OPTICAL-ELECTRONIC INSTRUMENT FOR MEASURING THE RADIATION COEFFICIENT AND TEMPERATURE OF THE CONTROLLED OBJECT

The operating principle of optoelectronic instruments for measuring the temperature of the heated products based on the measurement of the radiation flux from the heated product, which depends on the temperature and emissivity of the surface material. The main error of such optocal-electronic devices is the methodological component, which is due to the variability of the radiation coefficient of the surface of the product material. The radiation coefficient of an object depends on the material, the surface state of the material, and the temperature. In the measurement process, it is difficult to take this dependence into account, since there are no exact analytical expressions of these dependencies. In practice, the radiation coefficient of the surface of material the product is determined approximately using reference books. For a more accurate determination of the radiation coefficient, a preliminary study is necessary, which requires more complex equipment than a device for measuring the radiation flux from a heated body. To solve this problem, there are empirical generalized equations of the functional dependences of the radiation coefficient. The article analyzes the errors in determining the radiation coefficient using generalized equations in comparison with experimental data. The analysis indicates that the error in determining the radiation coefficient can reach large values that may not meet the requirements of consumers. To improve the accuracy of measuring the temperature of the object, a device has been developed that implements the method of sample signals. The developed device predetermines the radiation coefficient of the measured product at a certain temperature and introduces a correction when measuring the temperature.

Relationships between the Macrostructure Features and Acoustic Parameters of Resonance Spruce for Piano Soundboards

An experimental examination of the relationship between the macrostructure characteristics and the acoustic properties of Norway spruce was performed. The macrostructure features were found to comprise the density (ρ), percentage of latewood (%LW), slope of grain (α), and angle the annual rings in a cross section (β). The main acoustic parameters of the research were the sound velocity, dynamic Young’s modulus, acoustic impedance (Z), and radiation coefficient (R). The acoustic properties for both the cross section and the longitudinal direction were calculated. Non-destructive evaluation (NDE) is the appropriate approach to define acoustic properties. Ultrasonic direct transmission and a transitory excitation method were used to calculate and compare the acoustic properties. A modal analysis was performed to predict the frequency range that corresponded to the different mode shapes. There were no significant differences between the two methods, yet an 80% reduction of the velocity, Z and R was identified between the longitudinal direction and the cross section. The equations used to define acoustic radiation according to the latewood component were defined, and strong correlations between the macrostructure and acoustic parameters were confirmed. A tight relationship was observed between the reduction of sound velocity and material density exceeding 440 kg m−3.

Experimental and numerical investigation on the heat transfer of an automotive engine’s turbocharger

Measuring the temperature distribution in a complex and important engine part, such as a turbocharger, is essential for improving engine performance and efficiency. Heat transfer from the turbine to the compressor can strongly influence the turbocharger performance. One of the main measurement methods involves the installation of multiple K-type sensors. However, the location as well as the maximum and minimum temperatures of the turbocharger and the subsequent critical points may not be obtained by using sensors. In the current study, thermocouples, as well as an infra-red camera, are used to study the temperature distribution of the turbocharger housing in a spark ignition engine. A new method is introduced to determine the thermal radiation coefficient of the turbocharger housing by using a laboratory furnace and an infra-red camera. Together with experiments, the finite element method is used to find the temperature distribution in the turbocharger for all thicknesses. Comparing the temperature distribution obtained from simulation with experimental data, an acceptable level of agreement is observed. The location and temperature of the hottest area in experimental and numerical investigations are close to the waste gate. Temperatures using the finite element method for bearings exhibit maximum and minimum errors of 4.9% and 2.3%, respectively, indicating reasonable accuracy for the simulation.

What is the Trade-Off between Snowpack Stratification and Simulated Snow Water Equivalent in a Physically-Based Snow Model?

In Nordic watersheds, estimation of the dynamics of snow water equivalent (SWE) represents a major step toward a satisfactory modeling of the annual hydrograph. For a multilayer, physically-based snow model like MASiN (Modèle Autonome de Simulation de la Neige), the number of modeled snow layers can affect the accuracy of the simulated SWE. The objective of this study was to identify the maximum number of snow layers (MNSL) that would define the trade-off between snowpack stratification and SWE modeling accuracy. Results indicated that decreasing the MNSL reduced the SWE modeling accuracy since the thermal energy balance and the mass balance were less accurately resolved by the model. Nevertheless, from a performance standpoint, SWE modeling can be accurate enough with a MNSL of two (2), with a substantial performance drop for a MNSL value of around nine (9). Additionally, the linear correlation between the values of the calibrated parameters and the MNSL indicated that reducing the latter in MASiN increased the fresh snow density and the settlement coefficient, while the maximum radiation coefficient decreased. In this case, MASiN favored the melting process, and thus the homogenization of snow layers occurred from the top layers of the snowpack in the modeling algorithm.

ТЕПЛОФИЗИЧЕСКИЕ ХАРАКТЕРИСТИКИ И ТЕРМОЭРОЗИОННАЯ СТОЙКОСТЬ КЕРАМИЧЕСКОГО МАТЕРИАЛА НА ОСНОВЕ КАРБИДА БОРА

A study of the thermophysical characteristics, heat resistance, and thermal erosion resistance of high-temperature structural ceramics (SC), which was developed at NTUU "I. Sikorsky Kyiv Polytechnic Institute" under the supervision of Corresponding Member of the National Academy of Sciences of Ukraine, Professor P. I. Loboda was made. This high-temperature structural ceramics is intended for use in aerospace engineering, in particular - for the manufacture of aerodynamic surfaces of reusable hypersonic aircraft and heat-stressed elements of the gas-dynamic paths of their engines. The samples of B4C-SiC-B6Si ceramics of two compositions (No. 1 and No. 2) were studied, which differ in the mass content of the initial components. Temperature dependences of the specific heat and thermal conductivity of the spacecraft, radiation coefficient, heat resistance in an oxidizing environment, and the thermal erosion resistance in supersonic flow of combustion products of an air-kerosene fuel mixture were determined. The temperature dependence of the specific heat was determined using an IT-c-400 instrument (in the range of 40 °C - 440 °C) and by the calculation of the temperature dependences of the specific heat capacity of the system components following the Reno rule (up to 2100 °C). The temperature dependence of the thermal conductivity coefficient of the SC of composition No. 1 was determined by solving the inverse heat conduction problem on a computer model based on experimental data. Temperature fields and heat fluxes were obtained under conditions of one-sided heat-ing with a reducing flame of a propane-oxygen welding burner. The thermal conductivity coefficient of SC composition No. 1 increases from 11 W/(m×K) at 20 °С to 25 W/(m×K) at 1400 °С. Its radiation coefficient in the temperature range 1000 °С - 1400 °С is ε = 0.96 ± 0.02. Heat resistance of SC of both compositions in the oxidizing flame of an oxygen welding burner at a surface temperature of 1400 °C has demonstrated that after two hours of heating, the average values of mass ablation for the two tested samples of compositions №1 and № 2 respectively 2.1% and 1.4% (a sample thickness of 4 mm). Tests in the supersonic flow of combustion products at the same surface temperature confirm the high resistance of the material to thermoerosion in the oxidizing medium. The change in the morphology of the heated surface of the sample after six five-minute heating cycles was manifested only by an increase in its roughness without visible oxidation. High thermal conductivity, heat and thermoerosion resistance, radiation coefficient of the studied SC at a temperature of 1400 °C in combination with low density (2.7 g / cm3) make this high-temperature structural material of aerospace technology promising for use.

Reduced emissivity – a factor for the accuracy in pyrometric measurements

The problem of accuracy of pyrometric measurements connected with convergence of indications of various pyrometers is considered. Theoretically justified observed in the practice of pyrometric measurements over estimation of the measured temperature and the discrepancy between the readings of different pyrometers. The reason for the discrepancy in the readings is the use of an approximate calculation ratio for the reduced radiation coefficient in the pyrometric measurement equation. The conditions of application of this equation are formulated. The results of calculations of the reduced radiation coefficient are given and practical recommendations for improving the accuracy of pyrometric measurements are given.

Indonesian Wood as Material for Acoustic Guitars and Violins

Traditionally, acoustic guitars and violins are made from European woods. Spruce is most preferred for the top plate (soundboard), whereas maple, sycamore and rosewood are often used for the back plate. However, these woods are not easily available in Indonesia. In this paper, we present a study on the suitability of a selection of Indonesian woods, namely acacia, mahogany, pine, sengon and sonokembang, as materials for acoustic guitars and violins. The most important acoustical properties for selecting materials for musical instruments, i.e. the speed of sound, the sound radiation coefficient and the damping factor, were investigated. Furthermore, the performance of pine and mahogany were tested by making them into a violin and a guitar. The vibration frequency spectrum and the damping factor of the top plate were measured. The results show that the acoustical characteristics of mahogany are very close to those of maple and still quite close to those of Indian rosewood, which makes it a very suitable local material for back plates. Pine has quite similar acoustical characteristics to spruce. Although its sound radiation coefficient is slightly lower, its aesthetic appeal and workability makes pine a suitable alternative for top plates. However, instruments with pine top plates exhibit different tonal colour compared to instruments with spruce top plates, due to some differences in the vibration frequency spectrum. Furthermore, the generally higher damping factors of pine and mahogany compared to those of the European woods should be taken into account, because they affect the sustain-time of the generated sound.

An alternative approach to thermal analysis using inverse problems in aluminum alloy welding

Purpose The purpose of this article is the determination of the temperature fields in a weld region has always been an obstacle to the improvement of welding processes. As an alternative, the use of inverse problems to determine the heat flux during the welding process allows an analysis of these processes. Design/methodology/approach This paper studies an alternative for the thermal analysis of the tungsten inert gas welding process on a 6,060 T5 aluminum alloy. For this purpose, a C++ code was developed, based on a transient three-dimensional heat transfer model. To estimate the amount of heat delivered to the plate, the specification function technique was used. Lab experiments were carried out to validate the methodology. A different experimental methodology is proposed to estimate the emissivity (radiation coefficient). Findings The maximum difference between experimental and numerical temperatures is lower than 5 per cent. The determined emissivity value for the aluminum 6,060 T5 presented a good agreement with literature values. The thermal fields were analyzed as function of the positive polarity. The specification function method proved to be an adequate tool for heat input estimation in welding analysis. Originality/value The proposed methodology proves to be a cheaper way to estimate the heat flux on the sample. The estimated power curves for the welding process are presented. The methodology to calculate the emissivity (radiation coefficient) was validated.