Improvements of heat resistance and adhesive property of condensed poly-nuclear aromatic resin via epoxy resin modification

A bisphenol epoxy resin was used as modifier to increase the heat resistance of condensed poly-nuclear aromatic （COPNA） resin. The basic properties of COPNA resin and modified resin were characterized by Fourier transform infrared spectroscopy （FT-IR）, nuclear magnetic resonance spectroscopy （1H-NMR）, vapor pressure osmometry （VPO） and elemental analysis （EA）. Average structural parameters of resins were calculated by the improved Brown-Ladner method, and heat resistance of resins was tested by thermogravimetric analysis （TGA）. The chemical structure, mechanical properties and heat resistivity of the resin/graphite composites prepared with different resins were compared. The results show that the adhesive property and heat resistance of COPNA resin can be remarkably improved by addition of 5 wt.% epoxy resin. The reason is that the reactions between epoxy groups of epoxy resin and hydroxyl groups of COPNA resin improve the heat resistance and adhesive property of COPNA resin. Electric motor brushes with good mechanical properties and low electrical resistivity were successfully prepared by using the modified resin as binder.

Thermal Radiation Effects on 2D Stagnation Point Flow of a Heated Stretchable Sheet with Variable Viscosity and MHD in a Porous Medium

This paper proposes a mathematical modeling approach to examine the two-dimensional flow stagnates at x=0 over a heated stretchable sheet in a porous medium influenced by nonlinear thermal radiation,variable viscosity,and MHD.This study’s main purpose is to examine how thermal radiation and varying viscosity affect fluid flow motion.Additionally,we consider the convective boundary conditions and incorporate the gyrotactic microorganisms equation,which describes microorganism behavior in response to fluid flow.The partial differential equations(PDEs)that represent the conservation equations for mass,momentum,energy,and microorganisms are then converted into a system of coupled ordinary differential equations(ODEs)through the inclusion of nonsimilarity variables.Using MATLAB’s built-in solver bvp4c,the resulting ODEs are numerically solved.The model’s complexity is assessed by plotting two-dimensional graphics of the solution profiles at various physical parameter values.The physical parameters considered in this study include skin friction coefficient,local Nusselt number,local Sherwood number,and density of motile microorganisms.These parameters measure,respectively,the roughness of the sheet,the transformation rate of heat,the rate at which mass is transferred to it,and the rate at which microorganisms are transferred to it.Our study shows that,depending on the magnetic parameter M,the presence of a porous medium causes a significant increase in fluid velocity,ranging from about 25%to 45%.Furthermore,with an increase in the Prandtl number Pr,we have seen a notable improvement of about 6%in fluid thermal conductivity.Additionally,our latest findings are in good agreement with published research for particular values.This study provides valuable insights into the behavior of fluid flow under various physical conditions and can be useful in designing and optimizing industrial processes.

Influence of Heating Temperature on Property of Low Chromium Wear Resistant Cast Iron Containing Rare Earth

The influence of heating temperature on mechanical properties of low chromium wear resistant cast iron containing rare earth elements was studied by means of metallographic examination, scanning electron microscopic examination and mechanical property test. The experimental results show that heating temperature has great effect on impact toughness (α_k), bending fatigue (σ_(bb)) and relative toughness (σ_(bb)×f), but little effect on hardness (HRC). When the specimen was held at 960 ℃ for 3 h, it has better comprehensive mechanical properties, and the reason and regularity of the change for mechanical properties of the cast iron were reviewed.

Solid-phase sintering process and forced convective heat transfer performance of porous-structured micro-channels

A solid-phase sintering process for the low-cost fabrication of composite micro-channels was developed. Three kinds of composite micro-channels with metallic porous structures were designed. The sintering process was studied and optimized to obtain porous-structured micro-channels with high porosity. The flow resistance and heat transfer performance in the composite micro-channels were investigated. The composite micro-channels show acceptable flow resistance, significant enhancement of heat transfer and dramatic improvement of flow boiling stability, which indicates a promising prospect for the application in forced convective heat transfer.

Heat Transfer and Acoustic Properties of Open Cell Aluminum Foams

The aluminum open cell foams have been prepared by the conventional precision casting method to investigate the thermal and acoustic properties.A water heating system and silencers were organized as a first step for its applications.The temperature increase between the top and bottom of the foam became larger as the cell size increased in the heat transfer measurement.Sound absorption ratio of the close cell foams was 60%-100%, whereas the open cell aluminum foam showed only 10%-20% of sound absorption at low frequency.When the prototype electric water heater manufactured by combining aluminum open cell foam with a heater was heated to 100-400℃,the highest temperature of water was in the range of 16-46~C.This suggests that there could be potential for this type of heater to be used as a commercial electric water heater.Sound silencer made with the aluminum open cell foam was applied to exit of exhaustion side at air pressure line.Sound silencing effect of open-celled aluminum foam showed that the noise level went down by introducing smaller cell size foam.

Coupled models of heat transfer and phase transformation for the run-out table in hot rolling

Mathematical models are been proposed to simulate the thermal and metallurgical behaviors of the strip occtLrring on the run-out table （ROT） in a hot strip mill. A variational method is utilized for the discretization of the governing transient conduction-convection equation, with heat transfer coefficients adaptively determined by the actual mill data. To consider the thermal effect of phase transformation during cooling, a constitutive equation for describing austenite decomposition kinetics of steel in air and water cooling zones is coupled with the heat transfer model. As the basic required inputs in the numerical simulations, thermal material properties are experimentally measured for three carbon steels and the least squares method is used to statistically derive regression models for the properties, including specific heat and thermal conductivity. The numerical simulation and experimental results show that the setup accuracy of the temperature prediction system of ROT is effectively improved.

Optimization of Dividing Wall Column with Heat Transfer Process Across the Wall for Feed Properties Variation

This paper investigates the thermal-coupled effect across the wall and the optimal heat transfer region of the wall for enhancing the energy saving effect of dividing wall column (DWC), and also studies the effects of feed thermal condition (q) and middle component composition of feed (cB) on the heat transfer process, the optimal heat transfer region, and the maximum heat transfer quantity across the wall. The simulation results show that the maximum heat transfer quantity across the wall and the potential for energy saving increase with the increase of q, while with the limitation of temperature difference across the wall, the beneficial heat transfer effect between certain range of stages, which are involved in the optimal heat transfer region, cannot be realized completely for a specific value of q. Besides, compared with q, a changing cB does not change the degree of realizing the beneficial heat transfer effect, but can bring about the variation of liquid split ratio (RL) and vapor split ratio (Rv). Thus, for achieving a maximum energy-saving effect of DWC, different q and cB need to find its own corresponding suitable heat transfer process across the wall.

Formation Mechanism and Existing Form of Sb in Heat Resistance Mg-Gd-Y-Sb Alloy

The existing form and reaction mechanism of Sb in heat resistane Mg-Gd-Y-Sb rare earth magnesium alloy were investigated by inductive coupled plasma emission spectroscopy(ICP),scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and X-ray diffraction(XRD).It is found that Sb tends to form high melting point intermetallics with rare earth elements of Gd and Y.The existing form of Sb is determined to be GdSb and SbY,respectively,which has high melting point(GdSb:2142℃/SbY:1782℃).Meanwhile,the first principle calculation and electronegativity difference calculation were performed to further understand the reaction mechanism.Therefore,the forming heat and binding energy were calculated.The experimental results show that the binding tendency of Sb element to Gd and Y is much stronger than that of it with other elements in this alloy,which results in the formation of high melting point of Gd-Sb and Y-Sb intermetallics,and finally leads to the high temperature resistant further improvement of the Mg-Gd-Y magnesium alloy.

Measurement of Thermophysical Property of Energy Storage System (CaCl₂&#46NH₃System)

In order to measure the thermophysical properties of ammoniated salt (CaCl2.mNH3: m = 4, 8) as an energy storage system utilizing natural resources, the measurement unit was developed, and the thermophysical properties (effective thermal conductivity and thermal diffusivity) of CaCl2.mNH3 and CaCl2.mNH3 with heat transfer media (Ti: titanium) were measured by the any heating method. The effective thermal conductivities of CaCl2.4NH3 + Ti and CaCl2.8NH3 + Ti were 0.14 - 0.17 and 0.18 - 0.20 W/(m.K) in the measuring temperature range of 290 - 350 K, respectively, and these values were approximately 1.5 - 2.2 times larger than those of CaCl2.4NH3 and CaCl2.8NH3. The effective thermal diffusivities were 0.22 - 0.24 × 10-6 and 0.18 - 0.19 × 10-6 m2/sin the measuring temperature range of 290 - 350 K, respectively, and these values were approximately 1.3 - 1.5 times larger than those of CaCl2.4NH3 and CaCl2.8NH3. The obtained results show that the thermophysical properties have a dependence on the bulk densities and specific heats of CaCl2.mNH3 and CaCl2.mNH3 + Ti. It reveals that the thermophysical properties in this measurement would be the valuable design factors to develop energy and H2 storage systems utilizing natural resources such as solar energy.

Structure and Property of AgLaY Alloy

The structure of RE-Ag alloy was observed and analyzed using electron probe. The property changes of the alloy containing two rare earth elements AgLaY during cold forming and the high temperature softening-resistance during annealing were studied using Vickers hardness tester. The distribution and action of the rare earth elements in Ag-alloy were also analyzed. Experimental results show that AgLaY alloy has more remarkable work-hardening effect than AgLa and pure silver, and it also has better thermal-resistance. The effects of RE elements, La and Y, on the properties of Ag-alloy are attributable to their symbiotic distribution and complementary function. Because of the common properties of La and Y as RE elements, they have the completely similar distribution in Ag-alloy. At the same time, La and Y make full use of complementary role in the alloy since they belong to different periods in periodic table and have differences in atomic structure and properties.

Microstructures and Thermal Properties of Sn–Bi–Zn–Ga Alloys as Heat Transfer and Heat Storage Materials

Low melting point alloy is a potential high-temperature heat transfer medium because of the high thermal conductivity, low solidus temperature and wide range of use temperature. Consequently, we investigated the possibility of using Sn-Bi-Zn-Ga alloys as heat storage and heat transfer material. Moreover, we investigated the microstructure and phase compositions by electron probe micro-analysis (EPMA) and X-ray diffusion (XRD). Results show that the new structures and phases are formed in the alloy matrix with Ga additions, which lead to the improvement of the thermal properties. An extensive thermophysical characterization of the Sn-Bi-Zn-Ga alloys has been performed by differential scanning calorimeter (DSC) analysis. The addition of Ga lowers the peak temperature and increases the heat capacity of the alloys. The thermal expansion of the test alloys increases with increasing temperature and the densities decreases with Ga additions. As the density, specific heat capacity and thermal diffusivity change with temperature and physical state, the thermal conductivity of the alloys first decreases and then increases. These results demonstrate the feasibility of using Sn-Bi-Zn-Ga alloys as the high-temperature heat transfer fluid.

Unsteady Heat Transfer in Bilayer,and Three-Layer Materials

The heat transfer equation is used to determine the heat flow by conduction through a composite material along the real axis.An analytical dimensionless analysis is implemented in the framework of a separation of variables method(SVM).This approach leads to an Eigenvalues problem that is solved by the Newton’s method.Two types of dynamics are found:An unsteady condition(in the form of jumps or drops in temperatures depending on the considered case),and a permanent equilibrium(tending to the ambient temperature).The validity and effectiveness of the proposed approach for any number of adjacent layers is also discussed.It is shown that,as expected,the diffusion of the temperature is linked to the ratio of the thermo-physical properties of the considered layers and their number.

Research of Inorganic Heat Transfer Element Starting Proprerty

This article studies the wall temperature distribution of inorganic heat transfer element in different working conditions by experiments, and analyzes the impact of inclination angle, heating power, different kinds of cooling medium and different inlet temperature of cooling medium on the starting property of inorganic heat transfer element.

Study on the heat resistance of 55% Al- Zn steel plates

Post-treated 55% Al-Zn steel plates, which have adequate mechanical properties and corrosion resistance ,are widely used for automobiles, household appliances, and other products. The heat resistance of 55% Al-Zn steel plates is slightly lower than that of aluminum plates or hot-dip aluminized steel plates, but their corrosion resistance is better. Herein,by testing at different baking temperatures and for different periods,the trends of color,gloss,and loss weight have been analyzed. The heat-resistant properties of differently post-treated 55% Al- Zn steel plates,aluminum plates,and hot-dip aluminized steel plates have been studied.

Current progress of research on heat -resistant Mg alloys: A review

With the increasing attention received by lightweight metals,numerous essential fields have increased requirements for mag-nesium(Mg)alloys with good room-temperature and high-temperature mechanical properties.However,the high-temperature mechanic-al properties of commonly used commercial Mg alloys,such as AZ91D,deteriorate considerably with increasing temperatures.Over the past several decades,extensive efforts have been devoted to developing heat-resistant Mg alloys.These approaches either inhibit the gen-eration of thermally unstable phases or promote the formation of thermally stable precipitates/phases in matrices through solid solution or precipitation strengthening.In this review,numerous studies are systematically introduced and discussed.Different alloy systems,includ-ing those based on Mg–Al,Mg–Zn,and Mg–rare earth,are carefully classified and compared to reveal their mechanical properties and strengthening mechanisms.The emphasis,limitations,and future prospects of these heat-resistant Mg alloys are also pointed out and dis-cussed to develop heat-resistant Mg alloys and broaden their potential application areas in the future.

Role of Heat Treatment Temperatures on Mechanical Properties and Corrosion Resistance Properties of Mg-10.16Li-8.14Al-1.46Er alloy

The microstructure and phase evolution of Mg-10.16Li-8.14Al-1.46Er alloy of as-cast,250℃+12 h,300℃+12 h,and 400℃+12 h were studied by optical microscopy,scanning electron microscope,and X-ray diffraction.The mechanical properties of Mg-10.16Li-8.14Al-1.46Er alloy in different states were tested by microhardness tester and tension tester.The corrosion resistance of Mg-10.16Li-8.14Al-1.46Er alloy in different states was measured by electrochemical workstation combined with hydrogen evolution and mass loss tests.The results show that the microstructure of as-cast Mg-10.16Li-8.14Al-1.46Er alloy consists ofα,β,AlLi,Al3Er and MgAlLi_(2)phases.Changes of microstructure are morphology and quantity ofαphase,and second phases of MgAlLi_(2)and AlLi by heat treatments at different temperatures.The best comprehensive tensile properties of Mg-10.16Li-8.14Al-1.46Er at 400℃are attributed to theαphase structure,solution strengthening and second phase strengthening.After heat treatments at different temperatures,the corrosion resistance of Mg-10.16Li-8.14Al-1.46Er was improved compared with as-cast samples.The Mg-10.16Li-8.14Al-1.46Er alloy has the best corrosion resistance at 250℃due to the best homogenization at this temperature.

Effect of Mn addition on microstructure and mechanical properties of GX40CrNiSi25-12 austenitic heat resistant steel

Three types of steels were designed on the basis of GX40CrNiSi25-12 austenitic heat resistant steel by adding different Mn contents(2wt.%,6wt.%,and 12wt.%).Thermodynamic calculation,microstructure characterization and mechanical property tests were conducted to investigate the effect of Mn addition on the microstructure and mechanical properties of the austenitic heat resistant steel.Results show that the matrix structure in all the three types of steels at room temperature is completely austenite.Carbides NbC and M_(23)C_(6)precipitate at grain boundaries of austenite matrix.With the increase of Mn content,the number of carbides increases and their distribution becomes more uniform.With the Mn content increases from 1.99%to 12.06%,the ultimate tensile strength,yield strength and elongation increase by 14.6%,8.0%and 46.3%,respectively.The improvement of the mechanical properties of austenitic steels can be explained by utilizing classic theories of alloy strengthening,including solid solution strengthening,precipitation strengthening,and grain refinement.The increase in alloy strength can be attributed to solid solution strengthening and precipitation strengthening caused by the addition of Mn.The improvement of the plasticity of austenitic steels can be explained from two aspects:grain refinement and homogenization of precipitated phases.

HTPB对PYX耐热炸药性能微观影响的分子动力学模拟

为了研究聚合物粘结剂羟基封端聚丁二烯(HTPB)对2,6-双(苦氨基)-3,5-二硝基吡啶(PYX)耐热炸药性能微观影响,基于分子动力学(MD)方法,在PYX的(011)晶面建立了PYX/HTPB的高聚物粘结炸药(PBX)模型,并对其结合能、内聚能密度、径向分布函数和力学性能进行了模拟.结果表明:PBX在298K时拥有最高的结合能,随着温度升高,结合能总体呈下降趋势;PYX和PBX的内聚能密度随着温度的升高而降低,且PBX的内聚能密度比PYX低20%左右;径向分布函数显示,PYX和HTPB分子间存在氢键和范德华力的共同作用;添加HTPB降低了PYX的刚度,并提高了其延展性.

Study and Application of Heat Treat ment of Multi-Element Wear-Resistant Low-Alloy Steel

The effects of heat treatment on the properties of multi element wear-resistant low-alloy steel （MLAWS） which is used to make the liner of rolling mill torus were researched. The results show that when quenching temperature is lower than 900℃, the hardness increases with the increase of temperature, and when quenching temperature is higher than 900℃, the hardness decreases with the increase of temperature. As quenching temperature is lower than 920℃, the effect of quenching temperature on the impact toughness is not obvious. When quenching temperature is higher than 920℃ , impact toughness decreases with the increase of temperature. When tempering temperature is higher than 450 ℃ , the hardness begins to decrease obviously. After tempering at 350℃, the best wear resistance was obtained. According to the service condition of rolling mill torus liner, the MLAWS is quenched from 900-920 ℃ and tempered at 350-370℃.

FLOW RESISTANCE AND HEAT TRANSFER CHARACTERISTICS OF A NEW-TYPE PLATE HEAT EXCHANGER

A new-type corrugation Plate Heat Exchanger （PHE） was designed. Results from both numerical simulations and experiments showed that the flow resistance of the working fluid in this new corrugation PHE, compared with the traditional chevron-type one, was decreased by more than 50%, and corresponding heat transfer performance was decreased by about 25%. The flow field of the working fluid in the corrugation PHE was transformed and hence performance difference in both flow resistance and heat transfer was generated. Such a novel plate, consisting of longitudinal and transverse corrugations, can effectively avoid the problem of flow path blockage, which will help to extend the application of PHEs to the situation with unclean working fluids.