Heat Reaction Research Articles

Up-Flow Anaerobic Sludge Blanket (UASB) Technology for Energy Recovery: A Review on State-of-the-Art and Recent Technological Advances.

Up-flow anaerobic sludge blanket (UASB) reactor belongs to high-rate systems, able to perform anaerobic reaction at reduced hydraulic retention time, if compared to traditional digesters. In this review, the most recent advances in UASB reactor applications are critically summarized and discussed, with outline on the most critical aspects for further possible future developments. Beside traditional anaerobic treatment of soluble and biodegradable substrates, research is actually focusing on the treatment of refractory and slowly degradable matrices, thanks to an improved understanding of microbial community composition and reactor hydrodynamics, together with utilization of powerful modeling tools. Innovative approaches include the use of UASB reactor for nitrogen removal, as well as for hydrogen and volatile fatty acid production. Co-digestion of complementary substrates available in the same territory is being extensively studied to increase biogas yield and provide smooth continuous operations in a circular economy perspective. Particular importance is being given to decentralized treatment, able to provide electricity and heat to local users with possible integration with other renewable energies. Proper pre-treatment application increases biogas yield, while a successive post-treatment is needed to meet required effluent standards, also from a toxicological perspective. An increased full-scale application of UASB technology is desirable to achieve circular economy and sustainability scopes, with efficient biogas exploitation, fulfilling renewable energy targets and green-house gases emission reduction, in particular in tropical countries, where limited reactor heating is required.

Numerical studies on turbulent flame propagation in premixed gas deflagration inside a tube

Numerical simulation on turbulent flame propagation in premixed gas deflagration process in a tube will be reported in this paper, aiming at identifying the key factors affecting flame shape and flame velocity. Large eddy simulation with premixed gas combustion model is used to obtain results validated by full-scale experimental data. The effect of flow velocity and turbulence on flame propagation is discussed. The flow velocity of premixed gas is observed to be one of the main factors determining flame shape and affecting flame propagation process. The velocity difference of different parts of the flame front, both in magnitude and direction, will lead to tulip-shaped flame. Turbulence would accelerate the propagation of flame periodically. The cause of flame acceleration of low-intensity turbulence originates from two factors, namely, combustion and flow field, which transfer the heat and mass of chemical reaction from diffusion to vortex transport. As high-intensity turbulence will not affect the chemical reaction and the turbulent burning velocity, flame acceleration is controlled only by the characteristics of the flow field.

Numerical simulation on biomass-pyrolysis and thermal cracking of condensable volatile component

We studied the physical and chemical properties of the condensable volatiles of biomass pyrolysis products. We redefine the liquid product and divide the condensable volatiles into two categories, biomass oil and tar, the latter of which comes from the secondary pyrolysis or cracking reaction of the former. We further establish a kinetic model of biomass pyrolysis and secondary cracking. The chemical reaction kinetics equation and heat transfer equation are coupled to simulate the biomass pyrolysis process. For biomass solid particles, the model not only considers the initial reaction of biomass and secondary cleavage reaction of condensable gas, but also introduces a reaction mode in which biomass oil is converted into tar. When the pyrolysis temperature is below 500 °C, the pyrolysis products are essentially biomass oil. However, when the pyrolysis temperature exceeds 500 °C, the biomass oil gradually converts into tar. The model also considers characteristics of the reaction medium (porosity, intrinsic permeability, thermal conductivity) and the unsteady gas phase process based on Darcy's law of velocity and pressure, heat convection, diffusion, and radiation transfer. We analyze the relationships among the internal temperature of the particles, particle size and position, mass fraction of the reactants and products, the gas mixture, the production share of tar and biomass oil, and the relationship between gas pressure and time. The results show that the effects of the secondary cracking reaction and internal convective flow in the biomass pyrolysis process are coupled because the flow field in the porous medium determines the volatile residence time and thus species that affect the secondary cracking reaction. The rate of volatile formation in the initial and secondary cracking reactions affects the pressure gradient and gas diffusion. Additionally, the endothermic effect influences the temperature field of the pyrolysis reaction but has no apparent effect on small particles whose chemical reaction is the control mechanism. For large particles, heat transfer inside the particles is the diffusion control mechanism and the chemical reaction on the particle surface is the speed control mechanism. Two peaks are observed in the pyrolysis gas mass proportion curve, which result from the consumption of biomass oil and tar as they flow toward hot surfaces. The first peak is the decomposition of biomass oil into non-condensable volatile matter and tar, and the second peak is the further cracking of tar into gas and coke at high temperature.

Numerical investigation on activation energy of chemically reactive heat transfer unsteady flow with multiple slips

PurposeThe purpose of this study is to examine the impact of activation energy with binary chemical reaction for unsteady flow on permeable stretching surface.Design/methodology/approachThe simultaneous effects of multiple slip and magneto-hydrodynamic effects at the boundary are taken into account. The thermal buoyancy parameter and thermal radiation are included in both energy and momentum equations, while expression of activation energy is considered in concentration equation. Three-stage Lobatto IIIa finite difference collocation technique with bvp4c MATLAB package is used to obtained numerical results.FindingsThe influence of key elements (Schmidt number, buoyancy force ratio factor, factor of radiation, magnetic element, unsteadiness factor, suction/injection parameter, Prandtl number, activation energy, chemical reaction rate parameter, heat source and sink parameters, velocity, thermal and concentration slips, porosity parameter and temperature difference parameter) on velocity, temperature and concentration profiles are illustrated pictorially. A detailed discussion is presented to see how the graphical aspects justify the physical prospect.Originality/valueIn the best of author’s knowledge, this work is yet not available in existing literature.

Heat and mass transfer characteristics of three-dimensional bell-shaped polysilicon chemical vapor deposition reactor

Polysilicon, the crucial material of photovoltaic field, is commonly produced in a Siemens chemical vapor deposition (CVD) reactor with a complex physical and chemical phenomenon included inside as well as complicated geometry structure. In order to study the performance of silicon CVD reactor, a three-dimensional bell-shaped reactor model with 24 rods is constructed and verified to investigate the heat and mass transfer performance inside. The distributions of velocity, temperature, complex concentrations of six main components, silicon deposition rate, and energy of the reduction furnace at high and low inlet velocities are analyzed in detail. Results show that high inlet velocity is more conductive to obtain uniform distributions of velocity, temperature, complex concentration, and silicon deposition rate, leading to better silicon CVD performance. The inner rods are easier to collapse than the outer rods. In addition, radiation loss is the main energy consumption in the silicon reduction furnace and accounts for more than 60% of the total energy consumption. The convective heat transfer, chemical reaction heat, proportion of convective heat, and the proportion of chemical reaction heat increase with the rise in inlet velocity due to a fully developed flow field.

Study of the reactor temperature effect on H[formula omitted] production from steam decomposition using DBD plasma

Heat transfer data for the effect of the reactor and surrounding temperature on the hydrogen production from water vapour decomposition using Dielectric-Barrier Discharge (DBD) plasma are reported. The water vapour was injected into the plate micro channel reactor (PMCR) where the PMCR and its surrounding temperatures were raised using an insulated constant temperature heater type in a range of 20–130°C. This experiment was run at the following steam inlet conditions: pressure 100 kPa, temperature 300°C and flow rates of 100–200 ml/h, while the plasma applied voltage was in a range of 14–18 kV. In particular, the concentrations of hydrogen and oxygen species were analysed using gas phase chromatography (GC). It was observed that the hydrogen concentration percent increased with the reactor and surrounding temperature increased at all tested steam flow rates. Also, it was seen that the maximum obtained H2 concentrations were at high reactor temperature 130°C and plasma applied voltage of 18 kV. The effect of reactor temperature on the total heat transfer resistances at different steam flow rates was investigated. The trend behaviour of these resistances reveals interesting information about how these resistances interact and distribute according to the reactor heating temperature. Also, it was found that the total heat transfer rate decreased with the reactor temperature increased while the overall heat transfer rate increased with plasma voltage and reactor heating temperature. It can be concluded that the DBD plasma effect improved by decreasing the temperature difference between input steam and the PMCR temperatures. Further, it was clear that the steam dissociation processes not mainly depending on the plasma applied voltage but also the reactor heating temperature.

Microwave-assisted wet torrefaction of microalgae under various acids for coproduction of biochar and sugar

Wet torrefaction is a promising method to converts the high moisture microalgae to biofuel. In this study, the microalgae were torrefied in water or dilute acid solutions with the aid of microwaves irradiation. The reaction temperature and heating time were fixed at 160 °C and 10 min. The effects of sulfuric, phosphorus, and succinic acids on two different microalgae species (Chlorella vulgaris ESP-31 and FSP-E) were investigated. As a result, the disruption of the microalga FSP-E (high protein) was not notable in the acidic solution. The higher heating value of wet torrefied microalga ESP-31 (high carbohydrate) in succinic acid was enhanced up to 40% with at least 45% of energy yield. The use of 0.1 M of phosphorus acid in wet torrefaction produced the highest ash content of 1.61 and 11.60 wt% for microalgae ESP-31 and FSP-E, respectively. Thermogravimetric analysis revealed that the carbohydrate content of microalga ESP-31 has the highest degradation in sulfuric acid solution. In contrast, crystalline cellulose in the microalgae is hardly affected by the wet torrefaction process in low-temperature acidic solution. In terms of liquid product, a maximum glucose extraction of 35.39 g/L occurred with the use of 0.1 M of sulfuric acid. In conclusion, biochar produced using organic acid is desirable as solid fuel, whereas the use of sulfuric acid is more suitable to produce sugar for bioethanol production.

Theoretical study on ignition of titanium alloy under high temperature friction condition

Combustion of titanium alloy is a typical catastrophic failure of modern aeroengine. The abnormal friction between compressor rotor and stator is the main ignition source. A thermal theory model with friction heat source of titanium alloy is established based on the theory of heterogeneous ignition. The corresponding equation of critical temperature and ignition delay time are derived. The difference between the frictional ignition model and the classic model is discussed. The concept of critical heat generation temperature is proposed. The difference from the heterogeneous ignition model, and the effects of friction coefficient, oxygen concentration, flow velocity, contact radius and flame retardant layer thickness on the ignition parameters are analyzed. The research result shows that when the instantaneous temperature of the contact surface is lower than the critical heat temperature, the heat generation process is dominated by frictional heat, and when the temperature is higher than the critical heat temperature, the heat generation process is dominated by chemical reaction heat, that reducing the coefficient of friction can dramatically increase the critical temperature, but the change of friction coefficient has very little effect on the ignition delay time which can be ignored, that the critical temperature decreases significantly with the increase of oxygen concentration and the decrease of flow velocity. When the oxygen concentration increases from 21% to 42% and the flow velocity decreases from 310 m/s to 50 m/s, the critical temperature decreases by about 213 K and 197 K, respectively. The relative error between the experimental result and the theoretical result is 8.3%, which verifies the reliability of the model. The contact area has an effect on friction heat generation, reaction heat generation, and surface heat dissipation, and has a great influence on the critical temperature. The critical temperature decreases exponentially with contact radius increasing. When the contact radius increases to 0.007 m, the ignition temperature of the titanium alloy and its flame retardant layer are 899 K and 988 K, respectively. The increase of the thickness of flame retardant layer can effectively improve the critical temperature and ignition delay time. The critical temperature of titanium alloy with flame retardant layer is increased by about 172 K, and the ignition delay time is increased by about 3 s.

Computational Fluid Dynamic Studies of Autothermal Spiral Reactor

This research applied the fundamental concept of spiral heat exchanger to design a new reactor for autothermal coupling endo- and exothermic reactions. The autothermal coupling endo- and exothermic reactor can be used when heat have to be removed from exothermic reactions (heat source). Such heat is then used for endothermic reactions (heat sink) that requires high operating temperature. This brings various benefits in terms of energy saving, economics and environment. In this study, the Computational Fluid Dynamics (CFD) was utilized to predict the performance of the spiral heat exchanger. The optimal operating conditions i.e. pressure drop, velocity and temperature distribution were studied. Low fluid velocity was observed without dead and hot spot zone along the radius flow of the channel and good temperature distribution was noticed.

Exploration of the Significance of Autocatalytic Chemical Reaction and Cattaneo-Christov Heat Flux on the Dynamics of a Micropolar Fluid

During the homogeneous-heterogeneous autocatalytic chemical reaction in the dynamics of micropolar fluid, relaxation of heat transfer is inevitable; hence Cattaneo-Christov heat flux model is investigated in this report. In this study, radiative heat flux through an optically thick medium is treated as nonlinear due to the fact that thermal radiation at low heat energy is distinctly different from that of high heat energy, hence classical approach of using Taylor series for simplification is ignored and implicit differentiation is used leading to temperature parameter. Uniqueness of the present analysis is the consideration of cubic autocatalytic chemical reaction between the homogeneous bulk fluid and two species of catalyst at the wall. Application of similarity analysis enabled us to recast the flow equations into a set of coupled nonlinear ODEs. The resulting equations along with the appropriate conditions are solved computationally. Graphical illustrations of the effect of pertinent parameters on momentum, heat and mass boundary layers are presented and discussed. The concentration of the homogeneous bulk fluid with microstructures and catalyst at the surface decreases and increases with diffusion ratio, respectively. Buoyancy has a decreasing effect on temperature distribution.

Modeling and analysis of the impact of exothermic catalytic chemical reaction and viscous dissipation on natural convection flow driven along a curved surface

The impact of exothermic catalytic chemical reaction and viscous dissipation on natural-convection heat transfer along the curved shape is investigated. In this study, the trend of exothermic catalytic chemical reaction has been introduced in the energy and mass concentration equation. Furthermore, the tangential compo?nent of acceleration due to gravity, gx, as buoyancy force has coupled in momentum equation describe the curved shape. The flow model of the problem is formulated in terms of coupled non-linear PDE together with suitable boundary conditions. From the numerical solutions of the governing equations, it is found that velocity field, temperature distribution and the mass concentration is associated with the dimensionless parameters involved in the flow model. The novelty of the current study is that the characteristics of heat and fluid-flow mechanism are specifically associated with the different values of index parameter n.

MELTING AND CHEMICAL REACTION EFFECTS IN STAGNATION POINT FLOW OF MICROPOLAR FLUID OVER A STRETCHABLE POROUS MEDIUM IN THE PRESENCE OF NONUNIFORM HEAT SOURCE/SINK

In this present paper, we have investigated a numerical solution to the melting heat transfer on micropolar fluid flow over a stretchable porous medium. The partial differential equations of governing flow are changed to dimensionless ordinary differential equations by using similarity transformation and then solved by the Runge-Kutta-Fehlberg fourth- A nd fifth-order (RKF-45) method with shooting technique. The novelty of the present study is that it considers the influence of chemical reaction and nonuniform heat source/sink in stagnation point flow over a stretching sheet. The study looks at the impacts of different nondimensional parameters, namely chemical reaction parameter, melting parameter, stretching parameter, and space- A nd temperature-dependent heat source/sink parameters on velocity, microrotation, temperature, and concentration distributions. Additionally, the skin-friction coefficient, Nusselt number, and Sherwood number are examined in detail and the results are depicted graphically and in tabular form to illustrate the physical importance of the study. The results show that velocity enhances with stretching parameter. The temperature reduces as melting parameter rises, while temperature increases with the stretching parameter and the space- A nd temperature-dependent heat source/sink parameters. The impact of the chemical reaction parameter is to increase the mass transfer rate.

Numerical simulation of Joule heating and Arrhenius activation energy for nonlinear radiative flow of Casson nanofluid with Cattaneo–Christov heat flux model

This article explores the novel features of Cattaneo–Christov heat flux model for nonlinear radiative flow of Casson nanofluid over an inclined permeable stretched cylinder with joule heating mechanism. The novelty of the present study is to account for the effect of activation energy, dual stratification, nonlinear mixed convection, non-uniform heat generation/absorption, binary chemical reaction and Joule heating effect. The velocity and thermal slips are also accounted for present flow model instead of no-slip condition. Casson fluid nanomaterial model is measured that refers to the significant slip mechanism such as Brownian and thermophoresis diffusions. Suitable similarity transformations are employed to get the required coupled ODEs system. The developed nonlinear system is unravelled through shooting technique along with Runge–Kutta–Fehlberg (RK-45) approach. Physical quantities of interest are investigated through graphs and tables. From the present analysis, we will see the conflicting effect of chemical reaction parameter to that of activation energy parameter Further it will be also analyzed that the heat transfer rate at the cylindrical surface and thermal boundary layer thickness enhances within the frame thermal radiation It will also be observed that both thermophoresis and activation energy parameter become a source of enhancement in concentration frame. A validation of the work is offered by comparing the current results with published literature. Casson flow model as deliberated in the paper finds practical applications in polymer engineering, blood flow, silicon suspensions, and lithograph industry.

Semi-batch reactor control with NMPC avoiding thermal runaway

Several exothermic reactions are carried out in semi-batch reactors (SBR). A not suitable control system can lead to dangerous situations if thermal runaway develops. Reactor runaway can be avoided with application of a non-linear model predictive control (NMPC) with implemented runaway criterion to manipulate the feed flow rate of reagent, although the prediction horizon has to be chosen correctly. For this purpose, process safety time (PST) of the system is determined. Two different operation modes are considered. In the first case the loaded reagent is preheated to avoid accumulation, while in the second mode, only the produced heat by the reactions heat up the reactor. A simple PID controller and the proposed NMPC were tested in both cases. Operation results are compared to each other based on batch times and energy consumptions next to a safe operation. Runaway criteria can be successfully implemented in NMPC for the intensification of SBRs.

Impact of Nonlinear Chemical Reaction and Melting Heat Transfer on an MHD Nanofluid Flow over a Thin Needle in Porous Media

A novel mathematical model is envisioned discussing the magnetohydrodynamics (MHD) steady incompressible nanofluid flow with uniform free stream velocity over a thin needle in a permeable media. The flow analysis is performed in attendance of melting heat transfer with nonlinear chemical reaction. The novel model is examined at the surface with the slip boundary condition. The compatible transformations are affianced to attain the dimensionless equations system. Illustrations depicting the impact of distinct parameters versus all involved profiles are supported by requisite deliberations. It is perceived that the melting heat parameter has a declining effect on temperature profile while radial velocity enhances due to melting.

Preparation of two-dimensional molybdenum disulfide for NO2 detection at room temperature

In this work, the two-dimensional MoS2 film was prepared by sulfuring the molybdenum atomic layer on SiO2/Si substrate. The reaction temperature, heating rate, holding time and carrier gas flow rate were investigated comprehensively. The quality of MoS2 film was characterized by optical microscopy, atomic force microscopy, Raman and photoluminescence spectroscopy. The characterization results showed that the optimum synthesis parameters were heating rate of 25 °C/min, reaction temperature of 750 °C, holding time of 30 min and carrier gas velocity of 100 sccm. The MoS2 gas sensor was fabricated and its gas sensing performance was tested. The test results indicated that the sensor had a good response to both reducing gas (NH3) and oxidizing gas (NO2) at room temperature. The sensitivity to 100 ppm of NO2 was 31.3%, and the response/recovery times were 4 s and 5 s, respectively. In addition, the limit of detection could be as low as 1 ppm. This work helps us to develop low power and integrable room temperature NO2 sensors.

β-Si3N4 Microcrystals Prepared by Carbothermal Reduction-Nitridation of Quartz

Single phase β-Si3N4 with microcrystals was synthesized via carbothermal reduction-nitridation (CRN) of quartz and carbon coke powder as starting materials. The effects of reaction parameters, i.e., heating temperature, holding time, C/SiO2 ratio, Fe2O3 additive and β-Si3N4 seeds on the phase transformation and morphology of products were investigated and discussed. Rather than receiving a mixture of both α- and β- phases of Si3N4 in the products, we synthesized powders of β-Si3N4 single polymorph in this work. The mechanism for the CRN synthesis of β-Si3N4 from quartz and the formation mechanism of Fe3Si droplets were discussed. We also firstly reported the formation of Fe3Si Archimedean solids from a CRN process where Fe2O3 was introduced as additive. Comparing to the gear-like short columnar morphology observed in samples without β-Si3N4 seeding, the addition of β-Si3N4 seeds led to an elongated morphology of final products and much finer widths. In addition, the β-Si3N4 microcrystals exhibited a violet‒blue spectral emission range, which could be highly valuable for their future potential optoelectronic applications.

Zinc aluminate nanotubes fabrication based on heating-induced volatilization and Kirkendall effect in nanopores of anodic aluminum oxide template

The fabrication of zinc aluminate nanotubes attracted considerable attention due to their potential application as catalysts, catalyst supports, and electronics. In this paper, it is presented the influence of heating temperature and time on the Kirkendall effect-related evolution of Zn nanowires embedded in nanopores of anodic aluminum oxide (AAO) template. With increasing of the reaction temperature and heating time, zinc aluminate nanotubes can be gradually achieved from Zn nanowires embedded in AAO template under the air environment. In particular, ZnO was formed in the pores of AAO template by the volatilization and oxidation of Zn nanowires. And then through the solid-solid interfacial reaction of ZnO and AAO template, the nanostructures were transformed to zinc aluminate nanotubes conserving the shape of the corresponding ZnO nanostructures, which was induced by the nanoscale Kirkendall effect. Combined with the volatilization and oxidation time of Zn nanowires, the wall thickness of the formed nanotubes can be further precisely controlled. Our finding provides a simple and efficient pathway to fabricate the complex hollow zinc aluminate nanostructures, which are expected to have potential applications in catalytic related fields.

Overcoming Stability Problems in Microwave-Assisted Heterogeneous Catalytic Processes Affected by Catalyst Coking

Microwave-assisted heterogeneous catalysis (MHC) is gaining attention due to its exciting prospects related to selective catalyst heating, enhanced energy-efficiency, and partial inhibition of detrimental side gas-phase reactions. The induced temperature difference between the catalyst and the comparatively colder surrounding reactive atmosphere is pointed as the main factor of the process selectivity enhancement towards the products of interest in a number of hydrocarbon conversion processes. However, MHC is traditionally restricted to catalytic reactions in the absence of catalyst coking. As excellent MW-susceptors, carbon deposits represent an enormous drawback of the MHC technology, being main responsible of long-term process malfunctions. This work addresses the potentials and limitations of MHC for such processes affected by coking (MHCC). It also intends to evaluate the use of different catalyst and reactor configurations to overcome heating stability problems derived from the undesired coke deposits. The concept of long-term MHCC operation has been experimentally tested/applied to for the methane non-oxidative coupling reaction at 700 °C on Mo/ZSM-5@SiC structured catalysts. Preliminary process scalability tests suggest that a 6-fold power input increases the processing of methane flow by 150 times under the same controlled temperature and spatial velocity conditions. This finding paves the way for the implementation of high-capacity MHCC processes at up-scaled facilities.

Magnetized impacts of Brownian motion and thermophoresis on unsteady squeezing flow of nanofluid between two parallel plates with chemical reaction and Joule heating

AbstractPresent research article investigate the heat and mass transfer characteristics of unsteady magnetohydrodynamic Casson nanofluid flow between two parallel plates under the influence of viscous dissipation and first order homogeneous chemical reaction effects. The impacts of thermophoresis and Brownian motion are accounted in the nanofluid model to disclose the salient features of heat and mass transport phenomena. The present physical problem is examined under the presence of Lorentz forces to investigate the effects of magnetic field. Further, the viscous and Joule dissipation effects are considered to describe the heat transfer process. The non‐Newtonian behaviour of Casson nanofluid is distinguished from those of Newtonian fluids by considering the well‐established rheological Casson fluid model. The two‐dimensional partial differential equations governing the unsteady squeezing flow of Casson nanofluid are coupled and highly nonlinear in nature. Thus, similarity transformations are imposed on the conservation laws to obtain the nonlinear ordinary differential equations. Runge‐Kutta fourth order integration scheme with shooting method and bvp4c techniques have been used to solve the resulting nonlinear flow equations. Numerical results have been obtained and presented in the form of graphs and tables for various values of physical parameters. It is noticed from present investigation that, the concentration field is a decreasing function of thermophoresis parameter. Also, concentration profile enhances with raising Brownian motion parameter. Further, the present numerical results are compared with the analytical and semianalytical results and found to be in good agreement.