Insights into heat management of hydrogen adsorption for improved hydrogen isotope separation of porous materials

Separating high-purity hydrogen isotopes from their mixture still remains a huge challenge due to almost the identical physicochemical properties.Much importance has been attached to tune microstructure of porous materials,while heat management during hydrogen isotope separation tends to be ignored.Herein,a porous material 5A molecular sieve(5A)is mixed with graphene(GE)under ball grinding to enhance its thermal conductivity for hydrogen isotope separation.The thermal conductivity increases from 0.19 W m-1 K-1 of neat 5A,0.75 W m-1 K-1 of 5A/GE2(2 wt％GE)to 1.23 W m-1 K-1 of 5A/GE8.In addition,introducing GE into 5A promotes hydrogen adsorption and D2/H2 adsorption ratio.5A/GE2 shows the highest D2 adsorption capacity(5.40 mmol/g)and the largest D2/H2 adsorption ratio(1.07)among the composites.It also displays a high efficiency of heat transfer that contributes to a low energy consumption due to the shortened cycle time during hydrogen isotope separation.This work offers new insights into material design for improved hydrogen isotope separation,which is greatly crucial to scientific and industrial applications,such as fuel self-sustaining in fusion reactors.     

液氮温度下分子筛的真空吸附特性试验研究

为探究低温容器夹层所用分子筛吸附剂的吸附特性,采用静态膨胀法进行试验,获得了平衡压力为10-3Pa～103Pa范围内4A、5A和13X分子筛对N2、O2单一组分以及空气的吸附等温线,比较了不同分子筛对气体的吸附能力差异,探究了分子筛的吸附机理.研究结果表明:液氮温度下,5A和13X分子筛在真空条件下对N2及O2的吸附性...     

水分对分子筛结构及吸附性能的影响

分子筛是变压吸附制氧过程中最重要的组分,使用中该组分常出现吸水失效问题,极大地影响了氧产量及浓度.针对此问题,本文以HD-1型和PU-8型分子筛为原料,通过在不同温度(100、200、300、400℃)下活化得到不同含水量的分子筛,并通过对不同材料的结构形貌、热性能及吸附性能的表征分析了水分对分子筛结构及吸附性能的影响.研究结果表明:水分不会破坏分子筛的骨架结构,但会增大晶胞参数,并导致HD-1型分子筛中阳离子迁移;分子筛中的物理吸附水和化学结晶水会影响其吸附性能,其中物理吸附水的影响最大;活化有效提高了分子筛的吸附性能,且温度越高,含水量越少,吸附性能越好;在150~180℃下活化,将物理吸附水脱附后,分子筛的吸附能力可恢复70%,可在此温度下进行吸附器内低温活化;在400℃下活化,脱除化学结晶水,分子筛吸附性能可100%恢复,400℃为两种分子筛的最佳活化温度.     

变压吸附分离CH_4/N_2的分子筛吸附剂进展

综述了国内外变压吸附(PSA)分离CH4/N2所采用的分子筛吸附剂,包括沸石分子筛(ZMS)与碳分子筛(CMS)的研究和应用状况;介绍了ZMS和CMS的种类及其PSA分离CH4/N2的原理和效果;详细阐述了不同种类ZMS的组成、孔结构与其PSA分离CH4/N2效果之间的关系;分析了各种不同分子筛PSA分离CH4/N2中的优势与不足。具有动力学分离效应的分子筛型吸附剂在分离CH4/N2的PSA过程中具有能耗费用低、分离效果较好的优势,因此加强其研发将是今后的发展趋势。     

Investigation of thermal conductivity of liquid freons

The temperature dependence of the thermal conductivity of five liquid freons is experimentally investigated. An empirical relation for generalization of the obtained data is offered. The thermal conductivity of liquid Freons 11, 21, 114, and 115 is calculated.Notations thermal conductivity - C_c and C₀ total heat capacities of inner cylinder and layer of test liquid - D₂ and D₁ outside diameter of layer and inner cylinder, respectively - m cooling rate; M-correction for system heat loss - B constant coefficient for given liquid - n exponent - A molecular constant of liquid - a_r atomic constant - x, y, z, q number of atoms of carbon, fluorine, chlorine, and hydrogen in the freon molecule - density of liquid - molecular mass     

A Hierarchically Porous Carbon Fabric for Highly Sensitive Electrochemical Sensors

The hierarchically porous carbon fabrics with controlled conductivity and hydrophilicity have been fabricated by dual templating method of soft templates nested on hard templates. A non‐woven fabric coated with a solution of F127/resol has been carbonized for the synthesis of both macro‐porous structures of 10–15 µm in diameter having meso‐porous carbon structures of 4–6 nm, respectively. After carbonization treatment, not only conductivity is significantly improved, the hierarchically porous carbon also shows superhydrophilicity or water‐absorbing nature due to mild hydrophilic material and its dual scale roughness. The porous carbon becomes conductive with resistivity widely tuned from 5.4 × 10³ Ωm to 3.1 × 10^?3 Ωm by controlling the carbonization temperature. As the increased wettability for organic liquids could lead organic molecules deep into carbonized fabrics, the sensitivity of hierarchically porous carbon fabrics benefits the detection for methanol(CH₃OH) or hydrogen peroxide (H₂O₂). This new design concept of hierarchically porous structures having the multi‐functionality of high wettability and conductivity can be highly effective for electroanalytical sensors.

     

Thermal Conductivity in Zeolites Studied by Non-equilibrium Molecular Dynamics Simulations

The thermal conductivity of zeolites is an important material property. For example, this is the case for catalysis, where chemical reactions release heat either inside zeolites or at zeolite surfaces. At zeolite surfaces, heat is released during the adsorption of guest molecules. Unfortunately, it can be difficult to determine the thermal conductivity of zeolites from experiments or from equilibrium molecular dynamics simulations. Non-equilibrium molecular dynamics (NEMD) simulation is an interesting approach to determine thermal conductivities. Inducing a thermal gradient by moving kinetic energy between different parts of the simulation box, and then studying the resulting thermal gradient, will lead to direct access to the thermal conductivity of the zeolite. In this work, we have used NEMD simulations to determine the thermal conductivity of several pure silica zeolites. The zeolites are modeled using the Demontis force field, making it possible to screen many zeolite frameworks, and study finite-size effects. In addition, we have studied the influence of adsorbed guest molecules on the thermal conductivity. The thermal conductivity of zeolites is usually in order of 0.6  $\mathrm{W}\cdot \mathrm{m}^{-1}\cdot \mathrm{K}^{-1}$ W · m ? 1 · K ? 1 to almost 4  $\mathrm{W}\cdot \mathrm{m}^{-1}\cdot \mathrm{K}^{-1}$ W · m ? 1 · K ? 1 , with large differences between different crystallographic directions. We find that the loading of guest molecules adsorbed inside the zeolite has a minor influence on the thermal conductivity, and that in general the thermal conductivity increases with increasing framework density of the zeolite.     

Simulation and Experimental Study on Thermal Conductivity of [EMIM][DEP] + $$\mathbf{H}_\mathbf{2}{} \mathbf{O}$$ + SWCNTs Nanofluids as a New Working Pairs

In this paper, the single-wall carbon nanotubes (SWCNTs) were dispersed into ionic liquid, 1-ethyl-3-methylimidazolium diethylphosphate ([EMIM][DEP]), and its aqueous solution [EMIM][DEP](1) + \(\hbox {H}_{2}\hbox {O}(2)\) to enhance the thermal conductivity of base liquids, which will be the promising working pairs for absorption heat pumps and refrigerators. The enhancement effects on thermal conductivity were studied by experiment and molecular dynamic simulation (MD) methods. The thermal conductivities of [EMIM][DEP] + SWCNTs (INF) and [EMIM][DEP](1) + \(\hbox {H}_{2}\hbox {O}(2)\) + SWCNT(SNF) both with SWCNT mass fraction of 0.5, 1, and 2 (wt%) were measured by transient hot-wire method. The results indicate that the enhancement ratio of thermal conductivity of INF, and SNF can approach 1.30 when SWCNT is 2 (wt%). Moreover, SWCNTs has a higher enhancement ratio than multi-wall carbon nanotubes (MWCNTs). Density and thermal conductivity of [EMIM][DEP], [EMIM][DEP](1) + \(\hbox {H}_{2}\hbox {O}(2)\), INF and SNF systems, together with self-diffusion coefficients of \(\hbox {[EMIM]}^{+}\), \(\hbox {[DEP]}^{-}\), [EMIM][DEP] and water in solution [EMIM][DEP](1) + \(\hbox {H}_{2}\hbox {O}(2)\), were investigated by MD simulations. The results indicate that the maximum relative error between the simulated and experimental densities is about 2 %, and the simulated self-diffusion coefficient of [EMIM][DEP] is in the order of magnitude of \(10^{-11}\,\hbox {m}^{2}\cdot \hbox {s}^{-1}\). The average relative deviation for the simulated thermal conductivity of [EMIM][DEP](1) + \(\hbox {H}_{2}\hbox {O}(2)\), INF and SNF from experimental ones are 23.57 %, 5 %, and 5 %, respectively. In addition, the contributions of kinetic energy, potential energy, and virial and partial enthalpy terms to thermal conductivity were also calculated. The results indicate that virial term’s contribution to thermal conductivity is the maximum, which accounts for 75 % to 80 % of total thermal conductivity.     

Photoinduced Change of Thermophysical Properties of Chalcogenide As<Subscript><Emphasis Type="Bold">2</Emphasis></Subscript>S<Subscript><Emphasis Type="Bold">3</Emphasis></Subscript>Thin Films

The reversible photoinduced change exhibited by amorphous chalcogenide glasses has been extensively studied recently, partly as an interesting subject for fundamental research in the field of disordered solids and partly due to potential applications in optoelectronics such as photoresists, optical memories, optoelectronic circuits, etc. The illumination of many amorphous chalcogenides changes their internal and/or surface structure while preserving their amorphous state. In this study, amorphous arsenic trisulfide (As₂S₃) thin film samples whose thickness is 5 µm were prepared on silicon wafers by thermal evaporation, and their thermal diffusivity and thermal conductivity were measured by photoacoustic spectroscopy and a 3? method, respectively. These measurements were repeated after illumination by an Ar⁺ laser beam whose photon energy E _g is consistent with the energy band gap of As₂S₃. The results show that the thermal diffusivity and thermal conductivity increase by about 50% and 14–15%, respectively, by the photoinduced darkening, and this can be explained by the rearrangement of atoms and thermal expansion of the film.     

Cu Nanospring Films for Advanced Nanothermal Interfaces

An advanced thermal interface material comprised of dense and orderly arrays of 10‐µm high Cu nanosprings with tunable normal and shear compliance, lateral stability due to spring intertwining, and thermal resistance below 1 mm²KW^?1 is presented. The Cu nanospring films possess the compliance of soft polymers but up to 100 times higher thermal conductivity than materials with similar elastic modulus. This unique combination of mechanical and thermal properties makes it possible for the first time to populate the large empty space in the materials selection chart of thermal conductivity versus elastic modulus.

     

Effect of Iron Particle Size and Concentration on Thermal Conductivity of Iron/Polystyrene Composites

The present study deals with the thermal conductivity of iron/polystyrene (PS) composites containing iron particles of different sizes: (5, 50, 150, and 250)  $\upmu \mathrm{m}$ , and with different iron concentrations: (0, 5, 10, 20 and 30) mass%. The effects of iron particle size and concentration on the thermal conductivity of iron/PS composites are investigated in the temperature range: (30 to 120)  $^{\circ }\mathrm{C}$ . It was found that the addition of ultrafine iron particles enhances the thermal conductivity of the composites more than that of larger (coarser) particles. The thermal conductivity also increases with increasing temperature and iron concentration. The glass transition temperature was found to increase with decreasing size of iron particles. A correlation between the observed electrical and thermal conductivities of the iron composites as a function of iron particle size is presented. Fitting of some theoretical models results in predictions of smaller values of the thermal conductivity than are the experimental values.     

Measurement on the Thermal Properties of Graphene Powder

We report on an in-plane thermal diffusivity study of suspended graphene powder (GP) measured by the transient electro-thermal (TET) technique. The GP with a density of 0.24 \(\hbox {g}\,\cdot \,\hbox {cm}^{-3}\) is made up of five–six-layer graphene. And the average size of graphene flakes used in our study is 0.98 \(\upmu \)m. The intrinsic thermal conductivity perpendicular to in-plane of GP is determined at 18.8 \(\hbox {W}\,\cdot \,(\hbox {m}\,\cdot \,\hbox {K})^{-1}\) using the thermal conductivity instrument, and the range of the in-plane thermal diffusivity of GP is identified from \(0.86\times 10^{-5 }\,\hbox {m}^{2 }\,\cdot \,\hbox {s}^{-1}\) to \(1.52\times 10^{-5 }\,\hbox {m}^{2}\,\cdot \,\hbox {s}^{-1}\) measured by the TET technique. Accordingly, the corresponding intrinsic thermal conductivity is 13.5 \(\hbox {W}\,\cdot \,(\hbox {m}\,\cdot \,\hbox {K})^{-1}\)–23.8 \(\hbox {W}\,\cdot \,(\hbox {m}\,\cdot \,\hbox {K})^{-1}\). It is obvious that the two methods used in the experimental research on the intrinsic thermal conductivity of GP in different directions are not only the same order of magnitude but also have a maximum difference of only 5 \(\hbox {W}\,\cdot \,(\hbox {m}\,\cdot \,\hbox {K})^{-1}\). The results of our experiments are about one order of magnitude lower than those reported for four–five-layer graphene. There are various porosities in the whole sample after the compaction steps in the preparation of the samples, which gives rise to a large thermal contact resistance. And widely uneven surface defects observed under an optical microscope for the studied GP lead to substantial phonon scattering. Those factors combine together to give the observed significant reduction in the thermal conductivity.     

聚醚酰亚胺基炭分子筛膜的形成及其气体分离性能研究

以商用聚醚酰亚胺(PEI)作为前驱体,采用经过ZrO2-Al2O3复合溶胶修饰的陶瓷氧化铝为支撑体,浸渍涂膜制备聚合物膜,在空气中预氧化处理后,经500～800℃不同的炭化温度下制备出气体分离炭分子筛膜。为了考察炭化温度对炭膜结构和气体分离性能的影响,采用热重分析(TG)、拉曼光谱(Raman)、X射线衍射(XRD)、扫描电镜(SEM)和气体渗透等测试手段,对热解过程聚合物膜热稳定性、炭微晶结构及石墨化进程、微观形貌和气体分离性能进行了系统研究。结果表明,不同的炭化温度对所形成炭膜表现出不同物理和化学结构、炭结构和孔结构,最终影响炭分子筛膜的气体渗透性和分离选择性。     

The Prediction of the Emissivity and Thermal Conductivity of Powder Beds

The particle size distribution and packing (loose bulk and tapped density) of a mixture of ground biomass from Douglas fir wood particles was characterized by different practical methods: sieving, digital imaging and scanning electron microscopy. The ground mixture was analyzed using a set of 14 wire mesh sieves. The calculated mean diameter of mixture was 251 µm. The mixture was divided into four size fractions of mean size ranging from 74 to 781 µm. Particle length measured by imaging technique were 3–4 times larger than the mean diameter determined by sieve analysis. Similarly, particle width was 1.0–2.5 times larger than mean particle diameter. The sphericity of particles in each of the four fractions increased with decreasing size of the sieve indicating that smaller particles also have a smaller aspect ratio. Empirical power law equations were developed to correlate the packing and flow ability of ground particles (HR) to the mean diameter, with R² values of 0.88 and 0.91, respectively. The HR values indicated good flow ability for the large particles and poor flow ability for the smallest particles and the entire mixture. HR and porosity ratio reached an asymptote for particles larger than 400 µm.     

Investigation of the thermophysical properties of fireclay ceramics in the temperature range 80°–1200° K

The thermal conductivity, diffusivity, and specific heat of fireclay ceramics have been investigated over a wide temperature range in various gases. A method of calculating the thermophysical properties of the materials is given, whose use is fully justified by experiment. A method is described of theoretically determining the thermophysical properties of ceramics in various gases on the basis of investigations of these materials in air.Notation _eff effective thermal conductivity of porous material - _sk thermal conductivity of skeleton - _c thermal conductivity of continuous phase of skeleton - _d thermal conductivity of dispersed phase of skeleton - V_d volume fractions of disperse phase of skeleton - P) volume porosity, h/L=f(P) [5] - c) Stefan-Boltzmann constant - T) absolute temperature, °K - d) pore diameter - a thermal diffusivity     

Effect of pore size on the chemical removal of organic template molecules from synthetic molecular sieves

Various aluminophosphate and silicoaluminophosphate molecular sieves were treated with methanolic HCl to see its effectiveness as an alternative route for removing organic template molecules from molecular sieves. Both calcined and methanolic HCl-treated samples were characterized by X-ray powder diffraction and water adsorption-desorption isotherm measurements. The effectiveness of methanolic HCl in the removal of template molecules was found to be dependent on the pore size of the molecular sieves; that is, the template molecules were extracted effectively in sieves having a pore size ≥6 Å. This method is not effective for molecular sieves with a pore size <6 Å. This differential behavior is apparently a result of steric hindrance, that is, difficulty in removing template molecules from the zeolite cages as a result of their large size compared with the cage opening. This behavior has been exploited to stabilize the structure of the molecular sieve SAPO-37 against water by selectively removing the template molecules from the large cages (α cages) but keeping them intact in the small cages (β cages).     

Measurement and Estimation of High-Vacuum Effective Thermal Conductivity of Polyimide Foam in the Temperature Range from 160 K to 370 K for Outer Space Applications

Polyimide foam (PF) is a low-thermal conductivity and lightweight material with high resistances against heat, protons, and UV irradiation. A new thermal insulation composed of PFs and multiple aluminized films (PF–MLI) has potential to be used in outer space as an alternative to conventional multilayer insulation (MLI). As fundamental numerical data, the effective thermal conductivity of PF in wide ranges of density and temperature need to be determined. In the present study, thermal-conductivity measurements were performed by both the periodic heating method and the guarded hot-plate method in the temperature range from 160 K to 370 K and the density range from 6.67  \(\mathrm{kg} \cdot \mathrm{m}^{-3}\) to 242.63  \(\mathrm{kg}\cdot \mathrm{m}^{-3}\) . The experiments were carried out in a vacuum and under atmospheric pressure. For confirmation of the validity of the present guarded hot-plate apparatus under atmospheric pressure, the effective thermal conductivity of the lowest-density PF was measured with the aid of the heat flow meter apparatus calibrated by the standard reference material (NIST SRM 1450c) in the temperature range from 303 K to 323 K. In order to cross-check the present experimental results, the temperature and density dependences of the effective thermal conductivity of PF were estimated by means of the lattice Boltzmann method based on a dodecahedron inner microscopic complex structure model which reflects a real 3D X-ray CT image of PF.     

分子筛-聚合物共混气体分离膜研究进展

叙述了分子筛-聚合物共混制备气体分离膜的研究进展,包括不同类型的基体聚合物（橡胶态与玻璃态）与分子筛共混对分离膜渗透性能的影响、如何增强分子筛与聚合物膜材料相容性、共混膜选择分离皮层薄化等方面内容;并介绍了分子筛一聚合物共混膜气体渗透机理的理论研究,包括促进吸附扩散机理及分子筛分的Maxwell模型、Effective Medium Theory模型机理等．     

Preparation and Thermal Characterization of Nitrates/Expanded Graphite Composite Phase-Change Material for Thermal Energy Storage

Molten nitrate is widely used as thermal storage medium in the solar thermal power plants for its appropriate phase-change temperature, high heat storage density and low cost, etc. But its low thermal conductivity, heat absorbing and releasing rate limited its application. Expanded graphite (EG) can compensate the low thermal conductivity of nitrate. In this study, binary nitrates at the weight ratio of 4:6 for \(\hbox {LiNO}_{3}:\hbox {KNO}_{3}\) were prepared using static mixed melting method. EG with the mass fraction of 5 %, 10 %, 15 %, 20 % and 30 % was used to enhance the thermal conductivity. The compound of nitrates/EG was prepared using the ultrasonic smashing method. The thermal conductivity of binary nitrates, EG and nitrates/EG composite was measured by the transient plane heat source technique (TPS). The thermal behaviors were analyzed with a differential scanning calorimeter (DSC). Results showed that the addition of EG significantly enhanced the thermal conductivity, e.g., the thermal conductivity of 10 wt% EG composite phase-change material (PCM) is 8.5 \(\hbox {W}(\hbox {m}{^{-1}} \hbox {K}{^{-1}})\) to 9.5  \(\hbox {W}(\hbox {m}{^{-1}}\hbox {K}{^{-1}})\), which is about eight times larger than that of binary nitrates. To observe the combination morphology, pure EG, nitrates/EG composite PCM and binary nitrates were characterized using scanning electron microscope (SEM). The thermal reliability of the binary nitrates and the composite PCM was determined by DSC. Thermal cycling test showed that both binary nitrates and nitrates/EG composite material have good thermal reliability.     

Correlation on the Electrical and Thermal Conductivity for Binary Mg–Al and Mg–Zn Alloys

In this work, the electrical resistivity and thermal conductivity of both as-solution binary Mg–Al and Mg–Zn alloys were investigated from 298 K to 448 K, and the correlation between the corresponding electrical conductivity and thermal conductivity of the alloys was analyzed. The electrical resistivity of the Mg–Al and Mg–Zn alloys increased linearly with composition at 298 K, 348 K, 398 K, and 448 K, while the thermal conductivity of the alloys exponentially decreased with composition. Moreover, the electrical resistivity and thermal conductivity for both Mg–Al and Mg–Zn alloys varied linearly with temperature. On the basis of the Smith–Palmer equation, the thermal conductivity of both binary Mg alloys was found to be correlated quite well with the electrical conductivity in the temperature range from 298 K to 448 K. The corresponding Lorenz number is equal to $2.162\times 10^{-8} \,\hbox {V}^{2}\cdot \hbox {K}^{-2}$ 2.162 × 10 - 8 V 2 · K - 2 , and the lattice thermal conductivity is equal to $5.111 \,\hbox {W}\cdot \hbox {m}^{-1}\cdot \hbox {K}^{-1}$ 5.111 W · m - 1 · K - 1 . The possible mechanisms are also discussed.