A non-isothermal model of a nickel–metal hydride cell

A model for a nickel–metal hydride cell was constructed based on the planar electrode approximation. The mass balances of active species, the kinetics of electrochemical reactions, the ohmic effects of internal resistance, and the energy balance of the whole cell were considered in the model. An empirical approach was utilized to account for the hysteresis potential behavior of the nickel electrode. The model predictions showed favorable agreement with the experimental data.     

A two-dimensional mathematical model of annular-dispersed and dispersed flows—I

A two-dimensional mathematical model of two-phase flow is presented. The analytical formulation of the model involves the mass, momentum and energy conservation equations for vapour and droplet flows, liquid film and for the wall of the channel, and also a number of subsidiary relations incorporated to close the set of equations. The assumptions invoked are analysed.     

Numerical prediction of turbulent plane jets and forced plumes by use of the k-ε model of turbulence

A buoyancy-extended k-ε model of turbulence has been developed for calculating the dynamical and thermal fields in plane turbulent jets and forced plumes in a uniform stagnant environment. The governing partial differential equations (continuity, lateral and longitudinal momentum, thermal energy, turbulent kinetic energy k and its dissipation rate ε) are solved by means of an efficient computer program (called JEPHTE) for elliptic unsteady differential equations. A version assuming C_μ to be an empirical function of the densimetric Froude number at the source has been tested. The predictions are compared with experimental data and/or computed results obtained with more complex modellings of the buoyancy effects.     

A two-dimensional mathematical model of annular-dispersed and dispersed flows—II

The results of computation by a two-dimensional mathematical model of a droplet-vapour flow are presented. The predicted two-phase flow characteristics, such as temperature, velocity and phase concentration fields, specific deposition flows, and the temperature of heat emitting surfaces are compared with experimental data. Some specific features of two-phase flow identified in calculations are analysed. The degree of the conservatism of some closing coefficients is numerically investigated. The calculations are performed over a wide range of operational parameters: p = 0.147–13.7 MPa, ρw = 260–3000 kg m⁻² s⁻¹.The predicted results are found to be in reasonable agreement with the experimentally measured data.     

Furnace for biomass combustion – Comparison of model with experimental data

As one of the most easily accessible renewable energy resources, straw can be burned to provide heat energy. In this paper, results of theoretical and experimental research conducted under the proceedings of mathematical – numerical modeling of turbulent reacting flows has been presented. Two-dimensional turbulent flow model with homogeneous chemical reactions has been developed. The proposed model has been analyzed on the example of adiabatic combustion chamber for combustion of agricultural biomass. Turbulent flow is considered using time averaging Navier–Stokes equations that are closed by k–ε turbulence model. Calculations based on the proposed models were conducted using commercial CFD package FLUENT 6.3.26. For the purposes of experimental research, measurements of fluid flow and thermal parameters, such as continuous measurement of temperature in different points in the workspace furnace, air flow, flue gas flow, continual analysis of combustion products as well as setting heat and material balance, were carried out. Comparative analysis of the results of experiments and calculations indicate satisfactory agreement between the model and experiment.     

Analytical model of a solarium for cold climate—A new approach

In this present communication, a new approach has been evolved for analysing the thermal performance of a solarium useful in a cold climate. So as to trap the maximum solar radiation, the concept of glass windows (with movable insulation) in both the east and west walls of the sun space, besides in its south facing will and with the roof made of glass, has been introduced. Considering the ground temperature constant over a day, an overall heat transfer coefficient has been incorporated for the estimation of the heat flux transferred from the floor of the solarium to the ground. The introduction of this heat transfer coefficient eliminates the need of solving the conductivity equation for the heat flux conducted from the floor of the solarium to the ground. On account of the almost insulating behaviour of wood, an overall heat transfer coefficient has been taken for an all wooden structure of the solarium. Carrying out a transient analysis, explicit expressions for the temperatures of the sun space, the blackened absorbing surface of the water wall, the water itself, the living space and the isothermal masses have been developed as a function of time. These temperatures are required for the evaluation of the thermal energy taken in by the water wall, the heat flux entering the sun space and living space and the thermal energy distributed over the isothermal masses lying in the living space.     

Investigation of China's bio-energy industry development modes based on a SWOT–PEST model

Today more than ever before, the issues of energy shortage, global warming and climate change bound with greenhouse effect are dominating the international agenda, causing an increased interest in the renewable and alternative energy sector. With the development of the Chinese economy and scientific technology, the contradiction between energy, environment and economic growth has become ever-increasingly evident. Bio-energy, as an emerging and promising energy type, is of pretty importance for China's energy development from the strategic perspective. In this paper, the strategic analysis tools stemming from the SWOT (Strengths, Weaknesses, Opportunities, and Threats)–PEST (political, economic, social and technological) model have been adopted to explore the development modes of China's bio-energy industry. Afterwards, on the basis of the mode analysis, several corresponding recommendations have been put forward in an attempt to achieve the rapid and sound development of China's bio-energy industry.     

Flexibility improvement evaluation of hydrogen storage based on electricity–hydrogen coupled energy model

To achieve carbon neutrality by 2060, decarbonization in the energy sector is crucial. Hydrogen is expected to be vital for achieving the aim of carbon neutrality for two reasons: use of power-to-hydrogen (P2H) can avoid carbon emissions from hydrogen production, which is traditionally performed using fossil fuels; Hydrogen from P2H can be stored for long durations in large scales and then delivered as industrial raw material or fed back to the power system depending on the demand. In this study, we focus on the analysis and evaluation of hydrogen value in terms of improvement in the flexibility of the energy system, particularly that derived from hydrogen storage. An electricity–hydrogen coupled energy model is proposed to realize the hourly-level operation simulation and capacity planning optimization aiming at the lowest cost of energy. Based on this model and considering Northwest China as the region of study, the potential of improvement in the flexibility of hydrogen storage is determined through optimization calculations in a series of study cases with various hydrogen demand levels. The results of the quantitative calculations prove that effective hydrogen storage can improve the system flexibility by promoting the energy demand balance over a long term, contributing toward reducing the investment cost of both generators and battery storage and thus the total energy cost. This advantage can be further improved when the hydrogen demand rises. However, a cost reduction by 20% is required for hydrogen-related technologies to initiate hydrogen storage as long-term energy storage for power systems. This study provides a suggestion and reference for the advancement and planning of hydrogen storage development in regions with rich sources of renewable energy.     

A renovated Hamilton–Crosser model for the effective thermal conductivity of CNTs nanofluids

Thermal conductivity models for nanotube based nanofluids are less common than those for nanofluids containing spherical nanoparticles In this paper, a renovated Hamilton–Crosser model for the effective thermal conductivity of carbon nanotubes (CNTs) based nanofluids is proposed by simulating an equivalent anisotropic nanoparticle. The thermal conductivity of the anisotropic nanoparticle is deduced by analyzing the heat conduction process of a single CNT with an interfacial layer in an arbitrary direction. The present model which contains the effect of CNTs' diameter and aspect ratio as well as the interfacial layer was analyzed and validated with other models and available experimental data. The results show that the present model exhibits a more moderate variety rate driven by the diameter and aspect ratio of CNTs. And this characteristic results in a better adaptability than other models when compared with some available experimental results.     

A kinetic model for air-steam reforming of bio-oil over Rh–Ni/γ-Al2O3 catalyst: Acetol as a model compound

A new kinetic model is proposed for catalytic reforming of acetol to synthesis gas over a Rh–Ni/γ-Al₂O₃ catalyst. Acetol is one of the most important bio-oil model compounds formed under reactive flash volatilization reaction conditions. The model was implemented in the Aspen Plus simulation package and used to predict the product gas composition at different reaction temperatures and steam and oxygen ratios. The contributions of the reactions both in the reactor freeboard and the catalytic bed were assessed using CSTR and PFR reactor models, respectively. The reaction scheme included decomposition, steam reforming, and water-gas shift reactions. The results from the model predicted the product distribution within an acceptable degree of tolerance. This study confirms that thermal decomposition and partial oxidation of acetol precede the catalytic reactions involving steam. The effects of temperature, oxygen concentration in the feed, the volume of the freeboard, and the catalyst bed height can all be evaluated with this new kinetic model. This work suggests that bio-oil decomposed into different fractions of molecules like acetol can be successfully modelled by a series of decomposition reactions followed by partial oxidation and catalytic steam conversion. The heat transfer within the catalyst bed is found to be critical for achieving a good match with the experimental results.     

Hydrodeoxygenation of lignin model compounds to alkanes over Pd–Ni/HZSM-5 catalysts

In this work, a bimetallic catalyst of Pd and Ni supported on HZSM-5 was designed and evaluated in the hydrodeoxygenation of model compounds representing various C–O bonds in lignin. The effects of temperature, holding time, and initial H₂ pressure on the catalytic performance of the Pd–Ni/HZSM-5 catalyst were investigated. The results indicated that the Pd–Ni/HZSM-5 catalyst exhibited superior catalytic activity towards the conversion of the model compounds to alkanes compared to its monometallic counterparts. Direct cleavage of the C–O bond in DPE was achieved under low H₂ pressure, mainly producing benzene and minor amounts of phenol and cyclohexane, while at high H₂ pressure, the reaction pathway was altered towards hydrogenation of the benzene ring, followed by then cleavage of the C–O bond to afford only cyclohexane. Moreover, the Pd–Ni/HZSM-5 catalyst showed high activities when applying other substrates including anisole, veratrole, guaiacol, benzyloxybenzene, phenethyl phenyl ether, and dibenzyl ether.     

Three-dimensional model for numerical analysis of thermal phenomena in laser–arc hybrid welding process

This paper describes mathematical and numerical models of thermal phenomena developed for computational analysis of the laser–arc hybrid welding process. The mathematical and numerical models were established to estimate temperature field and velocity field of melted material in the welding pool. Different heat source power distribution models for electric arc and laser beam, latent heat of fusion and latent heat of evaporation as well as buoyancy and liquid material flow through a porous medium were taken into consideration in the computational model. The results of computer simulation of laser–arc hybrid welding process, including temperature field and melted material velocity field, are presented in this study. The correctness of elaborated models is verified by experimental results.     

Application of an entry–exit tariff model to the gas transport system in Spain

Under an entry–exit gas tariff system, reservation of capacity is split into entry capacity, to transport gas from the injection points to a virtual balancing point, and exit capacity, to transport gas from the balancing point to the exit points in the system.     

A complete model of the drying curve for porous bodies—experimental and theoretical studies

Non-hygroscopic, capillary porous bodies, saturated with liquids were dried in an experimental device. By systematically varying the drying agent, the liquids and the differently structured samples, a wide range of drying rate curves were found experimentally and evaluated. The basic equation for the model of the constant-rate drying period refers—according to Krischer—to capillary liquid transportation only. The liquid-diffusion coefficient dependent on moisture content is calculated on the basis of the model considerations of Rumpf. For the falling-rate period the well-known receding drying front model is modified with regard to the capillary liquid movement.     

Corrosion of pure and milled Mg17Al12 in “model” seawater solution

The corrosion behavior of pure Mg₁₇Al₁₂ and the effect of ball milling in presence of additives (i.e. graphite (G) and magnesium chloride (MgCl₂)) are evaluated in 3.5 wt% NaCl aqueous solution using electrochemical polarization and impedance measurements. Pure Mg₁₇Al₁₂ and milled Mg₁₇Al₁₂ without additives and with MgCl₂ present an open current potential (OCP) of −1.2 V/SCE while Mg₁₇Al₁₂ + G shows a slightly higher OCP (+10% maximum). Mg₁₇Al₁₂ corrodes with low kinetics and an increase of corrosion rate for the milled Mg₁₇Al₁₂ is observed. The corrosion current densities (J_corr) derived from the Tafel plots, exhibit their corrosion reactivity as follow: Mg₁₇Al₁₂ < Mg₁₇Al₁₂ 5h < Mg₁₇Al₁₂ + G 5h < Mg₁₇Al₁₂ + MgCl₂ 5h. Electrochemical impedance spectroscopy (EIS) results are in good agreement with the measured J_corr. Randles circuit models are established for all samples to explain their surface behavior in the aqueous NaCl solution. The variation of the fitted parameters is attributed either to the effect of ball milling or to the effect of the additive. Our results are helpful in elucidating the effect of ball milling and the additives.     

A new approach for the prediction of the heat transfer rate of the wire-on-tube type heat exchanger––use of an artificial neural network model

This study presents an application of artificial neural networks (ANNs) to predict the heat transfer rate of the wire-on-tube type heat exchanger. A back propagation algorithm, the most common learning method for ANNs, is used in the training and testing of the network. To solve this algorithm, a computer program was developed by using C++ programming language. The consistence between experimental and ANNs approach results was achieved by a mean absolute relative error <3%. It is suggested that the ANNs model is an easy modeling tool for heat engineers to obtain a quick preliminary assessment of heat transfer rate in response to the engineering modifications to the exchanger.     

Application of a laser induced fluorescence model to the numerical simulation of detonation waves in hydrogen–oxygen–diluent mixtures

A laser-induced-fluorescence model has been implemented and used to post-process detonation wave numerical simulation results to allow a direct comparison with previous experimental visualizations of detonations in hydrogen–oxygen–diluent mixtures. The model is first applied to steady one-dimensional simulation results obtained with detailed chemistry. The effects on the fluorescence intensity of the model parameters are examined to explore the dominant processes. The dominant interference process in the experiments carried out to date is the absorption of incident laser light by the high concentration of OH in and behind the reaction zone. The model is then applied to unsteady two-dimensional simulation results obtained with reduced chemical schemes to obtain synthetic PLIF image. The results demonstrate good qualitative agreement between the experimental and calculated laser-induced-fluorescence intensities. The model limitations and the experimental uncertainties are discussed together with a critical evaluation of the modeling approach.     

Effects of heat transfer on MHD suction–injection model of viscous fluid flow through differential transformation and Bernoulli wavelet techniques

In this study, a numerical solution of the velocity and heat transfer on the magnetohydrodynamic suction–injection model of viscous fluid flow has been studied. We use the differential transformation method and Bernoulli wavelet method to solve the highly nonlinear governing equations; applying appropriate similarity transformations and reducing governing equations to highly nonlinear coupled ordinary differential equations. The objective of this analysis is to determine how the suction parameter, Hartmann number, squeeze number, thermophoresis parameter, and Prandtl number affect the velocity and temperature profiles. When the current findings are compared with those that have already been published in the literature, confident suppositions are made, and it is discovered that there is considerable agreement. Graphs have been used to discuss the influence of nondimensional characteristics on velocity and temperature.