# Journal of the Brazilian Society of Mechanical Sciences and Engineering

Published by Springer Verlag

Published by Springer Verlag

Publications

In this paper, we address the problem of scheduling jobs in a no-wait flowshop with sequence-dependent setup times with the objective of minimizing the makespan and the total flowtime. As this problem is well known for being NP hard, we present two new constructive heuristics to obtain good approximate solutions for the problem in a short CPU time, named GAPH and QUARTS. GAPH is based on a structural property for minimizing makespan and QUARTS breaks the problem in quartets to minimize the total flowtime. Experimental results demonstrate the superiority of the proposed approaches over three of the best-known methods in the literature: BAH and BIH, from Bianco et al. (INFOR J 37(1):3-19, 1999) and TRIPS, by Brown et al. (J Oper Res Soc 55(6):614-621, 2004).

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- 84 Reads
- 15 Citations

This paper presents experimental results of vortex-induced vibrations (VIV), concomitantly carried out in water with a flexible cylinder, rigidly fixed, and with a ‘rigid’ cylinder, mounted on an elastic apparatus. The experiments were run at IPT towing tank facility, in a side-by-side arrangement. The flexible cylinder is simply fixed at the upper end. For the flexible cylinder, two degrees of freedom (2DOF) are implied for each vibration mode: crosswise and aligned with respect to the incident flow. The elastic support to which the ‘rigid’ cylinder is mounted is made of two vertical leaf-springs, fixed to two thick horizontal plates, conferring to the cylinder a single degree of freedom (SDOF) to oscillate transversally with respect to the incident flow. The mass ratios of the cylinders are almost the same, around 1.2 and 1.4, respectively, very low values, typical of long ocean pipe structures, as risers and pipelines. The structural damping ratio is also typically low and such as to guarantee high-amplitude responses. Besides usual spectral and statistical analysis, the Hilbert–Huang spectral analysis technique is applied, as, strictly, VIV is a non-stationary oscillation emerged from a nonlinear dynamic system. A discussion is made on the distinct VIV behaviors of the SDOF and the 2DOF systems.

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- 171 Reads
- 12 Citations

Starting friction torque is a very important characteristic for some applications and clearance influences the starting friction torque directly for those slewing bearings with negative clearance. The relationship between groove shape and clearance variation is established in the paper and two experiments are designed to verify the correctness of theoretic analysis. A new processing technology for final processing of groove in four-point-contact slewing bearings is suggested according to theoretic analysis and experiment research in the paper.

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- 112 Reads
- 7 Citations

Experiments on the effects due solely to a mobile granular layer on a liquid flow are presented (feedback effect). Nonintrusive measurements were performed in a closed conduit channel of rectangular cross section where grains were transported as bed load by a turbulent water flow. The water velocity profiles were measured over fixed and mobile granular beds of same granulometry by Particle Image Velocimetry. The spatial resolution of the measurements allowed the experimental quantification of the feedback effect. The present findings are of importance for predicting the bed-load transport rate and the pressure drop in activities related to the conveyance of grains.

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- 56 Reads
- 10 Citations

The objective of this paper is to investigate a new method to increase the efficiency of the centrifugal pump under the guidance of the bionic coupling theory. A centrifugal pump with a bionic coupling impeller called a bionic coupling centrifugal pump (BCCP) was developed. Either riblets or concave dimples were engraved on the flank or blade back of the impellers and then coated with polyurethane. This design was inspired by the specific skin structure of living creatures and the theory of biological coupling. The BCCP efficiency was investigated using the method of pseudo-level orthogonal testing. The results show that the efficiency of BCCPs obviously improved and the efficiency curve became more compressed than that of a conventional centrifugal pump over the effective working range. This indicates that the BCCPs would still function within a higher efficiency range even when they deviate from the highest efficiency point. The efficiency enhancement of the BCCP could be attributed to the effect of the delayed release of energy because of the elastic deformation of polyurethane. Polyurethane coupled with non-smooth surface structures stabilized the turbulent flow. This coupling consequently reduced the turbulence and stabilized the water in the boundary layer of the impeller blade.

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- 93 Reads
- 10 Citations

This work describes a numerical model for calculation of carbon monoxide (CO) emissions from spark ignition engines. The model calculates CO concentration from a kinetic mechanism and from the equilibrium combustion equation. A computer program that simulates the cycle of spark ignition engines performs the CO model calculations. The model was validated against experimental data from a single-cylinder research engine and from a production multi-cylinder engine. The varied parameters were air/fuel ratio, load and engine speed. From comparison with calculated equilibrium concentration, it is shown that CO should be modeled by chemical kinetics for better agreement with measured exhaust values.

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- 37 Reads
- 5 Citations

In the present work, the 1D flow and transport equations for open channels are numerically solved and coupled to a recently developed global search optimization, the particle collision algorithm (PCA), to estimate two essential parameters present in flow and transport equations, respectively, the bed roughness and the dispersion coefficient. The PCA is inspired in the scattering and absorption phenomena of a given incident nuclear particle by a target nucleus. In this method, if the particle in a given location of the design space reaches a low value of the objective function, it is absorbed, otherwise, it is scattered. This allows the search space to be widely explored, in such a way that the most promising regions are searched through successive scattering and absorption events. Based on real data measured in the Albear channel, Cuba, the bed roughness and longitudinal dispersion coefficient were successfully estimated from two numerical experiments dealing, respectively, with flow and transport equations. The results obtained were supported by the high correlations achieved between simulations and observations, demonstrating the feasibility of the approach here considered.

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- 155 Reads
- 4 Citations

Speed flame propagation in Otto cycle engines is one of the principal characteristics of fuel and is fundamental in defining the ignition advance. The greater the propagation speed the less the negative work required to compress the mixture before the piston reaches the top dead center and the higher the cycle’s efficiency. This paper presents experimental results of time measurements of the fuel’s ignition and the maximum pressure rating in the combustion chamber of a Cooperative Fuel Research engine specially instrumented. The combustion duration measurements of oxygenated and non-oxygenated fuels were taken as a function of the compression ratio (8:1, 10:1 and 12:1) and lambda (λ). The speed flame propagation in the combustion chamber is significantly changed with the change of the lambda different compression ratios. The VNG has a maximum in the speed flame propagation in the stoichiometric region (λ = 1.0) in all compression rates in this study. Similar behavior occurs with ethanol and gasohol, but only in compression ratio 12:1. Ethanol and gasohol have the higher rate of flame propagation for all compression ratios measured as compared to the non-oxygenated (isooctane) and oxygenated fuels (MTBE and TAEE).

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- 275 Reads
- 16 Citations

Super duplex stainless steels are extremely corrosion-resistant alloys designed for very demanding applications that expose them to corrosive environments, such as seawater. Due to their chemical composition and microstructure, which provide high mechanical strength and thermal resistance as well as high ductility, the machinability of these alloys is generally poor, resulting in long production cycles and high tooling costs. Moreover, machining may be harmful for the corrosion resistance of the alloy. The goal of this research is to study the turning operation of UNS 32750 alloy, known commercially as SAF 2507, and its influence on the alloy’s corrosion resistance in practical applications. Tests were performed, using cutting speed and cooling conditions with low and high fluid pressure as the input variables. The results indicate that turning with PVD-coated inserts under high-pressure cooling resulted in long tool lives, good workpiece roughness and high corrosion resistance of the material after machining. The most frequent wear mechanism found during the tests was notch wear, while the main tool wear mechanism was attrition.

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- 950 Reads
- 45 Citations

New technologies known as additive manufacturing (AM) are now available for producing prototypes directly from a 3D CAD model. However, prototypes made by AM usually have mechanical characteristics inferior to those of the final product. AM technologies are in increasing demand for use in the development of functional prototypes and the manufacture of final products. The main aim of this work was to evaluate the influence of deposition strategies on the mechanical behavior of the AM process known as fused deposition modeling (FDM) and to gain a better understanding of the stiffness behavior of the parts. Specimens with different raster orientations in each layer (sandwich-like configurations) were built. The final stiffness and strength of the specimens were determined in tensile and bending tests, and the stiffness was predicted using classical lamination theory. The stiffness in the two main directions for the specimens manufactured with the sandwich deposition configurations was higher than or at least equal to the stiffness of the specimens produced with the default FDM configuration. However, the results indicate that the analytical model used did not accurately predict the behavior in the experimental tests.

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- 168 Reads
- 56 Citations

This paper proposes a method to design multifunctional robot end-effectors that consider the weight as one of the main design constraint. The motivation for this work comes from aircraft industry. This sector, traditionally characterized by manual processes, has an increasing interest in the use of commercial off-the-shelf robots for the automation of their manufacturing processes. The design method proposed in this paper, named design to weight (DTW), is based on design for excellence (DFX) methodology. In order to illustrate and validate the DTW approach, it is applied to an end-effector that shall embed a set functions related to the riveting operation of aircraft fuselage barrels. The designed end-effector is compared with similar products described in the literature or available in the market. The results show that DTW is an efficient approach that not only provides low-weight solutions but also maintains a compromise with other requirements. On the other hand, the method is sensitive to the choice of relevance and quality factors that depends on the knowledge of the design team about the product under design.

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- 231 Reads
- 9 Citations

The research described in this paper was carried out to determine the hydrodynamic forces on the multi-hull tunnel vessel in steady motion. The hull form of vessel is fairly generated by the tunnel hull form generator code using the non-uniform rational B-Spline method. Then, the hydrodynamics simulation is carried out based on finite volume discretization method using volume of fluid model to consider free surface between water and air phases around the vessel. A dynamic mesh restructuring method is applied for grid generation regarding to the heave and pitch motions of vessel in each time step. The calculations of the center of gravity arising, trim angle, pressure, resistance and effective power are studied at various vessel’s speeds. The resistance plot versus velocity has an increasing trend having a hump velocity while the power curve shows a linear-like changes respect to speed increasing. Pressure calculations show that the ratio of hydrostatic pressure to total pressure is decreased at the end point of keel from 100 to 1 % as velocity increases from 5 to 20 m/s. The proposed numerical algorithm is a promising method for hydrodynamic analyses of wide-ranging high speed vessel types, particularly tunnel vessels.

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- 535 Reads
- 25 Citations

Milling is one of the most important processes to manufacture dies and moulds. However, it cannot machine regions with small sizes and difficult access to the cutting tool. Such regions must be machined by electro-discharge machining (EDM). It is known that EDM can damage the integrity of the machined surface, and also requires long processing time, due to both, the necessity to manufacture the electrode and its low material removal rate. The micromilling process, using high-frequency spindle together with cutting tools smaller than 1 mm of diameter has been emerging as an option for machining small regions in dies and moulds. In this context, this paper aims to help the understanding of the cutting phenomenon to manufacture small areas using both machining techniques, in order to identify the adequacy to replace EDM for micromilling in such circumstances. Machining experiments were carried out on AISI P20 (29HRC) and AISI H13 (45HRC) steels. These materials are commonly used in the mould and die industry. Residual stress on machined surface, surface finishing (2D and 3D), SEM images, microstructure and microhardness were accessed. The residual stress was tensile for the EDM pieces and compressive for the milled parts. The material had more influence on the residual stresses values than the process and H13 had higher values than P20. The surface roughness from the EDM machining pieces was not influenced by the material. The EDM caused white layer and microcracks on both materials, but much more intensely on H13. These occurrences were not found on the milled workpieces. Plastic deformation occurred on the micromilled surfaces, but without phase transformation of the material’s microstructure. Unexpectedly, the roughness on the hardest material (H13) was worse than P20 for the milling experiments. It was attributed to more intense tool deflection when milling H13. In general, roughness obtained in micromilling was about six times lower than that obtained using EDM and it presented a regular surface topography, unlike the EDM specimens.

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- 327 Reads
- 21 Citations

This paper describes the application
of the fuzzy logic analysis coupled to Central Composite Design to optimize the parameters of the carbon nanotube (CNT) mixed in dielectric fluids used in electrical discharge machining (EDM) process. This work investigates the surface characteristics of AISI D2 Tool Steel with graphite as a tool electrode during EDM process. The multiwall carbon nanotube is mixed with dielectric fluids to analyze the surface roughness and micro-cracks using atomic force microscope measurements. Response surface model has been developed to predict the surface roughness for EDM parameters. Analysis of variance and F test have been used to check the validity of response surface model and determine the significant process parameter affecting the surface roughness. A fuzzy logic model has been used to investigate relationships between the machining parameters and determine the efficiency of each parameter with and without using CNT-based EDM process.

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- 70 Reads
- 22 Citations

Enlargement of ship size in recent decades and no change in the harbors and approach channels have resulted in global attention toward navigation in shallow and confined waters. A phenomenon which restricts ship navigation in shallow waters is reduction of under-keel clearance in terms of sinkage and dynamic trim, which is called squatting. Due to the complexity of flow around the ship hull, one of the best methods for predicting the ship squat is the experimental approach based on systematic model tests in the towing tank. In this study, model tests for tanker ship model and traditional Persian Gulf and Oman Sea vessel called dhow had been performed in the towing tank and the squat of the models were measured and analyzed. Based on the experimental results, suitable formulae for the prediction of these types of ship squat in fairways are obtained.

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- 139 Reads
- 4 Citations

This work presents a study on the effect of low pressure cryogenic liquid nitrogen on cutting forces, friction coefficient, surface roughness of the machined surface and tool wear under high speed machining of a relatively new titanium alloy, Ti-5Al-4V-0.6Mo-0.4Fe. The experiments were conducted in dry and cryogenic conditions. The experimental results show that liquid nitrogen can reduce the friction force, friction coefficient and improve the surface roughness. © 2013 The Brazilian Society of Mechanical Sciences and Engineering.

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- 494 Reads
- 17 Citations

Predictive modeling is essential to better understanding and optimization of machining processes. Modeling of cutting forces has always been one of the main problems in metal cutting theory. In this paper, artificial neural networks (ANNs) were used for modeling correlations between cutting parameters and cutting force components in turning AISI 1043 steel. Cutting force components were predicted by changing cutting speed, feed rate, depth of cut and cutting edge angle under dry conditions. In order to improve generalization capabilities of the ANN models, Bayesian regularization is used in ANN training. Considering experimental data for ANN training, five ANN models were tested. For evaluating the predictive performance of ANN models, three performance criteria were given consideration. The overall mean absolute percentage error for cutting force components was around 3 %. This study concludes that Bayesian regularized ANN of quite basic architecture using small training data is capable of modeling multiple outputs with high prediction accuracy.

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- 97 Reads
- 22 Citations

This study makes an analysis of the radiation heat transfer in a turbulent non-premixed methane–air cylindrical combustion chamber. The highly complex dependence of the radiative properties with the wavenumber spectrum is modeled with the weighted-sum-of-gray-gas (WSGG), making use of the classical correlations of Smith et al. (J Heat Transfer 104:602–608, 1982) and of the more recently in obtained correlations of Dorigon et al. (IJHMT 64:863–873, 2013), based on HITEMP2010. The reaction rates were considered as the minimum values between the Arrhenius and Eddy Break-Up rates. A two-step global reaction mechanism was used, and turbulence modeling was considered via standard k–ε model. The source terms of the energy equation consisted of the energy involved in the reaction rates and radiation exchanges. The discrete ordinates method (DOM) was employed to solve the radiative transfer equation (RTE). The results show that the temperature, the radiative heat source, and the wall heat flux can be importantly affected by the WSGG correlations, while their influence on the species concentrations tends to be negligible. Numerical results considering the WSGG model with the new correlations were closer to experimental data presented in the literature.

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- 203 Reads
- 15 Citations

We consider a mathematical framework for spatially describing accessory aquatic systems that belong to a major hydric complex like a large reservoir created by damming a river. The central purpose is to provide a precise and complete mathematical covering of short-scale or localized water bodies, with typical lengths between 1 to 10 km, that are laterally attached to the main river. Such bodies may deserve a more detailed mathematical representation due, for instance, to their tendency to develop stagnant like hydric behaviors. The proposed framework may work as an infrastructure for developing and/or installing dynamic water quality models. It can generate tetrahedrizations of the aquatic system in question by working according to a procedure which builds, successively, reliable candidates for the following entities: (a) Free Surface Triangular Mesh; (b) Submerged Terrain Triangular Mesh; (c) Three Dimensional Partition of the Domain; (d) Basic Tetrahedrization of 3D Partitions; and (e) Refinement of the Basic Tetrahedrization through a Multi-Layer Tetrahedrization Algorithm. The required input for this procedure is only composed by terrain contour data and 3D located points. We present example applications including a real scenario belonging to a recent flooded system in Brazil.

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- 42 Reads

The synthesis of materials by high energy ball milling of powders was first developed for the production of complex oxide dispersion-strengthened nickel alloys for structural, high temperature applications but has been attracting attention in the field of fabrication processes like the production of intermetallic compounds, supersaturated solid solutions, amorphous materials and metal matrix composites. However, due to the high level of deformation imposed, the aluminum mechanically alloyed undergo extensive grain growth during the extrusion process, resulting in serious damage in the extruded materials. This work investigates the effects of mechanical alloying on the extrusion of AA6061 aluminum alloy and the same alloy reinforced with silicon nitride. In both cases, the energy of deformed particles produced extruded bars with coarse grains in the core, while in the periphery the higher rate of deformation in the extrusion process has prevented this coarsening, resulting in a material with heterogeneous microstructure and with poor mechanical properties. This grain growth can be prevented by a higher percentage of reinforcement in the composite materials or by annealing before extrusion.

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- 55 Reads
- 16 Citations

High-speed machining of aerospace alloys can be enhanced by the use of advanced cutting tool materials such as nano-grain size ceramics that exhibit improved physical and mechanical properties than their micron grain counterparts. The performance of recently developed nano-grain size ceramic tool materials were evaluated when machining nickel base, Inconel 718, in terms of tool life, tool failure modes and wear mechanisms as well as component forces generated under different roughing conditions. The tools were rejected mainly due to wear on the tool nose. It is also evident that chemical compositions of the tool materials played significant role in their failure. The alumina base ceramics performed better than the silicon nitride base ceramics. Severe abrasion wear was observed on both rake and flank faces of the cutting tools while cutting forces increased with increasing cutting speed when machining with the silicon nitride base nano-ceramic tools. This is probably due to the lower superplastic flow temperature of the nitride base nano-ceramics. The alumina base ceramics are more susceptible to chipping at the cutting edge than the silicon nitride base ceramics despite their higher edge toughness.

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- 436 Reads
- 21 Citations

This work presents the study of the effects of the milling parameters on the stress field for ASTM A36 plates, using a new technique, named the ultrasonic method with acoustoelastic theory. The parameters selected are the cutting speed, the feed per tooth, and the depth of cut, which are known as the main factors to influence the residual stress fields. The stress is calculated from the time-of-flight (TOF) of critically refracted longitudinal waves. The measurements of TOF were conducted with a probe, composed of acrylic shoes and 2.25 MHz longitudinal wave transducers. The shoes were machined so the wave would reach the surface of the sample at the first critical angle. Twenty samples of low carbon hot-rolled ASTM A36 steels plates were assessed. They were heat treated for stress relief before the machining. The contribution of each milling parameter is evaluated using the design of experiments and the response surface methodology with central composite design. The parameters listed were set in five levels each, and an adequate combination of parameters and levels lead to the stress results in six selected positions of each sample. For every position, three measurements were taken each one with five replicates, thus allowing the evaluation of the dispersion. Temperature effect was accounted for and its influence was corrected. The results showed that the proposed method is sensitive to variations of the machining parameters. It allows estimating the residual stresses and shows that, for the levels selected from each parameter, the main influence comes from the depth of cut and cutting speed, and the feed per tooth does not show significant effect on the stresses.

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- 1,572 Reads
- 9 Citations

This paper presents an experimental study aiming to identify the means to minimize the reduction of the overall performance of a gasoline engine when employing the Exhaust-Gas Recirculation (EGR) technique that reduces NOx emissions. The increase of the compression ratio and turbocharging was evaluated as a mean to recover the original performance. The formation of pollutants and the engine performance were verified at full and partial loads. The results show that the combination of exhaust gas recirculation with turbocharger or through an increase of the compression ratio enhance the relation between the engine performance and the emission of NO. However, the turbocharger seemed to be more sensitive to the negative effects of the EGR technology.

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- 1,505 Reads
- 17 Citations

Polymeric composites are frequently modeled as linear elastic materials. However, matrix-dominated properties, such as transverse and shear modulus, can display significant nonlinear time-dependence, especially under conditions of high stress and aggressive environment. This behavior is primarily due to the viscoelastic nature of the polymeric matrix. In addition, polymeric composites also present time-dependent damage growth. In this work, nonlinear viscoelastic constitutive equations were used to represent the time-dependent behavior of a rubber-toughened carbon/epoxy composite during damage growth. These equations were originally devised to characterize material response in a stable damage state. In this approach, however, nonlinearities due to damage and viscoelasticity were incorporated by the model stress-dependent functions, allowing its use in the presence of damage accumulation. A procedure was proposed and applied to separate viscoelastic and damage effects. An experimental program consisting of multiple cycle creep and recovery tests was performed to determine the time-dependence of the shear compliance and to verify the theory as well. The results obtained indicated an excellent agreement between theory and experiment. Constant stress rate tests were also used to validate the application of the theory.

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- 9 Reads

Acoustic scattering simulations with non-uniform potential flow effects are performed by two formulations described in the literature, valid under specific flow conditions. Both formulations require the solution of the Helmholtz equation for the acoustic scattering computation and the solution of the Laplace equation for the steady potential base flow. These equations are solved using the boundary element method (BEM), and the fast multipole method (FMM) is used to accelerate the matrix-vector products arising from the Helmholtz and Laplace BEM equations. An assessment of the solutions obtained by the two formulations is presented for a verification test case where analytical and full unsteady Euler solutions are available. Results of acoustic scattering for large-scale simulations of realistic airframe configurations are presented. Good agreement is found between Taylor’s low Mach number scattering formulation and the solution of the full unsteady Euler equations for high-frequency simulations of plane waves scattering from a rigid cylinder. The computational cost per iteration of the FMM–BEM for the acoustic scattering around a full airplane configuration discretized by 550,000 boundary elements in a non-uniform potential flow is 19 s.

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- 64 Reads
- 20 Citations

This work aims to investigate the efficiency of digital signal processing tools of acoustic emission signals in order to detect thermal damages in grinding processes. To accomplish such a goal, an experimental work was carried out for 15 runs in a surface grinding machine operating with an aluminum oxide grinding wheel and ABNT 1045 Steel as work material. The acoustic emission signals were acquired from a fixed sensor placed on the workpiece holder. A high sampling rate data acquisition system working at 2.5 MHz was used to collect the raw acoustic emission instead of the root mean square value usually employed. Many statistical analyses have shown to be effective to detect burn, such as the root mean square (RMS), correlation of the AE, constant false alarm rate (CFAR), ratio of power (ROP) and mean-value deviance (MVD). However, the CFAR, ROP, Kurtosis and correlation of the AE have been presented more sensitive than the RMS.

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- 166 Reads
- 32 Citations

The electromagnetic fuel injector (EFI) predominates in almost all electronic spark-ignited engine control systems because of its simple, precise and reliable functioning. A new non-linear general mathematical model to predict the EFI performance and to confront its theoretic response with experimental data is proposed. A confrontation to the Element Finite Method is also done.

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- 122 Reads
- 7 Citations

A numerical model to study the aerodynamic and aeroelastic bridge deck behavior is presented in this paper. The flow around a rigid fixed bridge cross-section, as well as the flow around the same cross-section with torsional motion, are investigated to obtain the aerodynamic coefficients, the Strouhal number and to determine the critical wind speed originating dynamic instability due to flutter. The two-dimensional flow is analyzed employing the pseudo-compressibility approach, with an Arbitrary Lagrangean-Eulerian (ALE) formulation and an explicit two-step Taylor-Galerkin method. The finite element method (FEM) is used for spatial discretization. The structure is considered as a rigid body with elastic restrains for the cross-section rotation and displacement components. The fluid-structure interaction is accomplished applying the compatibility and equilibrium conditions at the fluid-solid interface. The structural dynamic analysis is performed using the classical Newmark's method.

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- 281 Reads
- 22 Citations

This study presents mathematical modeling and calculation procedure for problems of electromagnetic forming of thin circular metal sheets using flat spiral coil as actuator. The method focuses specifically on the calculation of the electromagnetic field generated by the flat coil and analysis of the circuit that models the electromagnetic forming system. The flat coil is approximated by concentric circles carrying the current discharge from the capacitors. The calculation of electromagnetic force and magnetic couplings between the coil and metal sheet are made to the initial time, before the plastic deformation of the sheet. The method is based on the Biot-Savart law, and the solution of magnetic induction integral equations is performed by numerical methods specifically with the use of Matlab commercial software. A routine calculation, which models the problem as a set of differential equations was implemented in the Matlab, this provides important information that serves as feedback for system design. Free bulging experiments were performed to demonstrate a good relationship with the mathematical model predictions for electrical discharge current in the coil and induced currents in the metal sheet, behavior of the transient electromagnetic force between coil and workpiece and, distribution of magnetic field and electromagnetic density force along the coil. Also, achieved results showed that there is a strong dependence of the back electromagnetic force with respect to plate thickness for the system analyzed. The difference phase between the current induced in the coil and workpiece with higher negative peaks generate the back electromagnetic force.

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- 587 Reads
- 22 Citations

Dynamic positioning systems (DPS) comprise the deployment of active propulsion to maintain the position and heading of a vessel. Several sensors are used to measure the actual position of the floating body, while a control algorithm is responsible for the calculation of forces to be delivered by each propeller, in order to counteract all environmental forces, such as wind, waves and current loads. The controller cannot directly compensate motions in the sea waves frequency range, since they would require an enormous amount of power to be attenuated, possibly causing damage to the propeller system. That is the reason why a filtering algorithm is to be put in place to separate high-frequency components from the low-frequency ones, which are, then, fed into the control loop. Usual commercial systems apply Kalman filtering technique to perform such task, due to the smaller phase-lag introduced in the control loop compared to conventional low-pass filters. The Kalman filter draws on a model of the system to be controlled, which, in turn, depends on an unknown parameter, related to the wave frequency. Adaptive filtering is called upon with a view to perform an on-line estimation of such parameter. Most control algorithms, however, rely on fixed gains, thus making it possible for a noticeable performance degradation to take place in some situations, as those associated to mass variation during a loading operation. This paper presents the application of model-reference adaptive control (MRAC) technique to DPS's, cascaded with the commonly used adaptive Kalman filter. The model of a dynamically-positioned shuttle tanker exposed to waves and current is employed to highlight the advantages of the adaptive controller compared to commonplace fixed-gain controllers.

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- 852 Reads
- 15 Citations

This study deals with modelling of surface roughness with carbon nanotube (CNT)-based electrical discharge machining (EDM) of AISI D2 tool steel material by means of adaptive neuro-fuzzy inference system (ANFIS) approach. The full factorial design of experimental techniques was adapted to conduct the experimental works. The CNT mixed dielectric nanofluids were prepared and used in the EDM process to analyze the surface roughness. The first-order sugeno type fuzzy interference modeling was used to predict the output parameters and compared with experimental values. The ANFIS model has been developed in terms of machining parameters for the prediction of surface roughness using trained data. The ANFIS predictions for the surface roughness with CNT the testing error was 0.20276 and correlation coefficient was 0.997 with the experimental data and for without CNT the testing error was 0.26529 and correlation coefficient was 0.889. The developed ANFIS model were compared in terms of their performances and shows that high residual R
2 value indicate that the predicted model very well fits with the experimental data for using CNT on EDM process. The proposed model can also be used for estimating surface roughness on-line.

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- 59 Reads
- 21 Citations

A direct optimization study was performed to produce a preliminary evaluation of the potential benefits of a mission adaptive wing employing variable camber technology in typical jet transport aircraft missions, in terms of fuel efficiency increase directly obtainable from airfoil viscous drag reduction alone. A 2-D airfoil analysis approach was adopted, associated with an idealized variable camber mechanism based on elastic deformation and surface extension. Using a direct function optimization program coupled to a viscous-inviscid airfoil analysis routine, optimized variable camber configurations were obtained for several weight conditions of a typical transport aircraft along a sub-critical cruise mission leg. Independent runs were executed considering only trailing and both leading and trailing-edge camber variation and, for each of them, an integrated range parameter has been obtained, proportional to the maximum possible aircraft range. Results indicate that the range increases up to 7.03% over the base airfoil that could be reached with camber variation in the trailing edge region only, and up to 24.6% when leading edge adaptation was considered simultaneously. However, pressure distribution results indicate that the high leading-edge curvatures required for that would probably decrease cruise critical Mach. On other hand, the trailing-edge only approach may offer better conditions for supercritical cruise.

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- 206 Reads
- 45 Citations

The pneumatic conveying of solids in a gas stream is a recurrent process in petrochemical industries. However, due to practical limitations the majority of existing systems have capacities ranging from 1 to 400 tones per hour over distances less than 1000 m, mainly because of a high power consumption per transported unit mass. More specifically, to avoid the formation of dense structures such as dunes and plugs, which, depending on the characteristics of the material and on the availability of a pressure head from the carrier phase may cause a violent pressure surge or a possible line blockage, the system is preferably operated at homogeneous dispersed flow. To sustain such a flow regime high velocities are needed and, accounting for the resulting higher pressure drops, higher power consumption is demanded. An optimized pneumatic conveying system can be conceived with the help of adaptive control techniques. In the context described above, lower transport velocities are allowed if the formation of aggregates that precedes the transition to dense phase flow regimes are automatically detected and destroyed, thus, artificially stabilizing the light phase homogeneous flow regime. This work assesses the reduction in the necessary power that the application of such adaptive control technique could produce. Experimental results are presented for a 45 mm i.d. pneumatic conveying system used to transport Setaria Italica seeds. The instrumentation used to identify the flow regime is constituted of several pressure sensors installed along the transport line. The proposed control strategy is based on processing these signals through a neural network model to assess the flow condition and to mimic an optimized gain scheduled PID algorithm. Preliminary results show that reductions in power consumption can reach 50% when compared with classical non controlled transport.

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- 278 Reads
- 6 Citations

The development of computational models for the numerical simulation of chemically reacting flows operating in the turbulent regime requires the solution of partial differential equations that represent the balance of mass, linear momentum, chemical species, and energy. The chemical reactions of the model may involve detailed reaction mechanisms for the description of the physicochemical phenomena. One of the biggest challenges is the stiffness of the numerical simulation of these models and the nonlinear nature of species rate of reaction. This work presents a study of in situ adaptive tabulation (ISAT) technique, focusing on the accuracy, efficiency, and memory usage in the simulation of homogeneous stirred reactor models using simple and complex reaction mechanisms. The combustion of carbon monoxide with oxygen and methane with air mixtures are considered, using detailed reaction mechanisms with 4 and 53 species, 3 and 325 reactions, respectively. The results of these simulations indicate that the developed implementation of ISAT technique has a absolute global error smaller than 1 %. Moreover, ISAT technique provides gains, in terms of computational time, of up to 80 % when compared with the direct integration of the full chemical kinetics. However, in terms of memory usage the present implementation of ISAT technique is found to be excessively demanding.

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- 131 Reads
- 7 Citations

This paper deals with an experimental study of wear and friction responses from lubricated sliding. Tests were carried out using a tribometer having devices for both continuous and reciprocating motion. The tested specimens were pins of AISI 52100 steel and counter-faces of AISI 8640 steel. The lubricant was paraffin mineral oil, VI 100. The presence of additives and contamination in the lubricant was investigated under two mechanical loading levels, determined by the velocity/load relation. Wear was evaluated in terms of morphology of the worn surfaces and by dimensional analysis of worn area of the pins. It was possible to obtain a ranking of influences on wear of mechanical loading, mechanical motion, oil additive and contamination presence in oil.

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- 137 Reads
- 22 Citations

The present study reports the results of Alumina and CNT (carbon nanotube) nanoparticles blended biodiesel fuel on the performance, emission, and combustion characteristics of a diesel engine. The biodiesel is produced from the raw jatropha oil by standard transesterification process, and subsequently, the nanoparticles such as Alumina, CNT, and Alumina–CNT are blended with the biodiesel fuel in the mass fractions of 25 and 50 ppm with the aid of an ultrasonicator. The characterization studies of the nanoparticles such as TEM and XRD are carried out to analyze their morphology. The whole investigation is carried out in a constant speed diesel engine in four phases using neat biodiesel fuel, Alumina blended biodiesel, CNT blended biodiesel, and Alumina–CNT blended biodiesel fuels. The results revealed a considerable enhancement in the brake thermal efficiency and marginal reduction in the harmful emissions for the nanoparticles blended biodiesel fuels compared to those of neat biodiesel fuel. Furthermore, the hot-plate evaporation test confirmed a shorten ignition delay effect, and improved heat transfer rate associated with the nanoparticles blended biodiesel fuels, owing to their enhanced surface area/volume ratio, and heat conduction properties.

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- 1,538 Reads
- 183 Citations

This paper presents a case study on the re-design of polymeric greenhouse clips using function analysis (FA), advanced computer aided design/computer aided engineering, reverse engineering and additive manufacturing applications. In the case study, based on a reverse engineered existing clip, alternative re-designs for five concepts have been created in consideration of the initial design needs and FA response. Finite Element Analysis (FEA) has been utilised to simulate and validate the operating conditions of the selected candidate alternative design. No failure cases were observed in the FEA validation. Finally, physical prototypes were produced and the final decisions have concluded that the selected candidate design responded to the defined FA needs.

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- 95 Reads
- 5 Citations

Recent work on improving general thermal design methods for condensation inside plain, horizontal tubes is presented, summarizing primarily the advances proposed at the Laboratory of Heat and Mass Transfer at the EPFL in collaboration with the University of Padova and the University of Pretoria. This work has focused on the development of a unified flow pattern, two-phase flow structure model for describing local heat transfer coefficients for pure fluids, azeotropic mixtures and zeotropic mixtures. Such methods promise to be much more accurate and reliable than the old-style statistically-derived empirical design methods that completely ignore flow regime effects or simply treated flows as stratified (gravity-controlled) or non-stratified (shear-controlled) flows. To achieve these goals, first a new two-phase flow pattern map for condensing conditions was proposed, which has been partially verified by flow pattern observations. Secondly, a new condensation heat transfer model for pure fluids and azeotropic mixtures has been developed including not only flow pattern effects but also interfacial roughness effects. Finally, the widely used Silver-Bell-Ghaly condensation model for miscible vapor mixtures has been improved by including the effects of interfacial flow structure and roughness on vapor phase heat transfer and a new non-equilibrium effect added.

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- 623 Reads
- 43 Citations

This paper presents some recent advances in the dynamics and control of constrained multi-body systems. The constraints considered need not satisfy D'Alembert's principle and therefore the results are of general applicability. They show that in the presence of constraints, the constraint force acting on the multi-body system can always be viewed as made up of the sum of two components whose explicit form is provided. The first of these components consists of the constraint force that would have existed were all the constraints ideal; the second is caused by the non-ideal nature of the constraints, and though it needs specification by the mechanician who is modeling the specific system at hand, it nonetheless has a specific form. The general equations of motion obtained herein provide new insights into the simplicity with which Nature seems to operate. They are shown to provide new and exact methods for the tracking control of highly nonlinear mechanical and structural systems without recourse to the usual and approximate methods of linearization that are commonly in use.

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- 174 Reads
- 1 Citation

In this paper, a new advection algorithm is presented to model free surface flows using volume of fluid method. To model the fluid flow, Navier–Stokes equations are solved as governing equations using two-step projection method on the Cartesian staggered grids. In the volume of fluid method, several algorithms such as flux-corrected transport (FCT) and Youngs’ algorithms are used to model the free surface. In these methods, for staggered grids, fluxes to neighboring cells are estimated based on cell face velocities. It means that fluid particles in the cell have the same velocity of the cell faces. However, in practice, the particles velocity varies between two adjacent cell faces velocities. In the present research, modified Youngs’ and flux-corrected transport methods are presented. In these methods, the velocity in mass center of fluid cell is estimated and used to calculate cell face fluxes. The performance of the modified schemes has been evaluated using a number of alternative schemes taking into account translation, rotation, shear test and dam break on dry bed. The results showed that the modified Youngs’ method is more accurate than the original one particularly in coarse grid. It is also more accurate than the modified flux-corrected transport method.

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- 290 Reads
- 12 Citations

This work aims to apply the disturbance theory to accomplish sensitivity computations in problems of pollutant transported in liquid media modeled through the advection-diffusion-reaction equation. The numerical solution of the differential equation that describes the behavior of the system was found via the SUPG ("Streamline Unwinding Petrov Galerkin") finite element technique. Simulations were done for different Péclet numbers. Then, the adjoint equation of the advection-diffusion-reaction equation was derived for the one-dimensional case and the expression of the coefficient of sensitivity of a generic functional related to a generic parameter was obtained. The sensitivities of the mean and instantaneous pollutant rates were analyzed with relation to the following parameters: drag speed of the flowing current and Péclet number. Results of the sensitivity coefficient obtained with first and second order perturbation methodology satisfactorily matched the same values calculated by the direct method, that is, by means of the direct solution of the advection-diffusion-reaction equation by changing the values of input data parameters.

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- 15 Reads
- 6 Citations

Materials used in the manufacture of aero-engine components generally comprise of nickel and titanium base alloys. Advanced materials such as aero-engine alloys, structural ceramic and hardened steels provide serious challenges for cutting tool materials during machining due to their unique combinations of properties such as high temperature strength, hardness and chemical wear resistance. These materials are referred to as difficult-to-cut since they pose a greater challenge to manufacturing engineers due to the high temperatures and stresses generated during machining. The poor thermal conductivity of these alloys result in the concentration of high temperatures at the tool-workpiece and tool-chip interfaces, consequently accelerating tool wear and increasing manufacturing cost. The past decade has witnessed a radical approach to product manufacture, particularly in the developed economy, in order to remain competitive. Modern manufacturing philosophies, principles and techniques geared primarily towards reducing non value added activities and achieving step increase in product manufacture have been widely adopted. Recent advances in the machining of aero-engine alloys include dry machining at high speed conditions, the use of high pressure and/or ultra high pressure coolant supplies, minimum quantity lubrication, cryogenic machining and rotary (self-propelled) machining technique. Tool materials with improved hardness like cemented carbides (including coated carbides), ceramics, polycrystalline diamond and polycrystalline cubic boron nitride are the most frequently used for high speed machining of aero-engine alloys. These developments have resulted to significant improvement in the machining of aero-engine alloys without compromising the integrity of the machined surfaces. This paper will provide an overview on these recent developments and their application in the aerospace industry.

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- 1,183 Reads
- 142 Citations

Hypersonic flow past truncated wedges at zero incidence in thermal non-equilibrium is investigated for a range of Mach number from 5 to 12. The simulations were performed by using a Direct Simulation Monte Carlo (DSMC) Method. The study focuses the attention of designers of hypersonic configurations on the fundamental parameter of bluntness, which can have an important impact on even initial design. Some significant differences between sharp and blunt leading edges were noted on the heat transfer, pressure and skin friction coefficients as well as on total drag. Interesting features observed in the surface fluxes showed that small leading edge thickness compared to the freestream mean free path still has important effects on high Mach number leading edge flows. The numerical results present reasonable comparison for wall pressure and heat transfer predictions with experiments conducted in a shock tunnel.

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- 62 Reads
- 5 Citations

A numerical study is reported on power law shaped leading edges situated in a rarefied hypersonic flow. The sensitivity of the heat flux and drag coefficient to shape variations of such leading edges is calculated by using a Direct Simulation Monte Carlo method. Calculations show that the stagnation point heating on power law leading edges with finite radius of curvature follows the same relation for classical blunt body in continuum flow; it scales inversely with the square root of the curvature radius at the nose. Furthermore, for those leading edges with zero or infinity radii of curvature, the heat transfer behavior is in surprising agreement with that for classical blunt body far from the nose of the leading edge.

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- 307 Reads
- 15 Citations

The paper is concerned with downwash correction methods for aeroelastic stability analyses in the transonic regime. The effects of the formulation used in the calculation of nonlinear, unsteady reference pressures are addressed, together with the influence of the motion amplitude. A finite-difference Euler/Navier–Stokes code is used to calculate the unsteady aerodynamic loading due to dynamic angle of attack variations in three-dimensional transonic flow. The computed unsteady pressure coefficients are used as a reference state for flutter analyses using the downwash weighting method. The test case considered is the well-known AGARD wing 445.6 standard aeroelastic configuration. The configuration is subjected to rigid body pitching oscillation about the mid-chord point at the root section. Flutter boundaries are computed using either inviscid or viscous-based unsteady pressures in the downwash correction methodology. The results are compared with available experimental data and they indicate that both viscous and thickness effects play an important role on the flutter prediction capability.

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- 18 Reads
- 1 Citation

This work aimed at the development of the requirements of project of a self-propelled aerosol generator, product that performs the control of mosquitoes through the space application of insecticides in the ambient. The demand of this work was based on low efficiency currently obtained in the process, especially in inside of residence, together with the super sizing of the systems available for this purpose along with the need of the control of epidemics. The guiding methodology of the project was the Process of Development of Agricultural Machines, which followed four steps: (1) identification of factors of influence related to the project, (2) survey of the needs of the customer/users, (3) establishment of the requirements of customers; (4) transformation of the needs of the customer in requirements of project. Among the most important requirements were the “Costs of production”, “Number of information for monitoring the conditions of use of the machine” and “Percent of usual processes of fabrication”. Thus, this work will contribute to the development of the other stages of the product in study, allowing the insertion of devices to improve the quality of results obtained by applying the ultra low volume in the control of mosquitoes in urban areas.

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- 26 Reads

In order to solve the aerostatic stability problem of long-span bridges more effectively, an upper limit of the external iteration number is set optimally to improve the incremental double iteration method, and an optimum iteration method is brought forward. For new suspension bridges with multiple main spans, the assumption of the spatial uniformity of wind speed is invalid due to their long decks and high towers. Taking into account the spatial non-uniformity of wind speed, a program corresponding to the optimum iteration method is developed and used to analyze the full-range aerostatic stability of the Maanshan Bridge, which is a long-span suspension bridge with double main spans in China, and the effect of wind speed spatial non-uniformity on the aerostatic stability of the bridge is investigated analytically. The result shows that the lowest critical wind speed of aerostatic instability is gained when the distribution of wind speed is non-uniform and the spatial non-uniformity of wind speed has a considerable effect on the aerostatic stability of suspension bridges with multiple main spans. The optimum iteration method is compared with the method without improvement in analysis, and the result indicates that the accuracy and efficiency of the optimum iteration method are much better, so the validity and advancement of the optimum iteration method are proved.

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- 37 Reads
- 19 Citations

The paper describes the implementation details and validation results for an agglomeration multigrid procedure developed in the context of hybrid, unstructured grid solutions of aerodynamic flows. The governing equations are discretized using an unstructured grid finite volume method, which is capable of handling hybrid unstructured grids. A centered scheme as well as a second order version of Liou?s AUSM+ upwind scheme are used for the spatial discretization. The time march uses an explicit 5-stage Runge-Kutta time-stepping scheme. Convergence acceleration to steady state is achieved through the implementation of an agglomeration multigrid procedure, which retains all the flexibility previously available in the unstructured grid code. The calculation capability created is validated considering 2-D laminar and turbulent viscous flows over a flat plate. Studies of the various parameters affecting the multigrid acceleration performance are undertaken with the objective of determining optimal numerical parameter combinations.

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- 43 Reads
- 8 Citations

Evaporative cooling operates using water and air as working fluids. It consists in water evaporation, through the passage of an air flow, thus decreasing the air temperature. This system has a great potential to provide thermal comfort in places where air humidity is low, being, however, less efficient where air humidity is high. A way to solve this problem is to use dehumidifiers to pre-conditioning the process air. This paper presents a system that can be used in humid climates coupling desiccant dehumidification equipment to evaporative coolers. The paper shows, initially, the main characteristics of the evaporative cooling and of the adsorption dehumidification systems. Later on the coupled systems, in which occurs a dehumidification by adsorption in a counter flow rotary heat exchanger following the evaporate cooling of the air in evaporative coolers, are analyzed. The thermodynamic equations of state are also presented. Following, this paper analyzes some operation parameters such as: reactivation temperature, R/P relationship (reactivation air flow/ process air flow) and the thermodynamic conditions of the entering air flow. The paper shows the conditions for the best operation point, with regard to thermal comfort conditions and to the energy used in the process. In addition this paper presents an application of the system in different climate characteristics of several tropical and equatorial cities.

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- 1,183 Reads
- 71 Citations

Turbine air inlet cooling is one of many available commercial methods for increasing the performance of a gas turbine. The method that has different configurations could be applied for nearly all gas turbines. This paper offers a comparison between two standard and one exquisite inlet air cooling method, which are used to improve the performance of a gas turbine located at the Khangiran refinery in Iran. These methods have been applied to one of the gas turbines located at the Khangiran refinery. Two common air-cooling methods are based on fogging systems and absorption chillers. The idea behind the novel method is to utilize the potential cooling capacity of the refinery natural gas pressure drop station. The research is part of a plenary program developed to enhance the efficiency of the gas turbine used at the Khangiran gas refinery. Considering the results, it is found that the new method is the most feasible in economic terms, so it has been recommended to be used for improving the performance of the Khangiran refinery gas turbines.

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- 142 Reads
- 11 Citations

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