Microencapsulation of phase change material in water dispersible polymeric particles for thermoregulating rubber composites—A holistic approach

Summary To avoid the leakage of phase change materials (PCM) to its surrounding, microencapsulation of PCM in a polymeric shell is highly desirable. These microcapsules ideally should provide a platform to store and release latent heat of the PCM without undergoing any physicochemical transformation of core (PCM) as well as shell (polymer) materials. Several characteristics such as heat transfer efficiency, thermal conductivity, water dispersibility, and durability of the PCM capsules are dependent on the nature of shell materials. In the present study, a random copolymer of poly (methyl methcrylate-co-2-hydroxyethyl methacrylate) poly (MMA-co-HEMA) with an optimum ratio of 75/25 (methyl methacrylate (MMA)/2-hydroxyethyl methacrylate (HEMA)) was used as shell material to encapsulate paraffin wax (PCM), using emulsion solvent evaporation method. The microcapsules of ~5-μm size with a shell thickness of ~0.8 μm with high encapsulation efficiency (~92.34%) and thermal storage capability (99.85%) were fabricated. In addition to ease of water dispersibility, PHEMA (poly(2-hydroxyethyl methacrylate)) containing water absorbable shells also exhibit enhanced thermal conductivity from 0.1 to 0.49 W/(m·K) at 25°C in wet state compared with the dry capsule. The capsules show good durability by displaying no significant change in thermal properties and water dispersibility after running through 500 heating/cooling cycles. To test the feasibility of this novel water dispersible microencapsulated PCM, these were mixed with natural rubber latex at various blend ratios, and their thermal behaviour was evaluated. The obtained rubber composite showed good thermoregulation property with enhanced mechanical strength.     

Investigation of in-situ polymerization synthesized carbon-coated zinc oxide as anode material for Zn/Ni secondary battery

Using the resorcinol-formaldehyde (RF) resin as carbon source, core-shell structured carbon-coated zinc oxide (ZnO@RFC) was synthesized by cetyltrimethylammonium bromide (CTAB) assisted in-situ polymerization followed with carbonization process. The results showed that the ZnO particles were uniformly coated by an amorphous carbon layer. The excellent structural stability and high electrochemical performance depend it to be designed into carbon shell with a tunable thickness up to 14.4 nm, resulting in the ZnO@RFC anode delivers initial discharge specific capacity of 543 mAh g^?1 and optimized 125 cycle life with capacity retention of 97.5% for Zn/Ni secondary batteries. And the effects of the thickness of carbon shell on electrochemical performance, corrosion and hydrogen evolution reaction are fully investigated. The results indicate that the carbon shell not only improves the electrical conductivity between ZnO particles but also increases the stability of ZnO in electrolyte.     

A review on effect of phase change material encapsulation on the thermal performance of a system

This paper presents a detailed review of effect of phase change material (PCM) encapsulation on the performance of a thermal energy storage system (TESS). The key encapsulation parameters, namely, encapsulation size, shell thickness, shell material and encapsulation geometry have been investigated thoroughly. It was observed that the core-to-coating ratio plays an important role in deciding the thermal and structural stability of the encapsulated PCM. An increased core-to-coating ratio results in a weak encapsulation, whereas, the amount of PCM and hence the heat storage capacity decreases with a decreased core-to-coating ratio. Thermal conductivity of shell material found to have a significant influence on the heat exchange between the PCM and heat transfer fluid (HTF). This paper also reviews the solidification and melting characteristics of the PCM and the effect of various encapsulation parameters on the phase change behavior. It was observed that a higher thermal conductivity of shell material, a lower shell size and high temperature of HTF results in rapid melting of the encapsulated PCM. Conduction and natural convection found to be dominant during solidification and melt processes, respectively. A significant enhancement in heat transfer was observed with microencapsulated phase change slurry (MPCS) due to direct surface contact between the encapsulated PCM and the HTF. It was reported that the pressure drop and viscosity increases substantially with increase in volumetric concentration of the microcapsules.     

The superposition of effects produced by buckling, creep and fatigue

On the basis of the energy concept and of the principle of critical energy, this paper defines the general concept of deterioration (or damage) of a material subjected to a number of external actions. The deterioration concept permits one to establish a general relation defining the critical state produced by the simultaneous action of different loads. The critical state is produced by failure, by excessive deformation or by buckling. The results obtained were applied in the following cases: shells buckling under a group of loads, in the cases of linear and of non-linear behaviour of the shell material; fatigue and creep-fatigue interaction. The established relationships are experimentally verified. This approach makes it possible to calculate shell buckling under groups of loads as well as the fatigue or creep lifetime or the fatigue-creep lifetime under a group of different loads.     

Conjugate heat transfer analysis of copper staves and sensor bars in a blast furnace for various refractory lining thickness

Lining erosion is the most important factor for determining the campaign life of a blast furnace. To provide information about the heat transfer of the copper stave in the belly of the No. 1 blast furnace at CSC (China Steel Corporation), a conjugate heat transfer model, including the heat transfer of the stave and sensor bar in thermal conduction and radiation transmission from the gas temperature inside the blast furnace and convection heat transfer in cooling pipe, was developed for the steady state process. The simulations focus specifically on the effects of the gas temperature, the geometric thickness of the cooling stave, the slag layer thickness and the material and diameter of the sensor bar. The results show that the refractory lining and the slag shell provide significant protection for the stave body. A copper sensor bar can be used to measure the residual lining thickness of the cooling stave. To estimate a more reasonable stave thickness, several key factors, such as the diameter and material of the sensor bar, were examined in this study. The results can serve as important reference information for blast furnace operation and the prediction of its campaign life.     

Analysis of millisecond collision of composite high pressure hydrogen storage cylinder

For vehicle-mounted high-pressure hydrogen storage cylinders, impact resistance is an important indicator. This work aims at building a model of 70 MPa composite fully wound Ⅳ cylinder around T800 carbon fiber material, investigating the law of transient changes in the body of the bottle under different velocity impacts and the source of risk of bursting. Through millisecond impact analysis, the energy transfer path and transformation trend inside the cylinder are obtained. Meanwhile, it was found that there was a clear pattern of positive correlation between the tensile and compressive stresses generated by the difference between the internal pressure of the bottle and the impact pressure. The final results show that after the impact, the failure occurred firstly at the inner wall of the fiber corresponding to the impact point, and the fiber damage spreads in all directions. The thickness of the failure pavement increases from the inside to the outside.     

Failure correlation between cylindrical pressurized vessels and flat plates

Utilizing the theory of thin shell structures, a failure criterion is presented which one may use to predict, analytically, catastrophic failures, or unzipping, in cylindrical pressurized vessels, based on the fracture toughness profile K obtained from tests carried out on flat plates of the same material and thickness. These test results are plotted as a function of the characteristic ratio (h/c), where h represents the specimen thickness and c one-half of the crack length. Comparison with carefully controlled experimental data substantiates its validity and its potential use. The advantage of such an approach is that considerable amount of time and money can be saved.     

Nonlinear vibration and dynamic response of shear deformable imperfect functionally graded double-curved shallow shells resting on elastic foundations in thermal environments

In this article, nonlinear vibration and dynamic response of imperfect functionally graded materials (FGM) thick double-curved shallow shells resting on elastic foundations are investigated using Reddy's third-order shear deformation shell theory in thermal environments. Material properties are assumed to be temperature dependent and graded in the thickness direction according to a simple power-law distribution in terms of the volume fractions of the constituents. The FGM shells are subjected to mechanical, damping, and thermal loads. The Galerkin method and fourth-order \hboxRunge–Kutta method are used to calculate natural frequencies, nonlinear frequency–amplitude relation, and dynamic response of the shells. In numerical results, the effects of geometrical parameters, material properties, imperfections, shear deformation, the elastic foundations, mechanical, thermal and damping loads on the nonlinear dynamic response, and nonlinear vibration of FGM double-curved shallow shells are investigated. Accuracy of the present formulation is shown by comparing the results of numerical examples with the ones available in literature.     

Study of contact melting inside isothermally heated vertical cylindrical capsules

Close-contact melting processes of phase change material (PCM) inside vertical cylindrical capsule are studied. PCM are heated by the capsule isothermally at the bottom and side. The theoretical formulas of the melting rate and thickness of liquid layer during the heat transfer process are obtained by analysis, which are convenient for engineering predictions. Finally, the factors that affect melting are discussed, and conclusions are drawn.     

Hydrogen adsorption in nanotube and cylindrical pore: A grand canonical Monte Carlo simulation study

Physisorption of targeted amount of hydrogen within carbonaceous material is a formidable task. Even though at 80 K adsorption is satisfactory but at 298 K storing desirable amount of hydrogen is difficult. Here we report grand canonical monte carlo simulation of hydrogen adsorption within two different cylindrical pores in the temperature range 60–298 K and in the pressure range 1–500 bar. In one we construct a cylindrical pore (CP) of ≈2.0 nm diameter by removing carbon atoms from the center of stacked graphene sheets. In the other single walled carbon nanotube (SWCNT) of similar diameter is used for the adsorption. In all of our simulations intermolecular hydrogen interactions are modeled using the classical Silvera-Goldman potential, which contains both Lennard-Jones and electrostatic sites. Total amount of adsorbed hydrogen is always greater in SWCNT (adsorbed both inside and outside the wall) than in CPs, however amount of hydrogen adsorbed inside SWCNT only is always smaller than that inside CP. Surface defects created during removal of carbon atoms in CP results in almost 2 wt% increase in uptake compared to SWCNT.     

Analysis of contact melting of phase change materials inside a heated rectangular capsule

Close-contact melting processes of phase change material (PCM) inside a horizontal rectangular capsule are studied. The PCM is heated by the capsule at constant heat flux at the top and isothermally at the bottom, and the sides are adiabatic. The theoretical formulas of the dimensionless melting rate and the thickness of the liquid layer during the heat transfer process are obtained by analysing, which is convenient for engineering predictions. Finally, the influences on the melting process are discussed, and conclusions are drawn.     

Analysis on the heat transfer in a square cavity with a semitransparent wall: Effect of the roof materials

A theoretical study on conjugated heat transfer (natural convection, radiation and conduction) in a square cavity with turbulent flow is presented. The cavity is a representation of a room, where the left wall is isothermal, the right wall is semitransparent (glass), the lower wall is considered as insulated and on the upper opaque wall heat conduction is present. Both conductive walls (opaque and semitransparent) interact with the ambient. The semitransparent wall is subject to a constant heat flux (G₂ = 736 W/m²) whereas on the opaque wall a constant heat flux (G₁ = 875 W/m²) falls perpendicularly. The sizes of the cavity under study were 5.0, 4.0, 3.0 and 2.0 m. The upper opaque wall was considered as a mixture of concrete and a composite material (concrete–expanded polystyrene) with different thicknesses and diverse types of water-repellent coatings on top of it. From the results, it was found that the white coating on top of the opaque wall significantly reduces the amount of energy towards the inside of the cavity. It was also determined that the opaque wall with a 20 cm thickness shows the best thermal performance and it is the most adequate to reduce thermal gains inside the cavity. Correlations for the total heat transfer as a function of the cavity size, the type of coating and material of the opaque upper wall are proposed.     

CFD simulations of filling and emptying of hydrogen tanks

During the filling of hydrogen tanks high temperatures can be generated inside the vessel because of the gas compression while during the emptying low temperatures can be reached because of the gas expansion. The design temperature range goes from ?40 °C to 85 °C. Temperatures outside that range could affect the mechanical properties of the tank materials. CFD analyses of the filling and emptying processes have been performed in the HyTransfer project. To assess the accuracy of the CFD model the simulation results have been compared with new experimental data for different filling and emptying strategies. The comparison between experiments and simulations is shown for the temperatures of the gas inside the tank, for the temperatures at the interface between the liner and the composite material, and for the temperatures on the external surface of the vessel.     

Notch sensitivity of circular rings subjected to impact loading

‘Notch-sensitive regions’ have been observed during a series of experimental investigations into the dynamic plastic behaviour and failure of thin-walled metallic radially notched circular rings with arc-shaped supports subjected to concentrated impact loads. The experimental results show that the exterior notches at some regions have no effect on the deformation of the rings, but do have effect at the remaining regions. The notch-sensitive region is theoretically determined by using the equivalent structures technique; fairly good agreement has been reached between the simple theory and the experimental results. Both dimensional and theoretical analyses prove that whether a plastic hinge formed or not at the notched section does not depend on the mean radius of the ring and the input kinetic energy. It depends on the weak coefficient of the notched section and the angle of the support. Generally speaking, there are mainly three failure modes for a notched circular ring with arc-shaped support under impact loading: Mode I, large inelastic deformation when the notch is outside the sensitive region, in this case the ring deforms as a normal one; Mode II, large inelastic deformation only at some part of the ring and tearing occurred at the notched sections; mode III, large inelastic deformation and total rupture occurred at the notched sections. It is believed that the present study could assist the understanding of the dynamic behaviour and failure of other kinds of nonstraight components with macroscopic imperfections under impulsive loading.     

Preparation of n-tetradecane-containing microcapsules with different shell materials by phase separation method

Microcapsules for thermal energy storage and heat-transfer enhancement have attracted great attention. Microencapsulation of n-tetradecane with different shell materials was carried out by phase separation method in this paper. Acrylonitrile–styrene copolymer (AS), acrylonitrile–styrene–butadiene copolymer (ABS) and polycarbonate (PC) were used as the shell materials. The structures, morphologies and the thermal capacities of the microcapsules were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The ternary phase diagrams showed the potential encapsulation capabilities of the three shell materials. The effects of the shell/core ratio and the molecular weight of the shell material on the encapsulation efficiency and the thermal capacity of the microcapsules were also discussed. Microcapsules with melting enthalpy > 100 J/g, encapsulation efficiency 66–75%, particle size<1 μm were obtained for all three shell materials.     

Influence of sandblasting and hydrogen on tensile and fatigue properties of pipeline API 5L X52 steel

The evaluation of static properties and lifetime of a pipeline notched under the impact of sand with or without the presence of hydrogen has been performed. The material damage was made by electrolytic hydrogen and projecting corundum particles (aluminium oxide). It has been shown that sandblasting and hydrogen have little affect on the yield stress and ultimate strength. The material lifetime and elongation at fracture are clearly affected by hydrogen, which penetrates into the surface layers of the material and changes the local fracture mechanism. Despite the erosion of these layers, under the sand impacting, failure strain and lifetime are improved. The observation of failure mode shows that the deformation field, after sandblasting, is very important. The crack propagation and the failure seem to be intra granular. The cracks, in the pipeline API 5L X52 steel charged with hydrogen, propagate following the porosity path without any distinct direction. The absorbed hydrogen atoms placed inside the crystalline sites of steel cause the embrittlement of material so that a small effort is sufficient to create cleavage. Modified notch failure assessment diagram was used to evaluate the dangerousness of studied notch defect in different environments: air, hydrogen and sandblasting.     

安康水电厂3号发电机推力瓦磨损原因分析及处理

本文介绍了安康水电站３号水轮发电机推力瓦的磨损情况，对推力瓦磨损原因进行了分析，认为磨损是由于瓦中部凸变形引起的，而引起瓦变形的主要因素是热变形。推力瓦的热变形主要是由三个分量组成：瓦体与瓦面线胀系数不同引起的热变形，瓦厚度方向温差引起的热变形和瓦面热变形。叙述了推力瓦磨损处理的步骤和采取的主要措施。经过处理后推力轴承运行情况良好。     

Proportional loading of thick-walled cylinders

A generalized solution for small plastic deformation of thick-walled cylinders subjected to internal pressure and proportional axial loading is developed. The solution has been shown to reduce to the well-known Lamé's elastic solution and Nadai's general plane strain solution under appropriate assumptions. The influence of proportionality factor (ratio of axial strain to hoop strain) and hardening exponent on the induced strain, deformation fields and thickness reduction is systematically investigated. The formulation yields a singularity when the axial strain to hoop strain ratio is equal to ‘−2’. Based on the employed material parameters, power law constitutive model and proportionality factor, the maximum effective stress may occur at either the inside or outside of a tube shell. An equation to estimate ultimate internal pressure based on proportionality factor, material properties and tube geometry was derived. It is shown that maximum thickening occurs when the proportionality factor approaches ‘−2’.     

Thermal Buckling of Imperfect Deep Functionally Graded Spherical Shell

Thermal buckling analysis of deep imperfect functionally graded (FGM) spherical shell is considered in this paper. A mixture of ceramic and metal is considered for the FGM shell and the material properties, such as the modulus of elasticity and coefficient of thermal expansion, vary by a power law function through the thickness. Employing the Sanders non-linear kinematic relations, total potential energy function is derived and the equilibrium and stability equations are obtained for the imperfect shell. Approximate solutions satisfying the simply supported boundary condition are assumed and using the Galerkin method the error due to the approximation is minimized. The geometrically imperfect shell is considered and three types of thermal loadings, such as the uniform temperature rise (UTR), linear temperature rise through the thickness (LTR), and non-linear temperature rise through the thickness (NLTR) are considered and their associated buckling temperatures are obtained. The effects of different temperature functions and the magnitude of initial geometric imperfection are examined on the thermal buckling loads of the shell.