Experimental and analytical performance investigation of air to air two phase closed thermosyphon based heat exchangers

In recent years, the use of wickless heat pipes (thermosyphons) in heat exchangers has been on the rise, particularly in gas to gas heat recovery applications due to their reliability and the level of contingency they offer compared to conventional heat exchangers. Recent technological advances in the manufacturing processes and production of gravity assisted heat pipes (thermosyphons) have resulted in significant improvements in both quality and cost of industrial heat pipe heat exchangers. This in turn has broadened the potential for their usage in industrial waste heat recovery applications. In this paper, a tool to predict the performance of an air to air thermosyphon based heat exchanger using the ε-NTU method is explored. This tool allows the predetermination of variables such as the overall heat transfer coefficient, effectiveness, pressure drop and heat exchanger duty according to the flow characteristics and the thermosyphons configuration within the heat exchanger. The new tool's predictions were validated experimentally and a good correlation between the theoretical predictions and the experimental data, was observed. © 2014 Elsevier Ltd. All rights reserved

Book of abstracts of the 16th International Symposium of Croatian Metallurgical Society - SHMD \u272023, Materials and metallurgy

Book of abstracts of the 16th International Symposium of Croatian Metallurgical Society - SHMD \u272023, Materials and metallurgy, Zagreb, Croatia, April 20-21, 2023. Abstracts are organized into five sections: Anniversaries of Croatian Metallurgy, Materials - Section A; Process Metallurgy - Section B; Plastic Processing - Section C and Metallurgy and Related Topics - Section D

Forming-based geometric correction methods for thin-walled metallic components:a selective review

Geometric correction processes contribute to zero-defect manufacturing for improved product quality. Thin-walled metallic components are widely used in numerous applications such as electric vehicles and aircraft due to the lightweight feature, facilitating to achieve zero-emission goals. However, many components suffer geometric imperfections and inaccuracies such as undesired curvatures and twists, seriously affecting subsequent manufacturing operations, for example, automatic welding and assembly. Geometric correction techniques have been established to address these issues, but they have drawn little attention in the scientific community despite their wide applications and urgent demands in the industry. Due to the strict geometric tolerances demanded in high-volume automated production, it is urgent to increase the knowledge needed to develop new techniques to address future industrial challenges. This review paper presents an overview of typical geometric defects in thin-walled components and clarifies the associated underlying generation mechanisms. Attempts have also been made to discuss and categorize geometric correction techniques based on different forming mechanisms. The challenges in correcting complex thin-walled products are discussed. This review paper also provides researchers and engineers with directions to find and select appropriate geometric correction methods to achieve high geometric accuracy for thin-walled metallic components.</p

Structural integrity of pipelines using reeling installation method

In the reeling method for installing offshore pipelines, several miles of line are wound onto a large diameter drum onshore mounted on a vessel. The vessel travels to the installation site where the line is unwound gradually installing it to the sea floor. This process involves repeated excursions into the plastic strain range of 1-3%. This study examines three structural integrity issues that arise from the process. A full-scale numerical modeling scheme incorporating nonlinear kinematic hardening plasticity is developed for the reeling/unreeling process. The first issue studied is the degradation of the cross section of pipelines and its effect on the collapse pressure. To capture the ovalization induced and assess its impact on the structural performance of the pipeline in deeper waters, the complete 3-D finite element model and a simplified 2-D model are presented to simulate reeling/unreeling of up to three cycles and subsequent collapsing under external pressure. Comparison of the results of such simulations with experiments highlights when fully a 3-D model is required and when the simpler 2-D model is adequate for evaluating the structural performance of a reeled pipe. The second issue investigated is the discontinuity in pipelines. In order to show how discontinuities in geometry and mechanical properties can lead to buckling and failure, the 3-D numerical model is applied to simulate the reeling/unreeling of pipelines. Discontinuities are shown to result in sharp local changes in accompanied by severe local straining and ovalization. These local effects can be reduced by increasing the applied tension at the expense of additional ovalization of the pipeline. The last part of the study examines the complication brought in by reeling pipes that exhibit Lüders bands. To simulate this process, the material is modeled by a stress–strain response with a negative slope over the extent of the Lüders deformation. During reeling with some back tension, Lüders banding produces inclined bands of localized deformation organized in clusters with distinctly different spatial distribution than that of pure bending. As a consequence, the ovalization develops axial undulations. The influences of problem variables are examined in a detailed parametric study.Engineering Mechanic

NUMERICAL STUDY OF THE EXHAUST GAS FLOW OF TV3-117 TYPE ENGINES IN COMPOSITION WITH A SCREEN - EXHAUST DEVICE

The object of research&nbsp;is a screen-exhaust device in the TV3-117 engine of the Mi-8 helicopter. Investigated problem:&nbsp;The problem of equalizing the flow in the exhaust nozzle is solved. As a result of the numerical study, the total pressure losses are calculated and the flow structures in the structural elements of the exhaust nozzle and the screen-exhaust device (SED) are analyzed. Main scientific results:&nbsp;Obtained Gas-dynamic parameters of the flow in the SED flow path are obtained and the verification of injection processes between the working circuits along the path in the SED design is done. Numerical modeling of gas flows in the SED flow path makes it possible to study in detail the characteristics of the flow at any of its points, as well as to determine the values of hydrodynamic losses associated with the formation of a boundary layer and the emergence of separation zones. A constructive method for leveling the gas-dynamic flow is proposed by installing a blade in the form of an aerodynamic profile in a standard engine exhaust nozzle. Two variants of engine nozzles are investigated under the same boundary conditions using a standard exhaust nozzle with and without a blade. The influence of uneven flow in the exhaust nozzle on the nature of the flow in the SED is shown. An insignificant equalization of the flow in the exhaust nozzle using the installed blade led to a decrease in the total pressure loss in the SED by more than 1 %. The area of practical use of the research results:&nbsp;The results of calculations and modeling can be used for computational and experimental studies aimed at improving the flow path of the exhaust nozzle and the screen-exhaust device by the developers of new military aviation equipment or when modernizing the existing helicopter fleet. Scope of application of the innovative technological product:&nbsp;a new screen-exhaust device has been proposed for left and right TV3-117 engines of all types, which can be installed on the Mi-8MSB-V, Mi-8MT, Mi-14, Mi-24 helicopters. It is competitive and has significantly higher technical and economic indicators compared to known analogues

Index to 1984 NASA Tech Briefs, volume 9, numbers 1-4

Short announcements of new technology derived from the R&D activities of NASA are presented. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This index for 1984 Tech B Briefs contains abstracts and four indexes: subject, personal author, originating center, and Tech Brief Number. The following areas are covered: electronic components and circuits, electronic systems, physical sciences, materials, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Selected Papers from Experimental Stress Analysis 2020

This Special Issue consists of selected papers from the Experimental Stress Analysis 2020 conference. Experimental Stress Analysis 2020 was organized with the support of the Czech Society for Mechanics, Expert Group of Experimental Mechanics, and was, for this particular year, held online in 19–22 October 2020. The objectives of the conference included identification of current situation, sharing professional experience and knowledge, discussing new theoretical and practical findings, and the establishment and strengthening of relationships between universities, companies, and scientists from the field of experimental mechanics in mechanical and civil engineering. The topics of the conference were focused on experimental research on materials and structures subjected to mechanical, thermal–mechanical, and dynamic loading, including damage, fatigue, and fracture analyses. The selected papers deal with top-level contemporary phenomena, such as modern durable materials, numerical modeling and simulations, and innovative non-destructive materials’ testing

Investigation of thermal techniques to mitigate buckling distortion in welding panels

This thesis describes the advancements of the application of thermal tensioning techniques to different weld geometries in order to eliminate buckling distortion. The main goal of this work is to better understand these techniques through experimental and numerical investigation and increase their technological maturity to aid industrial implementation. The thermal tensioning techniques investigated in this work are Thermal Tensioning by Cooling and Thermal Tensioning by Heating. The investigation for both techniques encompasses thermal source characterisation, application to different weld geometries and residual stress measurements and analysis of both butt and fillet welded samples. A detailed technology transfer study of Thermal Tensioning by Cooling was carried out in which different aspects of the application of TTC to arc welding (Gas Metal Arc Welding and Gas Tungsten Arc Welding) was examined. This study focused on the influence of both the liquid CO2 delivery system installation and welding tooling and jigging on the effectiveness of Thermal Tensioning by Cooling in reducing buckling distortion. Experimental and numerical cooling source characterisation was also carried out in the Thermal Tensioning by Cooling work to investigate the characteristics of the cooling source under different cooling conditions. The Thermal Tensioning by Cooling work was then concluded with welding trials and residual stress measurement and analysis. The results of the Thermal Tensioning by Cooling study show that the installation of the liquid CO2 delivery system as well as the welding tooling and jigging has a major influence on the effectiveness of Thermal Tensioning by Cooling in reducing buckling distortion. The cooling source characterisation work reveals that the most important parameter of the cryogenic nozzle delivery system used in this work is the Air Entrainment Gap. A description of a control system of Thermal Tensioning by Cooling is suggested based on controlling the Air Entrainment Gap. The residual stress analysis shows a reduction in the Applied Weld Load and minor changes in the tensile peak of the residual stress distribution of both butt and fillet welded panels. The Thermal Tensioning by Heating investigation includes heat source characterisation, application of Thermal Tensioning by Heating on butt and fillet welds, utilisation of alternative heat sources and residual stress analysis. The results of these investigation show that Thermal Tensioning by Heating is also highly effective in eliminating buckling distortion in butt, fillet and overlapped panels. The applied heating temperature in this work is typically in the range of 160-250 °C but not greater than 330 °C. The residual stress measurements reveal that the additional heating of Thermal Tensioning by Heating generates a positive stress gradient at the location of heating

Book of abstracts of the 14th International Symposium of Croatian Metallurgical Society - SHMD \u272020, Materials and metallurgy

Book of abstracts of the 14th International Symposium of Croatian Metallurgical Society - SHMD \u272020, Materials and metallurgy held in Šibenik, Croatia, June 21-26, 2020. Abstracts are organized in four sections: Materials - section A; Process metallurgy - Section B; Plastic processing - Section C and Metallurgy and related topics - Section D

CHARACTERIZATION AND PROPERTIES INVESTIGATION OF AUTOMOTIVE STEEL EXHAUST PIPING FAILURE

Incident involving failures of steel exhaust elbow pipe connected to a muffler of Proton Persona investigated carrying raw gas has caused serious disruption within the system. This study looks at developing useful approaches and strategies to forecast failure of exhaust piping system for automotive applications. Existing design, manufacturing process and exhaust pipe material as well as operating condition have been reviewed and analyzed using Non-Destructive techniques (NDT) and Destructive techniques (DT). Vickers hardness test conducted using 100kgf load on the failed materials indicated the exhaust pipe fulfill the tensile strength requirement based on industry specification to carry out intended function. Metallographic analysis conducted using optical microscope as well as Scanning Electron Microscope (SEM) at various magnifications indicated multiple evidences of internal corrosion and micro-fractures on steel exhaust pipe surface. Besides, computational Fluid Dynamics (CFD) results showed that the elbow of the exhaust pipe have been exposed to an extreme exhaust gas flow gradient. The high risk elbow area exposed to high velocity, pressure and temperature simulated by Computational Fluid Dynamics (CFD) simulation coherence to the leakage area of the exhaust pipe. Root Cause Analysis (RCA) showed that phenomenon excessive thinning of steel pipe wall caused by erosion-corrosion mechanism exhaust pipe lead to the perforation of an exhaust pipe. Based on the data collected, it is suggested, proper process design of the product may be implemented during installation and fabrication of exhaust piping system, followed by revising and improving gas stream flow inside the exhaust pipe system as well as using corrosion inhibitor in order to avoid occurrence of same failure in future