Challenges in Nano and Micro Scale Science and Technology
Volume:10 Issue: 2, Summer-Autumn 2022

The present study follows a 3D modeling of the geometry of a parabolic trough solar collector (PTSC) equipped with a twised cross turbulator (TCT) and a Vortex Generator with Pitch Ratio (VGPR), considering the finite volume method (FVM) to solve the governing equations. The absorber tube (AT) of this PTSC is equipped with a TCT and a VGPR in order to increase thermal performance (TP). Also, the efficiencyof their use on different output parameters have been compared. In addition, in order to be more practical, the efficiencyof the geometric shape of the TCT and VGPR on various parameters in the output has been investigated. In order to make the study more practical, graphene oxide (GO) and double-walled carbon nanotubes (DWCNT) nanoparticles (NP) are dispersed in this base fluid (BF). The study is conducted at high Reynolds numbers (Re) (from 15,000 to 60,000). Numerical simulation results show that the velocity change in the AT is a positive factor in all cases of increase. Because in all these cases, the increase of this parameter has caused the average Nusselt number (〖Nu〗_ave) to rise. Also, Syltherm 800 BF has a lower thermal conductivity (k) coefficient than hybrid nanofluid (HNF) Syltherm 800/DWCNT- GO, resulting in lower TP in PTSC. The addition of TCT, VGPR, and their geometrical change has a positive role in the hydrodynamic behavior of Syltherm 800/DWCNT-GO HNF flow. In all geometric modes, the values obtained from the PEC index are more significant than one, so using these two mechanical parts always has a better TP than the pressure drop (P) resulting from their presence. Finally, by examining the exergy efficiency (_ex), It was observed that the maximum practical work received from the solar system (SS) was obtained when using the VGPR in the flow path of HNF Syltherm 800/DWCNT-GO.

This paper explores the lateral vibration behavior of a micro cantilever beam with an open edge crack under axial load using the modified strain gradient theory (MSGT). A concentrated mass, incorporating its rotational inertia, is positioned at the beam's free end. The open edge crack is represented using the Dirac delta function. By employing MSGT, Hamilton's principle, and the Dirac delta function, the governing equations for system motion and relevant boundary conditions are derived to examine the size-dependence effects. Analytical solutions for the first and second natural frequencies of the cracked cantilever beam are provided, and validated through finite element modeling. The study further investigates the impact of various system parameters, including material length scale parameters, crack depth, crack location, cantilever beam length, axial load, and the presence of the concentrated mass, on the natural frequencies. The findings demonstrate that the crack depth, crack location, and material length scale parameters considerably influence the lateral vibration characteristics of the system. Notably, increasing the values of l_i/h from 0 to 0.25 leads to an approximate 40% rise in the natural frequency.

Metastasis is the main origin of epithelial cancer-based mortality. Since circulating tumor cells (CTCs) are valid biomarkers to diagnose cancer, their isolation and analysis are crucial. Microfluidic technology has experienced remarkable potential to isolate CTCs due to its unique characteristics. The present paper analyzes the influences of Newtonian and non-Newtonian fluids on the continuous separation of CTCs using standing surface acoustic waves (SSAWs). The impacts of inlet velocity, oscillation amplitude, dynamic viscosity, CTC radius, power-law index, and sheath-to-sample flow velocity ratio on the isolation process are examined. The results demonstrate that the separation efficiency declines from 88% to 84% by augmenting the inlet velocity from 1.8 mm/s to 2 mm/s. It is found that for a certain value of CTC radius, the amount of sheath flow velocity can be changed to reach a maximum separation efficiency. Besides, the amount of separation efficiency decreases as the dynamic viscosity of the Newtonian fluid is enhanced and the power-law index of the non-Newtonian fluid is reduced.

Take in to account of metal foams properties like energy absorption; they have several implementations. The complication of foam structures leads difficulties in investigation of elastic and plastic modulus. In the present research, porosity of foam are modeled and analyzed, numerically. In this context, MATLAB and JavaScript have been developed for geometrical modeling of porous materials considering density, radius, and random distribution of porous. Several porous configurations are simulated using periodic boundary conditions on Micro/Meso Scale in order to numerically calculate their elastic mechanical properties like Young’s modulus and shear modulus as a function of the porous configuration. The porous are distributed randomly and the effect of configuration parameters (like shape, number, size) are investigated on elastic modulus. In order to simulate more accurately, porous characteristics were investigated using SEM experimental tests. Eventually, the calculated effective constants of porous materials are compared with numerical and experimental literatures. This comparison demonstrates that the proposed method can accurately model high range of porosity (from 5% to 65%) and estimate the effective constant of porous materials in 3 directions including of (E1, E2, E3, G12, G13, G23).