Simulative Study On Liquid/Gas Two–Phase Flow Measurement For Dual–Plane Ultrasonic Transmission–Mode Tomography

Abstract

Kajian simulatif telah dijalankan mengenai penggunaan teknik korelasi–silang untuk ultrasonik transmisi tomografi satah berganda. Teknik ini digunakan untuk membandingkan isyarat dari setiap satah yang masing–masing dinamakan satah–bawah dan satah–atas. Pemisahan jarak antara kedua–dua satah adalah tetap. Hasil dari perbandingan isyarat satah berganda, digabungkan dengan jarak pemisahan yang telah diketahui termasuk kelajuan sistem memproses maklumat, boleh digunakan untuk menganggarkan kelajuan aliran di dalam paip pemprosesan yang hendak diteliti. Penggabungan Ultrasonik Transmisi Tomografi (UTT) dengan teknik pengukuran korelasi–silang dapat memberikan maklumat yang lebih lanjut mengenai aliran jika dibandingkan dengan sistem UTT bersatah tunggal. Diskusi dalam artikel ini lebih memfokuskan kepada nilai min setiap gambar dan pekali korelasi 2D yang akan digunakan untuk mengkorelasikan gambar tomogram antara satah–bawah dan satah–atas. Prinsip pengukuran kelajuan pergerakan gas didalam keadaan gas dan cecair yg bergelembung berdasarkan pada korelasi–silang antara kedua–dua satah juga dijelaskan. Keputusan awal eksperimen menggambarkan kesesuaian kaedah yang dibentangkan di sini. Kata kunci: Korelasi–silang; corak beku; korelasi min; simulasi satah berganda; tomografi transmisi ultrasonik Simulative studies are done on the use of cross–correlation technique based on a dual–plane ultrasonic transmission tomography for liquid and gas two–phase flow measurement. This technique is used to correlate the signals from each sensing area namely downstream plane and upstream plane. Separation distance between both sensing areas is fixed. The result from cross correlating the dual–plane signals, combined with the known separation distance and the system’s acquisition rate is used to estimate the velocity of the flow inside the investigated process column. Combining Ultrasonic Transmission Tomography (UTT) with the cross–correlation flow measurement technique can provide more information on the flow than a single–plane UTT system. This paper focuses on the mean value of the images and the 2D correlation coefficient that is used to cross–correlate the tomogram images between the downstream and upstream plane of the simulated dual–plane ultrasonic transmission tomography system. The principle of measurement for local gas velocity distribution in a bubbly gas/liquid pipe flow based on crosscorrelation of two plane images is also described. Initial experimental results illustrate the feasibility of the method presented here. Key words: Cross–correlation; frozen pattern; mean correlation; dual–plane simulation; ultrasonic transmission tomography

Gas Hold-Up Profiles Determination by means of Ultrasonic Transducer

“…ka>>1, the diffraction can be ignored and these hold-ups will act as many acoustics opacities [6]. This is because when ka >>1, the surface of the sphere appears as a flat surface with respect to the wavelength and the scattering becomes the same as reflection from a flat surface [7].…”