Research Paper
Computational Fluid Dynamics (CFD)
Atie Farrokh; Miralam Mahdi
Abstract
Chillers are among the most widely used air-conditioning systems, and improving their thermal performance can significantly reduce energy consumption. In the present study, the effects of Al₂O₃/water and Al₂O₃–TiO₂/water nanofluids on the performance characteristics of a shell-and-tube ...
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Chillers are among the most widely used air-conditioning systems, and improving their thermal performance can significantly reduce energy consumption. In the present study, the effects of Al₂O₃/water and Al₂O₃–TiO₂/water nanofluids on the performance characteristics of a shell-and-tube chiller evaporator were numerically investigated using an Eulerian-Lagrangian Discrete Phase Model (DPM). The influences of nanoparticle volume fraction, inlet fluid temperature, evaporator temperature, mass flow rate, and number of baffles were examined. Three evaporator configurations with 3, 5, and 7 baffles were considered.The results showed that increasing the number of baffles from 5 to 7 enhanced the overall heat transfer coefficient by 6.94%. The addition of Al₂O₃ nanoparticles increased the overall heat transfer coefficient by 5.8%, while the use of Al₂O₃–TiO₂ hybrid nanoparticles resulted in an enhancement of up to 8.8%. Analysis of the performance evaluation criterion (PEC) indicated that nanoparticle volume fractions up to 0.03 provide favorable thermal performance, with an optimum value around 0.02. The results also demonstrated a significant difference between the DPM and conventional single-phase predictions, with a relative discrepancy of approximately 68% in the estimated heat transfer enhancement under the investigated conditions. The findings confirm the potential of nanofluids, particularly hybrid nanofluids, for enhancing the thermal performance of shell-and-tube chiller evaporators.
Research Paper
A. Zolfaghari; A. R. Shahani
Abstract
The first stage compressor blades of the gas turbine are subject to occasional failure due to their operating conditions. Initial evaluations indicate that microcracks that form in critical areas of the blade during fatigue loading make the blade prone to failure. Therefore, it is of great importance ...
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The first stage compressor blades of the gas turbine are subject to occasional failure due to their operating conditions. Initial evaluations indicate that microcracks that form in critical areas of the blade during fatigue loading make the blade prone to failure. Therefore, it is of great importance to find the locations of the blade where microcracks are most likely to form. In this study, extensive numerical and analytical investigations were performed to evaluate the observed failures, and Abaqus software was used for finite element analysis of the first stage compressor blade of the gas turbine model. In pursuit of this goal, initially, finite element simulations were conducted on an intact blade, followed by analyses on a blade incorporating a V-shaped notch, and subsequently, applying stress analysis, the critical positions that are the main candidates for the formation and initiation of microcracks in the blade were determined. In addition, a new critical plane fatigue model was applied to evaluate and investigate the fatigue behaviour of the compressor blade. Then, through coding in MATLAB software, the plane that suffered the maximum damage based on the critical plane fatigue model was determined and its direction was calculated for the critical positions of the compressor blade. Finally, the compressor blade fatigue life was determined based on this criterion and compared with traditional critical plane fatigue criteria such as Brown-Miller and SWT, and the reduction in life due to foreign object damage to the blade was determined and compared to an intact blade.
Research Paper
Forming
S. A. Alavi; S. M. H. Seyedkashi; M. Rakhshkhorshid
Abstract
This study investigates crack formation and rupture in a newly developed "SCDA expansion forming", which utilizes the pressure generated by a soundless chemical demolition agent (SCDA). The research integrates experimental analysis and finite element analysis (FEA) to examine the forming of a 1 mm thick ...
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This study investigates crack formation and rupture in a newly developed "SCDA expansion forming", which utilizes the pressure generated by a soundless chemical demolition agent (SCDA). The research integrates experimental analysis and finite element analysis (FEA) to examine the forming of a 1 mm thick St12 low-carbon steel sheet into a dome shape. The experimental phase involved using Green Rock SCDA within a rigid steel die under test conditions of 75°C temperature, 25% water content, and 300 g mixture mass. The corresponding FEA was performed in Abaqus, applying the forming limit diagram (FLD) damage model criteria to predict necking instability and crack formation. The results from both the simulation and the experimental tests demonstrated that rupture occurs in the areas between the dome's center and its corners. FEA revealed that the maximum plastic strain and stress are concentrated in these central regions, leading to localized thinning and eventual failure. The experimental findings confirmed the location of the crack, thereby validating the accuracy of the numerical model. Analysis of the fracture surface via scanning electron microscopy (SEM) indicated a ductile fracture mechanism, characterized by dimples formed through a combination of shear and tensile modes.
Research Paper
Optimization
Sachin Ghalme; Yusuf Fedai; Sandeep Thorat
Abstract
Computational models/methods are regularly used by the engineering community to evaluate the optimal set of solutions with respect to the defined performance criteria. In the case of multi-objective optimization problems, the set of Pareto front or optimal solutions needs to be evaluated with a simple ...
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Computational models/methods are regularly used by the engineering community to evaluate the optimal set of solutions with respect to the defined performance criteria. In the case of multi-objective optimization problems, the set of Pareto front or optimal solutions needs to be evaluated with a simple and effective search methodology to help the decision maker select the best parameters/factors. In this study an attempt has been made to optimize the content of MWCNTs, cutting speed, and feed rate to minimize delamination factor and thrust force during drilling of MWCNTs reinforced GFRP nano-composite. Entropy-weighted TOPSIS and BHARAT approaches are implemented successfully for evaluating optimal parameters. Experimental result analysis suggests that feed rate being the major contributing factor for affecting delamination factor and thrust force. The optimized levels for MWCNTs, cutting speed and feed rate are 3 (1%), 3 (75 mm/min), and 1 (0.1 mm/rev), respectively, as obtained by both methods. Comparative analysis of entropy-weighted TOPSIS and BHARAT approach has been performed in relation to multi-criteria decision-making problems. The evaluated Pearson's and Spearman's correlation coefficient for both methods are 0.98, suggesting a high correlation between both methods.
Research Paper
Welding
Worapong boy Boonchouytan; Watthanaphon Cheewawuttipong; Prapas Muangjunburee
Abstract
This study investigates the effects of tool rotational speed and traverse speed on the microstructural development and mechanical characteristics of friction stir welded (FSW) AA6082-T6 aluminum alloy joints. Welding was performed at rotational speeds of 710, 1000, and 1400 rpm and traverse rates of ...
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This study investigates the effects of tool rotational speed and traverse speed on the microstructural development and mechanical characteristics of friction stir welded (FSW) AA6082-T6 aluminum alloy joints. Welding was performed at rotational speeds of 710, 1000, and 1400 rpm and traverse rates of 14, 28, and 56 mm/min to elucidate the correlation between process parameters, relative heat input, and joint performance. The macrostructural analysis verified the presence of robust weld production devoid of macroscopic flaws across all parameter combinations. Optical microscopy demonstrated polished equiaxed grains in the stir zone, indicative of deformation-induced recrystallization during solid-state processing, while the redistribution of Mg2Si and Al6Mn containing phases facilitated microstructural homogenization. Mechanical tests indicated that hardness and tensile strength typically rose with higher rotational and traverse rates, reaching peak values of 73.77 HV and 111.77 MPa at 1400 rpm and 56 mm/min, respectively. Impact toughness attained a peak value of 13.00 Nm at 1000 rpm and 14 mm/min, where modest heat input and strain rate facilitated a more ductile fracture behavior. The results suggest that joint behavior is determined by the equilibrium between temperature exposure and plastic deformation, rather than by a singular predominant factor. A balance between strength and impact toughness was achieved within the current parameter range of 1000–1400 rpm and 14–56 mm/min, offering practical guidelines for the optimization of AA6082-T6 friction stir welds.
