Large Heat Load Research Articles

Real-time method for the identification and quantification of hydrocarbon pyrolysis products: Part I. Development and validation of the infra red technique

Due to large heat load encountered in high speed flight (over Mach 5), the regenerative cooling of the engine leads to the study of the endothermic pyrolysis of the onboard hydrocarbon fuel, which acts as a coolant. However the control and regulation of such a technology implies to have a correct knowledge of the endothermic pyrolysis of the onboard hydrocarbon fuel, which motivates the development of a quantitative measuring method adapted to in-flight applications. A Fourier transform infra red spectrometer is used and a specific method has been developed to identify and to quantify the major hydrocarbon products of the pyrolysis. The technique is validated and tested at the outlet of the experimental pyrolysis process which operates under steady-state conditions from 823 K to 1023 K and up to 60 bar. Two mass flow rates (0.05 g s −1 and 0.1 g s −1) are studied with titanium reactor to determine the limits of validity and to improve the method. Several synthetic and jet fuels have been tested (heptane, decane, dodecane and two kerosenes). The quantities of five light hydrocarbons (methane, ethane, ethylene, propane, propylene) are determined. The method, based on classical least square processing, is validated with respect to gas chromatograph (and mass spectrometer) analysis notably. A minimum molar fraction of 5 mol.% can be obtained and the accuracy is better than 2 mol.%.

Disruption mitigation studies on the Mega Amp Spherical Tokamak (MAST)

Disruptions pose a significant challenge in future devices where the increased stored energy can lead to unacceptably large transient heat loads on plasma facing components (PFCs). One means of mitigating disruptions is that of massive gas injection (MGI), which produces a radiative collapse of the plasma discharge through the injection of impurity gases. The MAST disruption mitigation system is capable of injecting up to 1.95bar litres into the MAST vacuum vessel over a timescale of 1–2ms, corresponding to a particle inventory of 5×1022, around 100 times the plasma particle inventory. High speed infrared thermography, offering full divertor coverage, has shown a 60–70% reduction in divertor power loads during mitigation. A combination of high temporal (0.2ms) and spatial resolution (1cm) Thomson scattering and soft X-ray camera array data show evidence for a cooling front associated with the inward propagation of the injected impurities.

Synthetic and jet fuels pyrolysis for cooling and combustion applications

Large heat load are encountered in hypersonic flight applications due to the high vehicle speed (over Mach 5, i.e. 5000 km h −1) and to the combustion heat release. If passive and ablative protections are a way to ensure the thermal management, the regenerative cooling is probably the most efficient one to enable the structures withstanding (notably for reusable structures). The present study is a part of COMPARER project (COntrol and Measure of PArameters in a REacting stReam) which aims at investigating the highly coupled phenomenon (heat and mass transfers, pyrolysis, combustion) in a cooling channel surrounding a SCRamjet combustion chamber and at proposing some parameters to enable the control of such a complex technology. In this paper, we present the comparative numerical pyrolysis study of some selected synthetic and jet fuels (heptane, decane, dodecane, kerosene surrogate). The fluid pyrolysis has been studied experimentally and the results of RESPIRE numerical simulation under lab and in-flight conditions are given with validation to provide a deep understanding of phenomenon. The impact of the density, of the critical parameters, of the viscosity and of the chemistry is investigated to analyze their effect on the cooling efficiency of the engine. That also enables to estimate properties which the best cooling fuel should have. Furthermore, a combustion study is conducted because the cooling fuel is the one that ensure the thrust. The RESPIRE code enables to conduct both coupled pyrolysis and combustion studies. A first approach of the dynamic regeneratively cooled SCRamjet is provided to get a large vision of the fuel nature impact on the system.

High temperature and pressure reactive flows through porous media

Large heat load are encountered in hypersonic and space flight applications due to the high vehicle speed (over Mach 5, i.e. 5000 km h −1) and to the combustion heat release. If passive and ablative protections are a way to ensure the thermal management, the active cooling is probably the most efficient way to enable the structures withstanding of such large heat load. In some conditions, transpiration cooling will be used. In this paper, the permeation of fuels and other fluids through porous media is studied up to 1150 K and 60 bars. A dedicated experimental bench has been established to ensure the monitoring of temperature, pressure, mass flow rate and chemical composition (Gas Chromatograph, Mass Spectrometer, Infra Red spectrometer) in stationary and transient conditions. The tests on metallic and composite samples have been conducted with N 2, CH 4, H 2 + CH 4 mixtures and synthetic fuels ( n-C 12H 26). The pressure losses comparison with the mass flow rate has enabled the determination depending on the temperature of the Darcian permeability, K D the linear contribution, and of the Forchheimer’s term, K F the quadratic one. The fuel pyrolysis in such low Reynolds flow has been investigated. The blockage effect due to coking activity has been estimated.

Thermal-fluid assessment of multijet atomization for spray cooling applications

Thermal management is a particularly difficult challenge to the miniaturization of electronic components because it requires high performance cooling systems capable of removing large heat loads at fast rates in order to keep the operating temperature low and controlled. To meet this challenge, the Intermittent Spray Cooling (ISC) concept has been suggested as a promising technology which uses a proper match between the frequency and duration of consecutive injection cycles to control heat transfer. This concept also depends on: the atomization strategy; a homogeneous dispersion of droplets impinging on the hot surface; and the quantitative control of the liquid deposited, avoiding excessive secondary atomization or pre-impingement-evaporation. In this work, the use of liquid atomization by multiple jets impact, also referred as multijet atomization, is the subject of a thermal-fluid assessment using heat transfer correlations previously derived for intermittent sprays. Simultaneous measurements of droplet size and velocity are provided as input for the correlations and the analysis explores the influence of the number of impinging jets on the heat removal pattern and magnitude. Emphasis is put on the promising applicability of multijet atomization for promoting an intelligent use of energy in the thermal management of electronic devices.

Heat Transfer in an Enhanced Cable Insulation Scheme for the Superconducting Magnets of the LHC Luminosity Upgrade

The next generation of superconducting magnets for the interaction regions of particle colliders, as well as for fast cycled accelerators, will be confronted with large heat loads. In order to improve the evacuation of heat from the Nb-Ti coil towards He-II bath, a porous (enhanced) all-polyimide cable insulation scheme was proposed recently. The first results were promising, featuring a larger permeability to helium with respect to existing schemes under low compressive stress. In this paper we present an extended experimental study of heat transfer through the Enhanced Insulation into He-II bath, and comparison to the standard LHC insulation, at different levels of applied pressure. The thermal coupling between adjacent cables was investigated, as well as the impact of a localized heat deposition versus a distributed one. The results of this study show that, up to high pressure levels, the enhanced insulation scheme can provide a major improvement of heat transfer compared to the standard scheme used in the main LHC magnets.

A novel vapor chamber and its performance

The performance of a novel vapor chamber is tested in this study. In this vapor chamber, parallel grooves are made on the inner surface of the top plate, with inter-groove openings, to replace the conventional porous wick. To the inner surface of the bottom plate is sintered a layer of porous wick as the evaporator. The peaks of the groove walls directly contact with the wick so that the grooves function as vapor path, condenser and structural supporters simultaneously. The corrugated groove walls provide not only an enlarged condensation area, but also a direct shortcut for a portion of the liquid condensed on the groove surface to be absorbed back to the wick. Thus, smaller liquid-flow resistance and hence high anti-dryout capability are achieved. The test module includes a copper plate-fin heat sink in combination with a top fan. In this study, the evaporator wick was made of sintered multi-layer copper screens and the footprint of the vapor chamber was 10 cm × 8.9 cm. With a 2.1 cm × 2.1 cm or a 1.1 cm × 1.1 cm heating area, the vapor chamber resistances were measured for heat load increasing from 80 W to beyond 300 W. Good performances with low vapor chamber resistance and large heat load limit were obtained under different orientations. In addition, the individual evaporation resistances and condensation resistances were measured for representative conditions. The evaporation resistance was the dominating part of the vapor chamber resistance. Both the evaporation resistance and the condensation resistance decreased with increasing heat load, except that the evaporation resistance increased after the occurrence of partial dryout.

The Cryogenic System for ITER

ITER cryogenic system is in its final design phase to be constructed at Cadarache, South of France. It shall use the most advanced cryogenic technologies developed for accelerators projects adapted and optimized to fulfil the requirements and constraints of a large fusion installation.A refrigeration capacity equivalent to 65 kW at 4.5 K is planned for the cooling of superconducting magnets, their HTS current leads and small users. It also includes the cooldown of the cryogenic pumps and their re-cooling after regeneration. A 1300 kW nitrogen plant provides cooling power for the thermal shields. The key design requirement is the capability to cope with large pulsed heat loads deposited in the magnets due to magnetic field variations and neutron production from the fusion reaction.The cryogenic distribution system is based on the design of a complex and compact transfer line system and several cryogenic distribution and feed boxes.After recalling the basic features we shall present the status of the design and the main magnet interfaces and key design requirements.

EXPERIMENTAL STUDY ON THERMAL EFFECT OF GREEN ROOF AND ROOF SPRAYING

As global environmental problem has become a significant issue, we have already installed various energy saving method into our building services.Especially, green roof and roof spraying have been watched keen interest, because they can reduce both heat load and carbon-dioxide emission from building services without using energy supply such as electricity.Generally speaking, as building with green roof has water spraying equipment for tree maintenance, if we control water rate appropriately, we can expect a large heat load reduction effect which is brought by synergy effect of green roof and roof spraying.

Excess heat from kraft pulp mills: Trade-offs between internal and external use in the case of Sweden—Part 2: Results for future energy market scenarios

In this paper the trade-off between internal and external use of excess heat from a kraft pulp mill is investigated for four different future energy market scenarios. The work follows the methodology described in Svensson et al. [2008. Excess heat from kraft pulp mills: trade-offs between internal and external use in the case of Sweden—Part 1: methodology. Energy Policy, submitted for publication], where a systematic approach is proposed for investigating the potential for profitable excess heat cooperation. The trade-off is analyzed by economic optimization of an energy system model consisting of a pulp mill and an energy company (ECO). In the model, investments can be made, which increase the system's energy efficiency by utilization of the mill's excess heat, as well as investments that increase the electricity production. The results show that the trade-off depends on energy market prices, the district heating demand and the type of existing heat production. From an economic point of view, external use of the excess heat is preferred for all investigated energy market scenarios if the mill is studied together with an ECO with a small heat load. For the cases with medium or large district heating loads, the optimal use of excess heat varies with the energy market price scenarios. However, from a CO 2 emissions perspective, external use is preferred, giving the largest reduction of global emissions in most cases.

Reduction of heat load of LCGT cryostat

An unexpected large heat load was observed in a cooling test of the cryostat for a prototype cryogenic interferometric gravitational wave detector. By conducting additional studies involving an experiment and a simulation, we found that the large heat load was caused by conduction of thermal radiation in a thermal radiation shield pipe, which was inserted in the beam duct to reduce solid angle from 300K to 4K. To achieve the design of LCGT cryogenic system, the heat load had to be reduced below a few percent. By introducing metal baffles in the shield pipe, this requirement was fulfilled.

Conceptual Design of Superconducting Magnet System for JT-60SA

The upgrade of JT-60U magnet system to superconducting coils (JT-60SA) has been decided by both parties of Japanese government (JA) and European commission (EU) in the framework of the Broader Approach (BA) agreement. The magnet system for JT-60SA consists of 18 toroidal field (TF) coils, a Central Solenoid (CS) with four modules, seven Equilibrium Field (EF) coils. The TF case encloses the winding pack and is the main structural component of the magnet system. The CS consists of independent winding pack modules, which is hung from the top of the TF coils through its pre-load structure. The seven EF coils are attached to the TF coil cases through supports which include flexible plates allowing radial displacements. The CS modules operate at high field and use Nb3 Sn type superconductor. The TF coils and EF coils use NbTi superconductor. The magnet system has a large heat load from nuclear heating from DD fusion and large AC loss. This paper describes the technical requirements, the operational interface and the outline of conceptual design of the superconducting magnet system for JT-60SA.

Flux Pump Excited Double-Helix Rotor for Use in Synchronous Machines

High temperature superconducting (HTS) machines have been demonstrated to benefit applications requiring high power density and torque. However, power density of existing superconducting machinery is limited by achievable flux density in the air gap and could be significantly increased with larger rotor currents. We propose a rotor based on MgB2 conductor running in persistent current mode. A novel MgB2 HTS flux pump transformer enables currents of several thousand amps in the rotor in a persistent mode. Large cryogenic heat loads associated with current leads are diminished by using a flux pump transformer for rotor excitation. All coils in the rotor and flux pump transformer are based on the double-helix winding configuration, which offers unmatched rotor robustness and reliability. This winding configuration also facilitates large bending radii, leading to an outstanding stress management and thus improved current carrying capacity of stress sensitive HTS conductors. The research presented in this paper analyses the performance of such a system through the design of a synchronous rotor for motors, generators and synchronous condensers.

Experimental investigation on a mechanically pumped two-phase cooling loop with dual-evaporator

This paper describes a well-known space activate thermal control system, two-phase mechanically pumped cooling loop (MPCL) with two evaporators, in ground-based testing. Each evaporator has an outer diameter of 3 mm and a length of 10 m and the total loop of the system is about 40 m. Tests conducted mainly included stable operation tests under sinusoidal temperature boundary condition and unbalanced heat load tests. Experimental data showed that the loop operated stably at about 30 °C variation of the boundary temperature without any temperature overshoot. Meanwhile, the operating temperature could be controlled within ±0.1 °C of the set point temperature with the new design based on TECs. Furthermore, heat load unbalanced between the two evaporators was also successfully demonstrated that the loop has a heat transport capability to deal with the maximal unbalanced heat loads limitation as Top_Load/Bottom_Load = 0 W/160 W or Top_Load/Bottom_Load = 130 W/0 W. When the heat load limitation is reached in one evaporator and a dry-out appears, some heat load employed on the other side such as 10 W will recover it to the set point evaporation temperature. In conclusion, important performance characteristics demonstrated by this MPCL included: (1) operation of the system about 30 m with a mechanical pump; (2) robustness and reliability of an MPCL with multiple evaporators; (3) effectiveness of TECs in controlling the MPCL operating temperature; (4) dealing with a large unbalanced heat load among MPCL evaporators; and (5) easy recovery from the pulse boiling or a dried out state.

Conduction Effect of Thermal Radiation in a Metal Shield Pipe in a Cryostat for a Cryogenic Interferometric Gravitational Wave Detector

A large heat load caused by thermal radiation through a metal shield pipe was observed in a cooling test of a cryostat for a prototype of a cryogenic interferometric gravitational wave detector. The heat load was approximately 1000 times larger than the value calculated by the Stefan–Boltzmann law. We studied this phenomenon by simulation and experiment and found that it was caused by the conduction of thermal radiation in a metal shield pipe.

Explosive Cladding for ITER Components

The International Thermo-nuclear Experimental Reactor (ITER) is a huge experimental facility for the fusion energy research field to be built in the coming years in France. The extreme conditions (high temperatures, extremely large heat loads, thermal fatigue, and nuclear radiation) require very special materials and bonding of dissimilar metals. TNO develops the explosive cladding technology (as an alternative bonding mechanism) in order to demonstrate the potential of this bonding route for selected ITER components.

Flow boiling heat transfer in microgravity: Recent results

Flow boiling heat transfer (FBHT) allows high performance heat transfer due to latent heat transportation and its use is therefore important to reduce size and weight of space platforms and satellites. Its knowledge is also important for the safe operation of existing single-phase systems in case of accidental increase of heat generation rate. The number of existing researches on flow boiling in reduced gravity is very small due to both larger heat loads and available room in a 0-g apparatus for experiments. Consequently, coherence in existing data is somewhat missing. This lecture will summarize the results of the few research carried out on FBHT in microgravity, with special emphasis to the recent research carried out at ENEA, in the frame of an ESA (European Space Agency) project.

Analysis of the ITER cryoplant operational modes

In the framework of an EFDA task, CEA is carrying out an analysis of the various ITER cryoplant operational modes. According to the project integration document, ITER is designed to be operated 365 days per year in order to optimize the available time of the Tokamak. It is anticipated that operation will be performed in long periods separated by maintenance periods (e.g. 10 days continuous operation and 1 week break) with annual or bi-annual major shutdown periods of a few months for maintenance, further installation and commissioning. For this operation schedule, auxiliary subsystems like the cryoplant and the cryodistribution have to cope with different heat loads which depend on the different ITER operating states. The cryoplant consists of four identical 4.5 K refrigerators and two 80 K helium loops coupled with two LN2 modules. All of these cryogenic subsystems have to operate in parallel to remove the heat loads from the magnet, 80 K shields, cryopumps and other small users. After a brief recall of the main particularities of a cryogenic system operating in a Tokamak environment, the first part of this study is dedicated to the assessment of the main ITER operation states. A new design of refrigeration loop for the HTS current leads, the updated layout of the cryodistribution system and revised strategy for operations of the cryopumps have been taken into consideration. The relevant normal operating scenarios of the cryoplant are checked for the typical ITER operating states like plasma operation state, short term stand by, short term maintenance, or test and conditioning state. The second part of the paper is dedicated to the abnormal operating modes coming from the magnets and from those generated by the cryoplant itself. The occurrence of a fast discharge or a quench of the magnets generates large heat loads disturbances and produces exceptional high mass flow rates which have to be managed by the cryoplant, while a failure of a cryogenic component induces a major disturbance for the magnet system. Thanks to this analysis, modifications of the architecture of the present PFD are proposed to make match the technical specifications of the cryogenic system with the ITER operation requirements.

Progress towards an integrated solution for the ITER baseline scenario based on high current and highly shaped plasma operation at JET

The latest results of analysis and modelling of high current and highly shaped plasma operation at JET are presented in order to explain the approach towards an integrated solution for the ITER baseline scenario. A strong link is found between edge localized mode (ELM) size, pedestal height and plasma performance, suggesting high performance must come at the expense of large ELM heat loads. However, promising results at the highest plasma shapes show that this link can be broken, with other mechanisms coming into play that appear to dissipate heat between ELMs, or extract the ELM heat loads more benignly. It is speculated that this is related to changes in the underlying stability of the ELM associated with highly shaped plasma operation. The way forward, in terms of the future programme and exploitation of upgrades to the JET device, is discussed.

F234 固体粒子添加による自励振動ヒートパイプの性能向上(ヒートパイプ)

The performance of pulsating heat pipe (PHP) was investigated by using 12 turn copper tubes with water, ethanol and R141b as the working fluids. In the case of small heat load, R141b is the best performance because of its higher vapor presser and lower viscosity. On the other hand, in large heat load, water is the best because of large thermal conductivity and large specific heat. In order to improve performance of R141b in large heat load region, two sizes of diamond particles, that is, large one (8-20μm) and small one (2-4μm), were added. It was found that the larger particle is more efficient than the smaller one, and an optimum concentration exists. The heat transport performance of PHP using R141b with diamond particle is superior to that with water over the whole range of heat load for all orientations.