Temperature Boundary Research Articles

Computational micropolar model of hybrid nanofluid flow across a wedge

Non-Newtonian flow from wedges is a vital problem in coatings, polymer processing etc. Hence the main aim is to investigate the convective boundary layer flow of micropolar hybrid nanofluid (MHN)from a wedge. It is assumed that the wedge surface is isothermal. The Eringen model is employed to define micropolar fluid. Nanoscale Tiwari–Das formulations are used to study the specific effects of nanoparticles and volume fractions. The dimensionless boundary value problem arises by suitable coordinate transformations as a system of nonlinearly coupled ordinary differential equations. The so-called Falkner Skan flow case is resolved. Dimensionless, transformed, coupled momentum, microrotation, boundary layer equations are resolved using the numerical scheme MATLAB bvp4c. The parameteric investigations are performed on hybrid nanofluids using water as the basis liquid and varying volume fractions from 0 to 8%. Affirmation with previous work is done. The consequence of Eringen micropolar parameter, Hartree pressure gradient parameter, nanoparticle volume fraction, Eckert number, heat absorption (sink) parameter, on the flow and physical characteristics are visualized graphically and in tables. With rising material factor and volume fraction of nanoparticle, temperature is markedly enhanced. Increases in volume fraction dampen angular velocity close to the wedge surface, while farther from the wall, the opposite effect is seen. Temperature and thermal boundary layer thickness are both greatly enhanced by increasing Eckert number. With an increase in the volume proportion of nanoparticles, velocity decreases. Heat generation raises temperatures while a heat sink lowers them. The pressure gradient parameter increases skin friction while decreasing Nusselt number. Nusselt number for hybrid nanofluid is higher than for nanofluid.

Numerical study of uranium hexafluoride desublimation process based on Eulerian two-phase model

This paper presents a numerical study on the condensation process of uranium hexafluoride (UF6) in the supply and extraction system of a uranium enrichment plant. The numerical study was conducted using a standard UF6 receiving container with a nominal diameter of 127 mm and a volume of 8L under constant temperature boundary conditions. A phase change heat and mass transfer model for the desublimation process of uranium hexafluoride gas was established, and this model was combined with the Euler two fluid model to predict the distribution of key parameters such as temperature, pressure, and volume fraction of each phase during the UF6 cooling process, as well as the gas flow characteristics inside the container. In addition, this study also investigated the influence of various factors on the cooling rate. The research results indicated that UF6 gas initially condensed on the container wall and gradually diffused inward, with the highest solid density observed on the wall. Furthermore, increasing the inlet gas temperature, inlet mass flow rate, and reducing the cooling temperature, initial pressure inside the container could all enhance the desublimation rate to various degrees. The optimization plan proposed based on the above influencing factors could increase the yield of UF6 solid by 64.20% in 2 h, compared to the basic operating conditions.

Thermoelastic response of a finite thick annular disc with radiation-type conditions via time fractional-order effects

The study investigates thermal interactions in a two-dimensional time fractional-order thermoelastic problem in a homogeneous, isotropic, and perfectly conducting thick annular disc subjected to a point impulsive sectional heat source. We utilize unconventional integral transformation techniques to study the thermoelastic response of a disc, in which an internal heat source is generated according to the linear function of the temperature and radiation-type boundary conditions. The time fractional-order thermoelastic theory is used to determine temperature, displacement, and stresses through a series of Bessel functions. Numerical calculations analyze fractional-order parameters on aluminum discs, incorporating time-based fractional derivatives into field equations for practical engineering scenarios, enhancing thermal properties analysis.

A two-phase flow node-solid joint simulation algorithm based on heat flow correction

In order to accelerate the temperature field calculation of fuel and tank wall protective materials, we propose a node-solid joint simulation method based on heat flow correction, in which the gas–liquid is used as a node for joint CFD (Computational Fluid Dynamics) calculation of the solid temperature field. Based on this method, we constructed a transient thermal analysis model of the fuel tank and performed a gas–liquid–solid conjugate heat transfer tight coupling simulation to obtain the wall heat transfer coefficient and the corrected heat flux under the specified thermal boundary conditions. The results show that the maximum relative errors of the average temperature of the gas–liquid node and the temperature field of the tank wall are less than 0.2 % and 6 %, respectively, and the calculation efficiency is about 160 times that of the traditional tight coupling calculation. When the solid boundary temperature is reduced by 200 K and increased by 500 K, the maximum relative error between the average temperature of the gas–liquid node and the solid temperature is less than 7 %. The algorithm has good robustness and accelerates the iterative design of the fuel tank. The accuracy of the algorithm was verified by the fuel temperature test experiment of the full flight profile.

Research on effective thermal conductivity of hollow glass microspheres under vacuum at low temperature

As insulation materials with excellent thermal insulation properties, high robustness, and low maintenance costs, hollow glass microspheres (HGM) are gradually being applied in large liquid hydrogen storage tanks. However, the low-temperature insulation mechanism of HGMs is still unknown, and the insulation effect of HGMs of different types under various conditions has been neglected in recent decades. In this study, an existing theoretical model was improved by considering the gas thermal conductivity equations under various pressure intervals, and an experimental platform was built based on the steady vertical heat flux method to measure the effective thermal conductivities of three commercially available HGM models. The effective thermal conductivities of HGM models K1, T15, and HL20 at 0.1 Pa were 10, 8.9, and 7.6 mW/(m·K), respectively. The values decreased to 2.5, 2.9, and 2.0 mW/(m·K), respectively, when the cold boundary temperature was 90 K. To analyse the effect of the HGM physical parameters and environment on the HGM insulation, the thermal conductivities were calculated using the derived theoretical model. It was found that continuing to reduce the pressure after the ambient pressure reached 10 Pa hardly improved the insulation performances of the HGMs. The radiative heat transfer was very sensitive to temperature changes and jointly dominated the heat transfer with integrated thermal conductivity in the low-temperature region. In summary, HGMs are advanced vacuum-insensitive insulation materials, which have great potential in the field of cryogenic liquid storage and transportation.

Interval forecasting strategy of photovoltaic generation considering multi-factor self-fluctuation

Nowadays, interval forecasting is crucial for the power dispatching department because it can provide reliable boundaries of photovoltaic (PV) generation. However, few countermeasures are proposed to avoid the multi-factor self-fluctuation involved in the forecasting. To enhance the credibility of PV interval forecasting, this paper mainly conducts the following research around two factors “temperature” and “solar irradiance”: 1. Considering the periodicity of temperature data, an interval forecasting strategy based on auto-regressive integrated moving average model (ARIMA) and Bootstrap algorithms is designed to obtain its fluctuation range. 2. For solar irradiance data, considering it has temporal and non-temporal features, an interval forecasting strategy based on interval optimization and multi-extreme learning machine (ELM) is designed to obtain its fluctuation range; 3. Based on the obtained fluctuation boundaries of temperature and solar irradiance, the ELM is combined with the empirical mode decomposition (EMD) to complete error fitting and apply it to complete the interval forecasting of PV generation. Related case studies are presented in this paper. Finally, on the basis of ensuring the interval coverage requirement, we find the proposed method improves the forecast performance by 7.5 % compared to the existing methods at least, which will provide more reliable data for decision-making and management.

FDM-based alternating iterative algorithms for inverse BVPs in 2D steady-state anisotropic heat conduction with heat sources

In the framework of steady-state inhomogeneous anisotropic heat conduction with heat sources, we study the convergent and stable numerical reconstruction of the missing boundary conditions (temperatures and normal heat fluxes) on an inaccessible boundary and the thermal field in a 2D solid from the knowledge of over-prescribed data on an accessible portion of the boundary and temperature data on the remaining boundary. This inverse boundary value problem is approached by employing the alternating iterative algorithms of Kozlov et al. (1991), in conjunction with the standard finite-difference method and a novel modified one, for both exact and perturbed data. For noisy data available on the over-prescribed boundary, the numerical solution is retrieved by using three regularising/stabilising stopping criteria. Numerical results are presented for 2D simply and doubly connected domains bounded by a (piecewise) smooth curve, as well as exact and noisy boundary data, whilst appropriate errors in the fractional Sobolev spaces corresponding to the boundary temperatures and normal heat fluxes, respectively, are computed efficiently.

On the dual diffusion flow of Powell–Eyring hybrid nanofluid with motile microorganism and non-uniform heat source using Darcy–Forchheimer model

This communication elaborates the rheological behavior of bioconvection flow of Powell–Eyring hybrid nanofluid over a stretchable heated cylinder embedded in Darcy–Forchheimer porous medium. The single and two-phase nanofluid models are used as mixture model by taking volumetric friction and dual diffusion of injected nanomaterial’s, while the Buongiorno model takes the dual diffusion of nanomaterials, allowing us to evaluate the thermophoresis and Brownian diffusion properties. The governing equations are solved with an efficient Runge–Kutta–Fehlberg numerical technique. The effects of appropriate parameters on flow, temperature, concentration, and motile microorganism. Our findings reveal that the fluid velocity increases with curvature parameter, while detract with Darcy and porosity parameter. Temperature is increasing function of Brownian, thermophoresis and heat source parameters. The concentration and motile profile increases with curvature parameter. An escalating trend for energy and mass transport was seen against curvature and thermophoresis parameter. Higher values of Curvature and Schmidt number depict positive impact on nanoparticle concentration, while the results for chemical reaction are conflicting. An increasing value of Brownian and thermophoresis parameters promote higher temperature. The temperature and thermal boundary layer thickness are also affected by the heat source and sink parameters in opposite manner.

Numerical analysis of magnetohydrodynamic free stream and radiative heat transfer flow of nanofluid in a permeable medium over a linearly stretched cylinder with Arrhenius activation energy

This research article explores the transport characteristics of magnetohydrodynamic Newtonian nanofluid flowing past a stretching cylinder in a permeable medium, considering the activation energy effects using Buongiornos mathematical model. Unlike conventional studies employing constant temperature, concentration and density boundary conditions, convective boundary conditions are utilized in this investigation. The analysis incorporates various significant parameters such as magnetic field, joule heating, viscous dissipation, thermophoresis, Brownian motion, Arrhenius activation energy, and chemical reaction. The governing equations in the form of ODEs are obtained by employing similarity variables.The MATLAB built-in solver bvp4c is employed for obtaining the solutions. The impacts of these parameters on the velocity profile, temperature profile, concentration profile, density profile, skin friction coefficient, Sherwood number, and Nusselt number are elucidated through graphical and tabular representations. The results indicate that an increase in the chemical reaction parameter leads to higher nanoparticle concentration distributions, while the activation energy parameter exhibits the opposite trend. This study holds relevance for various practical applications in applied sciences, including nuclear reactor cooling, geothermal reservoirs, chemical engineering, and thermal oil recovery.

Experimental Study on Cold Start Strategies of Fuel Cell Stack: Sensitivity Analysis, Optimization, and Boundaries

The adaptability of fuel cell vehicles in low-temperature environments remains challenging for their commercialization owing to the propensity of water within the fuel cell to freeze during a cold start, which impedes gas transmission and subsequent reactions. Consequently, the initial water content before cold start and the heat and water generated during this process are crucial for achieving a successful cold start. In this study, current- and voltage-controlled starting strategies are analyzed using a stack comprising 20 cells with an area of 285 cm2. Furthermore, key parameters related to shut down purging and cold start are optimized using starting time and reverse polarity cell count as optimization objectives. The optimal conditions for cold start include a current density of 0.5 A cm−2, voltage of 0.45 V, purging time of 180 s, and stack temperature (during purging) of 60 °C. Furthermore, the ambient temperature boundary is determined as −25 °C–−30 °C for a successful cold start without auxiliary heating in the stack.

Coupled thermo-mechanical analysis of creep in a rotating FGMEE annular plate under complex thermal loading considering solar radiation, convection, and internal heat source

In this analysis, the creep responses of a non-constant thickness annular plate was presented. The material of disc is assumed functionally graded magneto-electro-elastic (FGMEE) in which the material properties change through the radius. Also, the heat transfer coefficients for convection and conduction are functions of radius and temperature. At first, the equation of heat transfer accounting for thermal gradient, convection boundary conditions, internal heat generation, and solar radiation effects was derived. The differential transformation method (DTM) was used to solve the resulting nonlinear differential equation. The equilibrium equation for the annular plate including creep strain effects was then obtained. Ignoring creep strains, an analytical solution was obtained for the zero-time of this equation. Then, creep strains were introduced using Norton's law and the Prandtl-Reuss relations to find the stress and strain rates under fixed temperature boundary conditions. Next, the equation of strain rates including creep strains was solved analytically. Finally, an iterative approach was used to evaluate the time-dependent redistribution of creep stresses at any time point. Numerical examples highlighted the influences of key parameters like internal heat generation, convective heat transfer, grading index, solar radiation, thickness profile, and angular speed on the stresses, deformations and electric and magnetic potentials.

Elucidating optimal nanohole structures for suppressing phonon transport in nanomeshes

Nanomeshes, often referred to as phononic crystals, have been extensively explored for their unique properties, including phonon coherence and ultralow thermal conductivity (κ). However, experimental demonstrations of phonon coherence are rare and indirect, often relying on comparison with numerical modeling. Notably, a significant aspect of phonon coherence, namely the disorder-induced reduction in κ observed in superlattices, has yet to be experimentally demonstrated. In this study, through atomistic modeling and spectral analysis, we systematically investigate and compare phonon transport behaviors in graphene nanomeshes, characterized by 1D line-like hole boundaries, and silicon nanomeshes, featuring 2D surface-like hole boundaries, while considering various forms of hole boundary roughness. Our findings highlight that to demonstrate a disorder-induced reduction in κ of nanomeshes, optimal conditions include low temperature, smooth and planar hole boundaries, and the utilization of thick films composed of 3D materials.

An Edge-based Interface Tracking (EBIT) method for multiphase flows with phase change

In this paper, the Edge-Based Interface Tracking (EBIT) method is extended to simulate multiphase flows with phase change. As a novel Front-Tracking method, the EBIT method binds interfacial markers to the Eulerian grid to achieve automatic parallelization. To include phase change effects, the energy equation for each phase is solved, with the temperature boundary condition at the interface sharply imposed. When using collocated grids, the cell-centered velocity is approximately projected. This will lead to unphysical oscillations in the presence of phase change, as the velocity will be discontinuous across the interface. It is demonstrated that this issue can be addressed by using the ghost fluid method, in which the ghost velocity is set according to the jump condition, thereby removing the discontinuity. A series of benchmark tests are performed to validate the present method. It is shown that the numerical results agree very well with the theoretical solutions and the experimental results.

Thermal-hydraulic phenomena and heat removal performance of a passive containment cooling system according to exit loss coefficient

The natural circulation system has been widely studied for use in various applications because of its inherent advantage. However, it has a key weakness called flow instability that makes the system unstable. Through massive previous research, the mechanisms of flow instability were analyzed, but there was an ambiguous aspect related to the effect of experimental parameters on the phenomenon. Particularly, there has been no report on the heat transfer performance of the system when flow instability phenomena were present. In this study, thermal-hydraulic phenomena of a two-phase natural circulation system that functions as a passive containment cooling system (PCCS) was investigated according to experimental parameters, namely, the temperature boundary (120–158 °C) and exit loss coefficient (0–34.5) under atmospheric pressure conditions. The experimental results showed five different flow types in the loop. The flow modes that occurred by the interaction between flashing and boiling were classified by referring to the mass flow rate, void fraction, and visualization data. The system was more unstable when the temperature boundary conditions increased, but it was more stable when the exit loss coefficient increased. These results have only been confirmed in our research. The reason for the results is that the flow conditions are located on the boundary between Density Wave Oscillation I and the stable flow region, and that boundary does not have clear criteria. In addition, comparing the heat transfer performance of a system by heat rate can confirm the effect of flow instability on the thermal performance of the passive cooling system. As a result, the high exit loss coefficient stabilizes the system better than the low case and has similar heat removal performance.

Flow and Heat Transfer Characteristics in the Entry and Stabilized Flow Regions of a Circular Channel Rotating About a Parallel Axis

Abstract Cooling of heavy-duty electrical machines such as generators and motors is crucial for the smooth operations without thermal runaway. A commonly employed technique for the cooling of rotors in these machines is to place channels at different radial locations for the continuous passage of coolant. These channels are therefore rotating about a parallel axis, and the rotation-induced forces alter the flow and thermal behavior of the coolant compared to stationary channels. The present study reports a detailed numerical investigation on a long circular channel rotating about a parallel axis. The objective is to analyze the flow, heat transfer, and rotation-induced forces (Coriolis and centrifugal forces) in the entry region as well as in the region where flow is stable (the term ‘stable’ is used rather than ‘developed’ due to the presence of secondary flows in this region). The rotating channel was subjected to constant wall heat flux and constant wall temperature conditions at different Rotation numbers of 0, 0.15, 0.4, and 0.6. The Coriolis force is observed to be strong enough in the entry region to influence the flow. In the “stable flow” region, the centrifugal force becomes more dominant and forms counter-rotating secondary vortex pair, which causes circumferential variation in the Nusselt number. The flow and heat transfer characteristics for constant wall heat flux and wall temperature boundaries are the same for rotation conditions with similar values of rotational Grashof number. A correlation is presented for the circumferential variation of the Nusselt number in the stable flow region.

Nanoparticle aggregation kinematics and nanofluid flow in convectively heated outer stationary and inner stretched coaxial cylinders: Influenced by linear, nonlinear, and quadratic thermal radiation

The consequence of nanoparticle aggregation and convective boundary condition on the nanofluid stream past the co-axial cylinder with radiation impact is investigated in the present examination. The influence of linear, nonlinear, and quadratic thermal radiation on the nanofluid flow is analyzed. The outer cylinder stays stable, while the inner cylinder deforms horizontally in the axial direction, allowing fluid to flow. By using similarity variables, the governing equations are transformed into ordinary differential equations (ODEs). Subsequently, the Runge–Kutta–Fehlberg fourth-fifth order (RKF-45) method is employed to solve the reduced ODEs. The upshot of several nondimensional terms on the temperature and velocity profiles is displayed with graphical representation. The comparison of linear, quadratic, and nonlinear thermal radiation on the thermal profile is illustrated. The upsurge in curvature parameter increases velocity and thermal profile. The increase in radiation parameter intensifies the temperature profile. The thermal profile improves with a rise in the values of radiation parameter. The radiation parameter generates thermal energy in the flow zone, which is why the temperature field has improved. The thermal Biot number exhibits an increasing response with temperature and thermal boundary layer thickness. The linear thermal radiation shows better heat transfer compared to quadratic and nonlinear thermal radiation.

Study on multidimensional frost heave characteristics and thermal-hydro-mechanical predictive model

The multi-dimensional estimation of frost heave deformation is crucial for predicting soil deformation and the pressure generated during the freezing process. This study offers a comprehensive review and analysis of frost heave characteristics in the heat flow direction and the transverse direction to it. Based on the frost heave test results, an innovative method for calculating the anisotropic parameter has been introduced. This method includes only two parameters: one reflects the more pronounced characteristic of frost heave in the direction of heat flow, and the other represents the sensitivity of anisotropic parameters to constraint stress. Through comparative analysis with experimental results, this method can effectively express the evolution of the anisotropic frost heave with changes of the confining stress in different directions. Then, a combined thermal-hydraulic-mechanical coupling model is established, offering a way of applying the improved model. The coupling model can predict significant frost heave under conditions of sufficient water supply and effectively captures the frost heave characteristics under various temperature and stress boundary conditions. This research contributes significantly to predicting frost heave deformation in low-temperature natural gas pipelines and calculating the frozen soil pressure exerted on the pipelines.

Impact of the Stefan gusting on a bioconvective nanofluid with the various slips over a rotating disc and a substance-responsive species

This paper presents thorough computational and theoretical analyses of steady forced convective flow over a rotating disc submerged in a water-based nanofluid containing microorganisms. It delves into the examination of boundary layer flow characteristics of a viscous nanofluid, considering Stefan blowing effects and multiple slip conditions influenced by a magnetic field. Notably, the study accounts for novel aspects such as thermal radiation and both constructive and destructive chemical reactions. The movement of nanoparticles is elucidated based on thermophoresis and microscopic behaviors, while changes in volume fraction do not affect the thermo-physical properties of the nanofluid. To address the altered nonlinear set of differential equations, an effective numerical approach, the Keller-Box method, is implemented for critical and efficient solutions. These appropriate transformations are defined and applied. When compared to blowing suction, it shows a better enhancement in the rate of heat transfer, mass, and microorganisms. Some of the main observations are there is a decrease in wall skin friction in the directions of radial and tangential as magnetic field strength is increased. The evaluation of thermal boundary layer thickness and temperature is noted for the radiation parameter (Rd) improvement. The present analysis has applications in electromagnetic micro-pumps and nanomechanics. As to the applications in the science and engineering fields, technologies such as micro-electromechanical systems-based microfluidic devices and microfluidic-related technologies will be accepted.

Assessing salinity hazards in coastal aquifers: implications of temperature boundary conditions on aquifer–ocean interaction

Investigating the repercussions of climate change and irrigation timing on groundwater contamination necessitates thorough examination of the fluctuations in seawater and groundwater recharge temperature. This study introduces an innovative numerical approach to analyze groundwater salinity and temperature dynamics across three distinct scenarios using the SEAWAT code based on Henry's problem. The first scenario delves into the impact of seawater temperature, the second focuses on the consequences of aquifer freshwater recharge temperature, and the third amalgamates the effects of both scenarios. Remarkably, the study reveals that saltwater intrusion (SWI) experiences a decline attributable to the aquifer's heightened seawater temperature and the diminished inland freshwater temperature. Furthermore, combining these two scenarios has a more pronounced effect on aquifer pollution; the temperature-induced changes in SWI for this third scanrio reach + 8.10%, + 12.70%, + 16.20%, + 24.90%, + 28.30%, and + 31.80% compared to the case without considering the temperature effect. Notably, our results propose a potential strategy to mitigate SWI by introducing cold freshwater recharge into aquifers, such as irrigation at night time when water temperature is low. This innovative approach underscores the interconnectedness of various environmental factors. It provides a practical avenue for proactive intervention in safeguarding groundwater quality against the adverse impacts of climate change and irrigation practices.

Dynamic prediction of high-temperature points in longwall gobs under a multi-field coupling framework

Spontaneous coal combustion (SCC) in longwall gobs is a serious disaster and requires prediction tools to accurately and reliably predict the temperature in gobs, but currently, there has been a lack of simple and efficient predictors. To address this issue, the temperature distributions in a longwall gob under different mining state parameters were simulated using a multi-fields coupled model. The temperature distribution and the mining state parameters were extracted to serve as input variables for prediction. Two machine learning models, integrating parameter optimization and ensemble learning strategies, respectively, were proposed to establish the functional relationships between the dynamic change boundary temperature and the maximum temperature in the gob. The results show that these two models have good prediction accuracy on the high-temperature points in longwall gobs, indicating that the ensemble learning has improved prediction accuracy. There is a positive correlation between the number of measuring points and the prediction accuracy, and three measurement points at the key locations can deliver reliable predictive performance.