Fluid Stream Research Articles

Magnetohydrodynamic Stability of Self-gravitating Streaming Fluid Cylinder

Magnetohydrodynamic Stability of Self-gravitating Streaming Fluid Cylinder

Effect of Vortex Generators on Airfoil NACA 632-415 to Aerodynamic Characteristics Using CFD

To determine the aircraft’s flight performance, the airfoil type must be considered when designing the wing. A vortex can form when the airfoil travels through a fluid stream with a difference in velocity and pressure around it. Airfoil modification is carried out to delay the occurrence of flow separation by adding a vortex generator. This paper discusses how adding the vortex generator helps slow the stall’s onset and how the vortex generator affects the fluid flow and aerodynamic forces acting on the NACA 632-415. The vortex generator profile is positioned at an x/c = 20% of the chord line’s direction from the leading edge. The variation used is an airfoil’s angle of attack (α). Some parameters to be evaluated include the coefficient lift force (C­­L), the coefficient drag force (CD), and the gliding ratio (C­­L/CD). The research was conducted by the CFD method based on the angle of attack that produces the coefficient lift and drag forces. The addition of the vortex generator can delay the flow separation, increase the lift force coefficient by about 24.9%, the drag force coefficient by about 2.7%, and the gliding ratio by 9.1%.

Thermal and mass transfer aspects of MHD flow across an exponentially stretched sheet with chemical reaction

This investigation deals with the two-dimensional steady problem incorporating the magneto hydrodynamic effect with three distinct boundary layer streams of fluid across an exponentially stretched sheet under the influence of thermal radiation and chemical reactions. The concurrent flow model also accounts for the effect of Thermophoresis and Brownian movement, caused by temperature and concentration gradients between two boundaries, respectively. By using suitable similarity transformation variables, the nonlinear systems of governing PDEs are transformed into a system of nonlinear ODEs. The findings, obtained by using the Bvp4c strategy, are analysed and depicted graphically and through tables. Furthermore, the Nusselt number, Sherwood number and drag coefficient, which are crucial for industrial applications, are also shown in the table to demonstrate the impact of dimensionless physical parameters. In response to a steady rise in Lewis number and chemical reaction parameter, the heat transit rate tends to decline while the species transit rate increases.

Microfluidic Transport in Ternary Liquid Layers Due to Sinusoidal Thermocapillary Actuation

Abstract The large-scale applicability of the micro- and nanofluidic devices demands continuous technological advancements in the transport mechanisms, especially to promptly mix the analytes and reagents at such a small scale. To this end, thermocapillarity-induced Marangoni hydrodynamics of three-layered, immiscible fluid streams in a microchannel is analytically explored. The system is exposed to periodic and sinusoidal thermal stimuli, and a theoretical framework is presented. The diffusion of the periodic thermal stimuli across and along the fluidic interfaces creates axial surface tension gradients, which induce vortical motion of the participating fluids within the microconduit. We show that depending on the physical parameters of the three participating fluids, such vortex patterns may be fine-tuned and controlled to obtain desired transport behavior. An analytical solution for the thermal and the hydrodynamic transport phenomena is obtained by solving the momentum and energy conservation equations under the umbrella of creeping flow characteristics (very low Reynolds and thermal Marangoni numbers), and nearly undeformed fluid interfaces (negligibly small Capillary number). The approximate profiles of the deformed interfaces are also quantified theoretically to justify the assumption of flat and undeformed interfaces. The independent influence of crucial thermophysical properties, the microchannel system parameters, and features of the applied thermal stimuli are shown in detail for a fixed combination of other parameters.

Pre-arranged sequences of micropillars for passive mixing control of water and ethanol

Microfluidic reactors have enabled the continuous conduction of chemical reactions with exceptional control of fluids and operating conditions. To enhance reagent mixing in laminar flow conditions, the effective strategy of adding cylindrical obstacles (i.e., pillars) in the mixing channel is appealing. Indeed, they can passively extend the contact surface of the incoming fluid streams, where diffusion and reaction occur. From our previous work, optimized sequences of pillars in a T-microchannel – that differ in diameter and position – can significantly improve the mixing for single-phase flow (i.e., mixing of miscible fluids of similar density and viscosity). However, real-world mixing applications often require the merging of fluids with significantly different fluid properties before, during, and after mixing. Hence, further investigations are required to unveil efficiency and robustness in these more complex practical mixing conditions. We jointly carried out experiments and numerical simulations on miscible fluids in an optimized sequence of pillars called IAF. Our analysis shows how the fluid velocity (i.e., the Reynolds number, Re) and the pillar configuration affect the formation of horseshoe vortices, which we consider crucial for water mixing when 1<Re<100. Then, we analyzed water–water and water–ethanol mixtures at Re=40 to observe how fluid properties alter the flow passively controlled by the pillar sequence. Eventually, the analysis extends within Re=10–100, showing efficiency and pressure drops of optimized designs that depend on the evolution of physical properties. These findings provide insights into the predictions of confined fluid flow around obstacles and its optimization for engineering processes, e.g., nanoparticle precipitation.

Heat Transfer Analysis Using Thermofluid Network Models for Industrial Biomass and Utility Scale Coal-Fired Boilers

Integrated whole-boiler process models are useful in the design of biomass and coal-fired boilers, and they can also be used to analyse different scenarios such as low load operation and alternate fuel firing. Whereas CFD models are typically applied to analyse the detail heat transfer phenomena in furnaces, analysis of the integrated whole-boiler performance requires one-dimensional thermofluid network models. These incorporate zero-dimensional furnace models combined with the solution of the fundamental mass, energy, and momentum balance equations for the different heat exchangers and fluid streams. This approach is not new, and there is a large amount of information available in textbooks and technical papers. However, the information is fragmented and incomplete and therefore difficult to follow and apply. The aim of this review paper is therefore to: (i) provide a review of recent literature to show how the different approaches to boiler modelling have been applied; (ii) to provide a review and clear description of the thermofluid network modelling methodology, including the simplifying assumptions and its implications; and (iii) to demonstrate the methodology by applying it to two case study boilers with different geometries, firing systems and fuels at various loads, and comparing the results to site measurements, which highlight important aspects of the methodology. The model results compare well with values obtained from site measurements and detail CFD models for full load and part load operation. The results show the importance of utilising the high particle load model for the effective emissivity and absorptivity of the flue gas and particle suspension rather than the standard model, especially in the case of a high ash fuel. It also shows that the projected method provides better results than the direct method for the furnace water wall heat transfer.

Infrared thermography observations of crystallization fouling in a plate heat exchanger

Heat exchanger performance is significantly reduced in the presence of impurities in one or both fluid streams, frequently by deposits of inversely soluble salts. Accordingly, immense efforts were and still are spent to combat, predict, and investigate such fouling problems to mitigate the reduction of heat transfer performance. In this study, calcium carbonate crystallization fouling in a corrugated plate heat exchanger was investigated. Fouling was monitored using temperature and flow measurements, and, for the first time, coupled with infrared thermography observations. We show a clear and measurable local difference between clean and fouled conditions, regardless of operating conditions. Infrared measurements of temperature permit conclusions about flow distribution and the spatial location of areas with severe fouling. Compared to the clean state, completely skewed isotherms after fouling point out channel blockage and flow obstructions, resulting in large scale flow re-distribution within the channel. The presented results exhibit a clear benefit of this approach for heat exchanger fouling studies and serve as a foundation for future research of dynamic operation, transient response, and computational models.

Accurate Prediction of Transport Coefficients of an Evaporating Liquid Drop

Abstract Numerical simulations were carried out to study the evaporation of a drop that is released into a parallel stream of fluid at a higher temperature. A coupled level-set and volume-of-fluid (CLSVOF) interface capturing method was deployed to capture the dynamic interface between the drop liquid and the surrounding fluid. Modified forms of mass, momentum, and energy equations were solved together with the species concentration equation. The pressure jump at the interface was handled by accurate estimation of the continuum surface force. The jumps in mass and energy at the interface were carefully resolved by considering appropriate source terms in the continuity and energy equations. At the interface, the procedure of velocity computation was incorporated by extending the liquid-phase velocity onto the entire domain and by calculating the Stefan flow to predict the interface velocity accurately. The calculation of the velocity using this step leads to the exact estimation of mass transfer through the interface. The model was validated against both temperature gradient-based and vapor mass concentration gradient-based evaporation test cases. Temporal histories of the average Nusselt number and Sherwood number during the lifetime of an evaporating drop were predicted in terms of the pertinent input parameters, namely, Reynolds number, Prandtl number, and Schmidt number.

Recent Progress on High Temperature and High Pressure Heat Exchangers for Supercritical CO2 Power Generation and Conversion Systems

Heat exchangers for supercritical CO2 power generation and waste heat to power conversion systems have a significant impact on the overall cycle efficiency and system footprint. Key challenges for supercritical CO2 heat exchangers include ability to withstand high temperature and high pressure (typical temperature range of heat source 350 to 800 °C and typical required operating pressure range 150 to 300 bars), and large pressure differential between fluid streams. Other requirements are low pressure drop, high effectiveness and high reliability under thermal cycling. This paper presents recent developments in supercritical CO2 heat exchangers in terms of material selection, design, manufacture, and operation. Since heat exchangers represent a significant portion of the total system cost, another key challenge is to find a compromise between the heat exchanger type, cost, durability, and performance. This paper explores heat exchanger technologies, manufacturing techniques and materials for high temperature and high pressure heat exchangers for supercritical CO2 applications. It also identifies technology gaps and research needs to accelerate the development of effective designs to facilitate the commercialization of both supercritical CO2 heat exchanger technologies and power cycles.

Effect of single-phase flow maldistribution on the thermal performance of brazed plate heat exchangers

This paper presents an experimental and numerical investigation of the effect of single-phase flow maldistribution on the thermal performance of brazed plate heat exchangers (BPHEs). A thermal performance model of the BPHEs is developed with the consideration of flow maldistribution among the channels. The proposed model is validated against the experimental results. The model simulations reveal that the flow maldistribution has a trivial impact on the overall thermal capacity of the BPHEs if two fluid streams are supplied from the same side of the heat exchangers; if two fluid streams are supplied from the opposite side, the overall thermal performance is significantly deteriorated due to mismatched flow distributions of two fluid streams. Moreover, other factors are also proven to act in this issue, including the number of plates, plate length, header/port size, sudden expansion flow at the heat exchanger entrance, and heat capacity rate ratio of two streams. They either directly change the flow distribution or potentially affect the thermal effectiveness of the BPHEs. Based on the simulation results, correlations are generated, which can evaluate the thermal capacity degradation due to flow maldistribution without the necessity of knowing the detailed flow distribution and building heat exchanger models.

Learning to write with the fluid rope trick.

Direct ink writing, a versatile method of 3D and 4D printing, requires the precise placement of a nozzle just above the print surface to prevent fluid instabilities that cause deviations from the prescribed print path. But what if one could harness the instability associated with the spontaneously folding or coiling of a thin stream of viscous fluid, i.e. use the "fluid rope trick" to write specified patterns on a substrate? Here we use Deep Reinforcement Learning to derive control strategies for the motion of the extruding nozzle and thus the fluid patterns that are deposited on the surface. The method proceeds by having a learner (nozzle) repeatedly interact with the environment (a viscous filament simulator), and improves its strategy using the results of this experience. We demonstrate the outcome of the learned control instructions using experiments to manipulate a falling viscous jet and create cursive writing patterns and Pollockian paintings on substrates.

Numerical analysis of latent thermal energy storage system under double spirally coiled tube configuration with two separated paths

The current research attempts to illustrate results of a reliable 3-D numerical simulation to scrutinize the charging process of paraffin as the phase change material (PCM) in an innovative heat exchanger called double spirally coiled tube heat exchanger (DSCTHE) with two separated paths. The water as a heat-transfer fluid (HTF) streams through the double spiral tubes embedded throughout the latent thermal energy storage (LTES) system. The PCM melting characteristics under three different geometries are investigated. After validating the proposed numerical simulation model, the impacts of operational and geometrical factors including inlet temperature of HTF and radius of the inner spiral tube on the behavior of the LTES system in the course of the melting process are investigated in detail. In order to achieve better insight into practical aspects of the presented LTES system, the transient behavior of a PCM for all three considered cases under various working conditions is discussed. Moreover, the 3-D temperature and liquid fractions contours at various time frames are obtained. The findings reveal that a decrement in the radius of the inner spiral tube resulted in a lower capability to melt PCM at the commencement of the charging procedure but more efficiency at the final stages. Generally, the overall time essential for melting of 95 wt% PCM in the storage diminishes up to 126 % by reducing the radius of the inner spiral tube from 90 mm to 50 mm.

HOW THE ESTIMATION OF ENTROPY GENERATION AND EXERGY LOSS OF HYBRID NANOFLUIDS GOVERNS THE THERMAL PERFORMANCE OF HEAT EXCHANGER

The present study reports heat-transfer performance, exergy analysis, entropy generation, and pressure drop of shell and helically coiled heat exchanger (SHCHE) with Al&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;-CuO/water hybrid nanofluid (HYNF) as a working fluid. Helical coil is made of copper material with 54 turns and pitch ratio is 31.35 mm. Hot oil streams at the shell with 75&amp;deg; C, and the working fluid streams at the helical coil with 30&amp;deg; C. The volume fraction of the nanoparticles is considered as 0.1 vol.&amp;#37;. Reynolds number of the oil is fixed as 900 and the Reynolds number of the working fluid varies from 6000 to 15,000. The numerical code is validated with the earlier experimental work. Highest thermal performance is obtained by using 0.1 vol.&amp;#37; HYNF than nanofluids and base fluid. Role of mass flow rate, and Reynolds number on heat-transfer rate, effectiveness, total entropy generation, exergetic efficiency, exergy loss, and dimensionless exergy loss are investigated. An &amp;#126; 20&amp;#37; increase in Nusselt number and &amp;#126; 48&amp;#37; increment in exergetic efficiency are noted with the usage of HYNF. Entropy generation of SHCHE is lower by adding nanoparticles. This study enables the readers to understand the irreversibility of heat transfer in shell and helically coiled heat exchanger.

Hybrid CFD-ANN approach for evaluation of bio-inspired dolphins dorsal fin turbulators of heat exchanger in turbulent flow

The central aim of the present investigation is to evaluate the effects of bio-inspired Dolphin’s dorsal fin turbulators (DFTs) with a hybrid CFD-ANN approach in a counter flow double pipe heat exchanger. The DFT’s physical model is adapted from the infrared thermal image of a bottlenose dolphin dorsal fin. The effects of different influential parameters, such as the length scale (D) of DFTs including 4, 8, 12 mm and the number of turbulators (N) including 6, 10, and 14 are numerically examined at different Reynolds numbers. Also, using CFD data, the neural network is trained with great accuracy of R2 above 0.999. Important parameters such as Nu, f, Ɛ, NTU can be predicted in different conditions by the ANN method. This method greatly reduces the costs of CFD solutions, which is advantageous. The results indicate that the DFT's streamlined geometry could significantly reduce friction loss by streamlining the fluid flow. Also, colliding the fluid stream with the DFTs improves heat transfer by boundary layer destruction. The UA Ratio (UAR) of the Dolphin’s dorsal fin turbulator heat exchanger (DFTHE) to the simple heat exchanger (SHE) is between 1.02 and 1.74. Also, the ratio of Nu, Ɛ, NTU for the DFTHE to the SHE is equal to 2.48, 1.63, and 1.74, respectively.

Numerical Comparison of Stagnation Point Casson Fluid Stream over Flat and Cylindrical Surfaces with Joule Heating and Chemical Reaction Impacts

Numerical Comparison of Stagnation Point Casson Fluid Stream over Flat and Cylindrical Surfaces with Joule Heating and Chemical Reaction Impacts

Fluid flow past a rotating sphere in the presence of a toroidal magnetic field

AbstractA study on the conducting viscous fluid flow past a rotating sphere in the presence of a toroidal magnetic field is being studied. Exploration has been carried out by many researchers on the flow past a sphere. The governing equations related to the model are solved by a method of asymptotic expansion approach using boundary conditions. Several expressions for various approximations of fluid velocity and stream function have been obtained along with the separation parameters. The results for the first approximation were with the full agreement with the existing literature. The second approximation for the fluid properties has seen the impact of the magnetic parameter. The graph has been plotted for the obtained expressions. It has been observed that with the increase of magnetic Taylor number, there is an increase in the tangential velocity of fluid flow.

Use of cavitation to enhance the leaching kinetics of refractory gold ores

ABSTRACT The cyanidation process for refractory gold ores has been the subject of numerous investigations aimed at improving gold recovery and leaching kinetics. From recent literature investigations, hydrodynamic cavitation has been found to be a promising new approach which may modify the cyanidation processes. In this study, this approach results in the enhancement of mass transfer kinetics in multiphase fluid streams due to impacting two pulps streams against one another in a vessel called the Jetleach reactor. In this work, the Jetleach reactor was applied to a flotation concentrate from a South African gold tailings processing plant (Ergo) where an improvement of almost 10% in gold recovery was obtained while decreasing cyanide and oxygen consumption by almost 8% and 50%, respectively. The main reason for the improvement is surmised to be due to the generation of micro-cavitation which improves the mass transfer of oxygen and cyanide within the slurry.

Comparative thermodynamic analysis of an improved ORC process with integrated injection of process fluid

In contrast to water-steam Rankine cycles, the ORC process uses organic working fluids. For working fluids of the dry class, a recuperator heat exchanger is frequently installed to increase the cycle efficiency. This paper analyses an improved ORC process with these features: A liquid working fluid stream is injected into the vapour flow between the high-pressure and the medium-pressure stage of the turbine. Furthermore, the recuperator is replaced by a spray condenser. The main objective is to increase efficiency with moderate changes in the process layout. A thermodynamic comparison of the improved process with a state-of-the-art ORC process is carried out by simulations and optimisations. A significant efficiency gain for the improved ORC process is obtained by a combination of the aforementioned features, mainly because of an increase of the mass flow in the economiser of the vapour generator (better heat utilization) and a corresponding mass flow in the medium stage of the turbine (additional power production). As a use case, waste heat utilization from a clinker cooler at a temperature level of 275 °C was simulated. The improved process would lead to a significant increase in the overall net efficiency by up to 14%, compared to a state-of-the-art ORC process.

Simulation of the mixing process in a slot channel with jet injection

The article presents the results of modeling in a two-dimensional formulation of the hydrodynamic process of mixing two streams of Newtonian fluids in a channel with jet injection. The mixing process takes place in a turbulent flow mode, without chemical and thermal interaction. The article considers the flow of a mixture in a flat slit channel when mixing two liquids. The first component of the mixture flows through the main wide channel. At a distance of 50 mm from the point of entry into the channel perpendicular to the main channel, there is a radial jet nozzle with a width of 1 mm, through which the second component enters the mixing channel. The article discusses several problems with different initial mixing rates of components. The characteristics corresponding to water and ethyl alcohol were taken as test components for mixing liquids. The simulation was carried out in the ANSYS-Fluent software package. The purpose of this work is to study the process of mixing two liquids in a slit channel. The article presents the results of modelling the mixing process.

Multiphase numerical simulation of exergy loss and thermo-hydraulic behavior with environmental cosiderations of a hybrid nanofluid in a shell-and-tube heat exchanger with twisted tape

In the foreseeable future, heat exchangers will continue to play an important role in environmental management and have numerous applications, their geometry has been the subject of interest for many researchers. The main goal of this research is improving the heat exchangers' thermal performance and investigating the exergy using SIMPLE algorithm, k-w turbulent model and the Eulerian- Eulerian method for multiphase flow. Hence, the operation of Al2O3CuO-water hybrid nanofluid in a 3D shell-and-tube heat exchanger is simulated to enhance the contact surface of hot and cold fluid streams using computation fluid mechanics techniques. Reynolds number is 10,000, 15,000, 20,000, and 25,000 and volume fraction of nanoparticle is 2–6%. The innovations of this research are the use of the use of hybrid nanofluid and turbulator. The hybrid nanoparticles are employed to enhance the thermal conductivity and the turbulator is utilized to increase flow turbulence. The results demonstrated that the hybrid nanofluid, the turbulator, and high amount of Reynolds number can have a remarkable impact on increasing the thermal performance. The obtained results revealed that a 6% increment in hybrid nanoparticles volume fraction and an enhancement in Reynolds number from minimum to maximum lead to a 126% improvement in thermal performance in the presence of the turbulator. Lastly, environmental damage, energy consumption, and emissions are reduced by nanofluids.