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"Karakteristik refrigerant natural (Propane) perlu dikaji lebih dalam saat ini, karena penggunaan refrigerant konvensional (sintetis) sudah mulai dibatasi karena tingginya Ozone Depletion Potential (ODP) dan Global warming potential yang berbahaya untuk keberlangsungan ozon dan menaikkan peluang naiknya suhu bumi. Karakteristik yang ditinjau dalam penelitian ini adalah penurunan tekanan dari masing-masing refrigerant yang dilakukan dengan memvariasikan fluks massa dan fluks kalor. Variasi fluks kalor untuk kedua refrigerant pada penelitian ini adalah 0.20 KW/m2 - 0.69 KW/m2. Sementara untuk fluks massa dari kedua refrigerant diatur supaya mendekati nilai yang sama. Hasil yang didapat adalah penurunan tekanan dipengaruhi oleh fluks kalor danfluks massa serta R-290 mempunyai penurunan tekanan lebih rendah dibanding R-22.

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The characteristics of natural refrigerants (Propane) need to be studied more deeply at this time, because the use of conventional (synthetic) refrigerants is starting to be limited due to the high Ozone Depletion Potential (ODP) and Global warming potential which are dangerous for the sustainability of ozone and increase the chance of rising earth temperatures. The characteristic reviewed in this research is the pressure reduction of each refrigerant which is carried out by varying the mass flux and Heat flux. The variation in Heat flux for the two refrigerants in this study was 0.20 KW/m2 - 0.69 KW/m2. Meanwhile, the mass flux of the two refrigerants is adjusted to approach the same value. The results obtained are that the pressure drop is influenced by Heat flux and mass flux and R-290 has a lower pressure drop than R-22. This predicted result is in accordance with research conducted by A.S Pamitran et al (2010) in testing pressure drops for 5 types of refrigerants."

"ABSTRACT

The stress analysis on the chemical and volume control piping system of the reactor coolant for the AP600 nuclear power plant has been done. By using CAEPIPE computer code version 3.32 revision 0, the first step of analysis has shown that CVS-APGOO piping system would be over stress if the piping supports were not used in the piping system. Furthermore the displacement of the piping system were larger and the piping would be deflected and /or ruptured. The second step of analysis has shown that the piping system would be in accordance with the limit stress of ASME Code Section III Subsection ND , 1980 Edition, providing the piping supports are placed in the proper location. In addition the displacement of the piping system would be very small, both on the nuclear power plant operation condition or during seismic event. Therefore, the CVS-APGOO piping system, that has been completed with the supports in the proper location is feasible to be fabricated and constructed.ABSTRAK

Telah Dilakukan analisis beban (stress) sistim pipa pengendali volume dan kimiawi (CVS) pendingin reaktor pada PLTN AP600. Dengan menggunakan paket Computer Code "CAEPIPE" versi 3.32 revisi 0, hasil analisis pendahuluan menunjukkan bahwa sistim pipa CVS-APGOO akan mengalami tegang berlebih bila alat penunjang pipa tidak dipergunakan didalam sistim pipa. Selain itu sistim pipa akan bergeser terlalu besar yang memungkinkan pipa akan melengkung atau pecah. Bila alat penunjang pipa ditempatkan pada lokasi yang tepat pada sistim pipa CVS-APGOO, hasil analisis kedua menunjukkan bahwa sistim pipa memenuhi kriteria batas tegangan ASME Code Seksi III Subseksi ND Tahun 1980. Selanjutnya analisis kedua menunjukkan bahwa sistim pipa CVS-AP600 pergeserannya amat kecil baik pada saat sistim pipa dioperasikan ataupun pada saat mengalami gempa bumi dikemudian hari. Dengan demikian sistim pipa CVS-APGOO yang telah dilengkapi dengan alat penunjang pipa pada setiap lokasi yang diperhitungkan layak untuk di fabrikasi dan dikonstruksi."

"Sebuah experiment telah dilakukan untuk penggunaan refrigeran ramah lingkungan menjadi kebutuhan manusia. Dalam percobaan aliran mendidih R-22, diameter pipa konvensional 7,6 mm digunakan. Variasi fluks panas dari 5,9 kW / m2 hingga 25,04 kW / m2, fluks massa 282 kg / m2.s hingga 630 kg / m2.s, dan suhu saturasi dari -0,42 ° C hingga 11,97 ° C untuk hasil R- 22. Hasil tersebut dipengaruhi oleh penurunan tekanan di fluks massa, fluks panas dan temperature saturasi. Adapun perpindahan kalor dipengaruhi oleh fluks kalor dan temperatur, sedangkan fluks massa menunjukkan tidak ada perubahan dalam perpindahan kalor untuk nilai R-22. Dalam rangka untuk mencari dan membandingkan hasil, Computational Fluid Dynamics (CFD) telah menjadi pendekatan untuk desaindan evaluasi kinerja. Pada penelitian ini, simulasi numerik untuk internal pipa dilakukan dengan menggunakan model Eulerian dengan paket CFD, ANSYS Fluent 12.1. Turbulensi di fase cair dan gas dijelaskan menggunakan model k-ε. Parameter hidrodinamika global seperti fluks masa dan kecepatan cairan telah diteliti untuk berbagai dangkal uap dan kecepatan gas, dengan simulasi 3D. Selain itu, studi geometri dan skala pengaruh pada pipa horisontal telah dipertimbangkan. Hasil penelitian menunjukkan fluks massa dan fluks panas memiliki efek signifikan pada parameter hidrodinamik, yang dapat menyebabkan efek besar pada hasil penurunan tekanan. Perhitungan numerik dengan sistem aliran dua fase gas-cair telah dilakukan untuk mengetahui pengaruh penurunan tekanan, perbedaan suhu, dan massa penurunan fluks pada karakteristik hidrodinamika fluks massa yang berbeda dan fase atau jenis arus. Hasil ini diproduksi mengungkapkan bahwa CFD memiliki potensi yang sangat baik untuk mensimulasikan dua-fase sistem aliran.

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An experiment has been done previously to the use of environmentally friendly refrigerants into human needs. In the experiment of boiling flow conditions, R-22 is done in a conventional pipe diameter of 7.6 mm. Variation of heat flux of 5.9 kW / m2 to 25.04 kW / m2, the mass flux of 282 kg / m2.s up to 630 kg / m2.s, and the saturation temperature of -0.42 ° C to 11.97 ° C for R-22.The results are influenced by the pressure drop in the mass flux, heat flux and temperature saturation. As for the heat, transfer is affected by the heat flux and temperature saturation, whereas the mass flux showed no change in the heat transfer value for R-22. In order to find and compare results, Computational Fluid Dynamics (CFD) has become an approach for design, scale-up and performance evaluation. In the present work, numerical simulations for internal-pipe were performed using the Eulerian model with CFD package, ANSYS Fluent 12.1. The turbulence in the liquid and vapor phase are described using the k-ε model. Global hydrodynamic parameters like mass flux and liquid velocity have been investigated for a range of superficial vapor and gas velocities, only with 3D simulations. Moreover, the study of geometry and scale influence on the horizontal pipe have been considered. The results suggest mass flux and heat flux have significant effects on the hydrodynamic parameters, which may lead to substantial effects on the pressure drop results. Numerical calculations with gas-liquid two-phase flow system have been carried out to investigate the effect of mass flux and heat flux on the hydrodynamic characteristics of two-phase flows. These produced results reveal that CFD have excellent potential to simulate two-phase flow system."

"Two phase flow is a part of multi-phase flow that is distinguished according to its phase (liquid-gas, solid-liquid, and gas-liquid), flow direction (cocurrent and counter current), and pipe orientation (horizontal, vertical, and inclined). The objectives of this research were to observe pressure drop and visualization of the flow at test section. The experiment test was conducted for constant liquid velocity and variable gas velocity, at constant gas velocity and variable liquid velocity conditions in vertical upward gas-liquid two-phase flow.The research was conducted by using a transparant pipe (plexiglass) with diameter of 24 mm, air dan liquid (pure water u = 0,98E-3 Pa.s, solution of CMC u = 2,3E-3 Pa.s and 4,7E-3 Pa.s) as working fluids. The flow pattern was observed at JL= 0,007 m/s to 0,003 m/s, whereas JG was between 0,005 m/s to 0,1 m/s at air pressure of 1 atm and temperature of 27° C - 29° C.The result shows that the change of JG, JL and viscosity influence the pressure drop and flow pattern. Pressure drop increased with the increase of JL under the constant JG. Meanwhile the pressure drop decreases with the increase of JG under the constant JL. It were found that pressure drop increases with the increases of liquid viscosity and the flow pattern transitions strongly depend on the liquid viscosity."

"Pipa elbow biasanya digunakan sebagai sambungan (fitting) ketika terjadi perubahan orientasi yang cukup ekstrim pada jalur pipa transmisi. Jalur pipa transmisi biasanya ditanam didalam tanah (underground) yang rentan terhadap korosi eksternal sehingga perlu dilakukan analisis keandalan. Analisis keandalan dilakukan dengan menggunakan simulasi Monte Carlo dengan terlebih dahulu mengukur pH, resistivitas tanah dan menghitung laju korosi eksternal. Keandalan pipa elbow pada segmen I adalah 39.56%, segmen II adalah 75.68%, dan segmen III adalah 99.99% Nilai resistivitas tanah pada segmen I berada pada level very corrosive (<500Ω-cm), segmen II berada pada level corrosive (500-1000 Ω-cm), dan segmen III berada pada level moderately corrosive (1000-2000 Ω-cm). Nilai pH berada pada rentang 5-7 untuk semua segmen. Laju korosi pipa elbow berkisar antara 0.029-0.765 mm/year, dan meningkat seiring penurunan nilai resistivitas tanah. Pengamatan struktur mikro menunjukkan ukuran butir pipa elbow adalah sebesar 16,5 µm. Hasil permodelan Autodesk Inventor memperlihatkan bahwa terjadi konsentrasi tegangan pada pipa sebesar 160 MPa , sementara itu hasil permodelan Caesar II.5.1 menunjukkan bahwa bending stress pada pipa elbowmerupakan stress paling tinggi (666-679 kg./sq. cm) pada saat kondisi operasi.

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Elbow pipe is commonly used as fitting when pipeline shows an extreme change on its direction. Generally, transmission pipeline is buried underground which severe to external corrosion, thus reliability analysis is required. Reliability analysis was performed by using Monte Carlo simulation by first measured pH, soil resistivy and external corrosion rate. Reliability of elbow pipe at segment I was 39.56%, segment II was 75.68%, and segment III was 99.99%. Soil resistivity value at segment I was on very corrosive level (<500Ω-cm), while segement II was on corrosive level (500-1000 Ω-cm), and segment III was on moderately corrosive level (1000-2000 Ω-cm). pH value ranged from 5-7 for all segments. Corrosion rates ranged from 0.029-0.765 mm/year, and increased gradually as decreased of its soil resistivity value. Microstructure examination showed that grain size on elbow pipe was 16,5 µm. Autodesk Inventor modelling revealed that stress concentration was occured on innert side of elbow pipe as much as 160 MPa , while Caesar II.5.1 modelling showed that bending stress was the highest stress (666-679 kg./sq. cm) in operating condition."