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Abstrak :
Pada kondisi operasi normal fasilitas nuklir berpotensi melepaskan zat radioaktif ke badan air yang disebut dengan pelepasan rutin. Transfer radionuklida pada lingkungan sangat kompleks sehingga dibuat penyederhanaan dengan pendekatan model matematis menggunakan perangkat lunak Surface Water Modelling Systems yang menyelesaikan persamaan differensial hidrodinamika dengan metode elemen hingga. Penyebaran polutan sangat dipengaruhi oleh proses adveksi dan difusi. Tujuan dari penelitian ini adalah untuk memodelkan distribusi radionuklida pada Kali Cisalak yang terletak di sekitar Kawasan Nuklir Serpong. 60Co merupakan radionuklida paling dominan yang terkandung pada lepasan efluen radioaktif. Pada penelitian ini simulasi dibagi ke dalam dua tahap yaitu simulasi model hidrodinamika menggunakan modul Resources Management Associates-2 (RMA-2) untuk memodelkan arus dan RMA-4 untuk memodelkan sebaran 60Co. Sedangkan nilai dosis efektif pada kelompok kritis dihitung menggunakan software PC-Cream 98. Pada analisis sensitivitas, koefisien kekasaran manning dan koefisien viskositas Eddy tidak memberikan pengaruh yang signifikan terhadap pola sebaran konsentrasi 60Co di Kali Cisalak. Sedangkan koefisien diffusi dan settling velocity memiliki pengaruh yang cukup signifikan. Dari hasil pemodelan didapatkan konsentrasi 60Co tertinggi sebesar 5,38 Bq/L pada jarak 10 m dari titik pelepasan, sedangkan konsentrasi terendah sebesar 0,0005 Bq/L terdeteksi pada jarak 540 m. Perhitungan dosis individu orang dewasa akibat jalur paparan akuatik yaitu 14,094 μSv/tahun. ......Under normal operating conditions nuclear facilities have potential release of radioactive substances into water bodies called routine releases. Radionuclide transfer in the environment is very complex so that simplification is made with a mathematical model approach using the Surface Water Modeling Systems 10.1 software that resolves hydrodynamic differential equations with the finite element method. The goal of this research is to model the distribution of 60Co radionuclides in Cisalak River located around Serpong Nuclear Area. 60Co is the most dominant radionuclide contained in radioactive effluent discharges. In this research the simulation is divided into two stages, they are the simulation of the hydrodynamic model using the Resources Management Associates-2 (RMA-2) module to model the flow and continued using RMA-4 to model the distribution of 60Co. Whereas the effective dose in the critical group was calculated using PC-Cream 98 software. In the sensitivity analysis, the manning roughness coefficient and Eddy viscosity coefficient did not have a significant effect on the distribution pattern of 60Co concentrations in Cisalak River. But the diffusion coefficient and settling velocity have a significant influence. The result of modeling obtained the highest 60Co concentration of 5,38 Bq/L at a distance of 10 m from the release point, while the lowest concentration of 0,0005 Bq/L was detected at a distance of 540 m. Calculation of adult individual doses due to aquatic exposure pathways is 14,094 µSv/year.

Abstrak :
Salah satu upaya meningkatkan produksi bioetanol adalah melalui efisiensi fermentasi. Penelitian terkait upaya peningkatan efisiensi fermentasi yang meninjau tentang proses pencampuran bahan baku belum ditemukan dan hal ini sangat terkait dengan kondisi hidrodinamika dalam fermentor sebagai unit pemroses. Kondisi hidrodinamika suatu system dipengaruhi oleh desain dan kondisi operasi unit pemroses serta fluida kerja. Dengan desain dan kondisi operasi fermentor yang optimal maka proses pencampuran menjadi efisien distribusi bahan baku merata dan kondisi ini berpengaruh terhadap kinerja mikroorganisme yang terlibat sehingga diharapkan dapat meningkatkan hasil produksi bioetanol. Untuk mendapatkan desain dan kondisi operasi fermentor yang optimal diperlukan detail informasi tentang aliran di dalamnya kondisi hidrodinamika . Berdasarkan hal tersebut maka tujuan penelitian ini adalah mendapatkan detail informasi dan fenomena hidrodinamika proses pencampuran molase-air dalam fermentor skala industri dengan diameter 7 m dan tinggi 15 m. Pada kasus dengan sistem geometri skala industri, maka metode komputasi lebih efisien. Namun pada pelaksanaannya, untuk menerapkan model dan strategi solusi yang sesuai fenomena nyata, diperlukan kajian terkait karakteristik medan aliran dalam sistem, karakteristik dan perilaku pencampuran fluida kerja serta pengaruh parameter pengadukan terhadap fenomena pencampuran. Untuk melakukan kajian terhadap faktor-faktor tersebut perlu dilakukan scale down dari geometri skala industri menjadi geometri skala kecil diameter 0,28 m dan tinggi 0,52 m . Metode komputasi dinamika fluida pada penelitian ini mengaplikasikan kode komersial Ansys fluent 17.1. Metode eksperimen untuk karakterisasi reologi fluida kerja adalah menggunakan Rheometer Brookfield dan untuk pelacakan partikel serta perilaku pencampuran bahan baku adalah metode visualisasi. Detail informasi dan fenomena hidrodinamika proses pencampuran dalam fermentor bioetanol skala industri telah didapatkan dan didiskusikan. Model Large eddy simulation LES lebih sesuai untuk menggambarkan turbulensi dalam sistem. Model Sliding-mesh SM dan Eulerian menghasilkan prediksi yang lebih mendekati hasil eksperimen. Waktu pencampuran mixing time pada fermentor skala industri adalah 114 detik.

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One of the efforts to increase bioethanol production is through the efficiency of fermentation. The related Study as the efforts to improve the efficiency of fermentation by reviewing the mixing process of raw materials have not been found, and this is strongly related to hydrodynamic conditions in the fermentor as a processing unit. The hydrodynamic condition of a system is influenced by the design and operating conditions of the unit process and the working fluid. With an optimum fermentor design and condition, the mixing process becomes efficient uniform distribution of raw material and this condition has an effect on the performance of the microorganism involved so that it can increase bioethanol production. In order to obtain the optimal fermentor design and operating conditions, detailed information on the flow hydrodynamics condition is required. Based on this background, the purpose of this research is to obtain detailed information and hydrodynamic phenomena of molasses-water mixing process in industrial scale fermentor with diameter 7 m and height 15 m. In the case of industrial-scale geometry systems, the computational method is more efficient. However, in the implementation, to apply an appropriate model and solution strategy to represent the real phenomena, it is necessary to study the characteristics of the flow field in the system, the characteristics and the mixing behavior of the working fluid and the effect of the agitation parameters on the mixing phenomenon. To conduct a study of these factors, need to scale down the geometry of the industrial scale into small-scale geometry diameter 0.28 m and height 0.52 m . The commercial code Ansys fluent 17.1 was applied to study of the fluid dynamics computationally. The experimental tools for the rheological characterization of working fluids are to use the Brookfield rheometer and the methods for particle tracking, and the mixing behavior of the raw material is a visualization method. Detailed information and hydrodynamic phenomena of the mixing process in industrial scale bioethanol fermenters have been obtained and discussed. Large eddy simulation model LES is more suitable for describing turbulence in the system. The Sliding-mesh SM and Eulerian models produce predictions that are closer to the experimental results. The mixing time on an industrial scale fermentor is 114 seconds.

Abstrak :
Hydrodeoxygenation of palm oil and Jatropha curcas oil over NiMo/ZAL (nickel molybdenum/zeolit alam Lampung) catalyst was investigated under temperatures of 375°C and 400°C and H2 pressure of 15 bar in a semibatch stirred autoclave reactor. NiMo/ZAL catalyst was prepared using a rapid cooling method. NiMo/ZAL characterization revealed a crystal size of 70.07 nm, surface area of 12.25 m2/g, and pore size and pore volume of 9.83 Å and 0.0062 cm3/g, respectively. The hydrodeoxygenation removal pathway of palm oil and Jatropha curcas oil over NiMo/ZAL catalyst was primarily achieved through decarboxylation. Under hydrogen pressure of 15 bar and temperature of 375°C, palm oil and Jatropha curcas oil can be converted into paraffin chains (from n-C15 up to n-C18) by a decarboxylation reaction that produces water, methane, and COx gases as byproducts and contains some undesirable reactions. These byproducts can produce alkene bonds that form chains different from those in conventional diesel fuel. The conversion was 80.87%, selectivity was 52.78%, and yield was 45.66%. The hydrodeoxygenation reaction catalyzed by NiMo/ZAL catalyst was found to be suitable for removing oxygen and producing paraffin chains; this increased the heating value and stability of renewable diesel fuel.