Fluid Inlet Velocity Research Articles

Numerical simulation of the calcium hydroxide/calcium oxide system dehydration reaction in a shell-tube reactor

The Ca(OH)2/CaO system is a promising candidate for thermochemical energy storage because of its high energy density, low cost and negligible heat loss. Coupling mechanisms of multiple physiochemical processes still need further investigation and the system performance should be further improved. In this work, for the first time, a three-dimensional numerical model is developed to study the thermochemical energy storage process by Ca(OH)2 dehydration reaction in a shell-tube reactor. The turbulent heat transfer fluid flow in the shell side, and the steam flow, heat transfer and dehydration reaction in the tube side are comprehensively taken into account. Effects of operation conditions and reactor geometry parameters on the dehydration process are also investigated in detail. Five indicators are proposed to comprehensively evaluate the reactor performance, including reaction time, energy storage density, heat exchange power, heat exchange efficiency and energy storage efficiency. The results reveal that higher inlet temperature and inlet velocity of heat transfer fluid can enhance the heat transfer and accelerate the reaction. Lower porosity, although increases the energy storage density, leads to higher flow resistance and impedes the reaction. With deep understanding of the physiochemical processes, 16 more tubes are properly added in the by-pass flow region, leading to shorter reaction time and higher energy storage amount. The low values of heat exchange efficiency and energy storage efficiency reveal that the input heat cannot be efficiently transferred to the tube side. To improve the energy conversion performance of reactor, additional schemes are discussed including regenerative HTF, optimization of reactor geometry, increase of reactant thermal conductivity, reducing tube-side flow resistance and extending HTF residence time. The numerical model and simulation results in the present work could be helpful for optimizing the shell-tube Ca(OH)2/CaO reactor and improving the thermochemical energy storage performance.

Computational simulations using a low density ratio-based kinetic theory of granular flow in subcritical water fluidized beds

Hydrodynamics of fluid and particles were simulated using a low density ratio-based kinetic theory of granular flow (KTGF) in subcritical water (SbW) fluidized beds (FB). Results indicated that the fluidization state of the SbW-particles mixture changes progressively from particulate to aggregative, indicating that a transitional state exists between aggregative and particulate fluidization. Wavy-like and churn-like flows were found along bed height in SbW FBs, unlike the homogeneous fluidization found in atmospheric water (AW) FBs and wispy-annular-like flow found in supercritical water (SCW) FBs. The predicted axial velocities and RMS fluctuating velocities of particles agreed approximately with measurements reported in the literature. The effect of fluid pressure and temperature, inlet fluid velocity and particle density on distributions of solid volume fractions and velocities were analyzed in SbW FBs.

Computational Analysis of Conventional and Helical Finned Shell and Tube Heat Exchanger Using ANSYS-CFD

The summary of the proposed work is to compare the rate of heat transfer, logarithmic mean temperature difference (LMTD) and effectiveness (ε) for a conventional shell and tube heat exchanger with and without helical finned surfaces on tube side of heat exchanger. It is shown that the inlet velocity of cold fluid at the tube side varies, while the inlet velocity of hot fluid at the shell side remains constant. The percentage variations of heat transfer rates with theoretical and simulation methods are compared. The geometry is modelled in ANSYS design modeler and analysis have been carried out in ANSYS-CFD. The inlet velocity of shell side hot fluid is varied in both types of heat exchangers. The proposed work is tested for two configurations of counter flow heat exchanger (conventional and helical finned surfaces) under different shell side inlet velocities of fluids. Helical finned tube heat exchanger with counter flow has a higher LMTD than a conventional counter flow heat exchanger. Variation in heat transfer rates and heat transfer coefficients were observed in heat exchanger influenced by shell side hot fluid velocity. The study shows that helical finned tube surfaces have improved heat transfer rates, LMTD, effectiveness (ε) and overall heat transfer coefficients compared to the conventional heat exchangers.

Enhancement of the charging and discharging performance of a vertical latent heat thermal energy storage unit via conical shell design

Adopting phase change materials (PCMs), the latent heat thermal energy storage (LHTES) technology provides a potential solution to solve the fluctuation and instability of solar energy utilization. However, its applicability is strictly limited by the poor thermal conductivity of PCM. In this study, a novel shell structure of the LHTES unit was designed and optimized to enhance the charging and discharging performance. Verified by experimental data, a three-dimensional computational model considering the effect of natural convection based on the enthalpy-porosity method is established to simulate the melting and solidification processes of PCM. The results reveal that the melting time decreases with the increase of R/r (the ratio of the upper radius to the lower one of LHTES unit) until a nearly constant value is reached, while the solidification time first decreases and then increases. An optimum conical shell design was obtained based on the summation of melting and solidification time, which is independent on the inlet velocity and temperature of the heat transfer fluid (HTF). Although the deviation of heat stored or released varies little among different designs, significant reduction in the charging and discharging time is observed for the LHTES unit with the optimum conical shell if compared with the cylindrical shell under the same heat transfer area and PCM usage.

Computational fluid dynamic modeling of methane hydrate formation in a subsea jumper

Gas hydrate in subsea pipelines is a serious flow assurance issue that may impose operational challenges to offshore petroleum production and transportation. The effects of fluid properties on hydrate formation in complex geometries such as jumpers are not fully understood. This study aims to assess hydrate formation in the jumper for the water-methane system using the Eulerian multiphase flow model through employing computational fluid dynamic (CFD) software (STAR CCM+). The numerical model is developed through consideration of transport phenomena equations, including conservation of mass, momentum, and energy in which mass transfer, hydrate reaction kinetics model, and heat of hydrate formation are incorporated in the multiphase flow equations in the form of source terms in the CFD software. In this study, first, the hydrate mass fraction for the fluid velocity of 5 m/s with an inlet temperature of 7 °C and a gas volume fraction of 0.2 is calculated. The sensitivity analysis is then performed considering the influences of changes in the inlet fluid velocity, gas volume fraction, inlet temperature, and subcooling on the hydrate formation. The results reveal that the developed CFD model is capable of predicting hydrate formation behaviors in the jumper with acceptable precision. An increase in the liquid inlet velocity and gas inlet temperature lowers the amount of hydrate formed in the jumper. In contrast, an increase in the subcooling and gas volume fraction leads to more hydrate formation. The proposed CFD model can be successfully used to simulate hydrate formation in pipelines under various process and thermodynamic conditions so that it can help to find reliable/effective methods for hydrate management.

Numerical Modelling of a Photovoltaic Thermal (PV/T) System Using Nanofluid With Parallel Flow Thermal Absorber

In the present study, a numerical model of photovoltaic thermal (PV/T) system using alumina (Al2O3) nanofluid, and pure water are used as working fluid. The proposed PV/T model consists of parallel riser tubes that are connected to two header tubes and it is attached to an absorber plate to simulate the conduction and convection heat transfer mechanism of a conventional PV/T system. The energy efficiency of the PV/T model is analyzed by varying the solar radiation (Heat Flux), inlet fluid velocity, and the volume percentage of the nanofluids. The numerical simulation is performed by using a conjugate heat transfer method with a computational fluid dynamics (CFD) software. According to the simulation data, the energy efficiency and the heat transfer coefficient of the PV/T system increased by increasing the inlet fluid velocity. In comparison with water, alumina nanofluid showed better thermal and electrical efficiency due to its high thermal conductivity. The thermal efficiency increased by 5.55% for alumina, compared to pure water and the electrical efficiency increased by 0.15% for alumina. Moreover, the effect of inlet fluid velocity ranging from 0.04m/s to 0.2m/s was also evaluated, and the results showed that the increase in thermal efficiency for pure water and alumina are 18.15% and 25.77%, respectively. Subsequently, the electrical efficiency increased by 0.52% and 0.56% for pure water and alumina using the new parallel flow thermal absorber, respectively.

Studies on performance enhancement of heat storage system with multiple phase change materials

This paper aims to improve the heat storage system's performance by using multiple phase change materials (PCMs). A heat storage device is designed with multiple PCMs firstly. The heat storage device consists of three identical shell-tube phase change thermal storage units. The numerical method is developed and verified experimentally. Two parameters, namely the latent heat utilization of PCM (ω) and the heat transfer effectiveness of heat storage device (ε), are introduced to evaluate the performance of energy storage and the heat exchange of the heat storage system with multiple PCMs. The effects of factors on ω and ε are studied, including the thermal conductivity, latent heat and melting temperature difference of PCMs, and the inlet velocity and temperature of heat transfer fluid. Results indicate that increasing the inlet velocity and temperature of HTF can greatly improve ω, but reduce ε. Increasing the thermal conductivity of PCM can obviously improve ω, but it has little effect on improving ε. Multiple PCMs with suitable melting temperature difference can improve both ω and ε. In practice, multiple PCMs can be associated with the above methods to improve the overall performance of the phase change thermal storage system. This research is used to optimize the design of phase change thermal storage device and improve its performance.

Recovery and effective utilization of waste heat from the exhaust of internal combustion engines for cooling applications using ANSYS

The exhaust gases from an internal combustion (IC) engine carry away about 75% of the heat energy which means only 25% of heat energy is operated for power production. A recovery unit at the exhaust outlet port can ensure heat exchange between different temperature fluids through conjugate heat transfer phenomena. This study represents heat recovery from exhaust gases that are emitted from IC engines which can be utilized in various applications such as vapor absorption refrigeration systems. In the present work, a new type of perforated fin heat exchanger for waste heat recovery of exhaust gases is designed using SolidWorks, and the flow field design of the heat recovery system is optimized using ANSYS software. Various parameters (velocity, pressure, temperature, and heat conduction) of hot and cold fluid have been analyzed. Inlet velocity of cold fluids including refrigerant (LiBr solution), water, and graphene oxide (GO) nanofluid have been adopted at 0.03 m/s, 0.165 m/s, and 0.3 m/s, respectively. Inlet velocity of hot fluid is taken as 2 m/s, 4 m/s, and 6 m/s, respectively, to develop a test matrix. The results showed that maximum temperature reduction by the exhaust is achieved at 104.8°C using graphene oxide nanofluids with an inlet velocity of 0.3 m/s and exit velocity of 2 m/s in the heat recovery unit. Similarly, temperature reduction by exhaust gases is acquired at 102 °C using water and 96.34 °C by using a refrigerant (LiBr solution) with the same exit velocity (2 m/ s). Furthermore, maximum effectiveness of 0.489 is also obtained for GO nanofluid when compared with water and the refrigerant. On the other hand, the refrigerant has the maximum log mean temperature difference from all fluids with a value of 224.4 followed by water and GO.

Effect of spatial porosity of metal foams on heat transfer filled in a vertical channel

This paper presents the numerical examination of the effect of spatial porosity variation of aluminum metal foams filled in a vertical channel. The physical domain comprises of a vertical channel in which aluminum plate cum heater assembly is placed at the center of the channel. The heat transfer from the aluminum plate is enhanced by using aluminum metal foams of different pore densities of 10, 20, 30, and 45 with varied porosities are considered in the present examination. A conjugate heat transfer analysis is carried out with the help of ANSYS FLUENT for a fluid inlet velocity of 0.1 – 1.5 m/s. The flow-through metal foam porous medium is predicted with the help of Darcy Extended Forchheimer model while heat transfer is predicted using the local thermal non-equilibrium model. The numerical methodology adopted in the current work is validated by comparing the present results with the literature. The hydrodynamic characteristics such as pressure drop and friction factor and thermal characteristics represented by Nusselt number, Colburn j factor, and overall performance factor are discussed in the present numerical investigation. The results of spatially varied porosity of metal foams are compared with uniform porosity metal foam. It is observed from the results that the spatial variation in porosity for the considered metal foam and the considered thickness of the channel does not significantly improve heat transfer but a slight decrease in pressure drop is observed compared to uniform porosity metal foam.

Application of the combined CFD and swarm intelligence for optimization of baffles number in a mixer-settler

Process optimization in a mixer-settler is of great importance. Optimization algorithm of particle swarm optimization is one of the evolutionary algorithms to solve optimization problem which is used in many fields. In this study, the optimal condition is calculated in finite volume method in terms of the number of baffles, inlet velocity of fluid, and impeller speed in a mixer-settler with a specific dimension that can be extended to industrial dimensions using the PSO algorithm and the numerical solution of Navier-Stokes equations and k-ε standard.

Simulation-based Study of Graphene-water Nanofluid flow through Microchannel Heatsink

This study presents a CFD analysis of the laminar flow of graphene-water nanofluid through a Silicon microchannel heatsink using commercial software ANSYS FLUENT. The microchannel has a rectangular cross-section of given dimensions, and the base of the heatsink is subjected to a constant heat flux. Simulations of the coolant flow are performed at different fluid inlet velocities for nanoparticle concentrations of 0%, 3% and 6% in the base fluid-Water. Results for temperature and pressure distributions in the microchannel heatsink are presented. The cooling performance of the MCHS improves significantly by increasing the flow velocity and enhancing the nanoparticle concentration in the coolant.

Investigation on the influence of capillary number on drainage in porous media using a lattice Boltzmann method

This work investigates the effect of the capillary number on the saturation of wetting and nonwetting phases during processes of drainage. A multicomponent Lattice Boltzmann model with a two-relaxation time scheme is used to simulate the flow in 2D and 3D digital models of porous rocks. The capillary number is varied by setting different values of the fluid inlet velocity, while viscosity and interfacial tension are fixed. The results show the invasion of nonwetting phase in the narrow pores of the media, forcing the wetting fluid to leave through the outlet. Different patterns are observed depending on the capillary number and the degree of porosity and heterogeneity of the models. Several pore-scale events are observed and play an important role in the trapping of wetting fluid. The nonwetting phase saturation is measured at breakthrough and quasi-steady states. In 2D models, the effect of the low velocity of the fluid at low Ca provides a better condition for fluid redistribution, causing a higher nonwetting fluid saturation. In 3D models, a lower value of Ca leads to more trapped wetting fluid mainly because of the media geometries. In all cases, the highest Ca range resulted in the highest nonwetting fluid saturation at a quasi-steady state. The saturation and relative permeability curves at the point of irreducible wetting phase saturation show that the degree of heterogeneity in 3D models has an important effect on sweeping effectiveness, which seems to be more significant than porosity or intrinsic permeability of the models.

Enhanced hydrogen storage of a LaNi5 based reactor by using phase change materials

Safe and efficient hydrogen storage technology is of great significance for large-scale hydrogen energy utilization. Using metal hydride (MH) materials such as LaNi5 for hydrogen storage is an effective way. In application, the heat and mass transfer characteristics in the reactor are one of the important factors and key problems affecting the hydrogen storage performance of MH. This paper proposes a novel hydrogen storage reactor installing a concentric finned tube heat exchanger and using phase change materials (PCM) by surrounding the reactor to improve heat transfer and hydrogen storage performance. A numerical model is built to describe transportation and reaction of two reactors with or without PCM. By comparison, the reactor surrounded by PCM has faster heat discharge and hydrogen absorption rate, and the absorption time is shortened by 50%. For the reactor with PCM, the optimal amount of PCM and the inlet velocity of heat transfer fluid (HTF) are investigated. The results show that the effective thermal conductivity of MH play a key role to improve heat transfer and reaction rate rather than that of PCM. Furthermore, increasing hydrogen supply pressure can effectively accelerate heat discharge and hydrogen absorption rate owning to larger temperature differences and improved reaction kinetics.

ANALISIS EFEKTIVITAS PENUKAR KALOR PIPA HELIKAL DESTILASI MINYAK ATSIRI KAYU PUTIH

The Eucalyptus plant is one of the essential oil-producing plants. Eucalyptus oil processing generally uses the distillation method. Traditionally used eucalyptus oil distillation uses a straight pipe condenser. The weakness of the straight pipe condenser is that the temperature of the condensate that comes out is still very high, this shows that the effectiveness of the straight pipe condenser is not optimal. To optimize the effectiveness of the distillation system condenser, a condenser with a helical pipe type condenser is designed in the essential oil distillation system. This study will vary the ratio of the pitch distance to the diameter of the condenser pipe, which aims to obtain an effective helical coil pitch ratio to optimize the effectiveness of the helical pipe condenser. This study uses the simulation method on COMSOL Multiphysics 5.4. The pitch ratio variant used is 2.1; 2.62; 3.15; 3.67; 4.2. The parameters that are constant in this study are the inlet fluid temperature on the tube side 373 K, the inlet fluid temperature on the shell side 288 K, the fluid inlet velocity on the tube side 0.2 m/s, and the fluid inlet velocity on the shell side 1 m/s. The results of the simulation by varying the pitch ratio show that the effectiveness increases as the pitch ratio value decreases, where the highest effectiveness is shown at pitch ratio of 2.1 which 75.9% and the lowest effectiveness is shown to pitch ratio of 4.2 which 70.7%.

Numerical study of a photovoltaic thermal (PV/T) system using mono and hybrid nanofluid

Photovoltaic thermal systems (PV/T) are system that simultaneously turn solar energy into electricity and thermal energy. Through the working fluids (water, ethylene glycol) used in the solar collector, PV/T systems aiming to reduce solar cell temperature come to the fore with increase in electrical efficiency. In recent years, the use of mono nanofluid with superior to heat transfer properties comparison conventional fluids as working fluid in photovoltaic thermal systems has become widespread. The main purpose of this study is to investigate the improvements in the use of hybrid and mono nanofluid on the performance of sheet and tubes based PV/T systems compared to water. In numerical analysis, different velocity inlet (0.02–0.08 m/s) of base fluid, CuO + Fe/water and CuO/water (50:50) are investigated via ANSYS Fluent 18.2 software. The three dimensional geometry used includes serpentine channel, absorber plate and solar cells to examine heat transfer mechanisms via conduction and convection. The results indicate that increase in inlet fluid velocity positively affects the thermal efficiency, but also increases pressure drop. However, there is no significant effect in terms of electrical efficiency. The increase after 0.06 m/s velocity gradually decrease and a more stable value is reached. The maximum increase of electrical and thermal efficiency for (φ = 2%) hybrid nanofluid is 2.14% and 5.4% comparison to water. While this value for mono nanofluid is 1.32% and 3.33%. Using hybrid nanofluid, the pressure drop was 214.78 Pa. As a consequence of the study, it is determined that the using hybrid nanofluid improves the PV/T system performance.

Nanoparticles shape effect on the efficiency of microheat sinks with tightly packed pin-fins

In this paper, the effects of the nanoparticles shape on thermal efficiency, entropy generation for the application of a /boehmite alumina nanofluid in a microheat sink (MHS) are studied. The MHS is composed of a number of microchannels, the walls of which consist of circular pin-fins attached together. A constant heat flux enters the HS from the bottom and heat it up. On the other hand, the nanofluid is responsible for cooling the HS. To study the thermal efficiency and entropy, a simulation using the control volume method has been performed in Fluent software. The effect of the NP size has been reported in this research. The simulation results showed that the average HS temperature strongly depends on the inlet fluid velocity, and an increase in the nanofluid velocity decreases it. Moreover, the addition of NPs reduces the average temperature of the HS, but its impact is smaller than that of the fluid velocity. Adding 5% of the cylindrical nanoparticles reduces the average temperature of the heatsink by 0.72 K. In addition, increasing the velocity and volume fraction of NPs decreases the thermal resistance () and increases the pumping power. The addition of 5% platelet-shaped nanoparticles increases the pumping power required by up to 80%. Using cylindrical NPs leads to the best temperature uniformity and least thermal resistance in the HS. Adding NPs decreases entropy generation. Application of blade NPs in high volume fractions, as well as brick NPs in average volume fractions, leads the highest Figure of Merit (FOM).

Numerical study of mixed convection of nanofluid inside an inlet/outlet inclined cavity under the effect of Brownian motion using Lattice Boltzmann Method (LBM)

In the present numerical study, the mixed convection of Cu-water and CuO-water nanofluids is modeled inside an inclined square-shaped cavity by utilizing the thermal model of the Lattice Boltzmann Method (LBM). A cold fluid flow enters into the cavity at the upper side of the left wall and, after being heated by the hot obstacle, exits from the lowest right side of the cavity The effective thermal conductivity and viscosity of nanofluids are computed by the KKL (Koo-Kleinstreuer-Li) equation. The results are presented in the constant Rayleigh number of 104 and the Richardson numbers of 0.1,1 and 10. Obtained results reveal that by incrementing Ri because of the augmentation of inlet fluid velocity from the left side, the gradient of isothermal lines decreases, and temperature distribution becomes more uniform, leading to Nusselt number reduction on hot wall. Although the Nuavg enhances considerably in Ri of 0.1, in Ri = 1 and 10, there is no sensible change. In the angle of 0o, by augmenting Ri, Nuavg decreases, but in the angle of 60o, by increasing Ri from 0.1 to 1, Nuavg increments up to 22%. This augmentation is due to the change of angle of the collision of flow with the hot obstacle. Furthermore, when the hot obstacle is located in the flow path, heat transfer improves. Application of such studies shows its importance in the design of electronic components cooling systems, solar energy storage, heat exchangers, and lubrication systems.

Computer simulation of the effect of particle stiffness coefficient on the particle-fluid flows

The Computational fluid dynamics (CFD)–discrete element method (DEM) numerical simulation may be applied to predict the hydrodynamic behavior of dense particle–fluid flows. The main drawback of this simulation is the long computational time required owing to the large number of particles and the minute time-step required to maintain a stable solution. In this work, a new method to improve the efficiency and accuracy of CFD–DEM simulations is presented. The particle stiffness coefficient is used as a flexible parameter to improve the accuracy and efficiency of the model. The particle concentration distribution results are compared with experimental one’s to derive the optimum effective stiffness coefficient of particles for CFD-DEM simulations. The comparisons of the results indicate that although the application of stiffness coefficients with moderate values causes normal penetration depths of up to the particle radius, the simulations still show good results. The results also show that the stiffness coefficient and time step are strongly dependent of the fluid inlet velocities, particle diameters, particle inlet concentration and fluid type, and the simulation accuracy decreases greatly with increasing the time steps.

Computational Analysis of Water-Submerged Jet Erosion

Erosion causes substantial damage in many industrial equipment such as pump components, valves, elbows, and plugged tees. In most cases, erosion is coupled with corrosion, resulting in major financial loss (nearly 3.4% of the global gross domestic product) as evidenced in oil and gas industries. In most cases, the erosion occurs in a submerged water medium. In this paper, erosion characteristics of stainless steel 316 were investigated computationally in a water-submerged jet impingement setup. The erosion profiles and patterns were obtained for various parameters over ranges of inlet velocities (3 to 16 m/s), nozzle diameters (5 to 10 mm), nozzle–target distances (5 to 20 mm), nozzle shapes (circular, elliptical, square, and rectangular), impingement angles (60° to 90°), and particle sizes (50 to 300 µm). The range of Reynolds number studied based on nozzle diameters is 21,000–120,000. The Eulerian–Lagrangian approach was used for flow field prediction and particle tracking considering one-way coupling for the particle–fluid interaction. The Finnie erosion model was implemented in ANSYS-Fluent 19.2 and used for erosion prediction. The computational model was validated against experimental data and the distributions of the erosion depth as well as the locations of the of maximum and minimum erosion points are well matched. As expected, the results indicate an increase in loss of material thickness with increasing jet velocity. Increasing the nozzle diameter caused a reduction in the maximum depth of eroded material due to decreasing the particle impact density. At a fixed fluid inlet velocity, the maximum thickness loss increases as the separation distance between the nozzle outlet and target increases, aspect ratio of nozzle shape decreases, and impingement angle increases. The erosion patterns showed that the region of substantial thickness loss increases as nozzle size/stand-off height increases and as particle size decreases. In addition, increasing the aspect ratio and impingement angle creates skewed erosion patterns.

Three-phase alternating current liquid metal vortex magnetohydrodynamic generator

SummaryMagnetohydrodynamic (MHD) generators directly convert mechanical energy to electrical energy. However, due to production of low amplitude voltages at low fluid velocities, they are not useful for electronic devices requiring power at watt scale. This work introduces vortex MHD, capable of producing voltages on scale of volts and generating power on a scale of watts. This is achieved by using Galinstan, a highly conductive metallic fluid, which remains liquid at room temperature. The proposed device comprises an impeller and set of copper coils positioned in a ferromagnetic housing. Three-phase AC current is passed in the coils producing a rotating magnetic field. The interaction of a moving conductive fluid and rotating magnetic field governed by Faraday's law of induction serves as a mechanism of electrical current generation. The study investigates the system performance and, in particular, variation of power with respect to system parameters like fluid inlet velocity and stator current.