23800

مدل‌سازي احتراق غير پيش‌آميخته ي ابر ذرات در هندسه‌ي جريان‌متقابل

دكتري تخصصي

مهندسي مكانيك

1394

1399/07/08

دكتر مهدي بيدآبادي

دكتر حميد صفاري

مهندسي مكانيك

در اين رساله، ابتدا مدل‌هاي تحليلي مناسبي براي پيش‌بيني رفتار شعله‌هاي حاصل از احتراق‌هاي غير‌پيش‌آميخته‌ي جريان‌متقابل ابر ذرات لايكوپوديوم و زغال‌سنگ در حالت پايا با درنظر گرفتن فرايندهاي موثر نظير خشك ‌شدن، تجزيه‌ي حرارتي، تبخير و واكنش در شرايط آدياباتيك و غيرآدياباتيك ارائه مي‌گردد. همچنين تاثير پارامترهاي مهم احتراقي نظير عدد لوئيس سوخت و اكساينده، عدد دامكوهلر و نرخ كرنش جريان بر موقعيت تشكيل شعله، توزيع دماي سيستم، دماي شعله، توزيع جرم سوخت و اكساينده با درنظرگرفتن فرضيات ساده كننده و منطقي مورد تحليل قرار مي‌گيرد. در مدل‌هاي پيشنهادي، اثرات اتلافات حرارتي با ساز و كارهاي تشعشعي و جابجايي، تخلخل ذرات سوخت و نيروي ترموفورتيك بر ساختار شعله مورد بررسي قرار مي‌گيرد. سپس بمنظور بررسي نحوه‌ي حركت ذرات در طول سيستم احتراقي، مسير حركت ذرات زغال سنگ، چار، گاز و خاكستر حاصل از تجزيه‌ي حرارتي با استفاده از ديدگاه لاگرانژي ارائه مي‌گردد. سپس احتراق ناپاياي غير ‌پيش‌آميخته‌ي ابر ذرات لايكوپوديوم و آهن با در‌نظر‌گرفتن اتلافات حرارتي مورد تحليل قرار مي‌گيرد. در نهايت رفتار شعله‌ي حاصل از احتراق غير‌پيش‌آميخته‌ي ابر ذرات آهن در حضور يك منبع حرارتي نوساني سينوسي بررسي مي‌گردد.

1399/12/17

Analytical modelling of counter-flow non-premixed combustion of dust clouds

9/29/2020 12:00:00 AM

Due to the structure of non-premixed combustion, in which fuel and oxidizer are separately injected into the combustion system, safety and controllability can be noticeably enhanced. In this thesis, different comprehensive analytical models are proposed to investigate the combustion behavior of several micron-sized organic and inorganic fuels in non-premixed mode and counter-flow configuration under adiabatic and non-adiabatic conditions. Furthermore, trajectory of particles and effect of an oscillatory heat source on the structure of the non-premixed flames are presented. It should be noted that an asymptotic method is employed to analyze the non-premixed flames. In this study, lycopodium particles (organic fuel), coal particles (fossil fuel), and iron particles (metal fuel) are considered as the fuels. For lycopodium non-premixed combustion, preheating, drying, vaporization, reaction (homogeneous reaction) and oxidizer zones are studied. For coal non-premixed combustion, preheating, drying, pyrolysis, reaction (both homogeneous and heterogeneous reactions) and oxidizer zones are presented. It is worth mentioning that char, gas and ash are produced during the pyrolysis process. For metal combustion, preheating, reaction, melting and vaporization processes are analyzed. In order to mathematically study the combustion systems, mass, energy and momentum balance equations in steady and unsteady forms are obtained in each of the considered zones and solved by Matlab and Mathematica software using proper boundary and initial conditions. To make the models more reliable, influences of particle porosity, gravity force, buoyancy force, drag force, thermophoretic force and thermal-diffusive oscillations caused by an external oscillatory heat source on the structure of the non-premixed flames are included. In order to examine the performance of the system under non-adiabatic conditions, radiative and convective heat losses are involved. To preserve the continuity in the system, reasonable matching conditions are derived. Eventually, temperature and mass distributions of fuels, products and oxidizer are obtained in each of the zones. In addition, the influences of fuel and oxidizer Lewis numbers, particle size, particle porosity and equivalence ratio on the temperature and mass distributions, critical flow strain rate, flame temperature and flame front position are discussed. For validation purposes, results of the current analytical investigation are meticulously validated by the numerical and experimental results of former relevant studies on lycopodium, titanium and iron particles under the same conditions. Based on the comparisons, there are proper compatibilities between the results of the present study on counter-flow non-premixed combustion of micron-sized particles and those of prior results.

مدل‌سازي تحليلي , احتراق غير پيش‌آميخته , شعله‌هاي پايا و ناپايا , هندسه‌ي جريان‌متقابل , احتراق چند ‌‌ناحيه‌اي ابر ذرات , احتراق آدياباتيك و غير آدياباتيك , مسير حركت ذرات , منبع حرارتي نوساني

َAnalytical Study , Non-Premixed Combustion , Steady and Unsteady Conditions , Counter-Flow Configuration , Adiabatic and Non-Adiabatic Conditions , Particle Trajectory , Flame Oscillation , Multi-Zone Combustion