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This paper aims to study the thermal oxidation performance of antioxidant additives in ester base oils deeply.

ReaxFF molecular dynamics was used to simulate the thermal oxidation process of butyl octyl diphenylamine and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate as two antioxidant additives act on the Trimethylolpropane trioleate (TMPTO) base oil. Meanwhile, combining with the infrared spectroscopy characterization results of the thermal oxidation test, this paper provides theoretical support for the development of high-performance synthetic lubricants and their antioxidant additives.

The results show that butyl octyldiphenylamine easily removes the hydrogen atom on the secondary amine, which promotes the formation of more long carbon chain diene radicals or polyene hydroperoxides from TMPTO. Octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate could easily decompose into octadecyl hydroperoxide and 2,6-di-tert-butyl 4-propionylphenol, which could convert into 2-tert-butyl-4-peroxyethyl-6-hydroperoxy-tert-butylphenol in the middle of the thermal oxidation reaction, prompting TMPTO to form more short-chain alkenyl and olefin hydroperoxide or other oxide.

The main change characteristics of base oil molecules are the first thermal decomposition to form oleic acid groups and ethane cyclopropane methyl oleate. Under the action of butyl octyldiphenylamine and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl) propanoate, the deep oxidation and decomposition reaction are slowed down.

The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-01-2020-0037/

In various kinds of materials processes, heat and mass transfer control in nuclear phenomena, constructing buildings, turbines and electronic circuits, etc., there are numerous problems that cannot be enlightened by uniform wall temperature. To explore such physical phenomena researchers incorporate non-uniform or ramped temperature conditions at the boundary, the purpose of this paper is to achieve the closed-form solution of a time-dependent magnetohydrodynamic (MHD) boundary layer flow with heat and mass transfer of an electrically conducting non-Newtonian Casson fluid toward an infinite vertical plate subject to the ramped temperature and concentration (RTC). The consequences of chemical reaction in the mass equation and thermal radiation in the energy equation are encompassed in this analysis. The flow regime manifests with pertinent physical impacts of the magnetic field, thermal radiation, chemical reaction and heat generation/absorption. A first-order chemical reaction that is proportional to the concentration itself directly is assumed. The Rosseland approximation is adopted to describe the radiative heat flux in the energy equation.

The problem is formulated in terms of partial differential equations with the appropriate physical initial and boundary conditions. To make the governing equations dimensionless, some suitable non-dimensional variables are introduced. The resulting non-dimensional equations are solved analytically by applying the Laplace transform method. The mathematical expressions for skin friction, Nusselt number and Sherwood number are calculated and expressed in closed form. Impacts of various associated physical parameters on the pertinent flow quantities, namely, velocity, temperature and concentration profiles, skin friction, Nusselt number and Sherwood number, are demonstrated and analyzed via graphs and tables.

Graphical analysis reveals that the boundary layer flow and heat and mass transfer attributes are significantly varied for the embedded physical parameters in the case of constant temperature and concentration (CTC) as compared to RTC. It is worthy to note that the fluid velocity is high with CTC and lower for RTC. Also, the fluid velocity declines with the augmentation of the magnetic parameter. Moreover, growth in thermal radiation leads to a declination in the temperature profile.

The proposed model has relevance in numerous engineering and technical procedures including industries related to polymers, area of chemical productions, nuclear energy, electronics and aerodynamics. Encouraged by such applications, the present work is undertaken.

Literature review unveils that sundry studies have been carried out in the presence of uniform wall temperature. Few studies have been conducted by considering non-uniform or ramped wall temperature and concentration. The authors are focused on an analytical investigation of an unsteady MHD boundary layer flow with heat and mass transfer of non-Newtonian Casson fluid past a moving plate subject to the RTC at the plate. Based on the authors’ knowledge, the present study has, so far, not appeared in scientific communications. Obtained analytical solutions are verified by considering particular cases of the published works.

To amend the efficiency of engineering processes and electronic devices, it is very urgent to assess the irreversibility in the term entropy generation (EG). The efficiency of energy transportation in a system can be improved by minimization of the rate of EG. In this context, the aim of the present study is to estimate irreversible losses of an unsteady magnetohydrodynamic (MHD) flow of a viscous incompressible electrically conducting non-Newtonian molybdenum disulfide-polyethylene glycol Casson nanofluid past a moving vertical plate with slip condition under the influence of Hall current, thermal radiation, internal heat generation/absorption and first-order chemical reaction. Molybdenum disulfide (MoS₂) nanoparticles are dispersed in the base fluid polyethylene glycol (PEG) to make Casson nanofluid. Casson fluid model is considered to characterize the rheology of the non-Newtonian fluid, whereas Rosseland approximation is adopted to simulate the thermal radiative heat flux in the energy equation.

The closed-form solutions are obtained for the model equations by using the Laplace transform method (LTM). Graphs and tables are prepared to examine the impact of pertinent flow parameters on the pertinent flow characteristics. The energy efficiency of the system via the Bejan number is studied extensively.

Analysis reveals that Hall current has diminishing behavior on entropy production of the thermal system. Strengthening of the magnetic field declines the velocity components and prop-ups the rate of EG. Adding nanoparticles into the base fluid reduces the EG, whereas there are an optimum volume fraction of nanoparticles for which the EG is minimized. Further, the rate of decay of EG is prominent in molybdenum disulfide-polyethylene glycol in comparison to PEG.

The results of this study would benefit the industrial sector in achieving the maximum heat transfer at the cost of minimum irreversibilities with an optimal choice of embedded thermophysical parameters. In view of this agenda, this study would be adjuvant in powder technology, polymer dynamics, metallurgical process, manufacturing dynamics of nano-polymers, petroleum industries, chemical industries, magnetic field control of material processing, synthesis of smart polymers, etc.

The novelty of this study is to encompass the analytical solution by using the LTM. Such an exact solution of non-Newtonian fluid flow is rare in the literature. Limited research articles are available in the field of EG analysis during the flow of non-Newtonian nanoliquid subject to a strong magnetic field.

The purpose of this paper is to explore the flow of Cu-water and Ag-water nanofluids past a vertical Riga plate. The plate is infinite in height and has zero normal wall flux through its surface. Influence of thermal radiation, slip, suction and chemical reaction on the flow characteristics are reported.

Non-dimensional forms of the flow governing equations are obtained by means of a set of similarity transformations. Numerical solution is obtained with the help of fourth-fifth-order Runge–Kutta–Fehlberg method with shooting procedure. Comparison of solution profiles of Cu-water and Ag-water nanofluids are presented graphically and with the help of tables. Influence of pertinent parameters on skin friction and heat transfer rate is also reported.

Results reveal that the skin friction coefficient is more prominent in the case of Ag-water nanofluid for an increase in thermal radiation and volume fraction. The role of suction and slip is to increase velocity but decrease the temperature in both nanofluids. Temperature and velocity of both nanofluids increase as volume fraction and thermal radiation values are augmented. Heat transport increases with thermal radiation. Region near the plate experiences rise in nanoparticle concentration with an increase in chemical reaction parameter.

A complete investigation of the modeled problem is addressed and the results of this paper are original.

The purpose of this paper is to solve the problem of steady, laminar, coupled heat and mass transfer by MHD natural convective boundary‐layer flow over a permeable truncated cone with variable surface temperature and concentration in the presence of thermal radiation and chemical reaction effects.

The governing equations are derived and transformed into a set of non‐similar equations which are then solved by an adequate implicit finite difference method.

It is found that the presence of thermal radiation, magnetic field and chemical reaction have significant effects on the rates of heat and mass transfer. The variation of the wall temperature and concentration exponent contribute to significant changes in the Nusselt and Sherwood numbers as well.

The titled problem with the various considered effects has not been solved before and it is of special importance in various industries. The problem is original.

The purpose of this paper is to study the effects of chemical reaction, thermal radiation and Soret and Dufour effects of heat and mass transfer by natural convection flow about a truncated cone in porous media.

The problem is formulated and solved numerically by an accurate implicit finite-difference method.

It is found that the Soret and Dufour effects as well as the thermal radiation and chemical reaction cause significant effects on the heat and mass transfer charateristics.

The problem is relatively original as it considers Soret and Dufour as well as chemical reaction and porous media effects on this type of problem.

The purpose of this paper is to investigate the momentum, heat and mass transfer characteristics of magnetic-nanofluid flow past a vertical plate embedded in a porous medium filled with ferrous nanoparticles. The analysis is carried out in the presence of pertinent physical parameters such as aligned magnetic field, thermal radiation, chemical reaction, radiation absorption, heat source/sink.

The flow governing PDEs are transformed into ODEs using appropriate conversions. Further, the set of ODEs is solved analytically using the perturbation technique. The flow quantities such as velocity, thermal and concentration fields are discussed under the influence of above-mentioned pertinent physical parameters with the assistance of graphical depictions. Moreover, the friction factor, local Nusselt and Sherwood number are discussed in tabular form.

The results indicate that flow and thermal transport phenomenon is more effective in the case of the aligned magnetic field as compared with the transverse magnetic field. Also, the nanoparticle volume fraction plays a vital role in controlling the wall friction and heat transfer performance. The validation of the obtained results is done by comparing them with the results of various numerical techniques, and hence found them in excellent agreement.

In present days, the external magnetic fields are very effective to set the thermal and physical properties of magnetic-nanofluids and regulate the flow and heat transfer characteristics. The strength of the applied magnetic field affects the thermal conductivity of magnetic-nanofluids and makes it aeolotropic. With this incentive, the authors investigated the flow and heat transfer characteristics of electrically conducting magnetic-nanofluids over a vertical surface embedded in a porous medium. The authors discussed the dual nature of ferrous-water nanofluid in the presence of aligned magnetic field and transverse magnetic field cases. The influence of several physical parameters on velocity, thermal and concentration field converses with the succour of graphs.

The purpose of this paper is to present a complex pyrolysis computational fluid dynamics (CFD) model of timber protection exposed to fire in a medium size enclosure. An emphasis is placed on rarely used temperature-dependent thermal material properties effecting the overall simulation outputs. Using the input dataset, a fire test model with oriented strand boards (OSB) in the room corner test facility is created in Fire Dynamics Simulator (FDS).

Seven FDS models comprising different complexity approaches to modelling the burning of wood-based materials, from a simplified model of burning based on a prescribed heat release rate to complex pyrolysis models which can describe the fire spread, are presented. The models are validated by the experimental data measured during a fire test of OSB in the room corner test facility.

The use of complex pyrolysis approach is recommended in real-scale enclosure fire scenarios with timber as a supplementary heat source. However, extra attention should be paid to burning material thermal properties implementation. A commonly used constant specific heat capacity and thermal conductivity provided poor agreement with experimental data. When the fire spread is expected, simplified model results should be processed with great care and the user should be aware of possible significant errors.

This paper brings an innovative and rarely used complex pyrolysis CFD model approach to predict the behaviour of timber protection exposed to fire. A study on different temperature-dependent thermal material properties combined with multi-step pyrolysis in the room corner test scenario has not been sufficiently published and validated yet.

The purpose of this paper is to synthesise carboxymethylcellulose and methyl methacrylate graft copolymers (CMC‐g‐PMMA), which is used as an effective additive, for reinforcing the rice‐hull‐cement composite.

Various CMC‐g‐PMMA copolymers were synthesised at different reaction temperatures, pH values of reaction solution and the dosages of monomer and initiator (potassium persulphate). The copolymers were characterised by Fourier transforms infrared (FT‐IR) spectra, thermal analysis (thermogravimetric and differential scanning calorimeter), X‐ray diffractometry (XRD) and scanning electron microscopy.

An optimal CMC‐g‐PMMA copolymer is obtained. For synthesis of the CMC‐g‐PMMA, the optimal reaction temperature is 80°C and pH value is 9. FT‐IR test of CMC‐g‐PMMA confirmed the existence of a chemical link between carboxymethylcellulose (CMC) and methyl methacrylate (MMA). The content of initiator has little effect on the reaction for synthesising the graft copolymer. Thermal analysis indicates the occurrence of graft reaction in CMC and MMA. XRD test proved that the chains of the graft copolymer can enlarge the proportion of the amorphous regions of CMC. Adding MMA has damage effect on the crystallisation.

Since the results of this paper are obtained from the laboratory experiments, further research should be conducted for evaluating the performances of this copolymer in practical application.

The mechanical test of the rice‐hull‐cement composite proved that CMC‐g‐PMMA is an effective additive for reinforcing the rice‐hull‐cement composite. The synthesis of CMC‐g‐PMMA provides a new alternative for modifying cellulose derivatives.

The CMC‐g‐PMMA obtained in this paper is a new kind of effective agent. It can reinforce the rice‐hull‐cement composite and expands the application of the composite in building industries.

The purpose of this paper is to investigate the effects of thermal radiation and viscous dissipation on steady natural convection flow of a viscous incompressible fluid along a uniformly moving infinite vertical porous plate with Newtonian heating in the presence of transverse magnetic field. The governing non-linear boundary layer equations are solved by using homotopy analysis method (HAM). The effects of various system parameters on velocity and temperature fields are discussed graphically, and the numerical values for skin friction and Nusselt number are presented in tabular form.

The problem is formulated using the Boussinesq approximation under the effects of thermal radiation and transverse magnetic field. The resulting coupled system of non-linear differential equations is solved using HAM with appropriate boundary conditions for Newtonian heating of the plate. HAM is a powerful method which provides rapidly converging series solution for the velocity and temperature fields. The effects of Prandtl number, Grashof number, suction parameter, magnetic field parameter, radiation parameter and Eckert number on the fluid velocity, temperature, skin friction and Nusselt number have been investigated.

The HAM solution has been successfully applied to find the converging series solution for velocity and temperature fields in terms of pertinent system parameters. Comparison of the exact solution results agree well with the HAM solution results in the absence of Eckert number and this indicates that the HAM solutions are accurate. It is found that the velocity and temperature profiles decreases with the increase of thermal radiation and suction parameters. An increase in the magnetic field parameter leads to a rise in the fluid temperature and fall in the fluid velocity.

The present analysis is limited to steady state laminar natural convection flow only. Unsteady natural- /mixed-convection laminar flow in the presence of thermal radiation, chemical reaction and transverse magnetic field will be investigated in a future work.

The study provides very useful information for heat transfer engineers to understand the heat transfer rate when the moving vertical porous surface temperature is not known a prior. The present results have immediate relevance in the design of nuclear reactors where vertical moving porous plates are using as control rods.

The present research work is relatively original and illustrates the effects of thermal radiation, viscous dissipation and transverse magnetic field on natural convection flow past a uniformly moving infinite vertical porous plate with Newtonian heating.