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I Made Astina
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Mechanical Engineering

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SIMULASI BEBAN PENDINGINAN BATUAN DALAM REKAYASA TEROWONGAN I Made Astina; Prihadi Setyo Darmanto
Mesin Vol. 10 No. 1&2 (1994)
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Abstract

Rekayasa terowongan sering dihadapkan pada berbagai kendala. Salah satu kendala yang dikaji tulisan ini adalah adanya batuan panas pada suatu bagian tertentu dari terowongan yang akan digali. Kondisi ini tidak munguntungkan dari sisi teknik pengerjaannya mengingat kesulitan para pekerja. Salah satu solusi agar pekerjaan penggalian terowongan dapat dilakukan adalah dengan mendinginkan bagian batuan yang panas tersebut.Di dalam makalah ini akan dibahas teknik pendinginan yang akan digunakan dan estimasi beban di dalam terowongan agar proses penggalian dapat berjalan dengan lancar dan ekonomis. perhitungan beban pendinginan dengan cara numerik juga akan dibahas dalam makalah ini. Fenomenadan dan karakteristik fisik seperti sifat konduktifitas tanah dan batuan, kehomogenan sifat batuan panas dan sumber panas dari batuan panas perlu di pelajari lebih lanjut sehingga penyederhanaan berbagai parameter dalam perhitungan dan estimasi beban diharapkan tidak menyimpang jauh dari beban pendinginan sebenarnya yang terjadi di lapangan.
ANALYSIS OF USING ALTERNATIVE REFRIGERANTS FOR ENERGY SAVING IN DESIGN FRAMEWORK OF AIR-CONDITIONING SYSTEM I Made Astina; Prihadi Setyo Darmanto; Warsito Warsito; Edwin Adryanto
Mesin Vol. 20 No. 2 (2005)
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Environmental issues enforce us to find environmental friendly alternative refrigerants. Increasing energy consumption as consequence of widespread usage of air-conditioning systems needs effort to find efficient systems. Use ability of alternative refrigerants and effect of modified vapor-compression cycles were investigated in this research. In figuring effects of their application on a real air-conditioning system, analysis of redesign of air-conditioning system was concerned to make clear the problem. The results confirm that a right selection of refrigerants to air-conditioning system can improve its performance. Energy saving and economical costs can be reduced significantly. Several groups of hydrocarbons (HC) and hydrofluorocarbons (HFC) have good thermodynamic performance and better than R-22 that will be phased out. By introducing these alternative refrigerants, carbon-dioxide (CO2) emissions can be reduced due to energy saving caused by increasing of the coefficient of performance (COP).
THERMODYNAMIC PROPERTY MODEL OF WIDE-FLUID PHASE n-BUTANE Chan Sarin; I Made Astina; Prihadi Setyo Darmanto; Haruki Sato
Mesin Vol. 22 No. 2 (2007)
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New thermodynamic property model for n-Butane expressed in form of the Helmholtz free energy equation is presented. The formulation consists of eight terms of the so-called ideal-gas part and eighteen terms of the residual part. This is a relatively short equation in comparison to the existing equations, which are widely accepted, including the newly published in year 2006. In its development, available accurate experimental data of fluid properties and theoretical approach from the intermolecular potential were simultaneously considered to insure accuracy and to improve reliability of the equation of state over wide range of pressures and temperatures, especially at low temperatures in which the refrigeration field is concerned. From the coverage of experimental data used in model's development, the validity range is then from triple-point (134.895 K) to temperature of 589 K and pressure up to 69 MPa. The uncertainties with respect to different properties are estimated to be 0.02% in ideal-gas isobaric specific heat, 0.2% in density, 1% in heat capacities, 0.2% in vapor-pressure except at very low temperatures, 0.05% in saturated-liquid density, 0.02% and 0.8% in speed of sound in the vapour and liquid phases, respectively.
ANALISIS TERMODINAMIKA SIKLUS HIBRID UNTUK PEMBANGKIT LISTRIK TENAGA PANAS BUMI I Made Astina; Kadek Edy Kurniawan; Merly Pastalozi
Mesin Vol. 23 No. 2 (2008)
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Modification of the conventional cycle in a geothermaL power plant is an alternative way that can be conducted in efficient conversion of thermal energy to be electric energy. Combination of Brayton cycle with fossil fuel energy sources and Rankine cycle utilizing geothermal energy is interest of this study. Kamojang Geothermal power plant is chosen as an object of casestudy. A software was developed to accurately evaluate the thermodynamic cycle with any modification. The software is supported by thermodynamic properties database directly derived from equations of state. Hybrid cycle analysis was conducted by comparing the conventional geothermal system operating with independent Rankine cycle such as the current Kamojang geothermal power plant in accordance with rational data ernd assumptions.Simulation results show that 157.88% of power increment, 58.17% of efficiency increment for using organic working fluid R-134a. Replacing R-134a with organic working R-600 afford 162.89% of power increnrent and 63.76% of efficiency increment. Ratio of the net power increment respect to the heating input of fuel is 0.52. This high enhancement is achieved for gas turbine inlet temperature of 1100 celcius degree, pressure ratio of 20, gas temperatltre front steam heater at 350 celcius degree, steam temperature from the heater at 250 celcius degree, and organic turbine inlet pressure and temperature at 35 bars and 340 celcius degree, respectively.
Co-Authors Chan Sarin Edwin Adryanto Haruki Sato Kadek Edy Kurniawan Merly Pastalozi Prihadi Setyo Darmanto Warsito Warsito