Convective Flow Rate Research Articles

Predicting heat transfer rate and system entropy based on combining artificial neural network with numerical simulation

PurposeThe purpose of this paper is to present numerical simulations for magnetohydrodynamics natural convection of a nanofluid flow inside a cavity with an H-shaped obstacle based on combining artificial neural network (ANN) with the finite element method (FEM), and predict the heat transfer rate and system entropy.Design/methodology/approachThe enclosure is assumed to be inclined. Changing the inclination angle results in a different obstacle shape, which affects the buoyancy force. Hence, different configurations of the contours of the fluid flow, isotherms and the entropy of the system are obtained. The outer walls of the cavity as well as the central part of the obstacle are kept adiabatic. The left vertical portion of the hindrance is cooled, whereas the right vertical part of the obstacle is a heated wall. Using dimensionless variables allows obtaining a dimensionless version of the governing system of equations that is solved via the consistency FEM. The coupled problem of pressure and velocity is overcome via the Increment Pressure Correction Scheme, which is known for its accuracy and stability for similar simple problems. A numerical computation is performed across a broad range of the governing parameters. A total of 304 data sets were used in the development of an ANN model. That data set was conducted from the numerical simulations. The data set underwent optimization, with 70% sets used for training the model, 15% for validation and another 15% for the testing phase. The training of the network model used the Levenberg–Marquardt training algorithm.FindingsFrom the numerical simulations, it is concluded that the H-shaped obstacle boosts heat transfer rate in comparison with the I-shaped case. Also, raising the value of the inclination angle improves the entropy of the system presented by the Bejen number. Furthermore, strength heat transfer rate is obtained via decreasing the Hartmann number while this decrease decays the values of the Bejen number for both positive and negative amounts of the nonlinear Boussinesq parameter. Slower velocity and a better heat transfer rate characterize nanofluid compared with pure fluid. Leveraging the capabilities of the ANN, the developed model adeptly forecasts the values of both the average Nusselt and Bejen numbers with a high degree of accuracy.Originality/valueA novel fusion of FEM and ANN has been tailored to forecast the heat transfer rate and system entropy of MHD natural convective flow within an inclined cavity containing an H-shaped obstacle, amid various physical influences.

Solar radiation and heat sink impact on fluctuating mixed convective flow and heat rate of Darcian nanofluid: Applications in electronic cooling systems

One of the most effective techniques for electronic-cooling devices involves the use of nanofluid, a substance known for its superior heat transfer capabilities. The main challenge in modern production engineering lies in the efficient cooling of electronic devices. Nanofluids have attracted widespread interest in various technical fields due to their exceptional characteristics, which enable effective cooling of electronic devices while improving energy efficiency. In the field of electronic systems, engineers are exploring the potential of nanofluids in a range of applications and phenomena. Choosing the right heat transfer fluid to dissipate heat is crucial in managing electronic component temperatures. This study examines the effects of heat sinks and thermal radiation on the flow of Darcy-Forchheimer nanofluid over a vertical plate, with the aim of enhancing the thermal durability of electronic components. The governing mathematical model has been refined to accurately represent the physical coefficients. To develop a relevant algorithm in the FORTRAN environment, primitive variables are employed in steady-state and oscillatory models, nanomaterial and heat sink. Outputs are presented numerically and graphically using Tecplot 360, revealing that an increase in heat sink capacity leads to a reduction in surface temperature due to the heat sink's ability to absorb excess thermal energy. The use of porous Darcy-Forchheimer material is shown to lower the fluid temperature. The study also shows that the heat transfer rate decreases with an increase in the heat sink coefficient, and the oscillatory frequency of heat transfer reduces with a decrease in the Prandtl number. Decreasing behavior of heat transfer is depicted for maximum thermophoretic factor due to heat sink impact.

Magneto-double-diffusive natural convection and irreversibility analysis of a nanofluid flowing in an annular concentric space

In the present article, magneto-double-diffusive density driven convection accompanied by an entropy optimization analysis of Al2O3-water nanofluid filled in a horizontal coaxial annular space is numerically addressed. The double-diffusive natural nanofluid flow which is produced due to the maintaining of constant and different temperature and solute on the inner and outer cylinders is affected by a uniform vertical magnetic field. Dimensionless governed equations which are developed through law of conservation of mass, momentum, and energy are numerically solved via finite volume approach, and parametric control analysis is developed. By using Corcione empirical correlations considering the Brownian diffusion of 4% of Al2O3 nanoparticles in water, the thermal conductivity and viscosity of the mixture nanofluid are determined. Results are performed and interpreted in detail for wide range of relevant variables: Rayleigh (102 ≤ Ra ≤ 105), Hartmann (0 ≤ Ha ≤ 30), Lewis numbers (0 ≤ Le ≤ 10), and Buoyancy ratio (−4 ≤ N ≤ 4) to evaluate the double-diffusive convective nanofluid flow, heat and solute transfer rates as well as entropies produced in the system.

A newly designed BIPV system with enhanced passive cooling and ventilation

Nowadays, the application of renewable energies such as solar energy in the building sector has increased notably considering the adverse impacts of climate change on human life; hence many studies have focused on the application of photovoltaic panels in buildings. In the current study, a 3D computational fluid dynamics (CFD) model has been developed to evaluate the performance of a newly designed building-integrated photovoltaic (BIPV) system. Given the negative influence of overheating on the lifespan and performance of PV panels, their passive air cooling has been studied. Further, the potential of rooftop-mounted solar panels in passive ventilation of buildings by generating natural convective currents has been explored. The developed CFD model takes into consideration the effects of radiation, conduction, and buoyancy-driven natural convective currents generated by solar PV panels which are heated due to the exposure to solar radiation heat flux. The results suggest that applying a high surface emissivity for the part of the roof beneath the PV panels intensifies the natural convective currents which in turn provides better cooling for PV panels with higher cooling effects at higher solar heat fluxes. Up to a 34% increase in the convective mass flow rate and a 3 K decrease in the mean temperature of the panels were attained by modifying the emissivity of roof surface. Such a 3 K decrease in the operating temperature of the PV panels can enhance their efficiency and lifespan by about 1.56% and 21 %, respectively. Based on the operating conditions and system characteristics, the BIPV system yielded an air change rate (ACH) in the range of 3–13 which was considered to be highly prevalent in providing the required passive ventilation for a wide range of applications. It was also observed that the flow dynamics inside the building were affected by both the amount of solar heat load incident on the solar panels and the emissivity of the roof surface behind the panels.

Gas Production Potential in Geothermal-Energy-Enhanced CH4–CO2 Swapping Processes

Carbon capture and storage has become a practice to reduce the greenhouse effect of carbon dioxide (CO2) on the global climate. Recent studies have generated increasing concerns about CO2 leakage from underground structures. This has called for more research on CH4–CO2 swapping in natural gas hydrate (NGH) reservoirs to lock CO2 in a solid state in underground structures. Because the CH4–CO2 swapping is too slow to be efficient, this study proposes to use geothermal energy to accelerate the process. This paper presents a technical feasibility analysis of using geothermal energy to assist CH4–CO2 swapping for simultaneously storing CO2 in NGH reservoirs and producing the dissociated natural gas. Mathematical models were developed to compute heat transfer from geothermal zones to NGH reservoirs. A case study was carried out using the data from an NGH reservoir in the Shenhu area, Northern South China Sea. The result of the case study indicates that heat conduction dictates the heat transfer process when the heat convection flow rate is less than 0.01 m3/s over a heat-releasing borehole length of 2,000 m. Heat convection can significantly accelerate the heat transfer inside the gas hydrate reservoir. The 15°C (designed gas hydrate dissociation temperature in the studied case) heat front will propagate to the upper and lower boundaries of the gas hydrate reservoir (39 ft or 12 m) in 220 days by heat conduction only. This time can be shortened to 140 days with the aid of a fluid convection rate of 0.005 m3/s. Geothermal heating can significantly increase the initial productivity of wells in heated gas hydrate reservoirs in CO2 swapping processes. When the gas hydrate reservoir is heated from 6 to 16°C, the fold of increase is expected to exceed five in the studied case. This study shows that CH4–CO2 swapping process using geothermal stimulation is a promising method for producing natural gas and locking CO2 permanently in NGH reservoirs. Further studies should first focus on investigations of the effect of CO2-hydrate formation on the CO2 mass transfer inside reservoirs.

Reversed micellar-enhanced ultrafiltration removal of oil from concentrated phospholipids

The de-oiling of concentrated phospholipids through ultrafiltration (UF) enhanced by reversed micelles using a polyethersulfone (PES) membrane was examined. Phospholipids could form reversed micellar structures with larger molecular weights in non-polar solvents, which were significantly different from oils and solvents with smaller molecular weights confirming the feasibility of membrane separation. Under the conditions of membrane retentate molecular weight of 50 kDa, transmembrane pressure difference of 0.30 MPa, inlet crossflow velocity of 2.78 × 10−4 m·s−1, temperature of 333.15 K, phospholipid feed concentration of 26.12 kg·m−3% and cycle ratio of 20:1, the retentate phospholipid content and phospholipid yield were 84.97% and 96.4%, respectively, and the permeate flux was 4.65 × 10−6 m·s−1. Phospholipids increased the hydrophobicity of the membrane surface and promoted concentrated phospholipid de-oiling. Finally, a mathematical model was established based on the two-dimensional concentration polarization mechanism indicating that permeate flux was mainly controlled by the convective transfer flow rate.

Heat Transfer and Mixed Convection Flow of Non-Newtonian Thermo-Dependent Power Law Fluids with Thermal Radiation Effect

The current study explores numerically mixed convection of thermo-dependent power-law fluids in a square lid-driven enclosure, including the thermal radiation effect. The vertical sidewalls are sustained at both hot and cold temperatures. On the other hand, the cavity is insulated from the horizontal walls. The upper wall is moving along the x-axis. The main governing equations that the Boussinesq approximation is used for are solved using the finite difference method. The simulations focus on the effects of multiple pertinent parameters, including the Richardson number. (Ri = 0.1, 1, 10 and 100), thermal radiation parameter (Rd = 0 and 10), power-law index (0.6 ≤ n ≤ 1.4) and the Pearson number (0 ≤ m ≤ 6). The findings reveal that improving the Richardson number reduces heat transfer. Then, increasing Rd results in a domination of heat conduction for a fluid having a higher thermal conductivity. Also, the growth in the power law-index reduces heat transfer while improving convective flow. Finally, increasing the Pearson number improves the convective flow rate and also the average Nusselt number.

Effects of groove clearance size on gap bridging capacity in PWLBW of Ti6Al4V alloy sheet assembled in butt joint configuration: Numerical simulation and experimental assessment

In laser tailor-welding of metal sheets, it is difficult to keep the assembly clearance fixed due to plate specification deviation, tooling error, and thermal deformation. In this paper, the influence of clearance size on gap bridging capacity and in turn the seam appearance quality was investigated for thin Ti6Al4V alloy plates, configured by an improved pulse wave laser beam welding (PWLBW) scheme. The welding experiment and the numerical simulation were performed at 1.2 mm-thick workpieces assembled in a butt joint with a reserved clearance. With the clearance size enlarged from 0.2 mm to 0.4 mm, the gap bridging type changes from bilateral to unilateral, which results in the failure of the keyhole to rebound during the pulse interval, and causes an obvious reduction in metal bridge area at the cross-section. As the clearance increases further, a through-cavity geometry is generated between the weld spots and finally preserved within the solidified weld bead, indicating a poor overlapping effect. The dynamics of the weld pool, including thermal cycle, Marangoni convection, and molten metal flow rate are exquisitely sensitive to the change in clearance size. The clearance size during assembly and welding processes should be controlled below 0.4 mm to attain seam integrity, continuity, and sound tensile property.

Mathematical modeling of nano-particle transport in oil well cement cracks

Transport of nanoparticles (NPs) in fluids was analyzed in this study for sealing cement and micro-annuli fractures with nano-silica gels. Analytical models were developed to analyze NPs transport in cracks. The effects of gravitational, capillary, and viscous forces on NPs transport in oil well cement sheath cracks were investigated. It was found that the effect of gravitational force on the NPs transport in cracks is negligible owing to the small particle size. Gravity should not cause segregation of solid and liquid phases. Capillary force can induce spontaneous imbibition of nano-fluids that carries NPs into cement cracks. The imbibition rate is crack size-, fluid viscosity- and time-dependent. NPs can be effectively carried into cracks by viscous force. The viscous pressure gradients required for transporting NPs into the cement cracks are in the range between 0.04 psi/ft and 0.1 psi/ft at a convection flow rate of 1 gpm, depending on crack width and fluid viscosity. For a 500-ft long crack, the viscous pressure drop should be in a range from 20 psi to 50 psi, which is manageable in field operations.

A 3D Opened Hollow Photothermal Evaporator for Highly Efficient Solar Steam Generation

Herein, using hierarchical porous CuS–cellulose composite as photothermal materials, a 3D opened hollow photothermal evaporator is designed and fabricated to target high solar evaporation rates. Such a unique structure not only imparts the solar evaporator with an efficient water evaporation by minimizing energy loss, introducing cold evaporation surfaces for drawing additional energy from the bulk water and surrounding air, but also fully activates evaporation on both inner and outer evaporation surfaces, thus delivering superior evaporation rates compared to the enclosed evaporators. Moreover, under convective flow, this special structure effectively promotes the escape of vapor inside the evaporator to avoid the vapor accumulation, further enhancing the evaporation on inner evaporation surfaces, thus improving the evaporation rate up to11.911 kg m−2 h−1 under a convective flow rate of 4.0 m s−1 and 1.0 sun irradiation. The operability of the as‐prepared solar evaporator under natural environmental conditions is examined by outdoor evaporation tests. The obtained solar evaporator is demonstrated to be applicable for generating clean water from model seawater and dye wastewater. An impetus for promoting practical application of solar steam generation in seawater desalination and wastewater purification is provided.

Ultra-high evaporation rate 3D evaporator with vertical sheets based on full use of convection flow

Solar vapor generation technology is a promising strategy for clean energy-driven water treatments. The recently developed convection flow enhanced evaporator achieved a new breakthrough in the evaporation rate (over 10 kg m−2·h−1). However, the coupling of convection flow and evaporator is insufficient. The convection rate inside the evaporator is usually substantially lower than that outside, limiting the steam diffusion. In this study, a straightforward 3D evaporator with multi-vertical sheets was facilely obtained through 3D printing and assembly. The simulation results showed that the convection rate inside the evaporator is higher than that inside the inlet, and the humidity inside the evaporator is much lower than that inside the evaporator surface, resulting in enhanced vapor generation and diffusion. The ultra-high evaporation rate of 28.4 kg m−2·h−1 was finally achieved based on the full use of the convection flow. The correlation between convection flow and evaporation rate was linear, and the convection flow mechanism improving the evaporation rate was clarified. The cumulative mass change of the 3D evaporator in 8 h under an outdoor open system reached 70.7 kg m−2. The associated desalinated seawater ion concentrations met the standards for healthy drinking water.

Heat Transfer Model of Pneumatic End-Position Cylinder Cushioning

In this paper a thermal model of a pneumatic cylinder with an integrated pneumatic end cushioning is presented. Being a part of a multidomain model presented in former research, this model is needed to simulate and analyse the thermodynamic processes in the pneumatic end cushioning and to elaborate a novel design strategy for damping systems with a higher capability on kinetic energy absorption and robust performance under fluctuating operating conditions. For this purpose, a proper heat exchange model is inevitable to calculate the pressure in the cushioning volume and consequently the deceleration of the load. An approach of splitting the complex geometry of cylinder into simple geometries, such as plain or cylindrical surfaces, is used in this study for a fast computation of convective heat flow rates. To validate this approach, the simulation results were compared with the measurements, carried out at different supply pressures, piston speeds and end cushioning throttle openings. The model will be used further for sensitivity analysis and robust optimisation of the cushioning system design.

Numerical study on charging process inside a grid-structure thermal storage

Heat transfer enhancement in different engineering systems is a major challenge nowadays. Phase change materials can be used for this purpose due to moderate phase change temperature, great thermal capacity, and great latent melting energy. The melting process of phase change materials that can be used in the management and reserving solar energy has been studied numerically in various grided solar storages. The novelty of this research is a numerical analysis of the phase change process in a grid structure with different small cells having impermeable heat-conducting walls. The characteristic equations including continuity equation, motion, and energy equations were solved by the finite element method as the melting process was developing. The influence of grid sizes and thermal conductivity of the solid material of thermal storage partitions on the fluid flow and heat transfer performance was studied. The heat transfer rate in a thermal storage system filled with the phase change material depends on the grid sizes. Moreover, a growth of the abovementioned small cells filled with phase change material reflects a diminution of the convective flow rate and as a result, the charging time increases. At the same time, a reduction of the inner solid walls heat conductivity characterizes a significant raise of the system charging time. As a result, it is possible to find optimal structure of such a storage system with effective energy transport parameters.

Fractal analysis reveals functional unit of ventilation in the lung.

Ventilation is inhomogeneous in the lungs across species. It has been hypothesized that ventilation inhomogeneity is largely determined by the design of the airway branching network. Because exchange of gases at the alveolar barrier is more efficient when gas concentrations are evenly distributed at subacinar length scales, it is assumed that a 'functional unit' of ventilation exists within the lung periphery, where gas concentration becomes uniform. On the other hand, because the morphology of pulmonary airways and alveoli, and the distribution of inhaled fluorescent particles show self-similar fractal properties over a wide range of length scales, it has been predicted that fractal dimension of ventilation approaches unity within an internally homogeneous functional unit of ventilation. However, the existence of such a functional unit has never been demonstrated experimentally due to lack of in situ gas concentration measurements of sufficient spatial resolution in the periphery of a complex bifurcating network. Here, using energy-subtractive synchrotron radiation tomography, we measured the distribution of an inert gas (Xe) in the in vivo rabbit lung during Xe wash-in breathing manoeuvres. The effects of convective flow rate, diffusion and cardiac motion were also assessed. Fractal analysis of resulting gas concentration and tissue density maps revealed that fractal dimension was always smaller for Xe than for tissue density, and that only for the gas, a length scale existed where fractal dimension approached unity. The length scale where this occurred was seen to correspond to that of a rabbit acinus, the terminal structure comprising only alveolated airways. KEY POINTS: Gas ventilation is inhomogeneous in the lung of many species. However, it is not known down to what length scales this inhomogeneity persists. It is generally assumed that ventilation becomes homogeneous at subacinar length scales, beyond the spatial resolution of commonly available imaging techniques, hence this has not been demonstrated experimentally. Here we measured the distribution of inhaled Xe gas in the rabbit lung using synchrotron radiation energy-subtractive imaging and used fractal analysis to show that ventilation becomes internally uniform within regions about the size of rabbit lung acini.

Unsteady nonlinear mixed convective flow of nanofluid over a wedge: Buongiorno model

The article deals with 2D unsteady nanofluid flow past a vertical wedge along with nonlinear mixed convection. Brownian diffusion and thermophoresis effects are considered to model nanofluid flow. Convenient transformations are assumed to change the coupled nonlinear governing PDEs into ODEs. To analyze the problem, the solutions of transformed equations are numerically achieved via ‘bvp4c’, a MATLAB approach. Graphical presentation is adopted to see the impact of various influential parameters. Results reveal that nonlinear temperature and concentration convection parameters exhibit the same impact for velocity, temperature and concentration profile, though nonlinear convection parameter for temperature is more impactful than concentration. Velocity overshoot is observed for assisting flow situations. In nonlinear mixed convection flow, skin-friction coefficient, heat and mass transfer rates prominently change for favorable and adverse pressure gradient conditions.

Study on Heat Transfer Characteristics and Optimization of Spent Fuel Storage and Transportation Containers Based on Heat-Fluid-Solid Coupled Model for Radiation, Convection and Conduction

Based on the heat-fluid-solid coupled computational fluid dynamics (CFD) model for radiation,convection and conduction, this paper compares the changes in maximum temperature, natural convection flow rate, outer surface radiation and convection power of various parts under different storage status and ambient temperatures, with different packing media in the containers, and with or without annular fin. According to the study results, horizontal arrangement improves the convection heat transfer on the annular fin; each time the ambient temperature increases by 10 ℃, the fuel cladding temperature and outer wall surface temperature increase by 6.5 ℃ and 8.3℃, respectively; when the medium filling the fuel basket is changed from neutron absorption plate or aluminum block to helium, the overall heat transfer capacity of the container deteriorates dramatically, with the temperature inside the container increasing and the outer wall surface temperature remaining almost unchanged; with the solar radiation ignored, a annular fin will help improve convection heat transfer and thus decrease the overall temperature of the container, otherwise, the annular fin absorbs more solar energy, causing the overall temperature of the container to exceed that of a container with smooth wall; and the CFD radiation power is basically same as the calculation results gained in the formula method, as shown in the verification of the CFD radiation model based on the algebraic analysis method and diffuse gray surface model.

Onset of Linear and Nonlinear Thermosolutal Convection with Soret and Dufour Effects in a Porous Collector under a Uniform Magnetic Field

The present paper reports on an analytical and numerical study of combined Soret and Dufour effects on thermosolutal convection in a horizontal porous cavity saturated with an electrically conducting binary fluid under a magnetic field. The horizontal walls of the system are subject to vertical uniform fluxes of heat and mass, whereas the vertical walls are assumed to be adiabatic and impermeable. The main governing parameters of the problem are the Rayleigh, the Hartmann, the Soret, the Dufour and the Lewis numbers, the buoyancy ratio, the enclosure aspect ratio, and the normalized porosity of the porous medium. An asymptotic parallel flow approximation is applied to determine the onset of subcritical nonlinear convection. In addition, a linear stability analysis is performed to predict explicitly the thresholds for the onset of stationary, overstable and oscillatory convection, and the Hopf bifurcation as functions of the governing parameters. The combined effect of a magnetic field, Soret and Dufour parameters have a noticeable influence on the intensity of the convective flow, the heat and mass transfer rates, and the thresholds of linear convection. It is found that the imposition of a magnetic field delays the onset of convection and its intensification can lead to the total suppression of the convective currents. The heat transfer rate increases with the Dufour number and decreases with the Soret number and vice versa for the mass transfer rate.

Single-phase, natural circulation annular flow measurements for cartridge loop irradiation experiments

The nuclear industry is increasingly considering cartridge-style experiments for irradiation testing of advanced reactor fuels and materials under flowing conditions. Cartridge loops do not require the extensive support infrastructure that are necessary for external flow loops and minimize the possibility of coolant solidification over the long distance from the reactor to the external facilities. However, there is a general lack of quality flow data for internally heated fluids in an annular configuration representative of a cartridge-type irradiation experiment, particularly one with natural circulation. To address this data need, a series of experiments was conducted to measure the natural circulation flow rates of pressurized water in a sealed, internally heated vessel with annular flow conditions that represent a molten salt or sodium cartridge loop. Temperatures and flow rates were measured under steady-state and transient conditions. This paper describes the facility, methods, and results of the experiments, including the determination of nondimensional parameters. A simple 1D model of the natural convection flow rates agrees well with the experimental results. Applying this model to simulate a liquid salt cartridge experiment predicts that natural circulation flow might be able to provide liquid salt Reynolds numbers similar to those of some molten salt reactor concepts at relevant power densities.

Mixed convection–radiation in lid-driven cavities with nanofluids and time-dependent heat-generating body

The cooling process of electronic devices having heat-generating elements is a major challenge allowing to develop electronics industry. Therefore, a creation of novel cooling techniques is an important task that can be solved numerically taking into account the multiparametric character of this problem. The mixed convection heat transfer combined with thermal radiation in a lid-driven cavity filled with an alumina–water nanofluid under the effect of sinusoidal time-dependent heat-generating solid element is studied numerically. The partial differential equations formulated in stream function–vorticity variables are solved by the finite difference method. Effects of the Rayleigh number, Reynolds number, thermal radiation parameter, heater location, volumetric heat flux oscillation frequency and nanoparticles volume fraction on liquid flow and heat transfer are analyzed. It has been found that an addition of nanoparticles leads to reduction of the heater temperature, while convective flow rate decreases also.

Designing and Optimising the Parameters of Micro Channels

This paper documents the optimization of different parameters of micro channel heat sink which enhance the heat transfer. The objective is to find the major thermal resistance in micro channel and its effect on other parameters. Water is used as a coolant and the initial values of convective heat transfer coefficient and volume flow rate are 30000 W/m2K and 1 lpm respectively. Different graph are plotted between pressure drop,heat transfer co-efficient, pressure drop,thermal resistance and flow rate to finally achieve the optimized valus of channel width and height, hydraulic diameter, thermal resistance and pressure drop. The result achieved are in good agreement with the previous researches.