Studi Numerik Karakteristik Aliran di dalam Gradual Expansion dengan D/d = 2 Variasi Sudut Expansion 5°, 22°, 60°

Liska, Nofema Tria (2024) Studi Numerik Karakteristik Aliran di dalam Gradual Expansion dengan D/d = 2 Variasi Sudut Expansion 5°, 22°, 60°. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Gradual expansion banyak digunakan untuk menghubungkan pipa dengan diameter berbeda untuk menyesuaikan flow rate. Penerapan gradual expansion pada penelitian ini dikarenakan gradual expansion dapat mengurangi frictional loss lokal dibandingkan dengan sudden expansion yang disertai dengan perubahan dramatis pola aliran dan tekanan di daerah sudden contraction dan besar turbulence loss yang disebabkan oleh vortices di daerah sudden expansion. Pada gradual expansion mengalami perubahan pembesaran penampang sehingga menimbulkan pressure losses baik dalam pemasangan expansion maupun dalam sistem perpipaan yang berada bagian downstream expansion. Terdapat beberapa faktor penyebab tingginya pressure drop aliran di dalam gradual expansion di antaranya expansion angle dan bilangan Reynolds. Semakin besar nilai expansion angle akan memicu separasi aliran dan berdampak pada tingginya nilai pressure drop. Selain itu, seiring meningkatnya bilangan Reynolds maka dapat mempengaruhi pada daerah separasi aliran. Penelitian dilakukan secara numerik menggunakan software ANSYS 2024 R1 dengan 3D untuk mengetahui bentuk geometri gradual expansion yang menyebabkan terjadinya pressure drop paling minimal. Penelitian ini dimodelkan dengan model turbulensi k-ε realizable. Gradual expansion menggunakan diameter dengan rasio 1:2 dengan variasi expansion angle menggunakan 5°, 22°, 60° dan bilangan Reynolds 〖(Re〗_d) = 0,93 x 10^4, 2,80 x 10^4, dan 6,17 x 10^4. Berdasarkan studi numerik didapatkan hasil berupa parameter loss coefficient, coefficient of pressure, perubahan profil kecepatan, kontur kecepatan, kontur tekanan, dan vektor kecepatan. Hasil diperoleh bahwa semakin besar sudut expansion maka semakin besar nilai loss coefficient (K_L ) dan semakin kecil nilai coefficient pressure (Cp). Semakin besar nilai Re maka semakin kecil nilai K_Ldan semakin besar nilai coefficient pressure (Cp). Nilai K_L terbesar pada sudut 60° dengan nilai Red = 0,93 x 10^4 sebesar 0,83. Nilai Cp terbesar pada sudut 5° dengan nilai Red = 6,17 x 10^4 sebesar 0,67. Semakin besar nilai Cp maka pressure drop akan rendah, semakin besar nilai KL maka pressure drop akan tinggi. Semakin besar sudut expansion maka separasi akan terjadi lebih awal. Sedangkan semakin besar bilangan Reynolds yang digunakan, penundaan separasi lebih kebelakang. Pada θ = 5° tidak terlihat adanya aliran backflow akibat separasi. Pada θ = 22° penundaan separasi yang lebih terbelakang pada 〖Re〗_d = 6,17 x 10^4 dengan posisi separation point x = 5 mm. Pada θ = 60° penundaan separasi yang lebih terbelakang pada 〖Re〗_d = 6,17 x 10^4 posisi separation point pada x = 0,440 mm. Pada sudut expansion 60° dengan kecepatan 0,329 m/s, 0,987 m/s, dan 2,172 m/s mengalami peristiwa jet flow. Di daerah jetflow, wall separation sangat kasar dan meluas sehingga pada daerah ini gradual expansion mengalami performa yang sangat buruk.
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The gradual expansion is widely employed for flexibly connecting pipes with different diameters to adjusting the flow rates. The application of gradual expansion in this study is because gradual expansion can reduce local frictional loss compared to sudden expansion which is accompanied by dramatic changes in flow and pressure patterns in the sudden contraction area and large turbulence loss caused by vortices in the sudden expansion area. In gradual expansion, there is a change in cross-sectional enlargement that causes pressure losses both in the expansion installation and in the piping system that is downstream of the expansion. There are several factors that cause high flow pressure drop in gradual expansion including expansion angle and Reynolds number. The greater the value of expansion angle will trigger flow separation and have an impact on the high pressure drop value. In addition, as the Reynolds number increases, it can affect the flow separation area. The study was conducted numerically using ANSYS 2024 R1 software with 3D to determine the gradual expansion geometry that causes the minimum pressure drop. Ths research is modeled with a realizable k-ε turbulence model. Gradual expansion uses diameter with a ratio of 1:2 and expansion angle using 5°, 22°, 60°. For this research using Reynolds numbers 〖Re〗_d= 0,93 x 10^4, 2,80 x 10^4, and 6,17 x 10^4. Based on numerical studies, the results are obtained in the form of loss coefficient parameters, coefficient of pressure, velocity profile changes, velocity contours, pressure contours, and velocity vectors. The results obtained that the greater the expansion angle, the greater the loss coefficient (KL) and the smaller the coefficient pressure (Cp). The greater the Re value, the smaller the KL value and the greater the coefficient pressure (Cp) value. The largest KL value at an angle of 60° with a value of Red = 0,93 x 104 is 0,83. The largest Cp value at an angle of 5° with a value of Red = 0,93 x 104 is 0,67. The greater the Cp value, the lower the pressure drop, the greater the KL value, the higher the pressure drop. The larger the expansion angle, the earlier the separation will occur. While the greater the Reynolds number used, the separation delay is more backward. At θ = 5° there is no visible backflow due to separation. At θ = 22° the separation delay is more retarded at Red = 6,17 x 10^4 with separation point position x = 5 mm. At θ = 60° the retarded separation delay at Red = 6,17 x 10^4 separation point position at x = 0.440 mm. At an expansion angle of 60° with velocities of 0,329 m/s, 0,987 m/s, and 2,172 m/s, jet flow events occur. In the jet flow area, the wall separation is very rough and widespread so that in this area gradual expansion experiences very poor performance.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	Reynolds Number, Gradual Expansion, Pressure Drop, Diameter Ratio, Expansion Angle, Bilangan Reynolds, Rasio Diameter, Sudut Expansion
Subjects:	T Technology > TJ Mechanical engineering and machinery > TJ935 Pipe--Fluid dynamics. Tubes--Fluid dynamics
Divisions:	Faculty of Industrial Technology and Systems Engineering (INDSYS) > Mechanical Engineering > 21201-(S1) Undergraduate Thesis
Depositing User:	Nofema Tria Liska
Date Deposited:	26 Aug 2024 03:45
Last Modified:	26 Aug 2024 03:45
URI:	http://repository.its.ac.id/id/eprint/114437

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