Transient Heat Pulse Research Articles

Influence of transient heat pulse on heat transfer performance of vapor chamber with different filling ratios

Influence of transient heat pulse on heat transfer performance of vapor chamber with different filling ratios

Formation, cooling history and age of impact events on the IIE iron parent body: Evidence from the Miles meteorite

Most iron meteorites formed in planetary cores during differentiation, but the IIE iron meteorites have chemical and physical features that are inconsistent with this origin. By combining mineral chemistry, mineral modes and three-dimensional petrography, we reconstruct the bulk chemistry of the felsic silicate-bearing Miles IIE iron meteorite and demonstrate that the silicate inclusion compositions are similar to partial melts produced experimentally from an H chondrite composition. We use the reconstructed bulk composition, mineralogy and thermodynamic modelling to show that melting above ∼1200°C under reducing conditions formed metal (Fe-Ni alloy) and felsic silicate partial melts. Upon cooling, the melts crystallized Mg-rich pyroxenes, Na- and K-rich feldspars, and tridymite. Importantly, this mechanism enriches cosmochemically volatile elements (i.e., those with a 50% condensation temperature of ∼430–830°C, like Na and K) to the level found in the felsic silicate inclusions.The presence of crystallographically disordered srilankite (only stable above 1160°C) and an absence of Widmanstätten texture require both high peak temperatures and rapid cooling, which cannot be explained by core formation. Instead they point to small melt volumes, a transient heat pulse, and small thermal mass, and imply efficient physical segregation of silicate and metallic melts through buoyancy separation followed by rapid cooling that arrested the separation of metal and silicate liquid phases. In situ 207Pb/206Pb age of 4542.3 ± 4.0 Ma in Zr-oxide and phosphate minerals dates the melting event that formed the silicate inclusions. This age aligns with the earliest ages found in other IIE iron meteorite silicates and requires a heating event ∼25 million years after the solar system formed. We found 39Ar/40Ar ages of 3495 ± 52 Ma (low-T) and 4303 ± 7 Ma (high-T) in a K-feldspar grain, with the 3495 Ma age aligning with later thermal events recorded in other IIE iron meteorites. Dating reveals the complex petrogenetic and thermal history of Miles and the IIE iron meteorites. This is the first IIE iron meteorite found to record evidence of heating at 4.5 and 3.5 Ga likely from impact events.We propose that high-velocity impact(s) into an iron-rich, porous chondritic parent body at ∼4.54 Ga produced immiscible metal and silicate melts that cooled rapidly and trapped low density silicate inclusions within high density metal. Other IIE irons that formed at lower peak temperatures (900–1000°C) contain chondritic silicate inclusions and relict chondrules, supporting this conceptual model. This petrogenesis is consistent with thermodynamic modelling, experimental data and the wide range of peak temperatures and cooling rates observed in the IIE iron meteorites.

Transient Heat Pulse Testing to Monitor Subsurface Co2 Migration and Mobility

Transient Heat Pulse Testing to Monitor Subsurface Co2 Migration and Mobility

Transient pulse condensation

Transient convective droplet removal from condenser surfaces has the potential to significantly enhance thermal transport. Despite a century of progress in understanding of steady-state condensation, less is known about transient condensation. Here, we study transient pulse condensation of ethanol vapor. Using rigorous two-phase heat transfer measurements, we characterize transient heat transfer performance for filmwise and dropwise condensation of ethanol on smooth copper and nanostructured copper oxide lubricant-infused surfaces, respectively. We demonstrate an 8X and 5X enhancement in the condensation heat transfer coefficient during transient operation for dropwise and filmwise modes, respectively, when compared to the steady state. Beyond transient heat transfer enhancement, repeated cycles or pulses of dropwise condensation led to 30% higher time-averaged heat transfer performance due to higher nucleation site density and convective effects. Our work not only demonstrates transient condensation as a method to enhance heat transfer but also develops a methodology for enabling enhanced condensers for high power density thermal management systems for applications employing transient energy dissipation.

Analysis of Energy Transport Behavior and Geometric Effects in Graphene

Graphene is an excellent heat conductor, with the potential to be used as a heat spreader for applications where there are fast, transient heat pulses. In this study we analyze and describe energy transport in graphene subject to an initial pulse of energy. We analyze the effects of using harmonic, anharmonic, and a non-linear (Tersoff) potentials to describe the transient energy transport and compare these to classical continuum descriptions. The energy pulse produces pure wave-like behavior and a spatial energy distribution that has geometric features similar to the graphene geometry itself. Depending on the potential used, the energy travels outward from the impulse location following a similar pattern as the hexagonal shape of graphene. This pattern is clearly identified when the transport is treated with a harmonic potential. Increasing the anharmonicity and non-linearity dampens this effect and results in thermal transport that does not follow the geometry of graphene.

Conductive heat transfer in lamellar phase change material composites

Composite thermal energy storage materials consisting of highly thermally conductive and capacitive constituent elements can thermally buffer transient heat pulses. The ability to quantitatively describe these composite systems is valuable in the design of thermal management components to determine how a thermal load affects the necessary geometric aspects. Here, we develop numerical and analytical reduced-order solutions of 1D conductive heat transfer in lamellar multi-component thermal energy storage materials. Investigation of the limit in which conduction is the dominant term is important for the case where length-scales are small enough to limit convection or where the phase change material maintains a solid or high viscosity state at high temperatures. The response of lamellar PCM systems is herein described using (1) an effective medium approximation, and (2) a 1D “fin equation” approximation. Analytical solutions are compared against a higher resolution finite difference analysis numerical model in order to determine the length- and time- scales over which each expression is valid. The result of this work is a set of approximate solutions of transient thermal behavior in thermal energy storage composites, which can aid in the deliberate design of composite thermal energy storage materials to achieve desired performance characteristics. Remarkably, application of this approach predicts composite structures which absorb heat at much higher rates than pure metal conductors.

Neither heat pulse, nor multigenerational exposure to a modest increase in water temperature, alters the susceptibility of Guadeloupean Biomphalaria glabrata to Schistosoma mansoni infection.

There are increasing concerns regarding the role global climate change will have on many vector-borne diseases. Both mathematical models and laboratory experiments suggest that schistosomiasis risk may change as a result of the effects of increasing temperatures on the planorbid snails that host schistosomes. Heat pulse/heat shock of the BS90 strain of Biomphalaria glabrata was shown to increase the rate of infection by Schistosoma mansoni, but the result was not replicable in a follow up experiment by a different lab. We characterised the susceptibility and cercarial shedding of Guadeloupean B. glabrata after infection with S. mansoni under two temperature regimes: multigenerational exposure to small increases in temperature, and extreme heat pulse events. Neither long-term, multigenerational rearing at elevated temperatures, nor transient heat pulse modified the susceptibility of Guadeloupean B. glabrata to infection (prevalence) or shedding of schistosome cercaria (intensity of infection). These findings suggest that heat pulse-induced susceptibility in snail hosts may be dependent on the strain of the snail and/or schistosome, or on some as-yet unidentified environmental co-factor.

Quantitative Estimation of Leaf Heat Transfer Coefficients by Active Thermography at Varying Boundary Layer Conditions.

Quantifying heat and mass exchanges processes of plant leaves is crucial for detailed understanding of dynamic plant-environment interactions. The two main components of these processes, convective heat transfer, and transpiration, are inevitably coupled as both processes are restricted by the leaf boundary layer. To measure leaf heat capacity and leaf heat transfer coefficient, we thoroughly tested and applied an active thermography method that uses a transient heat pulse to compute τ, the time constant of leaf cooling after release of the pulse. We validated our approach in the laboratory on intact leaves of spring barley (Hordeum vulgare) and common bean (Phaseolus vulgaris), and measured τ-changes at different boundary layer conditions.By modeling the leaf heat transfer coefficient with dimensionless numbers, we could demonstrate that τ improves our ability to close the energy budget of plant leaves and that modeling of transpiration requires considerations of convection. Applying our approach to thermal images we obtained spatio-temporal maps of τ, providing observations of local differences in thermal responsiveness of leaf surfaces. We propose that active thermography is an informative methodology to measure leaf heat transfer and derive spatial maps of thermal responsiveness of leaves contributing to improve models of leaf heat transfer processes.

Heat pipe dryout and temperature hysteresis in response to transient heat pulses exceeding the capillary limit

The balance between the capillary pressure provided by the wick in a heat pipe or vapor chamber and the flow resistance to liquid resupply at the evaporator determines the maximum heat load that can be sustained at steady state. This maximum heat load is termed as the capillary limit; operation at steady heat loads above the capillary limit will result in dryout at the evaporator wick. However, different user needs and device workloads can lead to highly transient heat loads in applications ranging from consumer electronic devices to server processors. In these instances, the operation of heat pipes must be assessed in response to brief transient heat loads which could be higher than the notional capillary limit that governs dryout at steady state. In the current study, experiments are performed to characterize the transient thermal response of a heat pipe subjected to heat input pulses of varying duration that exceed the capillary limit. Transient dryout events due to a wick pressure drop exceeding the maximum available capillary pressure can be detected from an analysis of the measured temperature signatures. It is demonstrated that under such transient heating conditions, a heat pipe can sustain heat loads higher than the steady-state capillary limit for brief periods of time without experiencing dryout. If the heating pulse is sufficiently long as to induce transient dryout, the heat pipe may experience an elevated steady-state temperature even after the heat load is reduced back to a level lower than the capillary limit. The steady-state heat load must then be reduced to a level much below the capillary limit to fully recover the original thermal resistance of the heat pipe. This characteristic temperature hysteresis following transient dryout has significant implications for the use of heat pipes for pulsed power dissipation. Further experiments are performed to bound the range of heat loads over which the temperature hysteresis is present following a transient dryout event.

Optimizing Rotor Speed and Geometry for an Externally Mounted HTS Dynamo

High-temperature superconductor (HTS) dynamos provide a means of wirelessly exciting dc currents in HTS coils. By eliminating the need to connect a coil to a room-temperature power supply, an HTS dynamo of comparable performance would present significant improvements to the cost, complexity, and efficiency of HTS-based electromagnetic machines. But due to the lack of a predictive model, development of HTS dynamos must be carried out through empirical investigation. In this paper, we examine the effects of varying either the rotor speed or the number of magnets arranged symmetrically upon the rotor. Both approaches affect the frequency at which magnets cross the HTS stator wire. Here we present experimental results from an axial-flux HTS dynamo, employing an externally mounted rotor carrying m permanent magnets, where 2 ≤ m ≤ 9. We find that the open-circuit dc voltage, short-circuit dc current, and internal dc resistance are all determined solely by the magnet-crossing frequency, regardless of the number of rotor magnets and speed employed to achieve this frequency. For a fixed speed, all three parameters are found to be proportional to m across the full range of conditions studied in this work. However, for a fixed number of rotor magnets, we observe that the open-circuit voltage and short-circuit current both exhibit a similar sublinear dependence on rotor speed. Examination of the transient voltage waveform reveals that this nonlinearity is likely due to a periodic transient heat pulse absorbed by the stator wire each time the magnet traverses it at high speed.

Physics basis for the first ITER tungsten divertor

Abstract On the eve of component procurement, this paper discusses the present physics basis for the first ITER tungsten (W) divertor, beginning with a reminder of the key elements defining the overall design, and outlining relevant aspects of the Research Plan accompanying the new “staged approach” to ITER nuclear operations which fixes the overall divertor lifetime constraint. The principal focus is on the main design driver, steady state power fluxes in the DT phases, obtained from simulations using the 2-D SOLPS-4.3 and SOLPS-ITER plasma boundary codes, assuming the use of the low Z seeding impurities nitrogen (N) and neon (Ne). A new perspective on the simulation database is adopted, concentrating purely on the divertor physics aspects rather than on the core-edge integration, which has been studied extensively in the course of the divertor design evolution and is published elsewhere. Emphasis is placed on factors which may increase the peak steady state loads: divertor target shaping for component misalignment protection, the influence of fluid drifts, and the consequences of narrow scrape-off layer heat flux channels. All tend to push the divertor into an operating space at higher sub-divertor neutral pressure in order to remain at power flux densities acceptable for the target material. However, a revised criterion for the maximum tolerable loads based on avoidance of W recrystallization, sets an upper limit potentially ∼50% higher than the previously accepted value of ∼10 MW m−2, a consequence both of the choice of material and the finalized component design. Although the simulation database is currently restricted to the 2-D toroidally symmetric situation, considerable progress is now also being made using the EMC3-Eirene 3-D code suite for the assessment of power loading in the presence of magnetic perturbations for ELM control. Some new results for low input power corresponding to the early H-mode operation phases are reported, showing that even if realistic plasma screening is taken into account, significant asymmetric divertor heat fluxes may arise far from the unperturbed strike point. The issue of tolerable limits for transient heat pulses is an open and key question. A new scaling for ELM power deposition has shown that whilst there may be more latitude for operation at higher current without ELM control, the ultimate limit is likely to be set more by material fatigue under large numbers of sub-threshold melting events.

Summary of thermal analyses to determine the refrigeration power for the JT-60SA helium refrigerator

JT-60SA is an upgrade of JT-60U using exclusively superconducting coils to confine the plasma with a typical flat top duration up to 100 s in purely inductive mode. In order to define the helium refrigerator requirements for the superconducting coil system, their thermal protection and the cryopumps, heat loads at different temperature levels have been defined. Because of plasma pulse operation, transient heat pulses appear at the 4 K level for the superconducting coils and the cold structures as well as at the divertor cryopumps of JT-60SA.Since the heat loads were calculated at an earlier stage of the project, the loads of each component design had a certain amount of uncertainty. In JT-60SA, an attempt was made to define reasonable contingencies for the heat load by applying Monte Carlo simulation and put the 99% confidence value of the heat load as requirement for the refrigerator. Exergy analysis of heat loads at different temperatures and the helium mass flows of the JT-60SA resulted in an equivalent refrigeration power of about 9 kW at 4.5 K. This paper summarizes all the thermal analyses performed to determine the refrigeration power of the JT-60SA helium refrigerator.

Cooling power and characteristic times of composite heatsinks and insulants

Thermal energy storage materials for transient thermal management applications must exhibit large energy storage densities as well as large cooling/heating power densities. The latter property has proven difficult to quantify on a materials basis because it depends on extrinsic effects. Here, we apply a previously defined cooling power figure of merit, a measure of a material’s intrinsic capacity to absorb a transient heat pulse, to analyze composite phase change material heatsinks and insulants. The results demonstrate important limits on the effects of high- and low-conductivity component volume fractions, orientations, and the critical lengthscales of individual components. Champion composites are predicted to have up to 5 times greater figure of merit than pure high-conductivity materials and up to 30 times greater figure of merit than pure phase change materials. Furthermore, composites consisting of insulating materials containing dispersed phase change materials are predicted to exhibit an order of magnitude increase in their characteristic response time. These results demonstrate the utility of the cooling power figure of merit to design compact high power and energy density heatsink and insulant materials.

High pulse number transient heat loads on beryllium

The experimental fusion reactor ITER will apply beryllium as first wall armor material. In present fusion experiments, e.g. ASDEX Upgrade, it has been detected that up to 25% of the plasma energy loss is deposited in non divertor regions during edge localized mode (ELM) events. Therefore, the impact of transient heating events on beryllium needs to be investigated to reliably predict the performance of the beryllium armor tiles under ITER operational conditions. In the present experiments, the electron beam facility JUDITH 2 was used to exert transient heat pulses with power densities of 0.14–1.0GWm−2, as they can be expected for mitigated Type 1 ELMs in ITER, pulse durations in the range of 0.08–1.0ms, and a number of pulses in the range of 103–107 on S-65 beryllium specimens that were brazed on an actively cooled copper structure. Thereby, a strong drop of the melting threshold was discovered from a heat flux factor FHF = 22–25MWm−2s0.5 for 102 pulses to FHF < 12MWm−2s0.5 for 103 pulses. However, a saturation of the thermally induced damage was observed for FHF ≤ 9MWm−2s0.5 after 105 pulses. This result indicated a promising performance of beryllium under a high number of transient heat pulses in ITER. Nevertheless, the synergistic effects between thermal loads, particle loads, and neutron irradiation might affect the saturation threshold and need to be investigated in future studies.

Four-core optical fiber as a calorimetric gauge.

A four-core optical fiber is demonstrated as a calorimetric gauge for investigation of one-dimensional heat transfer measurements. Transient heat pulses from a Nd:YAG laser of 600 ms duration with a repetition rate of the order of 10 s are delivered onto the cleaved distal end face of the four-core fiber, aiming at one of the single cores only, which cause an optical path length difference between four guiding cores due to the temperature-induced change in the index of refraction and physical length of the targeted fiber core of concern. This results in a shift in the fringe pattern, which is operated in the reflection scheme. A phase shift of 0.43±0.015 rad is measured with a CMOS camera for 40 mW pulses. The thermal heat diffusion length in the selected fiber core is determined to be 2.8 mm, which contains 10.9±0.38 kJ/m2s heat, causing a temperature rise of 1.43±0.05 K.

Oxide segregation and melting behavior of transient heat load exposed beryllium

In the experimental fusion reactor ITER, beryllium will be applied as first wall armor material. However, the ITER-like wall project at JET already experienced that the relatively low melting temperature of beryllium can easily be exceeded during plasma operation. Therefore, a detailed study was carried out on S-65 beryllium under various transient, ITER-relevant heat loads that were simulated in the electron beam facility JUDITH 1. Hereby, the absorbed power densities were in the range of 0.15–1.0 GW m−2 in combination with pulse durations of 1–10 ms and pulse numbers of 1–1000.In metallographic cross sections, the emergence of a transition region in a depth of ~70–120 µm was revealed. This transition region was characterized by a strong segregation of oxygen at the grain boundaries, determined with energy dispersive x-ray spectroscopy element mappings. The oxide segregation strongly depended on the maximum temperature reached at the end of the transient heat pulse in combination with the pulse duration. A threshold for this process was found at 936 °C for a pulse duration of 10 ms. Further transient heat pulses applied to specimens that had already formed this transition region resulted in the overheating and melting of the material. The latter occurred between the surface and the transition region and was associated with a strong decrease of the thermal conductivity due to the weakly bound grains across the transition region. Additionally, the transition region caused a partial separation of the melt layer from the bulk material, which could ultimately result in a full detachment of the solidified beryllium layers from the bulk armor. Furthermore, solidified beryllium filaments evolved in several locations of the loaded area and are related to the thermally induced crack formation. However, these filaments are not expected to account for an increase of the beryllium net erosion.

Study of temporal pulse shape effects on W using simulations and laser heating

Transient heat pulses with triangular, square, and ELM-like temporal shapes are investigated in order to further understand how transient plasma instabilities will affect plasma facing components in tokamaks. A solution to the 1D heat equation for triangular pulses allows the peak surface temperature to be written analytically for arbitrary rise times. The solution as well as ANSYS simulations reveal that a positive ramp (maximum rise time) triangular pulse has a higher peak surface temperature by a factor of compared to that from a negative ramp (rise time = 0) pulse shape with equal energy density, peak power, and pulse width. Translating the results to ITER, an ELM or disruption pulse with the shortest rise time is the most benign compared to other pulse shapes with the same peak heat flux and same energy density.

Anomalous heat conduction in asymmetric graphene Y junctions

Through MD simulation of the transient heat pulse propagation in asymmetric Y junction, we report a novel type of controllable heat conduction in graphene nanostructure. The Y junction consists of a steam breaking into a wide branch and a narrow branch. In contrast to the classic situation where heat conductivity is proportional to the cross-sectional area of the material, the transmitted part of the heat pulse in the narrow branch is anomalously much stronger than that in the wide branch. As we increase the width ratio between the wide branch and narrow branch, transmitted coefficient in the narrow branch decreases a little, while in the wide branch, it decreases sharply. Specifically under 2:1 width ratio, transmitted coefficient of the narrow branch is three times that of the coefficient of the wide branch. Further analysis shows that the anomalous heat conduction is primarily induced by the behavior of the longitude vibrational modes.

Coupled interactions between tungsten surfaces and transient high-heat-flux deuterium plasmas

Fundamental studies on the interactions between transient deuterium-plasma heat pulses and tungsten surfaces were carried out in terms of electrical, mechanical and thermal response in a compact plasma device AIT-PID (Aichi Institute of Technology-Plasma Irradiation Device). Firstly, electron-emission-induced surface-temperature increase is discussed in the surface-temperature range near tungsten's melting point, which is accomplished by controlling the sheath voltage and power transmission factor. Secondly, anomalous penetration of tungsten atomic efflux into the surrounding plasma was observed in addition to a normal layered population; it is discussed in terms of the effect of substantial tungsten influx into the deuterium plasma, which causes dissipation of plasma electron energy. Thirdly, a momentum input from pulsed plasma onto a tungsten target was observed visually. The force is estimated numerically by the accelerated ion flow to the target as well as the reaction of tungsten-vapour efflux. Finally, a discussion follows on the effects of the plasma heat pulses on the morphology of tungsten surface (originally a helium-induced ‘fuzzy’ nanostructure). A kind of bifurcated effect is obtained: melting and annealing. Open questions remain for all the phenomena observed, although sheath-voltage-dependent plasma-heat input may be a key parameter. Discussions on all these phenomena are provided by considering their implications to tokamak fusion devices.

Combination of helical ferritic-steel inserts and flux-tube-expansion divertor for the heat control in tokamak DEMO reactor

Edge localized modes (ELMs) in the H-mode operation of tokamak reactors may be suppressed/mitigated by the resonant magnetic perturbation (RMP), but RMP coils are considered incompatible with DEMO reactors under the strong neutron flux. We propose an innovative concept of the RMP without installing coils but inserting ferritic steels of the helical configuration. Helically perturbed field is naturally formed in the axisymmetric toroidal field through the helical ferritic steel inserts (FSIs). When ELMs are avoided, large stationary heat load on divertor plates can be reduced by adopting a flux-tube-expansion (FTE) divertor like an X divertor. Separatrix shape and divertor-plate inclination are similar to those of a simple long-leg divertor configuration. Combination of the helical FSIs and the FTE divertor is a suitable method for the heat control to avoid transient ELM heat pulse and to reduce stationary divertor heat load in a tokamak DEMO reactor.