A scaled-down heat-tube air preheater is prepared in this paper, to study experimentally the local and overall characteristics of ammonium bisulfate (ABS) ash accumulation. The morphology, composition, distributions of ash accumulation are analyzed based on the approaches of visualization, SEM, EDS, XRD, as well as the pressure loss and heat transfer in the air preheater. The influences of key parameters including the flue-gas temperature (190-280 °C) and the ABS-ash ratio (1/120-1/30) on the ash accumulation features are also discussed. It is found that the fly-ash without ABS does not form a stable ash accumulation layer on the vertical smooth tube. By contrast, the addition of ABS makes the fly-ash particles rapidly accumulating on the tube and forming a bell-shaped dense accumulation layer, due to the liquid-phase ABS significantly enhancing the adhesion of fly-ash particles. The acidic decomposition products of ABS react chemically with the basic oxides in the fly-ash to form the sulfate compounds, which not only change the composition of the ash accumulation but also promote the compactness of the ash accumulation layer. The thickness of ash accumulation firstly rises then decreases with the flue-gas temperature increases, and reaches a maximum of 26.2 mm at Tg,i = 220 °C when the ABS reaches a more fully melted state. With the ABS-ash ratio increases from 1/120 to 1/30, the thickness of ash accumulation significantly increases by 217%, but the ABS-ash ratio has a limited impact on the reaction path of ABS with fly-ash components. Besides, the backflow vortex causes the ash accumulation layer at the second row of tube (Row #2) to be thickest.
Efficient and stable conversion of carbon sources within the reactor is a core prerequisite for the large-scale production and engineering application of carbon nanotube fibers (CNTFs). However, existing single-channel injection processes are limited by the thermodynamic constraint of low-entropy local concentration enrichment, leading to multi-field mismatch and catalyst sulfur poisoning, which in turn results in low carbon nanotube (CNT) yield and uneven CNTF diameter distribution. Based on the concept of entropy regulation, this study proposes a dual-channel multi-field synergistic matching strategy. By achieving spatial decoupling, thiophene is uniformly distributed locally within the reactor, thereby suppressing excessive catalyst poisoning, optimizing the matching conditions of concentration field, temperature field, and flow field during the preparation process, and effectively breaking through the technical bottleneck of CNTF growth. Experimental results show that, compared with the traditional single-channel injection process, this strategy can increase CNTF yield by approximately 80.1% under the Fe10S system constructed with an appropriate thiophene concentration, and improve the carbon conversion efficiency from 3.47% to 6.26%. Under higher catalyst precursor feed conditions, its advantages become even more significant, with a yield increase of up to 114.7% and a high production rate (6.2 mg/min). This study provides an innovative reactor engineering design approach for the continuous, stable, and large-scale preparation of high-performance CNTFs.
To address the limited understanding of phase-region reconfiguration and coupled pressure–temperature responses under time-varying coolant supply and nonuniform thermal loading, a transient local thermal non-equilibrium two-phase mixture model (LTNE-TPMM) was developed by introducing an unsteady-term effective heat-capacity coefficient, Cp,M, into an improved steady-state formulation. The predictive capability of the model was validated against experimental data. The model was then used to investigate the dynamic evolution of injection pressure, solid-skeleton temperature, and liquid saturation under a linearly increasing coolant mass flux, periodic mass-flux oscillations, and a transition from uniform to nonuniform heat-flux distributions. The results show that increasing the mass-flux ramp rate promotes an earlier transition from the vapor-phase region to the two-phase region at the heated-side outlet, thereby shortening the temperature stabilization time, but at the expense of increased injection pressure and pressure overshoot. At a fixed disturbance amplitude, the system becomes increasingly sensitive to longer-period mass-flux oscillations. As the oscillation period increases from 5 to 40 s, the relative pressure-fluctuation amplitude increases from 0.11% to 86.21%, while the migration range of the two-phase/vapor-phase interface increases from 0.17 to 0.97 mm. Under a nonuniform heat flux, penetration of the low-saturation region into the porous medium constricts liquid-flow pathways and increases two-phase flow resistance. At t = 200 s, the low-saturation-region area fraction and maximum penetration depth reach 15.00% and 12.64 mm, respectively, while the average injection pressure increases to 838.05 Pa. The delayed pressure and temperature responses arise primarily from the different timescales associated with liquid replenishment, phase change, saturation redistribution, and phase-interface migration. These findings provide a theoretical basis for dynamic coolant-flow regulation, injection-pressure margin design, and thermal-safety assessment of transpiration-cooling systems under transient thermal environments.
Spray cooling of a heated rotating cylinder is investigated experimentally in a non-boiling deposition–evaporation regime motivated by the cooling of rotating components in high-power-density electrical machines. The present configuration is used as a simplified canonical experiment to investigate liquid deposition, partial wetting, evaporation, and surface renewal on a heated rotating curved surface. A flat-fan spray of doubly distilled water impacts a pre-heated stainless-steel cylinder at controlled nozzle pressures and rotational speeds. The local mass flux distribution, droplet size distribution, and droplet velocity are determined experimentally, while the transient wall temperature and heat flux are reconstructed from subsurface thermocouple measurements. The results indicate that the effective liquid mass flux supplied to the cylinder surface strongly affects the cooling rate. The influence of rotational speed is weaker over the investigated range, although the heat flux trends suggest that rotation affects liquid residence time and surface renewal. A heat transfer model is formulated by combining sensible heating of deposited liquid with evaporation from wetted surface regions. Droplet clustering is represented through a percolation-based correction of the effective evaporating length scale. Within the investigated parameter range, comparison between reconstructed and estimated heat fluxes suggests that evaporation provides the dominant contribution to heat removal, whereas sensible heating remains secondary.
To accurately predict tube-side heat transfer coefficients of spiral wound heat exchangers (SWHEs) in liquefied natural gas (LNG) production facilities, this study conducted a numerical investigation on the heat transfer behaviors of upward hydrocarbon condensation in helical coils. An integrated experimental-numerical methodology was implemented. The numerical framework was validated against experimental data with deviations within ±15%. Subsequently, it was used to generate a comprehensive database of 455 points, covering six pure and mixed refrigerants across a wide range of parameters. Using these simulated data, 57 heat transfer correlations were assessed, covering seven distinct categories: equivalent Reynolds number-based, liquid-phase multiplier-based, shear-based, mixed convection-based, flow pattern-based, and general-type. The top five correlations were then identified, which are capable of predicting almost 80% of the data points with an error within ±30%. To further improve the prediction accuracy and expand the applicable range, a universally improved liquid-only multiplier-based correlation was developed by considering the comprehensive effects of major operational and structural parameters. Together with the modified Silver approach, it is able to reliably predict 91.58% of the data points with an error within ±30%. For a total of 867 data points (455 from new numerical simulations, 296 from new experimental studies, as well as 116 from experimental data reported in previous literature), the mean absolute relative deviation (MARD) is 13.29%. Its robustness was further verified against 130 independent R134a experimental data points with a MARD of 13.63%. This work is expected to provide constructive guidance for the design of SWHEs within large-scale LNG facilities.
Microwave hyperthermia applicators used for thermal therapy of cancer employ a water bolus for tissue surface cooling and power coupling. The temperature-dependent dielectric property of the water bolus causes impedance mismatch and thermally driven instability during an hour-long treatment. This paper presents an optimized water-cooled folded metal patch microwave antenna with integrated fins to maintain thermal stability thereby enabling stable power coupling during treatment delivery. The applicator was designed using coupled electromagnetic–thermal–fluid–structural simulation framework and validated experimentally on tissue-equivalent phantoms. The optimized applicator with aperture size of 48 mm × 55 mm has return loss > 20 dB at 434 MHz, −10 dB power coupling bandwidth of 42 MHz, and maintains > 90% tangential electric field coupling to the tissue layers. The coupled EM-thermal and fluid analysis of the fin assisted applicator reduced internal water bolus temperature gradient from 5.13 to 0.38 K, which significantly improved power coupling coefficient to 96%. Experimental results of the optimized applicator designed with convective and radiative cooling showed stable power coupling >96% for 60-min heating in tissue mimicking phantoms. The coupled multiphysics approach provided the design framework for realizing clinically robust hyperthermia applicator with thermal stability and mechanical strength essential for clinical deployment, and development of site-specific hyperthermia applicators.
To explore the mechanisms controlling the critical turning point in temperature decrease and entropy rise within the radial pre-swirl configuration, this study adopts a hybrid methodology integrating theoretical analysis, numerical simulation, and geometric optimization. Key design parameters comprise vane angles (Θv,r,in at inlet and Θv,r,out at outlet), ratio of vane height (rh), number of impellers (Ni), and axial clearance (rc). For the vaned receiver hole, the inlet-angle design (VRIA) exhibits a higher maximum temperature-decrease coefficient (Ψ) than the outlet-angle design (VROA). In VRIA, a sharp switch from a cooling state (Ψ = 0.0116) to a heating state (Ψ = −0.0065) is observed, whereas VROA exhibits a milder transition and thus more consistent performance. Introducing a single impeller that opposite the rotor direction reduces the entropy rise (Δsrot) by 21.61%. Furthermore, setting rc = 0.6 brings an additional 29.54% reduction in Δsrot. VRIA achieves a minimum total pressure loss (ζmin) that is 36.75% below that of VROA, but this advantage exists only within a restricted angle range. For VROA, the optimal angle lowers ζ by 28.44%; adding a single impeller opposite to rotor direction further reduces ζ by 6.69%.
Gold nanoparticles, serving as a photothermal agent, are often embedded in tumor tissue to enhance the efficacy of laser hyperthermia. This paper investigates the thermomechanical response of a two-layer semi-infinite biological tissue composed of tumor tissue embedded with gold nanoparticles and normal tissue under laser irradiation. By incorporating the Pennes bioheat equation, a fractional three-phase-lag (FTPL) thermoelastic model is formulated to address the problem. The gold nanoparticles affect the laser absorption and scattering at the tumor site. The exact analytical solution of the fractional thermomechanical coupling problem is obtained by coupling the state-space method with the Laplace transformation. The influence of the FTPL model parameters, the convective cooling coefficient at the boundary, the gold nanoparticle concentration, and the laser parameters on the thermomechanical behavior are analyzed. This study establishes a unified thermomechanical coupling solution framework via the state-space method for laser hyperthermia, and provide valuable insights for the application and development of gold nanoparticles in biological thermal therapy.
In this work, we show that the similarity transformation of the thermal diffusion equation in the thermal layer leads a generalization of the asymptotic theories of the dynamics of bubble growth in nucleate boiling in an infinite pool of superheated liquid. The transformation allows us to define similarity variable and to reduce the PDE for the diffusion equation to an ODE solving for the radial variation of liquid temperature and an ODE for the thickness of thermal boundary layer. Thus, the method efficiently solves the diffusion equation, eliminating the assumptions in our semi-analytical solution that ignored the thermal convection due to the moving surface of a growing bubble. We have obtained the rate of bubble growth from the energy balance at vapour-liquid interface. The work dispenses with the Rayleigh-Plesset equation for the growth rate. Interestingly, we have obtained the growth rate following Plesset-Zwick equation with the thin-thermal layer assumption. We have also studied the asymptotic features of the ODE of the thermal boundary layer. Thus, the asymptotic solution for the growth rate evolves to be our previous limiting solution at the initial stage (small-time asymptotic solution), t→0 and to be a new solution (large-time asymptotic solution) at the final stage, t→∞. These findings have been found to be well comparable with the experiments and our numerical model. Finally, we have formulated Nu as a function of Ja for t→0 and t→∞; Ja is Jakob number.
The safe operation of steam generators (SGs) is vital for the reliability of nuclear power systems, as they serve as the primary boundary for heat transfer. However, most available thermal-hydraulic analysis codes simplify the interaction between the two sides and do not fully capture the three-dimensional distribution of coupled heat source terms. To address this, we developed STAF 3.0, a full 3D thermal-hydraulic analysis code based on the OpenFOAM platform. The code's capability in modeling SG 3D flow fields was validated against scaled-down experimental data from the CNPOTC. Using a typical Gen-III 1000 MWe-class PWR SG as the research subject, we performed simulations under two characteristic design conditions. Subsequently, we carried out full-scale, non-linear constrained turbulent buffeting analyses on selected heat transfer tubes. The findings demonstrate that the asymmetric structure of the SG hot leg induces significant non-uniformity in primary side flow, subsequently impacting the temperature distribution across both sides and the secondary side void fraction. Specifically, the maximum primary-side temperature difference between symmetric positions in regions P1 and P2 was 2.22 K, while the secondary-side temperature and void fraction differences reached peak values of 2.06 K and 0.056, respectively. The outermost heat transfer tube exhibited the highest lateral impact stress, peaking at 5027 J m−3. Furthermore, the maximum in-plane and out-of-plane RMS amplitudes, at 0.141 mm and 0.202 mm respectively, were observed in the straight tube section.
This study systematically investigated the thermal behavior of lithium-ion batteries under different cooling strategies, including natural air convection, forced air convection, and phase change material (PCM) cooling, to mitigate thermal accumulation during operation. The experiments were performed under various discharge rates (1C, 2C, and 3C) and ambient temperatures (25, 30, and 35 °C). The results demonstrated that, under natural convection conditions, the battery temperature increased significantly with increasing discharge rate and ambient temperature. Under an ambient temperature of 35 °C and a discharge rate of 3C, the maximum surface temperature reached 86.45 °C, accompanied by a maximum temperature rise rate of 20.6 °C·min−1. At airflow velocities of 1 and 3 m s−1, the maximum surface temperatures of the lithium-ion batteries were reduced to 59.4 and 58.3 °C, respectively, corresponding to reductions of 31.29% and 32.61% compared with natural convection cooling. Under the forced convection condition with an airflow velocity of 3 m s−1, the maximum temperature rise rate was effectively suppressed below 6 °C·min−1. Among the investigated cooling strategies, PCM cooling exhibited the most stable thermal regulation capability and the highest temperature control effectiveness during repeated charge-discharge cycles. The maximum battery temperature was maintained below 50 °C, with a surface temperature difference of less than 3 °C and a temperature rise rate below 3 °C·min−1. This study provides further insights into the long-term thermal management performance of lithium-ion batteries through multi-cycle experimental evaluation and comparative analysis under various discharge rates and ambient temperature conditions. This study systematically investigates the thermal performance of lithium-ion batteries under different cooling strategies, including natural convection, forced convection at airflow velocities of 1 and 3 m s−1, and low-melting-point paraffin-based PCM cooling. Key thermal performance indicators, including the peak temperature, temperature rise rate, maximum temperature difference, and duration above 50 °C (t50), were quantitatively evaluated. The results provide valuable experimental insights into the design and selection of battery thermal management systems (BTMS) for high-rate operating conditions.
This paper investigates a computational study on magnetohydrodynamic (MHD) flow, exploring solution structure and unsteady nature of thermal flows, in a rotating curved rectangular duct (CRD) incorporating the effects of Hall and ion-slip currents, motivated by the board range of engineering applications involving magnetic flow control, thermomagnetic devices, filtration systems and thermal transport in a rotating system. The spectral method serves as the main computational approach, supported by Chebyshev polynomials, Collocation techniques, and Fourier series expansions, to study non-isothermal flow behavior across varying magnetic field strengths (M). Steady curves are obtained and linear stability of the flows is examined. The findings indicate that the asymmetry in the flow structure becomes weaker, eventually transitioning to a symmetrical state as M increases. The flux decreases, the intensity of the axial velocity reduces and moves to the middle of the duct as M is increased, while the linearly stable zone gradually expands. Furthermore, the linearly stable flow regime expands significantly with the increase of the magnetic field strength. The results further identify a magnetic parameter Mc = 10.15 as a critical value beyond which the flow transitions to a fully stable state. In the unsteady regime, oscillatory and chaotic flow behaviors are progressively weakened, and the steady-state region becomes dominant for higher values of M. The Hall parameter (m) is found to enhance both flux and axial velocity intensity, whereas the ion-slip parameter (α) shows minimal impact on secondary and axial flows. Heat transfer effects remain relatively unchanged within the curved channel under MHD influence. Overall, the findings provide valuable findings on MHD flow dynamics, with potential relevance to various industrial and engineering applications.
As MEMS/NEMS advance, compact devices require efficient heat dissipation, making thin film phase transitions a key heat transfer method, but molecular-level understanding of multi-factor regulated liquid film phase transitions and the heat and mass transfer coupling is still limited. In this study, molecular dynamics simulations are employed to systematically investigate how surface wettability, liquid film thickness, and nanopillar sizes jointly regulate phase transition modes and interfacial heat transfer, enabling nanoscale quantification of heat-mass transfer coupling. These factors influenced the phase-change mode and interfacial heat transfer mechanism by modulating bubble nucleation, heat conduction pathways, and local energy barrier distributions. From the phase diagrams of different phase transition modes, it is found that hydrophobic surfaces and thin liquid films favor pure evaporation, whereas hydrophilic surfaces, thicker films, and nanopillars promote local superheating and heterogeneous nucleation, leading to nucleate and film boiling. Moreover, bubble nucleation preferentially occurs at nanopillar corners due to lower local energy barriers, enhancing spatial heterogeneity and boiling heat transfer. Increasing liquid film thickness from 30 Å to 120 Å raises average heat flux by 75.2%, highlighting its dominant role in regulating heat-mass transfer. These results reveal the molecular mechanisms linking nanoscale structure to boiling dynamics and provide design guidelines for optimizing phase-change heat transfer in MEMS/NEMS devices.
Lithium-ion batteries (LIBs) have become the cornerstone of global clean energy transition with their superior energy density and long cycle life. However, the escalating energy density of LIBs intensifies critical thermal safety concerns, including severe heat accumulation and uncontrollable thermal runaway propagation. The organic phase change materials (PCMs) are limited by inherent flammability and low latent heat, whereas inorganic hydrated salts suffer from intractable supercooling and liquid leakage. To address these bottlenecks, this study develops a hydrated-salt composite PCM (CPCM) employing sodium sulfate decahydrate as the matrix, encapsulated within a synergistic framework of expanded graphite and porous calcium silicate. The optimized CPCM features a dual-stage heat storage mechanism by leveraging vaporization enthalpy, it delivers a phase-change enthalpy of 140.5 J g−1 and the remarkable total heat-storage density of 879.0 J g−1, while maintaining excellent cyclic stability. Notably, the optimized CPCM demonstrates superior flame retardancy, achieving a UL-94 V-0 rating. In flame-exposure tests, the material acts as an exceptional flame-insulating barrier, maintaining an impressively low back-side temperature of merely 30.2 °C even under direct burner exposure. In a module comprising five series-connected 23 Ah prismatic lithium iron phosphate (LiFePO4) cells, SPEC10 limits the maximum temperature to 57.6 °C at 2C discharge rate, representing reductions of 5.2 °C and 5.0 °C relative to the organic flame-retardant CPCM (FRCPCM) and the hydrated salt CPCM (SPE5) modules, respectively. Furthermore, it provides a robust thermal shock protection with heating plates reaching 200 °C by 8000 s. This multifunctional CPCM serves as a promising material candidate for enhancing the thermal safety of battery management systems.
Ignition of nearby insulating materials is a critical thermal consequence of fault arcs in low-voltage DC systems. Most studies on arc-induced ignition rely on one-dimensional heat transfer analysis, while arc power transfer coefficients and coupled multi-path heat transfer remain insufficiently understood. An ignition model based on two-dimensional heat transfer analysis is developed to account for direct arc radiation and heat transfer from heated copper electrodes. Results show that the arc-to-copper power transfer coefficient decreases with increasing mean arc power, whereas the arc-to-insulating-material power transfer coefficient increases. Approximately 45%–75% of the total arc power is transferred to the copper electrodes, while only 0.3%–1% is transferred directly to the insulating material. Nevertheless, direct arc radiation accounts for 8.70% of the cumulative heat input into the insulating material up to ignition, whereas heat transfer from the heated copper electrodes accounts for 91.30%. In equal-area local regions, the direct path contributes 67.54% of the cumulative heat. A higher mean arc power leads to a shorter ignition time, with measured ignition times ranging from 2 to 16 s. With a fixed ignition criterion of 330 °C, most deviations between the simulated and experimental ignition times fall within ±30%. When the measured ignition temperature variation of 310–350 °C is considered, 73.3% of the experimental ignition times fall within the corresponding simulated ranges, indicating that ignition temperature variability explains a substantial part of the discrepancy. The results provide a mechanistic basis for predicting the ignition of nearby insulating materials under coupled direct arc radiation and heat transfer from heated copper electrodes.
Thermoelectric cooling is one of the important methods for chip thermal management. In response to chip thermal shocks, precise regulation of thermoelectric cooling parameters becomes crucial for efficient chip cooling. This study establishes a thermoelectric cooling experimental system and investigates the impact of the operating time, start-up time, and operating current of the thermoelectric cooler (TEC) on the peak chip temperature and cooling energy consumption under thermal shock. The results indicate that under the condition of a thermal shock power of 80 W lasting for 30 s, the TEC operating at a current of 5.5 A for 17.5 s can effectively control the peak temperature of the chip within the safe threshold of 70 °C, resulting in a 41.7% reduction in cooling power consumption. By delaying the start-up of the TEC, the peak temperature of the chip can be further reduced. Lowering the operating current to 2 A results in a peak chip temperature of 69.5 °C, which does not exceed the chip's operational threshold. Moreover, the TEC energy consumption can be reduced by 96.5%. This study provides valuable guidance for precise and efficient chip cooling.
The non-destructive reconstruction of internal transient temperature fields in heterogeneous composite materials is crucial for the thermal safety assessment of high-end equipment. Addressing the limitation that traditional Time of Flight (TOF) features are prone to failure in strongly scattering media due to waveform distortion and noise interference, this work proposes a novel temperature field reconstruction method based on the ultrasonic upper envelope area (UEA) from a global energy perspective. First, a correlation model between the UEA and temperature is established. Subsequently, the thermometry problem is transformed into a nonlinear inverse heat conduction problem (IHCP) with Tikhonov regularization constraints, which is efficiently and stably solved using the conjugate gradient method. Taking ceramic particulate-reinforced metal matrix composites as the research object, systematic numerical and experimental validations are conducted. The results demonstrate that the proposed method successfully overcomes the phase distortion issue induced by strong scattering, enabling effective reconstruction of the temperature field even under extreme conditions where traditional TOF features completely fail. Under extreme numerical conditions with strong applied noise, the reconstruction error remains controlled within 10%. Furthermore, in actual physical heat transfer experiments, the mean relative error in the reconstructed temperature is approximately 5%. This study demonstrates that the UEA can serve as a robust temperature-sensitive parameter, providing a feasible technical solution for non-destructive internal thermometry in complex heterogeneous materials.
TC4 (Ti-6Al-4V) titanium alloy has high specific strength and good corrosion resistance, but its poor room-temperature formability and severe springback limit high-precision forming. This study investigated the temperature evolution and bending springback behavior of TC4 titanium alloy during current-assisted forming. Electric heating tests, current-assisted three-point bending tests, finite element simulation, and microstructural observation were conducted. A temperature equilibrium model was established from energy conservation by considering Joule heat input, convection, radiation, and contact heat dissipation. Duty-cycle correction, die heat dissipation, and the Biot number were introduced to improve temperature prediction. The optimized model predicted equilibrium temperature with maximum errors of 5.6% under different duty cycles and 5.2% under different current densities. The model was then implemented in Abaqus to simulate the complete heating-bending-unloading springback process. The results show that increasing current density and decreasing loading rate significantly reduce springback. The minimum springback angle was 5.7° at a current density of 4.25 A/mm2 and a loading rate of 10 mm/min. Microstructural observations indicate that current application promotes the transformation of lamellar α phase into equiaxed α phase, increases the β-phase fraction, and enhances dynamic recrystallization at higher temperatures and lower strain rates. These effects reduce deformation resistance, improve plasticity, and provide a theoretical basis for parameter optimization and springback control in current-assisted precision forming of TC4 titanium alloy.
