Experimental exergy and entransy analyses on designed and fabricated crossflow heat exchanger

A crossflow heat exchanger (CFHEx) is designed and fabricated in a workshop. For designing this heat exchanger (HEx), the number of passes, frontal areas, HEx volumes, heat transfer areas, free-flow areas, ratios of minimum free-flow area to frontal area, densities, mass flow rates of flowing fluids, maximum/minimum heat capacities, heat capacity ratio, outlet temperatures of hot/cold fluids, average temperatures, mass velocities, Reynolds numbers, and convective heat transfer coefficients are evaluated by considering Colburn/friction factors. After fabrication of the HEx, effectiveness, exergy destruction, entransy dissipation, entransy dissipation-based thermal resistance, entransy dissipation number, and entransy effectiveness for hot/cold fluids sides are found at different flow rates and inlet temperatures of fluids. By experimental results, optimum operating conditions are found, which gives maximum effectiveness and entransy effectiveness but minimum rates of exergy destruction, entransy dissipation, entransy dissipation-based thermal resistance, and entransy dissipation number for the fabricated CFHEx. This study is concluded as follows: minimum exergy destruction and entransy dissipation rates (ie, 3.061 kJ/s·K and 1125.44 kJ·K/s, respectively) are found during experiment 2. Maximum entransy effectiveness of hot/cold fluids (ie, 0.689/0.21) is achieved in experiment 1. Moderate values of entransy dissipation number (ie, 4.689), entransy dissipation-based thermal resistance (ie, 0.04 s·K/J), exergy destruction (ie, 3.845 kJ/s·K), and entransy dissipation (ie, 1374.04 kJ·K/s) rates are found during experiment 1. Maximum effectiveness (ie, 0.4) for the fabricated HEx is also obtained through experiment 1. After comparative analyses, it is found that experiment 1 provides optimum results, which shows the best performance of the fabricated HEx.     

Optimized performance of nickel in crystal-layered arrangement of NiFe2O4/rGO hybrid for high-performance oxygen evolution reaction

To rescue the future from the global energy crisis and to ensure it with clean and economical hydrogen energy, it is an urgency to develop an efficient OER catalyst, which intensely sluggish the kinetic process of hydrogen production. Herein, we have precisely synthesized an efficient, stable, earth-abundant metal-based NiFe₂O₄/rGO hybrid OER electrocatalysts by a simple solvothermal method. The measurements including XRD, FTIR, XPS, EDS, SEM, and TEM revealed the prominent structural integrity of catalyst with crystal-layered structure. The rich oxidation chemistry of transition metals and substantially active carbon substrate allows tuning of their electronic properties concerning their concentration, composition, and morphology. The effect of different Ni wt.% (0%, 2%, 4%, and 6%) on the morphology of hybrid as well as on electrochemical performance investigated. The protocols like overpotential required to achieve a current density of 10 mA/cm², Tafel slope, ECSA, RF, EIS, stability was utilized to examine the overall abilities of electrocatalyst in alkaline 1 M KOH solution. The optimized NiFe₂O₄/rGO hybrid with 2 wt % Ni exhibited the excellent OER performance, which delivers a current density of 10 mA/cm² at an overpotential of only 302 mV with a small Tafel slope of 63 mV/dec. The high activity of the catalyst is attributed to the synergistic effect of the crystal-layered structure as well as rapid mass-charge transfer. Such, rational design concept of anchoring non-precious metal on carbon in a controlled manner, offering splendid flexibility to tailor electrochemical OER performance. The optimized variations in metal concentration and morphologies, providing a promising route to develop a cost-effective catalyst for advanced energy conversion applications.     

Controlled growth of well-aligned GaS nanohornlike structures and their field emission properties

Here, we report the synthesis of vertically aligned gallium sulfide (GaS) nanohorn arrays using simple vapor-liquid-solid (VLS) method. The morphologies of GaS nano and microstructures are tuned by controlling the temperature and position of the substrate with respect to the source material. A plausible mechanism for the controlled growth has been proposed. It is important to note that the turn-on field value of GaS nanohorns array is found to be the low turn-on field 4.2 V/μm having current density of 0.1 μA/cm(2). The striking feature of the field emission behavior of the GaS nanohorn arrays is that the average emission current remains nearly constant over long time without any degradation.     

Approaches to controlled polymerization of methyl acrylate through functional anionic initiators

Summary Controlled living polymerization of methyl acrylate has been achieved at room temperature using functional carbanionic initiators in THF solvent. Methyl acrylate oligomers with reactive chain ends have been synthesized.NCL Communication No. 4990     

Identifying Prominent Explanatory Variables for Water Demand Prediction Using Artificial Neural Networks: A Case Study of Bangkok

The water demand of a city is a complex and non linear function of climatic, socioeconomic, institutional and management variables. Identifying the prominent variables among these is essential in order to adequately predict water demand, and to plan and manage water resources and the supply systems. Further, the need for such identification becomes more pronounced when data constraints arise. The objective of this study was to establish, using correlation and sensitivity analyses, a minimum set of variables required to predict water demand with significant accuracy. Artificial Neural Networks (ANN) models were developed to predict short-term (daily) and medium-term (monthly) demands for Bangkok. Using meteorological and water utility variables for short-term prediction, and different ANN architecture, 16 sets of models with a 1-, 2- and 3-day lead period were developed. Although the best fit models for the three lead periods used different input variables, prediction accuracies over 98% were achieved by using only the historic daily demand (HDD) as the explanatory variable. Similarly, for medium-term prediction, 11 sets of models with lead periods of 1-, 2- and 6-months were developed, using meteorological, water utility and socioeconomic variables. The best fit models for the three lead periods used all explanatory variables but prediction accuracies of more than 98% were obtained by downsizing the variable set. The meteorological variables have a greater influence on medium-term prediction as compared to short-term prediction, suggesting that future water demand in Bangkok could be significantly affected by climate change.     

Surface‐Functionalization‐Mediated Direct Transfer of Molybdenum Disulfide for Large‐Area Flexible Devices

The transfer of synthesized large‐area 2D materials to arbitrary substrates is expected to be a vital step for the development of flexible device fabrication processes. The currently used hazardous acid‐based wet chemical etching process for transferring large‐area MoS₂ films is deemed to be unsuitable because it significantly degrades the material and damages growth substrates. Surface energy‐assisted water‐based transfer processes do not require corrosive chemicals during the transfer process; however, the concept is not investigated at the wafer scale due to a lack of both optimization and in‐depth understanding. In this study, a wafer‐scale water‐assisted transfer process for metal–organic chemical vapor‐deposited MoS₂ films based on the hydrofluoric acid treatment of a SiO₂ surface before the growth is demonstrated. Such surface treatment enhances the strongly adhering silanol groups, which allows the direct transfer of large‐area, continuous, and defect‐free MoS₂ films; it also facilitates the reuse of growth substrate. The developed transfer method allows direct fabrication of flexible devices without the need for a polymeric supporting layer. It is believed that the proposed method can be an alternative defect‐ and residue‐free transfer method for the development of MoS₂‐based next‐generation flexible devices.     

Physical properties of hematite a-Fe2O3 thin films:application to photoelectrochemical solar cells

The physical properties and photoelectrochemical characterization of aluminium doped hematite α-Fe2CO3, synthesized by spray pyrolysis, have been investigated in regard to solar energy conversion. Stable Al-doped iron (Ⅲ) oxide thin films synthesized by a spray pyrolysis technique reveals an oxygen deficiency, and the oxide exhibits n-type conductivity confirmed by anodic photocurrent generation. The preparative parameters have been optimized to obtain good quality thin films which are uniform and well adherent to the substrate. The deposited iron oxide thin films show the single hematite phase with polycrystalline rhombohedral crystal structure with crystallite size 20-40 nm. Optical analysis enabled to point out the increase in direct band-gap energy from 2.2 to 2.25 eV with doping concentration which is attributed to a blue shift. The dielectric constant and dielectric loss are studied as a function of frequency. To understand the conduction mechanism in the films, AC conductivity is measured. The     

Structural, morphological, optical and photoluminescent properties of spray-deposited ZnSe thin film

Zn Se thin films are successfully deposited by spray pyrolysis deposition technique.Deposited thin films are characterized by X-ray diffraction study,and it reveals that spray-deposited Zn Se thin films are polycrystalline with hexagonal crystal structure.Surface morphology is carried out by scanning electron microscopy.It shows cotton-like morphology,and optical properties,such as absorbance,transmittance,reflectance,band gap,refractive index,extinction coefficient are studied.Photoluminescence shows strong emission at 497 nm.Also,spraydeposited Zn Se thin films are hydrophilic in nature,which is shown by contact angle meter.