Steady-state Laminar Flow Research Articles

High-fidelity experimental model verification for flow in fractured porous media

Mixed-dimensional mathematical models for flow in fractured media have been prevalent in the modeling community for almost two decades, utilizing the explicit representation of fractures by lower-dimensional manifolds embedded in the surrounding porous media. In this work, for the first time, direct qualitative and quantitative comparisons of mixed-dimensional models are drawn against laboratory experiments. Dedicated displacement experiments of steady-state laminar flow in fractured media are investigated using both high-resolution PET images as well as state-of-the-art numerical simulations.

Enhancing the heat transfer in CuO-MWCNT oil hybrid nanofluid flow in a pipe

Enhancing the heat transfer in CuO-MWCNT oil hybrid nanofluid flow in a pipe

Computational investigation on the energy efficiency of heat exchangers using Al2O3 nanofluids

In this research, we perform a numerical investigation to examine the dynamic and thermal properties of a rectangular counterflow heat exchanger under forced convection. Our specific focus is on a novel category of heat transfer fluids referred to as nanofluids, and we investigate their performance in conditions of steady-state laminar flow. The analysis is conducted through the application of the finite volume method within the Ansys-Fluent software. The findings obtained reveal that the heat exchanger attains its peak efficiency of 35% when operated with reduced flow rates ( m ̇ c = 0.08 kg s and m ̇ h = 0.03 kg / s ) and a significant nanoparticle volume fraction of 3%. Furthermore, it has been detected that the use of steel as a material enhances the overall efficiency of the thermal transfer device. These results highlight the enhanced efficiency of nanoparticle-infused fluids in improving the heat exchanger’s performance.

A comparative numerical study of three similar passive solar stills: Single slope, V-type, and greenhouse

In this paper, three solar stills with similar geometries are numerically investigated for analysis and comparison. The solar stills include single slope, V-type, and greenhouse stills. Steady-state laminar flow numerical simulations with different water surface temperatures and cover glass temperatures are performed. Simulation results were confirmed with data from analytical and experimental models to ensure reliability. The results showed that the V-type still has a higher number of recirculation zones than that of single slope and greenhouse stills. These vortex regions are small, but the velocity magnitude is no less than the other two stills. This difference makes the freshwater yield and convection heat transfer coefficient of V-type still the largest. Daily freshwater productions of single slope, V-type, and greenhouse stills are 0.592, 0.673, and 0.623 kg/m2, respectively. Productivity at 15 PM is 2.5 times higher than the hours from noon to 14 PM. The natural convection heat transfer coefficient seemed to be unvaried with the temperature difference but changed strongly with the still geometry.

Numerical and regression analysis of horizontal magnetic field in slippery nanofluid flow with Arrhenius activation energy

Numerical and regression analysis of horizontal magnetic field in slippery nanofluid flow with Arrhenius activation energy

Diffusion analysis of three kinds of species with two salts in two working fluids using Darcy's law using solar radiations

Diffusion analysis of three kinds of species with two salts in two working fluids using Darcy's law using solar radiations

Double-diffusive mixed convection with four heated square blocks for different working fluids in a square cavity

This paper investigates the flow behavior of a 2D, steady-state, and double-diffusive mixed convection laminar flow inside a square cavity with heated square blocks. The set of computational equations is discretized using the finite volume method (FVM). The effect of various operating parameters, such as Richardson Number (0.01 ≤ Ri ≤ 10), Grashoff number (102 ≤ Gr ≤ 105), Prandtl number (0.054 ≤ Pr ≤ 7.0.), the size of the heated blocks (BR = 1/4, 1/6, 1/8) are analyzed. Results show that the Nuavg and Shavg on the block surfaces are increased with Ri and decrease with Pr at any block ratio. Denser crowding for contour lines of temperature and concentration along the block was observed for Pr = 7.0 compared to Pr = 0.054. The heat and species transfer rates enhance with increased Ri and BR. Further, an empirical correlation is developed for Nuavg and Shavg.

Error estimates and physics informed augmentation of neural networks for thermally coupled incompressible Navier Stokes equations.

Physics Informed Neural Networks (PINNs) are shown to be a promising method for the approximation of partial differential equations (PDEs). PINNs approximate the PDE solution by minimizing physics-based loss functions over a given domain. Despite substantial progress in the application of PINNs to a range of problem classes, investigation of error estimation and convergence properties of PINNs, which is important for establishing the rationale behind their good empirical performance, has been lacking. This paper presents convergence analysis and error estimates of PINNs for a multi-physics problem of thermally coupled incompressible Navier-Stokes equations. Through a model problem of Beltrami flow it is shown that a small training error implies a small generalization error. Posteriori convergence rates of total error with respect to the training residual and collocation points are presented. This is of practical significance in determining appropriate number of training parameters and training residual thresholds to get good PINNs prediction of thermally coupled steady state laminar flows. These convergence rates are then generalized to different spatial geometries as well as to different flow parameters that lie in the laminar regime. A pressure stabilization term in the form of pressure Poisson equation is added to the PDE residuals for PINNs. This physics informed augmentation is shown to improve accuracy of the pressure field by an order of magnitude as compared to the case without augmentation. Results from PINNs are compared to the ones obtained from stabilized finite element method and good properties of PINNs are highlighted.

Investigation on the Effect of Length and Amplitude of Sinusoidal Wavy Vortex Generators on the Heat Transfer Rate, Pressure Drop, and London Factor in Compact Heat Exchangers

Compact heat exchangers (CHE) improve the heat transfer rate with lighter weight and lower volume than other counterparts. An important point in CHEs is their higher pressure drop relative to conventional heat exchangers. This study aims to investigate the heat transfer rate and pressure drop in some proposed models of these heat exchangers with/without vortex generators (VGs) in different cases. A hot fluid of temperature 350°C flowing through tubes and a cold fluid of temperature 300°C circulating inside the shell are assumed. To this end, several VGs with sinusoidal wavy shapes are designed and examined with different amplitudes of the sine wave and different lengths to determine the effects of these parameters on the heat transfer rate of tubes and pressure drop along the heat exchanger length. In the 2D steady-state laminar fluid flow, governing equations are discretized using the finite element method and analyzed for Reynolds numbers 400 to 1000 in the ANSYS software. Finally, with a 5.06% increase in the Nusselt number, the sinusoidal VGs of amplitude 1 and length 6 mm quantitatively indicated the best performance in terms of the heat transfer rate and pressure drop (London factor) among the studied cases.

Numerical studies of the simultaneous development of forced convective laminar flow with heat transfer inside a microtube at a uniform temperature

Abstract Conjugate heat transfer is a complex problem because heat is transferred from a solid medium to a liquid medium through their interfaces. The steady-state laminar flow formed inside the microtubules is subjected to a constant temperature at the outer sidewall surface. These images cover a wide range of wall-to-fluid thermal conductivity ratios (ksf = 1, 2, 3, 4, and 5) and wall thickness-to-inner diameter ratios (δ/Ri = 0.25, 0.5, 0.75, 1, 1.25, and 1.5) and Reynolds numbers (Re = 200, 400, 600, 800, and 1,000). The results are processed by a Fluent program based on the finite volume method to numerically integrate the driver’s differential equations. The results show that increasing the wall-to-fluid thermal conductivity ratio ksf increases the inner wall dimensionless temperature and decreases the average Nusselt number. Conversely, an increase in the ratio of wall thickness to inner diameter results in a decrease in the dimensionless temperature of the inner wall and an increase in the average Nusselt number.

Compensated Feed water Pump Control Analysis of Effect of Base-Load Electricity Demand Reduction on Nuclear Steam Supply System

The effect of compensated feedwater (FW) pump control on a nuclear steam supply system with a significant reduction of baseload electricity demand as a common-cause failure could result in temperature elevation of the reactor coolant system and corresponding pressure increases in the pressurizer and steam generators above the set points. The shutting and opening of the pressure relief valve causes the fluid flow rate to transition from laminar to turbulence flow, where a sudden burst, chaotic movement, and inertial forces and weight of the fluid have the potential to cause a break in pipelines leading to a loss-of-coolant accident. This study employs the Fourier transform to simulate the impact of force as the power spectral density (in dBm/Hz) measured in 1 to 99 label harmonics over a specified time window using MATLAB/Simulink library tools. The experimental results show that compensated FW pump control could significantly reduce the effect of turbulence and reveal a perturbation settlement state prior to steady-state laminar flow.

Modelling steady-state convective heat transfer in different periodic open cellular structures (POCS) – A superposition approach

• The convective heat transfer during laminar, steady-state flow in POCS with four different unit cell types is investigated. • Fluid deflection is a key factor to understand the convective heat transfer. • The heat transfer capability of POCS is relatable to the strut arrangements of which they are composed. • A physically founded model for the calculation of the convective heat transfer in POCS with arbitrary unit cell geometries is established, which is valid for porosities above 79.1%. Additively manufactured periodic open cellular structures (POCS) offer promising attributes for the intensification of heat transfer processes. Their geometry and consequently thermal transport properties are highly customizable resulting in a vast design freedom. To fully exploit their potential, a detailed understanding of the relationship between their geometric and thermal transport properties is crucial. Therefore, in this contribution the convective heat transfer in four different unit cell geometries and varying cell dimensions during fully developed laminar steady-state flow is investigated. Numerical simulations are used to get a detailed insight of the local flow structures and heat flux density distributions. A correlation between the heat transfer coefficient of each unit cell and the heat transfer capability of unconnected strut arrangements with similar flow paths is introduced. On this basis, a new modelling approach is established in combination with the concept of superposition. It takes into account the detailed geometry of the porous medium and shows good agreement with the simulation data of all unit cell geometries studied in this work with porosities above 79.1%. Thus, it is the first model applicable to different types of unit cells.

Enhanced Conjugate Gradient Method for Heat Flux Estimation in Laminar and T-Junction Turbulent Mixing Flow

In this paper, the Jaya algorithm is coupled with the traditional conjugate gradient method (CGM) for solving the inverse heat transfer problem. The coupling of two algorithms is termed as enhanced conjugate gradient method (ECGM). Two different applications have been considered to determine the accuracy and stability of ECGM. First, the algorithm is applied in a steady-state two-dimensional laminar flow through a duct for the boundary heat flux estimation. The accuracy of estimation has been compared with traditional CGM by calculating the root mean square (RMS) error. The ECGM algorithm (RMS =0.142 kW/m2) is found to be more accurate than conventional CGM (RMS = 0.198 kW/m2). ECGM is then applied to determine the peripheral variation of heat flux at the fluid-solid interface of a tube at a section downstream to the T-junction. The experimental temperature readings at the outer periphery of the tube required in the inverse algorithm are simulated by solving the direct heat conduction problem. Here, the heat flux at the fluid-solid interface is obtained by solving the governing equations of the turbulent flow by using commercial computational fluid dynamics software. ECGM is found to be a stable and accurate inverse heat transfer algorithm.

Numerical analysis of thermo-fluid problems in 3D domains by means of the RBF-FD meshless method

The use of CAE (Computer Aided Engineering) software, commonly applied to the design and verification of a great variety of manufactured products, is totally reliant on accurate numerical simulations. Classic mesh-based methods, e.g., Finite Element (FEM) and Finite Volume (FVM), are usually employed for such simulations, where the role of the mesh is crucial for both accuracy and time consumption issues. This is especially true for complex 3D domains which are typically encountered in most practical problems. Meshless, or meshfree, methods have been recently introduced in order to replace the usual mesh with much simpler node distributions, thus purifying the data structures of any additional geometric information. Radial Basis Function-Finite Difference (RBF-FD) meshless methods have been shown to be able to easily solve problems of engineering relevance over complex-shaped domains with great accuracy, with particular reference to fluid flow and heat transfer problems. In this paper the RBF-FD method is employed to solve heat transfer problems with incompressible, steady-state laminar flow over 3D complex-shaped domains. The required node distributions are automatically generated by using a meshless node generation algorithm, which has been specifically developed to produce high quality node arrangements over arbitrary 3D geometries. The presented strategy represents therefore a fully-meshless approach for the accurate and automatic simulation of thermo-fluid problems over 3D domains of practical interest.

Hydrothermal performance of twisted elliptical tube equipped with twisted tape insert

Twisted elliptical tube heat exchangers are promising in terms of improving the heat transfer efficiency on the tube side, decreasing the pressure drop on the shell side, and reducing the size of the equipment. Although offering immense potential, the examination of heat transfer enhancement techniques inside a heat exchanging twisted elliptical tube is less understood in the literature. In this study, the thermo-hydraulic performance of a twisted elliptical tube equipped with twisted tape insert is investigated. A three-dimensional steady-state laminar flow of the above-mentioned computational domain is developed in ANSYS Fluent. The effect of key design parameters including geometrical configurations, Reynolds number, and different pitches of twisted elliptical tube and twisted tape insert is analysed over the Nusselt number, the friction factor, and the PEC (performance evaluation criterion) number. The simultaneous implementation of twisted elliptical tube and twisted tape inserts at the pitch number equivalent to one-third of the tube length ( L /3) and Reynolds number of 1000 increases the Nusselt number and friction factor by 123.9% and 131.9% compared to the smooth elliptical tube case. The PEC number is above unity in most of the considered cases, verifying the effectiveness of the proposed technique. The highest PEC of 1.6 is achieved at the optimum P = L /3 for both twisted elliptical tube and twisted tape insert and Reynolds number of 1000.

Flow-assisted self-healing of the helical structure in a cholesteric liquid crystal.

We employ nonequilibrium molecular dynamics simulations to investigate the structure and dynamics of a cholesteric liquid crystal confined between atomically corrugated solid walls. By choosing walls normal to the helical axis, we can study systems with an arbitrary cholesteric pitch without exposing the cholesteric helix to a spurious stress. We investigate the effects of local heating and flow and their joint effects. A steady-state laminar Poiseuille flow is initiated by means of an external body force. Flow alone (i.e., without local heating) in a direction normal to the helical axis does not affect the cholesteric pitch. If the liquid crystal is heated in a small region, the cholesteric helix becomes unstable and melts locally. However, if local heating and flow are combined, a nontrivial synergistic effect is observed in that the helical structure recuperates the better, the higher the speed of the flow is.

Combined effect of roughness and suction on heat transfer in a laminar channel flow

A two-dimensional numerical simulation is carried with the aim to investigate the combined effects of roughness and wall suction on heat transfer performance of a steady-state laminar channel flow. The roughness considered as a square element mounted on the bottom wall of the channel and suction is applied on its walls. Different Reynolds numbers, different suction rates, and various locations of the suction area on the roughness elements are considered. The governing Navier-Stokes equations are solved using open source OpenFOAM software. The results are tested against theoretical results. It is shown that the simple addition of roughness element increases the local Nusselt number in comparison to that without roughness. That increase is further enhanced when localised suction is applied. In addition, it is observed that by applying suction strategically on the roughness, one can reduce the thickness of thermal boundary layer, and remove or at least weaken the vortical motion behind the back-face of element, which in turn leads to an increase in local Nusselt number, demonstrating that suction is an effective means for improving the heat transfer rate in a laminar channel flow. As continuation of study, the effect of space between two elements was investigated and the best space was obtained. It is found that this method is useful to enhance heat transfer performance, especially at high Reynolds numbers.

On the Control of the 2D Navier–Stokes Equations with Kolmogorov Forcing

This paper is devoted to the control problem of a nonlinear dynamical system obtained by a truncation of the two-dimensional (2D) Navier–Stokes (N-S) equations with periodic boundary conditions and with a sinusoidal external force along the x-direction. This special case of the 2D N-S equations is known as the 2D Kolmogorov flow. Firstly, the dynamics of the 2D Kolmogorov flow which is represented by a nonlinear dynamical system of seven ordinary differential equations (ODEs) of a laminar steady state flow regime and a periodic flow regime are analyzed; numerical simulations are given to illustrate the analysis. Secondly, an adaptive controller is designed for the system of seven ODEs representing the approximation of the dynamics of the 2D Kolmogorov flow to control its dynamics either to a steady-state regime or to a periodic regime; the value of the Reynolds number is determined using an update law. Then, a static sliding mode controller and a dynamic sliding mode controller are designed for the system of seven ODEs representing the approximation of the dynamics of the 2D Kolmogorov flow to control its dynamics either to a steady-state regime or to a periodic regime. Numerical simulations are presented to show the effectiveness of the proposed three control schemes. The simulation results clearly show that the proposed controllers work well.

Heat Transfer Performance of Uni-Directional and Bi-Directional Lid-Driven Cavities Using Nanoparticle Enhanced Ionic Liquids (NEILS)

Two-dimensional numerical investigation has been carried out using an in-house CFD code to obtain the heat transfer performance of normal, uni-directional and bi-directional lid-driven cavity. The 2D in-house code is based on single phase approach for studying steady state laminar flows. Pure water (PW), ionic liquid (IL): 1-ethyl-3-methylimidazolium methanesulfonate; [C2mim][CH3SO3], ionic liquid mixtures (PW + IL) and alumina (Al2O3) nanoparticle enhanced ionic liquids (NEILS) are used in the present investigation. The thermophysical properties of all the heat transfer fluids used in the present numerical investigation were obtained from the experimentally measured data available in the literature. The obtained results showed that uni-directional lid-driven cavity exhibits 68.78 % higher Nuavg value at Re = 1900 in comparison with normal lid-driven cavity for pure water. The use of [C2mim][CH3SO3] ionic liquid also enhances the heat transfer performance by exhibiting 115.48 % higher Nuavg value in comparison with pure water at Re = 1900. Moreover, 15 % wt Al2O3 nanoparticles in 0.25PW + 0.75IL gives 21.2 % and 161.16 % higher heat transfer performance in comparison with ionic liquid and pure water respectively at Re = 1900. Furthermore, it is also observed that 10 % wt Al2O3 nanoparticles in 0.25PW + 0.75IL shows similar heat transfer performance like ionic liquid at all Re.

Application of a MEMS heat flux sensor to heat transfer research on an impinging diesel jet

To clarify the mechanisms of heat transfer on an engine wall is an important challenge because the heat loss on the wall is one of the dominant factors that limit the thermal efficiency. A thin-film resistance type heat flux sensor fabricated with Micro-Electro-Mechanical Systems (MEMS) technologies was applied to research on the heat transfer of an impinging diesel jet. The MEMS sensor had a high sensitivity and multiple measurement points with a scale comparable to the turbulence of in-cylinder flow for the investigation of local instantaneous heat transfer characteristics in engines. Measurements of wall temperature and heat flux were conducted in a constant volume chamber under the reference conditions of Engine Combustion Network (ENC) Spray A with variations in injection pressure. As a result, the maximum heat flux and heat transfer coefficient reached about 5 MW/m2 and 3 MW/(m2 K), respectively. The results were compared to those obtained with a commercially available thermocouple, and both sensors produced similar trends. In addition, fluid motion near the wall was estimated from the heat flux fluctuations using a cross-correlation analysis. The relationship between heat transfer and flow was investigated in a dimensionless number fashion, and it was compared to a semi-theoretical prediction that was based on a steady state laminar flow heat transfer model.