Transient Heat Research Articles

Analysis of GAAFET’s transient heat transport process based on phonon hydrodynamic equations

Compared to the classical Fourier’s law, the phonon hydrodynamic model has demonstrated significant advantages in describing ultrafast phonon heat transport at the nanoscale. The gate-all-around field-effect transistor (GAAFET) greatly optimizes its electrical performance through its three-dimensional channel design, but its nanoscale characteristics also lead to challenges such as self-heating and localized overheating. Therefore, it is of great significance to study the internal heat transport mechanism of GAAFET devices to obtain the thermal process and heat distribution characteristics. Based on this, this paper conducts theoretical and numerical simulation analyses on the phonon heat transfer characteristics within nanoscale GAAFET devices. Firstly, based on the phonon Boltzmann equation, the phonon hydrodynamic model and boundary conditions are rigorously derived, establishing a numerical solution method based on finite elements. For the novel GAAFET devices, the effects of factors such as surface roughness, channel length, channel radius, gate dielectric, and interface thermal resistance on their heat transfer characteristics are analyzed. The research results indicate that the larger the surface roughness, the smaller the channel length and the channel radius, the larger the interface thermal resistance leads to the higher hot spot peak temperature. The non-Fourier heat analysis method based on the phonon hydrodynamic model and temperature jump condition within the continuous medium framework constructed in this paper can accurately predict the non-Fourier phonon heat conduction process inside GAAFET and reveal the mechanisms of resistive scattering and phonon/interface scattering. This work provides important theoretical support for further optimizing the thermal reliability design of GAAFET, improving its thermal stability, and operational performance.

Transient heat transfer of helium gas for forced convective flow through a narrow tube with different lengths

Transient heat transfer of helium gas for forced convective flow through a narrow tube with different lengths

Heat Transfer Modelling of Biomass Torrefaction

The depletion of coal reserves and the increase of environmental problems urge the use of renewable energy sources. Biomass is a renewable energy source and is also used as one of the feeds for cofiring, a promising energy generation technology. However, the shortcomings of biomass, such as low calorific value, hygroscopic, and low grindability, limit its usage. Torrefaction is a mild form of pyrolysis of biomass that results in better solid fuel properties. This study aims to model a simple heat transfer numerical equation to predict the torrefaction of biomass in various operating conditions. The temperature distribution in biomass during the torrefaction process is also predicted, as well as the mass yield, energy yield, and HHV behaviour of the torrefied biomass. The modelling was conducted based on Calliandra wood biomass. The pellet biomass diameter was modelled to vary within a range of 1-3 cm and a length of 10 cm. The operating conditions used for this modelling were the temperature of torrefaction with a range of 230- 270 °C. Heat transfer modelling was carried out by using MATLAB. The modelling produces a numerical equation of transient heat transfer with a radial axis base with the kinetic model used as TPR (Three Parallel Reaction). The modelling produces an error of 1.424% compared to the experimental data by Felfli et al. The simulation shows that torrefaction that makes a higher and more uniform temperature distribution will result in a higher HHV value. Based on the simulation, the recommendation of torrefaction operating conditions for Calliandra wood with a diameter of 1-3 cm is at a torrefaction temperature of 270℃ and residence time of 1.5 hours. This will result in a calorific value of approximately 5300 kcal/kg.

Numerical validation of ice formation on a lattice structure evaporator

This paper presents a comparative analysis between experimental and numerical results of the ice formation process on the surface of the evaporator in a Sparkling Water Dispenser. The experimental setup comprises an R290 refrigeration cycle that is fully equipped with thermocouples, pressure transducers, a wattmeter, and a Coriolis-meter. The evaporator, which is specifically designed to enhance the ice formation speed, is situated within a water-filled tank, where the ice formation process takes place. Due to the phase change phenomenon, which involves the interface between two phases moving, solving transient heat transfer problems involving solidifications can be inherently challenging. Analytical solutions are only possible under certain simplified circumstances. In cases where exact solutions are not available, semi-analytic, approximate, and numerical methods can be utilized to address phase-change problems. A numerical model of the solidification process based on the energy equation and conjugate heat transfer was developed using COMSOL Multiphysics. The software was found to be effective in simulating the physical processes associated with heat transfer through conduction and convection, as well as the behaviour of phase change. The results showed a very good agreement between experimental and numerical results.

Finite Difference-Peridynamic Differential Operator for Solving Transient Heat Conduction Problems

Finite Difference-Peridynamic Differential Operator for Solving Transient Heat Conduction Problems

Transient natural convection flows and heat transfer in a thermally stratified air-filled trapezoidal cavity

This paper focuses on studying the transient behavior of natural convective heat and fluid flow in a two-dimensional trapezoidal cavity subjected to a heated bottom surface, cooling from the top, and thermally stratified inclined surfaces. The Finite Volume (FV) method is employed to numerically simulate the transient flow. The study considers a thermally stratified environment with a Prandtl number of Pr set to 0.71 (for stratified air), an aspect ratio (A) of 0.5, and a large array of Rayleigh numbers (Ra) ranging from 100 to 108. The research examines how the Rayleigh numbers affect the flow structures, transient phenomena, and heat transfer (HT) characteristics within the cavity. The transitional flow reveals several supercritical bifurcations. These include a changeover from symmetric to asymmetric states known as a Pitchfork bifurcation, as well as a shift from a steady-state to a periodic state referred to as a Hopf bifurcation. The Pitchfork bifurcation happens between Ra values of 105 and 2 × 105, while the Hopf bifurcation happens within the range of the Ra values from 4.7 × 105 to 4.8 × 105. Moreover, another bifurcation from a periodic to a chaotic state is observed between Ra of 3 × 107 and 4 × 107. To examine the transient flows during the changeover to chaos, various techniques such as power spectral density (PSD), limit points, limit cycles, trajectory in phase space, and the largest Lyapunov exponent (LLE) are used. Furthermore, convective heat transfer is computed, and its corresponding impact on the Ra values is explained. The flow phenomena within the cavity are measured and verified.

Prediction of Residual Stresses in 316 Stainless Steel Pipes Welded Joint

Due to the extremely complicated thermal cycle for the welding process, the fusion zone and heat-affected zone (HAZ) produce irreversible elastic-plastic deformation and residual stresses. The differential heating of the pipes caused by the weld heat source causes residual stress as a result of the welding process. However, the strength and lifetime of the component are also decreased as a result of residual stresses in and around the weld zone. The objective of this research is to analyze the residual stresses created during the welding process and select the best welding parameters that give the lowest residual stresses in 316SS pipes with 50 mm diameter and 4 mm thickness that were manually welded by used (316) welding wire and using shielded metal arc welding (SMAW) in a single-pass butt joint with the various values for each of current (58, 68, 78, 88) amperes and voltage (22, 23, 24, 25, 26) volts. The shielded metal arc welding process involves heating, melting, and solidifying the parent metals and filler material in a localized fusion zone by a transient heat source to create a junction between the parent metals. The welding process free from preheating and heat treatment will be obtained. ANSYS Finite Element methods are used to calculate the welding residual stress distribution. The mechanical and thermal models were used to carry out the theoretical analysis. In general, the numerical study found that the residual stress distribution at the weld zone’s center is continuous, rising, and has a value of about (1738 MPa). Additionally, the residual stress at the boundary between the heat-affected zone and the weld zone climbs to a maximum value of around (3799.6 MPa). On the other hand, the magnitude of the residual stress in the heat-affected zone of the weld reduces significantly and achieves a minimum value at a position of (20 mm) with a value near zero.

Thermocapillary convection modes and phase change heat transfer characteristics of three-dimensional metal foam composited phase change materials with different aspect ratios under microgravity

This work aims to investigate the flow, heat transfer and phase change characteristics of porous media composite phase change materials with different aspect ratios in the thermocapillary mode under microgravity. A three-dimensional hydrodynamic model of thermocapillary-enhanced phase change heat transfer in the composite is developed. The model considers the shear stress boundary conditions on the porous free surface, employing the enthalpy-porosity method and the Darcy–Forchheimer model to describe the phase change process and fluid flow within the porous matrix, respectively, and the local thermal non-equilibrium model to describe the transient heat energy transfer between the paraffin and copper foam. The effects of different Marangoni numbers (Ma), aspect ratios (AR), Darcy numbers (Da) and porosities (ε) on the phase change heat transfer are compared. The results show that the increase of Ma from 6 × 104 to 2 × 105 accelerates the thermocapillary effect, and positively affect the thermal transport inside the cavity. The total melting time of the composite is reduced by 22.6 %, the heat storage efficiency is improved by 31.1 %, and secondary vortices appear in the convection zone. The large AR is favorable to the development of thermocapillary convection, but it also causes the reduced temperature gradient and heat transfer area of the heat source as well as the increased heat transfer distance. Compared to AR = 1, the total melting time increased by 34.4 % and 46.9 % for AR of 1.95 and 2.25 at a larger Ma, while the heat storage efficiency decreased by 26.5 % and 33.7 %, respectively. For a fixed ε, the decrease in Da hinders the development of convection, thus weakening the heat transfer and storage performance of the composite, and also causes heat conduction to dominate the phase change process in advance.

An implicit thermo-mechanical coupling model for heat conduction and thermal cracking in brittle materials

In this paper, an implicit thermo-mechanical coupling model is developed to simulate heat conduction and thermal cracking in brittle materials. In the thermal analysis, an implicit particle heat conduction model (PHCM) is proposed. A linear algebraic system of heat conduction equations is derived based on the temperatures of the particle system and the heat flux among adjacent particles. An analytical expression is introduced for the involved correction coefficient, with which the macroscopic thermal conductivity coefficient can be directly adopted without calibration. Furthermore, a thermal conductivity reduction coefficient is introduced to account for the thermal resistance of the cracks. In the mechanical analysis, particle discontinuous deformation analysis (PDDA), which is an implicit variant of the discrete element method, is employed. The PHCM is first verified against analytical and finite element solutions for transient heat conduction problems. The results show that the PHCM is an effective and accurate heat conduction model that readily reflects the thermal resistance of cracks. Then, the thermo-mechanical coupling model is verified by the expansion of heated specimens under different conditions. Finally, the successful application of the coupling model in the simulation of thermal shock tests demonstrates its effectiveness for thermal cracking problems.

Simulation of transient heat transfer in multilayer walls with photovoltaic cell and air by using efficient numerical methods

This paper focuses on simulating nonlinear transient heat transfer in multilayer walls under varying heat loads, using efficient numerical algorithms. The algorithms employed are completely explicit and unconditionally stable for the linear conduction-convection case. The study investigates heat transfer through building walls, considering different wall geometries and heat load scenarios, encompassing both cooling and heating. Our primary objective is to analyse how heat transfer depends on the wall materials and evaluate algorithm performance in cases involving heat transfer between solid surfaces and fluid (convection) on the outdoor surface, particularly across an air gap between insulation and Photovoltaic Cells (PVC). The results reveal that insulation prevents heat from entering the building, maintaining a comfortable indoor environment. Forced convection significantly enhances heat dissipation, especially during cooling operations to protect PVC with limited working temperature. Furthermore, the simulations highlight the air gap's efficiency in cooling PVC and reducing maximum temperatures on the insulation's outer surface, especially under forced convection conditions. The test results show that the leapfrog hopscotch algorithm offers the best solution for this highly stiff system, followed by the asymmetric and shifted hopscotch algorithms. This study offers insights into optimizing heat transfer within multilayer walls, with implications for building energy efficiency and thermal comfort.

Output and mechanical performance of thermoelectric generator under transient heat loads

Geometry optimization and pulsed inputs have been introduced as some of the effective methods to enhance the performance of thermoelectric devices. In this work, the geometric structure of a Bi2Te3-based thermoelectric module is optimized systematically using two-step integrated optimization method in steady state, and then the effect of transient heat flux on the output and mechanical performance is investigated deeply. The simulative results show that the optimization directions for mechanical and output performance are usually opposite. The optimal Ap/An, H/Anp and N of the Bi2Te3-based module are 1.6, 1.5 and 8, respectively. Moreover, the thicker He and thinner Hcs favor the improvement of output performance, however, considering the mechanical property, the optimal He and Hcs are regarded as 0.3 mm. In addition, using pulsed heat flux can improve the output performance and obtain a smaller average stress in a long period. The suitable duty cycle, smaller amplitude ratio and rectangular heat flux are beneficial for power enhancement and stress optimization. However, pulsed input brings frequent and repeated temperature changes, which is a challenge to the lifespan of thermoelectric modules. These simulated results will benefit the enhancement of output and mechanical performance of thermoelectric devices in the practical operation process.

Development of freezing process in presence of nanoparticles involving transient conduction heat transfer through finned wavy enclosure

The solidifying phenomena have been scrutinized in current work and techniques for expedition of process have been incorporated. The shape of geometry and shape of nanoparticles can alter the productivity of the unit. Utilizing higher concentration and bigger value of shape factor can accelerate the process. The present unsteady phenomena were simulated via Galerkin approach and to augment the accuracy, the shape of the mesh was adapted with location of the ice front. The existence of nanoparticles within water can enhance the freezing rate by about 26.73 %. The required time alters from 232.63s to 216.4s, when powders with bigger shape factor utilizes. Augment of concentration of powders from 0.02 to 0.04 can drop the solidification time around 13.78 %.

Heat Transfer Performance of a 3D-Printed Aluminum Flat-Plate Oscillating Heat Pipe Finned Radiator.

As electronic components progressively downsize and their power intensifies, thermal management has emerged as a paramount challenge. This study presents a novel, high-efficiency finned heat exchanger, termed Flat-Plate Oscillating Heat Pipe Finned Radiator (FOHPFR), which employs arrayed flat-plate oscillating heat pipes (OHP) as heat dissipation fins. Three-dimensional (3D)-printed techniques allow the internal microchannels of the FOHPFR to become rougher, providing excellent surface wettability and capillary forces, which in turn significantly improves the device's ability to dissipate heat. In this study, the 3D-printed FOHPFR is compared with traditional solid finned radiators made of identical materials and designs. The impacts of filling ratio, inclination angle, and cold-end conditions on the heat transfer performance of the 3D-printed FOHPFR are investigated. It is demonstrated by the results that compared to solid finned radiators, the FOHPFR exhibits superior transient heat absorption and steady-state heat transfer capabilities. When the heating power is set at 140 W, a decrease in thermal resistance from 0.32 °C/W in the solid type to 0.11 °C/W is observed in the FOHPFR, marking a reduction of 65.6%. Similarly, a drop in the average temperature of the heat source from 160 °C in the solid version to 125 °C, a decrease of 21.8%, is noted. An optimal filling ratio of 50% was identified for the vertical 3D-printed FOHPFR, with the minimal thermal resistance achieving 0.11 °C/W. Moreover, the thermal resistance of the 3D-printed FOHPFR is effectively reduced compared to that of the solid finned radiator at all inclination angles. This indicates that the FOHPFR possessed notable adaptability to various working angles.

Two-channel optimal energy-efficient control of distributed parameter systems

A formulation and method for solving the problem of the energy-efficient two-channel programmed control of an object with distributed parameters with a given-precision uniform approximation of the resulting spatial distribution of the controlled quantity to the required state is proposed. Two internal controls on the power of heat sources in the electromagnetic field of the inductor are considered as control actions. Proposed solution approach involves a special-form preliminary parametrization procedure for control actions on finite-dimensional subsets of the terminal values of conjugate variables in the boundary-value problem of Pontryagin’s maximum principle, in combination with the subsequent reduction to a semi-infinite optimization problem, which is solved with respect to the requisite parameter vector using the alternance method based on additional information about fundamental laws of the subject area. An example of optimal energy-efficient control of transient heat conduction, which is of independent interest, is given.

Modeling district heating pipelines using a hybrid dynamic thermal network approach

A novel numerical method is presented for fast and accurate simulation of the dynamic thermal behavior of buried pipelines such as those in district heating systems. The model is based on a combination of a conduction response factor method, known as the dynamic thermal network (DTN) method and a one-dimensional discretized heat transfer fluid flow model, the so-called plug flow N-continuously stirred tanks (PFST) model. This combination enables the model to effectively take into account the short timescale dynamic effects of pipelines including longitudinal dispersion of turbulent fluid and its thermal capacity and also transient ground heat transfer. The combined DTN-PFST model is validated by reference to experimental data from both the lab-scale representation of a district heating system and monitoring data from a full-scale operational system. The comparisons between simulation results and experimental data demonstrate a good level of accuracy of the proposed model in predicting the dynamic thermal behavior of pipelines. The model has also been found to be several orders of magnitude more computationally efficient than corresponding 3D numerical models. Both the accuracy and computational efficiency of the proposed model make it well-suited to the design and analysis of district heating distribution networks. The model is also expected to be well-suited to the modeling of horizontal ground heat exchange pipe systems.

Measuring Thermal Conductivity of Single Thickness Fibrous Gas Diffusion Layers Using Transient Plane Source Method

In a proton exchange membrane fuel cell (PEMFC), the gas diffusion layer (GDL) is a porous material placed between the flow field plates and the catalyst layer. Its primary responsibility is to distribute reactants evenly across the surface of the catalyst layer while allowing for the removal of excess water and heat produced during operation. The GDL is typically made of a carbon-based material, such as carbon paper or carbon cloth, which is treated with polytetrafluoroethylene (PTFE) to become hydrophobic. This treatment allows it to repel water and facilitate the transport of gases such as hydrogen and oxygen during operation. The thermal conductivity of the GDL plays a crucial role in managing the heat and water of PEMFCs.The Guarded Heat Flow (GHF) technique is a well-established steady-state method for measuring the thermal conductivity of carbon fiber papers. This is achieved by testing two different thicknesses of a material that have an identical structure [1-3]. Using this two-thickness method, as per ASTM standard C177-19e1 [4], enables the bulk thermal conductivity to be deconvoluted from the thermal contact resistance at the interface between the sample and the measurement device's surface (an interfacial phenomenon). However, materials with identical structures for two-thickness measurements are not always available for commercial GDLs. In this study, we compare the transient plane source (TPS) thin film method, which measures the thermal conductivity of single thickness GDL samples, with the two-thickness GHF method for measuring thermal conductivity.In this study, GDL samples with the same bulk structure and manufactured in two thicknesses were used: Sigracet series 24BA and 34BA with original thicknesses of 190 µm and 280 µm, respectively. A custom-built Thickness Under Compression and Resistance Under Compression machine (TUC-RUC) was utilized to measure the thickness of the samples under loads ranging from 0.35 MPa to 2 MPa. The thickness under compression was measured for five samples (25.4 mm diameter) of each type of GDL. The standard deviation for each sample thickness was below 4%. As shown in Fig. 1, the stress-strain response of the GDL samples was measured and analyzed to assess the similarity in their mechanical structures. Consistent with the assumptions that both samples have the same structure, the GDL samples with two different thicknesses displayed identical stress-strain behavior under compression, as shown by the curve-fit for stress-strain behavior in proposed Fig. 1.The thermal conductivity of the samples was measured using both the TPS thin films method, as per ISO 2207-2:2022 [5], and the GHFM. On the TPS, three samples of each type of GDL were measured three times. The measured thermal conductivities increased with compression, ranging from 0.15 to 0.47 W/mK, with a standard deviation of less than 5% for each measurement. The results from the TPS technique for a single thickness of GDL were compared with the two-thickness measurements conducted using the GHFM, as shown in Figure 2. The GHFM tests were conducted on three samples of each type of GDL at five compressive loads, and the standard deviation on the deconvoluted thermal conductivity was less than 7% for each measurement. The values measured by the two techniques were found to be in good agreement, with a relative difference of within 6%. This study demonstrates that the transient plane source (TPS) method, when combined with an accurate thickness measurement technique, is a precise technique for determining the bulk thermal conductivity of commercial GDLs produced in a single thickness.[1] H. Sadeghifar, N. Djilali, and M. Bahrami, “Effect of Polytetrafluoroethylene (PTFE) and micro porous layer (MPL) on thermal conductivity of fuel cell gas diffusion layers: Modeling and experiments,” Journal of Power Sources, vol. 248, pp. 632–641, Feb. 2014, doi: 10.1016/j.jpowsour.2013.09.136.[2] M. Ahadi, M. Andisheh-Tadbir, M. Tam, and M. Bahrami, “An improved transient plane source method for measuring thermal conductivity of thin films: Deconvoluting thermal contact resistance,” International Journal of Heat and Mass Transfer, vol. 96, pp. 371–380, May 2016, doi: 10.1016/j.ijheatmasstransfer.2016.01.037.[3] E. Sadeghi, N. Djilali, and M. Bahrami, “Effective thermal conductivity and thermal contact resistance of gas diffusion layers in proton exchange membrane fuel cells. Part 1: Effect of compressive load,” Journal of Power Sources, vol. 196, no. 1, pp. 246–254, Jan. 2011, doi: 10.1016/j.jpowsour.2010.06.039.[4] “Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus.” ASTM International. Doi: 10.1520/c0177-19e01.[5] “ISO22007-2, Plastics-determination of thermal conductivity and thermal diffusivity-part 2: transient plane heat source (hot disc) method”, 2022. Figure 1

Infrared Thermography Investigation of Crystallization in Acoustically Levitated Supersaturated Aqueous Solution

In this study, crystallization in highly supersaturated aqueous urea solutions was investigated using in situ infrared thermography facilitated by an acoustic levitation apparatus. A notable contribution of this thermographic approach is the identification of a transient heat release signature, particularly pronounced beyond the solubility limit, indicating the enhanced formation of bonds between urea molecules in the supersaturated states. Surprisingly, the temporal evolution of the heat release measurements on an acoustically levitated droplet strongly suggests a two-stage process for urea crystallization. A comprehensive statistical analysis based on classical nucleation theory is used to further investigate the exceptionally high degree of supersaturation and the emergence of prominent heat signatures observed toward the onset of crystallization.

Analysis of Heat Transfer Pathways That Affect Mitigation of Cascading Thermal Runaway

As the energy density of systems of lithium-ion batteries increases, and as they are employed in larger-scale energy storage systems, greater attention must be paid to the safety of these systems. Failure of a single cell can trigger thermal runaway processes that cascade through the system, endangering first responders and nearby structures. This cascading failure is driven by heat transfer through the system to vulnerable cells and other combustible materials. To understand how to mitigate thermal runaway, the most important heat transfer pathways must be characterized in terms of their magnitude and time scale.Heat must be removed from cells that have gone into thermal runaway without leading vulnerable cells into thermal runaway. The onset of thermal runaway typically occurs around 200oC and depends on the heating time (i.e. cells heated slowly in an oven will begin thermal runaway around 150oC). The objective then becomes avoiding these thermal runaway temperatures for surrounding cells while dissipating any heat released from an initial thermal runaway event.While there are many individual parameters that describe the cells and system, in this work it will be seen that the thermal analysis can be reduced to a collection of non-dimensional parameters. These parameters describe heat conduction within the cell, heat capacity of a cell, total heat released by a cell in thermal runaway, conductive heat transfer to adjacent cells and surroundings, and convective heat transfer to surrounding gases.A simple cell-to-cell propagation scenario is constructed to separately investigate the heat transfer parameter space. In this model scenario, an “initiating” cell is assumed to have just completed thermal runaway and exhausted all its reactants. This heats that cell to a high temperature that depends on the cell chemistry and state of charge. Adjacent to this “initiating” cell is the “target” cell. We use canonical heat transfer problems to identify a set of parameters that determine the temperature of the “target” cell. The attached figure depicts the prominent heat transfer pathways for a notional propagation scenario. The parameters space of interest includes the thermal resistance (left), the heat capacity of the involved materials (center), and heat losses to the ambient surroundings (right). The relative time scales of these heat transfer rates determine the propagation speed and ultimately the point at which cascading thermal runaway is mitigated.The thermal parameter space is interrogated by solving the transient heat transfer problem with a combination of analytical techniques, a quasi-1D finite volume software, and 3D finite element software. The maximum temperature reached by the edge of the target cell is recorded and used as the criteria for the boundary between propagation and mitigation. The scaling relationships developed through this analysis can provide thermal engineers and system designers with a framework for predicting the safety of battery pack designs in the context of cascading thermal runaway. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525 SAND2023-02583A Figure 1

Thermally Induced Vibrations of Functionally Graded Shallow Spherical Shells Under Cooling Shock

Based on the first-order shear deformation theory (FSDT), the large-amplitude vibration behavior of shallow spherical shells made of functionally graded materials (FGMs) due to the rapid decrease of temperature (cooling shock) is investigated. FGM is assumed to be a mixture of stainless steel and low-carbon steel whose properties are considered temperature dependent and are estimated based on the power-law model. According to FSDT and von Kármán assumptions, the governing equations of motion in conjunction with corresponding boundary conditions are obtained using Hamilton’s principle. The temperature distribution is also achieved by means of the 1D Fourier transient heat conduction equation, considering two time-dependent thermal loading scenarios. The considered thermal boundary conditions allow that a temperature difference is created with a time delay for the structure under cooling shock. Also, the results of recent experiments are employed to estimate the temperature-dependent properties of structures. In the solution approach, the generalized differential quadrature method and the Newmark-beta integration scheme are utilized. Selected numerical results are presented to study the effects of thermal load rapidity time, geometry, magnitude of thermal load, and material gradient index on the thermally induced vibrations of spherical shells. Stresses generated in the shell due to the thermally induced vibrations are also investigated.

Transient Tip Clearance Prediction Model Considering Transient Radial Temperature Distribution of Discs in a Gas Turbine Engine

Abstract The tip clearance of turbomachinery components, such as compressor and turbine, significantly impacts the gas turbine engine performance, including the thrust and fuel consumption. Therefore, an appropriate prediction of the turbomachinery tip clearance is indispensable in improving the accuracy of engine performance evaluations. The traditional 1D transient tip clearance prediction model does not consider the radial temperature distribution of the disk (also called disc). However, as the engine performance keeps improving, the radial temperature gradient of the disk also increases. In order to maintain the prediction accuracy within an acceptable range, a generic transient tip clearance prediction model is developed in this paper. Based on the special treatment of the axial and radial convective heat transfer boundary regions of the disk, a 2D transient heat transfer model is established, and the radial temperature of the disk is predicted. At the same time, the interaction effect of the thermal expansion between the two different layers of the shroud is studied to improve the prediction accuracy further. In addition, the centrifugal deformation of the blade and disk with variable-thickness characteristics is considered in the new transient model. Compared with the traditional 1D transient prediction model, the model developed in this paper further improves the predicting accuracy of the transient tip clearance, which is verified by the high-fidelity fluid–solid–thermal coupling method. The prediction model provides a useful tool for evaluating the transient tip clearance. It may also benefit the future design strategy of active clearance control.