High-power Heating Research Articles

Performance modelling on a thermoelectric air conditioning system using high power heat sinks and promoting waste heat utilization

Performance modelling on a thermoelectric air conditioning system using high power heat sinks and promoting waste heat utilization

A novel ultra-thin vapor chamber with composite wick for portable electronics cooling

With the development of integrated and ultra-thin portable electronics, the ultimate heat dissipation power in extremely narrow spaces (<1 mm) is increasing year by year. However, the current critical power of ultra-thin vapor chamber (UTVC) is still at a low level, which hinders the development of high-power portable electronic products. In this study, novel UTVCs with a thickness of only 0.5 mm are prepared by utilizing the composite capillary wick. Different from the traditional multi-layer 2D copper mesh wick, the composite (CA/CB) wick is composed of multi-layer 2D copper mesh and 3D spiral woven mesh. UTVCs prepared from three different wicks, referred as to 2D-UTVC, CA-UTVC, CB-UTVC, were compared. Under different working conditions, the CA/CB-UTVC has better heat transfer performance than 2D-UTVC. In the horizontal state, the maximum effective thermal conductivity (Keff) of CA-UTVC and CB-UTVC is significantly improved by 86.8% and 60.2% compared to that of reference 2D-UTVC. The CA design is recommended for low heating power within 40 W, while the CB design is the optimal choice for high heating power above 40 W. The maximum critical power of CB-UTVC is up to 60 W with gravity support. Even at 50 W under anti-gravity condition, the thermal conductivity of CB-UTVC is still up to 11817.1 W/(m K), which is 29.5 times that of copper. The improved heat dissipation is due to the enhanced capillary force of the composite wick. This positive effect is facilitated by the combination of multiple 3D spiral woven meshes in the CB design. The optimized UTVC effectively reduces the maximum temperature by 14.3 °C compared to copper sheet under natural convection at 10 W heating power. The novel UTVC could provide a guarantee for the heat dissipation of high-power integrated portable electronic devices in the future.

Heaterless 300A lanthanum hexaboride hollow cathode.

Hollow cathodes used in electric propulsion typically have an external heater to raise the thermionic electron emitter to emission temperatures. Heaterless hollow cathodes that are heated by a Paschen discharge have been historically limited to low discharge currents (<5A) due to arcing and inefficient heating. A new heaterless technology was previously developed for cathodes up to 50A, utilizing a refractory metal tube to extend the gas feed line partway into the thermionic insert region. A high voltage (>700V) Paschen discharge is ignited between the keeper and the tube, which quickly transitions to a lower voltage (<80V) thermionic discharge from the inner tube surface and heats the thermionic insert by radiation. This "tube-radiator" configuration eliminates arcing and inhibits the long-path-length discharge between the keeper and gas feed tube upstream of the cathode insert that caused inefficient heating in prior designs. This paper describes extending this technology developed for a 50A cathode to one that is capable of 300A. The larger cathode uses a 5-mm diameter tantalum tube-radiator and a 6-A, 5-minignition sequence. Ignition was challenging because the high heating power required (≥300W) is difficult to maintain with the low voltage (<20V) keeper discharge that exists prior to igniting the thruster discharge. To achieve self-heating from the lower voltage keeper discharge, the keeper current is raised to 10A once the LaB6 insert starts emitting. This work shows that the novel tube-radiator heater is scalable to large cathodes capable of tens of thousands of ignitions.

Study on divertor detachment and pedestal characteristics in the DIII-D upper closed divertor

Experiments performed in DIII-D demonstrate that higher plasma current and heating power combined with impurity seeding facilitate the achievement of divertor detachment with a higher pedestal pressure and higher plasma performance in H-mode plasmas with a baffled closed divertor compared with an open divertor. Dedicated experiments were carried out to study the impact of power, plasma current and impurity seeding on divertor detachment with ion directed into the divertor favorable for the L–H transition. With a factor of three variation in heating power and with only D2 puffing, no significant difference in the separatrix density at detachment onset was found. The higher heating power leads to higher impurity concentration and wider scrape-off layer (SOL) width, and reduces the detachment onset density to one similar to that in lower-power plasmas. Higher current requires higher pedestal and line-averaged densities to achieve divertor detachment; however, the increase in separatrix density at increasing plasma current is found to be less pronounced. Initial calculations found that both power scan and plasma current scan datasets are qualitatively consistent with theory after considering the change in impurity concentration and heat flux width. This also motivates the future extensive study of transport and divertor impurity behavior in order to have a quantitative comparison between experiment and theory. Compared with an open divertor, a closed divertor facilitates detachment onset at ∼40% lower line-averaged plasma density. Additional N2 seeding facilitates the achievement of detachment at a lower separatrix density and thus a higher pedestal temperature, which is beneficial for advanced tokamak scenarios. Higher heating power requires a higher N2 puffing rate to achieve the same degree of detachment, while a higher N2 puffing rate leads to lower detachment onset line-averaged density, both of which agree with theory. In contrast to the narrower pedestal in an open divertor approaching detachment, the pedestal density width in a closed divertor increases with density. The density gradient increases with line-averaged density at higher plasma current, but remains nearly unchanged at lower plasma current. In particular, compared with discharges with low power, at high heating power the pedestal density gradient is much weaker, while the SOL density is significantly higher and wider. At the same plasma current, both pedestal pressure gradient and temperature gradient decrease linearly with the line-averaged density but remain similar across different heating powers. Even with different plasma current and heating power, the normalized pressure gradient remains identical. As a result, achievement of divertor detachment with a higher pedestal pressure and higher plasma performance is shown in a closed divertor, which is important for improving core–edge integration as one of the critical issues for future tokamak fusion reactors.

Hybrid-kinetic simulation of synergy between fishbone/sawtooth and tearing mode-induced energetic-ion transport in a tokamak plasma

The resonant interaction between tearing mode (TM) and energetic ions redistributed by fishbone/sawtooth collapse has been observed recently in HL-2A neutral beam injection-heated high-density plasmas, where m is the poloidal mode number and n is the toroidal mode number. This event essentially results from a synergistic effect with a multiple-mode nature. Understanding such experimental phenomena, especially when using high-power auxiliary heating, is crucial for achieving high-performance plasmas with high confinement and high β N in the prospective thermonuclear fusion reactors. In this work, based on the typical experimental phenomenon of synergy between fishbone/sawtooth and TM on HL-2A, a self-consistent nonlinear hybrid-kinetic simulation is conducted utilizing the experimental parameters and profiles before the occurrence of this synergy as the code M3D-K input. In particular, we focus chiefly on the phase-space transport, loss and redistribution of energetic ions induced by two cases, one with only TM and one with synergy between fishbone/sawtooth and TM. It is found that the synergy of the fishbone/sawtooth and TM on energetic-ion transport, loss and redistribution is important and can dramatically enhance the loss rate of energetic ions compared with the case with only TM. It is due to the fact that such synergy can open up an efficient energetic-ion loss channel which connects the plasma center and edge. The phase space transport and redistribution of energetic ions induced by the two different cases are also respectively analyzed and compared in detail. Because of the overestimation of amplitudes of fishbone/sawtooth and TM in the simulations, the obtained energetic-ion transport level is only limited in the context of the numerical framework. These findings indicate that the synergy triggering the sawtooth collapse may lead to an enhancement of the energetic-ion transport and can help us understand the underlying mechanisms of synergy-induced energetic-ion transport.

The effect of pulse heating on saturated boiling heat transfer in rough surfaces

The boiling heat transfer efficiency in smooth surface can no longer meet the high-power equipment heat dissipation requirements. By changing the surface roughness and pulse heating conditions, we can have higher boiling bubble nucleation point density to achieve higher heat transfer efficiency. However, the influencing mechanism of the surface roughness and pulse heating conditions on boiling bubbles needs further study. In this paper, the effects of different cavities and pulse heating conditions on the boiling bubbles dynamics and the heat transfer enhancement are investigated by Lattice Boltzmann method (LBM). The results show that compared with constant heating, the nucleation sites of pulse heating are larger. As the pulse amplitude increase, the nucleation rate tends to be faster. The heat transfer curves of the most obvious difference in nucleation phenomenon under different heating conditions are also investigated. Compared with the constant heating at Tb<1.09Tc, the heat transfer coefficient (HTC) maximum increase being up to 30.54%. Under pulse heating, the increase of HTC decreases with the increase of superheat and eventually it is lower than that of constant heating.

Silicone-Based Thermally Conductive Gel Fabrication via Hybridization of Low-Melting-Point Alloy-Hexagonal Boron Nitride-Graphene Oxide.

Thermal contact resistance between the microprocessor chip and the heat sink has long been a focus of thermal management research in electronics. Thermally conductive gel, as a thermal interface material for efficient heat transfer between high-power components and heat sinks, can effectively reduce heat accumulation in electronic components. To reduce the interface thermal resistance of thermally conductive gel, hexagonal boron nitride and graphene oxide were hybridized with a low-melting-point alloy in the presence of a surface modifier, humic acid, to obtain a hybrid filler. The results showed that at the nanoscale, the low-melting-point alloy was homogeneously composited and encapsulated in hexagonal boron nitride and graphene oxide, which reduced its melting range. When the temperature reached the melting point of the low-melting-point alloy, the hybrid powder exhibited surface wettability. The thermal conductivity of the thermally conductive gel prepared with the hybrid filler increased to 2.18 W/(m·K), while the corresponding thermal contact resistance could be as low as 0.024 °C/W. Furthermore, the thermal interface material maintained its excellent electric insulation performance, which is necessary for electronic device applications.

Investigation of key factors for ITB formation and maintenance in EAST high βN discharges

Long-pulse high βN operation scenario with internal transport barrier (ITB) and central flat q profile has been achieved on EAST. Analysis shows that higher heating power is needed to obtain ITBs in higher density discharges. Analysis of EAST high βN experiments shows that fishbone activities are accompanied with formation ITB and high performance. Experimental and simulation analysis demonstrates that the increasing E x B shear flow by the neutral beam injection (NBI) is important for the formation of ion temperature ITB (Ti-ITB). And, Ti-ITB disappears with the reduction of plasma rotation. While ITBs in channels of electron density (ne) and temperature (Te) are not achieved until fishbone activities are observed, which means that E x B shear flow mainly affects the formation of Ti-ITB in EAST high βN experiments. Experimental analysis shows that the fishbone is accompanied by the increasing E x B shear flow, leading to the formation of Ti-ITBs. A possible explanation for the formation of ITBs in all channels is that fishbone activities in high βN discharges with central flat q-profiles (closed to unity) induce the feedback process of the formation of ITBs, and leading to the increase of E x B shear flow as well as the formation and sustainment of ITBs.

Large-eddy simulation on gas mixing induced by the high-buoyancy flow in the CIGMAfacility

The hydrogen behavior in a nuclear containment vessel is a significant issue when discussing the potential of hydrogen combustion during a severe accident. After the Fukushima-Daiichi accident in Japan, we have investigated in-depth the hydrogen transport mechanisms by utilizing experimental and numerical approaches. Computational fluid dynamics is a powerful tool for better understanding the transport behavior of gas mixtures, including hydrogen. This paper describes a Large-eddy simulation of gas mixing driven by a high-buoyancy flow. We focused on the interaction behavior of heat and mass transfers driven by the horizontal high-buoyant flow during density stratification. For validation, the experimental data of the Containment InteGral effects Measurement Apparatus (CIGMA) facility were used. With a high-power heater for the gas-injection line in the CIGMA facility, a high-temperature flow of approximately 390 °C was injected into the test vessel. By using the CIGMA facility, we can extend the experimental data to the high-temperature region. The phenomenological discussion in this paper helps understand the heat and mass transfer induced by the high-buoyancy flow in the containment vessel during a severe accident.

Investigation of assisted heating cold start strategies from -40 °C for proton exchange membrane fuel cell stack

ABSTRACT To investigate the effects of varying assisted heating methods on the proton exchange membrane fuel cell (PEMFC) stack in extremely low-temperature conditions, a quasi-two-dimensional dynamic model is developed. This model considers the effect of cooling channels on cold starts and has been verified by experimental data. The limited self-start ability of an adiabatic PEMFC is tested, and the result shows that the PEMFC cannot start successfully from −40°C. Then, the effects of resistance wire heating and recycled coolant heating methods on the PEMFC stack are analyzed at −40°C. For the resistance wire heating method, due to the limitation of thermal conductivity, higher heating power can hardly raise the temperature of the middle cells in the stack. Furthermore, only stacks with fewer than 6 cells can start successfully. For the recycled coolant heating method, the heat can be effectively transferred to the internal zone of the stack through the coolant. The maximum temperature difference in the stack is decreased (from 32.43°C to 7.64°C, 308.6 mW cm−2) with higher coolant flow rates. However, higher heating power is needed to achieve a successful cold start (205.8 mW cm−2 under 0.01 m s−1, 308.6 mW cm−2 under 0.05 m s−1). In summary, the recycled coolant heating method is more suitable for the cold start of the stack at −40°C.

The ECRH-Power Upgrade at the Wendelstein 7-X Stellarator

The existing ECRH system at W7-X consists of 10 gyrotrons, with output power levels ranging from 0.6 MW up to 1.0 MW each at a frequency of 140 GHz, quasi-optical transmission lines and microwave launchers at the plasma vessel. Compared to other large fusion experiments, W7-X has a relatively low power-to-volume ratio. However high heating power is particularly necessary for achieving high plasma beta values, where the improved confinement of fast ions, one of the optimization criteria of W7-X, can be examined. It is therefore necessary to expand the ECRH systems in several consecutive steps. It is planned to increase the number of gyrotron positions from 10 to 12 and at the same time to evolve the gyrotron output power in several development steps from 1 MW to nominal 1.5 MW and, finally, up to 2 MW. At the same time, the transmission lines will also be upgraded for 2 MW operation. A special effort is also made to improve the reliability of the system by the fast control system.

Improved Thermal Management and Analysis for High-Power Heat Pipe Cooled FSCW PMSM for HEV Auxiliary Power Unit Application

Improved Thermal Management and Analysis for High-Power Heat Pipe Cooled FSCW PMSM for HEV Auxiliary Power Unit Application

Peripheral temperature gradient screening of high-Z impurities in optimised ‘hybrid’ scenario H-mode plasmas in JET-ILW

Screening of high-Z (W) impurities from the confined plasma by the temperature gradient at the plasma periphery of fusion-grade H-mode plasmas has been demonstrated in the JET-ILW (ITER-like wall) tokamak. Through careful optimisation of the hybrid-scenario, deuterium plasmas with sufficient heating power ( 32 MW), high enough ion temperature gradients at the H-mode pedestal top can be achieved for the collisional, neo-classical convection of the W impurities to be directed outwards, expelling them from the confined plasma. Measurements of the W impurity fluxes between and during edge-localised modes (ELMs) based on fast bolometry measurements show that in such plasmas there is a net efflux (loss) between ELMs but that ELMs often allow some W back into the confined plasma. Provided steady, high-power heating is maintained, this mechanism allows such plasmas to sustain high performance, with an average D–D neutron rate of s−1 over a period of ∼3 s, after an initial overshoot (equivalent to a D–T fusion power of ∼9.4 MW), without an uncontrolled rise in W impurity radiation, giving added confidence that impurity screening by the pedestal may also occur in ITER, as has previously been predicted (Dux et al 2017 Nucl. Mater. Energy 12 28–35).

Optimal allothermal conversion of the quasi-renewable fuel composition

The low-grade fossil fuels and herbal oils attract more and more attention last years due to the low price and high availability of the first together with fast reproducibility of the last. Thermochemical conversion of the quasi-renewable fuel compositions of peat and herbal oil under the high-power heating was experimentally investigated in this paper. Such fuels have a quite low calorific value at self-sustaining combustion and, thus, just the allothermal approaches are mostly appropriate for their conversion. The component ratio allowing the maximal usage of the fuel oxidation heat as well as highest production of the combustible gases was determined (2:1 in favour of oil). The emission of the hazardous gases is 2–3 times lower for such composition in comparison with pure peat conversion. The light flux with intensity of more than 600 W/cm2 allows the fast increase of temperatures (up to more than 700 °C) that is high enough for thermochemical conversion of the fuel. The lower intensities mostly initiate the slow evaporation of the volatile oil components without essential oxidation of the fuel.

In situ consolidation of carbon fiber PAEK via laser-assisted automated fiber placement

Automated fiber placement (AFP) of thermosetting composites has been one of the leading manufacturing techniques for aerospace structures over the last decade. Thermoplastic composites (TPCs) offer several advantages including a high toughness, recyclability, weldability, and potential for rapid out-of-autoclave manufacturing. High-power heating sources and flexible compaction rollers can be used to melt and consolidate TPC tapes via AFP to form large structures in a layer-by-layer manner as used in additive manufacturing. This paper investigates the in-situ consolidation AFP of TPC tapes (ICAT) toward their process optimization and revealing mechanisms that govern the ICAT process. To this end, a laser-assisted AFP system was utilized to fabricate short beam strength samples from carbon fiber reinforced low-melt polyaryletherketone (LM-PAEK™) at various processing parameters. Analysis of results revealed how ICAT process parameters affect interlaminar bonding, crystallinity, and void content in manufactured parts. Multiphysics finite element analysis (FEA) was also carried out to reveal mechanisms that control void, crystallinity, and bonding in ICAT. Finally, a comparison of post-fracture specimens made via ICAT with traditional compression molding was used to explain the underlying failure mechanisms in ICAT coupons. This study shows that at AFP rates of up to 0.15 m/s, high interlaminar shear strengths, up to 60 MPa, are possible to achieve with low void content (<1%) and high crystallinity (>20%), proving that ICAT is potentially a viable process for manufacturing the next generation of aerospace composites.

Tritium Operation of the JET Neutral Beam Systems and Tritium NBI Power Calculations

Neutral beam injection (NBI) is a very flexible auxiliary heating method for tokamak plasmas, capable of being efficiently coupled to various plasma configurations required in the tritium and deuterium–tritium experimental campaign (DTE2) to be undertaken in the Joint European Torus (JET) device. In particular, experiments for high fusion yield and alpha particle studies require high-power NBI heating, and for maximum performance and optimum fuel mixture control in deuterium–tritium (D–T) plasmas, it is necessary to operate the JET NBI systems in both deuterium and tritium. The technical aspects of the JET NBI systems for compatibility with T operation are discussed, and the associated commissioning is described. The characterization of the JET NBI system in the tritium gas mode will be presented, with particular focus on the power and species mix measurements; this will be the first time that such data have been collected and analyzed for tritium neutral beams. Deuterium operation in the tritium gas mode was successfully carried out in 2019 with no loss in reliability. In this period of operation, the NBI power has been measured using beamline diagnostics and corroborated with plasma measurements. The species mix of the beam has been measured on the neutral beam test bed (NBTB) and also corroborated by plasma diagnostics on JET. These results will be presented alongside tritium NBI results allowing comparison of possible JET NBI performance between deuterium and tritium. Measurements of the NBI power in tritium show that there will be a higher neutralized fraction than in deuterium and a higher full energy fraction. When the effect of particle mass is also accounted for, this will lead overall to reduced beam penetration and lower particle flux per MW.

Experimental study on heat transfer performance of axially rotating heat pipe in steady state

Rotating heat pipe has a broad application prospect in the field of heat dissipation of rotating machinery due to its high heat transfer performance. However, researches on the heat transfer mechanism of the rotating heat pipe are insufficient, which limits its application. A horizontal axially rotating heat pipe with the cylindrical inner surface was made and tested with water and ethanol as the working fluids. The filling ratios of 65.3%, 39.2%, and 26.1% were experimentally studied, respectively. Then the heat transfer performances of the rotating heat pipes below 1100 RPM were mainly studied. Visualization of the flow pattern in the rotating heat pipe was carried out to explain the mechanism of the flow and heat transfer characteristics in the rotating heat pipe in detail. The thermal resistance was used to evaluate the heat transfer performance. Further, the thermal resistances at the evaporator and the condenser sections were also explored to reveal the intrinsic heat transfer mechanism of the rotating heat pipe. It is concluded that the thermal resistance of the rotating heat pipe is typically in the range of 0.1–0.6 K/W. The thermal resistance decreases monotonously with the increase of heating power and cooling temperature. It can be found that the optimal filling ratio is about 39.2% for the rotating heat pipe. Due to the transition of flow pattern, there is typically a maximum value of the thermal resistance of the rotating heat pipe with the variation of rotational speed, especially at high heating power, high cooling temperature, and low filling ratio.

Devices for Thermal Conductivity Measurements of Electroplated Bi for X-ray TES Absorbers

Electroplated bismuth (Bi) is commonly used in transition-edge sensors (TESs) for X-rays because of its high stopping power and low heat capacity (Collan in Phys Rev B 1:2888, 1970, Yan in Appl Phys Lett 111:192602, 2017). Electroplated Bi is usually grown on top of another metal that acts as seed layer, typically gold (Au), making it challenging to extrapolate its thermoelectric properties. In this work, we present four-wire resistance measurement structures that allow us to measure resistance as a function of temperature of electroplated Bi independently of Au. The results show that the thermal conductivity of the Bi at 3 K is high enough to ensure the correct thermalization of X-ray photons when used as an absorber for TESs.

Effect of continuously flowing liquid Li limiter on particle and heat fluxes during H-mode discharges in EAST

• Particle and heat fluxes were successfully controlled by using continuously flowing liquid Li (FLiLi) limiter in the H mode discharges with high plasma heating power in EAST. • By using flowing liquid Li limiter, the fuel recycling could effectively reduce by ∼ 50% and Zeff could decrease from 2.3 to 1.6. • The decreased recycling and impurity radiation led to the achievement of high energy confinement plasma with the average stored energy increased up to ∼ 290 kJ. • Due to Li vapor shielding effect, ∼40% plasma heat flux was dissipated before arrived at the Li limiter. Particle and heat fluxes were successfully controlled by using a continuously flowing liquid Li (FLiLi) limiter in the H-mode discharges with high plasma heating power in the Experimental Advanced Superconducting Tokamak device. There were strong interactions between the FLiLi limiter and high-power plasma with a ∼ 8.3 MW source heating power, and successively, a bright Li radiation ring was produced, which effectively decreased fuel particle recycling by approximately 50%. Due to Li efflux from FLiLi during a series of high-power discharges, an obvious real-time wall conditioning effect was produced, and fuel particle recycling further decreased. Moreover, the value of Z eff decreased from 2.3 to 1.6 due to a decrease in impurity sources; this was attributed to the accumulation of Li deposited on the first wall, which effectively protected the wall materials. The decreased recycling and impurity radiation achieved high-energy confinement plasma, and the average stored energy increased up to ∼ 290 kJ. Moreover, due to the effect of Li vapor shielding, nearly 30% plasma heat flux was dissipated before it arrived at the Li limiter. These results promote further exploration of liquid Li solutions for the critical challenge of heat flux handling and particle control in fusion power plants.

Heat transfer under high-power heat release: Not fully stable fluids as potential heat carriers

• Significant disturbance in heat transfer under high-power heating was detected. • Supercritical-pressure water and highly unstable aqueous mixture were studied objects. • Heat transfer deterioration stage preceding macroscopic phase transition was revealed. • This stage is assumed to have universal character for fluid phase transitions. • Its nature is associated with the violation of homogeneity of not fully stable system. In this paper, we present new data on non-stationary heat transfer in sub- and supercritical liquids due to high-power heat release in a wire probe immersed in an investigated liquid. In the performed experiments, the characteristic heating time was from 5 to 180 ms, while the corresponding thickness of the heated layer was in the magnitude order of 10 1 µm. The impetus for the study came from the previous discovery of two unexpected effects. The first was a deterioration of heat transfer during the rapid transition of a compressed fluid to the supercritical region of temperatures along the isobar. The second was the distinctive character of the change in the heat flux density of a binary, partially miscible liquid when going deeper into the region of its unstable states. The study is aimed at clarifying the prospects of using supercritical fluids and mixtures with lower critical solution temperatures as potential heat carriers in processes where the possibility of powerful local heat release cannot be excluded.