scholarly journals Structure and wear of gradient steel castings

2021 ◽  
Vol 100 (4) ◽  
pp. 16-23
Author(s):  
S.Ye. Kondratyuk ◽  
◽  
V.I. Veis ◽  
Z.V. Parkhomchuk ◽  
V.A. Loktyonov-Remyzovskii ◽  
...  
Keyword(s):  
Grain Size ◽  
Removal Rate ◽  
Heat Removal ◽  
Operating Conditions ◽  
Fine Crystal ◽  
Cross Sectional ◽  
Cast Structure ◽  
Steel Castings ◽  
Differential Properties ◽  
Structural Zones

The effect of overheating of the melt over the equilibrium liquidus in the temperature range 1570 °C – 1670 °C and the rate of its cooling during crystallization and structure formation of castings on the formation of the length and morphology of the main macrostructural zones, grain dispersion, characteristics of the fine crystal structure, hardness and intensity of abrasive wear over the section of 25L steel castings with a differentiated cast structure was investigated. Regular changes of these indicators depending on thermokinetic conditions of crystallization are established. The determining influence of the melt cooling rate on the morphology and dispersion of the cast structure due to different degrees of melt supercooling during crystallization of different structural zones of castings is shown. As the distance from the rapidly cooling surface of the castings and taking into account the increase in the temperature of the melt overheat from 1570 ºC to 1670 ºC, the grain size varies from 5… 7 numbers to 1… 2 numbers, respectively. In the case of normal heat removal rate during crystallization, the grain size in the castings varies from 4… 2 to -1… -2 numbers. The determined characteristics of wear resistance of steel in different structural zones correlate with changes in the characteristics of the cast structure and the cross-sectional strength of castings. The research results open the prospect of developing new foundry technologies for the production of cast products with differential properties for special operating conditions. Keywords: gradient structure, structural zones, melt, wear.

Design of a Microscale Breather for Two-Phase Thermal Management Devices

2008 ◽  
Author(s):  
B. R. Alexander ◽  
E. N. Wang
Keyword(s):  
Phase Change ◽  
Removal Rate ◽  
Heat Removal ◽  
Design Guidelines ◽  
Heat Sinks ◽  
Two Phase ◽  
Cross Sectional ◽  
Optical Visualization ◽  
Gas Removal ◽  
Microchannel Heat Sinks

Two-phase microchannels promise an efficient method to dissipate heat from high performance electronic systems by utilizing the latent heat of vaporization during the phase-change process. However, phase-change in microchannel heat sinks leads to challenges that are not present in macroscale systems due to the increasing importance of surface tension and viscous forces. In particular, flow instabilities often occur during the boiling process, which lead to liquid dry-out in the microchannels and severely limits the heat removal capabilities of the system. We propose a microscale breather device consisting of an array of hydrophobic breather ports which allow vapor bubbles to escape from the microchannels to improve flow stability. In this study, we use the combination of microfabricated structures and surface chemistry to separate vapor from the liquid flow. We designed test devices that allow for cross-sectional optical visualization to better understand the governing parameters of a breather design with high vapor removal efficiencies and minimal liquid leakage. We examined breather devices with average liquid velocities ranging from 0.5 cm/s to 4 cm/s and breather vacuum levels between 1 kPa and 9 kPa on the maximum gas removal rate through the breather. We demonstrated successful breather performance. In addition, a model was developed that offers design guidelines for future integrated breathers in microchannel heat sinks. The breathers also have significant promise for other microscale systems, such as micro-fuel cells, where liquid-vapor separation can significantly enhance system performance.

scholarly journals Cooling Performance of a Novel Circulatory Flow Concentric Multi-Channel Heat Sink with Nanofluids

Nanomaterials ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 647 ◽  
Author(s):  
Ravindra Jilte ◽  
Mohammad H. Ahmadi ◽  
Ravinder Kumar ◽  
Vilas Kalamkar ◽  
Amirhosein Mosavi
Keyword(s):  
Heat Sink ◽  
Volume Fraction ◽  
Removal Rate ◽  
Heat Removal ◽  
High Heat ◽  
Operating Conditions ◽  
Bottom Surface ◽  
Outlet Temperature ◽  
Cooling Performance ◽  
Heat Rejection

Heat rejection from electronic devices such as processors necessitates a high heat removal rate. The present study focuses on liquid-cooled novel heat sink geometry made from four channels (width 4 mm and depth 3.5 mm) configured in a concentric shape with alternate flow passages (slot of 3 mm gap). In this study, the cooling performance of the heat sink was tested under simulated controlled conditions.The lower bottom surface of the heat sink was heated at a constant heat flux condition based on dissipated power of 50 W and 70 W. The computations were carried out for different volume fractions of nanoparticles, namely 0.5% to 5%, and water as base fluid at a flow rate of 30 to 180 mL/min. The results showed a higher rate of heat rejection from the nanofluid cooled heat sink compared with water. The enhancement in performance was analyzed with the help of a temperature difference of nanofluid outlet temperature and water outlet temperature under similar operating conditions. The enhancement was ~2% for 0.5% volume fraction nanofluids and ~17% for a 5% volume fraction.

Effect of Two-Liquid Casting on the Microstructure of Sn-Pb Alloys

2010 ◽  
Vol 649 ◽  
pp. 415-418 ◽  
Author(s):  
Y.K. Kim ◽  
Rong Shan Qin
Keyword(s):  
Heat Transfer ◽  
Grain Size ◽  
Experimental Validation ◽  
Alloy Composition ◽  
Liquid Surface ◽  
Removal Rate ◽  
Heat Removal ◽  
Homogeneous Liquid ◽  
The Given

Traditional casting usually solidifies one homogeneous liquid by removing heat from liquid surface, by which the microstructure solely depends on the heat removal rate for the given alloy composition. The newly developed two-liquid composite simultaneous casting concept raises an alternative to control microstructure. The concept introduces the solidification while mixing technique so that the microstructure depends not only on the heat-removing from liquid surface but also the heat transfer from one liquid to another. The paper reports the experimental validation of the concept by two-liquid casting of Sn-Pb alloys. Reduced grain size, increased microhardness, rougher and more fractal grain surfaces are observed for the alloy solidified by two-liquid casting in comparison of the microstructure obtained by conventional solidification techniques.

scholarly journals Gradient structure and properties of steel castings

2021 ◽  
Vol 99 (3) ◽  
pp. 3-14
Author(s):  
S.Ye. Kondratyuk ◽  
◽  
V.I. Veis ◽  
Z.V. Parkhomchuk ◽  
G.I. Shevchenko ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Cooling Rate ◽  
Linear Regression Analysis ◽  
Dendritic Structure ◽  
Heat Removal ◽  
Decisive Role ◽  
Factor Space ◽  
Gradient Structure ◽  
Steel Castings ◽  
Structural Zones

The influence of melt overheating in the range of 50-150 °C on the equilibrium liquidus and its cooling rate during crystallization of castings on the formation of macrostructural zones along their cross section, on the change of grain dispersion, dendritic structure characteristics and mechanical properties was investigated on the example of 25L steel. It is established that the macrostructure of castings in the direction of unilateral heat removal as it moves away from the cooled surface consists of four main structural zones - small coaxial crystals, columnar, branched and large coaxial crystals, the length and morphology of which naturally change depending on thermokinetic conditions of crystallization. The decisive role of the cooling rate at significant overheating of the melt to increase the number of crystallization nuclei, the formation of a more dispersed cast structure by increasing the degree of supercooling of the melt during crystallization is shown. The regularities of quantitative characteristics change of microstructure and dendritic structure depending on change of temperature-time parameters of crystallization in different structural zones of castings and their connection with characteristics of mechanical properties of steel are established. On the basis of mathematical processing of experimental data by linear regression analysis interpolation models and their graphical interpretations are obtained, which allow to quantify and predict the change of mechanical properties in different structural zones of gradient castings depending on melt overheating temperature and cooling modes within the investigated factor space. Keywords: gradient structure, structural zones, melt, mechanical properties.

Structure formation and properties of overheated steel depending on thermokinetic parameters of crystallization

2019 ◽  
Vol 2 (97) ◽  
pp. 49-56
Author(s):  
S.Ye. Kondratyuk ◽  
V.I. Veis ◽  
Z.V. Parkhomchuk
Keyword(s):  
Mechanical Properties ◽  
Cooling Rate ◽  
Structure Formation ◽  
Quantitative Assessment ◽  
Mutual Influence ◽  
Structural Characteristics ◽  
Heat Removal ◽  
Melt Temperature ◽  
Cast Structure ◽  
Steel Castings

Purpose: The aim of the proposed research is to investigate the mutual influence of the temperature of an overheated melt and its cooling rate during crystallization on the formation of the cast structure and mechanical properties of structural steels. Design/methodology/approach: Two structural medium-carbon steels were melted in induction furnace and poured from temperatures 1520-1670°C into casting moulds with different heat removal ability. This ensured the crystallization and structure formation of the studied steel castings at cooling rates (Vc) of 5°C/sec (sand-clay mould), 45°C/sec (steel mould), 350°C/sec (water cooled copper mould). It was studied a change of structure formation, mechanical characteristics depending on the temperature-kinetic conditions of the processing of the melt. Based on the processing of the array of obtained experimental data using linear regression analysis and a software package, interpolation models and their graphic images obtained allow a quantitative assessment of the established patterns of structural characteristics and mechanical properties of the studied steels depending on melt temperature (T, °C) and its cooling rate (Vc, °C/sec) during crystallization and structure formation. Findings: Among the technological factors that determine the formation of the cast structure and the mechanical properties of steels, the dominant role is played by the intensity of heat removal during the solidification of castings. The high cooling rate of the melt during crystallization determines an increase in the number of crystallization nuclei due to an increase in the degree of supercooling of the melt, eliminates the negative effect of the high overheating temperature of the metal before casting. Research limitations/implications: In the future, the results can be complemented by studies of the influence of the duration of isothermal exposure of the melt at different temperatures of superheating and cooling conditions. Practical implications: The obtained mathematical models (regression equations) that determine the mutual influence of the cooling rate and the temperature of the melt overheating on the structure and mechanical properties of the studied steels make it possible to obtain steel castings with predetermined properties at the level of properties of wrought steel of similar chemical composition. Originality/value: Interpolation models that allow a quantitative assessment of the established patterns of structural characteristics and mechanical properties of the studied steels depending on the melt temperature (T, °C) and its cooling rate (Vc, °C/sec) during crystallization and structure formation are obtained.

Trends in the development of flexible thermal protection systems for modern aircraft

2020 ◽  
pp. 10-21
Author(s):  
V. G. Babashov ◽  
◽  
N. M. Varrik ◽  
Keyword(s):  
High Temperature ◽  
Thermal Protection ◽  
Heat Removal ◽  
Operating Conditions ◽  
Passive Protection ◽  
Thermal Protection Systems ◽  
Heat Protection ◽  
Protection Systems ◽  
Protected Surface ◽  
Flexible Panels

The emergence of new types of space and aviation technology necessitates the development of new types of thermal protection systems capable of operating at high temperature and long operating times. There are several types of thermal protection systems for different operating conditions: active thermal protection systems using forced supply of coolant to the protected surface, passive thermal protection systems using materials with low thermal conductivity without additional heat removal, high-temperature systems, which are simultaneously elements of the bearing structure and provide thermal protection, ablation materials. Heat protection systems in the form of rigid tiles and flexible panels, felt and mats are most common kind of heat protecting systems. This article examines the trends of development of flexible reusable heat protection systems intended for passive protection of aircraft structural structures from overheating.

Validation of mathematical model of electrothermal calculation of DC catenary on the basis of scale model

2018 ◽  
Vol 77 (4) ◽  
pp. 222-229 ◽  
Author(s):  
A. V. Paranin ◽  
A. B. Batrashov
Keyword(s):  
Mathematical Model ◽  
Operating Conditions ◽  
Scale Model ◽  
Contact Network ◽  
Scaled Model ◽  
Cross Sectional ◽  
Current Collection ◽  
Topological Features ◽  
Study Results ◽  
Real Physical Process

The article compares the results of calculation of the finite element simulation of current and temperature distribution in the scale model of the DC catenary with the data of laboratory tests. Researches were carried on various versions of the structural design of catenary model, reflecting the topological features of the wire connection, characteristic of the DC contact network. The proportions of the cross-sectional area of the scaled model wires are comparable to each other with the corresponding values for real DC catenary. The article deals with the operating conditions of the catenary model in the modes of transit and current collection. When studying the operation of the scale catenary model in the transit mode, the effect of the structural elements on the current distribution and heating of the wires was obtained. Within the framework of the scale model, theoretical assumptions about the current overload of the supporting cable near the middle anchoring have been confirmed. In the current collection mode, the experimental dependences of the current in the transverse wires of the scale model are obtained from the coordinate of the current collection point. Using the model it was experimentally confirmed that in the section of the contact wire with local wear, not only the temperature rise occurs but also the current redistribution due to the smaller cross section. Thus, the current share in other longitudinal wires of the scale model increases and their temperature rises. Scale and mathematical models are constructed with allowance for laboratory clamps and supporting elements that participate in the removal of heat from the investigated wires. Obtained study results of the scale model allow to draw a conclusion about the adequacy of the mathematical model and its correspondence to the real physical process. These conclusions indicate the possibility of applying mathematical model for calculating real catenary, taking into account the uneven contact wear wire and the armature of the contact network.

scholarly journals Multi-Scale Studies of 3D Printed Mn–Na–W/SiO2 Catalyst for Oxidative Coupling of Methane

Catalysts ◽  
2021 ◽  
Vol 11 (3) ◽  
pp. 290
Author(s):  
Tim Karsten ◽  
Vesna Middelkoop ◽  
Dorota Matras ◽  
Antonis Vamvakeros ◽  
Stephen Poulston ◽  
...  
Keyword(s):  
Oxidative Coupling ◽  
Oxidative Coupling Of Methane ◽  
Operating Conditions ◽  
Homogeneous Distribution ◽  
Silica Support ◽  
X Ray Diffraction ◽  
Cross Sectional ◽  
X Ray ◽  
Multi Scale ◽  
3D Printed

This work presents multi-scale approaches to investigate 3D printed structured Mn–Na–W/SiO2 catalysts used for the oxidative coupling of methane (OCM) reaction. The performance of the 3D printed catalysts has been compared to their conventional analogues, packed beds of pellets and powder. The physicochemical properties of the 3D printed catalysts were investigated using scanning electron microscopy, nitrogen adsorption and X-ray diffraction (XRD). Performance and durability tests of the 3D printed catalysts were conducted in the laboratory and in a miniplant under real reaction conditions. In addition, synchrotron-based X-ray diffraction computed tomography technique (XRD-CT) was employed to obtain cross sectional maps at three different positions selected within the 3D printed catalyst body during the OCM reaction. The maps revealed the evolution of catalyst active phases and silica support on spatial and temporal scales within the interiors of the 3D printed catalyst under operating conditions. These results were accompanied with SEM-EDS analysis that indicated a homogeneous distribution of the active catalyst particles across the silica support.

Determination of cost-efficient cooling power range for improving the performance of internally cooled ultrasonic atomization liquid desiccant dehumidifiers

2020 ◽  
Vol 29 (9) ◽  
pp. 1260-1276
Author(s):  
Zili Yang ◽  
Lu-An Chen ◽  
Ruiyang Tao ◽  
Ke Zhong
Keyword(s):  
Power Efficiency ◽  
Removal Rate ◽  
Operating Conditions ◽  
Cooling Power ◽  
Internal Cooling ◽  
Liquid Desiccant ◽  
Improvement Rate ◽  
Ultrasonic Atomization ◽  
Internally Cooled ◽  
Cost Efficient

Liquid desiccant dehumidifiers (LDDs) can be improved by adding internal cooling. However, the addition of excessive cooling power may deteriorate the system‘s cost-efficiency, whereas the addition of insufficient cooling power leads to negligible performance improvements. The objective of this study is to determine the suitable cost-efficient cooling power range for improving the performance of internally cooled LDDs (IC-LDDs). A novel method and a set of criteria related to the moisture removal rate, cooling-power efficiency ( ηc) and coefficient of dehumidification performance from cooling power ( DCOPcooling) were proposed to determine cost-efficient cooling power. The internally cooled ultrasonic atomization liquid desiccant system (IC-UADS), together with a well-validated model based on the conservation laws of mass and energy and the sensible heat balance, was adopted to demonstrate the analysis. The results showed that, although the dehumidification performance improves with increasing cooling power, the improvement rate decreases, while ηcand DCOPcoolingdecline quickly (by 87.9%). For cost-efficient improvement, the necessary power proportion of internal cooling to the system‘s target dehumidification capacity tends to be stable, which was about 29% for the IC-UADS, and independent of the operating conditions. The results may help to determine the reasonable cooling power range for cost-efficient improvement of IC-LDDs.

Study on De-Nitrification of Improved Step-Feed Progress

2014 ◽  
Vol 703 ◽  
pp. 171-174
Author(s):  
Bing Wang ◽  
Yi Xiao ◽  
Shou Hui Tong ◽  
Lan Fang ◽  
Da Hai You ◽  
...  
Keyword(s):  
Water Quality ◽  
Organic Matter ◽  
Fluidized Bed ◽  
Removal Efficiency ◽  
Nitrogen Removal ◽  
Removal Rate ◽  
Operating Conditions ◽  
Removal Mechanism ◽  
Aerobic Zone

Improved step-feed de-nitrification progress combined with biological fluidized bed was introduced in this study. The progress had good performance and capacity of de-nitrification and organic matter. The experiment result showed that the de-nitrification efficiency of the improved biological fluidized bed with step-feed process was higher than the fluidized bed A/O process under the same water quality and the operating conditions. When the influent proportion of each segment was equal, the system showed good nitrogen removal efficiency with the change of influent C/N ratio, HRT and sludge return ratio. The removal rate of TN reached up to 88.2%. It showed that the simultaneous nitrification and de-nitrification phenomenon happened in the aerobic zone. The nitrogen removal mechanism was also studied.

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