Transient Temperature Variation Research Articles

Surface temperature field real-time reconstruction of hot forging die based on 1DCNN

Accurate reconstruction of the die surface temperature field during the hot forging process is crucial for ensuring optimal control of die temperature and high-quality metal forgings. In this study, we propose a novel method that combines hot forging process parameters with a deep neural network to reconstruct the temperature field on the die surface in real-time. Firstly, a high-fidelity finite element model of the hot forging process is created and validated with a forging experiment. Secondly, temperature observation points are initially selected based on the simulated temperature distribution of the forging die, and the correlation coefficient method is used to optimize the layout of observation points to improve reconstruction accuracy and efficiency. Subsequently, multiple high-quality simulations with varying process parameters are conducted, generating a comprehensive dataset. The 1DCNN algorithm is then presented to produce a mapping from the input to the surface temperature field. Finally, the effectiveness of the surface temperature field reconstruction method is verified. The results indicate that the overall performance of the proposed 1DCNN algorithm is better than the traditional regression algorithms. In terms of reconstruction accuracy, it achieves a prediction accuracy within an absolute error of 3 °C for the outer surface points and within a relative error of 5 % for the cavity region. Regarding reconstruction efficiency, it requires an approximate execution time of 0.064 s for predicting a new sample. This paper presents a method for real-time reconstruction of the die surface temperature field, leveraging hot forging process parameters and temperature data from observation points. This approach enables reliable online monitoring of transient temperature variations on the hot forging die surface, offering valuable support for operational control and maintenance.

Thermoelectric active cooling for transient hot spots in microprocessors

Modern microprocessor performance is limited by local hot spots induced at high frequency by busy integrated circuit elements such as the clock generator. Locally embedded thermoelectric devices (TEDs) are proposed to perform active cooling whereby thermoelectric effects enhance passive cooling by the Fourier law in removing heat from the hot spot to colder regions. To mitigate transient heating events and improve temperature stability, we propose a novel analytical solution that describes the temperature response of a periodically heated hot spot that is actively cooled by a TED driven electrically at the same frequency. The analytical solution that we present is validated by experimental data from frequency domain thermal reflectance (FDTR) measurements made directly on an actively cooled Si thermoelectric device where the pump laser replicates the transient hot spot. We herein demonstrate a practical method to actively cancel the transient temperature variations on circuit elements with TEDs. This result opens a new path to optimize the design of cooling systems for transient localized hot spots in integrated circuits.

Ultrafast, self-powered monolithic pressure sensing technology induced by piezo-pyrophototronics

Pressure sensing is a pivotal aspect of modern technology that has been extensively explored, but still presents significant challenges. This work introduces an innovative ultrafast self-powered pressure sensing technology by harnessing the lateral photovoltaic effect (LPE) in a CIGS heterojunction via piezo-pyrophototronics. By utilizing non-uniform irradiation, a surface gradient of charge carriers is induced, resulting in the generation of a lateral photovoltage (LPV) that contributes to the excellent self-powered characteristic of the sensor. This gradient is then coupled with external pressure through the piezo-phototronic effect, enabling the sensing capability of the device. The enhancement of LPV, which is dependent on the irradiation position, power and wavelength, exhibits an extremely linear relationship with the applied external pressure ranging from 0 to 2.0 MPa. Besides, the pyroelectric field generated by transient temperature variations introduces an additional modulation to the pressure sensing effect, leading to an impressive pressure sensitivity of 64.25 mV/MPa, and a rapid response speed of 7.8/8.9 μs. This work highlights the benefits of the lateral photovoltaic effect, piezo-phototronic effect, and pyroelectric modulation in developing highly sensitive and ultrafast self-powered pressure sensors.

A comprehensive prediction model of drilling wellbore temperature variation mechanism under deepwater high temperature and high pressure

Comprehensively considering the impact of properties of drilling fluid at high temperature and high pressure (HTHP), drill string eccentricity, rotation, and rock breaking of drill bit on the annular temperature profile, transient temperature variations were predicted by using a wellbore heat transfer model. The model was numerically solved using the finite difference method. Compared to DRILLBENCH simulations, the predicted model was more consistent with the field-measured data. The calculations revealed that comprehensively considering various heat source factors made the annular temperature closer to the actual wellbore value, with a temperature difference of up to 10.66 °C. When considering variations of properties of drilling fluid at HTHP, the lower section of the annulus showed a significant decrease in temperature with depth, with a bottom-hole temperature difference of 5.4 °C. The bottom-hole temperature decreased by about 2.6 °C from concentric to eccentric drill string, and the pressure difference was about 1 MPa. Compared to drill string eccentricity, rotation and rock breaking of drill bit had a greater impact on annular temperature, with bottom-hole temperature differences of 13 °C and 22 °C, respectively. Accurate temperature modeling can better understand and predict the variation patterns of wellbore temperature, providing important guidance for the development of deepwater drilling.

Multiphysics modeling and experimental validation of heat and mass transfer for the vacuum induction melting process

Vacuum induction melting is crucial in casting nickel-based superalloy components, ensuring excellent properties for aero-engine applications. Precise melting temperatures are vital for achieving optimal metallurgical quality before casting. Hence, a multiphysics numerical model is developed to simulate the induction melting process for the Inconel 718 superalloy. The proposed holistic model integrates magnetic fields, induced currents, and heat and momentum transfer phenomena in a single coupled model. A moving mesh approach reproduces the magneto-hydrodynamic behavior of the free surface, simulating the oscillations of the melt. The stabilized deformed surface profile is correlated with experimental measurements, reporting a proper correlation. Then, the flow field and recirculation effect are modeled with a Low Reynolds Number turbulence approach and coupled with the melt convective heat transfer, developing a complete magneto-thermo-hydrodynamic model. In a laboratory-scale vacuum induction melting furnace, transient melting operation variables are characterized and introduced to the numerical model to compute the temperature evolution. An accurate reproduction of the transient melt temperature variations is reported with a relative error of less than 5%. The influence of the crucible thermal insulating capacity is assessed, emissivity dependence evaluated, and melt homogenization is reported at different process stages. This comprehensive numerical and experimental approach offers valuable insights for enhancing vacuum induction melting for Ni-based superalloys.

Conduit Processes at the Haukadalur Geyser‐Hosting Hydrothermal Field (Iceland) Revealed by In Situ Temperature and High‐Speed Camera Measurements

AbstractGeysers fascinate scientists and visitors for several centuries. However, many driving mechanisms such as heat transfer in the conduit and in the subsurface remain poorly understood. We document for the first time transient temperature variations inside the active Strokkur's and nearby quasi‐dormant Great Geysir's conduits, Iceland. While recording temperature inside the conduit, we visually monitored Strokkur's activity at the vent with a high‐speed camera, providing a high temporal resolution of the eruptions. Our results reveal heat transfer from a bubble trap to and through the conduit. We propose a model for the eruptive cycle of Strokkur that includes vapor slug rise, eruption, and conduit refill. Each water jet of an eruption is marked by an initial pulse of liquid water and vapor, emitted at a velocity between 5 and 28 m/s and generally followed by a second pulse less than a second later. The timing of eruptions coincides with temperature maxima in the conduit. After the eruption, the conduit is refilled by water falling back in the pool and drained from neighboring groundwater‐saturated geological units. This results in a temperature drop, the amplitude of which increases with depth while its period is reduced. This reflects faster heat transfer in the deeper than shallower part of the conduit. The amplitude of temperature drop following an eruption also increases with the eruption order, implying larger heat release by higher‐order eruptions. Temperature in the conduit subsequently increases until the next eruption, starting then a new cycle.

Thermal analysis methods for wound rotor synchronous motors with water-cooling jackets

A thermal equivalent circuit (TEC) was presented as an effective thermal analysis method for a wound rotor synchronous motor (WRSM) with a water-cooling jacket. The effectiveness of the TEC analysis was verified by comparison with the results of the experiments and numerical analysis. The steady-state temperature obtained from the TEC matched well with those obtained from the experiments and numerical analysis. The transient temperature variation in each part of the WRSM estimated by the TEC was in good agreement with the experimental results. Therefore, TEC can easily estimate the temperature information of the WRSM.

Resolving transient temperature and density during ultrafast laser ablation of aluminum

To understand the dynamics of ultrashort-pulse laser ablation, the interpretation of ultrafast time-resolved optical experiments is of utmost importance. To this end, spatiotemporally resolved pump-probe ellipsometry may be utilized to examine the transiently changing dielectric function of a material, particularly when compared to two-temperature model simulations. In this work, we introduce a consistent description of electronic transport as well dielectric function for bulk aluminum, which enables unambiguous quantitative predictions of transient temperature and density variations close to the surface after laser excitation. Potential contributions of these temperature and density fluctuations to the proposed optical model are investigated. We infer that after the thermal equilibrium of electrons and lattice within a few picoseconds, the real part of the dielectric function mostly follows a density decrease, accompanied by an early mechanical motion due to stress confinement. In contrast, the imaginary part is susceptible to a complicated interaction between time-varying collision frequency, plasma frequency, and a density dependency of the interband transitions. The models proposed in this study permit an outstanding quantitative prediction of the ultrashort-pulse laser ablation’s final state and transient observables. Consequently, it is anticipated that in the future, these models will provide a quantitative understanding of the dynamics and behavior of laser ablation.Graphical abstract

Investigating effects of pore-scale variables and pore geometries on the thermal behaviors of porous concretes

Thermal behaviors play significant roles in the design of porous concretes. However, the effects of pore geometries on microscopic thermal behaviors are not still well understood. This work aims to propose a microscopic analysis framework to construct different microstructure models and to study the effects of pore geometries on the thermal behaviors of porous concretes. The microstructures with pore and cement phases are generated using the random generation algorithm (RGA) and compared with realistic microstructures. Digital numerous simulations are conducted to investigate the temperate distribution and heat transfer properties in the pixelated microstructures. Pore-scale variables, such as pore fractal dimension, pore size and porosity, are defined to understand their effects on the thermal behaviors of concretes. Results show that the transient temperature variation behaviors occur in the microstructures, which may be caused by the non-equilibrium heat transfer in the transient time scale. The effective thermal conductivity (ETC) decreases with increasing the pore radius, circularity, porosity and pore number, and it increases as pore fractal dimension increases. The microstructures with square pores have the largest ETC than those microstructures with pentagon, hexagon, and circle pore geometries. Totally, the numerical ETC agrees well with the analytical ETC, showing the accuracy of the proposed microscopic analysis framework. The proposed microscopic concrete analysis framework can provide effective tools to the fire resistance design of concrete constructions used for the green buildings and deep projects such as the deep bury of nuclear wastes.

On the interfacial deformations and thermal characteristics exhibiting self-similar behavior under the action of a line heat source

Interfacial dynamics resulting from a heating source located near the interface play a crucial role in dictating the heat and momentum transport in the near-interface region. This paper aims toward simultaneous characterization of interfacial deformation and thermal behavior under the action of a line heating source placed below the interface. Experiments have been conducted on aqueous glycerol with a heating wire at different power inputs and depths from the interface. The interfacial deformations are mapped and quantified by employing moon-glade background oriented schlieren, which offers real-time, non-intrusive whole field measurements based on the deflection of light rays from liquid interface. Infrared thermography is used to measure transient interfacial temperature variations. Results show that the interface exhibits a convex-shaped deformation under the influence of the heating wire for all cases of heating power and depth. The maximum interface temperature coincides with the peak interfacial deformation. However, the region of thermal influence is smaller compared to the deformed region. Non-dimensionalization of transient interface deformation and temperature profiles establishes the underlying similarity of the phenomenon as non-dimensional interface perturbation profiles overlap for all cases of height and heating power. These characteristics are also observed for normalized temperature profiles at different wire depths.

Experimental study on sodium Screen-Wick heat pipe capillary limit

Heat pipes continuously transport the latent heat of vaporization from the evaporator to the condenser in the heat pipes due to the capillary pressure created by the menisci in the wick pumping the condensed fluid back to the evaporator. The heat pipe heat transfer capacity is then limited by the capillary limit. However, fewer capillary limit experiments were conducted to investigate the transient temperature variations and physical mechanism at the capillary limit for liquid metal wick heat pipes. This work presents capillary limit transient measurements on a sodium screen-wick heat pipe for high heat fluxes, high heating rates during frozen startup, and negative and positive inclination angles. It also investigates the special behavior before and after dryout, including dryout oscillations and the recovery process to understand the cause and physical mechanism at the capillary limit. The direct cause of the capillary limit is that the evaporation rate exceeds the capillary-driven liquid supply to the evaporator. The experiments show that the capillary limit creates a rapid temperature increase of about 5 °C/s at the evaporator end, while the condenser and adiabatic section temperatures decrease. Dryout oscillations were observed with positive inclinations before the capillary limit. After the capillary limit, reducing the power to just below the limit does not lead to heat pipe recovery, but the power needs to be reduced by about 30% of the critical heat flux to make the heat pipe return to its normal operating state.

Influence of Temperature on the EFT Immunity of Multistage Integrated Oscillators

The reliable operation of an integrated circuit (IC) can be affected by transient electromagnetic disturbances and temperature variations. In this paper, the performance of three oscillator circuits, namely 3- and 5-stage current-starved voltage controlled oscillators and a 3-stage ring oscillator, is compared with respect to electrical fast transients (EFT) under the influence of thermal stress. The main objective is to compare and assess, by means of measurements, the EFT immunities of integrated oscillators with the same electrostatic discharge (ESD) protections but different circuit topologies. The failure modes caused by EFT are proposed based on the considered failure criterion. Moreover, the importance of the IC package on the immunity levels of each oscillator is investigated. The output frequency response of each oscillator to the combined EFT and temperature stresses is analyzed without the external parasitics. The results show that the 5-stage CSVCO is most resilient towards temperature variations, whereas it is the least immune to the combined effect of EFT and temperature. Moreover, a distinct behavior in each tested oscillator's frequency is observed for the in-phase EFT injections due to the topology of the circuit. Relevant MOSFET characteristics such as on-state drain-to-source resistance, power dissipation, effective mobility and threshold voltage are further analyzed under the influence of thermal stress and EFT. The root cause of higher EFT susceptibility of the 5-stage CSVCO is found to be the considerable variation of the on-state resistance due to the combined reduction of effective mobility and absolute threshold voltage levels of the MOSFETs.

Analysis of Unsteady Heat Transfer during Ice-Making Process for Ice Rink Buildings

The ice-making process is an important factor that affects the ice quality and the energy consumption of ice rinks. An unsteady heat transfer model is established and validated for the ice-making process. The transient temperature variation and ice thickness growing characteristics during the ice-making process are analyzed. The freezing time of a water layer and the final temperature of the stabilized ice layer are quantified. The effects of ice rink structural parameters on the ice-making process are studied. The results show that the water temperature variations during the process go through three stages. The ice-growing process mainly occurs in the second stage. The ice-making process takes about 305 min–420 min for a water layer of 5 mm thickness. The reduction in the ice-making time and the decrease in the final temperature of the stabilized ice layer can be attained by reducing the water layer thickness, the surface heat flux, the cooling pipe spacing, the fluid temperature in the cooling pipe, or the top concrete thickness. Among them, the influences of the thickness of the water layer, the surface heat flux, and the fluid temperature in the cooling pipe are more significant. As the thickness of the water layer decreases from 7 mm to 3 mm, the total ice-making time decreases by about 37.6%. The ice-making time is reduced by 17.1% with the surface heat flux decreasing from 330 W/m2 to 250 W/m2. The ice-making time is reduced by 21.4% with the cooling pipe temperature decreasing from −15.5 °C to −19.5 °C.

Opto-electric flash Raman method for in situ measuring temperature variation of power device with a high temporal resolution

This paper develops an in-situ high temporal resolution opto-electric flash Raman method to accurately measure the temperature fluctuation of power devices caused by modulated driving voltage. By synchronous modulation, the pulsed laser can maintain the same frequency as the driving voltage of the power device, and the working temperature of the device during the laser pulse can be obtained from the excited Raman spectrum. By adjusting the time delay between the pulsed laser and the electric signal with 100 ps resolution, the temperature variation in a cycle can be accurately determined. This method measures the temperature changes of GaN high electron mobility transistors device versus a square wave driving signal with different frequencies. The experimental results show that, in amplitude modulation mode with 100 Hz, the maximum temperature change through a driving cycle can be more than 20 K. This illustrates that high temporal resolution measurement is significant in determining the peak temperature of hot spots in the power devices. Two samples fixed using different methods had considerably different transient temperature fluctuations under the same driving frequency, indicating that the transient temperature variation is a promising way to gauge how well the devices dissipate heat. The temperature variations caused by a complex driving signal were also determined in this work. As a transient method, the opto-electric flash Raman method is promising to be used in multi-type power devices to in situ detect temperature fluctuation and provide a reference for the evaluation and optimization of the device.

Thermal Behaviors of Thyristors in Repetitive Pulsed Power Applications

The temperature is closely related to the operating state of the thyristors in repetitive pulsed power applications. To study the thermal behaviors of the thyristor at high blocking voltage and repetition discharge frequency, the thermal calculation model, including the electrothermal model and the finite-element method (FEM) model, is established. The model is based on the practical conditions, the internal structure of the thyristor, and the heat transfer mechanism and is validated by comparing the experimental and calculation results. By the model, the transient junction temperature variation and the mathematical model among blocking voltage, repetition frequency, and junction temperature are obtained. The model presented is capable of evaluating the thermal behaviors, calculating the junction temperature of the thyristors in repetitive pulsed power applications, and providing optimal suggestions for the reliable operation of the pulsed power sources.

Coupled thermo-hydro-mechanical analysis of perforated cement sheath integrity during hydraulic fracturing

The wall of perforation hole was directly pressed by the high-pressure fracturing fluid, making cement integrity more challenged in fracturing process. However, the current calculation of perforated cement sheath stress neglects the influence of transient temperature variation during fracturing process. In this work, a fully coupled thermo-hydro-mechanical (THM) model incorporating the transient heat transfer process of fracturing fluid was set up to describe the transient stress variation of cement sheath during fracturing. The maximum tension stress criterion and Mohr-Coulomb criterion were chosen as the criterions for the cement failure. The proposed model was successfully verified through its excellent agreement with experimental observations. In addition, based on the proposed model, the influence of fracturing parameters and cement mechanical parameters on cement integrity was analyzed. The results illustrate that a spindle-shaped tensile-shear failure area is formed near the cement hole. The casing pressure and the cement mechanical parameters are the main controlling factors for the failure of the perforated cement sheath. The extremely low casing pressure are beneficial for maintaining cement sheath integrity. Besides that, only optimizing the Poisson's ratio or elastic modulus of cement cannot maintain the perforated cement integrity unless improving both simultaneously.

Understanding the influence of unsteady and convection terms in heat transfer model on the predicted heat flux in engines operated under different combustion modes

The aim of current research is to develop an enhanced heat transfer model to accurately predict the heat flux through the cylinder walls during the working process of internal combustion engines operated under different loads and combustion modes. Two enhanced models, i.e., the unsteady model and the steady convective contribution (SCC) model were respectively constructed based on the thermal wall function. The effects of the transient ambient gas temperature and pressure variations, as well as the chemical reaction source term, were included in the unsteady model. Then the contributions of the unsteady terms, such as the temporal derivative of gas temperature, the pressure work, and the chemical heat source in the energy equation were analyzed in detail. The results indicate that the mechanism of the unsteady heat transfer process is different in the engine operated under motored conditions and different combustion modes, including conventional diesel combustion (CDC), homogeneous charge compression ignition (HCCI), and reactivity controlled compression ignition (RCCI). Afterward, the influence of the gas velocity and the pressure difference perpendicular to the walls were included in the SCC model to consider their contributions to the heat fluxes near the chamber walls. It is found that the heat fluxes predicted by the SCC model are in better agreement with the experimental data, especially in the CDC mode under different swirl ratios and loads. The peak of the heat flux predicted by the SCC model shows superiority to that of the previous steady heat transfer models and the unsteady heat transfer model.

Input Uncertainty and Implication for Modeling Generic and High-Fidelity Transient Convection Problems

Transient processes and uncertainty propagation impacting the transient temperature variation profile for a plate heated from the top and convection cooled at the bottom surface are investigated. The model dimensionless input parameters, such as the Biot number Bi and dimensionless initial conditions, are formulated describing physical properties of the plate and ambient medium with subsequent impact on the dimensionless temperature variation. As is shown, in the case of small Bi, dimensionless relaxation time of the temperature variation toward its steady state is proportional to and can be very large. For large Bi, the temperature variation usually passes through a peak before reaching its stationary profile. Stochastic nature of the dimensionless temperature variation is explored. As is found, the amplitude of its stochastic spread depends, in general, on the mean values of the dimensionless inputs at a fixed standard deviation. As is also shown, dimensionless time evolution of the uncertainty amplitude depends crucially on standard deviations of the dimensionless input parameters; it may increase or decrease with time, or stay small over time. Finally, uncertainty propagation in a high-fidelity model of a copper block, used in an experimental setup, is compared with the developed generic plate model.

A physical depiction of a semi-spherical fin unsteady heat transfer and thermal analysis of a fully wetted convective-radiative semi-spherical fin

The current investigation scrutinizes non-Fourier heat conduction law to describe transient temperature variation through a convective-radiative wetted semi-spherical fin with internal heating. The fin is fully wetted with a hybrid nanofluid containing MnZnFe2O4−NiZnFe2O4 nanoparticles and water or methanol (methyl alcohol (MA)) as base liquids. Dimensionless terms are used to nondimensionalize the energy equation, and the finite difference method (FDM) is used to solve the nonlinear partial differential equation (PDE). In addition, graphs are drawn to explore the impact of several non-dimensional attributes on the temperature gradient, such as radiation-conduction, convection-conduction, and internal heat production parameters for hybrid nanofluid containing MnZnFe2O4 and NiZnFe2O4 nanoparticles with different base liquids. The major findings of the study show that as the magnitude of the wet parameter, and radiation-conduction parameters increases, the transient thermal distribution through the fin drops. Thermal distribution, on the other hand, improves for the parameter of heat generation.

Thermal Management of Small-Scale Li-ion Battery Module Using Graphite Matrix Composite with Phase Change: Effect of Discharge Rate

An experimental study is performed to investigate the performance (thermally and electrically) of a small-scale li-ion module (3s2p) using passive thermal management strategy of phase change material (PCM)/graphite matrix. The PCM/graphite matrix was obtained by impregnating the graphite matrix (bulk density: 75 g L-1) with phase change material (paraffin/organic, RT-35). The performance tests of a li-ion module are conducted at 1C and 1.6C discharge rates for graphite matrix composite with phase change (phase change composite or PCM/graphite matrix) and also air cooling, comparatively. To illustrate the performance of the PCM/graphite matrix, transient temperature variations, thermal imaging, discharge capacity, and energy capacity are achieved comprehensively. The results illustrate that graphite matrix composite with phase change has a significant contribution to melting heat transfer, operating temperature, utilized capacity, and energy capacity compared to air cooling. Effective thermal conductivity of PCM/graphite matrix is increased 35 times by comparison with pure paraffin. Operating temperature and temperature gradient throughout the li-ion surface decrease by 22 % and 43 % compared to the air cooling, respectively, for high discharge rate. Operating time and energy capacity is increased 33 % and 28% compared to natural air cooling, respectively, for high discharge rate. It is also disclosed that dominant heat transfer mechanism is conduction depending on micro/nano-size porous structure of graphite matrix.