Abstract
Many previous studies of ejector have been conducted to understand and maximize the ejector performance. The study can be in form of experiments, analytical, and numerical simulation. The numerical simulation looks for the most effective and efficient effort and time in modeling flow process inside the ejector. Model simplification becomes one of solution in conducting simulation effectively. Three dimensional models in general are applied to an ejector that would be analyzed. These models can be compared to the simpler model, namely axisymmetric 2D model. The current study investigated the comparison between 3D and 2D models using numerical solution. Three types of ejectors from different application were used as the objects of the study. The analysis was conducted by comparing the qualitative and quantitative results. The results show that qualitatively the 2D axisymmetric model has good comparison to the 3D model. Quantitatively, 2D axisymmetric model has good similarity to 3D model for ejector performance parameters, such as entrainment ratio and Mach number with biggest difference of 5.7%. However, the velocity and pressure distribution have bigger discrepancies at both axial and radial directions at the area with extreme change, such as at throat nozzle. It can be concluded that the 2D axisymmetric model can be used as substitution of 3D model when the objective is only to obtain ejector performance and qualitative study.
Highlights
PENDAHULUAN Ejektor telah diperkenalkan dalam dunia engineering di awal abad ke-20
The current study investigated the comparison between 3D and 2D models using numerical solution
The results show that qualitatively the 2D axisymmetric model has good comparison to the 3D model
Summary
Kondisi batas untuk model 2D axysimmetric terdapat penambahan pada sumbu dengan tipe boundary conditions axis sebagai fungsi percermnan. Validasi Hasil Simulasi Validasi dilakukan dengan dua metode, yang pertama uji grid independence dan yang kedua adalah Perbandingan dengan metode empiris. Validasi hasil simulasi yang pertama dilakukan adalah dengan uji Grid Independence. Parameter yang dipilih adalah parameter performansi ejektor, yaitu rasio entrainment dan Mach number maksimum untuk diobservasi perubahannya terhadap penambahan jumlah grid. Uji konvergensi dilakukan pada semua ejektor pada penelitian ini dan nilai error maksimum yaitu sekitar 7,7 % pada model 2D ejektor Korting. Dari hasil Uji Grid independence, didapatkan error terbesar pada ejektor Korting 7,7%, dari referensi [3], eror sebesar 8% masih dapat diterima. Pendekatan ini tidak dilakukan kepada ejektor Korting dan Jerguson karena tidak ditemukan teori untuk menghitung rasio entrainment kedua ejektor tersebut. Pendekatan empiris untuk mencari rasio entrainment pada ejektor PLTP X menggunakan metode Freeston. Dari data ejektor PLTP X, didapatkan compression ratio dan expansion ratio pada perhitungan berikut
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