Finite Volume Model Research Articles

Simulation of pressure pulsations for pumped-storage units with wide operating range and comparison to experiments

The diversity of energy conversion sources in the current energy market increases the demand for stabilizing the electrical grid through ancillary services, frequency and power regulation from the facilities. Pumped-storage units with reversible pump-turbines or ternary sets constitute the currently most advanced solution for providing these services. This implies that pumped-storage units are required to operate in larger head and power ranges than before. In order to increase their flexibility in pump mode, variable speed units have been applied more frequently with additional challenges for the operating range in pump mode.The extension of the operating flexibility in pump mode makes use of a large portion of the model pump characteristic curve, especially in the case of variable speed units. Important challenges to the hydraulic development are among others the cavitation behaviour, hydraulic stability and pressure pulsation level. This study concentrates on the pressure pulsations in pump mode, which are of great relevance for the machine smooth operation.The pressure pulsations in a regulated radial reversible pump-turbine with low specific speed are numerically simulated with computational fluid dynamics (CFD) for several points along the complete operating range of the pump characteristic curve. The finite volume model includes the complete hydraulic machine from draft tube to spiral case and hybrid turbulence models were used, in this case scale adaptive simulation (SAS). The numerical simulation offers the possibility to assess different flow quantities at any point of the finite volume model, providing additional data to the experimental model test results.The integral quantities, e.g. head, flow and efficiency, were compared to the model test results to validate the numerical model. The simulated pressure pulsation amplitude and frequency were also compared to the measured pressure pulsations at the model at the available measuring locations in the spiral case, vaneless space and draft tube cone. After the validation, the computed flow fields were used to derive the pressure pulsation amplitude at other machine locations and components, e.g. at the runner.

Improving Sonic Rarefactions in Elastic Vessels: Application to the Tourniquet Manoeuvre

Elastic vessels like arteries and specially veins are prone to sharp changes in their area or external pressure. These phenomena create discontinuities due to a sudden jump on mechanical properties, which is a challenge when trying to simulate unsteady blood flow circulation. This work compares numerical methods to face this challenge in the context of a finite volume model.

Phase Change Material Behavior in Finite Thickness Slabs Under a Step Response Heat

Abstract Phase change materials (PCMs) can provide thermal buffering to systems that experience transient heat loads, including electronics and optoelectronics packaging. Placing the PCM in the primary path of heat rejection decreases the thermal resistance between the heat source and the PCM volume, but increases the total thermal resistance between the heat source and heat sink. In systems that operate in both steady-state and transient regimes, this introduces tradeoffs between cooling performance in these distinct regimes. Employing a conductive finite volume model, Parapower, we investigate those tradeoffs considering the impact of adding a layer of gallium (Ga), a low melting point metal, and a layer of copper (Cu) between a planar heat source and a convective boundary condition heatsink. We demonstrate: (1) side-by-side comparisons of latent (Ga) and sensible (Cu) heat storage layers must consider different layer thicknesses to account for the different thermal storage mechanisms, (2) for short periods of time, conditions exist in which a PCM outperforms a traditional heat sink for transient thermal buffering at an equivalent steady-state temperature rise, and (3) under these conditions, the Ga layer is approximately an order of magnitude thinner than the equivalent Cu, leading to significant mass and volume savings.

Effect of heat input modes on microstructure, mechanical properties and porosity of laser welded NiTi-316L joints: A comparative study

Laser welding of NiTi to stainless steel (SS) wires is prospective in biomedical devices. In this work, the influence of different heat input modes, high power density with short welding time (HPDS) and low power density with long welding time (LPDL), on laser welded NiTi-316L wire joints was investigated. The HPDS mode resulted in non-uniform microstructure and hardness distribution in the fusion zone (FZ). On the contrary, a relatively uniform intermetallic compounds (IMCs) network of Fe2Ti + Ni3Ti formed in the FZ welded with LPDL mode. Finite volume modeling (FVM) was used to reveal the flow of molten metals between HPDS and LPDL modes. Different mechanisms for high porosity in the HPDS joint were proposed: processing-induced large pores were caused by the instability/collapse of laser keyhole, while diffusion-induced small pores initiated from the Ni vaporization. A low laser power density and long welding time in LPDL mode could significantly decrease the porosity by weakening laser keyhole, increasing time for pore escaping and uniformizing FZ microstructure. LPDL mode could result in an enhanced joint tensile strength to maximum 290.2 MPa because of the increased effective joining area (by decreasing porosity) and the reduced brittle Fe–Ti IMCs segregation in joints.

Dynamic simulation model with virtual interfaces of supercritical working fluid heat exchanger based on moving boundary method

The supercritical cycle has a better variable-temperature match between the working fluid and heat source, potentially providing higher efficiency. Accurate simulation of the transient performance of supercritical heat exchangers is significant in advanced thermal system control. This paper proposes a dynamic model of supercritical heat exchangers based on the moving boundary method. The model redefines the concept of “interface” in the traditional moving boundary model. The new interfaces are determined by the thermophysical properties of the working fluid, called “virtual interfaces”. A control-volume separation method is proposed based on the virtual interface. Additionally, the specific enthalpy is selected as the switching criterion for the configuration of the control volumes, so the model can dynamically adjust the number of control volumes. The integrity check results show that the simulation accuracy is at least equivalent to the finite volume model with 20 control volumes; however, the time cost is approximately 1/5 of that of the finite volume model with the same precision. An experimental study on the convective heat transfer of supercritical n-decane in an electrically heated vertical tube was conducted. The maximum absolute error of the steady-state outlet temperature is ±1.5 K, and the relative error is ±3% under different pressures.

Studies on navigational depth of a shipping channel using numerical modelling and bathymetric analysis in the Hooghly estuary, India

ABSTRACT Availability of navigational draft along the shipping channel is essential for effective freight transport of any port for its economic sustenance. Rangafala channel is one of the main channels leading to Kolkata port. The primary objective of this research work is to find the critical and vulnerable positions in the navigation channel. A Cartesian grid-based, two-dimensional, depth-averaged, finite volume model has been developed using existing bathymetry, water level, sediment data, and appropriate boundary conditions in hydrodynamic and sediment transport modelling. The developed model is first calibrated using observed velocity data, and then, it has been validated with observed water level data at the Haldia gauge station. The validated model has been simulated for 6-month boundary values, and it has been experienced that the depth-averaged model velocity is relatively high throughout the channel. The hydrodynamic and sediment transport model results suggest that the channel remains self-maintained, and only a few locations experience little deposition. Eleven years of channel bathymetric data are used to complement the simulated model results. It is observed that the required draft for navigation has always been maintained along the Rangafala channel.

Reduced-order modeling method for phase-change thermal energy storage heat exchangers

Thermal energy storage can facilitate the effective utilization of renewable energy. To speed up the design process of thermal energy storage devices, it is critical to develop fast and accurate modeling methods for phase change material embedded heat exchangers (PCM HXs). This study developed and compared two approximation-assisted reduced-order PCM HX models for the simulation of thermal storage components and systems, which were verified against a validated finite-volume model. They are a pure black-box model, and a grey-box model based on the Number of Transfer Units (or effectiveness-NTU) approach. We used the reduced-order models to predict the performance of standalone PCM HX for 1000 cases with different fluid inlet conditions and HX designs. We also integrated the models with a vapor compression system to predict the compressor energy consumption and total charging time under various conditions. The results show that overall, the black-box model gave more accurate results than the grey-box model. On average, the mean absolute deviation in the PCM HX fluid outlet temperature was 0.05 K and 0.1 K for the black-box model and grey-box model, respectively. The grey-box model gave larger temperature deviation toward the end of the phase change process, due to the simplified two-node PCM representation. On the system level, the mean absolute deviation in compressor energy consumption was 0.2% and 0.3% for the black-box model and grey-box model, respectively. Their mean absolute deviation in total charging time was 1.1% and 2.6%, respectively. In terms of computation efficiency, the system simulation speedup ratio gained by using the reduced-order models was 11 to 57. System simulation time was decreased from an average of 1465 s to an average of 59 s. This shows that the proposed reduced-order modeling methods can be used to predict system performance of PCM HXs with less than 3% accuracy penalty, and 25 times less computational time than finite-volume models, enabling faster design and evaluation of PCM thermal storage devices.

Numerical scheme for solving the Richard’s equation based on finite volume model with unstructured mesh and implicit dual-time stepping

In this paper, a novel finite volume model with unstructured mesh and implicit dual time stepping is proposed for simulating unsaturated infiltration flows based on Richards’s equation (RE), which is one of the most challenging problems in earth science. In time, a matrix-free fully implicit dual time stepping algorithm is developed to discrete the equation, and in space, the equation is discretized by the finite volume model with unstructured grid. The new method is assessed and evaluated by benchmark and engineering water infiltration cases. Both numerical solutions in the literature and solutions of a commercial package called GEO-Studio are used to verify the accuracy of the proposed algorithm. An unsteady water infiltration simulation case is carried out as the application of the current model by using the topographic dataset of the Monterey Bay in California. The results demonstrate that the new algorithm is robust and practical, with fast convergence and high accuracy.

Effect of Different Solder Volumes on the Laser Soldering Process: Numerical and Experimental Investigation

Abstract Laser soldering is becoming more popular for soldering pin through-hole (PTH) components onto printed circuit boards (PCBs). Solder volume influences soldering joint reliability. However, it is difficult to accurately measure the effect of solder volume during the laser soldering process. The finite volume method (FVM) is used to simulate the molten solder flow in laser soldering to connect the through-hole capacitor onto the PCB in ansysfluent software. The simulation results reveal the effects of different SAC305 solder volumes on joining quality in terms of fillet shape formation, pressure, and velocity. The preferred solder volume is 1.517 mm3 with a filling time of 1.7 s, a temperature of 642 K, a hole diameter of 1.0 mm, a lead diameter of 0.5 mm and a PCB thickness of 1.20 mm, produces a fillet shape similar to a real sample of PTH laser soldering joint from the industry. This ideal volume was chosen with a suitable pressure and velocity to create a nice concave fillet shape and minimize voids during soldering. The pressure and velocity increase when the solder volume increases causing solidified solder to melt. The discrepancy between numerical and experimental values of fillet height is comparable, which inferred that the numerical model was well-validated. The good consistency between both results proves that the finite volume model will effectively predict the optimum solder volume. This opens up new opportunities for the optimization of the laser soldering parameters in the application of electronic manufacturing.

Numerical simulation of the nozzle configuration in strip casting process

This work examines the design of nozzles in continuous strip casting process. Three-dimensional (3D) simulations of steady turbulent (k-ε) flow are done at the upper part of the mould using a finite-volume (CFX) model. This is performed for different inlet systems, including the inlet nozzle jets with a free stream, the submerged nozzle jets, the slot inlet system, and the slot-submerged inlet system. The resulting heat flux to the solidifying shell has also been studied. Numerous operating parameters are examined, including the shape, size, position, and thickness of the ports and the bottom geometry. It is found that different inlet nozzle configurations change the molten flow and heat patterns, mainly in the upper region of the mould. By applying the slot nozzle inlet system, turbulence and values of the averaged velocity field in that area decrease significantly.

Multiphysical and multidimensional modelling of Parallel-Plate active magnetic regenerator

Active Magnetic Refrigeration (AMR) is a complex multiphysical process that requires optimisation. A revised description of the analytical formulations is proposed, starting from the essentials of the magnetocaloric effect. Each physical aspect has been extensively investigated, including the actual magnetic field inside the ferromagnetic domain. An AMR test bench was modelled using a 3D magnetostatic finite-element model, thermofluidic finite-volume models (2D and 3D), and a 1.5D semi-analytical model. Different boundary conditions were simulated to understand the operation of the AMR system. Based on the temperature histories, an agreement was found between the models and the experimental results. In addition to its flexibility and simplicity, the 1.5D model had the lowest computation time of approximately 1.2 s cycle-1. This makes it an excellent tool for the optimal design of an active magnetocaloric device.

Smoothed embedded finite-volume method (sEFVM) for modeling contact mechanics in deformable faulted and fractured porous media

A smoothed embedded finite-volume modeling (sEFVM) method is presented for faulted and fractured heterogeneous poroelastic media. The method casts a fully coupled strategy to treat the coupling between fault slip mechanics, deformation mechanics, and fluid flow equations. This ensures the stability and consistency of the simulation results, especially, as the fault slip is implicitly found through an iterative prediction-correction procedure. The computational grid is generated independently for embedded faults and rock matrix. The efficiency is further enhanced by extending the finite-volume discrete space by introducing only one degree of freedom per fault element. The embedded approach can lead to an oscillatory stress field at the fault, which damages the robustness of the implicit slip detection strategy. To resolve this challenge, a smoothed embedded strategy is devised, in which the stress and slip profiles are post processed within the iterative loops by fitting the best curve based on a least-square error criterion. The sEFVM provides locally conservative mass flux and stress fields, on staggered grid. Its performance is further investigated for several proof-of-the-concept test cases, including a multiple fault system in a heterogeneous domain. Results indicate that the method develops a promising approach for field-scale relevant simulation of induced seismicity.

Interface Thermal Resistance between Monolayer WSe2 and SiO2: Raman Probing with Consideration of Optical–Acoustic Phonon Nonequilibrium

AbstractThis work explores the 2D interfacial energy transport between monolayer WSe2 and SiO2 while considering the thermal nonequilibrium between optical and acoustic phonons caused by photoexcitation. Recent modeling and experimental work have shown substantial temperature differences between optical and acoustic phonons (ΔTOA) in various nanostructures upon laser irradiation. Generally, characterizations of interfacial thermal resistance (R′′tc) at the nanoscale are difficult and depend on Raman‐probed temperature measurements, which only reveal optical phonon temperature information. Here it is shown that ΔTOA for supported monolayer WSe2 can be as high as 48% of the total temperature rise revealed by optothermal Raman methods—a significant proportion that can introduce sizeable error to R′′tc measurements if not properly considered. A frequency energy transport state‐resolved Raman technique (FET‐Raman) along with a 3D finite volume modeling of 2D material laser heating is used to extract the true interfacial thermal resistance R′′tc (determined by acoustic phonon transport). Additionally, a novel ET‐Raman technique is developed to determine the energy coupling factor G between optical and acoustic phonons (on the order of 1015 W m−3 K−1). This work demonstrates the need for special consideration of thermal nonequilibriums during laser–matter interactions at the nanoscale.

Thermal study of clogging during filament-based material extrusion additive manufacturing: experimental–numerical study

One of the major drawbacks of material extrusion additive manufacturing (AM) is hot-end clogging. This study aims to answer the question, “How clogging happens and what thermal conditions lead to clogging during filament-based material extrusion?” Answering this question requires a clear understanding of temperature distribution inside the liquefier. However, this could not be achieved only through experimental measurements. Therefore, numerical simulations were also carried out by developing a 3D finite volume model of the hot-end. The results obtained from numerical simulations show good agreement with experimental measurements. They also give us a detailed picture of the temperature gradient near the nozzle. A series of experiments were performed to determine at what thermal conditions clogging occurs, and some criteria for avoiding clogging were presented. The temperature distribution of those thermal conditions that leads to clogging is then investigated numerically to analyze the clogging mechanism. As the results show, overheating the heat barrier increases the length of the filament, whose temperature is above the glass transition temperature. As this length exceeds a critical value, the filament buckles under the extruder motor force, and consequently clogging occurs.Graphical abstract

Numerical simulation of airflow in naturally ventilated attics for different attic geometries

AbstractAttic geometry and ventilation in a different attic geometry play a very important role in residential building energy performance. To evaluate the effect of ventilation ratio and vent balance on attic performance, a two‐dimensional finite volume model is employed to simulate the buoyancy‐driven turbulent ventilation and heat transfer in an attic space of different geometries like gable, gambrel, and saltbox roofs of residential buildings under winter conditions. The impact of ventilation ratio on ventilating airflow rate, heating load rate, and rate of heat gained is investigated for all three types of roof geometries. The model under consideration consists of a passive ventilation system with a ridge and soffit vent. Meshing is done by using ANSYS Workbench and numerical simulations are carried out by using ANSYS FLUENT 19 analysis software. The effect of passive ventilation on ridge‐vent attic performance is evaluated in this study. Ventilation ratios for soffit vents ranging from 1/400 to 1/25 are investigated. Convection boundary conditions are used for the attic walls to account for thermal resistances of ceilings and roofs. In addition, the performance of these vented attics is compared to the heat transfer in a sealed attic. The results show that the symmetrical airflow pattern exists in a vented attic, in contrast to the asymmetrical airflow patterns found in a sealed attic. From the study, it is evident that an increase in ventilation ratio reduces attic heating load irrespective of the increase in ventilation airflow rate. The rate of airflow increases with an increase in ventilation ratio in all three types of roof geometries that is gable, gambrel, and saltbox roofs. In the case of gable roof configuration, increasing the ventilation ratio from 1/200 to 1/100 results in an increase in ventilating mass flow of 75%, while an increase of ventilation ratio from 1/50 to 1/25 only increases the ventilating mass flow by 40%. In the case of gable roofs increasing ventilation ratio from 1/200 to 1/100 results in a 20% decrease in attic heating, whereas an increase in ventilation ratio from 1/50 to 1/25 results in a 10% decrease in attic heating.

Estimating the state of charge in a latent thermal energy storage heat exchanger based on inlet/outlet and surface measurements

• Estimators for the total and partial stored energy are developed and validated. • The estimator for the heat transfer fluid energy is generally applicable. • A finite volume latent thermal energy storage model is developed and fitted. The performance of latent thermal energy storage (LTES) heat exchangers is related to the stored energy (i.e. state of charge) during the (dis)charging of the energy storage system. Therefore, measuring the stored energy is crucial to understand the behavior of LTES systems. However, technical considerations often oppose the measurability of the stored energy. The present article presents a case where only measurements at the in- and outlet of the heat transfer fluid and on the outer surface of the heat exchanger were possible. Based on this sparse set of measurements, estimators for the stored energy are developed. To test these estimators, a finite volume model of the LTES heat exchanger is made. The finite volume model is fitted by comparing the predicted heat transfer fluid outlet temperature for 36 experiments. The energy estimators are compared to simulation results. The estimators for the stored energy in the heat transfer fluid, metal and phase change material obtain an average deviation of respectively 0.5 %, 3.9 % and 0.6 % with the stored energy predicted by the finite volume model. The estimator for the stored energy in the heat transfer fluid should be applicable to all LTES heat exchangers while the applicability of the estimators for stored energy in the metal and phase change material depend on small temperature differences between surface and interior of the metal and negligible heat losses.

A Smart Sensor for the Heat Flow of an Extruder

Two mathematical models are derived to describe the thermal dynamics of a plastics production machine. The Smart Sensor design is based on the finite volume model. The accuracy of the derived finite volume model is validated by a high-order finite element model. Those models are validated by measurements. A Smart Sensor for the heat flow between the extruder cylinder and screw conveyor is designed. Such a configuration has the advantage to decouple the thermal control problem from the specific granulate.

Performance analysis of aqueous LiCl and CaCl2 based falling film dehumidifier with surface modification

• Analysis is carried out on a falling film based liquid desiccant dehumidifier. • The surface is modified with sinusoidal profile to increase the dehumidification. • The sinusoidal wavy profile increases the desiccant surface area by 7%. • Aqueous LiCl solution enhances the dehumidification by 29.15% compared to CaCl 2 . • With aqueous LiCl, the modified surface increases the dehumidification by 33.18%. In summer air-conditioning, conventional vapor compression systems cool the process air to its dew point temperature for dehumidification and further heat it to required supply temperature. This involves extra cooling and subsequent heating. Liquid desiccant systems avert this issue by separately handling latent and sensible loads, while running primarily on low grade thermal energy. Falling film type liquid desiccant dehumidifiers are advantageous over other types, mainly, as they reduce desiccant carryover into supply air stream. The current work aims towards the analysis and the performance improvement of a falling film type dehumidifier with the help of wavy profile of the working surface. Detailed comparison of the two commonly used desiccants, i.e., LiCl and CaCl 2 are carried out to analyse the performance of the dehumidifier. The present work also includes the characterisation of the wave profile and the analysis in terms of various important parameters, such as, the dehumidification effectiveness, the moisture removal rate and the change in specific humidity, missing in earlier studies. In order to study the performance, a simplified 2–D transient finite volume model is taken into consideration to simulate a multiphase, multi-component conjugate heat and mass transfer system using ANSYS Fluent 19.2. The volume of fluid method is used to trace out the liquid–gas interface. With back-end modification of the solver, the thermophysical properties of the liquid film are evaluated using empirical relationships, as a function of temperature and concentration. The penetration model of mass transfer provides the local mass transfer coefficients. The moisture removing the potential of the aqueous solutions of LiCl and CaCl 2 are evaluated at quasi steady-state conditions. The numerical solver is validated with the already published experimental results with a maximum deviation of 10.31%. A sinusoidal wavy profile of the wall introduced in the system enhances the turbulence intensity by 3.8% and the dehumidification performance by 33.18% and 18% for LiCl and CaCl 2 , respectively. It is due to the enhanced liquid–gas interface area. The mean film thickness is found to improve by 15.25% and 13.38% for LiCl and CaCl 2 , respectively. The effect of process parameters on the performance of the dehumidifier is also studied. It has been observed that the dehumidification effectiveness decreases from 86.14% to 31.1% with increase in inlet air velocity from 0.2 m/s to 2.0 m/s. It has also been found that a lower concentration of the desiccant solution and lower velocity of air yield higher dehumidification effectiveness. However, the moisture removal rate of the system will be compromised. Compared to the previously studied cases, the current configuration of the sinusoidal profile with amplitude to wavelength ratio of 1:15, yields superior dehumidification performance.

Faster than real-time path-sensitive temperature modeling of wire-arc additive manufacturing by a data-driven finite volume method

Wire-arc additive manufacturing uses arc welding to build 3D objects by progressive deposition of weld beads at high deposition rates. To minimize the distortion induced by the moving heat source, a model for predicting the transient temperature fields as a function of the deposition path is needed. This work proposes a new data-driven finite volume model that combines the semi-discrete form of the energy balance with a temporal convolutional neural network. Compared to recurrent neural networks, the model is energy-conserving and computes temperature profiles on a grid of positions in parallel, thus executing substantially faster than the actual process.

3-D Finite Volume Modeling for LWD Azimuthal Propagation Resistivity Tool With Multiple Annular Antenna Recesses Using Coupled Potentials on Cylindrical Grids

The sensors of logging-while-drilling (LWD) azimuth propagation resistivity (APR) tool are usually installed in the annular antenna recesses filled with ferrite or other magnetic materials on the grooved metal mandrel. In this article, we will improve the 3-D finite volume method (3-D FVM) on cylindrical grids to solve the Helmholtz equations about coupled potentials for precise simulation of the tool responses with multiple antenna recesses. The irregular and novel Yee’s staggered grids are designed to conform to the grooved mandrel surface. The electrical continuation technique is adopted to approximate the perfectly electrical conductor (PEC) boundary condition on the mandrel surface for efficient enhancement of the discretization precision of the potentials around the mandrel. The equivalent conductivity and permeability in heterogeneous elements are determined by the volume average. After that, the parallel direct sparse solver (PARDISO) is used to solve the discretized equation about coupled potentials for effectively ensuring the accuracy and stability of numerical solutions. Finally, we validate the 3-D FVM against results by the hybrid algorithm in homogeneous formation. Through numerical results, we further investigate the influence of both the mandrel and antenna recesses on the LWD tool responses, and its response characteristics in several different environments.