Design of Plate-Fin Tube Dehumidifiers for Humidification–Dehumidification Desalination Systems

A two-dimensional numerical model of a plate-fin tube heat exchanger for use as a dehumidifier in humidification–dehumidification (HDH) desalination systems is developed, because typical heating, ventilating, and air conditioning (HVAC) dehumidifier models and plate-fin tube dehumidifier geometries are not intended for the considerably higher temperature and humidity ratio differences that drive heat and mass transfer in HDH desalination applications. The experimentally validated model is used to investigate the influence of various heat exchanger design parameters. Potential improvements on common plate-fin tube dehumidifier designs are identified by examining various methods of optimizing tube diameter and longitudinal and transverse tube spacing to achieve maximum heat flow for a given quantity of fin material at a typical HDH operating point. Thicker fins are recommended than for HVAC geometries, as the thermal conductive resistance of HVAC fins restricts dehumidifier performance under HDH operating conditions.     

Design of efficient bimetallic Pt–Au nanoparticle-based anodes for direct formic acid fuel cells

Formic acid (FA) electro-oxidation (FAO) was investigated at a binary catalyst composed of Pt (PtNPs) and Au (AuNPs) nanoparticles which were electrodeposited simultaneously onto a glassy carbon (GC) substrate. The catalytic activity of the binary modified catalyst toward FAO was significantly influenced by the relative molar ratio of PtNPs and AuNPs. Interestingly, the catalyst with a molar ratio (1:1) of PtNPs and AuNPs showed the highest activity toward the favorable pathway of FAO (ca. 26 times increase in the direct peak current concurrently with a ca. 133 mV negative shift in the onset potential). Such enhancement was believed originating from the outstanding improvement of charge transfer during FAO via the desirable “non-poisoning” pathway along with a significant mitigation of CO poisoning at the electrode surface. The diversity of techniques (cyclic voltammetry, chronoamperometry, electrochemical impedance spectroscopy, field-emission scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction) employed in this investigation offered opportunities to assess and interpret the catalyst's activity and stability and to possess a deliberated overview about its morphology, composition and structure.     

Design of a novel hydrogen–syngas catalytic mesh combustor

A small-scale wire-mesh catalytic combustor is developed and evaluated for hydrogen–syngas combustion in domestic power/heating generator. The single- and double-layer wire-mesh catalysts are tested to verify their performance on CO conversions. Experimental results indicate that the double-layer wire-mesh catalytic combustor yields a higher CO conversion ratio (>90%) than that (<40%) of the single-layer wire-mesh catalyst in the range of fuel concentrations, fuel compositions, and flow velocities studied. In order to maintain a stable heterogeneous/homogeneous reaction at the second stage of wire-mesh catalyst, a minimum of 4% hydrogen in syngas and at least 200 °C of preheating temperature on the second wire-mesh catalyst are suggested. The advantages of the wire-mesh combustor are its compactness and ease of assembly and cleaning.     

Melnikov Functions in Quadratic Perturbations of Generalized Lotka–Volterra Systems

Journal of Dynamical and Control Systems - We present a detailed analysis of Melnikov functions which arise in quadratic perturbations of generalized Lotka–Volterra vector fields with the...     

Design of a compact absorber with a hydrophobic membrane contactor at the liquid–vapor interface for lithium bromide–water absorption chillers

In this study, design of a compact plates-and-frames absorber possessing a hydrophobic microporous membrane contactor at the aqueous solution–water vapor interface is performed analytically. The absorber is a component of a 5 kW cooling capacity single-effect lithium bromide–water absorption chiller that incorporates a hot water thermally driven generator and a water-cooled absorber and condenser. Good agreement prevailed for the analytically evaluated water vapor mass transfer flux and aqueous solution outlet temperature when compared with measured values at similar operating conditions. At design point conditions, the main design parameters obtained are a membrane contactor area of 6.06 m², a ratio of the mass transfer area to absorber net volume (_Am/_Vnet$A_m/V_{\mathit{net}}$) of 130.1(m²/m³), and ratio of the membrane area (mass transfer area) in this design configuration to the area required for heat transfer is 1.162, respectively. The results clearly indicate that the aqueous solution channel thickness is the most significant design parameter that affects the absorber size compactness; the thinner the thickness of the solution channel, the higher the ratio (_Am/_Vnet$A_m/V_{\mathit{net}}$). The results also show the countercurrent refrigerant flow with the aqueous solution has positive effects on the absorber size compactness.     

Design and reliability assessment of control systems for a nuclear-based hydrogen production plant with copper–chlorine thermochemical cycle

The thermochemical Copper–Chlorine (Cu–Cl) cycle is an emerging new method of nuclear-based hydrogen production. In the process, water is decomposed into hydrogen and oxygen through several physical and chemical processes. In this paper, a Distributed Control System (DCS) is designed for the thermochemical Cu–Cl cycle. The architecture and the communication networks of the DCS are discussed. Reliability of the DCS is assessed using fault trees. In the assessment, the impact of the malfunction of the actuators, sensors, controllers and communication networks on the overall system reliability is investigated. This provides key information for the selection of control system components, and determination of their inspection frequency and maintenance strategy. The hydrogen reactor unit, which is one of the major components in the thermochemical Cu–Cl cycle, is used to demonstrate the detailed design and analysis.     

Design,elaboration and characterization of a Ni–MH battery prototype

This paper shows advances achieved in the design and construction of a nickel–metal hydride (Ni–MH) battery prototype. The requirements of the design were to characterize the new variables appearing in a commercially assembled battery, such as limited physical space, electrical contact resistance, the behaviour of the system as a function of the gas evolution during fast charge and overcharge, and others. The electrochemical characterization was performed using laboratory equipment.     

The Phenomenon of Reversal in the Euler–Poincaré–Suslov Nonholonomic Systems

The development of robotics makes it necessary to study the problem of controlling nonholonomic systems (Svinin et al., Regul Chaotic Dyn. 2013; 18(1–2): 126–143, Borisov et al., Regul. Chaotic Dyn. 2013; 18(1–2): 144–158, Ivanova et al., Regul Chaotic Dyn. 2014; 19(1): 140–143). In this paper, the dynamics of nonholonomic systems on Lie groups with a left-invariant kinetic energy and left-invariant constraints are considered. Equations of motion form a closed system of differential equations on the corresponding Lie algebra. In addition, the effect of change in the stability of steady motions of these systems with the direction of motion reversed (the reversal found in rattleback dynamics) is discussed. As an illustration, the rotation of a rigid body with a fixed point and the Suslov nonholonomic constraint as well as the motion of the Chaplygin sleigh is considered.     

Optimization of the Pd–Sn–GNS nanocomposite for enhanced electrooxidation of methanol

Highly dispersed Pd nanoparticles with varying loadings (15–40 wt%) and (20 − x)%Pd–x%Sn (where x = 1, 2, 3 and 5) nanocomposites are obtained on graphene nanosheets (GNS) by a microwave-assisted ethylene glycol (EG) reduction method for methanol electrooxidation in alkaline solution. The electrocatalysts were characterized by XRD, SEM, TEM, cyclic voltammetry, and chronoamperometry. The study shows that the Pd nanoparticles on GNS are crystalline and follow the face centered cubic structure. Introduction of a small amount of Sn (1–5 wt%) shifts the characteristic diffraction peaks for Pd slightly to a lower angle. The electrocatalytic performance of the Pd/GNS electrodes has been observed to be the best with 20 wt% Pd loading; a higher or lower loading than 20 wt% Pd produces an electrode with relatively low catalytic activity. The apparent catalytic activity of this active electrode at E = −0.10 V is found to improve further by 79% and CO poisoning tolerance by 40% with introduction of 2 wt% Sn. Among the electrodes investigated, the 18%Pd–2%Sn/GNS exhibited the greatest electrocatalytic activity toward methanol electrooxidation.     

Design of organic–inorganic hybrid ion-gel electrolytes composed of borosilicate and allylimidazolium type ionic liquids

Research towards the design of novel electrolytes for the development of safer and efficient Li-ion batteries has gained widespread momentum in recent years. Design of novel borosilicate glass/ionic liquid hybrid type electrolyte was undertaken. Organic–inorganic hybrids have the dual advantages of high ionic conductivity due to the organic component and high thermal stability due to the inorganic components. In the present work, an in-situ sol–gel method using alkoxysilanes and alkoxyboranes was carried out, in the presence of low viscous ionic liquids. This resulted in the formation of highly homogenous organic–inorganic hybrids. A low viscous diallylimidazolium type ionic liquid was employed as the organic component. Arrhenius plots evinced constant temperature dependence of ionic conductivity. A maximum ionic conductivity of 2.0 mS cm⁻¹ at 51 °C, was observed among the prepared hybrids. LiPF₆ based hybrids showed higher ionic conductivity due to larger phase separation order of organic and inorganic components which enables better connection of ion-conductive organic components. On the other hand, LiTFSA based hybrids were highly homogenous and exhibited much improved thermal stability.     

Design of Ni/NiO–TiO2/rGO nanocomposites on carbon cloth conductors via PECVD for electrocatalytic water splitting

The facile synthesis and design of noble metal-free efficient catalysts to accelerate the sluggish kinetics of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is still a big challenge for electrolytic water splitting. In that context, the preparation of efficient catalysts with superior catalytic activity from cheap raw materials on a large scale is crucial. Briefly, Ni/NiO/TiO₂/rGO is designed using the environmental-friendly and easily up-scalable PECVD technique. This trinary composite presents significance in regulating the crystalline structure, composition and electronic properties towards superior HER and OER activity in acidic solution as bifunctional electrocatalysts for efficient water splitting. Together with the promising long-term stability and durability, Ni/NiO/TiO₂/rGO displays excellent electrocatalytic activity towards HER with η₁₀ of 130 mv vs RHE and a Tafel slope of 40 mV/dec.     

Design an in-situ reduction of Ni/C–SiO2 catalyst and new insights into pretreatment effect for CH4–CO2 reforming reaction

A series of Ni/C–SiO₂ catalysts with high Ni⁰ dispersion were prepared through impregnation method with glucose as the carbon source as well as the reduction agent. During the calcination process under N₂ atmosphere, the generated reductive substances, like CO, H₂ and carbon derived from decomposition and carbonization of glucose, which could transform NiO into Ni⁰ particles completely, according to XRD and H₂-TPR analysis. To improve the catalytic performance of CH₄–CO₂ reforming reaction, the Ni/C–SiO₂ catalyst was further pretreated under N₂, H₂ and CO₂ atmosphere prior to the reaction. The CO₂ pretreated catalyst exhibited excellent catalytic activity and superior stability comparing with other catalysts. A rapid deactivation occurred on the Ni/SiO₂ catalyst prepared by traditional impregnation method during 10 h test. Reversely, the CO₂ pretreated catalyst maintained a high CH₄, CO₂ and C_total conversion (71.1, 81.1 and 77.1%, respectively) during a 40 h time-on-stream test, which was attributed to homogenous Ni particles dispersion and strong interaction between metal and support. This methodology opens up a possibility for diversification in carbon-silica composite catalysts. The working catalyst without further reduction process will give the required metal-support interaction for the novel synthesis.     

Optimisation of real-time control for hybrid diesel–PV–battery systems

Hybrid diesel–PV–battery systems are one of the most cost effective options for off-grid power generation. A methodology for the optimal operation of such systems for an off-grid application is proposed in this paper. The methodology is based on the minimisation of an energy cost function. Based on this function, an optimal operating point for the diesel generator is identified, taking into account the characteristics of the diesel generator, battery bank and converter as well as the costs of fuel and battery usage. The operation of the diesel generator at this optimum operating point results in an overall energy cost reduction for the hybrid diesel–battery system. Simulation analysis shows that the proposed control strategy can achieve up to 4% reduction in the levelised cost of energy. This is mostly due to the savings made from the efficient usage of diesel generator and battery.     

Linear stability of Rayleigh–Benard–Poiseuille convection for electrochemical system

The effect of Poiseuille flow on the convective stability of electrochemical system is considered. It is found that the effect is destabilizing in the case of oscillatory instability in the system. It is shown that this effect is caused by the fact that the problem is not self-conjugate, because the system is multicomponent. In addition, it is found that the effect of Reynolds number on the stability of these systems is linear at small Reynolds number, in contrast to the self-conjugate Rayleigh–Benard problem, where the effect is quadratic.     

Uniform Deterministic Discrete Method for Three Dimensional Systems

INTRODUCTIONThefUndamentofzonalanalysisisthedirectex-changeaxeawhichrepreselltstheenclosuxe'sopticalandgeometricproperties.Thedefinitionsofdirectexchangeareasrelatingradiantexchangebetweentheareaelements(Ai,A,)andvolumeelements(V,,Vu)foranenc1ostirecontaininggrnylisotropicallyscatter-ingmediumareaasfollowsReciprocityrequiresForanenclosuretheunityrulededucedfromenergyconservationrequiresGenerallyspeaking,thedirectexchangeareasgivenbyfourtosixfoldintegralsaredifficulttoevalu-ateexceptfors…     

Design and fabrication of C–Mn0.5Cd0.5S/Cu3P ternary heterojunction catalyst for photocatalytic hydrogen evolution

Photocatalytic hydrogen evolution from water splitting is a promising strategy to solve the energy demand of human beings. Here, we first designed a C–Mn_0.5Cd_0.5S/Cu₃P ternary heterojunction catalyst for photocatalytic hydrogen production. The results show that the combination of C and Cu₃P can effectively improve the photocatalytic activity of Mn_0.5Cd_0.5S. C–Mn_0.5Cd_0.5S loading with 5 wt% Cu₃P exhibits the highest hydrogen evolution rate (44.1 mmol g⁻¹ h⁻¹), which is 3.2 and 2.8 times higher than that of pure Mn_0.5Cd_0.5S (13.7 mmol g⁻¹ h⁻¹) and Mn_0.5Cd_0.5S/3 wt%Pt (15.6 mmol g⁻¹ h⁻¹), respectively. In addition, it shows a high hydrogen evolution rate (19.6 mmol g⁻¹ h⁻¹) under visible light (≥420 nm) irritation and the apparent quantum efficiency (AQE) is detected to be 3.2% at 420 nm. The enhanced photocatalytic activity can be attributed to the good conductivity of C and the formation of p-n heterojunction, which is beneficial for light harvesting and the separation and transportation of charge carriers. Besides, a possible mechanism is proposed. This work provides an effective way to improve the photocatalytic activity of Mn_0.5Cd_0.5S by using non noble metal co-catalysts.     

DRIFTS study of Cu–Zr–Ce–O catalysts for selective CO oxidation

The effects of different components in Cu₁Zr₁Ce₉O_δ catalyst and the variations of the feed stream on the catalytic performance of selective CO oxidation were investigated by diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) technique. It is found that the active sites of Cu₁Zr₁Ce₉O_δ catalyst are mainly Cu⁺ species. Formate species is formed through the reaction between CO gas and hydroxyl groups on the reduced cerium surface. CeO₂ in the Cu₁Zr₁Ce₉O_δ catalyst facilitates the formation of Cu⁺ species and improves the amount of CO adsorption whereas it is unfavorable to the deep reduction of Cu⁺ species. ZrO₂ doped into the Cu₁Zr₁Ce₉O_δ catalyst increases the Cu coverage and CO adsorption capacity, while it decreases the adsorption of CO₂ on the catalyst surface. The adsorption capacities of oxygen and CO are associated with the catalytic performance for the selective CO oxidation at lower and higher temperatures, respectively. The presence of CO in the feed stream promotes the reduction of Ce⁴⁺ species and the production of geminal OH group on the reduced ceria surface. Hydrogen in the feed diminishes the CO adsorption ability but stimulates the CO desorption. CO₂ in the feed occupies the active sites and decreases the adsorption of the reactants, thus deteriorates the catalytic performance for the selective CO oxidation.     

Tuning of electrocatalytic activity of Mn–O–Co composite for alkaline hydrogen evolution reaction

We report the enhancement in electrocatalytic activity of Mn–O–Co composite electrode developed through chemical reduction method. The Mn–O–Co composite electrode exhibits high catalytic activity with a low Tafel slope of 123 mV dec⁻¹ and a low overpotential of 117 mV at a current density of 10 mA cm⁻². The enhancement in electrocatalytic activity of Mn–O–Co composite electrode is due to the synergistic activity of MnO and CoO with the NiP matrix. The intermetallic interaction among the half-filled orbitals of manganese with the fully occupied orbitals of cobalt and nickel leads to an effective electron delocalization in the catalytic system which enhances the HER performance of the coating. The C_dl value of the composite electrode is in the order of 254 μF, which is approximately ten fold higher than the bare NiP coating, due to the enhancement in interaction between the Mn–O–Co composite electrode and the reactive species in the HER medium. The Mn–O–Co composite electrode shows promising characteristics as an electrocatalyst with long term stability and remarkable competency with the commercially available electrodes.