Applied Mechanics and Materials Vols. 465-466

Abstract: Previous work shows that gas-jet ignition with two-stage injection technique is effective to extend lean combustible ranges of CNG engines. In this report, the robustness of the gas-jet ignition with two-stage injection method was investigated purposely to improve the performance of a lean burn direct injection CNG engine. The experiment was conducted using an engine at speed of 900 rpm, fuel-injection-pressure of 3MPa, equivalence ratio at 0.8, and ignition timing at top dead center. The effect of first injection timing on the test engine performance and exhaust emission was analyzed. First injection timings near the gas-jet ignition produced unstable combustion with occurrence of misfires except at a timing which produced distinctively good combustion with low HC and CO emissions. Computational fluid dynamics was used to provide hindsight of the fuel-air mixture distribution that might be the cause of misfires occurrence at certain injection timings.

Abstract: The failures of the crankshafts are constantly subjected to cyclic loading which will tend to display the effects of fatigue that is stochastic in nature. The maximum bending moment occurs during the combustion cycle, where the direction of forces acting on the crankshaft will be exactly towards the centre of the crank radius. The torsional stress occurs during the power cycle can be considered as a quasi-static torsion as it is in steady condition. The aim of this paper is to illustrate the development of the analytical stress analysis used to determine mixed mode loading acting on the crankshaft. The analytical method developed according to the geometric ratio of the connecting rod and crankpin web to determine the variation of bending moment and torsional stress. It was observed that the maximum bending moment and torsional stress acting on the crankshaft are at angles and respectively due to the geometric ratio of the connecting rod and crankpin web. The analytical method that was derived and used for this study provides a good accuracy in determining the critical angles for bending moment and torsional stress acting on the crankshaft based on the geometric ratio.

Abstract: Turbulent heat transfer to air flow in annular pipe with sudden contraction numerically studied in this paper. The k-ε model with finite volume method used to solve continuity, moment and energy equations. The boundary condition represented by uniform and constant heat flux on inner pipe with range of Reynolds number varied from 7500 to 30,000 and contraction ratio (CR) varied from 1.2 to 2. The numerical result shows increase in local heat transfer coefficient with increase of contraction ratio (CR) and Reynolds number. The maximum of heat transfer coefficient observed at contraction ratio of 2 and Reynolds number of 30,000 in compared with other cases. Also pressure drop coefficient noticed rises with increase contraction ratio due to increase of recirculation flow before and after the step height. In contour of velocity stream line can be seen that increase of recirculation region with increase contraction ratio (CR).

Abstract: The detection of water leakages in water distribution system has always been a challenge in the water industry as most water pipelines are laid foot underground which are normally unseen to human naked eyes until water starts to flow out from roads and creates puddles. The age in pipelines network is a major problem and the reduction of these has become a major priority for pipeline authorities around the world. This project method are developed based on pressure transient by using single pressure transducer and analyses on newly method of analyzing called synchrosqueeze wavelet transform (SWT) which is viable approach to detect and locate the leak in pipeline system. Transient analyses offer a plausible route towards leak detection due to their robustness and simplicity. The result show that newly developed techniques, SWT appears to improve the ability of the method to identify features in the signal.

Abstract: Drying is essentially a process of simultaneous heat and mass transfer, in general, to remove moisture from a wet material to give a long shelf-life or to facilitate further processing. The drying medium flowing around the material serves to remove the moisture. In most drying operations, water is the liquid evaporated using air as the drying medium [. For each individual particle, the drying process involves moisture migration from the inner core regions to the particle surface. The surface moisture is then vaporized or evaporated into the drying medium.

Abstract: Atrium is gaining popularity in the modern societies because of its special attraction. However, during fire incident it causes significant risk due to its open spaces between floors. In atriums smoke can move easily to upper floors through these open spaces and causes smoke contamination of the atrium upper floors. Moreover, presence of down stand structure at the fire compartment opening is required in any shop in atrium shopping mall to display the trade name of the shop. This study investigated the effect of down stand structure on smoke contamination of upper balconies of an atrium by using Fire Dynamic Simulator, CFD software. A correlation that predict the smoke contamination occurrence in the presence of fire compartment down stand structure is developed. The results shows that down stand structure resulted in increasing the effect of smoke contamination in upper floors of an atrium.

Abstract: The liquid jet breakup is a ubiquitous phenomenon in nature and a classic problem in hydrodynamics. The understanding of the jet breakup mechanism of hot liquids is still a challenge for researchers. The objective of this work was to understand and control the hot water spray jet breakup mechanism at moderate pumping pressures and elevated temperature. For this purpose, the visual and comparative studies were conducted on hollow cone water spray patterns generated by three hollow cone spray nozzles which were installed in an in-house built intermittently forced liquid spraying system. Using a high speed camera, the jet breakup dynamics were visualized as a function of system input parameters. The analysis of the grabbed images confirmed the strong influence of these processing parameters on spray characteristics. It was also predicted that heated liquids generate the dispersed spray patterns and the induction of thermal energy into the system enhances the jet disintegration ability. The spray cone width and angle were not varied significantly whereas the Weber and Reynolds numbers along with other spray parameters showed an appreciable response to the load pressure and water heating temperature at early stages of water injection.

Abstract: In this paper, a new meshless local B-spline basis functions-finite difference (FD) method is presented for two-dimensional heat conduction problem with spatially varying heat generation. In the method, governing equations are discretized by B-spline approximation in the spirit of FD technique using local B-spline collocation. The key aspect of the method is that any derivative at a point or node is stated as neighbouring nodal values based on the B-spline interpolants. Compared with mesh-based method such as FEM the method is simple and efficient to program. In addition, as the method poses the Kronecker delta property, the imposition of boundary conditions is also easy and straightforward. Moreover, it poses no difficulties in dealing with arbitrary complex domains. Heat conduction problem in complex geometry is presented to demonstrate the accuracy and efficiency of the present method.

Abstract: Efforts have been given to improve the turbine blades ability to withstand high temperature for a long period of time by implementing effective cooling system. There are many aspects that should be considered when implementing impingement cooling. This paper will only cover two trending aspects in impingement cooling implementation; the jet-to-target plate distance and the application of ribs in promoting better impingement cooling performance. For target plate distance to impingement jet diameter value, H/d > 1, the area-averaged Nusselt number also decreases as the H/d value increases. This may have been due to a reduction of the amount of momentum exerted by the impinging jets onto the target plate. For H/d < 1, the results have been proven otherwise. Heat transfer in impingement/effusion cooling system in crossflow with rib turbulators showed higher heat transfer rate than that of a surface without ribs because the ribs prevent the wall jets from being swept away by the crossflow and increase local turbulence of the flow near the surface. It could be concluded that both H/d ratio and ribs installation play an important role in enhancing impingement cooling systems heat transfer effectiveness.

Abstract: This paper presents the effect of the changes in fin geometry on pressure drop and heat transfer characteristics of louvered fin heat exchanger numerically. Three dimensional simulation using ANSYS Fluent have been conducted for six different configurations at Reynolds number ranging from 200 to 1000 based on louver pitch. The performance of this system has been evaluated by calculating pressure drop and heat transfer coefficient. The result shows that, the fin pitch and the louver pitch have a very considerable effect on pressure drop as well as heat transfer rate. It is observed that increasing the fin pitch will relatively result in an increase in heat transfer rate but at the same time, the pressure drop will decrease. On the other hand, low pressure drop and low heat transfer rate will be obtained when the louver pitch is increased. Final result shows a good agreement between experimental and numerical results of the louvered fin which is about 12%. This indicates the capability of louvered fin in enhancing the performance of heat exchangers.