Modeling the effects of calcination conditions on the physical and chemical properties of transition alumina catalysts

Calcination variables, temperature, time and heating rate, used in obtaining different transition aluminas were simultaneously investigated using statistical experimental design. Empirical models correlating catalyst final properties and calcination conditions were employed. It was found that all calcination variables play fundamental roles on textural properties and on acidity of alumina catalysts. Furthermore, interaction effects among these variables and the non-linear effects are also of fundamental importance for the catalyst final properties. Therefore, the use of simultaneous variation of calcination conditions through experimental design is of great significance in detecting such interactions, when compared to the traditional change one variable at a time procedure. It was observed that the use of high heating rates favor the formation of pore with larger diameters and with higher pore volume and, for short calcination time, high heating rate also contributes to the formation of higher concentration of acid sites. Therefore, a successful control of all calcination conditions can be an effective method to adjust the final physical and chemical properties of transition alumina catalysts.     

The role of microcrystalline structure on optical scattering characteristics of semi-crystalline thermoplastics and the accuracy of numerical input for IR-heating modeling

Infrared (IR) heating is widely used for thermoforming of thermoplastic polymers. The key benefit of radiation heating is that a significant amount of the radiative energy penetrates into the polymers thanks to their semi-transparency. For the case of heating unfilled semi-crystalline polymers, the relation between their microcrystalline structure and optical properties is the key to develop a predictive IR-heating model as microcrystalline structure introduces an optically heterogeneous medium. In this study, a relation between the microcrystalline structure of a polyethylene (PE) and its effect on the thermo-optical properties was experimentally analyzed considering a two-step analysis. At very first step, the relation was analyzed considering samples with identical thicknesses and different morphologies, characterized here in terms of degree of crystallinity (X_c (%)). Using Fourier Transform Infrared (FT-IR) spectroscopy and integrating sphere, optical characteristics of the PE samples were analyzed in near-infrared (NIR) and middle-infrared (MIR) spectral ranges. The analyses showed that a slight variation in X_c (%) has a great effect on the optical characteristics of PE, particularly the transmission characteristics in NIR range. The wavelength-dependent effect of X_c (%) on the transmission behaviors opened a discussion about the fact that the microcrystalline structures -in particular spherulites or their substructures such as lamellae- are responsible for optical scattering. Using the optical properties obtained from the two-step experimental analyses, two different thermo-optical properties were calculated, namely extinction and absorption coefficients, and used as a numerical input for the parametric numerical studies. The numerical studies were performed using an in-house developed radiation heat transfer algorithm -RAYHEAT-. Both the experimental and numerical analyses demonstrated the importance of the optical scattering regarding the identification of thermo-optical properties, used as a numerical input for radiation heat transfer models.     

Fast heating and melting of alumina under the effect of concentrated laser radiation

The results are given of calculations of temperature fields in a plane layer of Al₂O₃ crystal under conditions of combined radiative-conductive energy transfer under fast heating by concentrated radiation of a CO₂ laser with the formation of a thin layer of melt on the surface. Experiments are performed in the heating of ceramic samples of Al₂O₃ and samples remelted from Al₂O₃ powder; in these samples, the intensities of outgoing radiation and the reflectivity are measured for different wavelengths. The experimental results are compared with the calculation results. It is demonstrated that the adopted mathematical model, which fails to reflect the important part played by kinetics in the abrupt variation of the absorption coefficient in Al₂O₃ melt, needs to be refined.     

Specific Heat Capacity of Liquid Zirconium up to 4100 K

The temperature dependence of the specific heat capacity of liquid zirconium is investigated experimentally at atmospheric pressure and at temperatures from 2128 to 4100 K. Measured under conditions of pulsed (microseconds) electric heating of foil samples are the electric resistance, the specific energy input (equal to specific enthalpy E), and the temperature (with the aid of a high-speed pyrometer and solid-state light guide). Use is made of the specific enthalpy dependence of temperature, previously obtained [1] for two options of blackbody model, developed for investigation of liquid carbon. The first one of those models is a square tube made up of four zirconium strips, with the light guide introduced at the tube end. The second model is made up of two strips of zirconium, with the light guide introduced on the side into the gap between the two strips (two-strip blackbody model). The temperature dependence of the heat capacity of liquid zirconium up to 4100 K is given for both blackbody models. The random and systematic errors of the measured quantities are given. The values of specific heat capacity are compared with the available experimental data for the near melting stage of the liquid zirconium, obtained using a steady-state technique.     

T型圆钢管节点抗火性能的有限元研究

利用有限元软件ABAQUS建立T型圆钢管节点模型,采用间接热力耦合的方法,研究了节点在ISO834标准升温环境和不同荷载条件下的抗火性能。根据试验建立验证模型,将分析得到的结果与试验结果进行对比。通过比较,验证了模型的可靠性。在此基础上,建立管节点抗火模型,通过分析主管变形和主管端部轴向反力随温度变化曲线,以及管节点的失效机理,得到不同荷载比和节点的几何参数对节点抗火性能的影响。     

Facility for integrated studies of thermophysical characteristics of electrically conducting materials by the method of subsecond resistance heating

An experimental facility for the investigation of temperature dependence of the thermophysical properties of structural materials is described. The enthalpy, heat capacity, electrical resistance, and integral and spectral emissivities are determined under conditions of heating modes with rates of the order of 10³—10⁴ K/s. Special attention is given to the problems of optimization of geometry and size of samples depending on the concrete investigation problem.     

Computer modeling of temperature field in sintering carbide composites using induction and radiation heating

A computer model has been elaborated for the temperature field in a high-temperature furnace for sintering ceramic powder samples under induction and radiation heating conditions. For numerical solution of the set of equations describing the induction and radiation heating processes a finite-element method is used in combination with a finite-difference procedure in time, which is based on Newton-Raphson technique, and a radiosity method is used in modeling the radiation heat transfer. The temperature field in the furnace in the process of sintering has been numerically studied. The numerical results are compared to the data of temperature measurements at the infiltrator surface during the sintering of a composite blend with a silicon-carbide matrix. Based on the agreement between the calculated and experimental results, the computer model is inferred to be adequate.     

An in-vitro study of the effects of temperature on breast cancer cells: Experiments and models

This paper presents an implantable biomedical device for the localized killing of cancer cells through hyperthermia. Heating, accomplished via resistive heating, is modeled using numerical heat transfer techniques, which are tested under experimental conditions. The effect of temperature in the therapeutic domain of 37 to 45 °C as studied on breast cancer cell line MDA-MB-231 is also reported. The results show the predicted temperature variations are consistent with temperature measurements obtained from the experimental set-ups. The paper also examines the effects of isothermal heating on the cell morphology. Isothermal heating is shown to cause significant physical changes in the cell cytoskeleton. Finally, the paper explores the effects of hyperthermia on cell growth and cell death under isothermal and cyclic conditions. The underlying effects of heat shock protein expression are elucidated before discussing the implications of the results for cancer treatment via localized hyperthermia.     

低温陈化法制备纳米ZrO2及条件对粒径的影响

为了制得可控粒径的ZrO2粉并提高其均匀性,采用低温陈化法合成了ZrO2纳米粉,并讨论了反应条件对样品粒径的影响.通过DTA,XRD,TEM和粒度分布仪等检测手段对产品进行了表征.结果表明:在500℃得到了晶化较好的单斜相ZrO2,选择适当的合成条件:控制Zr4+与CO(NH2)2的摩尔比为1∶3,溶液pH为1.5,加入少量聚乙二醇800(PEG-800),可得到粒度分布集中,均匀性较好,粒径约为24.4 nm的样品.该法工艺简单、得到的ZrO2粉体粒径分布较窄.     

Zirconium Temperature Measurements from the Melting Point to 4100 K Involving the Use of Blackbody Models in the Liquid State

The temperature (2128–4100 K) dependence of specific enthalpy Eat atmospheric pressure is obtained under conditions of fast (microseconds) pulsed electric heating of zirconium foil samples. The enthalpy dependence of the spectral density of radiation at the wavelength of 0.855 m is measured for flat surfaces and for two blackbody models made of zirconium foil. The temperature is calculated by Planck's formula. The temperature plateau on the curve of the dependence of Ton Ein the melting of zirconium is used for calibration, and the value of the plateau temperature is taken to be equal to the equilibrium melting point of 2128 K. The blackbody models are assembled of separate flat strips of zirconium. The objective of this study is to develop and experimentally verify a blackbody model suitable for both metals and graphite and to derive the temperature dependence of the thermal properties of liquid metals and liquid carbon at high temperatures under conditions of fast pulsed heating. A Tektronix TDS 754C four-channel digital oscilloscope was used in the measurements.     

一种智能化热能测量仪

本根据热力学理论,建立了高精度、宽范围水蒸汽力学状态参数数学模型;分析了相应的测量技术问题;介绍了以８０９８单片机为数据处理核心的智能化热能测量仪的硬件结构和与软件设计。实验结果表明：该仪器是一种多功能综合性智能仪器,其测量精度优于０．５％。     

Thermophysical Properties of Diorites along with the Prediction of Thermal Conductivity from Porosity and Density Data

The main focus of this paper involves the use of models to predict the thermophysical properties of diorites. For the prediction of thermal conductivity, an existing mixing law and empirical models have been used. Due to the porosity dependence in all the existing models, ASTM (American Society for Testing and Materials) standard methods have been applied to measure the density, porosity, and specific gravity of diorite rocks taken from the Shewa-Shahbaz Garhi volcanic complex near Mardan, Pakistan. The chemical composition of these samples has been analyzed using the X-ray florescence technique. The theoretically calculated values of specific gravity and the density of the specimen based on the chemical composition and porosity are in good agreement with those obtained from experimental measurements at ambient conditions. The thermal conductivity and thermal diffusivity of these rocks have been measured simultaneously using the transient plane source (TPS) technique at room temperature. The effective thermal conductivity calculated from various models is in agreement with the experimental data within 15%. Simple correlations between estimated density and porosity and between the effective thermal conductivity and porosity are also established.     

Modelling the tension and compression strengths of polymer laminates in fire

Thermo-mechanical models are presented for predicting the time-to-failure of polymer laminates loaded in tension or compression and exposed to one-sided radiant heating by fire. Time-to-failure is defined as the time duration that a polymer laminate can support an externally applied load in a fire without failing. The models predict the temperature rise and through-thickness temperature profile in a hot decomposing laminate exposed to fire. Using this thermal data, mechanics-based models based on residual strength analysis are used to calculate the time-to-failure. A preliminary evaluation of the accuracy of the models is presented using failure times measured in fire-under-load tests on a woven glass/vinyl ester laminate. The model was evaluated at temperatures between ∼250 and 800 °C by testing the laminate at heat flux levels between 10 and 75 kW/m². It was found that the time-to-failure of the laminate decreased with increasing heat flux and increasing applied stress for both the compression and tension load conditions. The tests also revealed that the failure times were much shorter (by about one order of magnitude) when the laminate was loaded in compression. The models can predict the time-to-failure with good accuracy for both compression and tension loading for certain heat flux levels. However, because the models have only been evaluated for one type of laminate (woven glass/vinyl ester), further evaluation is necessary for other laminate systems. The paper also presents new experimental insights into the strengthening mechanisms of laminates at high temperature.     

Testing of Thermal Barrier Coatings by Laser Excitation

Thermal barrier coatings (TBCs) are used to increase the operating temperature of land‐, sea‐, or air‐based turbines. As failure of the coating may result in serious damage of the turbine, reliable estimation of the lifetime is essential. Most experiments to assess the lifetime or to determine parameters for simulations of the behavior of TBCs are done by burner‐rig‐tests, where the operating conditions are simulated by cyclic heating of the surface and cooling of the backside of a coated sample. In this work a possibility is presented to do comparable experiments by heating the surface with laser irradiation instead of a burner. For this purpose a Nd:YAG‐laser with a maximum output power of 1 kW and a wavelength of 1064 nm is used. The laser spot can be moved by integrated optics across the sample surface to achieve homogeneous heating of the coating. Cooling of the backside is done by air. The temperature of the sample surface is determined by an infrared‐camera which also enables the possibility to detect failures in the coating via thermography. Additionally, acoustic sensors attached to the sample holder are used to detect failures in the sample. The investigated ceramic material (yttria stabilized zirconia) has a very low absorption coefficient at the used laser wavelength. Therefore, a pre‐treatment of the samples was needed to increase the absorption coefficient to be able to heat up the samples. In this paper, the experimental setup and first experimental results are presented.     

The influence of correlated calibration samples on the prediction performance of multivariate models based on mid-infrared spectra of animal cell cultures

The effect of the presence of metabolism-induced concentration correlations in the calibration samples on the prediction performance of partial least-squares regression (PLSR) models and mid-infrared spectra from Chinese hamster ovary cell cultures was investigated. Samples collected from batch cultures contained highly correlated metabolite concentrations as a result of metabolic relations. Calibrations based on such samples could only be used to predict concentrations in new samples if a similar correlation structure was present and failed when the new samples were randomly spiked with the analytes. On the other hand, such models were able to predict glucose correctly even if they were based on a spectral range in which glucose does not absorb, provided that the correlations in the calibration and in the new samples were similar. If however, samples from a calibration culture were randomly spiked with the main analytes, much more robust PLSR models resulted. It was possible to predict analyte concentrations in new samples irrespective of whether the correlation structure was maintained or not. Validity of all established models for any given use could be predicted a priori by computing the space inclusion and observer conditions. Predictions from these computations agreed in all cases with the experimental test of model validity.     

Semianalytic method for heat transfer calculation in the liquid film under conditions of a constant heat flux on the wall

For calculating the heat transfer in the free-falling liquid film, a semianalytic method is offered in which the temperature field in the liquid is presented as a series of basis functions which satisfies boundary conditions. The proposed method is demonstrated by the example of the problem regarding the film heating under conditions of the constant heat flux on the wall taking into account the heat transfer on the interfacial surface. The analytical solution is derived for the thermal initial section, on which the liquid heating occurs in a thin layer near the wall. Calculations using the proposed method are well agreed with the numerical solution obtained by the finite-difference method and with experimental data.     

Temperature Dependence of the Density and Electrical Resistivity of Liquid Zirconium up to 4100 K

Experimental data on the temperature dependence of the density of liquid zirconium and its electrical resistivity are obtained under conditions of pulsed electric heating (for 5 to 10 s) of wire and foil zirconium samples. Samples in the form of a wedge-shaped blackbody model are prepared for use in temperature measurements. The thermal radiation from the model space is registered by a high-speed optical pyrometer at a wavelength of 855 nm. The temperature (up to 4100 K) is calculated by Planck's formula. The temperature plateau in the melting region of the blackbody model is used for calibration of the pyrometer. In so doing, it is assumed that this plateau has the equilibrium melting temperature of 2128 K. A digital oscilloscope is used for recording the current through the sample, the voltage across the sample, and the pyrometer signal. The density of zirconium is determined using the laser flash method while heating zirconium wires. The sample is illuminated by a Q-switched Nd-YAG laser. A CCD video camera is used for photographing. The experimental data on the density and electrical resistivity of liquid zirconium are essential for simulation of the behavior of nuclear power plants in the case of a serious emergency.     

Thermal wave interferometry for measuring the thermal diffusivity of thin slabs

Thermal wave interferometry applied to the evaluation of thermal diffusivity of freestanding coatings and single layers is herewith presented. Measurements on a set of eight different materials (oxides free copper, an aluminium alloy, Armco iron, AISI 316 stainless steel, Nimonic90 and IN738 nickel based alloys and Yttria partially stabilised Zirconia coatings) have been carried out. The corresponding thermal diffusivity values cover a very large range (about three order of magnitude). A comparison of 1D and 3D models has been done in order to optimise the main measurement parameters. Sample thickness, heating beam size and modulation frequency range have been selected in order to maximise the photothermal signal and its phase variation as a function of the frequency. Experimental results give evidence of a very good agreement between literature and experimental values for all samples confirming the capability of this technique for measuring the thermal diffusivity of thin slabs.     

Pulse method of measuring the thermal diffusivity of spherical samples

Consideration is given to a version of the pulse method of measurement of the thermal diffusivity of spherical samples with the use of laser heating. The method is based on solution of the heat-conduction equation in a spherical coordinate system. The computerized experimental setup used is described. Measurement results for the thermal diffusivity of Zr, Ni, Fe, Al are reported. The measurement error is no more than 5%.