Applied Mechanics and Materials Vol. 493

Abstract: Energy conservation is one of many technique applied to reduce the global warming effect. Sepuluh Nopember Institute of Technology (ITS) contributes to encourage energy conservation by ITS Eco Campus programs. It has so many activities, one of them is audit energy as one way to get energy efficiency in educational area. ITS central library is most accessable building both student and other academics community with total area more than 400 square matres and high occupation rate approximately 90% everyday. Energy audit techniques were carried out by an energy audit team to identify any energy conservation opportunities (ECOs). walk-through assessment and data analysis were conducted over all building zones. These levels of assessments proved that the building and its mechanical and electrical systems were improperly maintained and inefficiently operated. So that, ITS Central Library will be redesigned to be smart building by improving light intentensity level, humidity, and room temperature appropriate with ASHRAE90.1-2005. Thus exterior building like wall, glass, roof and floor will be redesigned to emphasize minimum total load. Replacement single glass to double glass reduce the load conduction and radiation through glass, approximately 2,7%.

Abstract: . This paper deals with an alternative design method of airfoil for wind turbine blade for low wind speed based on combination of smart computing and numerical optimization. In this work, a simulation of Artificial Neural Network (ANN) for determining the relation between airfoil geometry and its aerodynamic characteristics was conducted. First, several airfoil geometries were generated through transformation of complex variables (Joukowski transformation), and then lift and drag coefficients of each airfoil were determined using CFD (Computational Fluid Dynamics). In present study, the ANN training was conducted using airfoil geometry and its aerodynamic characteristics as input and output, respectively. Therefore, lift and drag coefficients can be directly determined only by giving the airfoil geometry without having to perform wind tunnel experiment or numerical computation. Moreover, the optimization was conducted to obtain an airfoil geometry which gives maximum lift to drag ratio (C_L/C_D) for specific Reynolds number. For this purpose Genetic Algorithm (GA) was applied as optimizer. The results were validated using commercial CFD and it can be shown that the result are satisfactory with error approximately of 6%.

Abstract: Flammability limits and flame speed of methane-carbon dioxide-air mixtures have been studied to understand the effect of carbondioxide on the flammability characteristic of biogas. The fuel of biogas discussed in this study was made by mixing gases of methane and carbon dioxide. The carbon dioxide was varied from 0% (by volume) untill reach the flammability limit of the stoikhiometri biogas-air mixtures. The observation was done using a cubic combustion bomb with the dimension of 500 mm x 200 mm x 10 mm with the initial condition being at room temperature and atmospheric pressure. The ignitor was set at the top of combustion bomb, so the flame propagated downward. Base on the observation results, the presence of carbon dioxide in the fuel ofbiogas caused the flammability limits of biogasair mixture narrower. The biogas-air mixture was still flammable with the highest content of carbon dioxide of 62.5 %vol when the mixture was sthoichiometri. Compared to methane-air mixture, the presence of carbon dioxide in biogas caused a reduction in the flame speed. The stoichiometri mixture has the highest flame speed when the carbon dioxide was not present in the fuel. However, when the carbon dioxide was added in the fuel, the rich mixture has the highest flame speed. This is a consequence of the rich biogas-air mixture having a higher fraction of the carbon dioxide components from the fuel compared to the stoichiometri and lean biogas-air mixture. The result also indicated that at the upper limit the flame still propagated downward to closed to the endwall. However, at the lower limit (lean mixtures), the flame did not intend to propagate downward, it was just at the top and propagate sideward.

Abstract: The effectiveness of heat transfer and the pressure drop coefficient of staggered elliptical tube banks are studied experimentally. The bank consists of 11 elliptical tubes of 0.75 equivalent diameter in an arrangement of 4-3-4. The major and the minor sub-axis of each tube are 24.70 mm and 12.35 mm respectively, and therefore the aspect ratio (AR) of the tube is 2.0. The geometric parameters of the bank are S_T = 24.70 mm, S_L = 37.00 mm and minimum frontal area B = 12.35 mm. Seven mid-tubes are internally heated by electrical heater of 69.6 Watt each. Experiment is conducted in a sub sonic wind tunnel and run with the wind velocities of 1 m/s 12.6 m/s which correspond with Reynolds number of = 346-6904. The results show that the effectiveness (ε) varied from 2144.44 to 15.26. It decreases exponentially at low Reynolds numbers and tended asymptotically at higher Reynolds number. The coefficient of pressure drop (CΔp) ranges from 7.21 to 4.41 decreases continuously at low Reynolds number and asymptotic at higher one.

Abstract: Experimental study on the effect of Reynolds number variation on drag force for various cut angles on D-type cylinders was performed. Five different cut angles on different cylinders were applied including: 35^o, 45^o, 53^o, 60^o, and 65^o. The free stream velocity was varied so the Reynolds number also varied.The experiment was carried out at a subsonic wind tunnel. Drag force for a cut D-type cylinder (for example 35^o) was measured using a force balance and wind speed was varied so that corresponding Reynolds number of 2.4×10⁴÷5.3×10⁴ were achieved. Wind turning angle was kept at 0^o (without turning angle). This experiment repeated for other D-type cylinders.Experiment results show that, for all D-type cylinders, drag force decreased as the Reynolds number increased, then it was increased after attain minimum drag force. For all D-type cylinders and all variations of Reynolds number the drag minimum is attained at cut angle of 53^o. This value is appropriate with previous experiment results.

Abstract: Liquid gas ejector uses liquid as the motive fluid and gas as the entrained fluid. The presence of gas in the liquid reduces the performance of the ejector, especially the diffuser. To observe the effect of entrained gas on the diffuser performance, a series of experiment was conducted.In this research, the motive flow rate was varied from 1.52 to 2.02 l/s and the entrained rate from 0.118 l/s to 0.944 l/s. Its effects on the pressure profile and pressure recovery were observed. If the entrained rate increase, the pressure of the throat upstream, as well as downstream, increase. In the diffuser, longer distance is needed for the pressure to reach its final value. Pressure recovery is mainly affected by void fraction. The higher the void fraction the lower the pressure recovery coefficient

Abstract: The purpose of this report is the effect of the drag coefficient on the car when it is travelling on the road and at different positions while overtaking. The investigation uses SolidWorks Flow simulation software to conduct CFD [. A car and truck has been designed in actual dimensions using SolidWorks. After performing the validation of the software, the simulation is performed having the car in four different positions. The results will determine the drag coefficient and how it is affected in the different positions.

Abstract: Dynamics of bubble in froth flotation have been studied. The purpose of this research is to study the effects of pine oil on the dynamics of small bubble in froth flotation. Dynamics of bubble is an important parameter which determines flotation eficiency. Acrylic pipe was setup as a flotation column and equipped with image capture and lighting equipments. Later on, bubble was generated by a nozzle. A different nozzle size and pine oil concentrations were used in this experiment. Eventually, the dynamics of the bubble were captured by camera and the images were then processed by image processing software. Therefore, bubbles size and its position can be determined. The results indicate that bubble movement can be divided into three stages: acceleration, deceleration and terminal velocity. It is also indicated that pine oil modify surface tension; hence the bubble size become smaller and its velocy decrease. Moreover, pine oil induces the bubble to reach terminal velocity faster then bubble in water wthout pine oil. Therefore, it can be concluded that pine oil affects bubble dynamics significantly.

Abstract: Auto-ignition behavior of lubricating oil is studied experimentally using a cone calorimeter. Based on its Material Safety Data Sheet (MSDS), the adopted lubricating oil has a flash point temperature of 228°C, The measurement of auto-ignition behavior was carried at atmospheric pressure in range of temperature between 350°C to 550°C. In this work, the optical density of smoke resulting from the combustion process was measured at auto-ignition temperature. The result of this study shows that the auto-ignition behavior of lubricating oil is strongly depend on conditions of gas mixture, i.e. oil vapor, nitrogen, and oxygen mixtures. The lubricating oil started to ignite at irradiance temperature of cone heater at 500°C with a measured heat flux value of 16,7 kW/m². At lower temperatures ignition of the mixture occured by piloted igniton sources. No ignition was observed at temperature less than 350°C. At higher irradiance temperature and heat flux (550°C and 21,1 kW/m2), auto-ignition occured at shorter time to ignition and producing higher value of smokes optical density of 1 - 1.4 m^-1.

Abstract: Indonesia has abundant renewable energy resources. In 2005 this country, however, only consumed 0.38% renewable energy of the total energy consumption. Most of the energy sources of the country are from fossil fuels which result in high CO₂ emissions. Solar energy systems would be as an option to reduce the CO₂ emissions of this country. This paper studied the application of solar energy to provide cooling for medium temperature food refrigeration based on Indonesian weather conditions. The paper additionally analyzed the environmental impact relating to CO₂ emissions, and investigated the economical aspect. CFD-Fluent software was applied on modeling the modification of the absorption chiller generator to enable it to operate with heat from solar radiation, while F-Chart and Microsoft Excel spreadsheet were used to analyze the solar system and the economical viability of the technology. The results showed that the optimum modification of the absorption chiller was to use a jacket for heat addition. CFD modeling with Fluent using Diphyl THT as the heat transfer fluid (HTF) indicated that the system would function optimally at fluid temperature input of 180°C, whereas the optimum average temperature of the chiller generator would be 170 °C. The proposed technology was found economically less viable for food refrigeration compared to the vapor compression cycle using R-404A but it could provide a significant impact on the environment by a reduction of 37% CO₂ emissions.