Heat Flow Control Research Articles

Study of technical means for heat generation, its application, flow control, and conversion of other types of energy into thermal energy

Abstract The relevance of the study of technical means for the production, management, application, and conversion of heat is conditioned by the rapid development of the energy sector, the global challenges of climate change, and the need for sustainable and efficient solutions for providing thermal energy, in connection with the need for energy efficiency, optimization of resource use, sustainability, and environmental compatibility, as well as technological progress and innovation. The purpose of this study is to investigate the problems associated with technical means for heat generation, identify shortcomings related to the production, use, and management of thermal energy flows, and consider technical devices for converting alternative types of energy into thermal energy to identify recommendations that would allow them to be used more efficiently. The main results of the study were the analysis of technical means and devices in the field of thermal power engineering and alternative energy, the main problems and shortcomings that lead to a decrease in the efficiency of the operation of technical means, heat loss, reduced comfort, and emissions of harmful substances into the environment, which can lead to a negative impact on human health, a decrease in quality, and other environmental problems.

Shaping Thermal Transport and Temperature Distribution via Anisotropic Carbon Fiber Reinforced Composites.

With the ongoing electrification of vehicles, thermal management is on everyone's lips. To prevent overheating in electronic systems, new design strategies for thermal dissipation are needed. Thermally anisotropic materials enable targeted directional heat transport due to their anisotropic thermal conduction. Laminates made of unidirectionally aligned carbon fibers in a polymer matrix can be tailored regarding their in-plane anisotropy. Exposing the laminates to a temperature gradient reveals that the thermal transport is determined by their anisotropic properties. The corresponding heat flow can be visualized by IR thermography. The combination of anisotropic laminate discs into composite materials, similar to building with toy bricks, enables precise control of heat transport in the macroscopic composite materials. Thus, we achieve control of heat flow at the level of the individual components. In addition, we show that the orientation of anisotropy relative to the temperature gradient is crucial to guide the heat flow selectively. We found that the ratio of thermal anisotropy, the amount and arrangement of anisotropic components, and their positioning in the composite strongly influence heat transport. By combining all these factors, we are able to locally control the heat flow in composites by creating materials to either dissipate heat or block heat transport. The proposed concept can be extended to different shapes of building blocks in two or three dimensions.

Research on the division of heat dissipation spaces for multiple heat sources based on the adiabatic characteristic of heat flow lines

Due to the pressing need for compact layouts, the spacing between high-power devices is gradually decreasing, making the mutual influence between multiple heat sources unavoidable. Therefore, this paper proposes a method based on the adiabatic characteristics of heat flow lines and their convergence positions to evaluate the rationality of the thermal space design of each heat source. This method has been validated for applicability in one-dimensional, two-dimensional, and three-dimensional multi-heat-source conjugate convection heat transfer. Heat flow lines have significant advantages in describing energy flow, as they align with the direction of the temperature gradient. In thermal spaces with adiabatic boundaries or mutual influences between multiple heat sources, heat flow lines converge at certain positions. The relationship between adiabatic boundaries and heat flow line convergence positions has been studied, and a more interpretative decoupling scheme for multi-heat-source systems has been proposed. The main feature of this scheme is the separation of each heat source in the same steady-state thermal space and assigning adiabatic boundaries to the solid partition surfaces, allowing efficient observation of the thermal conditions of individual heat sources and targeted layout optimization. Results indicate that this method can utilize changes in heat flow line convergence positions to assess current thermal conditions and can be used to compare the thermal performance of different shaped heat sinks. Simulation results show that under the same mass conditions, thin-fin heat sinks perform 47 % better than thick-fin heat sinks, providing a more comprehensive and intuitive assessment compared to metrics such as thermal resistance and average temperature. The proposed method offers new ideas for multi-heat-source layout optimization, heat flow control, multi-heat-source partitioned simulation, and abnormal heating detection in multiple heat sources.

A nanoscale photonic thermal transistor for sub-second heat flow switching

Control of heat flow is critical for thermal logic devices and thermal management and has been explored theoretically. However, experimental progress on active control of heat flow has been limited. Here, we describe a nanoscale radiative thermal transistor that comprises of a hot source and a cold drain (both are ~250 nm-thick silicon nitride membranes), which are analogous to the source and drain electrodes of a transistor. The source and drain are in close proximity to a vanadium oxide (VOx)-based planar gate electrode, whose dielectric properties can be adjusted by changing its temperature. We demonstrate that when the gate is located close ( < ~1 µm) to the source-drain device and undergoes a metal-insulator transition, the radiative heat transfer between the source and drain can be changed by a factor of three. More importantly, our nanomembrane-based thermal transistor features fast switching times ( ~ 500 ms as opposed to minutes for past three-terminal thermal transistors) due to its small thermal mass. Our experiments are supported by detailed calculations that highlight the mechanism of thermal modulation. We anticipate that the advances reported here will open new opportunities for designing thermal circuits or thermal logic devices for advanced thermal management.

Ultrafast Unidirectional On-Chip Heat Transfer.

Effective and rapid heat transfer is critical to improving electronic components' performance and operational stability, particularly for highly integrated and miniaturized devices in complex scenarios. However, current thermal manipulation approaches, including the recent advancement in thermal metamaterials, cannot realize fast and unidirectional heat flow control. In addition, any defects in thermal conductive materials cause a significant decrease in thermal conductivity, severely degrading heat transfer performance. Here, the utilization of silicon-based valley photonic crystals (VPCs) is proposed and numerically demonstrated to facilitate ultrafast, unidirectional heat transfer through thermal radiation on a microscale. Utilizing the infrared wavelength region, the approach achieves a significant thermal rectification effect, ensuring continuous heat flow along designed paths with high transmission efficiency. Remarkably, the process is unaffected by temperature gradients due to the unidirectional property, maintaining transmission directionality. Furthermore, the VPCs' inherent robustness affords defect-immune heat transfer, overcoming the limitations of traditional conduction methods that inevitably cause device heating, performance degradation, and energy waste. The design is fully CMOS compatible, thus will find broad applications, particularly for integrated optoelectronic devices.

Exploring the thermal shielding performance by coupling phase change material to liquid cooling plate

To enhance the thermal shielding performance of high-temperature heat source target, an evolved cold shield system coupling phase change material (PCM) and liquid cooling plate with serpentine flow channel is developed. The thermal shielding effectiveness of the proposed system is illustrated by comparing the duration maintained at a lower temperature on the cold surface, and the temperature uniformity of the cold surface is analyzed to describe the role of PCM in the thermal shielding performance. The influences of the operating parameters of the liquid cooling plate and PCM physical parameters on the thermal shielding performance of the heat source targets are investigated. The results indicate that coupling PCM to a liquid cooling plate can effectively improve the thermal shielding performance. Increasing the heat power of the heat source target from 190 W to 231 W will lessen the advantage time from 3090 s to 1980 s for the coupled system. The advantage time is shortened by 1500 s as increasing the liquid volume flow rate from 0.26 L/min to 1.30 L/min. Lifting the starting temperature of the coolant from 15 °C to 25 °C prolongs the advantage time from 2130 s to 3090 s. The advantage time is improved by 660 s as increasing the PCM phase transition temperature from 26 °C to 30 °C, and increasing the PCM covering thickness from 8 mm to 10 mm extends the advantage time from 1830 s to 3090 s. Meanwhile, the temperature equalization of the cold surface for the coupled system is better than the single liquid cooling. These results indicate that the proposed coupled system has potential applications in improving thermal shielding performance as well as heat flow control, thermal insulation, and other areas of heat regulation.

Lateral Heterostructure Formed by Highly Thermally Conductive Fluorinated Graphene for Efficient Device Thermal Management.

The continued miniaturization of chips demands highly thermally conductive materials and effective thermal management strategies. Particularly, the high-field transport of the devices built with 2D materials is limited by self-heating. Here a systematic control of heat flow in single-side fluorinated graphene (FG) with varying degrees of fluorination is reported, revealing a superior room-temperature thermal conductivity as high as 128W m-1 K-1. Monolayer graphene/FG lateral heterostructures with seamless junctions are approached for device fabrication. Efficient in-plane heat removal paths from graphene channel to side FG are created, contributing significant reduction of the channel peak temperature and improvement in the current-carrying capability and power density. Molecular dynamics simulations indicate that the interfacial thermal conductance of the heterostructure is facilitated by the high degree of overlap in the phonon vibrational spectra. The findings offer novel design insights for efficient heat dissipation in micro- and nanoelectronic devices.

Thermal management improvement in electric vehicles through design optimization of coolant distributor valves

On battery electric vehicles a precise control of heat flows is required for passenger comfort and for both performance and safety of battery packs. This is typically achieved with a thermal management system which employs some type of liquid coolant to transfer heat. Coolant distributor valves are used to regulate coolant flows through the exchangers, for example to recover heat from hot sources, thus to increase vehicle energy efficiency. The development of this type of component is high-priced and the design is generally complex since several operating functions and manufacturing constraints should be satisfied. Despite this complexity and the positive impact such valves have on the thermal management of electric vehicles, a few works are currently available in the literature on design procedures for this component, where only a partial overview of the topic is provided and a comprehensive design methodology considering the effective operating conditions is still missing. In this work we construct a physical model of the valve for torque, internal leakage and pressure drop, and we build an optimization procedure to improve the global performance of the valve. We compare the obtained designs with a simpler approach that optimizes performance parameters independently and we show that designs which severely under-perform with respect to the uncontrolled performance parameters can be produced if an over-simplified design approach is followed. We then show with a global vehicle thermal model that the impact of valve design on global vehicle performance crucially depends on the thermal exchanges at vehicle level and, thus, on its operating conditions. In particular, the impact is considerable when mixing of cold and hot flows through the valve occurs. For a specific example vehicle evaluated in a type-3a cycle of the Worldwide Harmonized Light Vehicle Test Procedure, a valve determined with the proposed optimization procedure allows us to obtain in this condition an increase of about 1 km in the vehicle driving range with respect to a valve defined with the simpler approach.

Multi-physical field null medium: new solutions for the simultaneous control of EM waves and heat flow

Multi-physical field null medium: new solutions for the simultaneous control of EM waves and heat flow

Study of Radiative Heat Transfer of Third-Grade Nanofluid Flow with Variable Viscosity in PostTreatment Analysis of the Wire Coating Process

Wire coating technology plays a pivotal role in ensuring the efficiency, safety, and sustainability of mining operations. Its contributions go beyond the surface, impacting various aspects of mining activities, from safety compliance to energy efficiency and environmental responsibility. To attain maximum efficiency in the wire/cable coating process, the foremost concern of any scientists, experts and technologists is to consider the concept of wall shear stress, heat, and mass transfer phenomenon in the interior of dyes. The fundamental requirement of the coating process is to improve the rate of heat transfer. Therefore, the purpose of the current work is to ascertain how suspended nanoparticles influence the phenomenon of heat and mass transfer rate during the post-treatment of the coating process in the presence of third-grade liquid. The Buongiorno model is employed to examine the thermophoresis and Brownian features of nano-liquid. The governing equations are formulated and simplified using suitable non-dimensional parameters. Solutions for the non-linear differential equations are obtained numerically. The outcome of various pertinent parameters on momentum, thermal, and nanoparticle concentration profiles are delineated graphically. Further, regression analysis has been carried out to understand the importance of the correlation between heat transfer rate and flow control parameters.

Спинтроника немагнитных хиральных сред на примере эффекта Зеебека

Spin transport in chiral materials is considered as the main direction for the spintronics development. Experimental work on the study of the spin Seebeck effect shows that in chiral materials it is possible to achieve effective generation of spin-polarized current at distances up to several millimeters. In the presented work, we develop a theoretical approach to describe the spin Seebeck effect based on the spin Hamiltonian for conduction electrons in a chiral medium. Taking into account this Hamiltonian, the equation of electron spin dynamics averaged over the polycrystalline sample is obtained. In the approximation of ideal Fermi-gas and local-quasi-equilibrium distribution, the spin density operator of conduction electrons is constructed. It is shown that averaging over randomly oriented crystallites does not destroy spin ordering at strong spin-orbit interaction, and the temperature gradient generates spin polarization directed predominantly along the temperature gradient. Spin polarization by the described in the paper mechanism does not require external magnetic fields and remanent magnetization and therefore does not interfere with the operation of micro- and nano-sized structures of spintronics. Since the spin Seebeck effect is reciprocal with the spin Peltier effect, the theoretical approach presented in this work can form the basis of new methods for controlling heat flow in spintronics systems.

Time-Resolved Structural Measurement of Thermal Resistance across a Buried Semiconductor Heterostructure Interface

The precise control and understanding of heat flow in heterostructures is pivotal for advancements in thermoelectric energy conversion, thermal barrier coatings, and efficient heat management in electronic and optoelectronic devices. In this study, we employ high-angular-resolution time-resolved X-ray diffraction to structurally measure thermal resistance in a laser-excited AlGaAs/GaAs semiconductor heterostructure. Our methodology offers femtometer-scale spatial sensitivity and nanosecond time resolution, enabling us to directly observe heat transport across a buried interface. We corroborate established Thermal Boundary Resistance (TBR) values for AlGaAs/GaAs heterostructures and demonstrate that TBR arises from material property discrepancies on either side of a nearly flawless atomic interface. This work not only sheds light on the fundamental mechanisms governing heat flow across buried interfaces but also presents a robust experimental framework that can be extended to other heterostructure systems, paving the way for optimized thermal management in next-generation devices.

Flexible and elastic thermal regulator for multimode intelligent temperature control

AbstractAs nonlinear thermal devices, thermal regulators can intelligently respond to temperature and control heat flow through changes in heat transfer capacities, which allows them to reduce energy consumption without external intervention. However, current thermal regulators generally based on high‐quality crystalline‐structure transitions are intrinsically rigid, which may cause structural damage and functional failure under mechanical strain; moreover, they are difficult to integrate into emerging soft electronic platforms. In this study, we develop a flexible, elastic thermal regulator based on the reversible thermally induced deformation of a liquid crystal elastomer/liquid metal (LCE/LM) composite foam. By adjusting the crosslinking densities, the LCE foam exhibits a high actuation strain of 121% with flexibility below the nematic–isotropic phase transition temperature (TNI) and hyperelasticity above TNI. The incorporation of LM results in a high thermal resistance switching ratio of 3.8 over a wide working temperature window of 60°C with good cycling stability. This feature originates from the synergistic effect of fragmentation and recombination of the internal LM network and lengthening and shortening of the bond line thickness. Furthermore, we fabricate a “grid window” utilizing photic‐thermal integrated thermal control, achieving a superior heat supply of 13.7°C at a light intensity of 180 mW/cm2 and a thermal protection of 43.4°C at 1200 mW/cm2. The proposed method meets the mechanical softness requirements of thermal regulator materials with multimode intelligent temperature control.

Modelling a Loop Heat Pipe as Heat Switch for Transient Application in Space Systems

Heat switches are devices for controlling heat flow in various applications, such as electronic devices, cryogenic cooling systems, spacecraft, and rockets. These devices require non-linear transient thermal simulations, in which there is a lack of information. In this study, we introduce an innovative 1D thermo-hydraulic lumped parameter model to simulate loop heat pipes as heat switches by regulating the temperature difference between the evaporator and the compensation chamber. The developed thermo-hydraulic model uses the continuity, energy, and momentum equations to represent the behaviour of loop heat pipes as heat switches. The model also highlights the importance of some thermal conductance parameters and correction coefficients for accurately simulating the different operational states of a loop heat pipe. The simulations are conducted using the proposed 1D model, solved through the application of the Mathcad block function. The numerical model presented is successfully validated by comparing the temperatures of the evaporator and condenser inlet nodes with those of a referenced loop heat pipe from the literature. In conclusion, in this research, the mathematical modelling of loop heat pipes as heat switches is presented. This is achieved by incorporating correction coefficients with Boolean logic that results in non-linear transient simulations. The presented 1D thermo-hydraulic lumped parameter model serves as a valuable tool for thermal system design, particularly for systems with non-linear operational modes like sorption compressors. The graphical and nodal representation of this proposed 1D thermo-hydraulic model further enhances its utility in understanding and optimising loop heat pipes as heat switches across various thermal management scenarios.

Electrically gated molecular thermal switch.

Controlling heat flow is a key challenge for applications ranging from thermal management in electronics to energy systems, industrial processing, and thermal therapy. However, progress has generally been limited by slow response times and low tunability in thermal conductance. In this work, we demonstrate an electronically gated solid-state thermal switch using self-assembled molecular junctions to achieve excellent performance at room temperature. In this three-terminal device, heat flow is continuously and reversibly modulated by an electric field through carefully controlled chemical bonding and charge distributions within the molecular interface. The devices have ultrahigh switching speeds above 1 megahertz, have on/off ratios in thermal conductance greater than 1300%, and can be switched more than 1 million times. We anticipate that these advances will generate opportunities in molecular engineering for thermal management systems and thermal circuit design.

Conjugated heat transfer simulation of flow mechanism and heat transfer characteristic of sweeping jet impinging on leading edge in turbine cascade

Increasing inlet temperatures of gas turbines is the way to go for the development of advanced aero engines. As the inlet gas temperature of modern gas turbine engines continues to increase, the operating temperature has far exceeded the melting temperature of the typical heated region. Excessive temperatures can cause turbine blade ablation and damage, thus affecting the reliability and safety of the engine. The sweeping jet actuator (SJA) is a fluid oscillator that has attracted considerable attention in the field of enhanced heat transfer and flow control due to its non-constant sweeping characteristics. As a new impinging cooling method, this paper adopts the device to carry out the research work on the flow mechanism and heat transfer characteristics of sweeping jet (SJ) impinging on leading edge in gas turbine blade. Firstly, the numerical investigation of conjugated heat transfer simulation combined with unsteady Reynolds-averaged Navier–Stokes (URANS) is conducted to analyze the cooling performance of SJ. Using a C3X high-pressure turbine blade as a prototype, the temperature drop with the SJ scheme was improved by 1.8 K and 8.7 K compared with the circle jet (CJ) scheme for H/D = 1 and H/D = 5, respectively. Finally, the internal flow field of the blade is reconstructed by combining the proper orthogonal decomposition (POD) method. Through the POD method, we can deeply analyze the mechanism of the effect of SJ on the non-constant heat transfer at the leading edge of the blade, which provides theoretical support for the practical engineering application of SJ in the future industrial field.

Coupled abrasion Erosion-Oxidation wear from particles in Concentrating solar thermal power facilities

Solid particles represent an attractive heat transfer and energy storage media for next generation solar thermal power facilities for their ability to operate at high temperatures without concerns for freezing or corrosion. A potential outstanding issue that still remains for particles as heat transfer media is the wear on components operating with particles flowing (sliding) in, along, or over them. Prior work has shown that even at the low velocities (∼1 cm/s to ∼ 1 m/s) expected in solar thermal facilities, material wear will still occur, and the lifetime and performance of components undergoing wear needs to be well understood. Abrasion erosion occurs when particles come into contact with containment materials at extremely shallow angles, and is likely to be seen in heat exchangers, storage bins, and flow control mechanisms. Additionally, because of the open nature of most of these systems to air, oxidation of metals is also of concern. Here, we show how critical the coupled erosion-oxidation mechanism is to understanding particle/material durability and therefore need for greater in-depth analysis. Abrasive wear experiments are conducted on metals such as SS316 (L and H grades), Inconel 740H, Haynes 230 with different particles (HSP 40/70, Wedload 430, and CarboMax HD) for different operating conditions. Results clearly indicate that oxide spallation and removal is critical to the overall wear seen at high temperatures.

Electric field-induced orientation of silicon carbide whiskers for directional and localized thermal management

Incorporating high thermal conductivity fillers into the matrix material and optimizing their distribution offers a targeted approach to controlling heat flow conduction. However, the design of composite microstructure, particularly the precise orientation of fillers in the micro-nano domain, remains a formidable challenge to date. Here, we report a novel method for constructing directional/localized thermal conduction pathways based on silicon carbide whiskers (SiCWs) in the polyacrylamide (PAM) gel matrix using micro-structured electrodes. SiCWs are one-dimensional nanomaterials with ultra-high thermal conductivity, strength, and hardness. The outstanding properties of SiCWs can be maximized through ordered orientation. Under the conditions of 18 V voltage and 5 MHz frequency, SiCWs can achieve complete orientation in only about 3 s. In addition, the prepared SiCWs/PAM composite exhibits interesting properties, including enhanced thermal conductivity and localized conduction of heat flow. When the SiCWs concentration is 0.5 g·L−1, the thermal conductivity of SiCWs/PAM composite is about 0.7 W·m−1·K−1, which is 0.3 W·m−1·K−1 higher than that of PAM gel. This work achieved structural modulation of the thermal conductivity by constructing a specific spatial distribution of SiCWs units in the micro-nanoscale domain. The resulting SiCWs/PAM composite has unique localized heat conduction properties and is expected to become a new generation of composites with better characteristics and functions in thermal transmission and thermal management.

Multiple control of thermoelectric dual‐function metamaterials

AbstractThermal metamaterials based on transformation theory offer a practical design for controlling heat flow by engineering spatial distributions of material parameters, implementing interesting functions such as cloaking, concentrating, and rotating. However, most existing designs are limited to serving a single target function within a given physical domain. Here, we analytically prove the form invariance of thermoelectric (TE) governing equations, ensuring precise controls of the thermal flux and electric current. Then, we propose a dual‐function metamaterial that can concentrate (or cloak) and rotate the TE field simultaneously. In addition, we introduce two practical control methods to realize corresponding functions: one is a temperature‐switching TE rotating concentrator cloak that can switch between cloaking and concentrating; the other is an electrically controlled TE rotating concentrator that can handle the temperature field precisely by adjusting external voltages. The theoretical predictions and finite‐element simulations agree well with each other. This work provides a unified framework for manipulating the direction and density of the TE field simultaneously and may contribute to the study of thermal management, such as thermal rectification and thermal diodes.

Nanoscale thermal interface rectification in the quantum regime

To enable the on-demand control of heat flow for sustainable energy solutions, we have been longing for functional thermal components at the nanoscale, in analogue to electronic diodes and transistors. Understanding and discovering fundamental mechanisms that drive thermal rectification are critical to advancing this field. Different mechanisms have been proposed for thermal rectification effects in the classical regime. Using anharmonic atomistic Green's function, we discovered a thermal rectification phenomenon in the quantum regime for nanometer-thick three-dimensional solid interfaces. We found that the anharmonic phonon scatterings across the interface act on the temperature-dependent phonon populations on both sides of the interface, generating the necessary nonlinearity to achieve thermal rectification. This intrinsic thermal interface rectification is a universal phenomenon that can be observed and engineered for nanoscale interfaces.