Three-dimensional Transient Model Research Articles

On the performance of solar humidification-dehumidification desalination system with subsurface condenser

The solar humidification-dehumidification desalination system with a subsurface condenser is a promising and sustainable approach to providing a sustainable water supply. In this study, a comprehensive three-dimensional transient computational fluid dynamics model of the system is developed. Due to the lack of an experimental study on the thermal performance of the subsurface condenser, an experimental setup of the subsurface condenser is built, and the obtained experimental results are used to validate the developed model of the subsurface condenser. The developed numerical model is used to evaluate the effect of several involving parameters on the system performance. The optimum system parameters are determined, and the annual simulation of the optimum system is performed. The results show that condenser inlet velocity is the most influential parameter on daily water yield and Gain Output Ratio (GOR). The GOR of the system with the maximum daily water yield is very low. However, despite having 60% less daily water yield, the proposed optimum system has a 1120 % higher GOR. Moreover, it is demonstrated that about 40% of vapor produced in the humidifier leaves the condenser without being condensed into freshwater. Therefore, it is recommended that the system be designed as a closed cycle.

A thermal performance-enhancing strategy of photovoltaic thermal systems by applying surface area partially covered by solar cells

In this work, a single unit called photovoltaic thermal with solar thermal collector enhancer has been developed, whose absorber plate is partially covered by photovoltaic cells. This design increases the photothermal energy conversion ratio and absorbed energy by the system, resulting in a higher thermal power, thermal exergy, and outflow temperature compared to a conventional photovoltaic thermal module. This research examines the impacts of different glazing arrangements on the system performance using a three-dimensional transient model to determine the most efficient design from energy and exergy viewpoints. Moreover, the effects of various parameters on system performance, such as tilt angle, azimuth angle, mass flow rate, and dust accumulation on the system surface, are discussed. Finally, a comparative study between the proposed system, the standalone solar thermal collector, and the standalone photovoltaic thermal system is carried out in terms of energy, exergy, and economics. Results indicate that the proposed system has 31.24 % greater overall power and 35.07 % shorter payback time than a conventional standalone unglazed photovoltaic thermal system when only its solar collector enhancer part is covered by glass.

Numerical investigation on the performance and vapor injection process of a scroll compressor with different injection features

Using the vapor injection scroll compressor in heat pump systems for electric vehicles is one of the promising solutions for promoting the driving range in extremely cold climates. In this paper, a three-dimensional transient simulation model of the vapor injection scroll compressor with different injection features, including injection positions, shapes, and inclinations, is established and verified with a deviation within 8 %. And the influence of the injection flow on the internal flow field and the performance of the scroll compressor is the key problem to be studied. The results show that when the injection port gets closer to the discharge port, the increment of isentropic efficiency and the decrement of discharge temperature increase, and the maximum values can reach 6.7 % and 11.3 K, respectively. From the results of the flow field distribution, the heat aggregation is observed at the internal engaging point, and a shock pressure and two vortexes occur at the bottom of the orbiting scroll as the injection flow rushes into the working chamber, which may bring the operational stability of orbiting scroll and leakage troubles. The heat aggregation is weakened with a smaller injection inclination. Shock pressure gets smaller from single-circle injection port to waist and from the injection inclinations of 90° to 30°, with a reduction of 9.5 % and 26 % respectively. Overall, a vapor injection scroll compressor using a waist-shaped injection port with an injection inclination of 60° is recommended, which shows a better comprehensive effect.

Numerical study on free-spinning performance of oscillating water column Wells turbine in reciprocating airflows

The axial-flow Wells turbine is one of the most widely used air turbines in oscillating water column wave energy converters. By Wells turbine, we mean a reaction air turbine developed by A. A. Wells of Queen's University Belfast in the late 1970s. A comprehensive understanding of its free-spinning performance is crucial for determining control strategies for output power enhancement in practical engineering applications. In the present study, a three-dimensional (3D) transient model was established on an ANSYS-Fluent® platform to simulate the time-varying flow field and motion state of the rotor during the free-spinning process. After the model was validated with our experimental data, it was used to investigate the operation patterns in airflows with various profiles. The magnitude and phase features of the pressure difference and turbine torque were examined to identify the mechanism for overcoming the gradually ascending stage and maintaining dynamic equilibrium in the stable state. Additionally, the 3D flow-field details for several instants were demonstrated, including the severe vortex from the suction side in the post-stall region, strong tip leakage vortex downstream of the rotor, downstream helical strip vortex, and cyclic-asymmetric surface pressure distributions over the turbine. Furthermore, the effects of the cyclic volume flux on the free-spinning performance were investigated.

An efficient transient three-dimensional thermomechanical modeling of dynamic thermal stress building and releasing in a selective laser melting process

The selective laser melting (SLM) process involves irradiation from a high-power laser to melt and sinter powdered material. The high temperature gradient near the laser spot generates high residual stress that can lead to failure of fabricated parts. Estimation of the residual stress for real transient SLM processes by simulation involves considerable computation effort which makes its application in real industrial SLM processes rather difficult. To tackle this challenge, a two-stage coupled transient thermomechanical model with a quasi-transient heat source was developed. In the first stage, a transient thermal analysis was performed to acquire temperature distribution of the full SLM process. The temperature distribution serves as thermal loading input for subsequent transient thermal stress analysis. This quasi-transient thermomechanical model can provide residual stress data consistent with that of a conventional full transient model in 68% less computation time. The data provided by the new model also includes the dynamic stress release due to re-heating and re-melting in overlapped laser scanned regions which was in close confirmation with experimental results. This efficient quasi-transient model is useful for rapid analysis and optimization of SLM processing parameters.

Geometry effect of phase change material container on waste heat recovery enhancement

Waste heat recovery from industrial exhaust gases is a key method to reduce fuel consumption and improve system energy efficiency. Phase change materials (PCMs) are one of the major media in the waste heat storing and recovering processes. The PCM container geometry is a crucial design factor but attracts less attention for its effect on the PCM melting and heat storage operation. This study simulates the melting behaviour and heat storage performance in the PCM storage containers with the same cross area but different configurations with the rectangular shape and ones with concave folded sidewalls and protruding folded sidewalls. The geometry variation on PCM containers influences both the contact area with the hot airflow and natural convection in the melting phase of PCMs. The three-dimensional transient modelling indicates that the natural convection currents enhance the PCM melting and thermal storage rates. The PCM container design angle, α, shows a remarkable impact on the natural convection strength, PCM melting time, and energy storage rate. The protruding-shaped container with α at 133.8∘ presents the least melting time of 4,645 s, reducing 24.9% of the melting time in comparison to the rectangular chamber as the baseline with α= 90 ∘. The study can inspire the design of PCM storage geometries with efficient waste heat recovery in the industrial applications.

Thermo-fluid flow behavior of the IN718 molten pool in the laser directed energy deposition process under magnetic field

PurposeThis paper aims to understand the magnetohydrodynamics (MHD) mechanism in the molten pool under different modes of magnetic field. The comparison focuses on the Lorenz force excitation and its effect on the melt flow and solidification parameters, intending to obtain practical references for the design of magnetic field-assisted laser directed energy deposition (L-DED) equipment.Design/methodology/approachA three-dimensional transient multi-physical model, coupled with MHD and thermodynamic, was established. The dimension and microstructure of the molten pool under a 0T magnetic field was used as a benchmark for accuracy verification. The interaction between the melt flow and the Lorenz force is compared under a static magnetic field in the X-, Y- and Z-directions, and also an oscillating and alternating magnetic field.FindingsThe numerical results indicate that the chaotic fluctuation of melt flow trends to stable under the magnetostatic field, while a periodically oscillating melt flow could be obtained by applying a nonstatic magnetic field. The Y and Z directional applied magnetostatic field shows the effective damping effect, while the two nonstatic magnetic fields discussed in this paper have almost the same effect on melt flow. Since the heat transfer inside the molten pool is dominated by convection, the application of a magnetic field has a limited effect on the temperature gradient and solidification rate at the solidification interface due to the convection mode of melt flow is still Marangoni convection.Originality/valueThis work provided a deeper understanding of the interaction mechanism between the magnetic field and melt flow inside the molten pool, and provided practical references for magnetic field-assisted L-DED equipment design.

Numerical modeling for the mechanism of shoulder and pin features affecting thermal and material flow behavior in friction stir welding

A three-dimensional transient computational fluid dynamics model is developed to analyze the influence of rotational/non-rotational shoulder and pin characteristics on the thermal and material flow behavior in friction stir welded (FSW) aluminum alloy joints. Four tool designs with rotational/non-rotational shoulder and the pin with/without triple facets are considered. The heat cycle of the rotational and non-rotational shoulder friction stir welded joint (RS-FSW and NRS-FSW) is simulated and experimentally verified, and the welding temperature fields are analyzed. The welding peak temperature of the RS-FSWed joint is the highest, and the non-rotational shoulder significantly reduces the welding peak temperature and the range of the heat-affected zone (HAZ). The rotational shoulder promotes material flow and enhances flow velocity, whereas the non-rotational shoulder reduces both. An increase in the triple facets on the pin facilitates the material flow during NRS-FSW. Viscosity is a physical quantity associated with the welding temperature and strain rate, which is affected by the tool characteristics. The deformation zone caused by the tool is related to the viscosity of the material, the closer the tool, the lower the viscosity of the material. The viscosity of the material gradually increases with an increase in the distance from the tool surface.

MXene incorporated nanofluids for energy conversion performance augmentation of a concentrated photovoltaic/thermal solar collector

This research work introduces emerging two-dimensional (2D) MXene (Ti3C2) and Therminol55 oil-based mono and hybrid nanofluids for concentrated photovoltaic/thermal (CPV/T) solar systems. This study focuses on the experimental formulation, characterization of properties, and performance evaluation of the nanofluid-based CPV/T system. Thermo-physical (conductivity, viscosity, and rheology), optical (UV-vis and FT-IR), and stability (Zeta potential and TGA) properties of the formulated nanofluids are characterized at 0.025 wt.% to 0.125 wt.% concentrations of dispersed particles using experimental analysis. By suspending the nanomaterials, photo-thermal energy conversion is improved considerably, up to 85.98%. The thermal conductivity of pure oil is increased by adding Ti3C2 and CuO nanomaterials. The highest enhancements of up to 84.55% and 80.03% are observed for the TH-55/Ti3C2 and TH-55/Ti3C2 + CuO nanofluids, respectively. Furthermore, dynamic viscosity decreased dramatically over the temperature range investigated (25°C-105°C), and the nanofluid exhibited dominant Newtonian flow behavior as viscosity remained nearly constant up to a shear rate of 100 s−1. Numerical simulations of the experimentally evaluated nanofluids are performed to evaluate the effect on a CPV/T collector using a three-dimensional transient model. The numerical analysis revealed significant improvements in thermal and electrical energy conversion performance, as well as cooling effects. At a concentrated solar irradiance of 5000 W/m2 and an optimal flow rate of 3 L/min, the highest thermal and electrical energy conversion efficiency enhancements are found to be 12.8% and 2%, respectively.

Simulation and prediction of the temperature field of copper alloys fabricated by selective laser melting

In the selective laser melting (SLM) process, the experimental approach to determine the optimal process parameters is labor-intensive, material-intensive, and time-consuming. The use of simulation methods also requires more time support and higher hardware requirements. In this paper, a three-dimensional transient heat transfer model and a neural network optimization process parameter model in the process of preparing copper alloys by SLM are developed by combining finite element simulation methods with neural network prediction. The thermal behavior of the multitrack molten pools was investigated by ANSYS APDL, and the effects of different laser powers and scanning speeds on the temperature field and structure dimensions of the molten pools were discussed. The results show that the current single-track has a significant preheating effect on the unmachined single-track and a reheating effect on the machined single-track during the multitrack forming process. The laser power and scanning speed can be controlled to regulate the temperature, 3D size, and heat spread area of the molten pool to avoid over-melting and under-melting. The accuracy of the temperature field model was verified by single-track experiments. A neural network prediction model was constructed to predict the maximum temperature and size of the molten pool by optimizing the backpropagation neural network with a genetic algorithm, providing a methodological guide for the study of SLM process parameters.

Mini-channel liquid cooling system for large-sized lithium-ion battery packs by integrating step-allocated coolant scheme

• Three types of liquid cooling systems are explored for large-sized batteries. • The fully-covered cold plate enables a more even temperature distribution. • The cooling performance is seriously deteriorated for the battery packs. • The optimized approach employing the step-allocated coolant scheme is verified. To regulate the temperature spikes and temperature gradients of large-sized lithium-ion battery packs, the mini-channel liquid cooling systems are developed and numerically investigated in this study. Three design schemes are firstly analyzed and compared at the cell level based on a three-dimensional transient thermal model. It shows that design scheme 2 using the fully-covered cold plate and segmented centralized minichannels performs best. However, the cooling performance is seriously deteriorated at the module level. At the same flow rate of 2 × 10 −5 kg/s, the maximum surface temperature and temperature gradient increase from 34.79 °C and 4.12 °C to 49.61 °C and 14.34 °C when the cell number increases from N = 1 to N = 3. Finally, an optimized approach employing the step-allocated coolant scheme is conceived, with which the maximum surface temperature and the largest temperature difference of the 3S1P pack can be controlled at 33.38 °C and 4.56 °C over the 5C discharge process. The research results suggest that the mini-channel liquid cooling system integrating the step-allocated coolant scheme can be a new approach for the thermal management of large-sized battery packs.

Computational Fluid Dynamics Studies in the Drying of Industrial Clay Brick: The Effect of the Airflow Direction

The manufacture of ceramic brick goes through the stages of raw material extraction, clay homogenization, material conformation, drying and firing. Drying is the phase that needs greater care, as it involves removing part of the moisture from the brick, in order to preserve its quality after process. This work aims to predict heat and mass transfer in the drying of ceramic bricks in oven using computational fluid dynamics. Considering the constant thermophysical properties, a transient three-dimensional mathematical model was used to predict mass and energy transfer between the material and air during the process. Drying simulations at temperature of 100°C were performed with the air flow in the frontal direction to the ceramic brick holes and the results were compared with those obtained for the air flow in the perpendicular direction to the brick holes reported in the literature. It was found that the position of the brick in relation to the direction of air flow inside the oven affected directly the drying and heating kinetics, and the distribution of temperature and moisture content inside the brick. The positioning of the holes in the brick parallel to the direction of the air flow resulted in reduction at the drying time and, consequently, in energy savings in the process, more uniform drying, and improvement in the product quality.

Optimal Temperature Rise Control for a Large-Scale Vertical Quench Furnace System

An optimal switching heating control strategy based on minimum margin (OS-MM) is proposed for high efficiency, low energy consumption, and high-uniformity fine control in a large-scale vertical quench furnace. This work was stimulated by the need for solving the contradiction between the heating rate and temperature overshoot to achieve a rapid rise in temperature with no overshoot. Based on a three-dimensional (3-D) transient temperature field model of the quenching furnace, the temperature field optimization control problem is transformed into a boundary optimization control problem of rapid heating, whereby it is rigorously proved that the fastest rise in temperature is attained by the full-power heating, which satisfies the bang-bang characteristics. The key parameter that determines the overshoot in the full-power heating mode is introduced and defined as the minimum margin in the temperature-rising process. The analytical expression for solving the minimum margin is calculated by the eigenfunction expansion method and using the strong metal thermal inertia of the internal temperature field, the OS-MM method is designed to stop the heating in advance at a calculated switching point to optimize full-power heating, thus conserving energy by reducing its consumption. The results of simulation and industrial experiments show that this strategy greatly shortens the temperature adjusting time, significantly reduces energy consumption, and effectively improves the control performance indices, such as overshoot and static error in the temperature holding period of the thermal treatment process, as compared to the existing heating methods.

Mesoscopic simulation of surface morphology and thermodynamic mechanism during laser powder-bed fusing Ni-based composite: Underlying role of WC weight fraction

This study demonstrates the significant effect of the interfacial heat and mass transfer during laser powder-bed fusion (LPBF) of WC/Inconel 718 composite due to its different laser absorptivity. A transient three-dimensional mesoscopic model was developed to simulate the thermal fluid flow and resulting surface evolution of a set of laser-scanned surface with different WC weight fraction during LPBF were studied using both numerical and experimental approaches. The thermal fluid flow model predicts that the interfacial heat and mass transfer is enhanced with increased WC weight fraction below 20 wt%. The more heated liquid with a reduced viscosity is understood to produce an adequate spreading of liquid and to favor the sufficient migration of WC particles, thereby contributing to a lower surface roughness. Using a further elevated WC weight fraction has a high tendency to result in an excessive heat and mass transfer of high-temperature WC particles /molten liquid, in turn disturbing the melt flow and causing the hindering migration of WC particles within pool. This can lead to an insufficient spreading of liquid and migration of WC particles, indicating a severely weakened surface roughness. The results are validated against the experiments and the underlying evolution mechanism of surface quality during LPBF of WC/Inconel 718 composite is further discussed. The meso-scaled modeling methodology considering the interfacial thermodynamics of WC /liquid provides a good predictive capability for the laser-powder-reinforcements interaction behavior, porosity development, and surface evolution.

Failure mechanism tracing of the crankshaft for reciprocating High-Pressure plunger pump

Crankshaft fracture is a typical failure form of reciprocating high-pressure plunger pump. Different from traditional power machinery, the number of plungers in plunger pumps is usually odd, which leads to unbalanced radial force of the crankshaft and greatly increases the risk of failure. The crankshaft of a 250 kW high-pressure plunger pump was fractured, and the fracture morphology was river-shaped, which was a typical fatigue failure. To trace the failure of the crankshaft, a Constructure-Kinematics-Materials-Craftsmanship (CKMC) method was brought out. The microstructure of the damage zone was observed, and a three-dimensional transient finite element model was established to find the most dangerous zone and damage mechanism. The results show that high-cycle fatigue of fillet zone is the main reason for crankshaft fatigue failure. Material defects and lack of nitrided layer at fillet are the key factors to accelerate crankshaft failure. Finally, recommendations for preventing future failures were presented.

Evaluation of energy recovery potential of solar thermoelectric generators using a three-dimensional transient numerical model

The solar thermoelectric generator (STEG) is regarded as a promising energy conversion technology to convert solar heat into electricity. Considering the real solar irradiance, impedance matching, and interface contacts, a comprehensive three-dimensional transient thermal-electric numerical model for the STEG is established to evaluate its dynamic response and energy recovery potential. The transient performance prediction of the STEG during the whole daytime is completed for the first time. Due to the temperature limitation of thermoelectric materials, the allowable concentration ratio for the Bi2Te3-based STEG is 150 suns, corresponding to the average daytime output power of 13.16 W and the average daytime conversion efficiency of 6.15%. Dynamic responses of output voltage and conversion efficiency present the same changing trend as solar irradiance. However, the steady-state numerical model underestimates the output power by 6.91% and overestimates the conversion efficiency by 1.85%, due to the ignorance of thermal inertia during thermal diffusion. The established transient model can predict more reasonable results and is well verified via transient experiments. It is obtained that the STEG can produce 491.4 kJ of electricity a day and 49.79 kW h a year, and the theoretical cost-recovery cycle for the cost of the thermoelectric generator module is 1.61 years.

Fast computation of the Lorentz force induced by longitudinal electromagnetic stirring

In this work, we revisit a recent transient three-dimensional (3D) model for longitudinal electromagnetic stirring in the continuous casting of rectangular steel blooms. Whereas the earlier work was able to demonstrate accurate approximations to the solutions in two asymptotic limits, both of which gave economical alternatives to time-consuming 3D computations, here we show that the original governing equations can be manipulated to a form that allows for rapid computation even outside of these asymptotic limits. The resulting formulation requires the numerical solution of two steady-state complex Helmholtz-like equations in two dimensions that are coupled via a non-standard internal interface condition that is reminiscent of that occurring in the study of Marangoni convection; these equations are then solved numerically using the finite-element software Comsol Multiphysics. With this formulation, it is possible to compute the time-averaged Lorentz force components in a way that requires around four orders of magnitude less computational time than the fully 3D approach.

Investigation of 3D Transient Flow and Discharge Pressure Pulsation of Helical Roots Air Compressor for Hydrogen Fuel Cell Vehicle

The Roots air compressor has a great potential for air supply in a hydrogen fuel cell vehicle (HFCV) because of its high efficiency, reliable operation, and wide range of flow rates. However, pressure pulsation of the Roots compressor could causes early failure of components of a fuel cell system. In this paper, numerical and experimental investigation on the discharge pressure pulsation of a helical Roots compressor was presented. First, a three-dimensional transient computational fluid dynamics model was built to examine and evaluate the pressure fluctuation amplitude. Then, the influences of angle steps and rotating speed on the fluctuation amplitude of discharge pressure were explored based on the numerical model. Meanwhile, a test rig was carried out to investigate the performance of the air compressor. The maximal discrepancy between experiment and simulation was within 8%. Finally, the effect of the opening angle of the discharge port profile on pressure pulsation was studied. The results showed that the fluctuation amplitude decreased from 6.48% to 1.87% with the opening angle increasing from 77° to 90°. The distribution of velocity showed that the dominating vortexes gradually dissipated with the increase of opening angle, and consequently contributed to the attenuation of the pressure pulsation. It provides new guidance for the structural optimization design of Roots air compressor.

On the thermal performance enhancement of spiral-coil energy piles with a thermal recovery system

The pile foundation designed to ensure building stability when equipped with heat exchanger pipes to harvest geothermal energy is called an energy pile. Ground Source Heat Pump (GSHP) systems combined with energy piles have been used and developed as sustainable and efficient HVAC systems. Energy piles suffer from cold or heat accumulation in and around the pile, degrading their long-term performance. The current study seeks to alleviate this problem by proposing a thermal recovery system. The proposed system circulates ambient air in the pile foundation to extract the accumulated heat. A three-dimensional transient computational fluid dynamics model of the GSHP system coupled with the energy pile and the suggested recovery system is developed. This model is then used to investigate the effect of the various design parameters on the performance of the system and to determine the optimum system parameters. It is demonstrated that the maximum provided cooling load of the system with the proposed recovery system is 50% higher than the conventional system without the recovery. Moreover, the fifteen-year average COPannual of the system with double Ground-Air Heat Exchanger (GAHE) pipes and the system with one GAHE pipe is 30% and 16% more than the system without recovery.

Finite Element Study on Temperature Field of Underwater Dredging Devices via the Artificial Ground Freezing Method

Increased urbanization has led to undesirable increases in the discharge of refuse waste and pollutants in urban and rural rivers. Blockages and river pollution adversely affect navigation and aquatic ecosystems and cause flooding during the flood season. Regular riverbed dredging is essential to protect local ecosystems and maintain waterways’ health. However, the current dredging methods cause secondary pollution during dredging. This study examined a new river dredging method with a parametric analysis of its reliability for different construction environments. ADINA software solved the temperature field model using the finite element method to build a three-dimensional transient heat conduction model. The analysis determined the distribution and development of the temperature field during the freezing process and the effective dredging range of the frozen device. We compared thermal conductivities, specific heat capacities, freezing device sizes, initial ground temperatures, and brine cooling plans to examine the effect of the soil’s thermophysical properties and construction environment on the dredging area of the freezing device.