STUDI EKSPERIMEN MENGENAI MEKANISME ALIRAN SLUG PADA ALIRAN DUA FASA ADIABATIS SEARAH DALAM PIPA HORIZONTAL

OKTO DINARYANTO, Prof. Dr. Ir. Indarto, DEA;Dr. Eng. Deendarlianto, S.T., M.Eng

2018 | Disertasi | S3 ILMU TEKNIK MESIN

Fenomena aliran dua fasa sering dijumpai pada berbagai aplikasi industri seperti minyak bumi, proses industri, dan pembangkit listrik. Salah satu kasus yang paling berbahaya, yaitu fenomena slugging, harus dihindari karena adanya tekanan osilasi tinggi di dalam pipa dan menghasilkan getaran tinggi pada struktur perpipaan. Karena momentum aliran slug yang tinggi, getaran dan kekuatan mekanis yang dihasilkan dari aliran slug harus dipertimbangkan untuk memastikan keamanan operasional dan disain dari sistem perpipaan. Fluktuasi cairan dan gas slug dapat menyebabkan kerugian struktural yang menyebabkan retak dan korosi pada pipa. Selanjutnya, aliran slug pada frekuensi tinggi mempercepat laju korosi pipa. Dari sudut pandang aliran multiphase, pemahaman tentang mekanisme inisiasi slug sangat penting dalam perancangan perpipaan. Studi eksperimental aliran slug dalam pipa horizontal dilakukan untuk menyelidiki mekanisme inisiasi dan perkembangannya. Air dan udara digunakan sebagai fluida kerja. Diameter pipa bagian dalam adalah 50, 26, dan 16 mm. Kecepatan superfisial air antara 0,1-0,77 m/s dan kecepatan superfisial udara masing-masing adalah 0,31-6,2 m/s. Dalam penelitian eksperimental ini, mekanisme inisiasi slug dan karakteristik aliran sub-regime aliran slug berdasar oleh pengamatan visual, fluktuasi tekanan, dan fluktuasi liquid hold-up. Selain itu, frekuensi inisiasi slug dan evolusi frekuensi slug sepanjang pipa juga diamati dengan menggunakan dua kamera video berkecepatan tinggi. Sebagai hasilnya, beberapa mekanisme dasar inisiasi aliran slug pada pipa horisontal berhasil diklarifikasikan. Mekanisme inisiasi terdiri dari tumbukan gelombang, pertumbuhan gelombang, dan gelombang gangguan. Peta inisiasi aliran slug diusulkan untuk menjelaskan mekanisme tersebut. Frekuensi inisiasi slug dan frekuensi perkembangan slug diperoleh dan dihubungan dengan posisi sepanjang pipa. Pengukuran tekanan statis juga digunakan untuk memverifikasi hasil pengolahan citra pada karakteristik mekanisme inisiasi slug. Selanjutnya, Karakterisasi sub-regime aliran slug pada pipa horisontal telah berhasil dilakukan. Hasilnya menunjukkan bahwa sub-regime aliran slug dapat dibagi menjadi lima pola aliran: Slug-Plug (SP), Low Bubbles (LB), Low dispersed Bubbles (LdB), High dispersed Bubbles (HdB), and Slug-Wavy (SW). Hasil kualitatif dan kuantitatif yang diperoleh dari penelitian dapat digunakan untuk mengembangkan dan mengevaluasi model yang ada

Two-phase flow phenomena are often encountered in various industrial applications such as petroleum, process, and power plant. One of the most dangerous cases, namely as the slugging phenomena, should be avoided due to the existence of high oscillation pressure inside the pipe and produces a high vibration on the piping structure. Due to the momentum of the slug flow, vibration and mechanical forces should be considered to ensure the operational safety and the design of the pipeline system. The fluctuating liquids and the gas slugs induce the structural disadvantages that lead to crack and corrosion of the pipe. Furthermore, the high frequency slug flows speed up the pipe corrosion rates. From the view point of multiphase flow, the understanding of the slug initiation mechanism is very important in pipeline design. The experimental investigation of gas-liquid slug two-phase flow in a horizontal pipe was carried out to investigate the initiation and flow development mechanisms. Air and water were used as the working fluids. The inner pipe diameter was 50, 26, and 16 mm. The water superficial velocity was between 0.1-0.77 m/s and the air superficial velocity were 0.31-6.2 m/s, respectively. In the present experimental study, the slug initiation mechanisms and sub-regime slug flow characteristics were elucidated by visual observation, pressure fluctuations, and liquid hold-up fluctuations. Moreover, the initiation frequency of slug flow and the evolution of passing slug frequency along the pipeline were also observed by using two high speed video cameras. As the results, several basic mechanisms of slug flow initiation in a horizontal pipe were clarified. Those were the wave coalescences, the wave growth mechanism, and the large disturbance waves. A flow initiation map was proposed to address those mechanisms. Here, the slug initiation frequency and the passing slug frequency were obtained in relation to the pipe length position. The static pressure measurement was also used to verify the image processing results on the characteristics of slug initiation mechanisms. Furthermore, characteristic of the sub-regime of air-water slug two-phase flow in horizontal pipes have been successfully conducted. The result indicates that sub-regime can be divided into five flows: Slug-Plug (SP), Low Bubbles (LB), Low dispersed Bubbles (LdB), High dispersed Bubbles (HdB), and Slug-Wavy (SW). The obtained qualitative and quantitative results from the investigation can be used to evaluate the recent available models.

Kata Kunci : inisiasi slug, frekuensi slug, perkembangan slug, sub-regime aliran slug.