Optimized solar-powered liquid desiccant system to supply building fresh water and cooling needs

This paper studies the feasibility of using a solar-powered liquid desiccant system to meet both building cooling and fresh water needs in Beirut humid climate using parabolic solar concentrators as a heat source for regenerating the liquid desiccant. The water condensate is captured from the air leaving the regenerator. An integrated model of solar-powered calcium chloride liquid desiccant system for air dehumidification/humidification is developed. The LDS model predicted the amount of condensate obtained from the humid air leaving the regenerator bed when directed through a coil submerged in cold sea water. An optimization problem is formulated for selection and operation of a LDS to meet fresh water requirement and air conditioning load at minimal energy cost for a typical residential space in the Lebanon coastal climate with conditioned area of 80 m² with the objective of producing 15 l of fresh drinking water a day and meet air conditioning need of residence at minimum energy cost. The optimal regeneration temperature increases with decreased heat sink temperature with values of 50.5 °C and 52 °C corresponding to sink temperatures of 19 °C and 16 °C.     

Novel, low cost CaCl2 based desiccants for solar crop drying applications

Drying with solar-heated air is satisfactory so long as the sun is shining. To continue this process through the night-time and periods of cloud cover, it is necessary to either store some of this energy in a thermal mass or incorporate desiccants within the drying system. This paper reports the results from studies undertaken to develop three low cost, solar regenerative clay–CaCl₂ based solid desiccant materials; establish their moisture sorption and regeneration characteristics; assess their performance when compared with commercial desiccants; and integrate these within a low cost solar drying system for small-scale village-based crop drying. The moisture sorption and desorption performance of the desiccants were characterised in a Fison Environmental Cabinet at conditions of 85% (RH) and 25°C for 120 h for moisture sorption and 50°C and 20% (RH) for 8 h for regeneration. These conditions were representative of the environmental conditions monitored in the solar drying system. The bentonite–CaCl₂ (type 1) desiccant gave a maximum moisture sorption of 45% dry weight basis (dwb) while bentonite–CaCl₂ (type 2) and kaolinite–CaCl₂ (type 3) solid desiccants each gave moisture sorption values of 30% (dwb). It was concluded from the moisture sorption and regeneration characteristics that their application in solar crop drying and air dehumidification is highly useful due to their low regeneration temperatures, sub 100°C.     

Hydrogen sorption performance of MgH2 doped with mesoporous nickel- and cobalt-based oxides

The effect of mesoporous Co₃O₄, NiCo₂O₄ and NiO on the hydrogen sorption performance of MgH₂ was investigated. These oxides were synthesized by multi-step nanocasting and introduced during the high-energy ball milling of MgH₂ powder to act as catalysts. Hydrogen desorption on the as-milled powders was assessed upon heating the samples from room temperature to 400 °C. In all cases, the onset temperature for desorption was lowered by taking advantage of the introduced additives. The NiO-doped sample displayed the best response, the desorption rate being 7 times faster than in pure MgH₂. Complementary kinetic studies on this particular sample revealed that the sorption activation energies were much lower (50 kJ/mol for absorption and 335 kJ/mol for desorption) than the corresponding ones for undoped MgH₂ (57 kJ/mol for absorption and 345 kJ/mol for desorption), thus proving the catalytic activity of the mesoporous NiO oxide. Significantly, the X-ray powder diffraction (XRPD) patterns taken on the NiO-doped sample after discharging/charging cycles revealed that Mg could fully hydrogenate at the end of the charging process, while Mg metal was still detected in the undoped (pure) sample. Favored conditions for dissociative chemisorption of hydrogen could be ascribed to the formation of metallic Ni arising from complete or partial reduction of NiO, as observed in the XRPD patterns.     

Modeling of a hazelnut dryer assisted heat pump by using artificial neural networks

The artificial neural network (ANN) approach is generic technique for mapping non-linear relationships between inputs and outputs without knowing the details of these relationships. In this paper, an application of the ANN has been presented for a PID controlled heat pump dryer. In PID controlled heat pump dryer, air velocity changed according to the temperature value which is set in process control device. Heat pump dryer was tested drying of hazelnut at 40 °C, 45 °C and 50 °C drying air temperatures. By training the experiment results with ANN, drying air velocities, moisture content of hazelnuts and total drying time were predicted for 42 °C, 44 °C, 46 °C and 48 °C drying air temperatures.     

Investigation of the intermediate oxidation regime of Diesel fuel

A very high temperature fuel-air mixture is necessary for the thermal partial oxidation process of hydrocarbon fuels in order to have a high reaction temperature which accelerate the reaction kinetics. For Diesel fuel and due to the ignition delay time behavior, different oxidation behavior can be realized at different preheating temperatures. In this work, the intermediate oxidation region of Diesel fuel is investigated. By making use of the ignition delay time behavior, an vaporizer like tube reactor is constructed in order to enable a very high preheating temperature without the risk of self-ignition in a time-independent experiment. The oxidation behavior of Diesel fuel in air is investigated numerically and experimentally. In the numerical part, the ignition delay time was estimated using CHEMIKIN tools for different air-fuel mixtures at different temperatures. The evaporation behavior of the Diesel fuel-air mixtures are investigated at relatively high air preheating temperatures ranging from 500 °C up to 680 °C. The amount of the process air was varied from an air ratio λ = 0.35 to λ = 0.6. The experiments are also performed with N₂ as an evaporation media and compared with those performed with air to detect any temperature increase in the case of Diesel-air mixtures. The amount of heat release in the low chemistry region as well as in the intermediate region is calculated for the case of Diesel/air mixtures.The experiments show that four different oxidation region of Diesel fuel can be distinguished depending on air inlet temperatures and on the air ratio. At a temperature lower than 723 K (450 °C), no chemical reaction takes place. The cool flame reactions start at temperatures above 723 K (450 °C). However, no stable cool flame can be achieved unless the air preheating temperature reached about 753 K (480 °C). The cool flame region is extended up to about 873 K (600 °C), at which the intermediate regime started. This regime stabilized to a short range up to about 923 K (650 °C) after which ignition takes place.     

Cycling degradation of an automotive LiFePO4 lithium-ion battery

Degradation of a high capacity prismatic LiFePO₄ cell with deep cycling at elevated temperature of 50 °C is studied by electrochemical impedance spectroscopy as well as capacity and power fading characterization at different test temperatures (45, 25, 0 and −10 °C). Capacity fade after 600 cycles is 14.3% at 45 °C and 25.8% at −10 °C. There is little power fade at 45 °C after 600 cycles, whereas the power fade after 600 cycles is 61.6% and 77.2%, respectively, at 0 and −10 °C. The capacity and power fade evidently becomes more severe at lower temperature. In particular, the power fade at low temperatures (e.g., 0 and −10 °C) rather than capacity loss is a major limitation of the LiFePO₄ cell. The primary mechanism for capacity fade is loss of cyclable lithium in the cell resulting from lithium-consuming solid electrolyte interphase (SEI) layer growth and side reactions. The increased interfacial resistance (R_w) due to the catalytic growth of SEI layer on the graphite anode and increased electrolyte resistance are the main sources for power fade.     

Synthesis,electrical and electrochemical properties of Ba0.5Sr0.5Zn0.2Fe0.8O3−δ perovskite oxide for IT-SOFC cathode

The Ba_0.5Sr_0.5Zn_0.2Fe_0.8O_3−δ (BSZF) complex oxide with cubic perovskite structure was synthesized and examined as a new cobalt-free cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The electrical conductivity was relatively low with a peak value of 9.4 S cm⁻¹ at about 590 °C, which was mainly caused by the high concentration of oxygen vacancy and the doping of bivalent zinc in B-sites. At 650 °C and under open circuit condition, symmetrical BSZF cathode on Sm-doped ceria (SDC) electrolyte showed polarization resistances (R_p) of 0.48 Ω cm² and 0.35 Ω cm² in air and oxygen, respectively. The dependence of R_p with oxygen partial pressure indicated that the rate-limiting step for oxygen reduction was oxygen adsorption/desorption kinetics. Using BSZF as the cathode, the wet hydrogen fueled Ni + SDC anode-supported single cell exhibited peak power densities of 392 mW cm⁻² and 626 mW cm⁻² at 650 °C when stationary air and oxygen flux were used as oxidants, respectively.     

Redox behavior of supported Pd particles and its effect on oxygen reduction reaction in intermediate temperature solid oxide fuel cells

Nano-structured Pd-infiltrated YSZ cathodes (Pd + YSZ) are prepared by impregnation method and their electrocatalytic activity and reduction-oxidation behavior are investigated. It is observed that nano-sized PdO particles are uniformly distributed on the surface of the YSZ scaffold and decomposed at a temperature below 800 °C in air. Coexistence of Pd and PdO in the Pd + YSZ cathode is detected at temperatures between 650 and 750 °C. The polarization resistance R_E of the Pd + YSZ cathode decreases continuously as oxygen partial pressure increases from 0.001 to 1 atm at 600 and 850 °C, whereas it reaches a minimum in the vicinity of 0.03 atm of oxygen partial pressure at 750 °C. In air with an oxygen partial pressure of 0.21 atm, the Pd + YSZ shows the lowest activation energy for the oxygen reduction reaction in the temperature range of 650 and 750 °C.     

Adsorption refrigeration—An efficient way to make good use of waste heat and solar energy

This paper presents the achievements gained in solid sorption refrigeration prototypes since the end of the l970s, when interest in sorption systems was renewed. The applications included are ice making and air conditioning. The latter includes not only cooling and heating, but also dehumidification by desiccant systems. The prototypes presented were designed to use waste heat or solar energy as the main heat source. The waste heat could be from diesel engines or from power plants, in combined cooling, heating and power systems (CCHP). The current technology of adsorption solar-powered icemakers allows a daily ice production of between 4 and 7 kg m⁻² of solar collector, with a solar coefficient of performance (COP) between 0.10 and 0.16. The silica gel–water chillers studied can be powered by hot water warmer than 55 °C. The COP is usually around 0.2–0.6, and in some commercially produced machines, it can be up to 0.7. The utilization of such chillers in CCHP systems, hospitals, buildings and grain depots are discussed. Despite their advantages, solid sorption systems still present some drawbacks such as low specific cooling power (SCP) and COP. Thus, some techniques to overcome these problems are also contemplated, together with the perspectives for their broad commercialisation. Among these techniques, a special attention was devoted to innovative adsorbent materials, to advanced cycles and to heat pipes, which are suitable devices not only to improve the heat transfer but also can help to avoid corrosion in the adsorbers. Recent experiments performed by the research group of the authors with machines that employ composite adsorbent material and heat pipes showed that it is possible to achieve a SCP of 770 W kg⁻¹ of salt and COP of 0.39 at evaporation temperatures of −20 °C and generation temperature of 115 °C.     

Understanding the effect of TiO2, VCl3, and HfCl4 on hydrogen desorption/absorption of NaAlH4

The main objective of this work was to investigate the different effects of transition metals (TiO₂, VCl₃, HfCl₄) on the hydrogen desorption/absorption of NaAlH₄. The HfCl₄ doped NaAlH₄ showed the lowest temperature of the first desorption at 85 °C, while the one doped with VCl₃ or TiO₂ desorbed at 135 °C and 155 °C, respectively. Interestingly, the temperature of desorption in subsequent cycles of the NaAlH₄ doped with TiO₂ reduced to 140 °C. On the contrary, in the case of NaAlH₄ doped with HfCl₄ or VCl₃, the temperature of desorption increased to 150 °C and 175 °C, respectively. This may be because Ti can disperse in NaAlH₄ better than Hf and V; therefore, this affected segregation of the sample after the desorption. The maximum hydrogen absorption capacity can be restored up to 3.5 wt% by doping with TiO₂, while the amount of restored hydrogen was lower for HfCl₄ and VCl₃ doped samples. XRD analysis demonstrated that no Ti-compound was observed for the TiO₂ doped samples. In contrast, there was evidence of Al–V alloy in the VCl₃ doped sample and Al–Hf alloy in the HfCl₄ doped sample after subsequent desorption/absorption. As a result, the V- or Hf-doped NaAlH₄ showed the lower ability to reabsorb hydrogen and required higher temperature in the subsequent desorptions.     

A two-stage hydrogen compressor based on (La,Ce,Nd,Pr)Ni5 intermetallics obtained by low energy mechanical alloying – Low temperature annealing treatment

La_0.67Ce_0.19Nd_0.08Pr_0.06Ni₅ was synthesized by low energy mechanical alloying. The AB₅ was milled up to completion stage to reach the final composition and appropriate particle size distribution and microstructure characteristics. Crystallite size, strain and sorption properties of as-milled samples were evaluated. After milling, La_0.67Ce_0.19Nd_0.08Pr_0.06Ni₅ and previously obtained LaNi₅ were annealed at 600 °C for 24 h. An improvement in both microstructural and hydrogen sorption properties was found. Equilibrium hydrogen sorption properties were obtained and quantified in the 25–90 °C range. From these results, a two-stage hydrogen compressor was proposed. In the first stage, hydrogen is absorbed by LaNi₅ at 575 kPa and 25 °C and desorbed at 1365 kPa and 90 °C. In the second stage, this fluid is absorbed by La_0.67Ce_0.19Nd_0.08Pr_0.06Ni₅ at 745 kPa and 25 °C and desorbed at 2100 kPa and 90 °C. As a result, a global compression ratio of 3.65 is reached using this scheme.     

Exploring the effects of symmetrical and asymmetrical relative humidity on the performance of H2/air PEM fuel cell at different temperatures

This article is dedicated to study the interlinked effects of symmetric relative humidity (RH), and asymmetric RH on the performance of H₂/air PEM fuel cell at different temperatures. The symmetric and asymmetric RH were achieved by setting the cathode relative humidity (RHC) and anode relative humidity (RHA) as equal and unequal values, respectively. The cell performance was evaluated by collecting polarization curves of the cell at different RH, RHC and RHA and at different cell temperatures (T_cell). The polarization curves along with the measured internal cell resistance (membrane resistance) were discussed in the light of the present fuel cell theory. The results showed that symmetric relative humidity has different impacts depending on the cell temperature. While at RH of 35% the cell can show considerable performance at T_cell = 70 °C, it is not so at T_cell = 90 °C. At T_cell = 70 °C, the cell potential increases with RH at lower and medium current densities but decreases with RH at higher currents. This was attributed to the different controlling processes at higher and lower current densities. This trend at 70 °C is completely destroyed at 90 °C. Operating our PEM fuel cell at dry H₂ gas conditions (RHA = 0%) is not detrimental as operating the cell at dry Air (O₂) conditions (RHC = 0%). At RHA = 0% and humidified air, water transport by back diffusion from the cathode to the anode at the employed experimental conditions can support reasonable rehydration of the membrane and catalysts. At RHA = 0, a possible minimum RHC for considerable cell operation is temperature dependent. At RHC = 0 conditions, the cell can operate only at RHA = 100% with a loss that depends on T_cell. It was found that the internal cell resistance depends on RH, RHA, RHC and T_cell and it is consistent with the observed cell performance.     

Improvement of hydrogen storage properties of the AB2 Laves phase alloys for automotive application

Hydrogen storage properties of the Ti_1.1CrMn AB₂-type Laves phase alloys, for both low (−30 °C) and high (80 °C) temperature applications, are improved by substituting Zr at Ti site. In agreement with the larger radius of Zr than Ti, the lattice volume of (Ti_1−xZr_x)_1.1CrMn (x=0, 0.05, 0.06 and 0.1) alloys, prepared by arc melting, increases with x. The increase in the Zr content leads to a decrease in the equilibrium hydrogen sorption pressure plateau and faster absorption kinetics, associated with an increase in the hydrogen storage capacity from 1.9 to 2.2 wt% for Ti_1.1CrMn and (Ti_0.9Zr_0.1)_1.1CrMn alloys, respectively. At −5 °C, (Ti_0.9Zr_0.1)_1.1CrMn alloy reversibly absorbs and desorbs 2.2 wt% at 160 bar within 250 s. Based on thermodynamic calculated values, the optimized Zr substituted alloy (Ti_0.9Zr_0.1)_1.1CrMn desorbs hydrogen at 3.2 bar at −30 °C and 135 bar at 80 °C. This is a significant reduction of the sorption pressure plateau as compared with the current technology for mobile applications based on Ti_1.1CrMn alloy with hydrogen desorption plateau above 400 bar at 80 °C. Finally, the mechanism of improved hydrogen storage properties is discussed based on the radius and the hydrogen affinity of the substituting element.     

Analytical method for evaluation of gas turbine inlet air cooling in combined cycle power plant

Gas turbine inlet air cooling technologies (GTIAC), mainly including chilling with LiBr/water absorption chiller and fogging as well, are being used during hot seasons to augment the power output. To evaluate the general applicability of inlet air cooling for gas–steam combined cycle power plant (GTCCIAC), parameters such as efficiency ratio, profit ratio and relative payback period were defined and analyzed through off-design performances of both gas turbine and inlet air cooling systems. An analytical method for applicability evaluation of GTCCIAC with absorption chiller (inlet chilling) and saturated evaporative cooler (inlet fogging) was presented. The applicability study based on typical off-design performances of the components in GTCCIAC shows that, the applicability of GTCCIAC with chilling and fogging depends on the design economic efficiency of GTCC power plant. In addition, it relies heavily on the climatic data and the design capacity of inlet air cooling systems. Generally, GTCCIAC is preferable in the zones with high ambient air temperature and low humidity. Furthermore, it is more appropriate for those GTCC units with lower design economic efficiency. Comparison of the applicability between chilling and fogging shows that, inlet fogging is superior in power efficiency at t_a = 15–20 °C though it gains smaller profit margin than inlet chilling. GTCC inlet chilling with absorption chiller is preferable in the zones with t_a > 25 °C and RH > 0.4.     

Predictions of moisture removal rate and dehumidification effectiveness for structured liquid desiccant air dehumidifier

In hot and humid climates such as in the Sultanate of Oman, the humidity puts extra load on the electric vapor-compression air conditioning (VAC) systems. Liquid and solid desiccants can reduce the moisture content of humid air and thus reduce the latent load imposed on the VAC systems. In the present work, the performance of air dehumidifiers using triethylene glygol (TEG) as desiccant was investigated. Three differently structured packing densities were used (77, 100 and 200 m²/m³). The performance of the dehumidifier was evaluated and expressed in terms of the moisture removal rate (m_cond) and the dehumidifier effectiveness (ε_y). The experimental work was undertaken to study the effects of several influencing design factors on this performance. The design factors covered included the air and TEG flow rates, air and TEG inlet temperatures, inlet air humidity and the inlet TEG concentration. The desiccant flow rate investigated was much less than that covered in previous studies and the range of the inlet temperatures of air and desiccant was significantly wider. The objective this study was to use the multiple regression method and the principal component analysis to obtain statistical prediction models for the water condensation rate and the dehumidification effectiveness in terms of these design factors. The results of both techniques agree with each other affirmed that the desiccant flow rate, desiccant inlet concentration and air inlet temperature are the most significant variables in predicting m_cond, whereas desiccant flow rate, air inlet temperature and packing density are the most significant variables in predicting ε_y.     

High temperature electrochemical performance of nanosized LiFePO4

The electrochemical performance of LiFePO₄ was tested at temperatures up to 150 °C for micrometric and nanometric size samples. Among the latter, both highly defective samples obtained by direct precipitation and annealed samples were tested. The comparison of voltage composition profiles for these samples coupled to GITT experiments allowed to conclude that defects seem to be the major factor in inducing the solid solution behaviour at room temperature. Good capacity retention is exhibited upon prolonged cycling at 100 °C in EC LiBOB electrolyte, also for nanosized samples that still maintain 75% of the initial capacity after 170 cycles. These results prove that the enhanced thermal stability of such electrolytes can be extended to temperatures much higher than those usually tested.     

Study of CO2 stability and electrochemical oxygen activation of mixed conductors with low thermal expansion coefficient based on the TbBaCo3ZnO7+δ system

The influence of different application-oriented factors on the electrochemical activity and stability of TbBaCo₃ZnO_7+δ when used as a solid oxide fuel cell cathode has been studied. Calcination at temperatures above 900 °C (e.g. 1000 °C) leads to a significant increase in the electrode polarization resistance. The effect of the sintering temperature of the TbBaCo₃ZnO_7+δ cathode seems to be more important than the effect produced by the Tb substitution as observed when compared with 900 °C-sintered YBaCo₃ZnO_7+δ; and ErBaCo₃ZnO_7+δ electrode performances. The presence of CO₂ in the air flow leads to an increase of roughly 10% in the polarization resistance for the whole studied temperature range (500-850 °C) while this effect is reversible. Analysis of the impedance spectroscopy measurements shows that the exchange rate constant (k_G from Gerischer element) is significantly affected by CO₂ at temperatures below 700 °C, while the diffusion coefficient related parameter is slightly influenced at low temperatures. Electrode degrades with a low constant rate of 1 mΩ cm² h⁻¹ after 60 h. This cathode material exhibits high CO₂ tolerance, as shown by temperature programmed treatment under a continuous gas flow of air with 5% CO₂, and a relatively low thermal expansion coefficient.     

Fabrication and electrochemical properties of lithium-ion batteries for power tools

204056-Type prismatic lithium-ion battery for power tools was developed by using LiMn₂O₄ as cathode and CMS (carbonaceous mesophase spheres) as anode. The performance of batteries and their electrodes were characterized by SEM, ac impedance and electrochemical tests. The bulk density of cathode after pressing was selected as a main factor and it effects on high current rate capability and discharge plateau distinctly, which were investigated in details. Being charged/discharged in the voltage range of 2.5–4.2 V, the normal LiMn₂O₄ battery with cathode bulk density of 2.7 g cm⁻³ shows excellent electrochemical performances. The discharge capacity at 20C rate is 94.1% of that at 1C rate, and the capacity retention ratio charged at 1C and discharged at 5C is 91.7% after 100 cycles at 25 °C. While modified LiMn₂O₄ is used as the cathode material, the cycling performance of batteries is better than that of batteries made from normal LiMn₂O₄. The capacity retention ratios of modified LiMn₂O₄ batteries after 100 cycles at 25 °C and 55 °C are 95.0% and 85.3%, respectively. The discharge capacity at low temperature was tested both at 1C rate and 5C rate, and the capacities discharged at −20 °C were 96.3% and 94.2% of that at 1C at 25 °C. Furthermore, the batteries also show good safety in the test of short circuit, overcharge, and nail penetration.     

Deuteration properties of CaNi5−xCux system

Intermetallic compounds with nominal formula CaNi_5−xCu_x (x = 0, 1, 2.5) have been prepared in order to investigate their hydrogenation properties. The samples were obtained by arc-melting and were deuterated in a Sieverts reactor. For x = 0 and 1, we have found that the fast kinetics and the different shape of the curve (non sigmoidal) in the second absorption process indicate an improvement of the hydrogen absorption due to the activation of the alloys. The deuterium desorption spectra are similar for x = 0 and 1 whereas for x = 2.5 the desorption ranges a broader temperature interval (∼100-350 °C) indicating a certain degree of chemical inhomogeneity or amorphization intrinsic to the parent sample or induced by the deuterium absorption. The formed deuterides were passivated in the presence of air in order to carry out a neutron diffraction study, allowing us to determine the deuterium positions in the samples. While in CaNi₄CuD_y the deuterium is randomly distributed over seven different positions, in CaNi₅D_y the deuterium only occupies five of them. This wider distribution in CaNi₄CuD_y can explain its higher stability, and therefore, its higher desorption temperature for deuterium.     

La substituted Sr2MnO4 as a possible cathode material in SOFC

Sr_2−xLa_xMnO_4+δ (x = 0.4, 0.5, 0.6) oxides were studied as the cathode material for solid oxide fuel cells (SOFC). The reactivity tests indicated that no reaction occurred between Sr_2−xLa_xMnO_4+δ and CGO at annealing temperature of 1000 °C, and the electrode formed good contact with the electrolyte after being sintered at 1000 °C for 4 h. The total electrical conductivity, which has strong effect on the electrode properties, was determined in a temperature range from 100 to 800 °C. The maximum value of 5.7 S cm⁻¹ was found for the x = 0.6 phase at 800 °C in air. The cathode polarization and AC impedance results showed that Sr_1.4La_0.6MnO_4+δ exhibited the lowest cathode overpotential. The area specific resistance (ASR) was 0.39 Ω cm² at 800 °C in air. The charge transfer process is the rate-limiting step for oxygen reduction reaction on Sr_1.4La_0.6MnO_4+δ electrode.