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2020年 第41卷 第11期    刊出日期：2020-11-01

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论文

Analytical transient phase change heat transfer model of wearable electronics with a thermal protection substrate

Yingli SHI, Junyun JI, Yafei YIN, Yuhang LI, Yufeng XING

2020, 41(11):  1599-1610.  doi:10.1007/s10483-020-2671-7

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As thermal protection substrates for wearable electronics, functional soft composites made of polymer materials embedded with phase change materials and metal layers demonstrate unique capabilities for the thermal protection of human skin. Here, we develop an analytical transient phase change heat transfer model to investigate the thermal performance of a wearable electronic device with a thermal protection substrate. The model is validated by experiments and the finite element analysis (FEA). The effects of the substrate structure size and heat source power input on the temperature management efficiency are investigated systematically and comprehensively. The results show that the objective of thermal management for wearable electronics is achieved by the following thermal protection mechanism. The metal thin film helps to dissipate heat along the in-plane direction by reconfiguring the direction of heat flow, while the phase change material assimilates excessive heat. These results will not only promote the fundamental understanding of the thermal properties of wearable electronics incorporating thermal protection substrates, but also facilitate the rational design of thermal protection substrates for wearable electronics.



Non-Newtonian biomagnetic fluid flow through a stenosed bifurcated artery with a slip boundary condition

Yaxin XU, Jing ZHU, Liancun ZHENG, Xinhui SI

2020, 41(11):  1611-1630.  doi:10.1007/s10483-020-2657-9

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The effects of a velocity slip and an external magnetic field on the flow of biomagnetic fluid (blood) through a stenosed bifurcated artery are investigated by using ANSYS FLUENT. Blood is regarded as a non-Newtonian power-law fluid, and the magnetization and electrical conductivity are considered in the mathematical model. The no-slip condition is replaced by the first-order slip condition. The slip boundary condition and magnetic force are compiled in the solver by the user-defined function (UDF). Numerical solutions are obtained by the finite volume method based on a nonuniform grid structure. The accuracy and efficiency of the solver are verified through a comparison with the literature. The results are presented graphically for different parameter values, and the effects of the magnetic number, the magnetic source position, the vascular obstruction ratio, the slip parameter, and the power-law index on the flow and temperature fields are illustrated.

Thermal instability of a viscoelastic fluid in a fluid-porous system with a plane Poiseuille flow

Chen YIN, Chunwu WANG, Shaowei WANG

2020, 41(11):  1631-1650.  doi:10.1007/s10483-020-2663-7

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The thermal convection of a Jeffreys fluid subjected to a plane Poiseuille flow in a fluid-porous system composed of a fluid layer and a porous layer is studied in the paper. A linear stability analysis and a Chebyshev τ-QZ algorithm are employed to solve the thermal mixed convection. Unlike the case in a single layer, the neutral curves of the two-layer system may be bi-modal in the proper depth ratio of the two layers. We find that the longitudinal rolls (LRs) only depend on the depth ratio. With the existence of the shear flow, the effects of the depth ratio, the Reynolds number, the Prandtl number, the stress relaxation, and strain retardation times on the transverse rolls (TRs) are also studied. Additionally, the thermal instability of the viscoelastic fluid is found to be more unstable than that of the Newtonian fluid in a two-layer system. In contrast to the case for Newtonian fluids, the TRs rather than the LRs may be the preferred mode for the viscoelastic fluids in some cases.

Optimal treatment of stratified Carreau and Casson nanofluids flows in Darcy-Forchheimer porous space over porous matrix

R. KUMAR, R. KUMAR, S. A. SHEHZAD, A. J. CHAMKHA

2020, 41(11):  1651-1670.  doi:10.1007/s10483-020-2655-7

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A comparative three-dimensional (3D) analysis for Casson-nanofluid and Carreau-nanofluid flows due to a flat body in a magnetohydrodynamic (MHD) stratified environment is presented. Flow is estimated to be suspended in a Darcy-Forchheimer medium. Soret and Dufour responses are also accommodated in the flow field. A moving (rotating) coordinate system is exercised to examine the bidirectionally stretched flow fields (flow, heat transfer, and mass transfer). Nanofluid is compounded by taking ethylene glycol/sodium alginate as base fluid and ferric-oxide (Fe₃O₄) as nanoparticles. Governing equations are handled by the application of optimal homotopy asymptotic method (OHAM), where convergence parameters are optimized through the classical least square procedure. The novel mechanism (hidden physics) due to appearing parameters is explored with the assistance of tabular and graphical expositions. Outcomes reveal the double behavior state for temperature field with thermal stratification/Dufour number, and for concentration field with Soret number due to the presence of turning points.

Flow of colloidal suspension and irreversibility analysis with aggregation kinematics of nanoparticles in a microchannel

S. SINDHU, B. J. GIREESHA

2020, 41(11):  1671-1684.  doi:10.1007/s10483-020-2669-9

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The current exploration focuses on the ethylene glycol (EG) based nanoliquid flow in a microchannel. The effectiveness of the internal heat source and linear radiation is reflected in the present investigation. The estimation of suitable thermal conductivity model has affirmative impact on the convective heat transfer phenomenon. The examination is conceded with the nanoparticle aggregation demonstrated by the MaxwellBruggeman and Krieger-Dougherty models which tackle the formation of nanolayer. These models effectively describe the thermal conductivity and viscosity correspondingly. The dimensionless mathematical expressions are solved numerically by the Runge Kutta Fehlberg approach. A higher thermal field is attained for the Bruggeman model due to the formation of thermal bridge. A second law analysis is carried out to predict the sources of irreversibility associated with the thermal system. It is remarked that lesser entropy generation is obtained for the aggregation model. The entropy generation rate declines with the slip flow and the thermal heat flux. A notable enhancement in the Bejan number is attained by increasing the Biot number. It is established that the nanoparticle aggragation model exhibits a higher Bejan number in comparision with the usual flow model.

Darcy-Forchheimer flow with nonlinear mixed convection

T. HAYAT, F. HAIDER, A. ALSAEDI

2020, 41(11):  1685-1696.  doi:10.1007/s10483-020-2680-8

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An analysis of the mixed convective flow of viscous fluids induced by a nonlinear inclined stretching surface is addressed. Heat and mass transfer phenomena are analyzed with additional effects of heat generation/absorption and activation energy, respectively. The nonlinear Darcy-Forchheimer relation is deliberated. The dimensionless problem is obtained through appropriate transformations. Convergent series solutions are obtained by utilizing an optimal homotopic analysis method (OHAM). Graphs depicting the consequence of influential variables on physical quantities are presented. Enhancement in the velocity is observed through the local mixed convection parameter while an opposite trend of the concentration field is noted for the chemical reaction rate parameter.

Machine learning of synaptic structure with neurons to promote tumor growth

Erhui WANG, Xuelan ZHANG, Liancun ZHENG, Chang SHU

2020, 41(11):  1697-1706.  doi:10.1007/s10483-020-2656-8

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In this paper, we use machine learning techniques to form a cancer cell model that displays the growth and promotion of synaptic and electrical signals. Here, such a technique can be applied directly to the spiking neural network of cancer cell synapses. The results show that machine learning techniques for the spiked network of cancer cell synapses have the powerful function of neuron models and potential supervisors for different implementations. The changes in the neural activity of tumor microenvironment caused by synaptic and electrical signals are described. It can be used to cancer cells and tumor training processes of neural networks to reproduce complex spatiotemporal dynamics and to mechanize the association of excitatory synaptic structures which are between tumors and neurons in the brain with complex human health behaviors.

Effects of g-jitter and radiation on three-dimensional double diffusion stagnation point nanofluid flow

M. H. A. KAMAL, N. A. RAWI, A. ALI, S. SHAFIE

2020, 41(11):  1707-1722.  doi:10.1007/s10483-020-2666-6

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The unsteady double diffusion of the boundary layer with the nanofluid flow near a three-dimensional (3D) stagnation point body is studied under a microgravity environment. The effects of g-jitter and thermal radiation exist under the microgravity environment, where there is a gravitational field with fluctuations. The flow problem is mathematically formulated into a system of equations derived from the physical laws and principles under the no-slip boundary condition. With the semi-similar transformation technique, the dimensional system of equations is reduced into a dimensionless system of equations, where the dependent variables of the problem are lessened. A numerical solution for the flow problem derived from the system of dimensionless partial differential equations is obtained with the Keller box method, which is an implicit finite difference approach. The effects studied are analyzed in terms of the physical quantities of principle interest with the fluid behavior characteristics, the heat transfer properties, and the concentration distributions. The results show that the value of the curvature ratio parameter represents the geometrical shape of the boundary body, where the stagnation point is located. The increased modulation amplitude parameter produces a fluctuating behavior on all physical quantities studied, where the fluctuating range becomes smaller when the oscillation frequency increases. Moreover, the addition of Cu nanoparticles enhances the thermal conductivity of the heat flux, and the thermal radiation could increase the heat transfer properties.

Consequence of exponential heat generation on non-DarcyForchheimer flow of water based carbon nanotubes driven by a curved stretching sheet

B. J. GIREESHA, B. NAGARAJA, S. SINDHU, G. SOWMYA

2020, 41(11):  1723-1734.  doi:10.1007/s10483-020-2647-7

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The present article comprises the study on the influence of exponential space based heat generation on the non-Darcy-Forchheimer flow of carbon nanotubes (CNTs). The flow is considered over a curved stretching sheet. Similarity variables are used to reduce the flow descriptive nonlinear partial derivative equations to simple equations. Simplified equations are then solved by the exploiting Runge-Kutta-Fehlberg fourth- and fifth-order methods. Obtained numerical solutions are shown in graphs and tables. Comparison between single and multi-walled CNTs has been established through the tabulated values and plotted graphs. It is concluded that the heat source parameter plays a prime role in enhancement of temperature, and the curvature parameter has adverse impact on velocity and temperature panels. Both the inertial parameter and inverse-Darcy number affect the fluid velocity.

New groups of solutions to the Whitham-Broer-Kaup equation

Yaji WANG, Hang XU, Q. SUN

2020, 41(11):  1735-1746.  doi:10.1007/s10483-020-2683-7

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The Whitham-Broer-Kaup model is widely used to study the tsunami waves. The classical Whitham-Broer-Kaup equations are re-investigated in detail by the generalized projective Riccati-equation method. 20 sets of solutions are obtained of which, to the best of the authors’ knowledge, some have not been reported in literature. Bifurcation analysis of the planar dynamical systems is then used to show different phase portraits of the traveling wave solutions under various parametric conditions.