Three-dimensional Heat Transfer Research Articles

Performance evaluation on a novel split thermoelectric system driven by solar energy for electric vehicle seats

This paper proposed a novel split thermoelectric system coupled with a photovoltaic panel for electric vehicle seats. The system separates the hot and cold ends of the thermoelectric device over a long distance with the flexible intermediate conductor, which solves the problem of poor heat dissipation at the hot end resulted from the integration of traditional TEC with the vehicle seats and improves the cooling and heating performance. A three-dimensional heat transfer model was established by COMSOL software to study the temperature field and the comprehensive performance. The results demonstrate that the system can maintain the seat temperatures in 27–30 °C in summer and 18–25 °C in winter, and there exists an optimum input power to maximize the COP. In addition, the seat temperature can be reduced from 60 °C to 31 °C in just 20 min under maximum heating load. The system performance is closely linked to the structure of the middle conductors, heat dissipation, solar radiation intensity, and ambient temperature. In winter, the power consumption of the system is reduced by about 84 % compared to the positive temperature coefficient thermistor with the COP being increased by 5.17. The contribution of the photovoltaic panel based on the studied conditions can save about 215.26 kWh of energy per year, and increase the driving distance of electric vehicles by approximately 1435 km.

Three-dimensional heat transfer analysis of Hot Gas Torch (HGT)-assisted Automated Fiber Placement (AFP) for thermoplastic composites

Automated Fiber Placement (AFP) is a key additive manufacturing process for the production of complex composite structures. This study focuses on the in-situ AFP process for thermoplastic composites with Hot Gas Torch (HGT), which includes heating, consolidation, and solidification steps. Temperature control is critical to achieving high quality parts as it affects bond quality, crystallization, and solidification. However, previous studies have oversimplified convective heat transfer by assuming a constant coefficient, resulting in discrepancies between simulations and experiments. This paper introduces a novel distribution function to model the convective heat transfer coefficient, thereby improving temperature predictions. An optimization loop is used to determine the parameters of the function, which ensures agreement with experimental data. The proposed approach accurately predicts the temperature distribution, which is validated against unseen experimental results. By incorporating the distribution of the convective heat transfer coefficient, this study improves the understanding of heat transfer mechanisms in AFP for thermoplastic composites, leading to improved manufacturing processes and part quality.

Simulation and on-line monitoring using optical fiber Bragg grating sensors of temperature history during laser-assisted automated fiber placement

Automated fiber placement (AFP) in situ consolidation (ISC) of thermoplastic composite possess the potential to reduce manufacturing costs and improve manufacturing efficiency. The properties of composite manufactured by the ISC are affected by several mechanisms including polymer degradation, crystallization, intimate contact, polymer healing and void dynamics. All these mechanisms are directly affected by the temperature history. Consequently, the control and accurate measurement of temperature history during ISC are particularly important for improving the properties of composite. In this study, a simplified three-dimensional transient heat transfer model was established. The effect of tool temperature and placement speed on the temperature history and peak temperature were predicted. Simultaneously, an online temperature monitoring system was built and the optical Fiber Bragg Grating sensors (FBGS) was used to measure the temperature history. The results indicated that the predicted results of the model were consistent with the measured results, the error was below 8%. In addition, the temperature history of layers was significantly affected by the tool temperature and placement speed. The temperature of the layers decreased to near the tool temperature after cooling, and a higher tool temperature increasing its peak temperature because of the reduce of the cooling rate. On the contrary, an increase in placement speed will reduce the peak temperature of the layers.

Heat exchange performance of an energy-pile group in a hybrid GSHP system and effects of pile spacing

In long-term operations, seasonal imbalance in the thermal load may adversely affect the heat transfer performance of the energy piles, potentially resulting in thermal accumulation within the ground and eventual system failure. The heat transfer performance of energy pile systems during long-term operation under unbalanced thermal loads must be investigated. Moreover, the design parameters of energy piles are usually constrained by the requirements of foundation structural design, resulting in energy piles being densely arranged. Hence, the influence of pile spacing on the heat exchange performence of energy piles must be comprehensively understood. In this study, two- and three-dimensional energy-pile heat transfer models were established and innovatively coupled based on an engineering project currently under design. Numerical simulations were performed to investigate the heat transfer behavior of energy-pile groups subjected to unbalanced thermal loads and the effect of pile spacing on their heat exchange performance. Furthermore, design recommendations regarding the determination of the proportion of thermal loads to be borne by the energy piles in a hybrid GSHP system were provided. The results indicate that the proposed 2D-3D coupled modeling approach is able to simulate the heat exchange performance of large-scale energy pile groups. Pile spacing considerably affects the long-term thermal performance of energy-pile groups, especially in cases with small pile spacings. The influence of pile spacing on the heat exchange capacity of energy piles can be considered in the design phase by incorporating a group effect coefficient η, which are calculated to be 0.165, 0.470, 0.732, and 1 for pile spacings of 2 m, 4 m, 6 m, and 10 m, respectively.

Modeling of laser-assisted micro-milling Inconel718

Nickel-based superalloy Inconel718 is a typical difficult-to-machine material with the characteristic of high strength and hardness. Demands for micro parts of nickel-based superalloy Inconel718 are growing in aerospace, biomedical and other fields. Laser-assisted micro-milling (LAMM) can realize precision machining of the workpiece because of its lower cutting force. However, the machining mechanism and the change law of cutting force during LAMM of nickel-based superalloy Inconel718 are still unclear. There is a crucial need for modeling of LAMM Inconel718. This paper explores LAMM of nickel-based superalloy Inconel718 and realizes the simulation of LAMM process. A three-dimensional transient heat transfer finite element (FE) model is established to predict the temperature distribution of a Gaussian heat source in LAMM. Multiple sets of simulations of laser pre-heating with various laser power are conducted to analyze the temperature fields of workpiece and determine the appropriate laser parameters. A novel 3D model of the full machining process of LAMM Inconel 718 is constructed by ABAQUS with multi-subroutine, a fully coupled thermal-mechanical process is achieved. A modified Johnson-Cook constitutive model is used to reflect the size effect and flow stress of LAMM Inconel 718. Finally, the validity of the models is verified by experiments. Based on the verified model, the appropriate laser pre-heating parameters are obtained, and the prediction of cutting forces of LAMM Inconel718 is achieved.

Optimization study on acid condensation and anti-corrosion performance of 3-D finned tube heat exchangers

Low-temperature acid corrosion on flue gas heat exchanger surfaces seriously reduces the stability, safety, and economy of equipment operation. Efficient strategies are urgently required to improve the anti-corrosion performance of heat exchangers. In present paper, a three-dimensional heat and mass transfer model integrating the acid dew point, acid condensation rate, and solution concentration was developed to predict the corrosion characteristics on the surfaces of 3-D finned tube heat exchangers. Firstly, a comparative analysis of acid condensate characteristics for 3-D finned tubes with different configurations was performed. The results showed that the elliptical tube effectively improves the distribution uniformity of acid condensate rate and promotes anti-corrosion performance. Then, the effects of five operating parameters (gas temperature, gas velocity, water vapor concentration, acid vapor concentration and wall temperature) on overall corrosion characteristics were systematically examined in terms of acid dew point, condensation rate and solution concentration using single-factor and orthogonal analysis, and the effect order of each factor was determined. Furthermore, optimization analysis of anti-corrosion performance was conducted based on the orthogonal results, and the optimum working conditions (water vapor concentration below 11.8% and wall temperature of 347 K to 355 K) are recommended. This research can provide theoretical guidance for the anti-corrosion designation and optimization of 3-D finned tube exchangers.

A combined experimental and numerical approach for heat transfer enhancement in a minichannel using half rectified pulsating flows

The miniaturization of electronic packages and their associated high-power density circuits requires more innovative cooling solutions. Single phase pulsating flows offer a promising solution due to their disruption of the thermal boundary layer. This study aims to bridge the knowledge gap by using experimental and computational methods to investigate the complex flow characteristics of laminar pulsating flows in a heated rectangular minichannel and couple that analysis with an investigation of thermal-hydraulic performance. Experimental analysis involves a uniformly heated thin foil approximating a constant heat flux bottom wall. Wall temperature measurements are recorded using an infrared thermography system. Analogous to the experimental conditions, a three-dimensional conjugate heat transfer computational model is developed with a volumetric heat generation source. Positive and negative half rectified sinusoidal pulsating flow waveforms are studied for dimensionless pulsation frequencies or Womersley numbers of Wo = 2.5 and 5.1 at a fixed flow rate amplitude A 0 = 3. For the positive half rectified waveform, a marginal enhancement in heat transfer of 2.2% for Wo = 2.5, A 0 = 3 was obtained. Whereas the negative half rectified case leads to a heat transfer enhancement of 9% and 6% for Wo = 2.5 and Wo = 5.1 respectively, with a high thermal performance of η = 2.4 over corresponding steady flow.

Insulation performance evaluation of stone-finished exterior insulation systems with insulation frames for green remodeling of concrete exterior walls

This study aimed to evaluate the thermal bridge reduction effect of insulation frames applied to a stone-finished exterior insulation system, which is commonly used in green remodeling projects. The insulation performance of the exterior walls and the energy performance of the building in a baseline case in which an existing steel pipe frame was applied were compared with those in cases alt 1 and alt 2, which included application of double- and single-wired truss-shaped insulation frames, respectively. First, a three-dimensional steady-state heat transfer simulation was conducted for the exterior wall-floor joint of the model building, and the effective U-factor was obtained. Next, mock-ups were constructed and the U-factor was tested to verify the insulation performance of cases alt 1 and alt 2. The heat loss decreased as the effective U-factors of alt 1 and alt 2 decreased by 19.0 % and 19.7 %, respectively, compared to the baseline case, according to the heat transfer simulations. In the mock-up test, the U-factors of alt 1 and alt 2 were similar to design U-factor, indicating almost no heat loss caused by the thermal bridges. Notably, the U-factor of alt 2 was 2.4 % lower than that of alt 1. Finally the energy performance of the entire building was compared through dynamic building energy simulations by reflecting the thermal bridging effect. The annual heating and cooling energy use of alt 1 and alt 2 were 2.5 % and 2.6 % lower than those of the baseline case, respectively, confirming the energy-saving effect of reducing thermal bridges.

Application of CNTs/H2O nanofluid and the wavy fin with dimples in thermal management of CPU: A numerical modeling of hybrid passive cooling

A study was conducted utilizing computational fluid dynamics (CFD) to explore a novel cooling technique for the central processing unit (CPU), involving the use of carbon nanotubes (CNTs)/H2O nanofluid-fin heat sinks with dimples. Different fin heat sink designs with varying dimple arrangements were created using AutoCAD software. The three-dimensional flow, heat transfer, and mass transfer of the nanofluid within the liquid block were simulated using a finite volume-based CFD code. The study investigated the influence of different nanoparticle concentrations and dimple arrangements on cooling performance, heat transfer coefficient, pumping power, and thermal efficiency. The results revealed that the maximum temperature reduction on the CPU's top surface was approximately 13.1 K for multi-walled carbon nanotube/H2O nanofluids and 14.34 K for single-walled carbon nanotube (SWCNT)/H2O nanofluids. The best thermal efficiencies were achieved using SWCNT (2%)/H2O with three rows of dimples on each fin, resulting in an 8.5% improvement in heat sink performance at Re = 1,500 and an 8.8% improvement at Re = 2,000 compared to fins without dimples. However, it was observed that increasing the number of dimples on the fins led to an increase in pressure drop within the liquid block, necessitating additional pumping power. The simulation results aligned well with earlier experimental data and numerical studies in terms of cooling and heat transfer.

A fast Bayesian parallel solution framework for large-scale parameter estimation of 3D inverse heat transfer problems

The inverse heat transfer problems (IHTP) have a wide range of applications in the engineering field. Bayesian methods using Markov Chain Monte Carlo (MCMC) have long been considered as a robust and effective method for solving inverse problems. However, the discretization of the problem domain by the spatio-temporal Galerkin skill, i.e., the finite element interpolation also includes the time dimension, making the scale of the unknown parameters extremely difficult for Bayesian calculations. In this paper, a fast Bayesian parallel sampling (FBPS) framework is proposed for large-scale parameter estimation of benchmark three-dimensional inverse heat transfer problems (3D-IHTP). The FBPS we developed achieves a parameter computation scale of 105 magnitude within minutes, through dimensionality reduction of the space-time dependent problem domain. The Hamiltonian Monte Carlo (HMC) sampler, which is proven to be more efficient for high-dimensional parameter estimation, is employed. Through several simulation tests of IHTP, it was confirmed that the solving efficiency of FBPS surpasses that of the traditional Bayesian strategy significantly. Finally, FBPS is successfully developed to estimate the unknown heat flux on the chip heat sink and pack interface effectively, given some simulated high resolution measurement data. The reliability and efficiency show that FBPS has the potential to support efficient prediction techniques for a class of IHTPs in engineering applications.

A new set of explicit solutions for postbuckling behaviour of anisotropic shear deformable laminated cylindrical shells with general imperfection distribution and thermal loading

Thermal postbuckling analysis is presented for shear-deformable anisotropic laminated cylindrical shell with general imperfection distribution under several typical temperature fields are analyzed, including uniform temperature, tent-like linear distribution, axial and circumferential quadratic parabolic temperature fields over the shell surface and through the shell thickness. On this basis, the general temperature distribution can be obtained based on the three-dimensional steady-state heat transfer equation. At the same time, based on the high order shear deformation theory including anisotropic coupling effect, geometrically nonlinear large deflection displacement-strain relationship, the general initial geometric imperfections obtained by measurement and analytical means are introduced, and the thermal buckling equilibrium differential equation of anisotropic shear deformable laminated cylindrical shell with initial imperfections is established. A two-step perturbation-Galerkin integral method is used to obtain explicit solutions for the path development direction of post-thermal buckling equilibrium. The results of parameter analysis show that the material properties and temperature dependence, temperature distribution, lay-up and geometric parameters such as radius-to-thickness ratio have important effects on the thermal buckling load and postbuckling equilibrium path. The present method provides an effective theoretical prediction and analysis method for the design of the carrying capacity of submarine pipelines.

Numerical simulation of single-well enhanced geothermal power generation system based on discrete fracture model

This study proposes a single-well enhanced geothermal system (SEGS) to mitigate the high-risk of traditional Enhanced Geothermal Systems (ESGs) with two or more wells and enhance the general applicability. A detailed thermodynamic model that couples the wellbore, reservoir, and organic Rankine cycle is built. For the reservoir, a three-dimensional flow and heat transfer model featuring a discrete fracture network is employed. The effects of injection flow rate, injection temperature, branch well length, and branch well spacing on net output work, pump power consumption, thermal efficiency, and exergy efficiency have been investigated. The results indicate that an increase in the injection flow rate improves the shaft power of the expander and the power consumption of the injection pump. An optimal flow rate of 30 kg/s is identified, which maximizes the annual net power output to 1221.2 kW. Additionally, an increase in the injection temperature is found to enhance the buoyancy effect, thereby improving both thermal and exergy efficiency, and reducing the power consumption of the injection pump. The maximum net output power is achieved at an injection temperature of 60 °C. The study also notes that the branch well length has a negligible effect on thermal and exergy efficiency and expander shaft work. However, a longer branch well length contributes to a decrease in the power consumption of the injection pump and an increase in the net power output. Finally, it is observed that increasing the lateral well spacing slows the rate decay of the production temperature. A spacing of 360 m is found to yield a maximum annual net output power of 1259.4 kW. In conclusion, this study offers significant insights and practical guidance for the development and utilization of SEGS, demonstrating its potential as an effective alternative to conventional EGS methodologies.

Research on performance of new separated thermoelectric cooler at different pulse currents

This paper studies the performance of a novel split thermoelectric cooler under the different pulsed electrical currents. The investigation focuses on analyzing changes in the cold side temperature of thermoelectric cooler when subjected to different pulse forms. The three-dimensional heat transfer model established through COMSOL was used to investigate the new thermoelectric cooler. The study focused on analyzing the impacts of pulse amplitude, pulse period, pulse waveform, and heat dissipation conditions on the performance of split cooler. The results show that the cooling temperature of split component can be reduced by about 13 K at constant electrical current compared with the conventional component. The temperature of the separated component can be decreased by an additional 2–5 K through the application of pulsed current. The triangle pulse is the best choice for the split component under continuous pulse when the heat dissipation is insufficient. The split thermoelectric component can work more smoothly by using the slant drop triangle pulse compared with the optimized triangle pulse form. The performance of the split thermoelectric component is optimal under a square pulse when there is adequate heat dissipation.

A new semi-analytical model for studying the performance of deep U-shaped borehole heat exchangers

In deep geothermal exploitations, the U-shaped borehole heat exchanger (UBHE) has a longer fluid retention time and a larger contact area with the formation. In order to improve the utilization efficiency of geothermal energy, it is becoming increasingly important to accurately evaluate the performance of the deep UBHEs. In this study, the authors develop a new semi-analytical model for characterizing the heat transfer behavior of the deep UBHE geothermal system. In this developed model, the temperature change within the wellbore is numerically simulated by the finite difference method, whereas the temperature change between the formation and the wellbore is analytically simulated by the Green's-function. Besides, the non-uniform heat flux distribution along the horizontal section is considered to characterize three-dimensional heat transfer behaviors. By means of this model, the influences of developing strategies and well configurations on the outlet temperature and total thermal power are investigated. The calculation results indicate that the traditional assumption of uniform temperature along the horizontal section can induce significant errors in evaluating the performance of the UBHE geothermal systems; the horizontal section length is more conducive to improving the extraction performance in a shallower geothermal formation, and a longer horizontal section leads to a higher outlet fluid temperature, together with a larger total thermal power; a higher injection rate, as well as a lower injection fluid temperature, is more favorable for improving the total thermal power; an insulation casing with a length equaling the depth of injection point can lead to the maximum thermal power of the UBHE geothermal system.

Optimization design of a hybrid thermal runaway propagation mitigation system for power battery module using high-dimensional surrogate models

The demand for high energy density in lithium-ion battery packs for electric vehicles poses a challenge to maintaining its optimum operating temperature while reducing the risk of thermal runaway (TR) propagation. This study proposes a novel hybrid TR propagation mitigation system that balances heat transfer and thermal insulation requirements using low and high thermal conductivity phase change materials (PCM), heat pipes (HP), and air-cooling. The design and optimization of such a mitigation system are complex due to the many design parameters involved. The Adaptive-Kriging-High dimensional model representation (Adaptive-Kriging-HDMR) is used to establish a surrogate model of the system, and the sensitivity of the system's design parameters is evaluated with the maximum battery temperature and the system weight as the targets, thereby improving the efficiency of model calculation and reducing the dimension of optimization parameters. Then, the design of the sensitive parameters is optimized using an extended elitist non‐dominated sorting genetic algorithm (E-NSGA-II) multi-objective optimization algorithm. The results show that the modeling difficulty and optimization calculation time are significantly reduced by using a surrogate model. The calculation time for a single surrogate model only takes a few seconds instead of several hours for the original three-dimensional heat transfer and flow calculation. The thermal conductivity of high thermal conductivity-PCM, the distance between battery and low thermal conductivity-PCM, the battery spacing, and the HP length significantly affect the system. The optimized system substantially reduces the overall weight of the battery system while ensuring its good heat dissipation capability. In the case of TR in a single battery, the system succeeds in limiting the TR propagation to the same row, with the maximum battery temperature in the second row being only 64.3 °C, well below the battery TR trigger point. Under more severe conditions, such as TR occurring in two batteries simultaneously, the maximum battery temperature in the second row is 155.5 °C, and no TR spreads to the adjacent row. This study provides a rapid and effective method for designing a TR propagation mitigation system. It can serve as a reference for the engineering design and optimization of battery thermal management systems.

Enhancing unsteady heat transfer simulation in porous media through the application of convolutional neural networks

This research describes a novel technique for anticipating unstable heat transfer in porous media. Convolutional neural networks (CNNs) are used with finite volume method (FVM) and long short-term memory (LSTM) networks to accomplish this. Heat transport networks are difficult to characterise using traditional numerical methodologies owing to their nonlinearity and complexity. The proposed solution combines FVM’s precise physical modelling with CNN’s and LSTM’s superior pattern identification and temporal analysis. This collaboration supports the suggested strategy. Heat transport dynamics simulations in porous materials are more accurate, efficient, and adaptable when employing this hybrid framework. The experimental setup focused on porous material properties and gathered and processed a large amount of data. The building’s three-dimensional shape, heat transfer, and time were investigated. Temporal fluctuations were also used. Multiple indicators are used to evaluate the overall performance of the model. These criteria include convergence speed, F1 score, accuracy, precision, recall, and computational cost. In the most notable numerical results, the proposed strategy surpasses both the Finite Element and the Lattice Boltzmann methods. The presented method enabled fast convergence and reduced processing costs. These results were: accuracy (0.92), precision (0.93), recall (0.91), and F1 score (0.92). The proposed method is generalizable and adaptable, and it can address a variety of heat transport simulation problems in porous media. Unlike CNNs, which can identify significant spatial patterns, LSTM cells can only see temporal dynamics. These two components are required to show heat transfer, which is a continually changing phenomenon. Modern technology enables more complex simulations. Processing expenses are lowered, and estimations are more accurate. These two discoveries were obtained through the inquiry and methodologies. Finally, the CNN-FVM-LSTM technique simulates heat transport using complicated computer models. Predicting unusually high temperatures in porous materials may improve the model’s accuracy, computational efficiency, and flexibility.

Numerical investigation of three-dimensional natural convection heat transfer on corrugated plates of variable height

PurposeThe purpose of this study is to numerically investigate the geometric influence of different corrugation profiles (rectangular, trapezoidal and triangular) of varying heights on the flow and the natural convection heat transfer process over isothermal plates.Design/methodology/approachThis work is an extension and finalization of previous studies of the leading author. The numerical methodology was proposed and experimentally validated in previous studies. Using OpenFOAM® and other free and open-source numerical-computational tools, three-dimensional numerical models were built to simulate the flow and the natural convection heat transfer process over isothermal corrugation plates with variable and constant heights.FindingsThe influence of different geometric arrangements of corrugated plates on the flow and natural convection heat transfer over isothermal plates is investigated. The influence of the height ratio parameter, as well as the resulting concave and convex profiles, on the parameters average Nusselt number, corrected average Nusselt number and convective thermal efficiency gain, is analyzed. It is shown that the total convective heat transfer and the convective thermal efficiency gain increase with the increase of the height ratio. The numerical results confirm previous findings about the predominant effects on the predominant impact of increasing the heat transfer area on the thermal efficiency gain in corrugated surfaces, in contrast to the adverse effects caused on the flow. In corrugations with heights resulting in concave profiles, the geometry with triangular corrugations presented the highest total convection heat transfer, followed by trapezoidal and rectangular. For arrangements with the same area, it was demonstrated that corrugations of constant and variable height are approximately equivalent in terms of natural convection heat transfer.Practical implicationsThe results allowed a better understanding of the flow characteristics and the natural convection heat transfer process over isothermal plates with corrugations of variable height. The advantages of the surfaces studied in terms of increasing convective thermal efficiency were demonstrated, with the potential to be used in cooling systems exclusively by natural convection (or with reduced dependence on forced convection cooling systems), including in technological applications of microelectronics, robotics, internet of things (IoT), artificial intelligence, information technology, industry 4.0, etc.Originality/valueTo the best of the authors’ knowledge, the results presented are new in the scientific literature. Unlike previous studies conducted by the leading author, this analysis specifically analyzed the natural convection phenomenon over plates with variable-height corrugations. The obtained results will contribute to projects to improve and optimize natural convection cooling systems.

NUMERICAL STUDY FOR A THREE DIMENSIONAL LAMINAR NATURAL CONVECTION HEAT TRANSFER FROM AN ISOTHERMAL HEATED HORIZONTAL AND INCLINED SQUARE PLATE AND WITH A CIRCULAR HOLE

A theoretical study for a three-dimensional natural convection heat transfer from an isothermal horizontal , vertical and inclined heated square flat plates (with and without circular hole) has been done in the present work. The study involved the numerical solution of the transient Navier-Stokes and energy equations by using finite deference method (F.D.M.). The complete Navier-Stokes equation are transformed and expressed in terms of vorticity-vector potential. The Energy and Vorticity equations were solved by using an Alternating Direction Implicit (ADI) method because they are transient equations of parabolic portion, and the Vector potential is solved by using an equations Successive Over-Relaxation (S.O.R) method because it is from elliptic portion. The numerical solution is capable of calculating the Vector potential, three components of Vorticity and temperature field of the calculation domain. The numerical results were obtained in rang of Grashof number (103≤Gr≤5x104 ) with Prandtl number of (0.72) for square flat plate and the other consist a circle hole with ratio 0.6 and 0.8 diameter of the hole to main square side length. The numerical results showed that the main process of heat transfer is conduction for Grashof number less than 103 and convection for Grashof number larger than 103 and the results of local Nusselt number show fairly large dependence on inclination angle. For horizontal plate facing upward and downward, average Nusselt number is proportional to one-fifth power of Rayleigh number, and there is a significant difference in heat transfer rates between the upward and downward cases. For horizontal plate with circle hole facing upward for Grashof number 104 , the effect of core portion caused a limited increment in the heat transfer rate, where as for the facing downward case, the effect was larger and the maximum value of heat transfer rates is be for square flat plate with circle hole by ratio 0.6 for all inclination angles. With the increase of Grashof number to 5x104 heat transfer rates decrease except the square horizontal flat plate with circle hole by ratio 0.6 . The average Nusselt number increases with the increase of inclination of plates facing upward to reach to the higher average Nusselt number at vertical position then decrease with increase of inclination of plates. And the maximum value of average Nusselt number is depended on the ratio of diameter of the hole to main square side length, showed that the maximum temperature gradient occurs at the external edge of the horizontal plate (with and without circle hole) facing upward and at the lower external edge in inclined case. The numerical results was made through comparison with a previous numerical and experimental work, the agreement was good.

A hybrid approach towards evaluation of average heat transfer coefficient in twin-roll strip casting mold

Continuous casting stands out as one of the most efficient and productive methods for producing billets, slabs, or thin sheets while conserving energy. Understanding the solidification dynamics and achieving defect-free sheets in continuous casting necessitates the accurate prediction of heat transfer coefficient (HTC) at the mold metal interface. Accurate prediction of HTC helps in selecting process parameters such as superheat temperature and casting velocity, which directly affect the production rate and quality of the cast component. Determining the HTC is a complex process, as it is influenced by various process parameters such as casting size, casting speed, superheat temperature, surface roughness, type of water used as a coolant, nozzle design and wettability. Therefore, the present study proposed a hybrid approach for finding HTC in a twin roll strip casting mold through a solidified shell shape, which is influenced by the factors affecting the heat transfer at the mold-metal interface. This approach integrates the experimental and simulation investigations. The numerical investigation used a three-dimensional coupled fluid flow and heat transfer equations with an assumed range of HTC (100–2000 W/(m2K)). The solidified shell shape for different HTCs was compared with the experimental solidified shape form at the outer wall of the mold using the solidification criteria. Results indicate that the initial HTC range of 100–1000 W/(m2K) does not lead to blockage of the graphite mold outlet. However, as HTC values approach 1000 W/(m2K) to 1400 W/(m2K), the melt obstructs the mold exit based on solidification criteria. The HTC values (1350 ± 150 W/(m2K)) obtained from the proposed methodology for mold, align well with the HTC values (1183 ± 593 W/(m2K)) calculated using lamellar spacing of the Al-Mg2Si composite microstructure. This hybrid approach presents a novel and straightforward method for determining HTC, offering accurate predictions that can enhance the precision of continuous casting models and provide a more nuanced understanding of solidification behavior.

Development and preliminary verification of a 1D–3D coupled flow and heat transfer model of OTSG

Introduction: A simulation model was developed by coupling a one-dimensional (1D) system code and 3D CFD software, to analyze the three-dimensional (3D) flow and heat transfer characteristics of the once-through steam generator (OTSG).Methods: The shell side of the OTSG was simulated by FLUENT, and the tube side was simulated by the system code LOCUST. Through spatial mapping, the 1D and 3D simulations were coupled along the outer wall of the OTSG's helically coiled tubes.Results and Discussion: This coupling method enabled the acquisition of high-resolution flow and heat transfer characteristics of the OTSG, and the error of heat flux calculation result by the coupled model is within 15%. Through coupling simulation analysis of the prototype OTSG, it was found that the inlet and outlet temperature difference reached as high as 150°C. The unevenness of the radial temperature distribution increased along the flow direction, and the wake swing effect caused by the sweeping flow of the tube bundle at the exit position was evident. The results of this study provide reference and a coupled simulation method for the engineering design and thermal-hydraulic characteristics analysis of OTSG.