Significant Heat Load Research Articles

APPLICATION OF UNMANNED AERIAL VEHICLES FOR LOCALIZED THERMOREGULATION AND VENTILATION OF WORKERS AT JOBSITES OF HIGH-TEMPERATURE INDUSTRIES

Problem statement. In metallurgical and petrochemical industries using high-temperature technological processes, there exists an issue of overheating of workers due to significant heat loads. To prevent such hazard, large industrial fans are installed directly at production sites providing air circulation over a wide area. However, their performance characteristics, operation modes and placement schemes do not always ensure adequate cooling of employees. There is a need to study this problem in order to develop measures for improving efficiency of such devices through their enhancement and optimized application. The aim of the article is a comprehensive study of possibilities of applying unmanned aerial vehicles (drones) for cooling of working zones at productions with high heat loads instead of traditional industrial fans. The main objectives include: Conducting analysis of modern workplace cooling systems and identifying their shortcomings; Exploring technical characteristics of drones that can be used for this purpose; Developing a concept of algorithm for drone-fan control system to ensure operation in automatic mode with preset parameters for a working post; Experimental verification of efficiency of such system on a laboratory model. Conclusion. Application of drones for localized cooling of working zones will increase efficiency and flexibility of ventilation systems compared to existing ones; Such a system will provide optimal microclimatic conditions directly for each employee; Energy efficiency of this approach will be higher as only necessary cooling power will be used; Expected improvement of occupational safety and reduction of professional risks due to lower heat loads.

Vertical instability prediction and its direction control using a support vector machine in integrated commissioning of JT-60SA solely based on magnetics

Abstract We developed a redundant logic for predicting Vertical Displacement Events (VDEs) using only magnetic diagnostics with a Support Vector Machine (Inoue et al 2022 Nucl. Fusion 62 086007). This logic was experimentally validated in the integrated commissioning of JT-60SA. Triggering of VDEs results in significant asymmetric heat loads on first walls and electromagnetic loads on conducting materials. These concerns are mitigated by a newly proposed direction control for VDEs. We successfully detected VDEs in experiments and controlled their direction by setting the control voltage to zero upon detection, thus guiding VDEs in an intended direction and reducing the risk to the device from unmitigated VDEs in either direction, although completely avoiding VDEs remains the ideal. In the developed predictor, VDEs are predicted using proxies to monitor the controller’s performance with an adaptive voltage allocation scheme (Inoue et al 2021 Nucl. Fusion 61 096009). For future experiments, we plan to extend our approach to monitor more detailed information from the equilibrium controller, including control values of each PID component, which has been shown to enhance the prediction accuracy of VDEs.

Potential of thermal protection improvements in large-scale cryostat development

Tremendous efforts are being pursued by experimentalists worldwide in the designing of cryostats to minimize the most dominant radiation heat load over the cryogenic liquid kept inside it. These endeavors are imperative to secure the safe, consistent, and reliable performance of detectors, notably for experiments delving into the investigation of rare physics events, particularly those moving towards ton-scale capacities. In these experiments, maintaining a stable temperature of the cryogenic liquid is crucial. This stability helps in minimizing thermal noise and reducing the loss of cryogenic liquid by mitigating its evaporation rate, and this can be accomplished by reducing the ambient heat load coming from the outer hot wall towards the inner cold wall of the cryostat. Current work scrutinized the impacts of having no insulation, a single-layer insulation, and Multilayer Insulation (MLI) techniques on thermal protection from environmental heat loads at the cryostat’s cold wall boundary, with a particular emphasis on the effectiveness of a single-layer insulation strategy against radiative heat load, a key precursor to MLI technology. The effectiveness of single-layer insulation was quantitatively analyzed for reducing heat load in large-scale rare event searches, using GERDA as an illustrative example and focusing on an optimized configuration. Performance metrics include ambient temperature, cryogenic liquid, emissivity, and the placement of insulation for optimal efficiency. The incorporation of a single intermediate layer positioned near the cold wall boundary results in a significant heat load reduction of 57% for the GERDA geometry compared to a scenario without such a layer. A feasible decrease in emissivity from the customary O(0.01) for insulation materials down to O(0.001–0.0001) could bring about substantial reductions in heat load, potentially by factors spanning approximately 8 to 90. In the scenario involving liquid helium (4.15 K), for example, as the ambient temperature surrounding the cryogen is lowered to (200, 150, 100, 50) K from room temperature, the heat load diminishes by 80%, 94%, 98.8%, and 99.9%, respectively. Moreover, optimally positioning single intermediate layer, crafted from ultra-radiopure material, as close as achievable to the cold wall boundary with minimal emissivity can yield a substantial reduction in heat load, estimated ∼(40–60)%, thereby diminishing the evaporation rate of the cryogenic liquid.

Optimising building heat load prediction using advanced control strategies and Artificial Intelligence for HVAC system

Amid the dynamic challenges posed by the COVID-19 era, this study offers a nuanced exploration, delving into the complexities of optimising building heat load prediction. This study addresses the imperative challenge of optimising building heat load prediction by implementing advanced control strategies and integrating Artificial Intelligence (AI) into air conditioning systems. The study emphasises the need to design HVAC devices for minimal energy consumption without compromising comfort conditions. The study introduces an intelligent predictive adaptive neuro-fuzzy inference system (ANFIS) model that proves highly capable of accurately predicting HVAC performance outcomes while contributing to the development of a comprehensive dataset. The uncertainty percentage is evaluated across various membership functions, with the trapezoidal membership exhibiting the lowest error rate, followed by the Gaussian membership function. Weather parameters crucial to ventilation efficiency and heat load are examined, leading to the identification of an optimal combination involving 45 % relative humidity, 13 °C dry bulb temperature, and 5 km/h wind speed. The current system demonstrates significant efficiency improvements, with ventilation and heat load rates reaching 93 % and 97 %, respectively, compared to pre-COVID-19 conditions. The findings underscore the importance of considering these parameters in future HVAC designs, particularly in the context of COVID-19 guidelines (75 % and 79 %, respectively).

Embrittlement of WCLL blanket and its fracture mechanical assessment

In the European fusion programme, the Water Cooled Lithium Lead breeding blanket (WCLL BB) uses EUROFER as a structural material cooled with water at temperatures between 295 °C–328 °C and a pressure of 155 bar. The WCLL BB will be significantly irradiated (>2 dpa), while some parts will not receive significant heat loads, e.g. the sidewalls or the back-supporting structures. The irradiation, together with the irradiation temperature of EUROFER below 350 °C, produces a shift of the ductile-to-brittle-transition temperature (DBTT) to levels above room temperature at neutron doses, causing material damage as low as 2–3 dpa. Even though the DBTT does not reach the operating temperature level, brittle/non-ductile fracture is a concern during in-vessel maintenance when the BB temperature is below the DBTT. Two loading scenarios were identified as severe in this respect: (i) re-pressurization of the WCLL BB cooling loop after in-vessel maintenance, and (ii) dead weight loads during lifting of the BB segment. The embrittlement of the WCLL BB was investigated by quantifying the local DBTT shift in its parts based on current knowledge of the embrittlement behaviour of EUROFER under neutron irradiation. Therefore, a suitable, not overly conservative procedure was derived considering dpa damage and transmuted helium effects. The results demonstrate the ability to identify the 3D spread of the severely embrittled zones in the structure whose impact on the structural integrity was assessed considering the risk of brittle/non-ductile fracture. Thereby, the fracture mechanics approach established in nuclear codes was applied assuming its applicability to EUROFER. The embrittled zones in the first wall (FW) and its sidewalls pass the criteria when assessing the relatively low stresses resulting from the coolant pressure. The assessment was then continued considering stresses appearing in the FW during maintenance, in particular, when lifting the BB segment and transporting it out of the vacuum vessel. In this context, the maximum tolerable flaw sizes were determined in a parameter study considering designs of the FW with different cooling channel wall thicknesses.

Effect of a DC transport current on the AC loss in no-insulation ReBCO racetrack coils exposed to AC parallel magnetic field at 77 K and 4.2 K

ReBCO coils are developed as DC field coils in linear motor systems to increase the force density, in favor of permanent magnets. Such coils have to sustain a relatively large heat load stemming from the AC magnetic field environment in which they operate. The use of no or partial turn-to-turn insulation can make them more stable against the effects of local heating. Conversely, the radial electrical connections in no-insulation (NI) coils allow for large coupling currents, causing additional AC loss on top of the already significant heat load. Here we report on the AC loss in sub-scale NI, 4 mm wide single-tape, ReBCO racetrack coils exposed to parallel-to-the-tape magnetic field in the frequency range of 10−4 to 1 Hz at 77 K and 4.2 K, while carrying a DC transport current. AC loss is measured magnetically and electrically. The main goal of these experiments is to validate our 2D numerical model, which provides more insight into the origin of the AC loss. At low frequencies, inter-turn coupling currents are spread more or less homogeneously throughout the winding pack. Whereas at high frequencies, the skin effect causes shielding of the interior of the coil and large induced currents only occupy the coil’s outer surface.

Thermal and hydrodynamic management of a finned-microchannel heat sink applying artificial neural network

Thermal management of microelectronic circuits will be one of the most difficult challenges facing engineering processes in the near future. High operating temperatures in these devices can degrade the reliability of the components and reduce their life. Therefore, effective cooling technologies that can disperse the significant heat load from the surface of microelectronic equipment are required. An appropriate microchannel heat sink (MCHS) system with optimized geometry can be one of the reliable choices. In the current work, an artificial neural network (ANN) is exerted to optimize the geometry of a finned-MCHS. The distance of fins from the inlet in the second row (l), the distance of fins from the side walls in the first and third rows (t), and the angle of hexagons (θ) are the input parameters. According to the obtained results, the ANN model with a coefficient of determination of 0.999 performed well in predicting the Nusselt number (Nu) and pressure drop (ΔP). Among the investigated input parameters, the variations of the parameter of t affected the thermal and hydrodynamic properties of the device noticeably. Besides, the ANN model suggested that when the optimum values of input parameters (i.e., l = 7.636 mm, t = 4 mm, and θ = 140) are used for the hexagonal fins inside a microchannel, the maximum relative efficiency index of 1.491 can be acquired.

Improvement in the simulation tools for heat distribution predictions and control of baffle and middle divertor loads in Wendelstein 7-X

In the first divertor campaign in Wendelstein 7-X (W7-X), unexpected significant heat loads were observed at particular plasma-facing components (e.g. baffle tiles and middle divertor part) which were not designed to receive high heat flux. In a prior investigation, it was concluded that the previous diffusive field line tracing (DFLT) model used for divertor design in W7-X cannot reproduce these loads, due to the missing physics in simulating the heat transport in the shaded flux tubes. To tackle this issue, two new efficient codes (DFLT_rev and EMC3-Lite) are introduced and validated against various experimental heat distributions in different magnetic configurations. The new tungsten baffle tiles have been designed with these codes and mounted in the machine, aiming for mitigated heat loads in the upcoming campaign.

Assessment of the Performance of Different Cooling Configurations for the Launcher Mirrors of the ECRH System of the DTT Facility

The launcher mirrors will allow the injection of microwave power from the gyrotrons in the plasma of the Divertor Tokamak Test facility, under construction in Italy. The active cooling of the elliptical M1 (curved and not-steerable) and M2 (flat and steerable) mirrors, both subject to a significant heat load, is investigated in this article. Several cooling solutions are analyzed: a spiral cooling for M1, both in a massive and in a lightened configuration, and also a radial-azimuthal cooling for M2, both in a massive and in a lightened configuration. Figures of merit are computed for the different configurations.

Radiative Coefficients and Their Influence on In-Depth Heating of Porous Ablators

High entry speeds and exotic planetary gases can result in significant radiative heat loads on space capsules. The mechanism behind the transport of radiative signatures is fundamentally different from the conductive mode of energy transport, and penetration of radiative signatures depends on the radiative coefficients of the thermal protection system (TPS) material that protects the space capsule. The radiative coefficients of carbon-based and silica-based fibrous materials have been computed as functions of wavelength using the photon path length Monte Carlo method by explicitly accounting for the microstructure of the material. Significant variations in the radiative coefficients are observed at wavelengths that are relevant to shock-layer emissions. Although carbon-based fibrous materials exhibit higher absorption coefficients in comparison to silica-based systems, the absorption coefficients of carbon-based material drop by two orders of magnitude in the range of 100–200 nm. The radiative coefficients of carbon-based fibrous material are seen to be dominated by scattering and absorption with minimal transmission. However, the transmission coefficients for the silica system dominated the radiative coefficients in the range of 100–1000 nm, which corresponds to most shock-layer emissions. The radiative coefficients are used to solve the radiative transfer equation using the P-1 approximation to obtain the in-depth radiative heat flux. The total energy equation for decomposing porous TPS materials is solved with the radiative heat flux from the P-1 approximation and the conductive heat flux using the Fourier law. It is observed that peak temperatures inside the material are higher when radiative transport is explicitly accounted for through the P-1 approximation. Small variations in the absorption coefficient of the silica-based materials also affected the in-depth temperature profiles. Additionally, a broader temperature distribution is obtained inside the material with a low absorption coefficient, and the charring density profiles are influenced by the radiative heat flux. This study demonstrates that it is important to include radiative transport in material response solvers, and radiative coefficients must be accurately computed by accounting for the microstructure of the material.

Energy savings for a junior high school classroom that actively uses daylighting and sensitivity study on the effect of the building envelope thermal performance

AbstractThis paper analyzes the energy‐saving potential of lighting, including its effect on heating and cooling, and analyzes the effect of the thermal performance of a building on the annual energy consumption of a classroom actively using daylighting. The subject of this study is M Junior High School, located in Gifu, Japan. This school has a classroom design with a sloping roof, allowing the installation of large windows from north to south. The window‐to‐wall ratio of 56% for the south wall and 41% for the north wall takes advantage of daylight. Simulation results of illuminance in the classroom were validated through comparison with field measurement data. The result demonstrated that daylight utilization decreases lighting electric power consumption by 66.6% when artificial lighting is controlled in the classroom. The results confirmed that there was no significant heat load increase for heating and cooling even though the window surface area was larger than that of a typical classroom. The sensitivity study showed that the thermal performance of the building envelope mainly affects the heating energy consumption, but it has no significant effect on cooling and lighting energy consumption. In terms of the thermal performance of the building envelope and the amount of energy saving by daylight utilization, it is necessary to consider the appropriate thermal performance to determine cost‐effectiveness.

Non-monotonic dependence of heat loads induced by electron cloud on bunch population at the LHC

Electron cloud effects are among the main performance limitations for the operation of the Large Hadron Collider with 25 ns bunch spacing. Electrons impacting on the beam screens of the superconducting magnets induce a significant heat load reaching values close to the full cooling capacity available from the cryogenic system in some LHC sectors. To better understand this performance limitation, numerical simulations with the PyECLOUD code were performed to study the dependence of the heat load on different beam and machine parameters, in particular the bunch population, which is foreseen to be considerably increased with the impending HL-LHC upgrade. The simulations predict a complex, non-monotonic behavior of the heat load with bunch population which has important implications in defining the upgrade of the cryogenic system required for coping with HL-LHC beam intensities. An in-depth analysis of the simulation results shows that the non-monotonic dependence of the heat load on the bunch population is driven by an interplay between the spectrum of the impacting electrons and the shape of the Secondary Electron Yield curve. Experimental data were collected at the LHC during normal operation and dedicated experiments in order to validate the simulation model and confirm the expected non-monotonic behavior. The simulation results are found to reproduce very well the measurement data.

Detecting Plasma Detachment in the Wendelstein 7-X Stellarator Using Machine Learning

The detachment regime has a high potential to play an important role in fusion devices on the road to a fusion power plant. Complete power detachment has been observed several times during the experimental campaigns of the Wendelstein 7-X (W7-X) stellarator. Automatic observation and signaling of such events could help scientists to better understand these phenomena. With the growing discharge times in fusion devices, machine learning models and algorithms are a powerful tool to process the increasing amount of data. We investigate several classical supervised machine learning models to detect complete power detachment in the images captured by the Event Detection Intelligent Camera System (EDICAM) at the W7-X at each given image frame. In the dedicated detached state the plasma is stable despite its reduced contact with the machine walls and the radiation belt stays close to the separatrix, without exhibiting significant heat load onto the divertor. To decrease computational time and resources needed we propose certain pixel intensity profiles (or intensity values along lines) as the input to these models. After finding the profile that describes the images best in terms of detachment, we choose the best performing machine learning algorithm. It achieves an F1 score of 0.9836 on the training dataset and 0.9335 on the test set. Furthermore, we investigate its predictions in other scenarios, such as plasmas with substantially decreased minor radius and several magnetic configurations.

Aerodynamics and Heat Transfer Inside a Gas Turbine Mid-Passage Gap

Abstract Gas turbine blades and vanes are typically manufactured with small clearances between adjacent vane and blade platforms, termed the mid-passage gap. The mid-passage gap reduces turbine efficiency and causes significant additional heat load into the vane platform. This paper presents a new low-order analytical model to quantify the effects of the mid-passage gap on aerodynamics and heat transfer, based only on geometric features and the passage static pressure field. This model is used to calculate losses and heat transfer due to the gap and to derive ideal distributions of purge flow which prevent ingress into the gap. A further simplified estimation method for the effect of gap flow is also presented, so that for any machine the significance of the gap can be quickly assessed based only on geometry and operating conditions. The analysis is validated against both an experimental campaign in a high-speed linear cascade and Reynolds-averaged Navier–Stokes computational fluid dynamics.

Divertor power loads and scrape off layer width in the large aspect ratio full tungsten tokamak WEST

WEST is a full W tokamak with an extensive set of diagnostics for heat load measurements especially in the lower divertor. It is composed by infrared thermography, thermal measurement with thermocouples and fibre Bragg grating embedded few mm below the surface and flush mounted Langmuir probes. A large database including different magnetic equilibrium and input power is investigated to compare the heat load pattern (location, amplitude of the peak and heat flux decay length) on the inner and outer strike point regions: from the first ohmic diverted plasma (obtained during the second experimental campaign C2 in 2018) up to the high power (8 MW total injected) and high energy (up to 90 MJ injected energy in lower single null configuration) experiments performed in the last experimental campaign (C4 in 2019). Concerning the peak location, a good agreement (<1 cm) is obtained between thermal inversions and flush-mounted LP measurements. The peak heat flux from the whole set of diagnostics is in good agreement and mainly in the ±20% range, while the heat flux decay length reported on the target shows significant discrepancy between diagnostics and location in the machine (±40% range). Despite such discrepancy, heat flux decay length at target is found to scale mainly with the magnetic flux expansion through the variation of the X-point height, as expected. The improved plasma performances achieved during C4 enabled to reach significant heat load in the divertor, up to 6 MW m−2 with 4 MW of additional heating power showing the capability to reach the ITER relevant heat load (10 MW m−2 steady state) with about 7 MW of additional power in L-mode discharge. The heat load distribution is clearly asymmetric with a 3/4 and 1/4 distribution on the outer and inner strike point region respectively for the parallel heat flux.

Preparation of a water activation experiment at JET to support ITER

Fast neutron induced water activation will result in significant additional nuclear heating loads to cryogenic components in the ITER fusion reactor during operation, which are considered as an important issue in the ITER design. A water activation experiment has been proposed at the Joint European Torus (JET) which would enable measurements of radiation dose rates and 16N concentrations in water, activated in the most representative fusion environment achievable, and extrapolability to ITER conditions. This paper presents a study aimed at establishing the experiment feasibility, in terms of the identification and selection of an experimental location at JET, and the definition of an experimental setup enabling accurate measurements of the quantities of interest. A suitable experimental location in JET was identified in the basement of the JET Torus Hall. The expected 16O(n,p)16N activation rates in the cooling water in the JET tokamak were determined through Monte Carlo particle transport calculations and the induced 16N activity in the water was propagated to the experimental location. Subsequent calculations were performed to determine the expected detector response to 16N γ rays for three different JET pulse scenarios. Two scintillator γ detectors were calibrated with standard γ calibration sources and tested with a 244Cm/13C neutron source, also emitting 6.13 MeV γ rays, corresponding to the 16N γ ray energy. The presented work demonstrates the feasibility of a water activation experiment at JET and provides valuable information for the experiment design.

Dynamic control of microchannel cooling system with unanticipated evaporator heat loads

This study presents a control strategy for electronic cooling systems incorporating microchannel evaporators that experience unanticipated and significant heat load variations. It complements prior studies that focus primarily on the steady operation of two-phase systems facing static heat loads. This study's overall objective is to maintain a fixed evaporator temperature, enable high system efficiency, and avoid critical heat flux (CHF) despite the presence of transient and unexpected variations in heat loads. In this regard, we developed a moving boundary model to account for the presence of single-phase and two-phase flow in the evaporator and account for their respective flow and heat transfer characteristics. We use this model to identify optimum operating conditions for different evaporator heat loads that avoid CHF and correspond to a high COP. Since the changes in the heat loads are unanticipated, we design a disturbance observer based on the optimum operating conditions to estimate the unanticipated evaporator heat loads, which could serve as the feedforward control signal for system inputs such as pump-speed and valve settings. This study demonstrates how the system can maintain a constant evaporator temperature when it experiences a three-fold increase in the heat load. We also extend this study to two evaporators operating in parallel and experiencing unanticipated and asynchronous variations in the evaporator heat load. Our results show that the system with a disturbance observer and controller can maintain a fixed evaporator temperature even under significant heat load variations.

Detachment in Fusion Plasmas with Symmetry Breaking Magnetic Perturbation Fields.

Power exhaust from the bulk plasma is significantly altered by symmetry breaking magnetic perturbation fields, because these create direct connections (perturbed field lines) from the confined high temperature plasma to solid surfaces. The same amount of power is distributed among those new exhaust channels as for a symmetric magnetic configuration, which reduces the local upstream heat flux flowing down the perturbed field lines, thereby making access to detachment easier (i.e., at lower upstream density) for the divertor plasma near the location corresponding to the symmetric magnetic separatrix. However, the divertor plasma regions with connection to the bulk plasma are extended nonaxisymmetrically further outside, where significant heat loads occur, unlike in the symmetric configuration. The temperature remains high at those locations, which reduces the divertor plasma dissipation capacity, making the mitigation of heat loads more difficult to achieve.

Economic and environmental impacts of a non-traditional combined heat and power system for a discrete manufacturing facility

Combined heat and power (CHP) is an electricity generation strategy that benefits all sides with a vested interest in the nations’ energy future. The technology allows for the efficient production of electricity and heat, which in turn reduces the carbon footprint and energy costs of a facility with significant heat and electricity loads. This paper investigates, through a detailed dynamic simulation, how a highly non-traditional CHP facility can leverage those forces to economically and environmentally benefit. Four system configurations of a composites manufacturing facility, one existing and three proposed systems, including two CHP configurations and one combined cooling, heating, and power (CCHP) configuration are evaluated from both economic and environmental views. The three proposed configurations are based on a 600 kW microturbine as the primary mover. The dynamic model showed great potential to capture the dynamics of the system configurations including the dynamics of temperature, oven exhaust fraction, electrical efficiency, and overall efficiency of the system configurations. All 3 CHP systems have a payback period between 8.03 and 8.33 years. The proposed system configurations reduce up to 22.7% of the CO2 emission compared to the existing facility, supplying the demands in a cleaner manner.

Vibration-heating in ADR Kevlar suspension systems

The cryogenics group at NASA’s Goddard Space Flight Center has a long-standing development and test program for laboratory and space-flight adiabatic demagnetization refrigerators (ADRs). These devices are used to cool components to temperatures as low as 0.05 K. At such low temperatures the ADR systems can provide a few micro-Watts of cooling power, so it is important to minimize the conduction of heat to these cold stages from the surroundings. The cold ADR elements are held in place by thin tensioned strings made of Kevlar, chosen for its high strength and stiffness and low thermal conductivity. During laboratory testing, we have observed that occasional significant additional heat loads on the coldest ADR stages correlate with unusually high vibration levels in the cryostat due to a noisy mechanical cryocooler. We theorized that this heat results from plastic deformation of the Kevlar fibers and frictional interactions among them, driven by the cryostat vibrations. We describe tests and calculations performed in attempt to confirm this source of the heating.