The aircraft thermal management system (TMS) is basically confined to the heat acquisition system. One of the major heat acquisition elements and, hence, a major power consumer of the TMS is the environmental control system (ECS). Presently, the ECS uses mixed circulation, i.e., a combination of outside fresh air and recirculated cabin air. This research paper defines a pathway to improve the performance of the ECS by employing a [Formula: see text] adsorption system in the cabin. The proposed method uses biochar for [Formula: see text] capture under cabin conditions. A comparative analysis has been conducted between the present ECS and the proposed improved ECS. The proposed ECS may contribute to improved energy efficiency; however, the extent of power reduction depends on system design and operating conditions. In addition to qualitative comparison, a simplified thermal balance framework is introduced to estimate adsorption-induced temperature rise and its impact on ECS heat rejection demand. The study explains that the additional heat released during [Formula: see text] adsorption in the cabin can be efficiently dissipated by implementing hybrid strategies without significant modification to the present ECS airflow pathways.
A procedure combining optical emission spectroscopy measurements and one-dimensional stagnation-line computations has been introduced, demonstrating that experimental observations align with boundary-layer simulations over a spectrum of Plasmatron operating conditions. This study focuses on a critical aspect of the procedure, specifically the choice of inlet boundary conditions used in the numerical simulations, and extends the methodology to a broader set of test conditions, covering most of the Plasmatron testing envelope in the subsonic regime. The results indicate that defining the inlet at six times the probe radius (6R) from the probe location, while imposing the temperature measured at 0.4R and the velocity measured at 0R, provides an optimal balance. The procedure is then applied to test cases that span chamber pressures from 200 to 15 mbar and input powers from 150 to 300 kW. The resulting freestream parameters range from 5400 to 8600 K in temperature, [Formula: see text] in enthalpy, and [Formula: see text] in velocity gradient. Additionally, a comparison between experimental and numerical heat fluxes provides a rough estimate of the surface recombination coefficient for copper oxide, which is found to be approximately 1 for the 100 and 200 mbar cases, and between 0.02 and 0.03 for the lower-pressure conditions.
This study numerically investigates [Formula: see text] nanofluid flow past a square cylinder under nonuniform inlet velocity and a transverse magnetic field. A higher-order compact finite difference scheme is formulated to investigate the flow physics. The analysis examines the combined influence of inlet shear flow, magnetic field strength, and nanoparticle concentration on the flow dynamics and heat transfer characteristics of the nanofluid. The magnetic field suppresses both primary and secondary vortices. Shear acts synergistically with the magnetic field to dampen primary vortices. Secondary vortices intensify with increasing shear rate. The magnetic field, however, ultimately overcomes this effect and suppresses these structures. Temperature contours and local Nusselt number distribution characterize thermal boundary-layer formation. Optimal thermal performance is achieved at the highest values of magnetic field strength, inlet shear, and nanoparticle concentration tested in this study. The average Nusselt number increases from 5.98 for uniform flow of pure water to 9.72. This enhancement provides new insight into the cooperative action of shear flow, magnetic stabilization, and nanoparticle addition in augmenting heat transfer.
Efficient thermal management is vital for lithium-ion batteries to ensure safety, reliability, and performance in electric vehicles. This study investigates passive cooling using phase change materials (PCMs) in a computationally complex scenario. Three PCMs (RT31, RT35, and RT38) were analyzed at three thickness levels (PCM_T1, PCM_T2, and PCM_T3) to evaluate their effects on battery surface temperature, melting behavior, and thermal energy storage. The best-performing PCM and thickness combination was further analyzed under Earth gravity, moon gravity, and microgravity conditions to examine the effect of gravity on the melting behavior and thermal performance of the optimized battery thermal management system configuration. Simulations employed the enthalpy–porosity method to model solid-to-liquid phase transitions while accounting for heat generation at a 3C discharge rate. Results show that both PCM type and thickness strongly affect cooling efficiency. RT31 offered the highest energy storage but led to elevated surface temperatures due to heat retention, while RT38 showed moderate cooling with delayed melting. RT35 at PCM_T1 achieved the lowest surface temperature (307.29 K) and minimal temperature difference (7.29 K), demonstrating the most balanced thermal behavior. Reduced gravity significantly prolonged melting time sixfold on the moon and slightly more under microgravity, highlighting the importance of gravity in PCM performance.
Spray cooling is a promising technique for the thermal management of high-heat-flux power electronic devices, particularly insulated-gate bipolar transistor modules used in compact electric-drive motor control systems. However, the roles of microstructure spacing and spray operating conditions in governing heat transfer performance have not yet been fully clarified. To address this issue, a closed-loop spray cooling experimental facility was established. By varying the spacing of elliptical micropillars, the effects of spray flow rate, coolant temperature, and spray height on spray cooling heat transfer were systematically investigated. The results show that the heat transfer coefficient (HTC) increases with spray flow rate over the entire tested range. Within the tested spacing range, the highest surface HTC of [Formula: see text] was achieved at [Formula: see text] with a spacing of 1.6 mm. As the coolant temperature increased, the HTC initially increased, then remained nearly constant above 30°C. In addition, at a spray height of 17.3 mm and a spacing of 1.6 mm, the surface HTC reached [Formula: see text], demonstrating the strongest heat transfer capability of the tested surface.
With the proliferation of high-power electronics, electric propulsion, and directed-energy weapons, thermal management has evolved from a high-speed flight concern into a systemic bottleneck across subsonic, transonic, and supersonic aircraft. Conventional fuel thermal management systems rely on engine inlet fuel temperature as feedback, a strategy effective under nominal conditions but inherently reactive. When mission heat loads exceed the system’s intrinsic heat-sink capacity, the lagging thermal response delays decisions on when to shed heat loads, while the lack of a predictive metric leaves how much to reduce undefined. This often causes excessive mission degradation or thermal safety violations. To overcome these issues, this paper proposes a real-time heat-sink capability monitoring framework based on two physically interpretable metrics: maximum thermal capacity and maximum thermal endurance. Embedded in a dual-tank fuel thermal management system, the framework continuously predicts thermal boundaries and, when thermal endurance falls below remaining mission time, proactively triggers precise, minimal-intervention heat-load adjustments, well before temperature limits are reached. Simulations on a high-dynamic fighter mission profile show the approach successfully completes scenarios otherwise infeasible due to thermal constraints, significantly improving thermal adaptability and mission reliability. This work provides a quantifiable, engineering-ready foundation for next-generation intelligent thermal management, enabling a shift from experience-dependent design to prediction-driven, mission-aware control.
Spinodoids exhibit unique nonperiodic architectures that offer distinct advantages in mechanical performance compared to conventional architected materials such as triply periodic minimal surfaces and lattice structures. In this study, spinodal topologies are optimized to enhance thermal conductivity, particularly for use in high-temperature aerospace applications. For this purpose, two-dimensional dual-phase spinodal structures are first generated and mapped into three-dimensional geometries, and their anisotropic thermal conductivities are evaluated along different spatial directions. A mathematical optimization framework is then implemented to perform topology optimization of spinodoids having a base material of SiC/SiC ceramic matrix composites. The spinodal structures are parameterized through orientation distributions constrained by conical angles. The steady-state thermal conduction is simulated numerically to compute elemental heat fluxes in three Cartesian directions, and effective thermal conductivities are extracted via the volume-averaging method. The optimization problem defines a composite objective function based on the anisotropic effective conductivities and is solved using a gradient-free heuristic algorithm. The resulting optimum design demonstrates the potential of spinodoid structures to improve thermal management in hot-section components of gas turbine engines.
Phase change materials (PCMs) have gained considerable attention in avionics applications, where aircraft and onboard electronic systems experience hypergravity (HG) during maneuvering. However, the melting behavior of PCMs in asymmetric partitioned enclosures under HG remains insufficiently explored. In this study, PCM melting in a stepped asymmetric partitioned enclosure is numerically investigated under HG for three aspect ratios ([Formula: see text], 0.5, and 0.33), with a 5% partition plate volume. The analysis considers configuration orientation, partition arrangement, HG effects, and comparison with nonpartitioned and symmetric configurations. Results show that downward configurations with lower [Formula: see text] enhance melting rates across all gravity levels, whereas upward configurations exhibit an initial improvement followed by a decline. The downward design with [Formula: see text] reduces energy storage by 4.4–5% while shortening melting time by 56.4–68.8% compared to the nonpartitioned case. Velocity analysis reveals stronger natural convection in upward configurations. For lower [Formula: see text] downward designs, two distinct peaks in the maximum velocity are observed, with a weaker secondary peak at later times, indicating gravity- and geometry-dependent convection intensity. The enhancement is attributed to intensified buoyancy-driven convection associated with an increased Rayleigh number. However, the enhancement effect diminishes with increasing gravity, indicating practical gravitational limits.
This research examines the use of the conjugate gradient technique to determine the time-varying base temperature of a porous fin, leveraging temperature data collected at the fin’s tip. The analysis focuses on the impact of measurement errors, porosity, initial guess, and sensor location on the accuracy of the inverse solution. Results demonstrate that the present algorithm accurately reconstructs the base temperature under various scenarios, including cases with and without measurement noise. It is observed that while the inverse solution remains stable and insensitive to the choice of initial guess, its accuracy deteriorates with increasing porosity. Moreover, although acceptable accuracy is achieved when the sensor is placed at the fin tip, relocating the sensor slightly toward the fin base significantly enhances the reconstruction precision. Overall, the results confirm the robustness, stability, and effectiveness of the proposed method for solving inverse heat transfer problems in porous fin.
This work presents a detailed description of the thermochemical nonequilibrium dissociation of diatomic molecules and applies this theory to the case of [Formula: see text] dissociation. In particular, the rovibrational state-specific master equations are analyzed in three key limits/regimes of dissociation-dominated flows: the thermal equilibrium limit, the quasi-steady-state (QSS) regime, and the pre-QSS regime. Under several simplifying assumptions, the macroscopic chemical source term and rovibrational energy expressions that hold in all of these regimes and are ultimately only a function of the translational temperature, [Formula: see text], and the degree of dissociation, [Formula: see text], are proposed. These expressions have two nonequilibrium input parameters: the QSS value in the absence of recombination, i.e., [Formula: see text] for the dissociation rate constant and [Formula: see text] for the rovibrational energy, and a pre-QSS correction factor, [Formula: see text]. Despite their simple functional forms, the proposed expressions are able to reproduce the majority of master equation results for a 0-D isothermal and isochoric reactor for the case of [Formula: see text] dissociation with the third bodies [Formula: see text], H, and He.
This work presents a numerical investigation of a laminar flow of [Formula: see text] tetra-hybrid nanoliquid in a microtube subjected to a constant wall heat flux. A numerical model was developed and validated using available experimental and analytical data. The combined effects of volume fraction, viscous dissipation, slip velocity, and external magnetic field on heat transfer and irreversibility parameters are investigated. The results revealed that tetra-hybrid nanoliquid enhances the heat transfer of the microflow in comparison with base liquid, mono, di, and ternary hybrid nanoliquids, with an increase in all irreversibility components and a reduction in the Bejan number. A higher slip velocity improves heat transfer and reduces total entropy production, while a higher Brinkman number reduces heat transfer and increases total entropy production. The increase in nanoparticle volume fraction, or the intensity of the magnetic field, leads to an increase in heat transfer and total entropy production. The evolutions of all irreversibility components are discussed in this paper.
Transpiration cooling is an active methodology in reducing surface heat flux for hypersonic vehicles, which offers the possibility of reducing nose bluntness and, therefore, increasing aerodynamic performance. This paper presents a numerical analysis of transpiration-cooled sharp leading edges made from ultra-high-temperature ceramics. The structural integrity of a 10 mm radius wedge leading edge is investigated numerically with regard to different coolant plenum geometries and pressurization magnitudes. It is found that the close spacing of individual plenum chambers reduces the stress in the material significantly and provides the maximum possible coolant mass flux. An optimization procedure of plenum pressure distribution is carried out using an analytical description of the porous flow in the leading edge. It is found that there exists an optimum plenum pressure that minimizes the probability of failure of the leading-edge model. Nitrogen coolant requires less pressure than helium to reach this criterion and, furthermore, requires less pressure to displace the air freestream and thus protect the leading edge from oxidation.
A master equation model resolving individual vibrational states via a database of ab initio rate coefficients is coupled to the Lees-Dorodnitsyn boundary-layer equations for stagnation-line flow. Using this framework, nitrogen and oxygen boundary layers are analyzed at pressures ranging from 10-3 to 10 atm with nose radii from 1 mm to 10 m, using a noncatalytic wall boundary condition. Significant differences between the translational-rotational and vibrational temperatures occur at the wall for small nose radii and low pressures, indicating incomplete vibrational thermalization. Overpopulation of high-lying vibrational levels due to recombination is observed in all calculations, even when the translational-rotational and vibrational temperatures are equilibrated. This non-Boltzmann overpopulation suppresses recombination rates by a factor of 1.4-6 relative to Boltzmann predictions, with stronger effects observed in oxygen than in nitrogen. These differences substantially alter wall heating: in oxygen, Boltzmann versus non-Boltzmann rates yield differences exceeding 50% when the nose radius is 1 m or larger and up to 20% for a 10 cm nose; in nitrogen, differences are typically 10% or less, except for the largest nose radius of 10 m. Sensitivity analysis further reveals that atomic mass fractions and convective heating are controlled by recombination pathways to intermediate vibrational levels.
This is a theoretical inspection of magnetohydrodynamic (MHD) natural convection in a vertical microchannel in the presence of a micropolar fluid. The motion is described by a system of simultaneous ordinary differential equations and solved numerically by spectral collocation techniques. The microchannel is shaped by two electrically nonconducting, vertical, and parallel plates. The objective of this research is to understand the effects of nondimensional parameters, such as the micropolar fluid material parameter (K), Knudsen number (Kn), Hartmann number (M), and rarefaction parameter (beta vKn) on the velocity, induced magnetic field, induced current density, microrotation profile, and skin friction. These results are shown graphically, and we found that the impact of the micropolar fluid material parameter inhibits the velocity, induced magnetic field, and microrotation velocity. The Hartmann number and material parameters help decrease volume flow rate and skin friction. The point of inflection also appeared on the microrotation profile, and it is removed as the micropolar fluid material parameter K increases. This investigation concludes that the micropolar fluid plays an important role in stabilizing the system.
A novel approach to the reconstruction of the gauge heat flux based on discrete embedded temperature measurements is presented to improve the performance of inverse heat conduction methods when there is significant lateral heat flux. The technique aims at reconstructing both the lateral and normal components in space-time bases and introduces two main innovations: 1) a least-squares approach to balance the impulse response for mismatched gauge materials, and 2) an advanced regularization approach based on cross-validation of samples distributed in a K-fold time series. Validation is carried out on hypersonic wind tunnel tests with both matched and mismatched gauge article materials conducted in a Mach 6 facility. The main findings are that the intergauge heat flux due to mismatched materials is important and accounts for more than 10% of the normal heat flux, that the multidimensional reconstruction is superior to the one-dimensional method that uses single-surface sensors, that glue layers have a marginal effect on embedded sensor gauges, and that the novel approach to regularization can resolve strong lateral heat flux with few sensors. A new predictive elastic-net model is derived from the time-series cross-validation that leads to properly accounting for the variation of the model's effective degrees of freedom.
The study of microsystems that considers different flow patterns with arbitrary geometrical configurations for microchannel design permits us to understand that the combined influence of surface and non-isothermal effects occupies a privileged place in predicting electroosmotic behavior. For this reason, in this work, we develop a theoretical analysis based on a perturbative scheme that permits us to predict the hydrodynamic effects generated in an electroosmotic flow when the slip condition on the walls of the microchannel is taken as a function of pressure, together with the Joule heating effect, and when these effects operate together to determine the fluid dynamics. For this purpose, when the governing equations are written in dimensionless form, we can identify some relevant dimensionless parameters associated with the previous condition. In this manner, the dimensionless volumetric flow rate that occurs in the microchannel is controlled by the combined influence of the previous effects, causing the volumetric flow rate to increase or decrease depending on the assumed values of the combined influence of these effects.
A coaxial thermocouple is a robust heat flux sensor with a fast response time, capable of operating in harsh environments such as high-temperature flows and mechanical vibrations. Although originally designed for short-duration measurements, this study investigates its suitability for long-duration heat flux measurements in hypersonic flow regimes. Experiments were conducted at Mach 5.3 in the Hypersonic Wind Tunnel (H2K) with test durations of up to 30 s. An E-type coaxial thermocouple was embedded in cylindrical specimens made of stainless steel, poly ether ether ketone (PEEK), and copper. Experimental measurements were complemented by coupled fluid-structure numerical simulations to resolve inhomogeneous and transient heat transfer on the flow-exposed surface as well as conductive heat transfer within the probe. Methods accounting for temperature-dependent material properties of sensor components were assessed for long-duration measurements. The results indicate that the coaxial thermocouple is, in principle, suitable for long-duration heat flux measurements. However, the measurement accuracy is strongly affected by the thermal coupling between the sensor and the surrounding material. Numerical analyses reveal that the dominant radial heat flux occurs within the first few millimeters downstream of the flow-exposed front surface. A parametric investigation of contact length and contact geometry further confirms a significant influence on long-duration heat flux measurements.
