Hot Component Research Articles

Measurement of the Charge Exchange Cross Section for N7+, O7+ Ions in Collision with Atomic H

The absolute total cross sections for the charge exchange between highly charged ions 15N7+, O7+, and atomic H have been measured with the ion-atom merged-beams apparatus at Oak Ridge National Laboratory. The collision energy range is from 1224 down to 2 eV u−1, which covers outflowing hot components of astrophysical charge exchange plasmas like stellar-wind and supernova remnants. Good agreement with the previous measurements and theory is found for the collision energies above 100 eV u−1, while below 100 eV u−1 limited agreement is achieved with the available calculations. These cross-section data are useful for modeling X-ray emission resulting from the charge exchange at the interface of hot plasma interacting with ambient neutral gas.

Airside pressure drop characteristics of three analogous serpentine tube heat exchangers considering heat transfer for aero-engine cooling

This study explores the design, analysis, and air pressure drop assessment of three analogous air–fuel heat exchangers consisting of thin serpentine tube bundles intended for use in high Mach number aero-engines. In high speed flight, the compressor bleed air used to cool high temperature turbine blades and other hot components is too hot. Hence, aviation kerosene is applied to precool the compressor bleed air by means of novel air–fuel heat exchangers. Three light and compact heat exchangers including dozens of in-line thin serpentine tube bundles were designed and manufactured, with little difference existing in aspects of tube pitches and outer diameters among three heat exchangers. The fuel flows inside a series of parallel stainless serpentine tubes (outer diameter: 2.2, 1.8, 1.4 mm with 0.2 mm thickness), while the air externally flows normal to tube bundles and countercurrent with fuel. Experimental studies were carried out to investigate the airside pressure drop characteristics on isothermal states with the variation of air mass flow rates and inlet temperatures. Non-isothermal measurements have also been performed to research the effect of heat transfer on pressure drops. The experimental results show that inlet temperatures have significant influence on pressure drops, and higher temperatures lead to higher pressure drops at the same mass flow rate. The hydraulic resistance coefficient decreases quickly with Reynolds number, and the descent rate slows down when Re > 6000 for all three heat exchangers. Additionally, the pressure drop on heat transfer states is less than that on isothermal states for the same average temperatures. Moreover, the pressure drop through heat exchangers is greatly affected by attack angles and transverse pitches, and an asymmetric M-shaped velocity profile is generated in the cross-section of sector channels.

Non-destructive Metallurgical Failure Investigation of Erroneously Heat Treated Hot Gas Path Component Using Replica Technique

Abstract Metallic heat shields, used in combustion chambers of heavy-duty gas turbine engines and made of nickel-based superalloys, were accidentally heat treated during fabrication, using wrong parameters. There were concerns about embrittlement. Nondestructive metallurgical material characterization using the replica technique verified embrittlement by secondary phases. In spite of this, it was recommended to the client to use the affected parts as is, this on the grounds that no grain growth was observed and hardness was not elevated. While the case study presented in this contribution may appear trivial at first sight, it interestingly shows how metallographic examinations may sometimes be performed non-destructively, without sacrificing any engine components. The inclined reader should also note the superb quality of the photomicrographs presented in this contribution. They were taken from replica foils, not actual metallographic sections.

Kinematic Decomposition of the H i Gaseous Component in the Large Magellanic Cloud

Abstract We perform a profile analysis of the combined H i data cube of the Large Magellanic Cloud (LMC) from observations with the Australia Telescope Compact Array and the Parkes radio telescope. For the profile analysis, we use a newly developed algorithm that decomposes individual line profiles into an optimal number of Gaussian components based on a Bayesian nested sampling. The decomposed Gaussian components are then classified into kinematically cold, warm, and hot gas components based on their velocity dispersion. The estimated masses of the kinematically cold, warm, and hot gas components are ∼12.2%, ∼58.3%, and ∼29.5% of the total H i mass of the LMC, respectively. Our analysis reveals the highly complex H i structure and kinematics of the LMC that are seen in previous studies but in a more quantitative manner. We also extract the undisturbed H i gas bulk motions and derive new H i gas bulk rotation curves of the LMC by applying a 2D tilted-ring analysis. In contrast to previously derived H i rotation curves, the newly derived bulk rotation curves are much more consistent with the carbon star kinematics, with rotation velocity linearly increasing in the inner part and reaching a maximum of ∼60 km s−1 at the outermost measured radius. By comparing the lower bulk rotation curves with previous studies, we conclude that there is a lower dynamical contribution of dark matter in the central part of the LMC.

A novel low-damage and low-abrasive wear processing method of Cf/SiC ceramic matrix composites: Laser-induced ablation-assisted grinding

• Laser-induced ablation-assisted grinding (LIAAG) method is first proposed. • C f /SiC composites occur chemical transformation, resulting in loose SiO 2 . • Grinding force and temperature are significantly reduced with laser ablation. • Surface morphology of C f /SiC composites shows as microfracture and crushing. • Cleavage fracture of diamond grain is reduced during LIAAG. Continuous fiber-reinforced ceramic matrix composites are promising materials for advanced hot end components and safety-critical components of aeronautics and astronautics; however, the difficult-to-process problem of these materials has been one of the technical bottlenecks restricting their high-performance service. The present work proposed a novel high-efficiency, low-damage, and low-abrasive wear processing method based on the chemical properties of the materials, which used lasers to ablate workpieces before grinding—laser-induced ablation-assisted grinding (LIAAG). The material removal mechanism of C f /SiC composites was investigated by single-grain scratching tests; the grinding performances of LIAAG in terms of grinding force, grinding temperature, surface integrity, abrasive wear, grinding chips were evaluated by a contrast abrasive belt grinding test. It was found that C f /SiC composites were chemically transformed into relatively loose and homogeneous ablation products (SiO 2 and recrystallized SiC) at high laser ablation temperatures, which were easier to remove during grinding. In this case, surface morphologies displayed the microfracture and crushing of carbon fibers and SiC matrixes, and the grinding-induced damages, such as macro fracture, fiber pull-out, interface debonding, were significantly contained. Abrasive belt was primarily worn in micro-adhesion and micro-abrasion, rather than cleavage fracture and the fall-off in traditional grinding. Under optimum parameters, the grinding force, grinding temperature, and average surface roughness of belt grinding were reduced by 47 %, 40 %, and 26 %, respectively. Consequently, the surface integrity was improved greatly, and the abrasive wear was reduced significantly. The work provides a vital high-performance processing method for ceramic matrix composites components.

NEW PHOTOMETRY AND SPECTROSCOPY OF DW CANCRI

We present new observations of the cataclysmic variable DW Cancri, after the system recovered from a low state. We performed a power spectrum analysis that reveals a clear signal of the 38 min spin period in our photometric data. Our spectroscopic power spectrum search was consistent with studies performed before the low state, showing the orbital and spin modulations. Our Doppler Tomography study exhibits a disc structure and an enhanced asymmetric region, possibly related to a hot spot component. Furthermore, a wavelet transform analysis reveals the 70 min spin-orbit beat period. We interpret these results as an indication of a partial recovery of the system. However, DW Cnc does not yet show all the original photometric modulations reported before the low state. Thus, we propose further observations to elucidate if such original signals require more time to reactivate.

Overall thermal performances of backward film cooling with simulated surface thermal barrier coatings at various walls

Backward film cooling can protect more efficiently some regions of turbine hot components, in comparison with the forward jet. The rapid increase of operational temperature requires the developments of the coupling of active cooling and thermal barrier coating (TBC). A study on the overall thermal performances of the system of TBC and backward film cooling was conducted through both the overall effectiveness experiments and predictions in a lab environment. The models feature the engine-matched hot-side Biot numbers to acquire the actual overall effectiveness. The concerned factors include the jet-orientation, TBC-thickness, spraying-induced hole-geometry, blowing ratio, and wall curvature. The present TBC-spraying can induce the standard cylindrical (SC) and transverse trenched (TT) holes. In general, the backward film cooling can reduce the potential of TBC insulation, due to the favorable cooling air coverage. The hole-geometry-induced difference in metal overall effectiveness can be significantly weakened by the backward jet. However, the TT design is more proposed, due to the lower TBC temperature. Moreover, relative to the forward jet, the backward one features the larger potential to prevent the thermal damage of exposed metal inside trench from the ingestion of hot gas. Additionally, the wall curvature effect on the TT cooling is insignificant.

Trifurcate structure of oxygen band EMIC waves excited in a warm magnetospheric plasma

Applying linear dispersion theory to a warm collisionless plasma, we investigate the effect of hot ion composition on electromagnetic ion cyclotron (EMIC) wave generation. The growth rate of oxygen band waves can divide into three components if hot anisotropic heavy ions are included. Their wave frequencies (0.05 ΩH+, 0.03 ΩH+, and 0.01 ΩH+) are sorted in relation to the cyclotron frequencies of H+, He+, and O+ ions (ΩH+, ΩH+/4, and ΩH+/16). The three sub-bands within the oxygen band form an unusual trifurcate structure of growth rate. A link between the three sub-bands and three hot species has been definitively established. That is to say, hot H+, He+, and O+ ions are responsible for the generation of sub-bands. The unstable frequencies of oxygen band waves are directly modulated by the actual composition of magnetospheric ions. The largest growth can arise between the extremely low frequency and the gyrofrequency of O+ (ΩO+). When O+ ions become the dominant hot component during the storm phase, oxygen waves can be generated at much lower frequencies than ΩO+. We perform a parametric study of oxygen sub-band generation in the magnetosphere by using a statistical survey of the plasma composition measured by the Van Allen Probes. The trifurcate structure of growth rate appears at wide L shells from the outer plasmasphere to the geostationary orbit. The new findings demonstrate that wave structures in the oxygen band are more complex than the hydrogen and helium bands. This may provide insight into the nature of the EMIC instability.

Repurposing steel press production lines for hot formed high-strength aluminium automotive body components

Climate change and normative requirements are forcing car manufacturers to make their products ever lighter despite the highest safety requirements. For this case study a high-strength EN AW-7075 alloy is used as an example of how hot formed aluminium components for vehicle bodies can be produced on existing steel hot forming lines. Reusing production plants not only shortens the start-up time for mass production of hot formed and high-strength aluminium components, but also makes a significant contribution to the sustainable use of existing plant technologies and thus to improving the carbon footprint of manufacturing companies.In addition to the presentation of the process control and the necessary conversion measures for the modification of a hot forming process from steel to aluminium, the most significant technological properties and the production costs of hot formed components made from both materials are compared. To be able to show the economic viability of a reallocation of existing and depreciated manufacturing plants, investigations of possible manufacturing parameters are carried out and presented.The case study shows that by converting the furnace technology to Jet-Heating, significantly higher heating rates can be realised when compared with using radiation furnaces. As the furnace holding time was found to have no influence on the final strength in T4 and T6 state of EN AW-7075 specimens, the overall furnace cycle time is significantly lower than for press-hardened steels. Although the modifications necessary for the forming of aluminium alloys result in changed requirements for existing production plants, the additional costs per component for the plant conversion are marginal in relation to the assumed delivery volumes. It is demonstrated that for components with low material input, the use of 7000 series aluminium alloy components can become economically viable on a larger scale for OEMs.

Mid-infrared Variability of Low-redshift Active Galactic Nuclei: Constraints on a Hot Dust Component with a Variable Covering Factor

Abstract We utilize mid-infrared multiepoch data from the Wide-field Infrared Survey Explorer over a ∼10 yr period in the W1 (3.4 μm) and W2 (4.6 μm) bands to investigate the structure of dusty torus in low-redshift (0.15 < z ≤ 0.4) active galactic nuclei (AGNs). We calculate a Spearman correlation coefficient (r 12) between the W1 magnitude and W1 − W2 color based on the light curve in individual objects. Interestingly, r 12 spans a broad range from −1 to 1 and is detected to be correlated with mean W1 − W2 color and AGN bolometric luminosity, in the sense that objects with a blue W1 − W2 color and low AGN luminosity tend to become redder (bluer) with increasing (decreasing) W1 brightness in the light curve (i.e., r 12 < 0), although the correlation of r 12 with the bolometric luminosity is relatively weak. The fit for the spectral energy distribution reveals a significant contribution from the host galaxy in the W1 and W2 bands. However, the dependencies of r 12 on the W1 − W2 color and AGN luminosity still persist even after careful elimination of the host light contribution. We propose that this result can be explained if the covering factor of the hot dust component decreases as the AGN luminosity increases.

Improved strong lensing modelling of galaxy clusters using the Fundamental Plane: Detailed mapping of the baryonic and dark matter mass distribution of Abell S1063

Aims. From accurate photometric and spectroscopic information, we build the Fundamental Plane (FP) relation for the early-type galaxies of the cluster Abell S1063. We use this relation to develop an improved strong lensing model of the cluster, and we decompose the cluster’s cumulative projected total mass profile into its stellar, hot gas, and dark matter mass components. We compare our results with the predictions of cosmological simulations. Methods. We calibrate the FP using Hubble Frontier Fields photometry and data from the Multi Unit Spectroscopic Explorer on the Very Large Telescope. The FP allows us to determine the velocity dispersions of all 222 cluster members included in the model from their measured structural parameters. As for their truncation radii, we test a proportionality relation with the observed half-light radii. Fixing the mass contribution of the hot gas component from X-ray data, the mass density distributions of the diffuse dark matter haloes are optimised by comparing the observed and model-predicted positions of 55 multiple images of 20 background sources distributed over the redshift range 0.73 − 6.11. We determine the uncertainties on the model parameters with Monte Carlo Markov chains. Results. We find that the most accurate predictions of the positions of the multiple images are obtained when the truncation radii of the member galaxies are approximately 2.3 times their effective radii. Compared to earlier work on the same cluster, our model allows for the inclusion of some scatter on the relation between the total mass and the velocity dispersion of the cluster members. We notice a lower statistical uncertainty on the value of some model parameters. For instance, the main dark matter halo of the cluster has a core radius of 86 ± 2 kpc: the uncertainty on this value decreases by more than 30% with respect to previous work. Taking advantage of a new estimate of the stellar mass of all cluster members from the HST multi-band data, we measure the cumulative two-dimensional mass profiles out to a radius of 350 kpc for all baryonic and dark matter components of the cluster. At the outermost radius of 350 kpc, we obtain a baryon fraction of 0.147 ± 0.002. We study the stellar-to-total mass fraction of the high-mass cluster members in our model, finding good agreement with the observations of wide galaxy surveys and some disagreement with the predictions of halo occupation distribution studies based on N-body simulations. Finally, we compare the features of the sub-haloes as described by our model with those predicted by high-resolution hydrodynamical simulations. We obtain compatible results in terms of the stellar over total mass fraction. On the other hand, we report some discrepancies both in terms of the maximum circular velocity, which is an indication of the halo compactness, and the sub-halo total mass function in the central cluster regions.

New Massive Contact Twin Binary in a Radio-quiet H ii Region Associated with the M17 Complex

Early-B stars, much less energetic than O stars, may create an H ii region that appears as radio-quiet. We report the identification of new early-B stars associated with the radio-quiet H ii region G014.645–00.606 in the M17 complex. The radio-quiet H ii region G014.645–00.606 is adjacent to three radio-quiet WISE H ii region candidates. The ionizing sources of the radio-quiet H ii regions are expected to be later than B1V, given the sensitivity about 1–2 mJy of the MAGPIS 20 cm survey. The stars were first selected if their parallaxes of Gaia EDR3 match that of the 22 GHz H2O maser source within the same region. We used the color–magnitude diagram made from the Zwicky Transient Facility photometric catalog to select the candidates for massive stars because the intrinsic g − r colors of massive stars change little from B-type to O-type stars. Five stars lie in the areas of the color–magnitude diagram where either reddened massive stars or evolved post-main sequence stars of lower masses are commonly found. Three of the five stars, sources 1, 2, and 3, are located at the cavities of the three IR bubbles, and extended Hα emission is detected around the three IR bubbles. We suggest that sources 1, 2, and 3 are candidates for early-B stars associated with the radio-quiet region G014.645–00.606. Particularly, source 1 is an EW type eclipsing binary with a short period of 0.825 day, while source 2 is an EA type eclipsing binary with a short period of 0.919 day. The physical parameters of the two binary systems have been derived through the PHOEBE model. Source 1 is a twin binary of two stars with T eff ≈ 23,500 K, and source 2 contains a hotter component (T eff ≈ 20,100 K) and a cooler one (T eff ≈ 15,500 K). The O − C values of source 1 show a trend of decline, implying that the period of the source is deceasing. Source 1 is likely a contact early-B twin binary, for which mass transfer might cause its orbit to shrink.

Damage Evolution of Hot Stamped Boron Steels Subjected to Various Stress States: Macro/Micro-Scale Experiments and Simulations.

Hot stamping components with tailored mechanical properties have excellent safety-related performance in the field of lightweight manufacturing. In this paper, the constitutive relation and damage evolution of bainite, martensite, and mixed bainite/martensite (B/M) phase were studied. Two-dimensional representative volume element (RVE) models were constructed according to microstructure characteristics. The constitutive relations of individual phases were defined based on the dislocation strengthening theory. Results showed that the damage initiation and evolution of martensite and bainite phases can well described by the Lou-Huh damage criterion (DF2015) determined by the hybrid experimental–numerical method. The calibrated damage parameters of each phase were applied to the numerical simulation, followed by the 2D RVE simulations of B/M phase under different stress states. To study the influence of martensite volume fraction (Vm) and distribution of damage evolution, the void nucleation and growth were evaluated by RVEs and verified by scanning electron microscope (SEM). Three types of void nucleation modes under different stress states were experimentally and numerically studied. The results showed that with the increase of Vm and varying martensite distribution, the nucleation location of voids move from bainite to martensite.

High-temperature electrical properties of polymer-derived ceramic SiBCN thin films fabricated by direct writing

The in situ temperature monitoring of hot components in harsh environments remains a challenging task. In this study, SiBCN thin-film resistance grids with thicknesses of 1.8 μm were fabricated on alumina substrates via direct writing. Owing to their dense microscopic morphology and extremely high graphitisation level, the produced SiBCN films exhibited large high-temperature oxidation resistance and electrical conductivity. The resistance–temperature, stability, and repeatability characteristics of these films were examined in an aerobic environment at temperatures up to 800 °C. The obtained results revealed that the thermistor resistance decreased monotonously with increasing temperature from room temperature to 800 °C. The SiBCN film resistance variations observed during repeated temperature cycling in the regions of 505–620 °C and 610–720 °C were 0.09% and 1.7%, respectively. The high cyclability and stability of the SiBCN thin film thermistor suggested its potential applicability for the in situ temperature monitoring of hot components in harsh environments.

Ultrasonically stimulated thermography for crack detection of turbine blades

The hot gas components in a gas turbine have to withstand extreme loads. As failure of turbine blades could have catastrophic consequences, the integrity of the entire engine must always be guaranteed, hence quick and reliable structural health monitoring (SHM) or nondestructive testing techniques (NDT) are essential.In this work, an ultrasonic stimulated thermographic test system was developed to efficiently detect cracks in turbine blades. The used technique is based on the ultrasound excitation with a piezo actuator, where the contact surfaces of the crack are excited and generate frictional heat, which is captured by a thermal imaging camera. A method was developed, where the temperature increase is measured as a function of the electrical energy supply to the actuator. This allows understanding crack topology and the prediction of preloads in the crack. Numerical analysis were conducted for optimising the frequency to be excited for the type of damage experienced by the blade and for understanding the basic physics of the coupling between cracks configuration, local crack velocity and temperature increase. The procedure presented helps to efficiently detect cracks and to optimize the inspection cycles of these components.

The limit of hot isostatic pressing for healing cracks present in an additively manufactured nickel superalloy

Inconel 738LC (IN738LC) is a nickel-based superalloy specially used in the hot section components of turbine engines due to its outstanding hot corrosion resistance and mechanical properties under high temperatures. However, one of the main drawbacks of this superalloy is its susceptibility to cracking when it is manufactured by Laser Powder Bed Fusion (LPBF). This paper describes the effect of 400 W laser power and 90° rotation strategy on the formation of cracks and the capability of Hot Isostatic Pressing (HIP) post-treatment to substantially reduce them in the LPBF manufactured IN738LC samples. Based on the characterization of the cracks, the most important finding from this research work was the identification of the limit of crack width at 6 μm, beyond which the HIP treatment is unable to effect crack healing. Furthermore, this research shows that the HIP treatment leads to microstructural changes in the IN738LC samples with a massive precipitation of γ´ phase. Indeed, the formation of precipitates implied an increase in the microhardness of up to 23 %, which demonstrates that the HIP treatment also affects the mechanical properties of the IN738LC superalloy. It was therefore shown that the HIP treatment could be a crucial process to substantially reduce the defects of the additively manufactured parts.

Non-star-forming molecular gas in the Abell 1367 intra-cluster multiphase orphan cloud

We report the detection of CO emission in the recently discovered multiphase isolated gas cloud in the nearby galaxy cluster Abell 1367. The cloud is located about 800 kpc in projection from the center of the cluster and at a projected distance of > 80 kpc from any galaxy. It is the first and the only known isolated “intra-cluster” cloud detected in X-ray, Hα, and CO emission. We found a total of about 2.2 × 108 M⊙ of H2 with the IRAM 30-m telescope in two regions, one associated with the peak of Hα emission and another with the peak of X-ray emission surrounded by weak Hα filaments. The velocity of the molecular gas is offset from the underlying Hα emission by > 100 km s−1 in the region where the X-ray peaks. The molecular gas may account for about 10% of the total cloud’s mass, which is dominated by the hot X-ray component. The previously measured upper limit on the star formation rate in the cloud indicates that the molecular component is in a non-star-forming state, possibly due to a combination of low density of the gas and the observed level of velocity dispersion. The presence of the three gas phases associated with the cloud suggests that gas phase mixing with the surrounding intra-cluster medium is taking place. The possible origin of the orphan cloud is a late evolutionary stage of a ram pressure stripping event. In contrast, the nearby ram pressure stripped galaxy 2MASX J11443212+2006238 is in an early phase of stripping and we detected about 2.4 × 109 M⊙ of H2 in its main body.

Slow Shock Formation Upstream of Reconnecting Current Sheets

Abstract The formation, development, and impact of slow shocks in the upstream regions of reconnecting current layers are explored. Slow shocks have been documented in the upstream regions of magnetohydrodynamic (MHD) simulations of magnetic reconnection as well as in similar simulations with the kglobal kinetic macroscale simulation model. They are therefore a candidate mechanism for preheating the plasma that is injected into the current layers that facilitate magnetic energy release in solar flares. Of particular interest is their potential role in producing the hot thermal component of electrons in flares. During multi-island reconnection, the formation and merging of flux ropes in the reconnecting current layer drives plasma flows and pressure disturbances in the upstream region. These pressure disturbances steepen into slow shocks that propagate along the reconnecting component of the magnetic field and satisfy the expected Rankine–Hugoniot jump conditions. Plasma heating arises from both compression across the shock and the parallel electric field that develops to maintain charge neutrality in a kinetic system. Shocks are weaker at lower plasma β, where shock steepening is slow. While these upstream slow shocks are intrinsic to the dynamics of multi-island reconnection, their contribution to electron heating remains relatively minor compared with that from Fermi reflection and the parallel electric fields that bound the reconnection outflow.

Probing Hot Gas Components of the Circumgalactic Medium in Cosmological Simulations with the Thermal Sunyaev–Zel’dovich Effect

Abstract The thermal Sunyaev–Zel’dovich (tSZ) effect is a powerful tool with the potential for constraining directly the properties of the hot gas that dominates dark matter halos because it measures pressure and thus thermal energy density. Studying this hot component of the circumgalactic medium (CGM) is important because it is strongly impacted by star formation and active galactic nucleus (AGN) activity in galaxies, participating in the feedback loop that regulates star and black hole mass growth in galaxies. We study the tSZ effect across a wide halo-mass range using three cosmological hydrodynamical simulations: Illustris-TNG, EAGLE, and FIRE-2. Specifically, we present the scaling relation between the tSZ signal and halo mass and the (mass-weighted) radial profiles of gas density, temperature, and pressure for all three simulations. The analysis includes comparisons to Planck tSZ observations and to the thermal pressure profile inferred from the Atacama Cosmology Telescope (ACT) measurements. We compare these tSZ data to simulations to interpret the measurements in terms of feedback and accretion processes in the CGM. We also identify as-yet unobserved potential signatures of these processes that may be visible in future measurements, which will have the capability of measuring tSZ signals to even lower masses. We also perform internal comparisons between runs with different physical assumptions. We conclude (1) there is strong evidence for the impact of feedback at R 500, but that this impact decreases by 5R 500, and (2) the thermodynamic profiles of the CGM are highly dependent on the implemented model, such as cosmic-ray or AGN feedback prescriptions.

Resolving Two Distinct Thermal X-Ray Components in a Compound Solar Flare

Abstract X-ray emission provides the most direct diagnostics of the energy release process in solar flares. Occasionally, a superhot X-ray source is found to be above hot flare loops of ∼10 MK temperature. While the origin of the superhot plasma is still elusive, it has conjured up an intriguing image of in situ plasma heating near the reconnection site high above the flare loops, in contrast to the conventional picture of chromospheric evaporation. Here we investigate an extremely long duration solar flare, in which EUV images show two distinct flare loop systems that appear successively along a Γ-shaped polarity inversion line (PIL). When both flare loop systems are present, the hard X-ray spectrum is found to be well fitted by combining a hot component (T e ∼ 12 MK) and a superhot component (T e ∼ 30 MK). Associated with a fast coronal mass ejection (CME), the superhot X-ray source is located at the top of the flare arcade that appears earlier, straddling and extending along the long “arm” of the Γ-shaped PIL. Associated with a slow CME, the hot X-ray source is located at the top of the flare arcade that appears later and sits astride the short “arm” of the Γ-shaped PIL. Aided by observations from a different viewing angle, we are able to verify that the superhot X-ray source is above the hot one in projection, but the two sources belong to different flare loop systems. Thus, this case study provides a stereoscopic observation explaining the coexistence of superhot and hot X-ray-emitting plasmas in solar flares.