KAJIAN EKSPERIMEN MENGENAI MEKANISME FLOODING PADA ALIRAN GAS DAN CAIRAN BERLAWANAN ARAH PADA SISTEM PIPA KOMPLEKS
APIP BADARUDIN, Prof. Dr. Ir. Indarto, DEA.; Dr. Deendarlianto, S.T., M.Eng.
2018 | Disertasi | S3 ILMU TEKNIK MESINAliran dua fase dalam pipa mempunyai bentuk yang kompleks karena antarmuka udara-air dipengaruhi beragam konfigurasi geometri serta berubah terhadap waktu. Oleh karena itu untuk mempelajari perilaku aliran dua fase berlawanan arah (CCFL) diperlukan cara untuk menangkap perubahan gerakan antarmuka udara-air. Pengamatan fenomena flooding dan karakteristik geometris dilakukan dengan mengukur tebal film (cairan), drop tekanan pada saluran, debit udara-air dan visualisasi aliran. Penelitian ini dilakukan pada aliran berlawanan arah dua-fase udara-air pada pipa berdiameter 25,4 mm menggunakan perbandingan panjang pipa horisontal dan diameter pipa L/D =25, L/D = 50 dan L/D = 94,5. Selanjutnya untuk untuk mendapatkan data tebal film (film thickness) dilakukan menggunakan program image processing dan sistim akuisisi data dengan sensor parallel wire. Rentang kecepatan superfisial gas dan cairan dalam eksperimen yakni JG (0,16 - 2,79 m/detik) dan JL (0,003 - 0,115 m/detik). Hasil eksperimen menunjukkan CCFL dapat diamati mulai kondisi stratified flow, onset of flooding sampai zero liquid penetration. Pada JL rendah, mekanisme flooding diinisiasi oleh antarmuka yang bergelombang sepanjang pipa horisontal yang diakhiri terbentuknya liquid slug di belokan. Pada JL sedang, fenomena slug terjadi namun pecah di pipa horisontal. Fenomena tersebut terjadi berulang-ulang sampai slug mencapai belokan. Pada JL tinggi, fenomena slug juga terjadi di pipa horisontal dan pecah di belokan. Pengukuran film thickness dapat mengungkapkan karakteristik dari gelombang yang menginisiasi terjadinya slug serta perkembangannya. Perbandingan L/D memberikan pengaruh signifikan terhadap posisi terjadinya fenomena hydraulic jump, onset of flooding dan batas zero liquid penetration pada simulator hotleg. Pengamatan visual menunjukkan dua mekanisme flooding: front-flooding dan rear-flooding. Front-flooding terjadi di pipa horisontal dengan L/D = 50 dan 94,5. Selain itu ditemukan juga di pipa horisontal dengan L/D = 25 pada kecepatan superfisial air rendah dan menengah (JL*)^0.5< 0,32). Hal ini diinisiasi oleh pembentukan liquid slug yang menyebabkan gelombang tak stabil pada hydraulic jump. Sedangkan rear-flooding ditemukan di pipa horisontal dengan L/D = 25 pada kecepatan superfisial air tinggi (JL*)^0.5> 0,32). Hal ini diinisiasi oleh pembentukan gelombang besar yang menutup penampang pipa di dekat keluaran air (water outlet).
The counter-current two-phase flow in the pipe has a complex shape because the air-water interface is influenced by various geometric configurations and changes over time. Therefore, to study the counter-current flow behavior, a way is required to capture the changes of air-water interface movement. Observation of flooding phenomena and geometric characteristics is done by measuring the film thickness, pressure difference in the channel, air-water flow rate and flow visualization. The experiment was carried out in a counter-current two-phase of air-water on a 25.4 mm diameter pipe using a ratio of horisontal pipe length and diameter of pipe L/D = 94.5, L/D = 50 and L/D = 25. To obtain the film thickness data, an image processing program and data acquisition system with parallel-wire sensor were used. The superfisial velocity range of gases and liquids in the experiments is JG (0.16 - 2.47 m/s) and JL (0.003 - 0.118 m/s). Experimental results show that flooding can be observed from the state of stratified flow, onset of flooding to zero liquid penetration. At low JL, the flooding mechanism is initiated by the presence of wavy interface along the horisontal pipes which finally form a liquid blockage on the elbow. At medium JL, slug phenomena occur along the horisontal pipe. However, the liquid is insufficient to maintain the blockage so the slug starts to collapse. It triggers another slug, and the phenomena occur repeatedly until reach a particular point near the elbow area. At high JL, the slug is also formed along the horisontal pipe and maintains its form until collapse on the elbow and initiates the onset of flooding. The film thickness measurement can reveal the characteristics of wave initiating the slug as well as its development. The L/D ratio gives significant influence to the hydraulic jump position, onset of flooding and zero liquid penetration limits in hotleg simulator.The visual observation shows two flooding mechanisms: front-flooding and rear-flooding. Front-flooding was found to occur at the horisontal pipe with L/D = 50 and 94.5. Beside it is found also at horisontal pipe with L/D = 25, on low and medium superfisial liquid velocity (JL*)^0.5< 0.32). This was initiated by the formation of a liquid slug that begins unstable waves on a hydraulic jump. While rear-flooding was found to occur at horisontal pipe with L/D = 25 at high superfisial liquid velocity (JL*)^0.5 > 0.32). This was initiated by the sudden formation of a large wave that completely blocks the whole cross section of the pipe near the water outlet.
Kata Kunci : flooding, CCFL, front-flooding, rear-flooding, film thicknes, image processing, parallel-wires
