Transient Heat Transfer Analysis Research Articles

Numerical Analysis of Transient Convective Heat Transfer in a Dental Implant

Hot substance consumption can have adverse effects on the neighbouring bone tissue in proximity to a dental implant. Elevated temperatures at the interface between the bone and implant could potentially disrupt the local cellular processes crucial for osteointegration. The primary goal of this study was to analyse the temperature and heat flux distributions within the implant body, surrounding bone, and bone-implant interface when the implant system subjected to a thermal load of transient nature. Transient thermal finite element analysis was utilised to analyse a three-dimensional model of dental implant with three different lengths – 6, 10, and 13 mm – placed in a mandible section. In order to obtain realistic results, thermal load was applied through convection on the outer surface of the prosthesis, simulating exposure to a hot liquid with the temperature and convection heat transfer coefficient of 67°C and 0.005 W/mm2°C, respectively. The temperature of the other components in the model was maintained at a constant 37°C. The results showed that increasing the implant length generally led to lower temperature and heat flux levels in the implant body, bone, and bone-implant interface. The highest temperature and heat flux values were concentrated in the superior region, gradually decreasing toward the inferior region. Importantly, all maximum temperature values remained below the limits associated with cellular bone necrosis and remodelling, thereby reducing the risk of osteoporosis. It is noteworthy that, when considering transient thermal load, shorter implants pose a significantly higher risk of implant failure compared to longer ones.

A new analytical model for transient heat transfer modeling of geothermal monotube heat exchangers

In this study, we present a new analytical model for the analysis of transient heat transfer (the model is solved after Laplace transformation) in geothermal monotube heat exchangers (GHE). The model accounts for various factors, including the heat exchanger's geometric parameters, the nature of the fluid (air and water), flow characteristics (laminar and turbulent), and heat transfer boundary conditions. Initially, the model's performance is validated by comparing its results with those obtained from computational fluid dynamics simulations using OpenFOAM. This validation process ensures the reliability and accuracy of the model. Additionally, an analysis of the heat transfer mechanisms and key modeling parameters identified from the comparison is provided. In the subsequent section, the analysis is extended by comparing the proposed model to four existing analytical models available in the literature. These reference models employ distinct approaches to simulate heat transfer to the ground. By examining a range of cases, the performance of the model is systematically evaluated against these conventional methods. This work closes by an analysis of the analytical models and the impact on the accuracy of the results highlighting the advantages of the proposed method in geothermal applications.

Transient Heat Transfer Analysis in Metal Plates with Variable Thickness

Nonlinear transient heat transfer via conduction–radiation is a dynamic topic of long-standing interest with applications ranging from aeronautical and mechanical engineering to industrial and civil security. To gain a better understanding of the performances of materials having thermal proprieties that change during nonlinear heat transfer, several studies using the finite element method (FEM) have been conducted. Such studies apply nonlinear thermal material characteristics to describe the complete system under different loading conditions in each region by adjusting the temperature values for the other three edges and the thickness parameter with Dirichlet boundary conditions. As a result, while modeling and simulating temperature distributions for such situations, nonlinearities generated by temperature-dependent thermal conductivity must be considered. In this work, we focus on the analysis of coupled transient heat transfer through two metal plates with temperature-dependent thermal characteristics in which the temperature is fixed along the bottom edge and heat is transferred from both the top and bottom faces of the two plates. FEM is employed to solve the nonlinear heat equation and compute the temperature as a function of time for variable thickness. The study examines the effect of modifying the thickness parameter values on the temperature distribution over time for various edge values over 5,000 s.

LES investigations of turbulent heat transfer structures with exponential power escalation

The BORAX-type accident is a key scenario in the safety design of pool-type experimental nuclear reactors. It considers a reactivity insertion large enough to initiate an exponential power escalation with a period as small as tens of milliseconds, necessitating effective heat removal by the coolant system. This study presents a computational analysis of single-phase transient heat transfer under thermal-hydraulic conditions relevant to such reactors, focusing on turbulent channel flow between planar fuel plates with highly subcooled water. Our investigation uses Large Eddy Simulation (LES) performed with TrioCFD, the open-source CFD code developed by the French Atomic Energy Commission (CEA). Several modeling options are tested: incompressible flow with temperature as a passive scalar, incompressible flow with varying viscosity, and quasicompressible flow with temperature-dependent viscosity and mass density. To evaluate the accuracy of our physical models, all simulations were performed under uniform conditions, using the same experimental parameters, mesh, and numerical strategies. The specific examined scenario involves a highly subcooled turbulent channel flow at moderate pressure, experiencing an exponential power increase. We ensure detailed turbulence resolution at the Batchelor scale in the wall normal direction close to the heating wall. This communication presents a comparative study of LES simulations of the single-phase flow under exponential power excursion at the wall. Subsequent analyses focused on the impact of different velocity-temperature couplings on the prediction of wall heat transfer, incorporating comparisons with experimental infrared thermometry measurements. Early in the transient phase, temperature peaks are confined within turbulent streaks, as reported in the existing literature. However, as the exponential power transient unfolds, the viscous layer and streak structures destabilize, leading to a more dispersed distribution of hot spots. Preliminary findings suggest a transition in heat transfer modes from turbulence-driven to conduction during the final stages of the single-phase transient.

A methodology for the optimal placement of conformal cooling channels in injection molds: 2D transient heat transfer analysis

A methodology for the optimal placement of conformal cooling channels in injection molds: 2D transient heat transfer analysis

Numerical investigation and optimisation of solid–solid phase change material composite-based plate-fin heat sink for thermal management of electronic package

Phase Change Material based Thermal Management Systems show promise in electronic packaging systems for safe operation, acting as a thermal storage element to prevent sudden temperature surges, enhancing operational time and mitigating electronic system failures. Therefore, the meticulous design of a solid–solid phase change material (SSPCM) based heat sink with fins is imperative for effective electronic thermal management by improving its safe operational time. This study performs a numerical analysis of two-dimensional transient heat transfer for the SSPCM-based plate-fin heat sink using the modified enthalpy porosity method, where the plate fins serve as Thermal Conductivity Enhancers (TCEs). Neopentyl glycol with 6% (w/w) Copper oxide nanoparticle is used as the SSPCM composite. Enhancement ratio based on safe operational time at different power levels (2–6 W) with different percentages of TCE and fin count recorded variation from 1.32 to 13.7. The TCE integration is more effective at higher power levels. The optimisation of SSPCM-based heat sink design for maximum safe operational time is accomplished through Response Surface Methodology. The significance of the TCE fraction, number of fins, heat generation rate, and interaction effects over the safe operational time are observed. The correlation for safe operational time as a function of TCE volume fraction, fin count and heat generation rate is developed. TCE volume fraction possesses the highest influencing factor over safe operational time at lower and higher power levels compared to fin count. At 2 W and 6 W, a maximum change in safe operational time is observed from 72.7% at 2 W to 83.45% at 6 W. The heat sink with 0.262 volume fraction of TCE and 11 fins is the optimised design that can provide the desirable safe operational time for the tested range of power levels.

Thermal boundary conditions for heat transfer analysis of bridges considering non-uniform distribution of internal air temperature by computational fluid dynamics

Heat transfer analysis has been used to calculate the temperature distribution in bridges. Thermal boundary conditions play a critical role in this analysis. However, existing studies on thermal boundary conditions simplify the air temperature inside the bridge deck as uniform, which is not realistic and thus causes inaccurate simulation results. This study proposes a new approach to thermal boundary conditions in the heat transfer analysis of bridges. For the first time, computational fluid dynamics is used to calculate non-uniform air temperatures inside the bridge deck. In addition, non-approximate heat exchange equations for long-wave radiation are also incorporated into the approach. The techniques are applied to the 1377-m main span Tsing Ma Suspension Bridge to calculate the internal air temperatures of a deck segment. Transient heat transfer analysis is then conducted to calculate the time-dependent temperature distribution of the segment. As compared with the field monitoring results, the proposed approach can simulate the temperature distribution of the bridge with an average discrepancy of 0.88 °C and is more accurately than other existing approaches.

Transient magnetohydrodynamic heat and mass transfer analysis of chemically reacting fluid flow over oscillatory permeable media

This study focuses on the numerical observation of the convective motion of chemically active magnetohydrodynamic (MHD) fluid through a vertically oriented permeable medium, incorporating variations in mass and heat transfer. The fluid type is assumed to be incompressible, chemically strongly ionized and viscous with some mass infusibility. The model associated with this problem is solved by a highly stable Implicit Finite Difference Method (IFDM). The method is used for small and large deflection of the physical parameters, which results in a noticeable fluid flow behavior. Numerical configuration is graphically depicted to scrutinize the fluid behavior. The momentum, energy, concentration diffusion, skin friction, Nusselt number and Sherwood number are investigated for numerous factors such as magnetic field, permeability and chemical reaction rate. The current study unveils significant findings, demonstrating that a heightened rate of chemical reaction in the presence of magnetic effects, coupled with specific porosity, diminishes ionization energy, resulting in a concurrent decrease in the concentration and momentum profiles of the fluid flow. The rise in the viscous diffusion rate is attributed to escalating values of the Schmidt number, causing an augmentation in dynamic viscosity and consequently resulting in an overall reduction in the momentum of the fluid flow.

Numerical Modeling and Analysis of Transient and Three-Dimensional Heat Transfer in 3D Printing via Fused-Deposition Modeling (FDM)

Fused-Deposition Modeling (FDM) is a commonly used 3D printing method for rapid prototyping and the fabrication of plastic components. The history of temperature variation during the FDM process plays a crucial role in the degree of bonding between layers. This study presents research on the thermal analysis of the 3D printing process using a developed simulation code. The code employs numerical discretization methods with an implicit scheme and an effective heat transfer coefficient for cooling. The computational model is validated by comparing the results with analytical solutions, demonstrating an agreement of more than 99%. The code is then utilized to perform thermal analyses for the 3D printing process. Interlayer and intralayer reheating effects, sensitivity to printing parameters, and realistic printing patterns are investigated. It is shown that concentric and zigzag paths yield similar peaks at different time intervals. Nodal temperatures can fall below the glass transition temperature (Tg) during the printing process, especially at the outer nodes of the domain and under conditions where the cooling period is longer and the printed volume per unit time is smaller. The article suggests future work to calculate welding time at different conditions and locations for the estimation of the degree of bonding.

Prediction of latent heat storage transient thermal performance for integrated solar combined cycle using machine learning techniques

The objective of this work is to develop a prediction methodology for latent heat storage thermal performance to reduce computational efforts. Thermal storage can effectively compensate for the limitations of solar energy by extending operation time and leveling fluctuations. Although latent heat storage is advantageous compared to sensible heat storage for its large energy density and stable output temperature, its thermal performance has strong nonlinearity. With the conventional numerical simulations, it takes large computational time to obtain the one year or longer thermal performance of the latent heat storage. In this study, the exit steam enthalpy of latent heat storage for an integrated solar combined cycle (ISCC) is predicted using machine learning techniques. As latent heat storage is used to store solar thermal energy, the inlet steam properties such as enthalpy, pressure, and flow rate are continuously altered. Heat charged-discharged history in the regression model inputs significantly improves the prediction accuracy. The regression models are trained with transient heat transfer analysis results based on meteorological data of Bawean Island, Indonesia. Seven regression algorithms (Gaussian process regression (GPR), kernel approximation, ensemble of trees, support vector machines (SVM), artificial neural networks (ANN), linear regression, and regression trees) are compared and GPR is selected for its root mean square error (RMSE) of 16.9 kJ/kg or less. The RMSE values are equivalent to Bawean results even when the GPR is applied to two other locations: Kupang and Cikarang. Meanwhile, an ensemble classifier, which is selected from nine classification algorithms (Ensemble classifiers, ANN, SVM, decision trees, nearest neighbor classifiers, naive bayes classifiers, kernel approximation classifiers, discriminant analysis, and logistic regression classifiers), is used to determine when to terminate the latent heat storage operation. Owing to its short calculation time, the developed methodology is advantageous at the early design stages of latent heat storage, especially when multiple locations need to be compared.

Preliminary analysis of maximum hypothetical accident for a solid core space nuclear reactor power system

In order to study the safety characteristics of the solid core space nuclear reactor power (SNRP) system under the maximum hypothetical accident, a two-dimensional entire core transient heat transfer analysis model was established, and the key parameters response characteristics of the ultra-small lithium-cooled SNRP under two maximum hypothetical accidents, namely, loss of heat sink (LOHS) and loss of coolant accident (LOCA), were calculated and analyzed. In the maximum hypothetical accidents, the coolant cooling capacity is lost, thus the core decay power is discharged into space only through the radiation of the residual heat removal system and the side surface of the reactor vessel. During the accidents, the heat transfer of the core deteriorated, and the fuel temperature may rise to the melting point, resulting in radioactive leakage. The results show that: (1) In the LOHS accident, the maximum fuel temperature reaches 2150 K at 550 s, and the pressure of the primary system volume accumulator continues to increase to the set system pressure safety limit of 2 MPa, resulting the primary loop overpressure failure. And the fuel matrix temperature is close to the set cladding limit temperature of 2200 K; (2) In the LOCA, the deterioration of heat transfer in the core makes the temperature increase rapidly, reaching a maximum of 3016 K at about 630 s, which is very close to the melting temperature of UN fuel 3123 K. As the decay power decreases, the maximum core temperature decreases to less than 1600 K after 24 h of the accident. The auxiliary cooling system of the solid core SNRP system under the maximum hypothetical accident is optimized, and the design parameters of the auxiliary cooling system meeting the safety requirements are obtained.

Nonlinear transient heat transfer analysis of multilayered thermal protection systems by incremental differential quadrature element method

As a first attempt, the incremental differential quadrature element method (IDQEM) is used for the one-dimensional nonlinear transient heat transfer analysis of multilayered thermal protection systems (TPSs) under time-dependent aerodynamic heating. All thermophysical properties are considered to be temperature-dependent (TD). Based on the IDQEM, the multilayered TPS is divided into several spatial sub-domains along the layer interfaces, and the entire heating process is also divided into several temporal sub-domains. For each temporal sub-domain, the governing equations are discretized by the differential quadrature method and then solved by the Newton-Raphson method. The initial condition of each temporal sub-domain is defined by the temperature results at the end of the previous sub-domain. The temperature profile of the TPS during the entire heating process can be obtained by repeating the calculation procedure from the first temporal sub-domain to the last one. Convergence and accuracy of the method are confirmed. Numerical examples are carried out to show the effects of TD thermophysical properties, thermal boundary, and layer thickness on the temperature profile of a three-layer TPS. The results show that the temperature dependency of thermophysical properties is worthy of consideration in predicting the temperature profile of the TPSs.

Transient heat transfer study of small-caliber barrel in continuous fire

In this paper, the barrel of small-caliber automatic rifle is taken as the research object. An experiment was taken on the gun barrel and an infrared thermal imager was used to measure the change of barrel temperature field during the continuous shooting, and the finite difference model of barrel heat transfer was established. The formula of the correction coefficient of heat transfer of gunpowder gas on the inner surface of the body tube was obtained by fitting with the experimental results. The barrel transient heat transfer analysis calculation software with independent intellectual property rights was developed by C++, and the characteristics of temperature field were analyzed. The experimental results show that the temperature of the outer surface of the barrel rises and then falls along the axial direction from the bottom of the barrel to the muzzle, and the rising slope will decrease in the next 30 rounds of continuous firing. The calculation results of the small-caliber barrel with chromium layer show that the temperature of the outer surface of the chromium layer of each shot rises instantaneously and then drops rapidly, in the form of pulse, and the temperature of the steel matrix rises continuously, but it is significantly lower than the peak temperature of the chromium layer, and the presence of the chromium layer provides buffer protection for the barrel matrix material. There is still an influence region in the matrix behind the interface between the chromium layer and the barrel matrix, and the temperature of the steel matrix in this region fluctuates. The thickness of the influence region is determined by analysis. The temperature of the inner surface of the barrel reaches a maximum at the tail of the barrel along the axial axis and then slowly decreases in the direction of the muzzle, the radial temperature distribution of the barrel is steeper at the tail end and the muzzle area is relatively flat. The calculation results of the model in this paper are basically consistent with the experimental results, which provides a rapid calculation model and tool for the thermal design and analysis of the gun barrel.

RC-Network based thermal bridge calculation method for transient heat transfer analysis of multidimensional building envelope details: A frequency response analysis-based method

Thermal bridges have a significant impact on the overall energy performance and thermal comfort of buildings. Proper accounting of thermal bridge effects through model coupling leads to more accurate predictions of heating and cooling loads and narrows the performance gap between the design and the actual energy consumption of buildings. In this paper, a dynamic thermal bridge calculation method is introduced in a frequency domain to transform a broad range of multidimensional building envelope assemblies to thermally equivalent RC-Network simple models. RC-Network model with three resistances, four capacitances, and internal and external surface resistances at the ends is found to represent multidimensional thermal bridge assemblies more accurately with minimal computational time. The method is applied for the simulation of diverse two- and three-dimensional thermal bridge details of lightweight and mass constructions exposed to hourly varying sol–air temperature boundary conditions, and the results are compared to reference solutions obtained from transient finite element modeling of the original thermal bridge details. The highest RMSE of the proposed RC-Network model for the lightweight and mass construction details are 0.12 W/m2 and 0.37 W/m2, respectively. The low RMSE values reaffirm the good performance of the method and its appropriateness for the calculation of hourly heat flux through multidimensional thermal bridge details.

3D-Simulation of Heat Flow in Indexable Drilling

In machining, the heat flow into the workpiece during the cutting process is often a major concern. The temperature rise can lead to substantial residual stresses or elastic in-process deformations which may result in the dimensional tolerance requirements being violated. In the present study a modelling strategy is developed for determination of the heat load during indexable drilling. The heat load on the workpiece is determined from 3D thermomechanical Coupled Eulerian Lagrangian analyses of orthogonal turning for various chip thicknesses and cutting speeds. The determined heat load is then transferred to a 3D transient heat transfer analysis of the indexable drilling process for the determination of the temperature field. Thereby, this modelling technique avoids the complex cutting process that is performed in real cutting simulations and thereby reducing the computational complexity of the problem considerably. The simulated temperatures are compared with experimentally measured temperatures and some conclusions are drawn regarding the modelling approach.

Analysis of transient laminar forced convective heat transfer in parallel-plate channels with time-varying thermal boundary conditions of the inlet and wall

The problem of transient laminar forced convective heat transfer in parallel-plate channels with time-varying thermal boundary conditions of the inlet and wall is thoroughly investigated in this study. By employing the methodologies of generalized integral transform technique (GITT) and Duhamel's theorem, we successfully derive an analytical solution for this problem. To validate the accuracy of our analytical findings, a comparison is made with the corresponding numerical solution, demonstrating a remarkable level of agreement between the two approaches. In order to obtain the general patterns of heat transfer, we employ a decoupling technique to separate the thermal response in the case of harmonic temperature boundary conditions of the inlet and wall. This approach enables us to uncover the intricate relationship between the weight coefficient of heat input and the two-dimensional spatial location of the channel, as well as the dimensionless angular frequency of heat input. Furthermore, we present the corresponding dimensionless cut-off angular frequency of heat input at various locations within the channel. To gain further insights, we conduct an in-depth analysis of the effects of integration time or distance on the dimensionless optimum angular frequency corresponding to the dimensionless maximum average heat flux.

Numerical analysis of transient heat and mass transfer for a water heat pipe under non-uniform heating conditions

Non-uniform loads are widely present in heat pipe applications and have significant effects on their performance. In this work, a transient 3D CFD model is developed to investigate the liquid–vapor flow and heat transfer for a water heat pipe under various non-uniform loads. The source terms are added to the governing equations using the User-Defined Function (UDF) to simulate the evaporation and condensation process. The model is verified using the experimental and simulated data under uniform and non-uniform loads in the literature. The effects of key parameters including adiabatic length, heating power, and heat distribution on the thermal performance of heat pipes are analyzed. The results show that the non-uniform conditions would shift the maximum axial velocity of vapor to the unheated side and induce a significant circumferential flow in the wick region, especially in the evaporator section. The short adiabatic length and high heating power could reduce the elapsed time of reaching the steady state. The heat distribution in the evaporator section exhibits little effect on the elapsed time reaching the steady-state and the average steady-state vapor temperature

Research on transient heat transfer of ball valves in high-pressure liquid hydrogen receiving stations

As one of the most important fluid control devices in the liquid hydrogen receiving station, the liquid hydrogen ball valve's performance directly affects the system's stability. Aiming at the problem of insufficient cold shrinkage compensation ability of ball valve under high-temperature difference and excessive flow rate during the working process, a high-pressure liquid hydrogen hollow ball valve with elastic compensation ability is designed. Based on the conjugate heat transfer method, the transient conjugate heat transfer and transient thermal stress analysis were carried out on the high-pressure hollow ball valve of the liquid hydrogen receiving station. The results show that the transient temperature of each part of the ball valve decreases under different flow rates, and the closer to the flow part of the medium, the faster the cooling. In the initial stage, the larger the flow rate of liquid hydrogen, the greater the heat flux density of the fluid-solid interface, but after a certain period, the large flow rate is cooled to a greater extent, the heat transfer is weakened, and the heat flux density is smaller. Under different flow rates, the transient thermal stress of the key components of the ball valve first increases sharply and then decreases. At large flow rates, the temperature change is more obvious, and the maximum stress of each component increases. The research results have guiding significance for designing and applying ball valves in high-pressure liquid hydrogen receiving stations.

Transient heat transfer analysis of the porous nonhomogeneous material structure

Transient heat transfer analysis of the porous nonhomogeneous material structure

Impact of oxidized HANATM and Zircaloy-4 cladding materials under high temperature on the coolability of light water reactors

In this study, oxidized HANATM and Zircaloy-4 exposed to steam at a temperature of 1200 °C for a duration of 136–1536 s were characterized, and their coolability under nuclear accident conditions was discussed. Under the given environmental oxidization conditions, the differences in the surface conditions and effective thermal properties of oxidized HANATM and Zircaloy-4 resulted in different degrees of coolability. For different oxidation resistances of these cladding materials, the reduction in their thermal conductivity by oxidation showed a difference, resulting in different heat transport phenomena that determine the Leidenfrost temperature, TL. However, TL did not increase further after the oxide layer reached an equivalent cladding reacted (ECR) of at least 24%, which is the penetration depth of the oxide layer. A 1-D transient heat transfer analysis based on the droplet behavior showed that TL did not increase even after reaching the penetration depth of the oxide layer. The analysis results also indicated that the delay in the heat transfer in the oxide layer did not affect TL after reaching the penetration depth of the oxide layer.