Flow In Parallel-plate Channel Research Articles

Combined Radiation and Convection in Developing Flow in a Parallel Plate Channel With Real Gas Behavior: The Case of Gas Cooling

Abstract The effect of real gas volumetric radiation on the thermal development in laminar parallel plate channel flow of H2O and/or CO2 in the case of gas cooling has been investigated numerically. The nongray radiation effects of the gas have been treated using a global spectral approach, the Spectral Line Weighted-sum-of-gray-gases model. The results reveal that gas radiation results in significantly higher total heat transfer to the cooled channel wall, with an attendant more rapid drop in gas mean temperature. Gas radiation is seen to increase the local convective and total (radiative plus convective) Nusselt number for increasing radiating species mole fraction for both H2O and CO2 and for increasing gas inlet temperature. The influence of gas radiation on the thermal development is less pronounced for CO2 than for H2O. An apparent thermally fully developed condition may exist for this combined convection-radiation problem with real gases in the gas cooling scenario, and radiation has the effect of significantly extending the thermally developing region. Combined hydrodynamic and thermal development yields higher heat transfer than the thermally developing condition. Smaller channel wall spacing results in lower radiative heat transfer and the aforementioned radiation effects are diminished. Local convective and radiative flux and thermal entry length also increase with elevated gas total pressure.

Parallel performance analysis of coupled heat and fluid flow in parallel plate channel using CUDA

The heat transfer analysis coupled with fluid flow is important in many real-world application areas varying from micro-channels to spacecraft’s. Numerical prediction of thermal and fluid flow situation has become very common method using any computational fluid dynamics software or by developing in-house codes. One of the major issues pertinent to numerical analysis lies with immense computational time required for repeated analysis. In this article, technique applied for parallelization of in-house developed generic code using CUDA and OpenMP paradigm is discussed. The parallelized finite-volume method (FVM)-based code for analysis of various problems is analyzed for different boundary conditions. Two GPUs (graphical processing units) are used for parallel execution. Out of four functions in the code (U, V, P, and T), only P function is parallelized using CUDA as it consumes 91% of computational time and the rest functions are parallelized using OpenMP. Parallel performance analysis is carried out for 400, 625, and 900 threads launched from host for parallel execution. Improvement in speedup using CUDA compared with speedup using complete OpenMP parallelization on different computing machines is also provided. Parallel efficiency of the FVM code for different grid size, Reynolds number, internal flow, and external flow is also carried out. It is found that the GPU provides immense speedup and outperforms OpenMP largely. Parallel execution on GPU gives results in a quite acceptable amount of time. The parallel efficiency is found to be close to 90% in internal flow and 10% for external flow.

Semi-analytical models of mineral dissolution in rough fractures with permeable walls

Mineral dissolution in fractures is largely affected by the flow field within the fracture opening. The flow field maintains transport of the dissolved solutes and influences the concentration gradient and thermodynamic driving force for the mineral dissolution. In this study, we focus on investigating two factors that influence mineral dissolution in fractures: fracture wall roughness and interporosity fluid exchange or the flux through the fracture walls. The classical cubic law for the flow in parallel-plate channels cannot describe the flow in a fracture with rough permeable walls. The wavy, irregular shape of the rough boundaries can result in local flow features and might cause a shift of the overall flow and dissolution regime. At low Reynolds numbers, roughness simply increases the surface area available for mineral dissolution. Moreover, at higher Reynolds numbers, the inertial effects become important and the non-linear flow, flow instabilities, and reverse flow will form. With the creation of eddies and vorticities in the area adjacent to the walls, a flow dead zone forms that reduces the reactive surface area. In the presence of interporosity fluid exchange between the fracture and its surrounding rock, the non-zero fluid velocity on the fracture walls influences the local concentration gradient. In addition, the newly introduced fluid may facilitate or suppress the fracture wall mineral dissolution depending on its composition. This work highlights the compound effect of roughness and fluid flux through the walls on fracture mineral dissolution. For this purpose, the asymptotic solutions of the steady-state Navier–Stokes equations with non-zero velocity on the borders are used to determine the velocity field within the fracture opening. The quadratic and cubic corrections to Darcy’s law are expected as a result of the wall roughness and the flow through the walls. The flow field is coupled with a transport module and a geochemical model (PHREEQC). As a test case, we investigate calcite dissolution in a single fracture at a different influx rate. For each flow rate, a flat fracture and two sets of rough profiles with and without the permeable walls were compared. The simulation results showed that compared to impermeable walls, the pervious walls result in a non-uniform non-periodic mineral dissolution along the fracture, which is more focused at the inlet. At low Reynolds numbers, the hotspots of dissolution are slightly shifted from the smaller cross sectional area to the larger cross sectional area. The effective reaction rate for mineral dissolution of fracture walls increases with an increase in fracture surface roughness. It is shown that at low Reynolds numbers, the permeable fracture walls can improve the effective reaction rate significantly. At relatively larger Reynolds numbers, the impact of flux through the walls on the effective reaction rate is less important, but for some roughness profiles, still not negligible.

Heat transfer regimes in fully developed circular tube flows, a map of flow regimes

Heat transfer in fully developed pipe flows is investigated and combinations of laminar, turbulent, and transitional flow and heat transfer are identified. The analysis is based on governing equations conserving mass, momentum and energy and are also informed by Direct Numerical Simulation (DNS). Six regimes are identified: 1. Laminar flow and laminar heat transfer (LamF-LamH); 2. Transitional flow and laminar heat transfer (TraF-LamH); 3. Transitional flow and transitional heat transfer (TraF-TraH); 4. Turbulent flow with laminar heat transfer (TurF-LamH); 5. Turbulent flow with transitional heat transfer (TurF-TraH); and 6. Turbulent flow with turbulent heat transfer (TurF-TurH). The subdivisions of flow is based on the Reynolds number and the fluid Prandtl number. One finding is that the TurF-LamH regime only exists for very low Prandtl number flows (Pr ≪ 1). Another critical demarcation for this type of flow exists for ReτPr1/2 ≲ 50. The friction-Reynolds number Reτ is based on the pipe radius and the friction velocity. The model used here was based on the approach, already used with success, for flow in parallel-plate channels. The simplified model predicts a Nusselt number of 8 in the TurF-LamH regime; recommended Nusselt correlations are provided for other regimes. A discussion of the demarcation for the transitional regimes is also included along with guidance for Nusselt numbers within those ranges.

Modified algebraic model of laminar-turbulent transition for internal flows

PurposeFor internal flows with small values of the Reynolds number, there is often at a considerable distance from the pipe inlet cross-section a change of the flow form from laminar to turbulent. To describe this phenomenon of laminar-turbulent transition in the pipe, also parallel-plate channel flow, a modified algebraic intermittency model was used. The original model for bypass transition developed by S. Kubacki and E. Dick was designed for simulating bypass transition in turbomachinery.Design/methodology/approachA modification of mentioned model was proposed. Modified model is suitable for simulating internal flows in pipes and parallel-plate channels. Implementation of the modified model was made using the OpenFOAM framework. Values of several constants of the original model were modified.FindingsFor selected Reynolds numbers and turbulence intensities (Tu), localization of laminar breakdown and fully turbulent flow was presented. Results obtained in this work were compared with corresponding experimental results available in the literature. It is particularly worth noting that asymptotic values of wall shear stress in flow channels and asymptotic values of axis velocity obtained during simulations are similar to related experimental and theoretical results.Originality/valueThe modified model allows precision numerical simulation in the area of transitional flow between laminar, intermittent and turbulent flows in pipes and parallel-plate channels. Proposed modified algebraic intermittency model presented in this work is described by a set of two additional partial differential equations corresponding with k-omega turbulence model presented by Wilcox (Wilcox, 2006).

The Impact of the Thickness of the Porous Material on the Parallel Plate Channel Flow of Ree-Eyring Fluid when the Walls are Provided with non-Erodible Porous Lining

The Impact of the Thickness of the Porous Material on the Parallel Plate Channel Flow of Ree-Eyring Fluid when the Walls are Provided with non-Erodible Porous Lining

An improved algebraic model for bypass transition for calculation of transitional flow in parallel-plate channel

This paper presents the phenomenon of laminar turbulent transition simulated by modified algebraic intermittency model based on well known k-ω turbulence model by Wilcox for flows in parallel-plate channels. Results of simulations using described model were obtained for low Reynolds numbers 1000≤Re≤75000 with different turbulence intensity in inlet cross-section of the parallel-plate channel. Results were compared to and validated with existing data available in literature both experimental and theoretical. Implementation of described model with pre-processing and post-processing was made using open source software OpenFOAM.

DNS of Turbulent Heat Transfer of Pulsating Flow in Parallel Plate Channel

DNS of Turbulent Heat Transfer of Pulsating Flow in Parallel Plate Channel

Inertial effects on thermal transport in superhydrophobic microchannels

This paper presents a numerical investigation on the effects of inertia for laminar fully developed flow in superhydrophobic microchannels where the surface structure consists of a square array of square pillars aligned with the flow direction. Infinite parallel plate channel flow is considered where the flow is assumed to be non-wetting and the meniscus is idealized as flat. A constant heat flux condition is imposed at the tops of the posts whereas the gas/liquid interface is assumed to be adiabatic. A wide range of Peclet numbers (1–10,000), relative channel spacing sizes (3 orders of magnitude), and solid fractions (0.02–0.9) are considered. The effect of these on friction factor-Reynolds number product, Nusselt number, hydrodynamic slip length and temperature jump length is explored. Frictional drag and convective heat transfer are reduced for all cases explored. These reductions are greater for small solid fractions, small relative channel sizes, and low Peclet numbers. Interestingly, over a wide range of explored parameters the results correspond well with the analytical diffusion dominated results present in the literature. It is only at the highest Peclet numbers and smallest relative channel sizes that the results deviate significantly from the diffusion dominated Stokes flow scenario. A mapping is presented that illustrates for which parameter ranges the influence of inertia and relative channel size become significant.

Simulation of heat transfer enhancement by longitudinal vortex generators in dimple heat exchangers

A three-dimensional DDF-MRT-LBE (double distribution function multi-relaxation-time lattice Boltzmann equation) is presented to study the flow and heat transfer in dimple heat exchangers. Results are obtained for periodically fully-developed laminar flow in parallel-plate channels with spherical dimples symmetrically opposing onto both walls. Both the heat transfer and flow resistance are discussed. Furthermore, to enhance the heat transfer with low pressure penalty, a small crescent-shape protrusion was added as a LVG (longitudinal vortex generator). And a grooved LVG was developed to reduce the drop loss caused by the crescent-shape protrusion. The streamline contours, isotherms, Nusselt numbers and friction coefficients at various Reynolds numbers are presented. The results show that the thermal performance of the LVG cases is higher than that of the dimple cases with similar flow characteristics. Moreover, from the viewpoint of energy saving, LVG cases perform better than the dimple cases.

Numerical simulation of laminar breakdown and subsequent intermittent and turbulent flow in parallel-plate channels: Effects of inlet velocity profile and turbulence intensity

The nature of flow development in a parallel plate channel has been investigated by making use of a newly developed model of intermittency. That model, taken together with the RANS equations of momentum conservation, the continuity equation, and the SST turbulence model, was employed to provide a complete chronology of the development processes and the derived practical results. A major focus of the work is the effect of inlet conditions on the downstream behavior of the developing flow. It was observed that the flow development process depends critically on the specifics of the inlet conditions characterized here by the shape of the velocity profile and the magnitude of the turbulence intensity. Two velocity profile shapes (flat and parabolic), are regarded as limiting cases. Similarly, two turbulence intensities, Tu = 1% and 5%, are employed. From the standpoint of practice, the relationship between the friction factor and the Reynolds number is most significant. It was found that this relationship reflects that of standard practice for only one of the investigated cases (flat velocity profile, Tu = 5%). For the other cases (flat profile, Tu = 1% and parabolic profile, Tu = 1% and 5%), the breakdown of laminar flow is delayed and the onset of full turbulence occurs rather abruptly at Re ∼10,000. Three unique fully developed flow regimes are existent, depending on the inlet conditions and on the value of the Reynolds number. In addition to the standard laminar and fully turbulent regimes, another regime, fully developed intermittent, can occur. Specifically, in the latter regime, laminar and turbulent flows occur intermittently.

Entrance and Exit Losses for Developing Flow in Parallel Plate Channels

An analysis is presented to calculate the entrance and exit losses for developing flow in parallel plate channels. Such an analysis is of value for air-cooled heat sinks with short flow length, such as electronic heat sinks. These predictions are typically done using inlet (K c ) and exit (K e ) loss coefficients for parallel plate channels from the Kays and London book, Compact Heat Exchangers. However, the information presented in Compact Heat Exchangers assumes fully developed flow at the exit. Electronic heat sinks operate in the developing flow region. Thus, the use of the published K c and K e from Compact Heat Exchangers will result in an overestimation of the actual K c and K e values. The present author has completed an analysis that allows the accurate calculation of K c and K e values with parallel plate channels in the developing flow region. The results are presented in graphical and equation form as a function of contraction ratio and 4x+ (= 4x/D h Re). Entrance and exit losses can account for as much as 30% of the total pressure drop in electronic heat sinks having short flow lengths. Fortunately, the error associated with evaluation of K c and K e based on fully developed flow for parallel plates is small and expected to be less than 2%.

Turbulent natural convection in vertical parallel-plate channels

The problem of buoyancy driven turbulent flow in parallel-plate channels is investigated. The investigation is limited to vertical channels of uniform cross-section with different modes of heating. The details of the flow and thermal fields are obtained from the solution of the conservation equations of mass, momentum, and energy in addition to equations of the low Reynolds number turbulence model. The study covers Rayleigh number ranging from 105 to 107 and focuses on the effect of channel geometry on the characteristic of the flow and thermal fields as well as the local and average Nusselt number variation. A Nusselt number correlation has been developed in terms of a modified Rayleigh number and channel aspect ratio for the cases of symmetrically heated isothermal and isoflux conditions.

Electroosmotic Flow in Nanoscale Parallel-plate Channels: Molecular Simulation Study and Comparison with Classical Poisson–Boltzmann Theory

Molecular dynamics simulations have been carried out for simple electrolyte systems to study the electrokinetically driven osmotic flow in parallel-plate channels of widths ∼10–120 nm. The results are compared with the classical theory predictions based on the solution to the Poisson–Boltzmann equation. We find that despite some of the limitations in the Poisson–Boltzmann equation, such as assumption of the Boltzmann distribution for the ions, the classical theory captures the general trend of the variations of the osmotic flow with channel width, as characterized by the mobility of the fluid in channels between ∼10 and 120 nm at moderate to low ion concentration. At moderate concentration (corresponding to relatively low surface potential), the classical theory is almost quantitative. The theory and simulation show more disagreement at low concentration, primarily caused by the high surface potential where the assumption of Boltzmann distribution becomes inaccurate. We discuss the limitations of the Poisson–Boltzmann equation as applied to the nanoscale channels.

Magnetic field effects on g-jitter induced flow and solute transport

Numerical modeling and analyses are presented of magnetic damping of g-jitter driven fluid flow and its effect on the solutal striation in a simplified Bridgman–Stockbarger crystal growth system under microgravity. The model development is based on the finite element solution of the momentum, energy and solute transport equations under g-jitter conditions in the presence of an external magnetic field. The numerical model is verified by comparison with analytical solutions obtained for a simple parallel plate channel flow driven by g-jitter in a transverse magnetic field. Simulations are carried out to study the behavior of convective flow and solutal transport induced by the combined g-jitter and magnetohydrodynamic forces. Both the idealized single frequency g-jitter force and the real g-jitter perturbation taken during space flight are considered. Results indicate that an applied magnetic field can effectively damp the velocity caused by g-jitter and help to reduce the time variation of solute redistribution. A stronger applied field is more effective in suppressing the convective flows and hence reducing concentration variation. It is found that g-jitter driven flows have the same oscillation period as the driving force with or without the applied field. However, an applied magnetic field shortens the transient period over which the flow field evolves into a quasi-steady state time harmonic oscillation after g-jitter sets in. The flow intensity increases with an increase in g-jitter magnitude but decreases with an increase in the applied field strength. The reduced convection in the liquid pool by the applied magnetic field results in a reduction of the concentration oscillation. The magnetic field is very useful in suppressing the spiking velocities that are induced by the spikes in the real g-jitter data. The damping effect is more pronounced if the magnetic field is switched on before the onset of g-jitter disturbances.

The effect of the local inertial term on the fluid flow in channels partially filled with porous material

The transient hydrodynamics behavior of the fluid flow in parallel-plate channels partially filled with porous material is investigated numerically. The role of the local macroscopic inertial term in the porous domain momentum equation is studied. It is found that the effect of the local inertial term on the channel hydrodynamics behavior is insignificant when Da<1×10 −6, over the entire range of 0.1< μ R <10, 0< A<10 4, and for all porous substrate thicknesses. Also, it is found that the deviation between the predictions of the transient and the quasi-steady models is more significant in the porous domain and the deviation decreases as the time proceeds.

Unsteady non-darcian fluid flow in parallel-plates channels partially filled with porous materials

Using Green's function method, analytical solutions are obtained for the problem of transient fluid flow in parallel-plate channels partially filled with porous materials. The unsteadiness in the fluid flow is caused either by a sudden change in the imposed pressure gradient or (and) by a sudden change in the velocity of the channel boundaries. The Brinkman-extended Darcy model is used to model the flow inside the porous domain.

Forced convection in a parallel plate channel partially filled with a high porosity medium

This paper presents a numerical study of non-Darcy effects on the fully developed forced convection parallel plate channel flow partially filled with a porous medium. The Navier-Stokes equations govern the fluid motion in the fluid region, while Darcy-Brinkman-Forchheimer model is assumed to hold within the porous media. The effect of thermal dispersion in the porous matrix is also considered. Inclusion of these effects significantly alters the velocity and temperature profile for those predicted by Darcy and Darcy-Brinkman models. It is shown that the Nusselt number strongly depends on the open space thickness ratio S, and a critical value of the porous layer thickness exists at which the Nusselt number reaches a minimum. The critical value of the porous layer thickness shifts to lower S as the Darcy number decreases. In addition, it is found that thermal dispersion effect is only significant for small values of open space thickness ratio S.

The effect of diffusion on the settling of aerosol particles in flow in a parallel plate channel

Aerosol particle deposition due to simultaneous settling and diffusion from slug or Poiseuille flow in a horizontal parallel plate channel is studied. Solutions are presented for the deposition flux and bulk mean concentration variations along the channel for the case when the settling is large compared to the diffusion.

Analysis of counterflow heat exchanger for non-newtonian fluids

ANALYSIS of convective heat transfer in channel flow involves the solution of the appropriate energy equation with specified conditions at the channel wall. The conditions normally used are those of uniform wall temperature, uniform wall heat flux or the boundary condition of the third kind. Considerable work has appeared in the literature on these problems. In the last decade, attention was directed towards problems associated with countercurrent heat exchange with assigned temperatures of each stream at the inlet and coupling conditions in the form of temperature and flux continuity at the boundary of the two streams. Nunge and Gill [ 1 ] analysed the convective heat transfer during laminar Newtonian flow in parallel plate channels for counter flow of the two streams assuming the same physical properties in both the streams. This analysis was extended to laminar flows in double pipe heat exchangers by Nunge and Gill [2], Blanco et al. [3] and Stein [4], and for turbulent flow by Blanco and Gill [5]. For a class of countercurrent systems characterized by the feature that the resistance to transfer in one of the phases is negligibly small, Safonov and Potapov [6, 7~ developed a method for obtaining the local and asymptotic Nusselt numbers and applied it to countercurrent heat or mass transfer during laminar flow in parallel plate channels and in circular tubes. This analysis is particularly suitable for systems in which the two streams differ sharply in their physical properties. Hitherto all the studies have considered that both the fluid streams are Newtonian. In practice, counter flow heat exchangers where one of the stream fluids is non-Newtonian find wide applicability in polymer processing operations. It is the objective of the present work to provide a simplified analysis of the counter flow heat exchanger problem with one non-Newtonian fluid stream in which lies the major resistance to the transfer and negligible resistance in the annular stream. The non-Newtonian fluid considered is of the power law type and it will be shown that the results of Safonov and Potapov [7] for Newtonian flow and the Graetz-Nusselt problem for power law flow [8] are par. ticular cases of the present work.