganese chloride (3LiBH4 + MnCl2) mixture

A mixture of [3LiBH₄ + MnCl₂] was processed by high energy ball milling in ultra-high purity hydrogen gas for 0.5 and 1 h. The XRD patterns of milled powders show the sole diffraction peaks of LiCl. The reaction occurring during milling of [3LiBH₄ + MnCl₂] seems to have all characteristics of the metathesis-type reactions occurring between borohydrides (LiBH₄ and NaBH₄) and metal chlorides (MCl_n) induced in a solid state by a mechano-chemical activation synthesis (MCAS). Under pressure of 0.1 MPa H₂ (atmospheric) the ball milled [3LiBH₄ + MnCl₂] mixture is able to desorb ∼4.0 wt.% H₂ at 100 °C within 21,000 s and ∼4.5 wt.% H₂ at 120 and 200 °C within 8000 s and 4000 s, respectively. The addition of n-Ni with SSA = 60.5 m²/g allows desorption of ∼3.7wt.%H₂ within 8,700 s at 100 °C. This is one of the highest H₂ desorption capacities obtained for a complex hydride at 100 °C under atmospheric pressure of H₂ taking into account the fact that the microstructure contains some amount of a useless LiCl constituent. The activation energy of hydrogen desorption for a ball milled undoped [3LiBH₄ + MnCl₂] is ∼102 kJ/mol and ∼98 and 92 kJ/mol after doping with 5 wt.% of nanometric Ni having specific surface area (SSA) of 9.5 and 60.5 m²/g, respectively. After volumetric desorption from 100 to 450 °C the XRD patterns show only LiCl. The n-Ni additive slightly lowers the total quantity of desorbed H₂. Re-absorption tests, under pressure of 10 MPa H₂ at 200 °C, show that the system is, most likely, irreversible. Flammability studies show that the ball milled [3LiBH₄ + MnCl₂] mixture can be ignited by scraping the cylinder walls with a metal tool as well when it is thrown and dispersed in air in a powder form. It also reacts violently in contact with water and a nitric acid.     

Comparative analysis of a solar‐driven novel salt‐based absorption chiller with the implementation of nanoparticles

The present study exemplifies the comprehensive thermal analysis to compare and contrast ammonia‐lithium nitrate (NH₃‐LiNO₃) and ammonia‐sodiumthiocynate (NH₃‐NaSCN) absorption systems with and without incorporation of nanoparticles. A well‐mixed solution of copper oxide/water (CuO/H₂O) nanofluid is considered inside a flat‐plate collector linked to an absorption chiller to produce 15‐kW refrigeration at ?5°C evaporator temperature. Enhancements in heat transfer coefficient, thermal efficiency, and useful heat gain of the collector are evaluated, and the effect of these achievements on the performance of both absorption chillers have been determined for different source temperatures. A maximum 121.7% enhancement is found in the heat transfer coefficient with the application of the nanofluid at 2% nanoparticle concentration. The maximum coefficient of performance observed for the NH₃‐NaSCN chiller is 0.12% higher than that for the NH₃‐LiNO₃ chiller at 0°C evaporator temperature. Contradictory to this, the average system coefficient of performance of the NH₃‐LiNO₃ absorption system has been found 5.51% higher than that of the NH₃‐NaSCN system at the same evaporator temperature. Moreover, the application of the nanofluid enhanced the performance of the NH₃‐NaSCN and NH₃‐LiNO₃ systems by 2.70% and 1.50%, respectively, for lower generator temperature and becomes almost the same at higher temperatures, which altogether recommends the flat‐plate collector–coupled NH₃‐LiNO₃ absorption system be integrated with a nanofluid.     

A study on lithium/air secondary batteries—Stability of the NASICON-type lithium ion conducting solid electrolyte in alkaline aqueous solutions

The stability of the high lithium ion conducting glass ceramics, Li_1+x+yTi_2−xAl_xSi_yP_3−yO₁₂ (LTAP) in alkaline aqueous solutions with and without LiCl has been examined. A significant conductivity decrease of the LTAP plate immersed in 0.057 M LiOH aqueous solution at 50 °C for 3 weeks was observed. However, no conductivity change of the LTAP plate immersed in LiCl saturated LiOH aqueous solutions at 50 °C for 3 weeks was observed. The pH value of the LiCl-LiOH-H₂O solution with saturated LiCl was in a range of 7-9. The molarity of LiOH and LiCl in the LiOH and LiCl saturated aqueous solution were estimated to be 5.12 and 11.57 M, respectively, by analysis of Li⁺ and OH⁻. The high concentration of LiOH and the low pH value of 8.14 in this solution suggested that the dissociation of LiOH into Li⁺ and OH⁻ is too low in the solution with a high concentration of Li⁺. These results suggest that the water stable LTAP could be used as a protect layer of the lithium metal anode in the lithium/air cell with LiCl saturated aqueous solution as the electrolyte, because the content of OH⁻ ions in the LiCl saturated aqueous solution does not increase via the cell reaction of Li + 1/2O₂ + H₂O → 2LiOH, and LTAP is stable under a deep discharge state.     

Synthesis and electrochemical properties of Li1−xFe0.8Ni0.2O2–LixMnO2 (Mn/(Fe + Ni + Mn) = 0.8) material

A new type of Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ (Mn/(Fe + Ni + Mn) = 0.8) material was synthesized at 350 °C in air atmosphere using a solid-state reaction. The material had an XRD pattern that closely resembled that of the original Li_1−xFeO₂–Li_xMnO₂ (Mn/(Fe + Mn) = 0.8) with much reduced impurity peaks. The Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell showed a high initial discharge capacity above 192 mAh g⁻¹, which was higher than that of the parent Li/Li_1−xFeO₂–Li_xMnO₂ (186 mAh g⁻¹). We expected that the increase of initial discharge capacity and the change of shape of discharge curve for the Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell is the result from the redox reaction from Ni²⁺ to Ni³⁺ during charge/discharge process. This cell exhibited not only a typical voltage plateau in the 2.8 V region, but also an excellent cycle retention rate (96%) up to 45 cycles.     

Lithium difluoro(oxalato)borate/ethylene carbonate + propylene carbonate + ethyl(methyl) carbonate electrolyte for LiMn2O4 cathode

Lithium difluoro(oxalato)borate (LiODFB) was investigated as a lithium salt for non-aqueous electrolytes for LiMn₂O₄ cathode in lithium-ion batteries. Linear sweep voltammetry (LSV) tests were used to examine the electrochemical stability and the compatibility between the electrolytes and LiMn₂O₄ cathode. Through inductively coupled plasma (ICP) analysis, we compared the amount of Mn²⁺ dissolved from the spinel cathode in 1 mol L⁻¹ LiPF₆/EC + PC + EMC (1:1:3 wt.%) and 1 mol L⁻¹ LiODFB/EC + PC + EMC (1:1:3 wt.%). AC impedance measurements and scanning electron microscopy (SEM) analysis were used to analyze the formation of the surface film on the LiMn₂O₄ cathode. These results demonstrate that ODFB anion can capture the dissolution manganese ions and form a denser and more compact surface film on the cathode surface to prevent the continued Mn²⁺ dissolution, especially at high temperature. It is found that LiODFB, instead of LiPF₆, can improve the capacity retention significantly after 100 cycles at 25 °C and 60 °C, respectively. LiODFB is a very promising lithium salt for LiMn₂O₄ cathode in lithium-ion batteries.     

Ni–Fe + SDC composite as anode material for intermediate temperature solid oxide fuel cell

Composite materials of Sm_0.2Ce_0.8O_1.9 (SDC) with various Ni–Fe alloys were synthesized and evaluated as the anode for intermediate temperature solid oxide fuel cell. The performance of single cells consisting of the Ni–Fe + SDC anode, SDC buffer layer, La_0.8Sr_0.2Ga_0.83Mg_0.17O_2.815 (LSGM) electrolyte, and SrCo_0.8Fe_0.2O_3 − δ (SCF) cathode were measured in the temperature range of 600–800 °C with wet H₂ as fuel. It was found that the anodic overpotentials of the different Fe–Ni compositions at 800 °C were in the following order: Ni_0.8Fe_0.2 < Ni_0.75Fe_0.25 < Ni < Ni_0.7Fe_0.3 < Ni_0.9Fe_0.1 < Ni_0.95Fe_0.05 < Ni_0.33Fe_0.67. The single cell with the Ni_0.8Fe_0.2 + SDC anode exhibited a maximum power density of 1.43 W cm⁻² at 800 °C and 0.62 W cm⁻² at 700 °C. The polarization resistance of the Ni_0.8Fe_0.2 + SDC anode was as low as 0.105 Ω cm² at 800 °C under open circuit condition. A stable performance with essentially negligible increase in anode overpotential was observed during about 160 h operation of the cell with the Ni_0.8Fe_0.2 + SDC anode at 800 °C with a fixed current density of 1875 mA cm⁻². The possible mechanism responsible for the improved electrochemical properties of the composite anodes with the Ni_0.8Fe_0.2 and Ni₀₇₅Fe_0.25 alloys was discussed.     

Effect of heat treatment and chemical composition on the corrosion behavior of FeAl intermetallics in molten (Li + K)carbonate

The corrosion performance of various Fe–Al alloys in 62 mol. %Li₂CO₃-38 mol.%K₂CO₃ at 650 °C has been studied using the weight loss technique. Alloys included FeAl with additions of 1, 3 and 5 at.% of either Ni or Li with or without a heat treatment at 400 °C during 144 h. For comparison, 316L type stainless steel was also studied. The tests were complemented by X-ray diffraction (XRD), scanning electronic microscopy and microchemical studies. Results showed that FeAl base alloy without heat treatment had the highest corrosion rate but by either heat treating it or by adding either Ni or Li the mass gain was decreased. When the FeAl base alloy was heat treated and alloyed with either 5Ni or 1Li the degradation rate reached as low values as those found for 316L stainless steel which had the lowest degradation rate. Both Ni and Li improved the adhesion of external protective layer either by avoiding the formation of voids or by lowering the number of precipitates and making them more homogenously distributed.     

Hydrogen storage properties of Mg–30 wt.% LaNi5 composite prepared by hydriding combustion synthesis followed by mechanical milling (HCS + MM)

A Mg–30 wt.% LaNi₅ composite was prepared by hydriding combustion synthesis followed by mechanical milling (HCS + MM), and the hydriding and dehydriding properties of the HCS + MM product were compared with those of the HCS product and the MM product. The dehydriding temperature onsets of the MM and HCS + MM products were both 470 K, which were lower than that of the HCS product by 100 K. Moreover, the HCS + MM product desorbed faster than the MM product, e.g., the former desorbed completely upon heating to 510 K, whereas the latter did not decompose completely until 590 K. Additionally, the HCS + MM product reached a saturated hydrogen absorption capacity of 3.80 wt.% at 373 K in 50 s, but both the HCS product and the MM product absorbed less than 1.50 wt.% of hydrogen at 373 K in 1800 s. These results suggest the potential of the HCS + MM processing in preparing Mg-based hydrogen storage materials.     

5 kWe + 5 kWt reformer-PEMFC energy generator from bioethanol first data on the fuel processor from a demonstrative project

A power unit constituted by a reformer section, a H₂ purification section and a fuel cell stack is being tested c/o the Dept. of Physical Chemistry and Electrochemistry of Università degli Studi di Milano, on the basis of a collaboration with HELBIO S.A. Hydrogen and Energy Production Systems, Patras (Greece), supplier of the unit, and some sponsors (Linea Energia S.p.A., Parco Tecnologico Padano and Provincia di Lodi, Italy). The system size allows to co-generate 5 kW_e (220 V, 50 Hz a.c.) + 5 kW_t (hot water at 65 °C) as peak output. Bioethanol, obtainable by different non-food-competitive biomass, is transformed into syngas by a pre-reforming and reforming reactors couple and the reformate is purified from CO to a concentration below 20 ppmv, suitable to feed a proton exchange membrane fuel cell (PEMFC) stack that will be integrated in the fuel processor in a second step of the experimentation. This result is achieved by feeding the reformate to two water gas shift reactors, connected in series and operating at high and low temperature, respectively. CO concentration in the outcoming gas is ca. 0.4 vol% and the final CO removal to meet the specifications is accomplished by two methanation reactors in series. The second methanation step acts merely as a guard, since ca. 15 ppmv of CO are obtained already after the first reactor.     

Augmentation of heat transfer coefficient by using 90° broken transverse ribs on absorber plate of solar air heater

An experimental investigation has been carried out to study the heat transfer coefficient by using 90° broken transverse ribs on absorber plate of a solar air heater; the roughened wall being heated while the remaining three walls are insulated. The roughened wall has roughness with pitch (P), ranging from 10–30 mm, height of the rib of 1.5 mm and duct aspect ratio of 8. The air flow rate corresponds to Reynolds number between 3000–12,000. The heat transfer results have been compared with those for smooth ducts under similar flow and thermal boundary condition to determine the thermal efficiency of solar air heater.     

Oxidation of methanol on perovskite-type La2-xSrxNiO4 (0 ≤ x ≤ 1) film electrodes modified by dispersed nickel in 1 M KOH

Finely-dispersed nickel particles are electrodeposited on high surface-area perovskite-type La_2-xSr_xNiO₄ (0 ≤ x ≤ 1) electrodes for possible use in a direct methanol fuel cell (DMFC). The study is conducted by cyclic voltammetry, chronoamperometry, impedance spectroscopy and anodic Tafel polarization techniques. The results show that the apparent electrocatalytic activities of the modified oxide electrodes are much higher than those of unmodified electrodes under similar experimental conditions; the observed activity is the greatest with the modified La_1.5Sr_0.5NiO₄ electrode. At 0.550 V (vs. Hg|HgO) in 1 M KOH + 1 M CH₃OH at 25 °C, the latter electrode delivers a current density of over 200 mA cm⁻², whereas other electrodes of the series produce relatively low values (65–117 mA cm⁻²). To our knowledge, such high methanol oxidation current densities have not been reported on any other non-platinum electrode in alkaline solution. Further, the modified electrodes are not poisoned by methanol oxidation intermediates/products.     

The reaction pathway and rate-limiting step of dehydrogenation of the LiHN2 + LiH mixture

The reaction pathway and rate-limiting step of dehydrogenation of the LiNH₂ + LiH mixture have been investigated. The study reveals that dehydrogenation of the LiNH₂ + LiH mixture is diffusion-controlled and the rate-limiting step is NH₃ diffusion through the Li₂NH product layer outside the LiNH₂ shrinking core. This phenomenon is explained based on a model describing the major steps of the dehydriding reaction of the mixture, and related to the evidence obtained from X-ray diffraction and specific surface area measurements of the mixture before and after isothermal hydrogen uptake/release cycles at high homologous temperatures.