78 research outputs found
Geometry Effect Investigation on a Conical Chamber with Porous Media Boundary Condition Using Computational Fluid Dynamic (CFD) Technique
The present study is an attempt to introduce a method for optimizing the geometry of a unit process. The comprehensive unit process performances are generated by a CFD engine. The CFD engine can simulate the unit process performances at whatever conditions. Both design geometry and operating variables were used on the CFD simulation. The burden on a simplified process was taken out from CFD simulation. A complex geometry of a unit process is represented by a secondary reformer. A secondary reformer has a conical chamber as a space to undergo a combustion reaction before entering a catalyst bed. This complexity is added by the boundary on a porous solid surface as the top surface of the catalyst bed. The conical angle affects the flow pattern inside the conical chamber having a porous solid surface as its base. The conical angle above 65° results the disappearing of the recirculation flow. The inlet distance from the porous solid surface also can exhibit different characteristics of recirculation flow. The closer the distance to the porous solid surface, the stronger the recirculation is. The inlet velocity values have no significant effect on the flow pattern. The introduction of a solid volume inside the geometry creates distortion in the flow pattern. In the application, the inserted solid volume is equivalent to a burner. It means that the use of the burner inherently produces some problems of the flow distribution
New Correlations for Coal and Biomass Pyrolysis Performances with Coal-Biomass Type Number and Temperature
The pyrolysis of coal and biomass is generally reported as the mass yield of released chemicals at various temperatures, pressures, heating rates and coal or biomass type. In this work, a new coal-biomass type number, NCT, is introduced. This number is constructed from the mass fractions of carbon, hydrogen, and oxygen in the ultimate analysis. This number is unique for each coal or biomass type. For 179 different species of coal and biomass from the literature, the volatile matter mass yield can be expressed by the second order polynomial function ln(NCT). This unique correlation allows the effects of the temperature and heating rate on the volatile yield YVY for coal and biomass to be empirically correlated as well. The correlation for the mass fraction of each chemical component in the released volatile matter correlation is obtained from the YVY correlation. The weight factor for some of the components is constant for the variation of NCT, but not for others. The resulted volatile matter and yield correlations are limited to atmospheric pressure, very small particles (less than 0.212 mm) and interpreted for wire-mesh pyrolysis reactor conditions and a nitrogen gas environment
Geometry Effect Investigation on a Conical Chamber with Porous Media Boundary Condition Using Computational Fluid Dynamic (CFD) Technique
The present study is an attempt to introduce a method for optimizing the geometry of a unit process. The comprehensive unit process performances are generated by a CFD engine. The CFD engine can simulate the unit process performances at whatever conditions. Both design geometry and operating variables were used on the CFD simulation. The burden on a simplified process was taken out from CFD simulation. A complex geometry of a unit process is represented by a secondary reformer. A secondary reformer has a conical chamber as a space to undergo a combustion reaction before entering a catalyst bed. This complexity is added by the boundary on a porous solid surface as the top surface of the catalyst bed. The conical angle affects the flow pattern inside the conical chamber having a porous solid surface as its base. The conical angle above 65° results the disappearing of the recirculation flow. The inlet distance from the porous solid surface also can exhibit different characteristics of recirculation flow. The closer the distance to the porous solid surface, the stronger the recirculation is. The inlet velocity values have no significant effect on the flow pattern. The introduction of a solid volume inside the geometry creates distortion in the flow pattern. In the application, the inserted solid volume is equivalent to a burner. It means that the use of the burner inherently produces some problems of the flow distribution
EFISIENSI PEMBAKARAN NYALA TURBULEN TAK-PRACAMPUR YANG DIPENGARUHI ANGIN SILANG DAN PENAMBAHAN STEAM
Artikel ini memaparkan hasil yang diperoleh dari dinamika fluida komputasi (DFK) untuk mensimulasi nyala turbulen tak pra-campur. Konfigurasi, diskretisasi dan kondisi batas nyala digambarkan menggunakan perangkat lunak pra-prosessor Gambit dan kalkulasi turbulensi dan pembakaran menggunakan perangkat lunak Fluent. Penelitian ini memfokuskan pada kajian pengaruh berbagai kecepatan angin silang dan penambahan steam terhadap karakteristik nyala hidrokarbon dan pengaruhnya terhadap efisiensi pembakaran yang dihasilkan. Model turbulensi yang digunakan pada penelitian ini adalah model k-ε standard dan model pembakaran Eddy Dissipasi. Kajian dilakukan pada berbagai kecepatan angin silang yaitu 3,77 m/s, 7,5 m/s dan 10 m/s dan ratio steam terhadap bahan bakar 0,14, 0,25, dan 2,35 serta dilakukan pada kecepatan bahan bakar tetap 20 m/s. Hasil yang diperoleh ditampilkan dalam bentuk kontur temperatur dari berbagai kecepatan angin silang dan penambahan steam. Dari kontur tersebut terlihat bahwa besarnya nilai S yang diberikan pada berbagai kecepatan angin sangat mempengaruhi terhadap temperatur pembakaran yang dihasilkan, dimana dari hasil kontur tersebut dapat diketahui bahwa temperatur nyala menurun seiring peningkatan jumlah steam yang diberikan di dalam aliran bahan bakar, dan hal tersebut secara nyata terlihat pada nilai S yang besar (2,35). Efisiensi pembakaran pada berbagai kecepatan angin silang semakin menurun seiring bertambahnya ratio steam terhadap bahan bakar
ANALISIS EFISIENSI DAN PENURUNAN TEKANAN PADA SIKLON PERSEGI MENGGUNAKAN CFD
Artikel ini memaparkan hasil penelitian yang diperoleh melalui aplikasi komputasi dinamika fluida (Computational Fluida Dynamic,CFD) untuk mensimulasi medan alir di dalam siklon persegi. Perangkat lunak Gambit digunakan sebagai pre-processor untuk menggambar konfigurasi, diskritisasi, dan pendefinisian kondisi batas siklon. Geometri siklon silinder Lapple dan persegi ditinjau dari volume yang sama. Diameter siklon yang digunakan 0,2 m menyesuaikan dengan diameter siklon silinder Lapple yang digunakan Wang pada eksperimennya, dengan kondisi operasi ditentukan pada laju alir gas sebesar 0,1m3/s sementara beban partikel dalam laju alir gas sebesar 0,01kg/m3. Perangkat lunak CFD FLUENT 6.2.16 digunakan untuk simulasi medan alir dan dinamika partikel dalam siklon. Penelitian ini bertujuan untuk mengetahui pengaruh geometri siklon persegi terhadap medan alir, efisiensi dan penurunan tekanan. Prediksi yang dihasilkan memberikan informasi mengenai medan alir berupa kecepatan axial dan tangensial di dalam siklon serta informasi efisiensi dan penurunan tekanan. Hasil kajian menunjukkan bahwa kecepatan tangensial mendominasi medan alir di luar garis tengah siklon, sementara kecepatan aksial mendominasi medan alir di daerah garis tengah siklon. Penurunan tekanan yang terjadi pada siklon persegi lebih tinggi dari siklon silinder, namun efisiensi untuk siklon persegi lebih tinggi dibandingkan siklon Lapple
Operating Variables on Production of High Purity Bio-silica from Rice Hull Ash by Extraction Process
The huge amount of rice hull biomass available in Indonesia can be utilized as raw material for bio-silica production. This study investigated the production of high-purity bio-silica from rice hull ash through an alkaline extraction process. A full factorial design (FFD) was used to screen for significant effects of the observed variables. Three operating variables – acid concentration, solvent to feed ratio (RS/F), and extraction time – were investigated with the purpose of obtaining a high yield and high purity of bio-silica. Yield and purity above 96% were achieved by using pretreatment with 1 mol/L HCl. Employing an RS/F of 5 and a longer extraction time improved the bio-silica yield. The operating variable that enhanced the bio-silica yield and purity most was acid concentration. All variable interactions had an insignificant effect on purity, while two interacting variables had a significant effect on bio-silica yield. Based on the results of this study, rice crop residue can be optimally converted to a bio-silica product in terms of yield and purity by optimizing the most effective operating variables
Pressure Drop Correlation Covering Dilute to Dense Regimes of Solid Particle-Gas Flow in a Vertical Conveying Pipe
More general correlations between pressure drop and gas-solid flow variables are developed from the present experimental data. The correlation was modeled for a pneumatic conveying system in a vertical pipe. The transition boundary between dense and dilute regimes is constructed from the pressure drop correlations. The gas-solid particle flow variables are quantified by the gas Reynolds (Nref) and the solid Froude (Frp) numbers. The dense flow regime is indicated by the decrease of the pressure drop with the increase of the gas Reynolds number. In contrary, the dilute regime exhibits the increase of the pressure drop with the gas Reynolds number. The proposed correlations were built at the range of gas Reynolds number f from 360 to 500 and solid Froude number from 0,01 to 0,02
EFISIENSI PEMBAKARAN NYALA TURBULEN TAK-PRACAMPUR YANG DIPENGARUHI ANGIN SILANG DAN PENAMBAHAN STEAM
Artikel ini memaparkan hasil yang diperoleh dari dinamika fluida komputasi (DFK) untuk mensimulasi nyala turbulen tak pra-campur. Konfigurasi, diskretisasi dan kondisi batas nyala digambarkan menggunakan perangkat lunak pra-prosessor Gambit dan kalkulasi turbulensi dan pembakaran menggunakan perangkat lunak Fluent. Penelitian ini memfokuskan pada kajian pengaruh berbagai kecepatan angin silang dan penambahan steam terhadap karakteristik nyala hidrokarbon dan pengaruhnya terhadap efisiensi pembakaran yang dihasilkan. Model turbulensi yang digunakan pada penelitian ini adalah model k-ε standard dan model pembakaran Eddy Dissipasi. Kajian dilakukan pada berbagai kecepatan angin silang yaitu 3,77 m/s, 7,5 m/s dan 10 m/s dan ratio steam terhadap bahan bakar 0,14, 0,25, dan 2,35 serta dilakukan pada kecepatan bahan bakar tetap 20 m/s. Hasil yang diperoleh ditampilkan dalam bentuk kontur temperatur dari berbagai kecepatan angin silang dan penambahan steam. Dari kontur tersebut terlihat bahwa besarnya nilai S yang diberikan pada berbagai kecepatan angin sangat mempengaruhi terhadap temperatur pembakaran yang dihasilkan, dimana dari hasil kontur tersebut dapat diketahui bahwa temperatur nyala menurun seiring peningkatan jumlah steam yang diberikan di dalam aliran bahan bakar, dan hal tersebut secara nyata terlihat pada nilai S yang besar (2,35). Efisiensi pembakaran pada berbagai kecepatan angin silang semakin menurun seiring bertambahnya ratio steam terhadap bahan bakar
KAJIAN PENGARUH ANGIN SILANG TERHADAP KARAKTERISTIK NYALA HIDROKARBON
Artikel ini memaparkan hasil yang diperoleh dari kajian dinamika fluida komputasi (DFK) untuk mensimulasi nyala turbulen tak pra-campur akibat pengaruh angin silang. Konfigurasi, diskretisasi dan kondisi batas nyala digambarkan menggunakan perangkat lunak pra-prosessor Gambit. Pengaruh angin silang terhadap nyala hidrokarbon (nyala dengan pengaruh angin silang) dilakukan pada kondisi kecepatan bahan bakar tetap 20 m/s dengan kecepatan angin berubah-rubah dan pada kondisi kecepatan angin silang tetap 1,1 m/s dengan kecepatan bahan bakar berubah - ubah . Hasil penelitian dengan kondisi bahan bakar tetap menunjukkan bahwa peningkatan kecepatan angin silang memberikan pengaruh yang signifikan terhadap medan alir dan temperatur. Pada kajian dengan kondisi bahan bakar berubah - ubah ketika kecepatan angin silang tetap, terlihat bahwa peningkatan kecepatan bahan bakar memberikan dampak positif pada nyala, karena nyala semakin mampu melawan pengaruh angin silang terhadap nyala
Operating Variables on Production of High Purity Bio-silica from Rice Hull Ash by Extraction Process
The huge amount of rice hull biomass available in Indonesia can be utilized as raw material for bio-silica production. This study investigated the production of high-purity bio-silica from rice hull ash through an alkaline extraction process. A full factorial design (FFD) was used to screen for significant effects of the observed variables. Three operating variables – acid concentration, solvent to feed ratio (RS/F), and extraction time – were investigated with the purpose of obtaining a high yield and high purity of bio-silica. Yield and purity above 96% were achieved by using pretreatment with 1 mol/L HCl. Employing an RS/F of 5 and a longer extraction time improved the bio-silica yield. The operating variable that enhanced the bio-silica yield and purity most was acid concentration. All variable interactions had an insignificant effect on purity, while two interacting variables had a significant effect on bio-silica yield. Based on the results of this study, rice crop residue can be optimally converted to a bio-silica product in terms of yield and purity by optimizing the most effective operating variables
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