International Journal of Thermal Sciences最新文献

The Arctic is melting rapidly and is more than 75% likely to experience its first ice-free summer by 2060 even if a pathway of 1.5 °C with overshoot is achieved (Dunne, 2019). The loss of Arctic ice could have a severe impact on the climate. Therefore, targeted action in the Arctic is required. The proposed method examined herein is Ice Volcanoes: pumping seawater onto the ice in winter so that it freezes faster and the ice can survive the following summer months. Thickening ice by pumping water over its surface is investigated theoretically and experimentally. The change in thickness of the ice with water flowing over its surface is modelled for channel flow. Short time scales are considered during which the dominant heat transfers are advection from water to the water–ice interface and conduction through the ice away from the interface. At short time scales the rates of heat transfer by advection and radiation to the atmosphere are much smaller and so not considered. Advection of heat by the water is modelled for three flows: an inviscid flow without a thermal boundary layer; an inviscid flow with a thermal boundary layer; and a viscous shear flow with a thermal boundary layer. The three models are assessed in the context of experimental results for water injected at 0.5 °C and 0.8 °C. The viscous shear flow with a thermal boundary layer is found to be the most accurate when compared with experimental results. However, the models do not accurately predict the experimental data for water injected onto the ice at 2 °C. Potential reasons for this are discussed. Finally, the paper concludes with suggestions for further work and some implications for ice volcanoes.

The welding process is the most used technique for metal joining. Understanding the temperature variation along the welded part during the process can prevent the appearance of failures. The experimental investigation process is quite time-consuming and costly. Therefore, numerical simulation processes based on the finite difference method, finite element method, finite volume method, or meshless Element-Free Galerkin (EFG) methods are important tools to optimize the welding process. The main goal of the present study is to show the feasibility of the Element-based Finite-Volume Method (EbFVM) approach for actual engineering applications. To solve the unsteady 2D and 3D thermal energy equation using enthalpy as an independent variable, an in-house Fortran code has been developed based on the EbFVM approach in conjunction with unstructured and structured meshes. The numerical simulations, with four types of different heat sources, were performed for applications of real welding processes with variations in density and enthalpy as a function of temperature. The results are presented in terms of thermal cycles and temperature fields. Furthermore, the developed code was confronted against experimental works from the literature, simulated and lab-controlled experiments with AISI 409 ferritic workpieces, and exact analytical solutions with thermocouples fixed in different positions. In general, the numerical results from the current investigation are in close agreement with the results from the literature and the experimental results performed by the authors. The numerical results also highlighted the differences between the 2D and 3D models for thermal cycles near the bead weld.

The presence of turbine blade tip clearance can cause tip leakage losses and enhance the thermal load on the tip region. The continuously increasing inlet temperature of the turbine poses a tremendous challenge for turbine blade tip design. Reasonable turbine blade tip configurations can effectively reduce the thermal load on the tip region and enhance aerodynamic characteristics. Here, surface Nu distributions of flat, cavity, and five modified tip configurations are obtained through transient liquid crystal measurement technology. Furthermore, a numerical study combined with experimental results is conducted to investigate the aerothermal characteristics of the tip regions for each configuration. The results indicate that the flat tip (FT) has the highest tip surface thermal load and maximum aerodynamic loss, and the cavity structure can effectively reduce the average Nu on the tip surface. Among the five modified configurations, the SS ribbed configuration (SRT) and the lateral ribs configuration (SLCT) exhibit relatively optimal aerothermal performance. Specifically, compared to FT, the SRT tip configuration shows an average Nu reduction of 27.4 % on the tip surface and a 16.3 % decrease in tip clearance leakage compared to FT; the average Nu on the SLCT tip surface and the tip clearance leakage relative to the FT are reduced by 27.2 and 17.3 %, respectively.

The research focused on a high-pressure turbine outer ring with an impingement-film composite cooling structure. Two methods of experimental measurements and numerical calculations were employed to investigate the outer ring cooling performance under typical thermodynamic parameters, such as the blowing ratio (M), temperature ratio (τ), and Mach number (Ma). The study aimed to elucidate the coupling effects between different thermodynamic parameters. It is revealed that increasing M led to improved cooling performance as it increased the cooling air flow rate and film hole outlet momentum. However, increasing Ma resulted in a less effective coverage of cooling air film on the outer ring, resulting in reduced cooling performance. Elevating the τ lowered the temperature of cooling air and outer ring but decreased the efficiency of cooling air utilization, leading to poorer cooling performance. The influence of M on the outer ring cooling property was independent of the τ, but M affected the magnitude of the change in cooling characteristics at different τ. A lower M enhanced τ effect on the cooling performance, while a higher M had the opposite effect. Increasing τ effectively mitigated the Ma impact on the outer ring cooling performance, especially at lower τ. Ma altered τ influence trend on the cooling performance. When 0.2 ≤ Ma < 0.6, increasing τ led to a decrease in cooling performance, but the extent of this decline decreased. When 0.6 < Ma ≤ 0.8, increasing τ resulted in an increase in cooling performance, but the improvement rate was moderated. Elevating the Ma enhanced M effect on the outer ring cooling performance. Specifically, when Ma is 0.2, increasing M from 0.7 to 3.0 elevates the outer ring overall cooling effectiveness from 0.3 to 0.45, reflecting a change of approximately 50 %. Similarly, when Ma is 0.8, an increase in M from 0.7 to 3.0 raises the overall cooling effectiveness from 0.1 to 0.35, indicating a more significant change of around 250 %.

Thermal plasmonic nanoparticles offer a novel and significant approach for photothermal therapy in the medical field, which is photothermal therapy of cancer. This study introduces a type of core-shell nanorods with internal coupling of titanium nitride (TiN) and gold (Au) nanomaterials. The photothermal properties of these nanorods in the near infrared (NIR) band were investigated using COMSOL Multiphysics software and the finite element method. Results indicate that TiN@Au and Au@TiN core-shell nanorods exhibit superior photothermal properties in the NIR band compared to pure TiN nanorods of similar volume. Furthermore, core-shell nanorods with polarization angles of 0° and 45° demonstrate enhanced optical absorption properties in the near infrared range. Furthermore, the study on the tunability of localized surface plasmon resonance with variations in core diameter, shell thickness, and combined changes of core diameter and shell thickness for core-shell nanorods of equal volume suggests that TiN@Au core-shell nanorods with a 10 nm Au shell offer increased optical absorption efficiency and photothermal conversion capability. Ultimately, the TiN and Au core-shell nanorods proposed in this research offer valuable insights for the structural design and heat transfer control of nanoparticle heat generators to enhance fluid temperature, as well as provide practical guidance for the preparation of core-shell nanoparticles.

In this study, in order to improve the efficiency of direct contact heat exchanger (DCHE), SK static mixers with different perforation index (PI) were applied. Numerical simulation (volume of fluid model) were used to investigate the performance of the static mixer, which shape was designed as long-holes, under fixed aspect and helical ratios. The feasibility and accuracy of numerical simulation results were verified by self-established direct contact heat transfer (DCHT) experimental platform. Under six different PI values (0 %, 10 %, 18 %, 26 %, 32 %, and 38 %), the heat transfer performance of DCHE was evaluated by applying two heat transfer mediums (THERMINOL62 and R141b). The results indicated that the gaseous working medium outlet temperature, turbulence intensity, turbulence kinetic energy, and volumetric heat transfer coefficient (VHTC) of the system showed an increasing trend as PI increased from 0 % to 32 %, then a decreasing trend can be observed from 32 % to 38 %. The maximum turbulence intensity and turbulence kinetic energy of 17.56 % and 0.015 m²/s² can be found in PI = 32 %, as well as a maximum enhancement ratio of 49 % in VHTC compared to PI = 0 % can be achieved. In addition, only a small pressure drop increase is observed in PI = 32 % compared to PI = 0 %.

During a tunnel fire incident, a substantial volume of high-temperature smoke gathers and disperses beneath the tunnel ceiling, posing significant risks of casualties and structural harm. A comprehensive comprehension of the temperature distribution of smoke beneath the ceiling is pivotal for the fire-resistant design and formulation of rescue plans for tunnel structures. This paper initially employs the FTP theory to analyze the fire scene resulting from fire spread under vehicle congestion. Subsequently, A set of numerical simulations is performed, and a prediction model of the temperature field for transverse symmetrical double fires is established according to the simulation results. Finally, an air entrainment model for transverse symmetrical double fires is proposed. The air entrainment amount under different fire spacing is obtained by theoretical derivation. Combined with the relationship between air entrainment amount, flame height, and maximum temperature, the variation of temperature field under the ceiling with fire spacing is explained from the mechanism. The results show that: the maximum temperature beneath tunnel ceiling increases with the increase of the fire power, decreases and then increases with the increase of the fire spacing and the variation has symmetry; The temperature attenuation along transverse and longitudinal directions under the ceiling following the exponential attenuation model, and the temperature attenuation rate is positively correlated with the maximum temperature. The transverse temperature attenuation is smaller than that of the longitudinal temperature under the same conditions; There is an internal relationship between the air entrainment, flame height and temperature field of the transverse double fires. The variation law of the temperature field beneath the ceiling depends on the degree of air entrainment limitation. Based on mirror model, this paper indicates that when the fire spacing is within a certain range, the combustion of the double fires can be effectively represented as near-wall fire.

Diamond (pointed twill) and diaper (herringbone twill) woven assemblies are considered ideal for applications where thermal insulation, heat retention, wrinkle resistance, strength, softness, and breathability attributes are crucial. Limited research has been found on the optimization of thermal comfort and mechanical performance of warp face, weft face and balanced float diaper and diamond woven assemblies. In this work six different woven assemblies have been engineered using cotton (cellulosic yarn) on a dobby machine, having warp face (4/2) weft face (2/4) and balanced float (3/3) based diamond and diaper weave designs with equal number of thread densities. Thermal comfort (dry fluid transmission, thermal resistance, stiffness, and overall wet fluid management capability) and mechanical (tensile, puncture and tear strength) tests were performed for developed woven fabrics. The results of diamond warp face sample showed the highest dry fluid transmission and volume porosity. Diamond weft face specimens showed the highest thermal conductivity behavior and diaper weft face exhibited the highest overall wet fluid management capability behavior. Stiffness was the highest in diamond balanced float. Diamond warp faced fabric showed the highest tearing durability and diaper weft face showed the highest tensile resilience in mechanical performance attributes.

Accurate identification of the total heat exchange factor (THEF), which serves as the foundation for online control data in the reheating furnace, holds significant importance for enhancing the digitization and intelligence level of the furnace, mitigating environmental pollution, and improving the economic performance of enterprises. For this purpose, based on the theory of inverse heat transfer problem, a solver combining Sequential Quadratic Programming and Broyden Combined Method (SQPBC) was developed to accurately identify high-dimensional and strongly nonlinear THEF in the reheating furnace. Integrating the efficient Broyden Combined Method (BCM) into Sequential Quadratic Programming (SQP) enables the rapid and accurate estimation of the Jacobian matrix to effectively enhance computational speed without compromising accuracy. Experimental data has been employed to validate the accuracy of the inversion results. The performance of SQPBC has been comprehensively analyzed through a series of numerical experiments, with a particular focus on investigating the impact of sampling frequency and sensor location on the inversion results. The findings reveal that after reducing the sampling period to 2 min, further decreasing the sampling period has a minor effect on the average relative error of the identification results; the closer the measurement points are to the surface of the slab, the more accurate the identification of THEF on the slab's surface.

This study is aimed to present an ultra-broadband metamaterial absorber for infrared detection and thermal emitter applications. Despite numerous studies on metamaterial absorbers, achieving ultra-broadband absorption remains a challenge. We introduce a dual-gold square array with transverse magnetic polarization and combine it with an anti-reflective (GaAs) layer and metal-insulator (gold-Al₂O₃) configurations. The absorber achieves over 90 % absorption between 0.63 μm and 2.90 μm, with average and effective absorptions at 94.60 % and 94.68 %, respectively. Through impedance matching theory, we validate the performance of the absorber, analyze electric field distributions to explain its mechanism, and assess manufacturing tolerance for practical application viability. Our findings reveal robust performance of the metamaterial absorber across a wide spectral range, including insensitivity to incidence angles, with absorption over 80 % in 20–60°, highlighting its potential in the infrared detection and the thermal emitter.