From sawdust waste to high-value hierarchical ceramics-based phase change materials: Efficient dual functional thermal and solar energy storage

Latent heat thermal energy storage(LHTES) technology is gaining extensive attention due to its capability to balance supply and demand mismatch in solar energy utilization. However, phase change material as the core of storing latent heat still suffers from low thermal conductivity and poor shape stability, which severely restricts its practical application. Here, an eco-friendly strategy for achieving high-performance dual functional thermal and solar energy storage is proposed via turning wood processing waste into high-value hierarchical porous SiC ceramic-based composite phase change materials. The porosity of prepared porous SiC skeletons is highly adjustable from 59.4% to 90.2%, overcoming low porosity limitations of traditional wood materials and enabling tunable energy storage density for various applications. High thermal conductivity is achieved by benefiting from large grains and continuous skeletons with a value up to 37.93 and 1.87 W/(m K) for porosity of 59.4% and 90.2%, respectively.Excellent stabilities are demonstrated with only slight decreases of thermal conductivity and energy storage density over 1000 cycles and good anti-leakage properties are confirmed due to capillary adsorption forces induced by hierarchical pores. Benefiting from high thermal conductivity and high solar absorptance, fast and efficient solar thermal energy storage is successfully demonstrated. This work provides a new strategy for the high-value utilization of wood processing waste and efficient thermal/solar energy storage.

Thermal Feature Analysis of a New Hot-Air Anti-Icing Structure

Ice accretion on surfaces of the aircraft and engine is a serious threat to the flight safety.In this paper,a novel hot air anti-icing method is proposed based on the porous foam.Taking the NACA0012 airfoil as an example,the traditional thermal protection structure is proved to exist the deficiency in balancing the heat exchange caused by route loss of the heat.By dividing the hot chamber into multiple regions to fill with various foam metal,flow resistance characteristics and heat transfer characteristics for this protection mode are analyzed in order to derive the maximized benefit in anti-icing process.The calculation results reveal that,under the same condition,the region filled with foamed copper not only improves the temperature uniformity on the anti-icing area,but also achieves a better protection effect for enhancing heat transfer between the tube and the hot gas,averagely above 20℃higher than it without porous foam filling in surface temperature.Additionally,the minimum mass flow rate of the protection hot air is reduced by 16.7%.The gratifying efficiency of the porous filler in fortifying heat transfer confirms the potential of replacing the efficient but complex heat transfer design with simple structure filled with foam metal.

A comprehensive set of criteria for evaluating thermal management systems of aerial vehicles

Thermal management has become a significant concern in the design of advanced air vehicles.However,an effective evaluation method is needed when designers need to evaluate aircraft thermal management systems comprehensively.This paper proposes an evaluation method in which several evaluation directions concerned with thermal management systems(TMSs) are put forward to form an evaluation index system.The effect of temperature control,heat sink utilization efficiency,energy utilization efficiency,flight performance penalty,thermal endurance,space occupancy ratio,and economy are chosen as the direction of evaluation for TMS,considering its primary function,system performance,and impact on aerial vehicles.This method is comprehensive,intuitive,and user-friendly,along with the intensely subjective user-defined weight parameters,which provide rational metrics for thermal management techniques involved in aerial vehicles.The evaluation method could potentially be helpful for designers to comprehensively analyze the performance of aircraft thermal management systems and provide a basis for practical application.Two examples are provided to demonstrate the application of the method to evaluating TMS comprehensively.

工程热物理学科与能源可持续发展

工业化以来支撑人类社会发展的化石能源面临枯竭,解决能源利用与环境相容协调的难题,加速发展可持续能源,尽快实现从化石能源向可持续能源过渡是解决人类发展面临的共同挑战的必由之路.能源技术革命给工程热物理学科的发展带来了新的机遇与挑战.中国工程热物理学会根据能源、动力与环境问题的迫切需求和学科发展的新进展,面向构建可持续能源体系,开展我国能源发展模式和工程热物理学科前沿增长点的战略研究.能源、资源与环境有机结合的一体化发展新模式是实现可持续能源战略的有效保障,其关键在于开拓新能源和能源多元化,重点解决能源利用与环境相容协调的难题,包括发展绿色能源、洁净利用化石能源,以及实现能源、资源与环境一体化.凝练的工程热物理学科未来发展的重要研究方向包括:环保工质热物性、新能源的现代分析方法;极端条件下的燃烧,高效、洁净、低碳燃料转换理论与方法;太阳能光热高效转换与利用;地域化、智能化和多样化的风能利用;生物质高效低成本利用新方法及机理;燃料化学能与物理能的综合梯级利用;多能源互补的分布式能源系统及其优化集成理论;基于能量综合梯级利用的二氧化碳捕集能耗最小化原理;基于等熵原理的新型高效储能方法等.

高温条件下的固-固界面接触热阻测试方法与系统

高温条件下的固-固界面接触热阻是航空航天、能源、热核反应等领域中热控制和热防护系统设计的关键参数之一.针对高温条件下界面接触热阻测量系统设计与研制中存在的高温界面温差的高精度测量、热流量和压力的精确加载与计量、高温测试本体的绝热防护等技术问题,本文提出了一种上下对称布置稳态双向加载热流的高温条件下界面接触热阻测试方法,分析阐明了影响高温条件下接触热阻测量数据准确性的主要因素,建立了高温接触界面温差的红外热像测试与分析方法,攻克了钨热流计和接触界面处压力的精确加载与计量技术,设计了功率、温度全闭环精确控制的盘式钨丝高温加热器和高温测试本体的真空多层隔热结构,研制了高温条件下界面接触热阻的测试系统,实验测试了高温合金、C/C材料等材料对之间的接触热阻.结果表明,本文建立的高温条件下界面接触热阻测试方法和系统,实现了界面温度达1200℃的高温条件下接触热阻的高精度测量,测试误差小于10%.

Simulation and control scheme of microstructure in magnetic fluids

By accounting for the external and internal force acting on the suspended magnetic nanoparticles and motion characteristics of the suspended magnetic nanoparticles in the magnetic fluids,the three-dimensional microstructure of magnetic fluids is investigated by means of the molecular dynamics simulation method. The distribu-tion of suspended magnetic nanoparticles and microstructure of the magnetic fluid are simulated in both absence and presence of an external magnetic field. The ef-fects of the nanoparticles volume fraction,the dipole-dipole interaction potential and the particle-field interaction potential on the microstructures of the magnetic fluids are discussed. The main results obtained here are summarized as follows. The suspended magnetic nanoparticles tend to aggregate and make the irregular distribution structure in the absence of an external magnetic field. When the mag-netic fluid is exposed to a magnetic field,the magnetic nanoparticles suspended in the carrier fluid tend to remain chained-alignment in the direction of the external magnetic field. The tendency of chain-alignment morphology of the suspended magnetic nanoparticles is enhanced with the nanoparticles volume fraction,the dipole-dipole interaction potential and the particle-field interaction potential.

Granular porous calcium carbonate particles for scalable and high-performance solar-driven thermochemical heat storage

Calcium carbonate is promising thermochemical heat storage material for next-generation solar power systems due to its high energy storage density,low cost,and high operation temperature.Researchers have tried to improve energy storage performances of calcium carbonate recently,but most researches focus on powders,which are not suitable for scalable applications.Here,novel granular porous calcium carbonate particles with very high solar absorptance,energy storage density,abrasive resistances,and energy storage rate are proposed for direct solar thermochemical heat storage.The average solar absorptance is improved by 234%compared with ordinary particles.Both cycle stability and abrasive resistances are excellent with almost no decay of energy storage density over 25 cycles nor apparent particle weight loss over 24 h of continuous operation insides a planetary ball mill.In addition,the decomposition temperature is reduced by 2.8%–5.6%while the reaction rate of heat storage is enhanced by 80%–205%depending on the CO_(2) partial pressure.The decomposition process of doped granular porous CaCO_(3) particles is found to involve three overlapping processes.This work provides new routes to achieve scalable direct solar thermochemical heat storage for next-generation high-temperature solar power systems.

Perfect solar absorber based on nanocone structured surface for high-efficiency solar thermoelectric generators

Nanostructured surface is a promising photon management strategy to tune spectrum in design of the selective solar absorber.In this paper,we propose a nanocone structured surface as a perfect solar absorber in application of the solar thermoelectric generators(STEGs).The trade-off between the solar absorption and the mid-infrared emission is obtained to maximize the STEG efficiency.The effects of the geometric parameters,thermal concentration,incident angle and polarized state as well as the lattice arrangement are systematically investigated.The results show that the STEGs equipped with our proposed selective solar absorber can achieve a peak efficiency of 6.53%under AM1.5G condition(no optical concentration).Furthermore,the selective solar absorber exhibits insensitive behavior to the incident angle and polarization angle as well.This means that the proposed selective solar absorber can utilize solar energy as much as possible and be generally suitable in equipping the STEGs without optical concentration.

A novel method to determine effective thermal conductivity of porous materials

A 2D Lattice-Boltzmann (LB) model is proposed for analyzing the heat conduction process in the porous media. The effective thermal conductivities of several porous materials are calculated by means of this model. The calculated results are found to be in excellent agreement with the experimental data of the existing references. The factors affecting the effective thermal conductivity of porous materials are discussed. The results show that the effective thermal conductivity is strongly dependent upon the porosity and the pore structure and only has imperceptible dependence on the pore density. Then the correlation for estimating the effective thermal conductivity of the porous material is established. This LB model can be used conveniently to calculate and analyze the heat conduction problems of porous media or other materials with complex geometry boundary in pore scale.

Preparation of polystyrene spheres in different particle sizes and assembly of the PS colloidal crystals

Monodisperse polystyrene (PS) colloidal spheres were successfully prepared through emulsifier-free emulsion polymerization by controlling the polymerization reaction time, ionic strength of the system, concentration of the ionic copolymer (sodium p-styrenesulfonate) and other factors. The PS colloidal spheres were assembled into colloidal crystals whose structures were mainly face-centered cubic (fcc) close-packed. Then FDTD method was used to calculate the color-rendering characteristics of the colloidal crystals surface. The calculated results were consistent with the experimental results.

Particle image velocimetry for an automatic cooling device using temperature-sensitive magnetic fluid

An automatic cooling device has been developed by using a temperature-sensitive magnetic fluid as the coolant. A particle image velocimetry (PIV) system was used to measure the flow velocity of the fluid inside the loop. The efficiency of the device under varying conditions such as the heat load and the power of cooling were ex- perimentally investigated. The effect of cooperation between external magnetic field and thermal field on the performance of the device was studied. As expected, a continuous flow induced by the thermal and magnetic field was observed in the loop, where heat was transferred by the circulating magnetic fluid. The synergic effect between the magnetic field and the temperature gradient has impact on the performance of the device.

Preparation and characterization of magnetic phase-change microcapsules

Magnetic microcapsules containing paraffin cores within urea-formaldehyde shells were fabricated utilizing in situ polymerization, with iron nano-particles as magnetic particles. The thermal properties, surface morphologies, magnetic properties and iron nano-particles content of the magnetic phasechange microcapsules were investigated by scanning electronic microscopy (SEM), differential scan- ning calorimetry (DSC), vibrating sample magnetometry (VSM) and inductively coupled plasma quantometry (ICP). The influence of iron nano-particles on morphologies was also considered. The results indicate that the melting point of magnetic phase-change microcapsules is almost identical to that of paraffin. The magnetism parameters such as specific saturation magnetization and residual magnetization of magnetic phase-change microcapsules increase with the increase of iron nano-particles content.

Thermal analysis and optimization of the emitter in the solar thermophotovoltaic (STPV)

A model for predicting the performance of the emitter in the solar thermophotovoltaic (STPV) system is presented in this article. The effect of non-parallelism of sun rays on concentration capability is numerically calculated,also the flow field in the emitter cavity and the temperature distribution of the emitter with different inlet conditions are compared. Numerical results show that free convection of the air inside the emitter cavity has great effect on the emitter temperature and may reduce the electricity output of the cells. At last,a new kind of selective film is put forward. Through optimizing the cut-off wavelength of a selective film,radiation loss is further reduced and system efficiency is improved.

Super-Planckian thermal radiation enabled by hyperbolic surface phonon polaritons

Excitation of surface resonance modes and presence of resonance-free hyperbolic modes are two common ways to enhance the near-field radiative energy transport, which can find wide applications in noncontact thermal management and energy harvesting.Here, we identify another way to achieve the super-Planckian thermal radiation via hyperbolic surface phonon polaritons(HSPhPs). Based on the fluctuation-dissipation theory, the near-field radiative heat flux between bulk hexagonal boron nitride(hBN) planes with the optical axis perpendicular to the radiative energy flow can be 120 times as large as the blackbody limit for a gap distance of 20 nm. When the film thickness is reduced to 10 nm, the radiative heat flux is found to increase by 26.3%.The underlying mechanism is attributed to the coupling of Type I HSPhPs inside the anisotropic hBN film, which improves the energy transmission coefficient over a broad wavevector space especially for waves with extremely high wavevectors. This work helps to deepen the understanding of near-field radiation between natural hyperbolic materials, and opens a new route to enhance the near-field thermal radiation.

The application of the microstructured metallic grating to light emission extraction

Microstructured metallic gratings can be used to enhance the light emission efficiency of LEDs,and the spectral radiation properties of the LEDs vary with the different metallic materials used,leading to variation of the light emission enhancement at the same wavelength for different metallic grating materials.In this paper,the finite difference time domain(FDTD) method has been used to investigate the light emission extraction enhancement of LEDs in which gratings with different metallic materials have been applied.Through analysis of the permittivity of the metals and the quality factors of the surface plasmons(SPs),we concluded that the larger the plasma frequency obtained for the metallic interband transition,then the more suitable the metals are for light emission extraction of photons with relatively short wavelengths.This is because of the abundance of free electrons in the metals with large plasma frequencies.We also found that the wavelength-dependent trends of the extraction enhancement resulting from the scattering mechanism for different metallic materials are similar to each other.For SP-induced enhancement,either the enhancement peak position or the peak value changes significantly with the different metals.

Analysis of influence factors of negative refraction phenomenon in particulate composite

The effective optical constants that describe the interaction between electromagnetic wave and particulate composite are calculated based on effective medium theory and Mie theory.The negative refractive phenomenon is compared between the Ge-particle-dispersed LiTaO 3 composites and Ag-particle-dispersed LiTaO 3 composites.It is indicated that the negative refraction phenomenon for semiconductor Ge particulate composite occurs in higher frequency range than that of noble Ag particulate composite.By take the Ge particulate composite as an example,the influence of size and number density of spherical particles on the negative refraction phenomenon is analyzed.It is indicated that the frequency range where negative refraction phenomenon occurs can be shifted to higher frequency by adjusting these two influencing factors.