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Thermal engineering experiments were carried out with laboratory water-to-water tube-in-tube heat exchangers of the same design parameters with smooth and profiled inner tubes. The tubes were profiled by confuser–diffuser constrictions of the flow section of the inner channel, which were formed by the deformation of their walls and placed along the length at a step that was constant and equal for all profiled tubes. The obtained results showed a dependence of the heat transfer enhancement in the tube channel on the Reynolds and Prandtl numbers, with the dependence on the latter being much stronger than that on the former, at least in cases where the heat carrier is water.

The results of thermal engineering experiments on a water–water tubular heat exchanger of the tube-in-tube type with heat transfer intensified by periodic confuser–diffuser elements arranged along the channel length at a step equal to the doubled inner diameter of the inner tube are compared with the results of experiments on a similar smooth-tube heat exchanger and the results of calculations by the criterial models of B.S. Petukhov, S.S. Kutateladze, W. Nusselt, and M.A. Mikheev. The comparison showed that the ratio of heat transfers in the tube channels of the intensified and smooth-tube heat exchangers, being a function of the Reynolds and Prandtl numbers, depends on the latter to a much higher extent. As a consequence, at least for water as a medium where the Prandtl number depends on temperature, the intensification of heat transfer is determined not only by the profiling parameters, but also by the parameters of the heat transfer process itself. In addition, the comparison demonstrated that the replacement of experimental data on smooth-tube heat exchangers by the results of calculation by the criterial models worsens the accuracy of estimates and leads to an increase in deviations with an increase in the Reynolds number Re.

For solving the problems of closed-loop optimization on controller parameters of multiple-controller single-output thermal engineering system, this paper proposes a recurrent optimization method that is based on the particle swarm computing and closed-loop simulation (PSO-RCO). It consists of a set of closed-loop identification, simulation, and optimization functions that are organized in a recurrent working flow. The working flow makes one controller tuned at a time whilst others keep their values. It ends after several rounds of overall optimizations. Such a recurrently alternative tuning can greatly speed up the convergence of controller parameters to reasonable values. Verifications on practical data from a superheated steam temperature control system show that the optimized control system performance is greatly improved by reasonable controller parameters and practicable control action. With the advantage of not interfering system operation and the potential supporting on big data identification method, the PSO-RCO is a promising method for control system optimization.

With the integration and miniaturization of electronic devices, thermal management has become a crucial issue that strongly affects their performance, reliability, and lifetime. One of the current interests in polymer-based composites is thermal conductive composites that dissipate the thermal energy produced by electronic, optoelectronic, and photonic devices and systems. Ultrahigh thermal conductivity makes graphene the most promising filler for thermal conductive composites. This article reviews the mechanisms of thermal conduction, the recent advances, and the influencing factors on graphene-polymer composites (GPC). In the end, we also discuss the applications of GPC in thermal engineering. This article summarizes the research on graphene-polymer thermal conductive composites in recent years and provides guidance on the preparation of composites with high thermal conductivity.

The complex structure of wood, one of the most abundant biomaterials on Earth, has been optimized over 270 million years of tree evolution. This optimization has led to the highly efficient water and nutrient transport, mechanical stability and durability of wood. The unique material structure and pronounced anisotropy of wood endows it with an array of remarkable properties, yielding opportunities for the design of functional materials. In this Review, we provide a materials and structural perspective on how wood can be redesigned via structural engineering, chemical and/or thermal modification to alter its mechanical, fluidic, ionic, optical and thermal properties. These modifications enable a diverse range of applications, including the development of high-performance structural materials, energy storage and conversion, environmental remediation, nanoionics, nanofluidics, and light and thermal management. We also highlight advanced characterization and computational-simulation approaches for understanding the structure–property–function relationships of natural and modified wood, as well as informing bio-inspired synthetic designs. In addition, we provide our perspective on the future directions of wood research and the challenges and opportunities for industrialization. The porous hierarchical structure and anisotropy of wood make it a strong candidate for the design of materials with various functions, including load bearing, multiscale mass transport, and optical and thermal management. In this Review, the composition, structure, characterization methods, modification strategies, properties and applications of natural and modified wood are discussed.

High temperature causes thermal damage to rock; the macrofracture and microfracture of rock can be produced under the action of temperature treatment. Under the influence of high temperature, the surrounding rock of deep underground engineering will suffer instability damage and cause serious harm to the people. In order to use the electromagnetic radiation (EMR) technology (a non-contact geophysical method) for evaluating the thermal stability of rock in underground thermal engineering applications, we established the EMR testing experimental system of rock under the action of a continuous heat source. The variation of EMR signals of rock under different temperatures was tested, and the EMR signals generates during the process of rock thermal deformation and thermal fracture, which were later analyzed. Under the action of a continuous heat source, the rock materials produced EMR signals with three kinds of frequencies. With the increase of rock temperature, the variation trends of EMR signals varied from the slow growth rate to the rapid growth rate, EMR signals can be divided into five stages. The increase of EMR signals is positively correlated with temperature, the Hurst exponent was higher than 0.7. The thermal stress was responsible for thermal deformation and fracture, thus generating the EMR signals. The research results have important guiding significance for the application of EMR technology to the evaluation of rock thermal stability.

Hydrogen has emerged as a crucial energy carrier for achieving a carbon-neutral society. Among its diverse applications, fuel cell vehicles (FCVs) are expanding rapidly. These vehicles store hydrogen at pressures of up to 82 MPa, while hydrogen refueling stations operate at even higher pressures, nearing 100 MPa, to enable refueling within three minutes. However, such rapid filling results in significant temperature rises within onboard tanks due to adiabatic compression, approaching the safety limit of 85 °C. Although precooling is often employed to mitigate this temperature rise, it brings secondary issues such as post-fill pressure spikes and nozzle frosting. To address these challenges, we developed a high-accuracy thermophysical property database for hydrogen and incorporated it into a dynamic simulation (DS) tool for predicting transient behaviors during refueling. During the development and validation of this system, we encountered various hydrogen-specific phenomena, including measurement difficulties, sensor anomalies, material incompatibilities, and gas permeation effects. This paper presents and analyzes these challenges, offering valuable insights for the engineering and operation of high-pressure hydrogen systems.

Nanofluids achieve high thermal transport efficiency by uniformly dispersing small particles in base liquids, significantly enhancing the heat transfer coefficients and making them vital in various thermal engineering applications. The research examines non-uniform thermal conductivity and activation energy critical for accurately describing fluid behaviour. The study incorporates bioconvection to prevent nanoparticle settling and ensure fluid stability through motile microorganisms. The governing partial differential equations are converted into ordinary differential equations that are solved using the Homotopy Analysis Method (HAM), to provide a strong mathematical framework for the analysis. This study finds that the velocity of the fluid decreases with magnetic constraint intensification and time retardation. however, heat transfer increases at higher radiation, and heat absorption/emission parameters but decreases with a higher Prandtl number, while an increased Schmidt number leads to decreased concentration profiles. This paper investigates a nano-Williamson fluid (NWF) flow over an exponentially stretched surface in a permeable medium, considering essential variables such as mixed convection, electromagnetic forces, non-linear thermal radiation, heat production, Joule heating and ohmic dissipation that are essential for understanding its complicated behavior.

Phonon engineering at gigahertz frequencies forms the foundation of microwave acoustic filters 1 , acousto-optic modulators 2 and quantum transducers 3 , 4 . Terahertz phonon engineering could lead to acoustic filters and modulators at higher bandwidth and speed, as well as quantum circuits operating at higher temperatures. Despite their potential, methods for engineering terahertz phonons have been limited due to the challenges of achieving the required material control at subnanometre precision and efficient phonon coupling at terahertz frequencies. Here we demonstrate the efficient generation, detection and manipulation of terahertz phonons through precise integration of atomically thin layers in van der Waals heterostructures. We used few-layer graphene as an ultrabroadband phonon transducer that converts femtosecond near-infrared pulses to acoustic-phonon pulses with spectral content up to 3 THz. A monolayer WSe 2 is used as a sensor. The high-fidelity readout was enabled by the exciton–phonon coupling and strong light–matter interactions. By combining these capabilities in a single heterostructure and detecting responses to incident mechanical waves, we performed terahertz phononic spectroscopy. Using this platform, we demonstrate high- Q terahertz phononic cavities and show that a WSe 2 monolayer embedded in hexagonal boron nitride can efficiently block the transmission of terahertz phonons. By comparing our measurements to a nanomechanical model, we obtained the force constants at the heterointerfaces. Our results could enable terahertz phononic metamaterials for ultrabroadband acoustic filters and modulators and could open new routes for thermal engineering. In an application of terahertz phonon engineering, terahertz phonons were generated, detected and manipulated through precise integration of atomically thin layers in van der Waals heterostructures.