M. M. Rahman

Numerical Simulation and Experimentation of Warm Metal Powder Compaction Process

Powder compaction at elevated temperature or known as warm compaction is a process of producing green compacts from metal powder, which is generally conducted between the ambient and the recrystalization temperature of the main powder constituent. Even though, warm compaction was initiated at around 1998, not a lot of information can be found in the literature especially on the numerical simulation of the process. Therefore, this paper presents the simulation of warm metal powder forming process by using the developed computer code. The Elliptical Cap yield model has been used to represent the deformation behaviour of the powder mass during the forming process at above ambient temperature. The material properties of powder mass, i. e., friction coefficient, elastic index, and plastic index, at different forming temperature, are established through warm compaction experiment. The simulation was conducted to generate a green compact of a plain bush component. Some numerical simulation results were validated through experimentation, where a good agreement was found between the numerical simulation and the experimental results.

Effect of Feedstock Preparation and Forming Temperature to the Characteristics of Green Compacts

This paper presents the outcomes of an experimental investigation on the effect of feedstock preparation to the mechanical properties and microstructures of green compacts formed at above ambient temperature. A lab-scale uni-axial die compaction rig was designed and fabricated which enabled the powder forming at elevated temperature. Iron powder ASC 100.29 was mechanically mixed with different quantity of zinc stearate for 10, 30, and 60 minutes, respectively. Green compacts were generated by forming the prepared feedstock at room temperature and 180oC through simultaneous upward and downward axial loading. The defect-free green compacts were subsequently characterized for their physical and mechanical properties and their microstructures were evaluated. The results revealed that the characteristics of green products were affected by feedstock preparation as well as forming temperature. From this study, the suitable zinc stearate content, mixing time, and forming temperature were identified for the generation of high quality green compacts through warm forming route.

Numerical simulation of fluid flow and heat transfer in enhanced copper tube

Inner grooved tube is enhanced with grooves by increasing the inner surface area. Due to its high efficiency of heat transfer, it is used widely in power generation, air conditioning and many other applications. Heat exchanger is one of the example that uses inner grooved tube to enhance rate heat transfer. Precision in production of inner grooved copper tube is very important because it affects the tubes performance due to various tube parameters. Therefore, it is necessary to carry out analysis in optimizing tube performance prior to production in order to avoid unnecessary loss. The analysis can be carried out either through experimentation or numerical simulation. However, experimental study is too costly and takes longer time in gathering necessary information. Therefore, numerical simulation is conducted instead of experimental research. Firstly, the model of inner grooved tube was generated using SOLIDWORKS. Then it was imported into GAMBIT for healing, followed by meshing, boundary types and zones settings. Next, simulation was done in FLUENT where all the boundary conditions are set. The simulation results were observed and compared with published experimental results. It showed that heat transfer enhancement in range of 649.66% to 917.22% of inner grooved tube compared to plain tube.

Verification and Validation of Fire Dynamic Simulator for Enclosed Car Park

When fire occurs, smoke is detrimental to human health and interrupts the evacuation process if it is not controlled properly. Due to the existence of beams in a building, smoke tends to stagnate near the obstacles and recirculates, further delaying the evacuation process. In the current study, Fire Dynamic Simulator (FDS) is employed as a numerical tool to simulate smoke propagation. The numerical result is then compared with the available experimental data obtained from the literature. It is found that the agreement between the numerical and experimental results is promising. From this study, it is shown that FDS can indeed be used to model the smoke propagation in an enclosed car park; hence, it can be utilised to generate other CFD models related to fire simulation.

A parametric analysis of the strength-porosity relationship of green compacts formed through powder compaction route

The strength of a green compacts formed through warm powder compaction route is strongly dependent on the forming load and temperature. As the forming load increases, the powder particles move from its initial position by sliding among them and die wall. This movement results in new arrangement and packing order of the particles. However, due to this movement, pores among the particles are generated that affects the mechanical properties of the green compacts. Having pores in green compacts lead to strain intensification at ligaments between pores during sintering at later stage, hence serve as areas for crack initiation. Therefore, as the powder forming relates directly to the load and temperature, strength to porosity relationship has to be analyzed based on those parameters. This paper presents the effect of porosity to the strength of green compacts formed at different load and temperature (70 kN to 130 kN; 30°C to 200°C). The bending strengths of green compacts are measured while Scanning Electron Microscopy is used for porosity evaluation. It has been found from the results that porosity and strength are related to each other at all forming parameters. In addition, high forming load and temperature give better strength due to porosity reduction.

An experimental study on condensation and evaporation heat transfer and pressure drop in microfin copper tubes

This paper presents the experimental investigation to determine the condensation and evaporation heat transfer coefficients and pressure drops for the flow of R22 through internally grooved copper tubes namely B16-46 and D12-52. A series of experiments were conducted to evaluate the condensation and evaporation performances of the internally grooved copper tubes. Condensation tests were conducted at mass flux rates of 180 to 537 kg m−2 s−1 and the vapor qualities ranged from a nominal value of 83% at the test section inlet to 6% at the outlet. Evaporation tests were conducted at mass flux rates of 110 to 404 kg m−2 s−1 and the nominal vapor qualities at the inlet and outlet were 0 and 85%. For both the condensation and evaporation tests, the heat transfer coefficients and pressure drops are found to increase as the mass flux rate increases.

Characteristics of FeCuAl powder compacts formed through uniaxial die compaction route

This paper presents the development of FeCuAl powder compacts through uniaxial die compaction process. Iron powder ASC 100.29 was mechanically mixed with other elemental powders, i.e., copper (Cu), and aluminum (Al) for 30 minutes at a rotation of 30 rpm. The feedstock was subsequently shaped at three different temperatures, i.e., 30°C, 150°C, and 200°C through simultaneous upward and downward axial loading of 325 MPa. The as-pressed samples termed as green compacts were then sintered in argon gas fired furnace at 800°C for three different holding times, i.e., 30, 60, and 90 min at a rate of 10°C/min. The sintered samples were characterized for their relative density, electrical resistivity, and bending strength. The microstructure of the sintered samples was also evaluated through scanning electron microscopy (SEM). The results revealed that the sample formed at 150°C and sintered for 30 min obtained the best final characteristics, i.e., higher relative density, lower volumetric expansion and electrical resistivity, and higher bending strength. Microstructure evaluation also revealed that the sample formed at 150°C and sintered for 30 min obtained more homogeneous distribution of grains and less interconnected pores compared to the other samples.

Corrosion of aluminum alloy used as sacrificial anode for steel embedded concrete transmission tower in brackish mud

This paper presents the cathodic protection of steel embedded concrete of aluminum based alloy in brackish mud. In this experiment, aluminum based alloys containing 5% zinc, 2% magnesium, and 0.5-2% stannum were fabricated. These elements were added because they produce heat treatable alloys, improved anti friction characteristics, fluidibility, and contain highest strengthening effect on aluminum alloys. These alloys were tested as sacrificial cathodic protection for the standard steel embedded concrete exposed to sea water and brackish mud. Surface morphology of the samples after subjected to corrosion was investigated through scanning electron microscopy (SEM) and anode capacity test (efficiency test). The results revealed that sample with the composition of 95.6% of aluminum, 3.83% of zinc, and 0.19% of stannum showed the best performance hence it was selected for cathodic protection in brackish mud.

Effect of Poly(Vinyl Alcohol) Addition on the Properties of Hydrothermal Derived Calcium Phosphate Cement for Bone Filling Materials

The effect of addition of poly(vinyl alcohol) on hydrothermal derived calcium nphosphate cement has been studied. The precursors used to prepare the cement were calcium noxide (CaO) and ammonium dihydrogen phosphate (NH4H2PO4); the reaction was conducted nin water at 80-100°C. To improve properties of CPC, poly(vinyl alcohol) (PVA) of 1wt% and n2wt% was added to the liquid phase of CPC and the results were compared to CPC without nPVA addition. The addition of PVA was proved to bring remarkable effects on cohesion, nsetting time and mechanical strength of CPC which make it suitable physically for injectable nbone filler applications.

Application of response surface methodology for optimizing evacuation time in enclosed car park

Smoke fills the car park area due to smoke back layering occurred during a fire. The presence of the beam which leads to the smoke back layering phenomena is investigated to remain smoke layer longer at the upper level with fewer occurrences of backflow. In the current study, a combination of Design of Experiment (DOE); Central Composite Design, (CCD) and statistical tools Response Surface Methodology, (RSM) were utilised to evaluate an optimal design for longer smoke residing time. The Fire Dynamic Simulator (FDS), a CFD model for the fire-driven fluid flow, was employed as a flow simulation tool. The result of six replication model produced by DOE, the error that ranged from 0.48% to 1.77% indicating that the model is reliable. It was also found that the polynomial regression result was linear with predicted R2 of 97.64%, which was within the actual R2 (99.45%). The effects of five control parameters such as ceiling height, beam spacing, transversal beam, extraction rate and longitudinal beam on the smoke descend time has been found to be significant. In the optimal design, the smoke remained longer at the upper level with the percentage of improvement 217.95%. The contribution of the study is the time measured in this analysis is adequate within the beam span only. Interestingly, it effects to the overall geometry with having a lengthier time of smoke to descend. The polynomial model should be used for future engineering design in an enclosed car park.