A new approach to the electrostatic pull-in instability of nanocantilever actuators using the ADM–Padé technique

AbstractIn this paper, the Adomian decomposition method and Padé approximants are integrated to study the deflection and pull-in instability of nanocantilever electromechanical switches. In a distributed parameter model, intermolecular forces, including Casimir forces, are taken into account considering their range of application. A closed form power series solution based on Adomian polynomials is obtained. The obtained analytic results are compared with numerical solution. The Adomian method is accurate for small deflections, but the results of a pull-in instability study demonstrate that the accuracy of the Adomian solution is not as good for small deflections. Thus, to increase the accuracy of the Adomian solution for the pull-in instability, the Adomian power series is converted to Padé approximants. The results of the present method are compared with the numerical results as well as those of the Adomian decomposition method and other methods reported in the literature. The results obtained using the ADM–Padé are remarkably accurate compared with the numerical results. The proposed technique can be easily extended to solve a wide range of instability problems. Finally, the minimum initial gap and the detachment length of the actuator that does not stick to the substrate due to the intermolecular attractions, which is an important parameter for the pull-in instability of a nanocantilever actuator, are calculated using Adomian–Padé approximants

Free convection in a parallelogrammic porous cavity filled with a nanofluid using Tiwari and Das' nanofluid model

The free convection heat transfer of Cu-water nanofluids in a parallelogrammic enclosure filled with porous media is numerically analyzed. The bottom and top of the enclosure are insulated while the sidewalls are subject to limited temperature difference. The Darcy flow and the Tiwari and Das’ nanofluid models are considered. The governing dimensionless partial differential equations are numerically solved using a finite difference code. The results are reported for isotherms and streamlines as well as Nusselt number as a function of the volume fraction of nanoparticles, porosity, types of the porous matrix, inclination angle, aspect ratio and different Rayleigh numbers. It is found that the presence of the nanoparticles inside the enclosure deteriorates the heat transfer rate, which is caused due to the increase of dynamic viscosity by the presence of nanoparticles. Therefore, in applications in which the nanofluids are used for their advantages, such as enhanced dielectric properties or antibacterial properties, more caution for the heat transfer design of the enclosure is necessary

CONVECTIVE FLOW AND HEAT TRANSFER OF NANO-ENCAPSULATED PHASE CHANGE MATERIAL (NEPCM) DISPERSIONS ALONG A VERTICAL SURFACE

Nano-encapsulated phase change suspension is a novel type of functional fluid in which the nanoparticles undergo phase change that contribute to heat transfer. Thus, the working fluid carries heat not only by sensible heat but also in the form of latent heat stored in the particles. The natural convection and heat transfer of Nano-Encapsulated Phase Change Materials (NEPCMs) suspensions within a boundary layer along a heated flat surface are theoretically investigated in this work. The nanoparticles are core-shell structured with the core fabricated from PCMs covered by a solid shell. A similarity solution approach along with the finite element method is employed to address the phenomena. The outcomes indicate that a decisive factor in boosting the heat transfer is the temperature at which NEPCM particles undergo the phase transition. The heat transfer parameter can be enhanced by about 25% by just adding 5% of NEPCM particles, compared to the case with no NEPCM particles

Fluid–structure interaction of free convection in a square cavity divided by a flexible membrane and subjected to sinusoidal temperature heating

Purpose: The purpose of the present paper is to model a cavity, which is equally divided vertically by a thin, flexible membrane. The membranes are inevitable components of many engineering devices such as distillation systems and fuel cells. In the present study, a cavity which is equally divided vertically by a thin, flexible membrane is model using the fluid–structure interaction (FSI) associated with a moving grid approach. Design/methodology/approach: The cavity is differentially heated by a sinusoidal time-varying temperature on the left vertical wall, while the right vertical wall is cooled isothermally. There is no thermal diffusion from the upper and lower boundaries. The finite-element Galerkin technique with the aid of an arbitrary Lagrangian–Eulerian procedure is followed in the numerical procedure. The governing equations are transformed into non-dimensional forms to generalize the solution. Findings: The effects of four pertinent parameters are investigated, i.e., Rayleigh number (104 = Ra = 107), elasticity modulus (5 × 1012 = ET = 1016), Prandtl number (0.7 = Pr = 200) and temperature oscillation frequency (2p = f = 240p). The outcomes show that the temperature frequency does not induce a notable effect on the mean values of the Nusselt number and the deformation of the flexible membrane. The convective heat transfer and the stretching of the thin, flexible membrane become higher with a fluid of a higher Prandtl number or with a partition of a lower elasticity modulus. Originality/value: The authors believe that the modeling of natural convection and heat transfer in a cavity with the deformable membrane and oscillating wall heating is a new subject and the results have not been published elsewhere

Ferro-hydrodynamic induced convection flow and heat transfer of nanofluids in a corrugated wall enclosure

This study aims to improve heat transfer by utilizing Kelvin forces and inducing magnetic-induced convection in ferro-hydrodynamic convection, in conjunction with nanoparticle migrations. The fundamental equations governing the conservation of mass, momentum, energy, and nanoparticle mass were formulated as partial differential equations. As primary terms, the model incorporated the buoyancy, Lorenz, and Kelvin forces. In this context, temperature variations in the presence of a variable magnetic field generate a temperature-dependent body force. This can induce fluid circulation. Thus, even without gravitational force, magnetic force can stimulate convection heat transfer flows. The study thoroughly examined the impact of magnetic source placement on heat transfer. An increase in Ha from 0 to 100 reduced the average Nusselt number (NuAvg) by approximately 60% in all cases, regardless of the magnetic source position. However, the magnetic field number (Mnf) and its effect on NuAvg are dependent on the magnetic source's position

Free convection heat transfer and entropy generation in an odd-shaped cavity filled with a Cu-Al2O3 hybrid nanofluid

The present paper aims to analyze the thermal convective heat transport and generated irreversibility of water-Cu-Al2O3 hybrid nanosuspension in an odd-shaped cavity. The side walls are adiabatic, and the internal and external borders of the enclosure are isothermally kept at high and low temperatures of Thand Tc, respectively. The control equations based on conservation laws are formulated in dimensionless form and worked out employing the Galerkin finite element technique. The outcomes are demonstrated using streamlines, isothermal lines, heatlines, isolines of Bejan number, as well as the rate of generated entropy and the Nusselt number. Impacts of the Rayleigh number, the hybrid nanoparticles concentration (ϕhnf), the volume fraction of the Cu nanoparticles to ϕhnf ratio (ϕr), width ratio (WR) have been surveyed and discussed. The results show that, for all magnitudes of Rayleigh numbers, increasing nanoparticles concentration intensifies the rate of entropy generation. Moreover, for high Rayleigh numbers, increasing WR enhances the rate of heat transport

NUMERICAL STUDY OF A NON-NEWTONIAN PHASE CHANGE FLOW IN FINNED RECTANGULAR ENCLOSURES

Phase change materials (PCMs) are widely used for thermal energy storage systems due to their effective thermal properties for energy accumulation. Simultaneously, this material has poor thermal conductivity, and for the optimization of such systems, many techniques are used. This study focuses on an analysis of PCMs in a vertical cavity with one, two, or three solid fins and differential heating. The finite element procedure has solved governing equations formulated using the power-law approach for the non-Newtonian PCM and enthalpy-porosity method. The developed code has been verified using numerical and experimental data from other authors. Effects of fins number and power-law index on flow and thermal structures within the cavity have been studied. It has been found that a rise in the power-law index illustrates a growth of time for the charging level of the storage system, while the addition of a solid fin from one to three allows for reducing the charging time. The extended heat transfer surface can be applied to optimize the thermal energy storage system

Latent heat thermal storage of nano-enhanced phase change material filled by copper foam with linear porosity variation in vertical direction

The melting flow and heat transfer of copper-oxide coconut oil in thermal energy storage filled with a nonlinear copper metal foam are addressed. The porosity of the copper foam changes linearly from bottom to top. The phase change material (PCM) is filled into the metal foam pores, which form a composite PCM. The natural convection effect is also taken into account. The effect of average porosity; porosity distribution; pore size density; the inclination angle of enclosure; and nanoparticles’ concentration on the isotherms, melting maps, and the melting rate are investigated. The results show that the average porosity is the most important parameter on the melting behavior. The variation in porosity from 0.825 to 0.9 changes the melting time by about 116%. The natural convection flows are weak in the metal foam, and hence, the impact of each of the other parameters on the melting time is insignificant (less than 5%)

Effect of Salicylic Acid Foliar Application on Physiological Indices and Induction of Terminal Heat Stress Tolerance of Quinoa in Ahvaz

IntroductionQuinoa (Chenopodium quinoa L.) is a dicotyledonous, allotetraploid, three-carbon, annual, optional salt-loving plant and is native to South America and the Andean highlands. The growth period of the plant varies between 70 and 240 days depending on the cultivated area. The main product of this plant is the seed, which has a high nutritional value in terms of protein, amino acid balance, unsaturated fat, vitamins, and minerals. Like other plants, quinoa faces various environmental stresses during its growth period, and its growth and yield are a function of environmental factors and their mutual effects. The occurrence of high temperatures during the sensitive stages of plant growth, such as flowering and seed formation, may cause a significant decrease in quinoa yield, and high temperature has been cited as one of the most important challenges for the cultivation and expansion of quinoa in the world. Salicylic acid acts as a signal molecule and plays an important role in regulating growth and development processes in plants under environmental stress. Salicylic acid increases the content of relative humidity, accumulation of dry matter, and the amount of chlorophyll.Materials and MethodsThe objective of this research is to assess the physiological responses of quinoa cultivars to varying planting dates and the impact of foliar application of salicylic acid in mitigating the adverse effects of end-of-season heat stress during the 2021-2022 crop year. The study was conducted at the research farm of the Faculty of Agriculture, Shahid Chamran University of Ahvaz, using a split-split plot design within a randomized complete block framework, with three replications. In this experiment, three factors a) planting date including October 12, November 11, and December 11, and b) foliar application of salicylic acid in the two stages of budding and the beginning of flowering including non-application, 1.5 mM and 3 mM and c) Quinoa cultivars including Titicaca, Giza, Q12 and Redcarin were investigated.Results and DiscussionThe effect of investigated factors such as planting date, salicylic acid, and variety on different traits had statistically significant differences. The results showed that the maximum amount of stomatal conductance and the relative content of leaf water belonged to the date of October 12. The highest biological yield and seed yield were observed under conditions of application of 1.5 and 3 mM salicylic acid, respectively. Probably, salicylic acid has increased the growth and accumulation of dry matter by improving carbon fixation, synthesis of metabolites, and maintaining the water status of plant tissues. Based on the results of the comparison of the mean of the three-way interaction, the maximum amount of biological yield and seed as the most important goals of quinoa plant cultivation, respectively, in the treatment of not using salicylic acid in the Redcarin cultivar on the planting date of December 11 and the application of 3 mM salicylic acid was obtained in the variety Redcarin on the planting date of October 12. The highest rate of net assimilation and the growth rate of the product belonged to the treatments of no application of salicylic acid in the Redcarin cultivar on December 11 and no application of salicylic acid in the Giza cultivar on October 12, respectively. The treatment of not using salicylic acid in the Redcarin variety on the planting date of October 12 was also able to achieve a high harvest index.Conclusion According to the obtained results, it seems that to achieve a high seed yield of quinoa, it is possible to benefit from the treatment of 3 mM salicylic acid in the Redcarin variety on the planting date of October 12