Three-dimensional Computational Fluid Dynamics Approach Research Articles

Computational Fluid Dynamics Process for Front Windshield Mist Deposition and Its Subsequent Demisting

<div>A vehicle’s heating, ventilation, and air-conditioning system plays a dual role in passenger thermal comfort and safety. The functional aspects of safety include the front windshield demist and deicing feature of the system. The thin-film mist is a result of condensation of water vapor on the inner side of the windshield, which occurs at low ambient temperatures or high humidity. This mist deposition depends on the air saturation pressure at the front windshield. Indian regulation AIS-084 defines the experimental setup for testing, which encompasses both the mist deposition and its subsequent demist process. This regulation mandates testing, which occurs at a later stage of product development. This performance validation can be performed using a three-dimensional computational fluid dynamics approach.</div> <div>Current work summarizes the simulation process for both the mist deposition and the subsequent demisting phenomenon. The complexity of the flow physics is captured via the transient multiphase fluid flow phenomenon subjected to buoyancy effects. This phenomenon is simulated using the Eulerian wall film approach. The wall film deposition of the mist is modeled via species transport. Further, the near-wall thermal effects of surface conduction and heat transfer are simulated by modeling shell conduction layers. Vapor diffusion and relative humidity inside the cabin are modeled using a user-defined function. The process correlation is achieved for two categories of vehicles to establish the process efficacy and robustness. Moving ahead, a design of experiments (DOE) is planned to mitigate the need to simulate mist deposition. The DOE is planning to incorporate deviations in both the input airflow conditions and the imposed ambient conditions. The results from DOE point toward factors that might cause deviations in simulation results with respect to the test. Importantly, the study concludes that the uniform initial thickness assumption of the mist layer can be used for subsequent demist analysis.</div>

Thermal management of shelter building walls by PCM macro-encapsulation in commercial hollow bricks

Maintaining building indoor temperature within comfort zone has been identified as one of the major reasons for energy consumption. The incorporation of phase change materials (PCMs) in various regions in buildings is introduced as a solution that can significantly reduce energy consumption. In the current research, a three-dimensional computational fluid dynamics approach is taken to evaluate the influence of incorporating three PCMs from the Rubitherm® RT line (RT15, RT18, and RT22) in two widespread commercial hollow brick types in Iran for keeping the indoor environment of a shelter warm in a cold climate. These enhanced bricks are compared with their solid and hollow counterparts. Furthermore, efforts were made to examine various configurations of these PCMs, with melting temperatures in obedience or contrast with the thermal stratification of the bricks. Several combinations of the PCM with air layers are studied to assess the best way to place the air and PCM layers. It was found that the RT18 PCM-filled brick can present lower heat fluxes than the hollow one for over 42 h. Also, the findings showed that RT22 PCM-filled brick can provide 66.79% lower average heat flux compared to the hollow brick for the first 24 h of the process.

Recommendation for strut designs of vertical axis wind turbines: Effects of strut profiles and connecting configurations on the aerodynamic performance

The strut is a necessary support structure that connects the vertical axis wind turbine blade to the rotating shaft and transfers the torque, and is one of the key factors affecting the aerodynamic performance of the wind turbine. However, research on struts is limited and the appropriate strut design remain uncertain. Therefore, in this paper, the struts of a straight-bladed vertical axis wind turbine are investigated by a three-dimensional computational fluid dynamics approach, to find the appropriate strut design parameters that minimize the impact on the aerodynamic performance. Thirty strut profiles with different chord lengths, thicknesses, areas, and streamlined shapes were parametrically created and analyzed, including a novel strut-specific profile proposed in this paper. Furthermore, all strut connecting parameters, such as spanwise and chordwise positions, connecting angle and fairing were investigated. The results show that the power loss of a vertical axis wind turbine has a relatively linear relationship with the dimensionless absolute thickness of the strut within a certain range. The strut chord length is another important influencing factor. Equal chord lengths of the strut and the blade should be avoided as much as possible. The proposed novel olivary strut profile has lower drag characteristics and more favorable geometrical structural properties compared to the most used NACA airfoil. The influence of the spanwise connecting position (within the range around the blade quarter span) is minor. But the chordwise position has a significant effect, and special attention should be paid to avoid the strut maximum thickness position connecting with the blade aerodynamic center, which will result in the greatest performance degradation. Analysis of the connecting angles shows that inclined struts are suitable for small wind turbines. The fairing is effective when the strut chord length is equal to or longer than the blade chord length. With these results, a set of recommended design parameters for vertical axis wind turbine struts is presented.

Employing computational fluid dynamics technique for analyzing the PACK-1300XY with methanol and isopropanol mixture

In this study, an innovative wire gauze structured packing, namely PACK-1300XY with a specific surface area of 1300 m2/m3 has been characterized by performing computational fluid dynamics (CFD) approach. Indeed, different features of this packing (height equivalent to a theoretical plate, wet/dry pressure drop, and mass transfer efficiency) were analyzed by analyzing the flow regime using the three-dimensional CFD approach with the Eulerian–Eulerian multiphase scenario. The results showed the mean relative deviation of 16% (for wet pressure drop), 14% (for dry pressure drop), and 17% (for mass transfer efficiency) between the CFD predictions and experimental measurements. These excellent levels of consistency between the numerical findings and experimental observations approve the usefulness of the CFD-based approach for reliable simulation of separation processes.

Hydrodynamical Fingerprint of a Neighbour in a Fish Lateral Line.

For fish, swimming in group may be favorable to individuals. Several works reported that in a fish school, individuals sense and adjust their relative position to prevent collisions and maintain the group formation. Also, from a hydrodynamic perspective, relative-position and kinematic synchronisation between adjacent fish may considerably influence their swimming performance. Fish may sense the relative-position and tail-beat phase difference with their neighbors using both vision and the lateral-line system, however, when swimming in dark or turbid environments, visual information may become unavailable. To understand how lateral-line sensing can enable fish to judge the relative-position and phase-difference with their neighbors, in this study, based on a verified three-dimensional computational fluid dynamics approach, we simulated two fish swimming adjacently with various configurations. The lateral-line signal was obtained by sampling the surface hydrodynamic stress. The sensed signal was processed by Fast Fourier Transform (FFT), which is robust to turbulence and environmental flow. By examining the lateral-line pressure and shear-stress signals in the frequency domain, various states of the neighboring fish were parametrically identified. Our results reveal that the FFT-processed lateral-line signals in one fish may potentially reflect the relative-position, phase-differences, and the tail-beat frequency of its neighbor. Our results shed light on the fluid dynamical aspects of the lateral-line sensing mechanism used by fish. Furthermore, the presented approach based on FFT is especially suitable for applications in bioinspired swimming robotics. We provide suggestions for the design of artificial systems consisting of multiple stress sensors for robotic fish to improve their performance in collective operation.

Numerical Analysis of Microchannels Designed for Heat Sinks

Conjugate heat transfer is numerically investigated using a three-dimensional computational fluid dynamics approach in various microchannel geometries to identify a high-performance cooling method for piezoelectric ceramic stacks and spindle units in high-precision machines. Straight microchannels with rectangular cross sections are first considered, showing the performance limitations of decreasing the size of the microchannels, so other solutions are needed for high applied heat fluxes. Next, many microchannel designs, focusing on streamwise geometric variation, are compared to straight channels to assess their performances. Sinusoidally varying channels produce the highest heat transfer rates of those studied. Thus, their optimization is considered at a channel width and height of 35 and 100 μm, respectively. Heat transfer increases as the amplitude and spatial frequencies of the channels increase due to increased interfacial surface area and enhanced Dean flow. The highest performance efficiencies are observed at intermediate levels of amplitude and frequency, with efficiency decreasing as these geometric parameters are increased further at the onset of flow separation. The sinusoidal channel geometries are then optimized with respect to minimizing the system’s pressure drop for all applied heat fluxes between 5690 and 6510 kW/m2. Doing so created an optimal geometry curve and showed that all geometries in this region had amplitudes close to 40 μm. Therefore, imposing a fixed heat flux requirement for a case study of cooling piezoelectric ceramics, the optimized sinusoidal geometry decreases the system pressure drop by 79% relative to a straight channel while maintaining a larger minimum feature size.

A new CFD approach for proppant transport in unconventional hydraulic fractures

For hydraulic fracturing design in unconventional reservoirs, the existing proppant transport models ignore the fluid leak-off effect from the fracture side wall and the effect of fracture roughness. In this paper, a model is proposed using three-dimensional computational fluid dynamics approach with fluid leak-off rate defined along the fracture length and considering the effect of fracture roughness on proppant distribution. Based on the simulation results, it is recommended that neglecting the fracture roughness in the proppant transport model can result in over predicting the proppant bed length and underpredicting the proppant suspension layer by 10–15%. Furthermore, neglecting the fluid leak-off effect can result in under predicting the proppant bed height by 10–50% and over predicting the proppant suspension layer by 10–50%. This study has enhanced the understanding of the proppant-fracturing fluid interaction phenomenon by accounting detailed physics to optimise the hydraulic fracturing design.

Comparative performance assessment of plate heat exchangers with triangular corrugation

A three-dimensional computational fluid dynamics approach with the Reynolds stress model is considered to investigate the influence of the apex angle on the thermal and hydraulic features of triangular cross-corrugated heat exchangers for a range of Reynolds numbers 310–2064. The influence of the intensity and complexity of the recirculation zones along with the turbulence intensity on those characteristics and corresponding viscous and pressure forces are studied. The choice of the computational domain as a unitary cell with periodic boundary condition versus a long channel with several cells is discussed. One on one comparison between the Reynolds stress model and experimental results shows less than 5% deviation, which is within the uncertainty of the experiment. By increasing the apex angle both pressure drop and heat transfer coefficient increase, due to the increase of the pressure force and the vorticity magnitude along the flow direction. The pressure force is the dominant force, contrary to pipe flow, where the viscous force is dominant. The influence of the apex angle on the friction factor and the Colburn j factor follows two distinguished trends. The apex angles around of 90°–100° are the transitional angles for the flow regime. Peak of turbulence intensity, friction factor and Colburn j factor are observed around these angles. The ratio between pressure and viscous forces decays after angle 100°, resulting in a smaller recirculation zone and lower turbulence intensity. Finally, the thermo-hydraulic performance of the considered geometries is compared with respect to each other based on a performance evaluation criterion. It is found that the geometry with the largest apex angle has the highest thermo-hydraulic performance.

Numerical investigation of the heat transfer performance of water-cooled incineration grates with various channel designs

This study investigates the effect of the geometry of the cooling channel on the cooling performance of a unit grate using a three-dimensional computational fluid dynamics approach. Three different geometries of the cooling channel, i.e., serpentine, wavy, and baffle channels are considered. To evaluate the cooling performance, evaluation indicators, including the maximum temperature, average temperature, temperature uniformity, and pressure drop are compared. In addition, figure of merit, i.e., heat transfer per unit pumping power, is also compared for three channel designs. According to these indicators, it is concluded the baffle channel is the best choice.

Mixing behaviors in an industrial-scale spout-fluid mixer by 3D CFD-TFM

A new industrial-scale spout-fluid mixer (H=3.4m and I.D.=0.8m) was proposed for mixing 18.75t/h of biomass (ρb=400kg/m3, db=2mm) and 281.25t/h of heat-carrier (ρc=2600kg/m3, dc=0.5mm), and the corresponding three-dimensional computational fluid dynamics approach, facilitated with the Eulerian-Eulerian multiphase fluid model (CFD-TFM), was developed to simulate the three-phase mixing behaviors in the mixer. The performance of the mixer and effects of operating parameters were numerically investigated. It was found that the mixing effectiveness, Me, can reach over 80% under the proposed industrial operational conditions (for example, a spouting gas flowrate Qs=0.067kg/s and fluidizing gas flowrate Qf=0.035kg/s), and the flow pattern in this case is a “jet in the fluidized bed with bubbling”. Increasing Qs will increase the sizes of bubbles, as well as their generation frequency and rising velocity, which are conducive to the mixing of heat-carrier and biomass particles. However, a too large Qs will affect the falling solid flows in the distribution region and transition region of the mixer. Conversely, increasing Qf will aggravate the swaying and leaning of bubbles or jets towards the mixer walls, leading to a slight decrease of Me.

The influence of differential evaporation on the structure of a three-component biofuel spray

A high-pressure spray injected under gasoline engine conditions in a constant volume chamber is studied in detail using a three-dimensional computational fluid dynamics approach. Both single-component and ternary mixture (n-alkane and alcohols) spray results are compared with the experimental data from shadowgraphy, Schlieren imaging and phase-Doppler anemometry. Activity coefficient models are used to cover non-ideal thermodynamic effects occurring when mixtures of structurally dissimilar components such as alcohols and n-alkanes are considered. Here, the non-random, two-liquid and universal quasi-chemical functional group activity coefficients methods are applied. A ternary mixture composed of ethanol, n-butanol and n-hexane representing the research octane number (RON 95) of gasoline is considered and investigated in detail. To illustrate the non-ideal mixture effects, first the binary mixtures ethanol/n-butanol, n-butanol/n-hexane and ethanol/n-hexane are studied as subsets of the ternary mixture using a zero-dimensional single-droplet evaporation solver. Introducing a differential evaporation factor for multicomponent mixtures, the mixture segregation is characterized. Additionally, a separation factor indicating which component depletes first (volatility) is presented for both binary and ternary mixtures. The zero-dimensional results are then correlated with the three-dimensional computational fluid dynamics simulation results. Looking at the vapor–liquid equilibria of the different binary mixtures, the non-ideal effects are identified. The evaporation behavior of the binary mixtures is compared with the ternary mixtures in terms of droplet lifetimes, temperature and mixture decomposition, where the latter is characterized with the differential evaporation factor and separation factor. These results are afterwards compared with the three-dimensional computational fluid dynamics simulations, which are validated against the experimental data for single-component sprays regarding the liquid and vapor penetration depths. Finally, in the ternary mixture, n-butanol is replaced with iso-octane, the most widely used gasoline surrogate, to illustrate the differential evaporation behavior for a mixture with a higher alkane content than the ternary mixture used for the experiments. Strong non-ideal effects causing significant changes in the vapor composition are presented, as well as changes in the characterization factors, differential evaporation factor and the separation factor, respectively. These results are compared with the single-droplet simulations.

Analysis of parameter effects on chemical reaction coupled transport phenomena in SOFC anodes

Mass, heat and momentum transport processes are strongly coupled by internal chemical reforming reactions in planar design solid oxide fuel cell (SOFC) anodes. In this paper, a three-dimensional computational fluid dynamics approach is applied to simulate and analyze reforming reactions of methane and various transport processes in a duct relevant for SOFC anodes. The results show that the anode duct design and operating parameters, grouped as three characteristic ratios, are significant for the chemical reactions and further for multi-species distribution, fuel gas transport and heat transfer in the sub-domains of the anode.

Effect of bifurcation angle in tree-shaped microchannel networks

Tree-shaped microchannel networks are being considered for thermal designs that require high heat transfer densities for the cooling of modern electronics. Here we investigate the effect of the bifurcation angles in the constructal nets on the fluid flow and heat transfer characteristics of such networks using a three-dimensional computational fluid dynamics approach. Results show that the bifurcation angle is an important factor which determines the performance of such cooling nets. Surface temperature distributions and pressure drop along the flow paths are analyzed and compared. For the same boundary conditions, a lower temperature and pressure variation is observed at lower bifurcation angles.

Thermal Characteristics of Microscale Fractal-Like Branching Channels

Heat transfer through a fractal-like branching flow network is investigated using a three-dimensional computational fluid dynamics approach. Results are used for the purpose of assessing the validity of, and providing insight for improving, assumptions imposed in a previously developed one-dimensional model for predicting wall temperature distributions through fractal-like flow networks. As currently modeled, the one-dimensional code fairly well predicts the general wall temperature trend simulated by the three-dimensional model; hence, demonstrating its suitability as a tool for design of fractal-like flow networks. Due to the asymmetry in the branching flow network, wall temperature distributions for the proposed branching flow network are found to vary with flow path and between the various walls forming the channel network. Three-dimensional temperature distributions along the various walls in the branching channel network are compared to those along a straight channel. Surface temperature distributions on a heat sink with a branching flow network and a heat sink with a series of straight, parallel channels are also analyzed and compared. For the same observed maximum surface temperature on these two heat sinks, a lower temperature variation is noted for the fractal-like heat sink.

Fluid Flow Through Microscale Fractal-Like Branching Channel Networks

Flow through fractal-like branching networks is investigated using a three-dimensional computational fluid dynamics approach. Results are used to assess the validity of, and provide insight for improving, assumptions imposed in a previously developed one-dimensional model. Assumptions in the one-dimensional model include (1) reinitiating boundary layers following each bifurcation, (2) constant thermophysical fluid properties, and (3) negligible minor losses at the bifurcations. No changes to the redevelopment of hydrodynamic boundary layers following a bifurcation are recommended. It is concluded that temperature varying fluid properties should be incorporated in the one-dimensional model to improve its predictive capabilities, especially at higher imposed heat fluxes. Finally, a local pressure recovery at each bifurcation results from an increase in flow area. Ultimately, this results in a lower total pressure drop and should be incorporated in the one-dimensional model.