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Flow patterns and heat transfer inside mini twisted oval tubes (TOTs) heated by constant-temperature walls are numerically investigated. Different configurations of tubes are simulated using water as the working fluid with temperature-dependent thermo-physical properties at Reynolds numbers ranging between 500 and 1100. After validating the numerical method with the published correlations and available experimental results, the performance of TOTs is compared to a smooth circular tube. The overall performance of TOTs is evaluated by investigating the thermal-hydraulic performance and the results are analyzed in terms of the field synergy principle and entropy generation. Enhanced heat transfer performance for TOTs is observed at the expense of a higher pressure drop. Additionally, the secondary flow generated by the tube-wall twist is concluded to play a critical role in the augmentation of convective heat transfer, and consequently, better heat transfer performance. It is also observed that the improvement of synergy between velocity and temperature gradient and lower irreversibility cause heat transfer enhancement for TOTs.

The application of a flapping wing mechanism offers a vast range of development possibilities for unmanned aerial vehicles (UAVs) and autonomous underwater vehicles (AUVs). The influence of wake transitions on flapping wing mechanism’s capabilities is not fully understood particularly at low Reynolds numbers. The numerical investigation of a symmetric airfoil performing sinusoidal heaving oscillations is performed to explore the wake transitions. The influence of heaving parameters on wake transitions when exposed to a constant velocity flow is investigated. The existence of reverse von Karman vortex street, deflected wake and chaotic wake is observed. The wake deflection is found to switch its direction before transforming into a chaotic wake. The coherent structures and its evolution with the flow are presented using proper orthogonal decomposition (POD). The underlying structures and their interactions for different wake situations are identified. Correlations for the nondimensional maximum velocity in the wake in terms of frequency and amplitude is proposed. The wake dynamics is found to depend significantly on the leading edge vortices. The time-varying velocity fluctuations in the flow field are presented and discussed in detail. The velocity fluctuation contours are used to identify the regions of momentum transfer. The transient nature of the flow field is studied using the phase plot. A transition route from the periodic to chaotic regime though a quasi-periodic regime is established using time series analysis. The wake transitions are observed to be more sensitive towards heaving frequency than the heaving amplitude.

The two-dimensional laminar flow over a simultaneously pitching-heaving teardrop airfoil is studied numerically. The influence of frequency and amplitude on the wake structure and aerodynamic performance is investigated at a constant Reynolds number, $\mathrm{\text{Re}}=2640$. The computational modeling accurately depicts the changes in the wake structure that occur between the von Karman, reverse von Karman and deflected conditions. Investigations at low flapping frequencies and amplitudes identified the presence of additional wake structures that had not been reported previously. The interaction between the flapping frequency and vortex shedding frequency appears to govern the formation of such multiple vortex wakes. The wake structures identified are presented in the form of a wake map where the transitions between the wake structures are visible. This study correlates the wake arrangement with the variation in force coefficients and explains why the presence of a reverse von Karman street is necessary but not a sufficient condition for thrust production. The time history of the drag coefficient and the phase relation between lift and drag show the dynamics of the wake. The variation of force coefficients and efficiency at different flapping conditions is evaluated, and the influence of flapping parameters is assessed. The underlying vortex interactions that influence the aerodynamic performance are identified. The development and distribution of stress fields developed due to periodic fluctuations behind the flapping airfoil have not been discussed previously. The velocity fluctuations in the wake due to the periodic flapping are presented, and regions of maximum stress distribution are identified.

Four different kinds of laminar flows between two parallel plates are investigated using the Lattice Boltzmann Method (LBM). The LBM accuracy is estimated in two cases using numerical fits of the parabolic velocity profiles and the kinetic energy decay curves, respectively. The error relative to the analytical kinematic viscosity values was found to be less than one percent in both cases. The LBM results for the unsteady development of the flow when one plate is brought suddenly at a constant velocity, are found in excellent agreement with the analytical solution. Because the classical Schlichting’s approximate solution for the entrance-region flow is not valid for small Reynolds numbers, a Finite Element Method solution was used in order to check the accuracy of the LBM results in this case.

Heat transfer is an important phenomenon in the industrial sector. Thus, the simulation is made to compute the distribution of heat in a rectangular channel in this paper. A heated rod is inserted at the center of the rectangular channel. The fluid flowing in the rectangular channel is considered to be a viscous fluid. Navier–Stokes equations of motion for laminar flow are used. The medium for the fluid motion is considered to be a porous medium. Heat transfer is computed for nonlinear two-dimensional incompressible and unsteady flows. The Fourier’s law of heat conduction is used for the transmission of heat in the rectangular channel. The Finite Element Method (FEM) is applied to the solution of the problem. For different values of the permeability parameter, Prandtl number and Rayleigh number, the graphic solution for the velocity and temperature fields is shown.

The model presented in this paper deals with the investigation of the unsteady laminar flow past a stretchable disk. The nanofluids Al₂O₃/H₂O and Cu/H₂O are considered for the analysis where the thermal characteristics and flow behavior of these nanofluids are compared. In addition, the system is subjected to the suction force that has significant impacts on velocity of the nanofluid flow. Further, the nanoparticle solid volume fraction is another important parameter that is discussed which has a prominent role on both profiles of the nanofluid. Furthermore, the investigated mathematical model is framed using PDEs that are transformed to ODEs using suitable transformations. The system of equations obtained in this regard is solved by employing the RKF-45 numerical method where the results are obtained in the form of graphs. Various nanofluids flow parameters arise in the study and the impact of all these parameters has been analyzed and interpreted. Some of the major outcomes are that the higher values of nanoparticle solid volume fraction enhance the temperature while it decreases velocity of the flow. The comparison of flow of the two nanofluids concluded that alumina–water nanofluid has a better velocity while the copper–water nanofluid has a better thermal conductivity.

Hybrid nanomaterial exergy drop and thermal manners were examined in this work with involving the porous media in middle part of the pipe. Moreover, to augment the rotational velocity, disturber device was applied in test section. The two sections near the entrance and outlet were in absence of disturber and porous zone because of importance of shun of backflow and reach of fully developed condition. Laminar flow with assume of homogeneous mixture for hybrid nanomaterial (Al₂O${}_3+\mathrm{\text{MWCNT}}$ and water) results in final model with involving the non-Darcy approach for permeable media. Finite volume approach was applied for achieving the outputs which are exergy loss (Xd) and hydrothermal behavior. Use of additives results in lower Xd more than 7.7% when $\mathrm{\text{Re}}=10\mathrm{\text{Da}}=\mathrm{\text{1e2}}$. With growth of Re, the Xd declines around a bit greater than 19%. Utilizing higher permeability allows the hybrid nanofluid moves quicker and exergy loss augments less than 10.5%.

The investigation of fluid flow and forced convective heat transfer in microchannels with square barriers is the focus of this study. The positioning of obstacles was varied in three cases: at the top wall, bottom wall, and symmetrically distributed on both sides of the microchannel wall. The thermal Lattice Boltzmann Method in conjunction with the Double Distribution Function and Bhatnagar–Gross–Krook approach was used for simulation through computer code in Python. Slip velocity and temperature jump were considered in the boundary conditions for the walls of the microchannel and obstacles. The results demonstrate that the rarefaction effect, placement of barriers, and choice of square obstacles significantly impact fluid flow and heat transfer. An increase in Knudsen numbers (Kn) leads to a decrease in temperature and velocity. The presence of obstructions on both sides of the microchannel walls reduces the fluid’s velocity and cools the fluid at the microchannel’s exit. The third case, with obstacles on both sides, presents a practical approach for reducing the fluid’s temperature at the exit, resulting in the lowest level of skin friction (Cf) and a reduction in the Nusselt number (Nu). The proposed configurations can be utilized to enhance the geometry of microchannels and for cooling purposes in small-scale devices and systems with miniature mechanical and electrical components. The study’s findings suggest that the placement of obstacles at the bottom or on both sides, depending on the need for best cooling on both sides or only at the top to reduce material consumption, can achieve low temperature at the exit of a rectangular microchannel.

This study investigated fluid flow and forced convective heat transfer in rectangular microchannels with square barriers, as illustrated in Fig. 1. In the first situation, three obstacles were positioned along the microchannel’s top wall. In the second scenario, obstacles were positioned along the microchannel’s bottom wall. In the final example, three square obstacles are placed symmetrically on either side of the microchannel wall. With the help of the Finite Element Method (FEM), we investigate the physicochemical behavior of the microchannel. The development of computer code within COMSOL multiphysics made it possible to simulate heat transport and fluid flow. The results include the implications of the rarefaction effect on fluid flow and heat transmission and decisions regarding the location of barriers and the shape of obstacles in squares. In addition, with the lowest value in skin friction and a lower Nusselt number, the third example, which has barriers on both sides, provides a valuable method for reducing the fluid temperature at the exit of the microchannel. This is because it has barriers on both sides. In the section under “Results and Discussion,” we provide an in-depth analysis of the numerical data derived from the microchannel.

• •Objective: This study aims to numerically investigate forced convective heat transfer in a rectangular channel featuring multiple square obstacles. The simulation employs the FEM to model fluid flow and temperature distribution.
• •Geometry and complexity: The channel geometry incorporates square obstacles, introducing geometric complexity. The FEM is chosen for its capability to handle intricate geometries accurately.

The primary intent of this paper is to examine the influence of radiation, Soret, and Dufour on the laminar flow of a rotating fluid through a permeable plate undergoing a chemical reaction. The Soret effect, for example, has been employed to differentiate isotopes and to combine gases of different molecular weights. Many real-world applications, including geosciences and chemical engineering, comprise the Soret and Dufour effects. Using similarity variables, the governing equations and allied boundary conditions (BCs) are simplified to a dimensionless form and then solved using the finite element method (FEM). In order to get the numerical approximations of velocity, temperature, and concentration, dimensionless parameters of the flow were utilized, and the consequences were envisioned visually. The most significant results of this research are that raising the Soret and Dufour parameters causes an upsurge in the velocity profile and enhancing the radiation factor causes an upsurge in the temperature distribution. Enhancing the values of permeability causes a reduction in skin friction. Enhancing the accuracy of heat absorption factor estimations leads to an increase in the values of the Nusselt number. A comparison case study has been made among the outcomes of well-existing repository literature with the current solutions and detected a great correlation.

A noniterative method for nonlinear parabolic partial-differential equations is described and applied to boundary-layer equations for two-dimensional incompressible laminar flows. Comparison of calculated results indicates that the accuracy of this method is comparable to those obtained with the iterative method.

A noniterative method for nonlinear parabolic partial-differential equations is described and applied to boundary-layer equations for two-dimensional laminar and turbulent flows. Comparison of calculated results indicates that the accuracy of this method is comparable to those obtained with an iterative method.