Hot Gas Research Articles

Sweeping jet impingement heat transfer on concave surface: Influence of trapped vortex ring revealed by generalized k-ω (GEKO) model

Jet impingement-based heat transfer enhancement is widely employed due to the significant mass, momentum, and energy it accompanied. While the steady jet with high energy flux is commonly favored, it still exhibit few defects, including heat transfer deterioration away from the stagnation point and mutual flow interference in the jet arrays, which are particularly critical in demanding applications. Recently, the sweeping jet has been proposed to resolve the above challenges owing to its self-excited and self-sustaining unsteady oscillation. However, current research predominately focuses on impinging on the flat surface, neglecting impinging on the concave surface, such as internal cooling at the gas turbine blade leading-edge as well as the hot gas de-icing at the aircraft wing leading-edge. Understanding the heat transfer characteristics in these scenarios is crucial as they notably differ from those on flat surfaces. Therefore, this paper investigates the heat transfer characteristics and the related essential flow dynamics of a sweeping jet with a Reynolds number of 2577 impinging on a concave surface, and those of a steady jet under the same conditions are compared. The jet-to-wall distance and the curvature of the impingement surface are 4 and 10 times the jet's hydraulic diameter, respectively. To correctly capture the three-dimensional characteristics of the sweeping jet, this research employs the Reynolds stress model for turbulence modeling and the Generalized k-ω (GEKO) model for better calibration of the jet's spreading and dissipation rates, as well as the characteristics of trapped vortex generated due to the confined concave flow channel. The study initially focuses on the average Nusselt number on the impingement surface, revealing a 15.2% increase in heat transfer intensity of the sweeping jet compared to the steady jet, and the sweeping jet covers a larger area with enhanced uniformity. Subsequent analysis on streamlines in two perpendicular planes and Q criterion iso-surfaces in the spatial domain shows the formation of a trapped vortex ring with a constant location around the jet, restricting the effective cooling range to its inner side and thus resulting in a steep temperature rise on the two lateral sides of the vortex ring. The stability of the trapped vortex is enhanced by the curved impingement wall in the oscillation plane, which on the one hand forces the high-temperature fluid that has exchanged heat with the wall to repeatedly wash the same location, and on the other hand significantly reduces the jet oscillation angle compared to a free sweeping jet. Consequently, the heat transfer intensity of the sweeping jet is lower in the main oscillation plane than in the non-oscillation plane. Analysis of the near-wall flow parameters indicates that the sweeping jet generates higher velocity and turbulence kinetic energy in the wall jet zone far away from the stagnation point compared to the steady jet, which results in a higher local heat transfer intensity. The unsteady transverse oscillation of the sweeping jet disturbs the wall jet zone and disrupts the formation of the wall boundary layer, causing a higher velocity gradient at the wall and hence the lower thicknesses of the velocity boundary layer and the thermal boundary layer than those of the steady jet. In conclusion, this study reveals the flow and heat transfer features of the sweeping jet impingement on confined concave surface, with the influence of the trapped vortex ring mattering significantly. The findings provide a reference for designing a more effective jet arrangement. Future work will focus on investigating the effects of jet Reynolds number and impingement distance variations on the trapped vortex ring, and how to mitigate the adverse effects of the trapped vortex ring on impingement heat transfer.

Resolving high-z galaxy cluster properties through joint X-ray and millimeter analysis: Case study of SPT-CLJ0615-5746

We present a joint millimetric and X-ray analysis of hot gas properties in the distant galaxy cluster SPT-CLJ0615-5746 ($z = 0.972$). Combining Chandra observations with the South Pole Telescope (SPT) and Planck data, we performed radial measurements of thermodynamical quantities up to a characteristic radius of $1.2\ $. We exploited the high angular resolution of Chandra and SPT to map the innermost region of the cluster and the high sensitivity to the larger angular scales of Planck to constrain the outskirts and improve the estimation of the cosmic microwave background and the galactic thermal dust emissions. In addition to maximizing the accuracy of radial temperature measurements, our joint analysis allows us to test the consistency between X-ray and millimetric derivations of thermodynamic quantities via the introduction of a normalization parameter ($ between X-ray and millimetric temperature profiles. This approach reveals a substantial high value of the normalization parameter, $ $, suggesting that the gas halo is aspherical. Assuming hot gas hydrostatic equilibrium within complementary angular sectors that intercept the major and minor elongation of the X-ray image, we infer a halo mass profile that results from an effective compensation of azimuthal variations of gas densities by variations in the $ parameter. Consistent with earlier integrated X-ray and millimetric measurements, we infer a cluster mass of HE odot

Galaxy clusters in Milgromian dynamics: Missing matter, hydrostatic bias, and the external field effect

We study the mass distribution of galaxy clusters in Milgromian dynamics, or modified Newtonian dynamics (MOND). We focus on five galaxy clusters from the X-COP sample, for which high-quality data are available on both the baryonic mass distribution (gas and stars) and internal dynamics (from the hydrostatic equilibrium of hot gas and the Sunyaev-Zeldovich effect). We confirm that galaxy clusters require additional `missing matter' in MOND, although the required amount is drastically reduced with respect to the non-baryonic dark matter in the context of Newtonian dynamics. We studied the spatial distribution of the missing matter by fitting the acceleration profiles of the clusters with a Bayesian method, finding that a physical density profile with an inner core and an outer $r^ $ decline (giving a finite total mass) provide good fits within sim 1 Mpc. At larger radii, the fit results are less satisfactory but the combination of the MOND external field effect and hydrostatic bias (quantified as 10$<!PCT!>$-40$<!PCT!>$) can play a key role. The missing mass must be more centrally concentrated than the intracluster medium (ICM). For relaxed clusters (A1795, A2029, A2142), the ratio of missing-to-visible mass is around $1-5$ at $R kpc and decreases to $0.4-1.1$ at $R Mpc, showing that the total amount of missing mass is smaller than or comparable to the ICM mass. For clusters with known merger signatures (A644 and A2319), this global ratio increases up to sim 5 but may indicate out-of-equilibrium dynamics rather than actual missing mass. We discuss various possibilities regarding the nature of the extra mass, in particular `missing baryons' in the form of pressure-confined cold gas clouds with masses of $<10^5$ M$_ and sizes of $< 50$ pc.

In-situ consolidation of thermoplastic composites by automated fiber placement: Characterization of defects

The emergence of automated manufacturing of composites has not only transformed the manufacturing of optimized and geometrically complex structures but has also expanded the promising prospect of in-situ manufacturing of thermoplastic composites (TPC), where both material placement and consolidation are carried out by automated fiber placement (AFP) equipment, streamlining the process into single step manufacturing. However, the inherent complexities in different aspects of robotic automation, imperfections in the supplied material, and the occurrence of multi-physical phenomena during in-situ consolidation introduce various manufacturing-induced defects. While the defects in thermoset composites (TSC) made by AFP have been widely studied in the past, this study explores the diverse defects at micro and macro scales for TPCs made by AFP, with a focus on carbon-fiber/poly-ether-ether-ketone (CF/PEEK) tapes consolidated using hot gas torch (HGT) heating system. An overview of defects and associated characteristics is presented across three phases: defects in supplied impregnated tapes, defects and limitations in performance of AFP system, and defects in the final in-situ consolidated composite. For the defects subject to studies in the past, the description is limited to a concise review, while those with limited understanding are supported by new empirical observations in this work.

The case for hot-mode accretion in Abell 2029

Abstract Radiative cooling and AGN heating are thought to form a feedback loop that regulates the evolution of low redshift cool-core galaxy clusters. Numerical simulations suggest that formation of multiphase gas in the cluster core imposes a floor on the ratio of cooling time (tcool) to free-fall time (tff) at min (tcool/tff) ≈ 10. Observations of galaxy clusters show evidence for such a floor, and usually the cluster cores with min (tcool/tff) ≲ 30 contain abundant multiphase gas. However, there are important outliers. One of them is Abell 2029, a massive galaxy cluster (M200 ≳ 1015 M⊙) with min (tcool/tff) ∼ 20, but little apparent multiphase gas. In this paper, we present high resolution 3D hydrodynamic AMR simulations of a cluster similar to A2029 and study how it evolves over a period of 1-2 Gyr. Those simulations suggest that Abell 2029 self-regulates without producing multiphase gas because the mass of its central black hole (∼5 × 1010 M⊙) is great enough for Bondi accretion of hot ambient gas to produce enough feedback energy to compensate for radiative cooling.

A novel mathematical optimization method to obtain the maximum-power electrical configuration of thermoelectric generators for energy harvesting

Waste thermal energy recovery with thermoelectric generators has been widely studied as a method to make systems that produce hot exhaust gases, such as aircrafts, ground vehicles and factories, more sustainable. In this type of applications, the mismatch in hot and cold side temperatures of thermoelectric modules (TEMs) creates a mismatch in the electrical output. For each situation, there is a certain electrical interconnection between the modules that gives the maximum global power output. Three optimization models to find what is the best way of connecting the TEMs without a trial-and-error process, as usually done in previous literature, based on mathematical programming are proposed: single branch of series-connected TEMs, multiple parallel-connected branches of series-connected TEMs, and multiple groups of independent series-connected TEMs. The main novel contributions of this paper are: (i) a mathematical optimization approach that provides how to connect the thermoelectric modules one by one, (ii) the application of the above-mentioned method in a common case study: an automotive thermoelectric generator, (iii) information about how the optimal connection between modules changes if the heat source changes its operation (iv) a method for selecting a fixed optimal connection even when the heat source operation changes, e.g. different operation modes in a thermal engine, based on introducing weighting parameters in the optimization mathematical model. The optimization approach followed here is novel and has not been applied before to thermoelectric generators.

Numerical Investigation on Overall Cooling Effectiveness of Narrow-Channel Double-Wall Cooling

Abstract In the double-wall cooling of turbine blades, coolant migration can lead to uneven flow distribution, which, in severe cases, can cause hot gas intrusion into the film holes, affecting the lifespan of the blade. To mitigate the negative influence of coolant migration, this study proposes a novel double-wall system called the narrow-channel double-wall cooling (NCDW) system, where thin walls are arranged inside the internal channel of double-wall cooling to achieve a more balanced coolant distribution for film holes. However, the addition of thin walls alters the flow and heat transfer distributions within the double-wall structure, ultimately affecting the overall cooling effectiveness. Therefore, numerical methods are employed in this study to analyze the flow distribution characteristics, overall cooling effectiveness, and internal heat transfer characteristics of the narrow-channel double-wall cooling. The numerical results demonstrate that narrow-channel double-wall cooling, with or without pin fins, significantly improves the uneven mass flow distribution in the film holes while maintaining an overall cooling effectiveness that is comparable to that of the double-wall effusion cooling (DWEC) system. It is worth noting that although the overall cooling effectiveness difference is slight, there are significant differences in the internal-heat-transfer characteristics between the two double-wall cooling systems. Additionally, the study discusses the influence of narrow wall thickness on the overall cooling effectiveness and flow distributions, revealing that a thinner wall can lead to higher overall cooling effectiveness in narrow-channel double-wall cooling.

Highly-mass-loaded hot galactic winds are unstable to cool filament formation

Abstract As cool clouds are entrained by a hot supersonic galactic wind, they may be shredded by hydrodynamical instabilities and incorporated into the hot flow. One-dimensional steady-state calculations show how cool cloud entrainment affects the bulk thermodynamics and kinematics of the hot gas: mass-loading decelerates the hot flow and changes its entropy. Here, we investigate the stability of mass-loaded hot winds using both perturbation analysis and 3D time-dependent radiative hydrodynamical simulations. We show that mass-loading is stable over a broad range of parameters and that the 1D time-steady analytic solutions exactly reproduce the 3D time-dependent calculations, provided that the flow does not decelerate sufficiently to become subsonic. For higher values of the mass-loading, the flow develops a second sonic point, with the first being at the edge of the wind-driving region. Strong deceleration increases the wind density and the flow becomes radiative, undergoing a thermal instability to form elongated dense cometary filaments. We explore the mass-loading parameters required to trigger this behavior. For certain approximations, we can derive analytic criteria. In general a mass-loading rate similar to the initial hot mass outflow rate is required. In this sense, the destruction of small cool clouds by a hot flow may ultimately spontaneously generate fast cool filaments, as observed in starburst winds. Lastly, we find that the kinematics of filaments is sensitive to the slope of the mass-loading function. Filaments move faster than the surrounding wind if mass-loading is over long distances whereas filaments move slower than their surroundings if mass-loading is abrupt.

Taming the TuRMoiL: The Temperature Dependence of Turbulence in Cloud–Wind Interactions

Taming the TuRMoiL: The Temperature Dependence of Turbulence in Cloud–Wind Interactions

Infall Motions in the Hot Core Associated with the Hypercompact H ii Region G345.0061+01.794 B

We report high angular resolution observations, made with the Atacama Large Millimeter Array in band 6, of high excitation molecular lines of CH3CN and SO2 and of the H29α radio recombination line toward the G345.0061+01.794 B HC H ii region in order to investigate the physical and kinematical characteristics of its surroundings. Emission was detected in all observed components of the J = 14 →13 rotational ladder of CH3CN and in the 304,26–303,27, and 324,28–323,29 lines of SO2. The peak of the velocity-integrated molecular emission is located ∼0.″4 northwest of the peak of the continuum emission. The first-order moment images and channel maps show a velocity gradient of 1.1 km s−1 arcsec−1 across the source and a distinctive spot of blueshifted emission toward the peak of the zero-order moment. The rotational temperature is found to decrease from 252±24 K at the peak position to 166±16 K at its edge, indicating that our molecular observations are probing a hot molecular core that is internally excited. The emission in the H29α line arises from a region of 0.″65 in size, where its peak coincides with that of the dust continuum. We model the kinematical characteristics of the “central blue spot” feature as due to infalling motions, suggesting a central mass of 172.8±8.8 M ⊙. Our observations indicate that this HC H ii region is surrounded by a compact structure of hot molecular gas, which is rotating and infalling toward a central mass, that is most likely confining the ionized region. The observed scenario is reminiscent of a “butterfly pattern” with an approximately edge-on torus and ionized gas roughly parallel to its rotation axis.

Pressure Balance and Energy Budget of the Nuclear Superbubble of NGC 3079

Superbubbles in the nuclear region of galaxies could be produced by active galactic nuclei (AGN) or nuclear starburst via different driving forces. We report analysis of the multiwavelength data of the kiloparsec-scale nuclear superbubble in NGC 3079 in order to probe the mechanisms driving the expansion of the superbubble. Based on the Chandra X-ray observations, we derive the hot-gas thermal pressure inside the bubble, which is about 1 order of magnitude higher than that of the warm ionized gas traced by optical lines. We derive a [C ii]-based star formation rate (SFR) of SFR ∼ 1.3 M ⊙ yr−1 from the nuclear region using the SOFIA/FIFI-LS observation. This SFR infers a radiation pressure toward the bubble shells much lower than the thermal pressure of the gases. The Very Large Array radio image infers that magnetic pressure at the northeast cap above the superbubble is less than the thermal pressure of the hot gas enclosed in the bubble but has a clearly larger extension. The magnetic field may thus still help to reconcile the expansion of the bubble. The observed thermal energy of the hot gas enclosed in the bubble requires an energy injection rate of ≳1042 erg s−1 within the bubble’s dynamical age, which is probably larger than the power provided by the current nuclear starburst and the parsec-scale jet. If this is true, stronger past AGN activity may provide an alternative energy source to drive the observed bubble expansion.

CHANG-ES. XXX. 10 kpc Radio Lobes in the Sombrero Galaxy

We report the discovery of the 10 kpc scale radio lobes in the Sombrero galaxy (NGC 4594), using data from the Continuum Halos in Nearby Galaxies—an Expanded Very Large Array Survey project. We further examine the balance between the magnetic pressure inside the lobes and the thermal pressure of the ambient hot gas. At the radii r of ∼(1–10) kpc, the magnetic pressure inside the lobes and the thermal pressure of the ambient hot gas are generally in balance. This implies that the jets could expand into the surroundings to at least r ∼ 10 kpc. The feedback from the active galactic nucleus jet responsible for the large-scale lobes may help to explain the unusually high X-ray luminosity of this massive quiescent isolated disk galaxy, although more theoretical work is needed to further examine this possibility.

Heat supply to and hydrogen desorption from magnesium hydride in a thermally insulated container with hot gas flow

We experimentally studied hydrogen desorption from MgH2 by supplying heat via a hot gas flow. Porous sheets of MgH2 held in a sponge-like carbon nanotube (CNT) matrix were developed and placed in a coaxial double-tube reactor. Ar gas was heated using a cylindrical heater and then flowed alongside the MgH2-CNT sheets, thereby increasing the temperature of the sheets and enabling the desorption of hydrogen into the gas flow. The total energy efficiency was approximately 6.2% when 64% of hydrogen in MgH2 was desorbed. A numerical simulation was conducted for the heat transfer and hydrogen desorption, and the obtained results were consistent with the experimental results. According to the simulation, the low energy efficiency was attributed to the small heat capacity ratio of MgH2 to the reactor (0.082) and considerable radiative heat loss (53%). The simulation was used to predict energy efficiency improvements, and the efficiency was considered to increase to 12% upon increasing the heat capacity ratio from 0.082 to 1.4, and further to 21% upon doubling the Ar flow rate, which enhanced the convective heat transfer from the heater to MgH2.

Modeling of micron-sized aluminum particle combustion in hot gas flow

This paper presents a model for micron-sized aluminum (Al) particle combustion in hot oxidizing environments, forming hollow spheres. The model comprises four sub-models describing the physical and chemical processes during Al combustion: melting of the solid core, ejection of liquid Al droplets from the breaking solid shell, vaporization of liquid droplets, and ignition and establishment of vapor flame surrounding the solid particles. The model is of critical importance when the ambient gas temperature is higher than the melting point of the Al core, Tc,m, but lower than the alumina (Al2O3) shell’s melting point, Ts,m. In the model, the Al core is assumed to be surrounded by a thin, compact alumina shell that blocks the diffusion of oxidizer into the core and prevents surface reactions. The alumina shell’s cracking and liquid Al’s eruption are triggered by thermal expansion and pressure buildup in the liquid core. The splashed liquid Al droplets vaporize quickly and initiate gas-phase reactions, followed by the vaporization of the liquid Al core as the particle temperature Tp increases. Al vapor combustion heat is redistributed to simulate the gaseous flame near the particle. The model is implemented using the Lagrangian particle tracking method and is validated through simulations of micron-sized Al particle combustion in hot gas and comparison with experiments. The results can explain the formation of the sharp-edged holes on hollow aluminum oxide spheres and the ignition behavior observed in the experiments.

Beyond radial profiles: Using log-normal distributions to model the multiphase circumgalactic medium

Abstract Recent observations and simulations reveal that the circumgalactic medium (CGM) surrounding galaxies is multiphase, with the gas temperatures spanning a wide range at most radii, ∼104 K to the virial temperature (∼106 K for Milky Way). Traditional CGM models using simple density profiles are inadequate at reproducing observations that indicate a broad temperature range. Alternatively, a model based on probability distribution functions (PDFs) with parameters motivated by simulations can better match multi-wavelength observations. In this work, we use log-normal distributions, commonly seen in the simulations of the multiphase interstellar and circumgalactic media, to model the multiphase CGM. We generalize the isothermal background model by Faerman et al. 2017 to include more general CGM profiles. We extend the existing probabilistic models from 1D-PDFs in temperature to 2D-PDFs in density-temperature phase space and constrain its parameters using a Milky Way-like Illustris TNG50-1 halo. We generate various synthetic observables such as column densities of different ions, UV/X-ray spectra, and dispersion and emission measures. X-ray and radio (Fast Radio Burst) observations mainly constrain the hot gas properties. However, interpreting cold/warm phase diagnostics is not straightforward since these phases are patchy, with inherent variability in intercepting these clouds along arbitrary lines of sight. We provide a tabulated comparison of model predictions with observations and plan to expand this into a comprehensive compilation of models and data. Our modeling provides a simple analytic framework that is useful for describing important aspects of the multiphase CGM.

Characterisation of the creep cavitation process on grain boundaries in a polycrystalline nickel-base alloy 247

ABSTRACT Hot gas components such as gas turbine blades are loaded with constant centrifugal stress at high temperatures and thus the formation of creep cavitation on grain boundaries is expedited. Conventionally cast polycrystalline Nickel-base superalloys used as blade materials are prone to creep cavitation as unfavourably orientated grain boundaries exist. This research presents a diffusion-based probabilistic creep model which describes the creep cavitation process on grain boundaries. It includes the three mechanisms: pore nucleation, growth, and coalescence. The calibration of the model has been carried out by analysing Alloy 247 as-received specimens and specimens with pre-strain. For the evaluation of the pore numbers and sizes, a deep learning model for pore detection was trained on light microscopic and scanning electron microscopy images. Electron backscatter diffraction images are analysed for further investigations regarding grain orientations and grain boundary angles to the loading direction. The calibrated model allows predictions of pore size distributions over time.

Ceramization of coordinated Zr4+ and Hf4+ in polysiloxane conferring silicone/phenolic hybrid resin with excellent thermal protection

Silicon/phenolic hybrid resins are one of the most commonly used materials for thermal protection. However, the weak ability of SiO2 generated by silicone during ablation to resist the impact of high-speed hot gas flow hinders further improvement of the performance. Therefore, in this work, the ultrahigh-temperature ceramic elements Zr4+ and Hf4+ were integrated into hyperbranched polysiloxanes in the form of coordination bond and then introduced into phenolic resin (PR), obtaining hybrid resin with excellent ablative resistance. During ablation, Zr4+ and Hf4+ will first undergo ceramization, producing ZrO2 and HfO2. Subsequently, they will undergo a solid solution sintering reaction to produce complex-phase ceramic particles (ZrxHf1-x)O2, which are embedded in the SiO2 liquid film and provide excellent pinning effect. This gives the hybrid resin excellent ablation resistance, whose linear ablation rate can be as low as 0.038 mm/s, a 58 % decrease compared to pure PR. This work not only provides a new pathway for ceramization through metal ion coordination bonding, but also provides a new way to prepare high-performance TPS materials.

A novel data-driven reduced order modelling methodology for simulation of humid blowout in wet combustion applications

Computationally inexpensive reduced order models such as Chemical Reactor Networks (CRN) are encouraging tools to obtain fast numerical solutions. However, the accuracy of such models is usually compromised compared to experiments or high-fidelity numerical simulations. Therefore, continued improvement of such models is necessary to ensure reasonable accuracy and fill the need for computationally inexpensive tools. To that end, inputs from computational fluid dynamics simulations have been used to build CRNs in the last 25 years. This can be further improved by the application of data-driven techniques. The present work uses a novel data-driven analysis based on high-fidelity simulation results where the high-dimensional data is first reduced to a low-dimensional manifold and is then clustered into chemically coherent regions. These results along with the high-fidelity simulation results are used to construct a CRN for wet combustion simulations. Wet combustion is a novel clean combustion technique, where an increase in the level of steam dilution distributes the flame, with a risk for flame extinction. This phenomenon, i.e., humid blowout (HBO), was modelled using the above-mentioned CRN. The HBO predicted by the CRN was also tested for thermal power, equivalence ratio, and fuel conditions different from its design point. The error in HBO prediction was quantified by comparing the steam-dilution level at HBO obtained using CRN and that obtained experimentally. The CRN predicted the HBO with an error magnitude less than 5% when the thermal power was unchanged. The maximum error in all tested conditions was 16.65%. Furthermore, a sensitivity analysis revealed that the inclusion of hot gas recirculation through the central recirculation zone, quantified by the mass flow split between the post-flame region and the CRZ, is important in the prediction of HBO, although its accuracy is inconsequential.

Heating and defrosting performance assessment of dual-source heat pump operational modes under various ambient conditions

Multifunctional dual-source heat pump systems, featuring two sets of heat exchangers (air-to-refrigerant and water-to-refrigerant) in series or parallel, aim to boost efficiency. However, these systems often require extensive piping, leading to power losses, higher energy consumption, and increased installation space requirements. Furthermore, few comparative studies have assessed the effectiveness of dual-source versus single-source heat pump systems under various ambient conditions. This study introduces a novel air-water dual-source evaporator design that enables efficient heat exchange using air, water, or both. With this design, the heat pump system can be tuned according to three distinct modes: pure water-source mode (WSHP), pure air-source mode (ASHP), and dual air-water-source mode (AWSHP). The heat pump's efficiency across these modes was evaluated under various weather conditions, adhering to the CNS15466 and GB/T21362 standards. The findings reveal a strong correlation between the operational modes and ambient temperatures, indicating that maximum efficiency is achieved with the WSHP mode below 7 °C, AWSHP mode between 10 °C and 35 °C, and ASHP mode above 35 °C. Moreover, three defrosting methods were evaluated: hot gas bypass, hot water bypass, and a combination of both. The hot water bypass, in conjunction with the proposed dual-source evaporator design, efficiently performed full defrosting, boosting system efficiency. The ability of the heat pump to switch between operating modes enhances the overall energy efficiency during space heating and defrosting, reduces installation space requirements and compressor oil loss, and facilitates hot water production. The proposed system is ideal for various industrial applications requiring efficient operation under diverse ambient conditions.

Constraining the coronal properties of AB Dor in the radio regime

ABSTRACT We present a multiwavelength study of AB Doradus, combining modelling that incorporates a spectropolarimetric magnetic field map with 8.4 GHz radio interferometry to measure the coronal extent and density of this young star. We use the surface magnetic field map to produce a 3D extrapolation of AB Dor’s coronal magnetic field. From this model we create synthetic radio images throughout the stellar rotation period which we can compare with the interferometric radio observations. Our models reproduce the two-lobe structure seen in the radio observations. We successfully fit the observed flux magnitude and lobe separation with our model. We conclude that that the features seen in the radio images are a result of centrifugal containment of hot gas at the peak of closed magnetic loops, and that the corona of AB Dor extends to about 8–10 stellar radii, making it much more extended than the present-day solar corona.