Transient Temperature Response Research Articles

Carbon-decorated diatomite stabilized lauric acid-stearic acid as composite phase change materials for photo-to-thermal conversion and storage

Diatomite is a promising supporting matrix in the preparation of composite phase change material for latent thermal energy storage. Raw diatomite has the advantages of porous space but with a shortage of thermal conductivity than carbon materials. In this work, the carbon-decorated diatomite (DC) matrix was synthesized by a novel template-carbonization method at different calcination temperatures of 600 °C, 800 °C, and 1000 °C. Then, the matrix was used to stabilize binary lauric-stearic acid of LA-SA for the preparation of diatomite-based composite phase change material which is used to explore the application of composite in photo-to-thermal conversion/storage. Results show that the carbon-decorated process on diatomite causes an increment of specific surface area and pore space. Thus, more phase change material being loaded in the matrix leads to a larger heat storage capacity of the composite. The designed composite with a matrix carbonization temperature of 1000 °C, LA-SA/DC-1000, has a loadage of 49.92 %, melting temperature of 31.48 °C, and latent heat of 70.07 J g-1 which is improved by 23 %. Compared with the raw diatomite-based composite, the enhancements of thermal conductivity were 90 % for that of LA-SA/DC-1000. Moreover, the corresponding composite exhibits better photo-to-thermal conversion performance and transient temperature response.

An apparatus to measure thermal conductivity of ceramic pebble beds under uniaxial compressive stress

Pebble beds have various applications in many industrial and research sectors. Lithium ceramic pebble beds have specific application in fusion reactors as one of the most promising candidates for tritium breeding material. During the operation of the fusion reactor, these pebble beds will have to sustain various thermal and mechanical stresses. Therefore, it is necessary to do thermal characterisation of these pebble beds under different stress conditions and generate sufficient data on their thermal properties, which is essential for designing breeder units of fusion reactors. In this work, an apparatus has been designed to evaluate the thermal conductivity of ceramic pebble beds under compressive stress. It can be mounted to any standard universal testing machine with the necessary adjustments. The apparatus is based on the transient hot-wire method, widely used to evaluate the thermal conductivity of porous materials. A platinum wire with a diameter of 0.5 mm was used as a hot-wire. Instead of utilising a thermocouple, the 4-wire approach was used to obtain the temperature. The transient temperature response of the hot-wire was obtained by applying a 7A constant current to it and monitoring the voltage drop along its 40 mm length. The thermal conductivity of the water gel was measured to assess the accuracy of the apparatus; the results showed a less than 1.5 % variation from the reference value. In this study, the thermal conductivity of Li2TiO3 pebbles was measured in an air and helium environment in different stress conditions. In an air environment, measurements were done at atmospheric pressure, whereas in a helium gas environment, they were performed at gauge pressures of 0.05 bar, 0.5 bar, and 1 bar. The measurements were conducted in two scenarios: (i) constant stress condition at 0, 3, and 6 MPa, and (ii) Cyclic loading-unloading of 0.037–3 MPa and 0.037–6 MPa. It was found that the pebble bed's thermal conductivity rose in tandem with increased compressive stress in both the helium and air environments. Pebble bed’s thermal conductivity was found to be higher in a helium gas environment than in air. The thermal conductivity of the pebble bed increased slightly with rising helium gas gauge pressure from 0.05 bar to 1 bar. This work provides a design to incorporate 4-wire temperature measurement in the hot-wire method for thermal conductivity measurement of compressed pebble beds. It also contributes to the thermal conductivity data of Li2TiO3 pebbles in cyclic stress conditions in helium and air environments.

Transient wall temperature response during liquid nitrogen nucleate pool boiling: CFD analysis and experimental validation

The phenomenon of heat transfer by phase change (liquid/vapor) is used for wall cooling in a number of fields, including power generation, renewable energy and nuclear reactors. This choice is explained by its ability to evacuate high surface heat fluxes at relatively low wall temperatures. In most cases, cooling systems are designed based on steady-state experimental studies. However, during start-up phases or when sudden flow variations occur in cooling systems, surface heat fluxes or wall temperatures may vary considerably from values determined under stationary conditions. Boiling under transient conditions, therefore, reveals a number of peculiarities whose understanding will contribute to fundamental knowledge of this phenomenon. This paper focuses on the numerical study of the transient nucleate pool boiling heat transfer due to the horizontal immersion of a brass ribbon in liquid nitrogen. In addition, the superheat nucleate boiling and the critical heat flux (CHF), which is a critical factor for system safety, has been specifically analyzed. Finally, these numerical results obtained based on a CFD analysis using COMSOL Multiphysics software were compared to experimental data and the percentage error was no more than 13%.

Heat transfer characteristics of subsea long-distance pipeline subject to direct electrical heating

For deep-water pipelines with long tie-back distances, high external pressure, and low ambient temperature, it is a key issue to ensure flow safety by controlling the generation of hydrates and waxes through electric heating technology. In-detail analysis of the heat transfer performance of electric heating pipelines is of great engineering significance for developing the safety of pipeline flow in offshore oil-gas fields. This paper proposed an electrical heating analytical method applicable to long-distance submarine pipelines. Based on the thermal equilibrium theory and the differential equation of heat conduction, a mathematical model of heat-fluid coupling for electric heating pipes is established, involving the theoretical model of the steady-state distribution of the electric heating in the axial and radial directions. Then, the definition of the average temperature of the pipeline is introduced and combined with the two-point Hermite approximation interpolation method, and an improved lumped parameter model of the transient heat transfer of the electric heating pipeline is established. Meanwhile, the finite difference method is applied to solve the ordinary differential equation of the pipeline and the energy equation of the internal fluid. The steady-state calculation result is utilized as the initial value of the transient heat transfer process, and the model is applied to analyze the influence variation on the transient temperature response characteristics of the pipeline under different working conditions, finally determining the prediction formula of the average temperature of the fluid under normal transportation and shutdown conditions.

Converting bio-waste rice into ultralight hierarchical porous carbon to pack polyethylene glycol for multifunctional applications: Experiment and molecular dynamics simulations

A structural-functional integrated shape-stabilized composite phase change material (PCM) was synthesized by converting biowaste rice into ultralight (0.08 g/cm3) hierarchical porous carbon (CNR) to pack polyethylene glycol (PEG) PCM. The thermal property and corresponding mechanism were analyzed. The results show that the composite PCM exhibits excellent thermal storage efficiency (93.3 %), considerable solar photothermal conversion efficiency and superior thermal stability. The interfacial thermal resistance (ITR) of PEG/CNR is 73 % lower than graphene foam-based composite PCM thus a fast transient temperature response. Particularly, the package of PEG endowed composite PCM with elastic characteristic thereby an enhanced compressive strength. Furthermore, covering PEG/CNR results in a delay of approximately 1.3 times in reaching the peak temperature on the surface of electronic components, and a delay of 5 times in cooling time. This study presents solid guidelines for societal development that is sustainable and makes some recommendations for construction of composite PCMs combining multifunctional applications.

Evaporation Properties of Water through Floating Porous Structures for Desalination

The floating porous structure consists of an optical absorption layer, a porous layer, and an insulating layer. Water is pumped through a porous structure to the top absorption surface for evaporation. A numerical model of interfacial evaporation of floating porous structure is established. A multiphysical field coupling model for heat transfer, flow, and mass transfer within porous structures is simulated. The transient temperature response, evaporation flux, and vapor concentration distribution inside the structure are calculated. Effects of porous structure characteristics, such as size and porosity, on evaporation performance are discussed. With the increase of structure radius, the evaporation amount increases gradually, but the evaporation per unit area decreases with the radius. With the increase of the structure height, the evaporation amount and the evaporation flux decrease, but the decrease is relatively small. The porosity of the porous layer ε1 has a significant effect on the evaporation performance. The increase of ε1 is beneficial to the evaporation of water. When ε1 < 0.3, the effect of the porosity of insulation layer ε2 on the evaporation performance can be neglected.

A novel efficient method for transient heat analysis of cylindrical periodic structure based on the physical features and group theory

In this paper, a novel efficient and accurate numerical method is developed for analyzing the transient temperature responses of cylindrical periodic structures. By exploiting the structure’s circumferential cyclic periodic property and leveraging group theory, a circumferential decomposition strategy is presented to transform the temperature response analysis of the cylindrical periodic structure into the analyses of a series of one-dimensional periodic structures. Then, based on the physical nature of the transient heat conduction, an axial decomposition strategy is developed to convert the computations of the temperatures of these one-dimensional periodic structures into the calculations of the temperatures of a series of small-scale structures. The computational cost of these small-scale structures is further reduced by using the group theory. Several numerical examples demonstrate that the proposed method has higher accuracy and computational efficiency in comparison with the Crank-Nicolson method. When the Crank-Nicolson method attains the acceptable results, the proposed method is about 10 and 20 times faster than the Crank-Nicolson method with direct and preconditioning conjugate gradient solvers, respectively.

Three dimensional hybrid microcrystalline graphite-silica sol stabilized stearic acid as composite phase change material for thermal energy storage

Solid-liquid phase change material (PCM) is widely investigated, however it's low thermal conductivity and leakage issue hinder its large-scale commercial application. Numerous researchers have taken different approaches to enhance its thermal property, and have verified the optimized performance of the newly developed series of PCMs through experimental data and simulation results. In this report we developed a form-stable composite with the three-dimensional (3D) hybrid structure matrix to tackle this issue. Microcrystalline graphite (MG) was used as the structure material, and silica sol was used as a binder and porous skeleton to design and prepare the microcrystalline graphite-silica sol matrix in a 3D hybrid structure. Stearic acid (SA) was introduced to the 3D hybrid matrix to form composite PCM. The effects of the mass ratio between MG and silica sol on the pore structure of the 3D hybrid matrix were investigated systematically. With increasing the mass content of silica sol in the hybrid matrix, the loading capacity increases followed by decreasing, with a maximum loading of stearic acid as high as 49.94 % observed. The composite PCM could achieve the highest melting/cooling latent heat of 95.76 J g−1/96.04 J g−1 and higher thermal conductivity by 90.9 % than pure SA. The thermal infrared image indicated that the optimized composite had a better transient temperature response than pure SA. The leakage test proved that the 3D hybrid matrix stabilizes SA well, exhibiting excellent shape stability during phase change. These results demonstrated that the composition of MG/silica gel is an effective strategy, giving enhanced energy storage characteristics, including thermal stability, energy storage capacity, and thermal reliability.

A peridynamic model based on generalized thermoelastic theory in a plate with oblique cracks

In this paper, a peridynamic model based on generalized thermoelastic theory is derived by irreversible thermodynamics. This model avoids the spatial derivative and can be easily applied to generalized thermoelastic problems with discontinuities. The transient temperature response is captured using the non-Fourier CattaneoVernotte (C-V) model. The interaction integral is employed to calculate the transient thermal stress intensity factors (TSIFs). Numerical examples are presented for analyzing the effects of crack orientation angle and multi-crack distribution on transient thermoelastic response. And the crack propagation behavior under non-Fourier thermal shock is further discussed in detail. It is found that with the increase of the angle between inner crack and heating boundary, the sensitivity of mode-I TSIFs to the non-Fourier effect increases, while the sensitivity of mode-II TSIFs to the non-Fourier effect decreases. This peridynamic model may be useful for understanding the crack behaviors of thermal protection materials under thermal shock.

Inverse Piezoelectric and Trap Effects With Temperature Dependence in AlGaN/GaN HEMTs Under Narrowband Microwave Pulses

This article aims to study the thermal effect, inverse piezoelectric effect, and trap effect of aluminum gallium nitride (AlGaN)/gallium nitride (GaN) high-electron mobility transistors (HEMTs) with injection of narrowband (NB) microwave pulses where sensitive semiconductor devices are often disturbed or even damaged by intentionally electromagnetic interference. A series of AlGaN/GaN HEMT-based power amplifiers is designed and measured by utilizing an NB microwave system. The thermal analysis is performed by observing the temperature and thermal stress distributions over the structure and the temperature transient response in different dc conditions. Moreover, in the inverse piezoelectric analysis, the elastic energy density of AlGaN is calculated using a simulated vertical electric field and compared with the critical value of the material itself. Lastly, to fully understand these two failure mechanisms above on the device degradation, the influences of traps generated by these two effects above are investigated by analyzing the electron movement, trap behavior, and output drain current.

A thermal resistance detection of heteromorphic devices using SiC diode’s temperature-sensitive parameters

Certain special-shaped devices, such as traveling wave tubes, can be called hollow cylindrical structures in aerospace engineering and other applications. However, the structural complexity of such devices means that their heat dissipation characteristics cannot be measured directly using conventional techniques. The present work describes a method to directly measure such devices’ thermal resistance by semiconductors’ temperature-sensitive parameters. We prepared a special probe to collect transient temperature response, and the differential structure-function curves were obtained by processing the data using the structure-function method. We demonstrate that this method can effectively characterize cylindrical devices’ thermal resistance and detect differences caused by different processes and structures.

A Large-Scale Identification Approach for Thermal Parameters of Multichips IGBT Modules Based on LLSO-SQP Algorithm

This paper proposes a large-scale optimization approach for identifying thermal parameters of multi-chip IGBT modules. State-space equation, in which the coefficient matrix comprises the thermal resistance and capacitance, is provided to represent the compact three-dimensional thermal network model. Then, the level-based learning swarm optimization (LLSO) algorithm is firstly utilized to identify large-scale thermal parameters. Additionally, to solve the inefficient convergence problem, the optimization results obtained from the LLSO is provided as the initial value of the sequential quadratic programming (SQP) algorithm to find the global optimal solution. Hence, the proposed LLSO-SQP algorithm can identify the large-scale thermal parameters efficiently and accurately. The training dataset for the algorithm is derived from the transient temperature response of a finite element model (FEM) of the IGBT module under power step excitation. Since only one-time simulation is in-demand, this approach needs less computational effort than others. The identified thermal network model is utilized to estimate junction temperature profiles taking a two-level inverter as a case study. In comparison to that of the experiment and FEM, the results validate the feasibility and accuracy of the junction temperature estimation method based on the compact three-dimensional thermal network model.

Review on PCM Heat Sink for Electronic Thermal Management Application

A significant challenge in thermal management has arisen as a result of the rising demand for high-performance electronic devices. The efficiency, size, and weight of conventional cooling methods like liquid and air cooling are constrained. Due to their high storage of latent heat capacity and isothermal phase transition behavior, phase change materials (PCMs) have become a promising thermal management solution. The purpose of this experimental study is to evaluate the performance of a PCM heat sink for electronic thermal regulation. The PCM heat sink is made up of a PCM module attached to a typical heat sink. To improve heat dissipation capabilities, the PCM module uses a PCM material with a suitable phase change temperature and encapsulation. The experimental setup involves simulating real-world operating conditions by applying controlled heat loads to electronic components. By observing temperature changes, thermal resistance, and transient response, the PCM heat sink’s thermal performance is assessed. To evaluate the superiority of the PCM heat sink, a comparison is made with traditional air-cooled and liquid-cooled heat sink configurations. The experimental investigation’s findings show that the PCM heat sink performs better in terms of thermal management than traditional cooling techniques. The phase change process used by the PCM efficiently absorbs and stores extra heat produced by electronic parts, improving temperature regulation and lowering temperature gradients. Lower component temperatures and higher operational reliability are the results of the PCM heat sink’s improved thermal resistance and heat dissipation efficiency. A further benefit of the PCM heat sink’s isothermal behavior during the phase transition is that it prevents temperature spikes and lessens the effects of heat stress on the electronic devices. The long cooling times provided by the PCM material’s high latent heat storage capacity allow for prolonged operation without affecting device performance. This experimental study concludes by demonstrating the efficiency of a PCM heat sink for electronic thermal management. The design of heat sinks with PCM integration offers notable enhancements in temperature control, thermal resistance, and system overall reliability. The results of this research help to advance thermal management strategies, which makes it easier to create efficient electronic devices with better cooling capacities.

Fractional Dual-Phase-Lag Non-Fourier Heat Transfer in a Bimaterial with a Circular Interface Insulator

The transient temperature response of a bimaterial with a circular insulated interface region is studied under sudden heating or cooling. The time-fractional dual-phase-lag heat conduction model is adopted to simulate the non-Fourier effect. The problem is reduced to an initial-boundary value problem. The Laplace transform is applied to convert the problem to a mixed boundary value problem, and then the Hankel transform reduces it to a Fredholm integral equation. Special situations for asymptotic thermal behavior near the insulated circular edge and for the steady-state cases are discussed, respectively. The dynamic intensity factors of heat flux and temperature gradient near the insulated circular edge are computed numerically through Stehfest’s Laplace inversion transform technique. The influences of fractional order and relaxation times on the instantaneous temperature change are analyzed. The exact solution of temperature fields for the steady-state case is derived and displayed graphically. The wave-like diffusion behavior of the fractional dual-phase-lag model is interpreted.

Experimental Determination of Thermal Couplings in Packages Containing Multiple LEDs

Light Emitting Diodes (LEDs) are the most commonly used light sources. Temperature strongly affects their operation. Considering that multiple devices are often placed in a single housing, thermal couplings between devices become important. This problem is illustrated here based on the example of a light source containing four LEDs in a single package. Thermal analyses are carried out based on measured transient temperature responses. The measurement results are processed employing the Network Identification by Deconvolution method. The obtained results demonstrate clearly that depending on the device mounting manner and applied cooling condition the temperature rise value induced in neighboring devices can exceed 70% of the rise in the heating diode. Consequently, thermal models of such LEDs should consider not only self-heating effects, but also thermal interactions with the other diodes.

A thermal boundary resistance measurement method based on a designed chip with the heat source separated from the temperature sensor

Measurements of thermal boundary resistance (TBR) are of great significance in the fields of electronic packaging and thermal management. In this study, a measurement method based on a designed 1 × 1 mm2 chip with a heat source separated from a temperature sensor was developed. The chip consists of a temperature sensor with nine Schottky diodes connected in series and a heat source composed of metal wires, which are separated by SiO2 to realize electrical isolation. With this chip, the TBR of samples can be extracted from transient temperature response curves of GaN on a Si wafer using the structure function and transient dual interface test methods. In particular, the surface of samples was etched with uniform arrays to increase the measurement accuracy. The TBR measurements of four samples etched on the same wafer under different conditions were 1.62 ± 0.22 × 10−8, 1.6 ± 0.38 × 10−8, 1.49 ± 0.18 × 10−8, and 1.6 ± 0.35 × 10−8 m2K/W, indicating consistency of the results. This chip effectively expands the application of the structure function method to TBR measurements, which can be helpful for further research on interfacial heat transport.

3D-FEM thermal transfer analysis of MEMS-based thermal infrared emitter integrated with microchannel heatsink

Structure design and thermal simulation of MEMS-based thermal infrared (TIR) emitter integrated with Si-based microchannel heatsink (MCHS) were presented for gas sensing application. The MCHS attached on the bottom of TIR emitter was used to transfer heat to coolant for improving the transient response characteristics of TIR emitters. A three-dimensional finite element method was used to analyze the electrical heating and heat transfer behaviorsof the TIR emitter with MCHS through COMSOL Multiphysics® platform. The surface temperature distribution and transient response were simulated when different flow velocities of coolant passed through the MCHS, and the influence of the flow velocity on the response characteristics was analyzed. The result shows that the temperature in the Si frame of TIR emitters will be significant reduced when the flow velocity of coolant is larger than 0.5 m/s, which will enable an effective improvement in the response characteristics of MEMS TIR emitters.

A peridynamic model for non-Fourier heat transfer in orthotropic plate with uninsulated cracks

In this paper, the transient temperature response of a cracked plate under thermal shock is investigated. To eliminate the problems caused by the assumption of infinite heat propagation speed, the non-Fourier heat transfer theory is adopted. A peridynamic model is developed to consider the non-Fourier effect, the orthotropy of thermal conductivity, and the crack thermal resistance. This model avoids the spatial derivative and is efficient to analyze the problems with discontinuities. Based on the Kapitza thermal resistance model, a thermal resistance bond is proposed to deal with the uninsulated crack. The explicit and implicit discrete schemes of peridynamic formulation are presented to solve the temperature field. The model is verified by the analytical solution and excellent agreements are obtained. For the non-Fourier phenomenon observed in bismuth, numerical examples are presented for analyzing the effects of crack thermal resistance, crack orientation angle, and multi-crack distribution on non-Fourier heat transfer.

An Artificial Neural Network Model for Electro-Thermal Effect Affected Hot Carrier Injection Reliability in 14-nm FinFETs

FinFETs have a bright future for advanced analog/RF and digital circuit design in 5G/6G technology. As the integration density increases, the self-heating effect (SHE) becomes more severe, and the hot carrier injection (HCI) reliability of FinFETs further deteriorates since it is highly dependent on temperature. In this article, an artificial neural network (ANN) model for HCI prediction is proposed for 14-nm FinFET with consideration of SHE under various voltage stresses and environment temperature. The HCI numerical simulation can be mainly divided into two parts: 1) the temperature responses for the device under different stresses are obtained by numerically solving time-dependent thermal conduction equation with heat generation in the nanoscale FinFET and 2) based on the transient temperature response to different stress voltages, HCI-induced threshold voltage shift (TVS) as a function of time is captured numerically. Our HCI-induced TVS simulation results agree well with others’ experiment results, which verifies the simulation methods. An ANN model is then developed to predict the TVS induced by HCI with the training data obtained from numerical simulations. The ANN model has good accuracy with an average relative error of 0.36% in predicting TVS and greatly reduces simulation cost once the ANN model is built for the HCI prediction of FinFETs, which has great potential for reliability design in circuits and systems.

Transient heat transfer analysis of an orthotropic composite plate with oblique cracks using dual-phase-lagging model

Cracks have a significant effect on heat transfer in composites, yet the influence of oblique cracks on the temperature response of composites has not been fully investigated under strong transient thermal shock, in which the heat propagation velocity cannot be assumed to be infinite. In this work, the dual-phase-lagging heat transfer model is employed to capture the transient temperature response. By imposing different boundary conditions on the crack surface, an extended boundary correction algorithm has been derived to avoid the problem of non-convergence when dealing with large and small angle cracks. The effects of crack orientation angle and interaction between cracks on dual-phase-lagging heat conduction in orthotropic materials are analyzed at the macroscale. For the two-dimensional representative volume element (RVE) of fiber reinforced composite material, the influence of the multi-crack distribution on dual-phase-lagging heat conduction at the mesoscale is further discussed in detail.