High Heat Load Research Articles

Superstructures of water-dispersive hydrophobic nanocrystals: specific properties.

Here, we describe water-soluble superstructures of hydrophobic nanocrystals that have been developed in recent years. We will also report on some of their properties which are still in their infancy. One of these structures, called "cluster structures", consists of hydrophobic 3D superlattices of Co or Au nanocrystals, covered with organic molecules acting like parachutes. The magnetic properties of Co "cluster structures" a retained when the superstructures is dispersed in aqueous solution. With Au "cluster structures", the longer wavelength optical scattered spectra are very broad and red-shifted, while at shorter wavelengths the localized surface plasmonic resonance of the scattered nanocrystals is retained. Moreover, the maximum of the long-wavelength signal spectra is linearly dependent on the increase in assembly size. The second superstructure was based on liquid-liquid instabilities favoring the formation of Fe3O4 nanocrystal shells (colloidosomes) filled or unfilled with Au 3D superlattices and also spherical solid crystal structures are called supraballs. Colloidosomes and supraballs in contact with cancer cells increase the density of nanocrystals in lysosomes and near the lysosomal membrane. Importantly, the structure of their organization is maintained in lysosomes for up to 8 days after internalization, while the initially dispersed hydrophilic nanocrystals are randomly aggregated. These two structures act as nanoheaters. Indeed, due to the dilution of the metallic phase, the penetration depth of visible light is much greater than that of homogeneous metallic nanoparticles of similar size. This allows for a high average heat load overall. Thus, the organic matrix acts as an internal reservoir for efficient energy accumulation within a few hundred picoseconds. A similar behavior was observed with colloidosomes, supraballs and "egg" structures, making these superstructures universal nanoheaters, and the same behavior is not observed when they are not dispersed in water (dried and deposited on a substrate). Note that colloidosomes and supraballs trigger local photothermal damage inaccessible to isolated nanocrystals and not predicted by global temperature measurements.

An Experimental Study of the Effect a Ground-Source Heat Pump with a Soil Temperature Potential Recovery System Has on the Soil Thermal Imbalance under Cold Climate Conditions

Ground thermal balance disturbance is a serious problem that arises during the operation of heat pumps with a geothermal circuit. In regions with cold climate and high space heating loads, ground freezing leads to a significantly degraded performance of heat pumps during their long-term operation. Experimental studies to estimate the effect the ground temperature potential recovery system operation has on the ground thermal imbalance under the climatic conditions of the city of Moscow were conducted. The system considered includes three fan coils, which operate for air conditioning of building rooms. The excess heat extracted from air is transferred through a storage tank to the geothermal circuit wells. The system has shown its good performance, because with a longer time of heat pump operation with commensurable load, an insignificant decrease in the average ground temperature and in the heat carrier temperature at the heat pump evaporator inlet were noted. The use of such systems will help increase the effective service life of heat pumps with a geothermal circuit and expand their possible application field to colder regions with a strongly pronounced imbalance of thermal loads.

Refurbishment of W/B4C multilayers on Si substrate by etching a chromium buffer layer.

In synchrotron facilities, optics with multilayer coatings are used for beam monochromatization, focusing, and collimation. These coatings might be damaged by high heat load, poor film adhesion, high internal stress, or poor vacuum. Optical substrates always need high quality, which is expensive and has a long processing cycle. Therefore, it is desired to make the substrate reusable and the refurbished coating as good as a brand-new one. In this study, a W/B4C multilayer coating with a 2 nm Cr buffer layer was prepared on a Si substrate. The coating was successfully stripped from the Si substrate by dissolving the Cr buffer layer using an etchant. The roughness and morphology after the different etching times were investigated by measuring the GIXRR and 3D surface profiler. It is shown that the time required to etch the W/B4C multilayer coating with a Cr buffer layer, is quite different compared with etching a single Cr film. A layer of silicon dioxide was introduced during the fitting. After the new etching process, the roughness of the sample is as good as the one on a brand-new substrate. The W/B4C multilayer coatings with a Cr buffer layer were recoated on the etched samples, and the interface roughness was not damaged by the etching process.

Investigation of the dynamics of a Capillary Pumped Loop assisted with a mechanical pump: Influence of pump location

Capillary driven two-phase loops are promising solutions for cooling high power electronic devices. A significant upgrade of the operating conditions can be achieved by a small mechanical pump assistance removing the pumping limit inherent to the evaporator porous wick. However, in this couplings, the key issue is to maintain a steady vaporization regime in the evaporator. In the present study, the dynamics of a Capillary Pumped Loop assisted with a centrifugal pump is investigated with both experiments and modeling efforts. The results have revealed (i) that changing the pump location can deteriorate the system robustness with 5 times larger (2.25 kPa) evaporator pressure deviations and (ii) the appearance of a system bifurcation to undamped oscillations at high heat load. A theoretical analysis was performed in frequency domain. It has shown that the loop dynamics is affected by an unexpected transient positive feedback between the pump and the condenser. It has also shown that the loop robustness could be enhanced within a significant range of heat load by a suitable improvement of the condenser efficiency.

Optimal Multi-Mode Flexibility Operation of CHP Units with Electrode Type Electric Boilers: A Case Study

With the in-depth development of flexibility retrofit in combined heat and power (CHP) units, the unit commitment mode of energy supply equipment in CHP plants is more flexible. This paper presents a multi-mode flexible operation method for CHP plants with electrode electric boilers. Firstly, a simulation model of the operation characteristics of each unit in different operation modes is established, and the corresponding features of electrical and thermal outputs are obtained. Subsequently, a decision-making model of the unit commitment mode of energy supply equipment is set up, and the selection rules of the unit commitment mode of the unit under low heat load, medium heat load, and high heat load are achieved. Finally, under different unit operation combinations, a plant-level optimum load dispatch model is obtained, and the actual operating data of the CHP plant is used for optimization and comparison analysis. The results show that compared to the unit commitment mode of high back pressure and low-pressure cylinder cutting-off (HBP + LPCC), the unit commitment mode of high back pressure and extraction heating (HBP + EH) has more room for energy-saving optimization. Under the premise of safe and reliable operation, the high back pressure (HBP) unit can be loaded as much as possible. While in the combined operating of HBP + EH, the energy-saving space for optimized load dispatching is not large, so a fixed proportion of the electrical load may be considered; under the auxiliary service subsidy policy, the input power of the electric boiler can be appropriately increased; the greater the heat load of the whole plant, the more pronounced the energy-saving effect of optimum load dispatch.

Study on the Performance of a Newly Designed Cooling System Utilizing Dam Water for Internet Data Centers

A novel energy-saving hybrid cooling system that combines a forced-cooling cycle and a free-cooling cycle was developed to increase the energy efficiency of cooling systems in year-round operation of an internet data center with high heat loads. This system effectively utilizes a dam deep water source to reduce energy consumption in internet data centers. The hybrid cooling system operates in forced-cooling mode when the entering water temperature exceeds the mode change temperature of 9 °C, but switches to free-cooling mode when the ambient temperature falls below the mode change temperature. In this paper, the cooling performance of the hybrid system was assessed under various operating conditions based on entering water temperature fluctuation. Because the cooling effectiveness of this type of system is highly dependent on the outside climate, its usefulness and suitability for different periods and zones must be investigated. The annual energy saving performance of the new system was estimated and compared to a conventional cooling system in terms of the integrated coefficient of performance, based on the hourly weather air temperature and water temperature bin data collected from 16 cities of different climate zones in South Korea. The experimental findings revealed that the novel hybrid internet data center cooling system showed a 67% annual operating performance over a conventional air source internet data center cooling system due to the adoption of a dam deep water source.

Intra-Lid Multi-Core Vapor Chamber Architecture for Heterogeneous Electronic Packages: Technology Concept to Prototype Evaluation

Thermal management of future heterogeneous electronic packages with extreme heat fluxes relies on effective spreading of heat in the package lid. Intra-lid integration of vapor chambers is a promising strategy for simultaneous dissipation of large total heat loads and localized high-flux hot spots. However, conventional vapor chambers comprising a single vapor core require relatively thick evaporator wicks to prevent dry out at high total heat loads, thereby imposing a large temperature drop across the wick at the hot spot location. We recently proposed a cascaded multi-core vapor chamber (CMVC) architecture comprising a single-core vapor chamber stacked on an array of smaller footprint vapor cores having relatively thinner wicks. The multi-core array is designed to spread heat from arbitrarily distributed high-flux hot spots before they enter the top vapor chamber having a thicker wick. Then, the top vapor chamber spreads the high total heat loads to the base of the mounted heat sink. To evaluate the proposed CMVC technology, we make a weighted decision to identify an appropriate minimum viable prototype for subsequent design and testing. A reduced-order model is used to determine the dimensions and properties of the wick and vapor core that minimize the temperature drop across the down-selected multi-core vapor chamber architecture for a given power map, considering manufacturing process constraints. Finite element analysis (FEA) simulations are employed to decide a condenser wall thickness that avoids permanent deformation in the vapor chamber architecture under a mechanical load. A prototype is manufactured by a commercial vendor following these parameters and manufacturing constraints. As predicted by the thermal model, experimental characterization of this first-reported multi-core vapor chamber array prototype offers a notable reduction in temperature drop relative to a benchmark solid copper spreader, owing to attenuation of hot spots at a low temperature difference.

Damage simulation due to heat load from X-ray FEL beam at European XFEL

In the X-ray FEL beam transport system, the optic components which have direct contact with the beam, e.g. mirror, absorber and beam shutter, etc., could exceed 10 kW peak heat load on a sub-mm spot. Therefore, the thermo-mechanical performance of these components under the extreme high heat load will limit the maximum allowed pulses for the safety operation of the facility. In this contribution, a selection of multi-scale and multi-physics numerical models using finite element tools is introduced to describe the interaction of X-ray laser beam with different materials, taking into consideration of the multi-coupling of heat transfer, solid mechanics, fluid dynamics and phase transitions. The verified and validated models can be referred to define damage threshold of the optic components, and to virtually reproduce the damage mechanism of the materials.

Study of ruthenium film grown in oxygen environment for x-ray optics application

Ru shows high damage threshold as compared to other standard materials Au, Rh and Pt for high heat load applications in high brilliance synchrotron radiation source and x-ray free electron laser. It is also a promising candidate to be used as a protective capping layer in multilayers for increasing their life time. In the present study, Ru thin films of 500Å thickness were deposited in oxygen environment at different substrate temperatures varying from 70°C to 500°C. In reactive ion beam sputtering process, the flow of Ar and reactive O2 gas was maintained in 4:1 ratio keeping total flow 3 SCCM constant. The deposited films were characterized using grazing incidence x-ray reflectivity (GIXRR), grazing incidence x-ray diffraction (GIXRD) and secondary ion mass spectroscopy (SIMS) techniques. A significant change in GIXRR profile was observed in the sample grown at 100°C and 500°C whereas the GIXRD measurements indicated no significant formation of ruthenium oxide at different temperatures. However, a strong peak of Ru2Si3 (222) at 500°C was observed indicating a strong interfacial reaction at ruthenium/ substrate interface.The experimental data suggested a weak signature of RuO2 phase in the films deposited at RT, 70°C and 100°C and therefore the effect of ruthenium oxide with 10% composition in pure ruthenium was calculated on optical performance in extreme ultra violet region of photon energy (85-115 eV).

Performance assessment of planar and non-planar cryogenic pulsating heat pipe with novel condenser

Pulsating heat pipe (PHP) is gaining popularity as a viable solution for thermal conductive links associated with a cryogenic cooling system. A competitive commercial environment requires PHP with a more compact configuration, high heat load removal capacity, and free of orientation dependency. Making orientation-free PHP, a planar PHP (2D layout), requires a large number of turns, increasing the overall size of the PHP device. A PHP with a non-planar (3D layout) layout is capable of accommodating a large number of turns in a short area to tackle both compactness and orientation-dependent issues. The present paper focuses on a comparative thermal performance assessment of planar and non-planar configurations of cryogenic PHP by developing a novel cylindrical shell-type condenser (CSTC). Liquid nitrogen is used as a working fluid. Two separate test setups are developed with 2D Four-Turn PHP (2D FT-PHP) and 3D Four-Turn PHP (3D FT-PHP) with a novel CSTC. The condenser, adiabatic, and evaporator lengths of PHP are kept as 60 mm, 120 mm, and 50 mm, respectively. The thermal performance is assessed by varying Filling Ratio (FR) (38−95 %) and heat load (1 W–130 W) with an evaporator at the bottom position. It is observed that, for a particular heat load, a 3D FT-PHP performed better than a 2D FT-PHP, irrespective of FR. The anti-dry-out ability of 3D FT-PHP is observed to be superior to 2D FT-PHP at a low FR. The frequency analysis results with Wavelet transform show that the working fluid oscillates with a more dominant frequency in 3D FT-PHP than in 2D FT-PHP configuration.

Can heat pump heat storage system perform better for space heating in China’s primary schools? A field test and simulation analysis

The space heating system has a significant influence on the energy consumption and comfortable indoor environment for primary schools in China’s cold area. This study investigated the operational performance of heat pump systems in two primary schools. Results showed that the primary school buildings had high heating load at turn-on period every morning, which then quickly decreased when the students came to classroom. With this wide-range variation of heating load and unreasonable control strategy, the mismatch between heat source and heating demand happened very easily among the whole heating season. It then led to typical issues and poor energy efficiency of heat pump systems, including excessive space heating after school, low load ratio and frequent start-stop operation of heat pump systems, small water temperature difference and excessive water flow rate of water distribution system, etc. In allusion to those core issues, the heat pump heat storage system (HPHS) was raised for space heating in primary schools to decouple the heat supply side and the heat demand side. Then this study simulated and analyzed the operational performance of HPHS. Results showed that with reasonable control strategy, the excessive heat supply after school was effectively avoided to save almost 51% of the total heat consumption. Besides, the heat pumps could operate stably with almost full heating load for heat storage, thus reaching better energy performance with annual average COP of 5.13. Also the water distribution systems in the ground side, heat storage side and user side could reach better energy performance with high energy efficiency and reasonable water temperature difference among the heating season. Therefore, the HPHSs with reasonable control strategy could effectively solve those typical issues and are more suitable for primary schools.

Passive Cooling Analysis of an Electronic Chipset Using Nanoparticles and Metal-Foam Composite PCM: An Experimental Study

Thermal management of electronic components is critical for long-term reliability and continuous operation, as the over-heating of electronic equipment leads to decrement in performance. The novelty of the current experimental study is to investigate the passive cooling of electronic equipment, by using nano-enriched phase change material (NEPCM) with copper foam having porosity of 97%. The phase change material of PT-58 was used with graphene nanoplatelets (GNPs) and magnesium oxide (MgO) nanoparticles (NPs), having concentrations of 0.01 wt.% and 0.02 wt.%. Three power levels of 8 W, 16 W, and 24 W, with corresponding heating inputs of 0.77 kW/m2, 1.54 kW/m2 and 2.3 kW/m2, respectively, were used to simulate the heating input to heat sink for thermal characterization. According to results, at 0.77 kW/m2 heating input the maximum base temperature declined by 13.03% in 0.02 wt.% GNPs-NEPCM/copper foam case. At heating input of 1.54 kW/m2, the maximum base temperature reduction of 16% was observed in case of 0.02 wt.% GNPs-NEPCM/copper foam and 13.1% in case of 0.02 wt.% MgO-NEPCM/copper foam. Similarly, at heating input of 2.3 kW/m2, the maximum temperature of base lessened by 12.58% in case of 0.02 wt.% GNPs-NEPCM/copper foam. The highest time to reach the set point temperature of 50 °C, 60 °C, and 70 °C was in case of GNPs-NEPCM/copper foam composites, while at all power levels MgO-NEPCM/copper foam gave comparable performance to GNPs based composite. Similar trend was observed in the study of enhancement ratio in operation time. From the results, it is concluded that the copper foam incorporation in NEPCM is an effective measure to mitigate the heat sink base temperature and can provide best cooling efficiency at low and higher heating loads.

Soil nutrient release and microbial changes after burning of masticated fuels

AbstractSoil temperature extremes are not uncommon when woody fuels are ignited in prescribed burns or wildfires. Whether this leads to substantial loss of soil organic matter or microbial life is unclear. We created a soil heat gradient by burning four levels of masticated woody fuels (0, 34, 101, and 169 Mg ha−1) to determine if heat thresholds produce abrupt changes in soil C, N, microbial biomass, or fungal hyphae. Twenty‐four burns were conducted with masticated fuels overlaying a clay loam soil equilibrated at either 4 or 25% volumetric soil water content. Maximum temperatures ranged from 40 to 450 °C depending on fuel load and soil moisture content, with heat duration (>60 °C) as great as 22 h. Moist soil quenched temperatures two‐ to threefold compared with dry soil at comparable fuel loads. A slight, gradual decline in total C and N was found with increasing temperature and heat duration, reaching a maximum loss of 14–18% of the total at the highest heat load. Available NH4 increased linearly starting at 150–175 °C and reached a maximum 15‐fold increase relative to unburned soil by 450 °C. Nitrification (30 d post‐fire) was low regardless of treatment and was essentially eliminated at the highest temperatures. Microbial biomass declined curvilinearly with increased heating, approaching 65% loss compared with unburned soil, and was most rapid in moist soil once temperatures exceeded 60–70 °C. Ultimately, we found no evidence of abrupt heat thresholds for these common soil properties. Instead, property changes followed a slightly declining trajectory (soil C, N, NO3, fungal hyphae) or a steady incremental increase (NH4) or decrease (microbial biomass).

Hypersonic shock impingement studies on a flat plate: flow separation of laminar boundary layers

Interactions between shock waves and boundary layers produce flow separations and augmented pressure/thermal loads in hypersonic flight. This study provides details of Mach 7 impinging-shock-flat-plate experiments conducted in the T4 Stalker Tube. Measurements were taken at flow conditions of Mach 7.0 (2.44 MJ kg $^{-1}$ ) and Mach 7.7 (2.88 MJ kg $^{-1}$ ) flight enthalpies with a range of freestream unit Reynolds numbers from $1.43 \times 10^{6}$ m $^{-1}$ to $5.01 \times 10^{6}$ m $^{-1}$ . A shock generator at $12^{\circ }$ or $16^{\circ }$ to the freestream created an oblique shock which impinged on a boundary layer over a flat plate to induce flow separation. The flow field was examined using simultaneous measurements of wall static pressure, heat transfer and schlieren visualisation. Measured heat transfer along the flat plate without the shock impingement indicated that the boundary layer remained laminar for all flow conditions. The shock impingement flow field was successfully established within the facility test duration. The onset of separation was observed by a rise in wall pressure and a decrease in heat transfer at the location corresponding to the stem of the separation shock. Downstream of this initial rise, an increased pressure and higher heating loads were observed. The heat-transfer levels also indicated an immediate boundary layer transition due to the shock impingement. The separation data of the present work showed good agreement with our previous work on shock impingement on heated walls (Chang et al., J. Fluid Mech., vol. 908, 2021, pp. 1–13). A comparison with the previous scaling indicated that the separation also relates to the pressure ratio and the wall temperature parameter.

Condensation regimes inside a vapor chamber with transparent hollow fins of circular, triangular or fluted cross section

A vapor chamber with integrated hollow fins was manufactured and tested, with the aim of identifying the optimal fin geometry to prevent liquid hold-up and flooding at the condenser. In particular, the influence of the transverse cross section was experimentally investigated. Circular, triangular and fluted cross sections were compared, with inscribed diameters ranging from 1.3 to 2.6 mm. The air-cooled fins were made of polymer in order to visualize the condensation regimes. When operating with HFE-7100, three regimes were identified with increasing heat load (up to 95 W): filmwise condensation, plug condensation and flooding, which significantly deteriorates the heat transfer performance. The triangular cross section is the most interesting shape among those tested because flooding occurs at higher heat load and/or smaller diameter than in other shapes thanks to drainage into the corners. Circular fins have the worst performance and fluted ones are in-between. The critical diameter below which flooding occurs even at low heat load is around 2.0 mm for a triangular section and 2.5 mm for a circular one. Consequently, with an optimum fin placement, the total convective surface area at the condenser could be increased by about 15% when using triangles instead of circles.

The Development and Application of Microchannel Heat Sink on W/Cu Flat-Type Mock-Up

The targets of divertor are subjected to a huge heat load of 20 MW/m2 during the operation of future fusion device. Microchannel cooling technology is an efficient method to dissipate high heat load on the divertor targets. However, the pressure drop of W/Cu flat-type mock-up with traditional rectangular microchannel (RMC) heat sink is particularly large under high flow rate. Here, we proposed a W/Cu flat-type mock-up with optimized microchannels of intermittent open semicircular rectangular (OSCR) architecture to reduce the pressure drop. Simulation study was carried out to examine the pressure drop and maximum temperature on the heating surface of the mock-up. The water was used as a coolant, and the inlet temperature, flow rate, and heat flux on heating surface were set to 298 K, 30 L/min, and 20 MW/m2, respectively. The results demonstrated that the temperature on the W surface of OSCR microchannel mock-up (834.7 K) is comparable with that of traditional RMC mock-up (821.7 K), both of which are much lower than the recrystallization temperature of W (1473 K). However, compared with traditional RMC mock-up (2.9 MPa), the pressure drop of the OSCR microchannel mock-up (0.7 MPa) was reduced significantly, which might be attributed to the increase of the cross-sectional area enabled by the intermittent open microchannels. The present study provides a reference for the optimal design of China Fusion Engineering Test Reactor (CFETR) divertor.

Molecular dynamics simulations of the microscopic mechanism of thermal conductivity enhancement of ethylene Glycol–Water–Au nanofluids

With an increase of the heat load of internal combustion engines, the heat dissipation of the equipment increases accordingly. Traditional ethylene glycol (EG)–water coolants are unable to meet the heat dissipation demands of high heat load internal combustion engines. Nanofluids have better heat transfer performances than conventional fluids, suggesting they can be used to solve the problem of the insufficient heat dissipation capacity of internal combustion engines. In this paper, EG–water–Au nanofluids are formed by adding Au nanoparticles with a volume fraction of 1.5% to EG–water solutions. These are used to investigate the effect of the EG mass concentration on the thermal conductivity of the EG–water solutions and their nanofluids, and to analyze the microscopic mechanism of thermal conductivity enhancement of the nanofluids. It is found that the thermal conductivity of the EG–water solutions are positively correlated with the water content of the system, and the higher the water content of the system, the better the diffusion performance of the system components. The thermal conductivity of the EG–water solutions increase for all EG mass concentrations after the addition of Au nanoparticles, up to 17.20%. The presence of an adsorption layer of base liquid molecules on the surface of the nanoparticles is an important reason for the improved thermal conductivity of the nanofluids. According to the analysis of molecular radius of gyration, end-to-end distance and intermolecular interaction energy in the systems, it is found that the addition of the nanoparticles has no significant effect on the conformation of EG molecular chain, and the van der Waals interaction energy in the nanofluid systems is slightly enhanced. Through an analysis of the radial distribution function and density distribution of the nanofluid systems, it is found that the base liquid molecules that adsorb on the surface of the nanoparticles are stratified. The high-density interval of EG molecules is (0.65, 1.25) nm, while water molecules mostly gather in the form of clusters in the (1.15, 1.65) nm interval, and the arrangement of base liquid molecules in the adsorption layer is similar to the orderly arrangement of solids. The properties of some components in the nanofluids show a solid-like microstructure, which makes the thermal conductivity of the nanofluids higher than that of the base solution. These research results can provide an important reference for improving the heat transfer performance of traditional alcohol–water coolants.

Producing high quality LTCC sensors for ITER in-vessel magnetic diagnostics

Inductive magnetic sensors inside the vacuum vessel of ITER tokamak are crucial for plasma operation, plasma control and physics studies. This set of sensors was designed based on the LTCC (Low Temperature Co-Fired Ceramic) technology in order to survive the hostile environment inside ITER vacuum vessel with restricted space, high vacuum, high heat load, and high radiation level. Some features were also integrated into the sensor design to address specific service loads, for instance, accidental superheated steam intrusion. As per ITERs diagnostics design, in total 300 LTCC magnetic sensors have been successfully produced according to the manufacture design and following the specifically developed fabrication process. Extensive quality control program and rigorous factory acceptance tests had been implemented throughout mass production (final 300 sensors). These practices ensured that the sensors were produced to the desired quality and with high reliability.

Pulsation incitation and performance investigations for 3D Fin-and-Tube heat pipe heat exchanger by inserting dividing boards for various working fluids

In our previous study, we have shown that a heat pipe heat exchanger system modified from a commercial air-to-air heat exchanger operates without pulsations for working fluids of dielectric HFE-7000 or R134a, or under low heat loads for water, due to the large internal tube diameter of 5.6 mm. To incite pulsation and enhance the thermal performance, a straight dividing copper board is inserted into the straight section of each of the tube to form two semicircular compartments with an effective hydraulic diameter of 3.4 mm. The heat transfer characteristics and thermal performance against the hot air inlet temperature for the novel boarded model and the non-boarded model are experimentally explored with three working fluids (water, HFE-7000 and R134a) under six filling ratios (35%, 38.5%, 50%, 55%, 65%, 71.5%). Because water already works in a PHP mode in the non-boarded model under high heat loads, the thermal performance in the boarded model improved mildly by 2.7%–10.6%. Whereas, for HFE-7000 and R134a, the heat transfer mode is successfully incited from thermosyphon in the non-boarded model into PHP in the boarded model. The most significant thermal performance improvement was observed for HFE-7000 by 8.3%–24.5%. The improvement can be attributed to the switch of heat transfer mode, the generated corners for condensate accumulation, and the additional heat conduction via the copper board.

Internal rotation of ELM filaments on NSTX

Edge localized modes (ELMs) are a threat to tokamaks due to their high heat and particle loads on plasma facing components. A significant portion of this energy is carried and deposited by the emerging ELM filaments, whose dynamics are directly connected to their impact. Therefore, understanding their underlying physics is important for the operation of future fusion reactors. Our paper extends our knowledge of ELM filaments by reporting on their internal rotation (spinning) around the magnetic field lines along which they are extended. Our analysis of gas-puff imaging data on National Spherical Torus Experiment shows that ELM filaments are characterized by internal rotation in the direction of the ion-gyromotion with ω=15.2 krad/s median angular velocity, which is approximately three times faster than the blob rotation in the background turbulence. The characteristic size of the ELM filament was also assessed and found to be similar to the blobs. A nearly linear trend was found between the angular velocity and the radial velocity of the ELM filament. The angular velocity was found to be linearly dependent on the distance of the filament from the separatrix, as well. An analytical model called the shear-induced rotation model was identified as a candidate for explaining the physics of the observations. Our results show that the modeled mechanism could significantly influence the rotation of the ELM filament; however, it cannot be a sole contributor.