پدرام حنفی زاده
استادیار، دانشکده مهندسی مکانیک، پردیس دانشکده های فنی، دانشگاه تهران، تهران
[ 1 ] - استفاده از ارزش فعلی خالص به عنوان یک تابع هدف تنها برای بهینه‌سازی ترمو-اقتصادی رکوپراتور صفحه پره دار میکروتوربین
در این مقاله رکوپراتور یک میکروتوربین200 kW با در نظر گرفتن ارزش فعلی خالص به عنوان تابع هدف، با الگوریتم‌های ژنتیک و اجتماع ذرات بهینه‌سازی شده است. مبدل حرارتی صفحه پره‌دار با پره نواری و آرایش جریان‌های عمود و مخالف برای بهینه‌سازی انتخاب شده است. گام پره، ارتفاع پره، طول نوار، طول مسیر جریان رکوپراتور، ارتفاع و عرض رکوپراتور به عنوان شش پارامتر طراحی در نظر گرفته شده‌اند. برای بررسی اثر هر ...
[ 2 ] - اثر تنش و انتقال جرم فصل مشترک مایع-بخاربر روی عملکرد ترموسیفونها
چکیده در این مقاله اثر تنش برشی و انتقال جرم در فصل مشترک فیلم مایع و جریان بخار روی عملکرد یک ترموسیفون با استفاده از روش انتگرالی بررسی شده است. با حل معادلات حاکم در بخش چگالنده، توزیع سرعت و ضخامت فیلم مایع به دست می‌آید. سپس دبی جرم فیلم مایع و نرخ انتقال حرارت قابل محاسبه است. نتایج برای یک ترموسیفون با طولcm 5/30 و قطر داخلیcm 42/2 با سیال عامل متانل در دمای اشباع 63 درجة سانتیگراد و دما...
[ 3 ] - بررسی عملکرد ترموسیفون با استفاده از روش سرعت سنجی تصویر ذرات
ترموسیفون نوعی لوله‌ی گرمایی است که در آن برای بازگرداندن سیال عامل از سردکننده به تبخیرکننده از نیروی ثقلی استفاده می‌شود. بیشتر تحقیقات انجام شده پیرامون ترموسیفون درمورد مشخصات حرارتی آن بوده و کم‌تر به مشخصات هیدرولیکی آن توجه شده است. در این پژوهش، با استفاده از روش سرعت‌سنجی و کاربرد تصویر ذرات و مدل‌سازی عددی، ارتباط بین مشخصه‌های هیدرولیکی و حرارتی ترموسیفون با یکدیگر و بررسی اثرات متق...
[ 4 ] - مدل‌سازی عددی و بهینه‌سازی رفتار ایرلیفت پمپ
ایرلیفت پمپ دستگاهی است که با بهره‌گیری از نیروی شناوری ایجادشده براثر تزریق گاز در یک ستون مایع، قادر به پمپاژ مایع مورد نظر یا حتی ذرات جامد موجود در مایع به ارتفاع بالاتر است. در این نوشتار تأثیر پارامترهای مؤثر ـ نظیر قطر لوله، نسبت شناوری، رژیم جریان و طول لوله ـ بر عملکرد یک ایرلیفت پمپ، به‌صورت عددی مورد بررسی قرار گرفته است. همچنین در این تحقیق شرایط و ناحیه‌ی کارکرد بهینه‌ی این پمپ‌ها ...
[ 5 ] - Drag coefficient and strouhal number analysis of a rectangular probe in a two-phase cross flow
In some case of laboratory and industrial applications, various kind of measurement instruments must be placed in a conduit, in which multiphase fluid flows. Vortex shedding for any immersed body in flow field is created with a frequency, which according to flow conditions such as flow rates, geometry of body, etc. may be constant or variable. Failure may happen, if this frequency is close to o...
[ 6 ] - A method for bubble volume measurement under constant flow conditions in gas–liquid two-phase flow
Measuring the volume of a bubble, especially at its detachment, is a basic subject in gas-liquid two-phase flow research. A new indirect method for this measurement under constant flow conditions is presented. An electronic device is designed and constructed based on laser beam intensity. This device calculates the frequency of the bubble formation by measuring the total time of the formation p...
[ 7 ] - Exergy , economy and pressure drop analyses for optimal design of recuperator used in microturbine
The optimal design of a plate-fin recuperator of a 200-kW microturbine was studied in this paper. The exergy efficiency, pressure drop and total cost were selected as the three important objective functions of the recuperator. Genetic Algorithm (GA) and Non-dominated Sorting Genetic Algorithm (NSGA-II) were respectively employed for single-objective and multi-objective optimizations. By opt...
[ 8 ] - Wind resource assessment of Khuzestan province in Iran
In this research paper, a 10 minute period measured wind speed data at 10 m, 30 m, and 40 m heights are presented for one of the major provinces of Iran. Four stations in Khuzestan- Abadan, Hosseyneh, Mahshahr, and Shushtar- are analyzed to determine the potential of wind power generation in this province. From the primary evaluation and by determining mean wind speed and also the Weibull f...
[ 9 ] - The effect of hemispherical chevrons angle, depth, and pitch on the convective heat transfer coefficient and pressure drop in compact plate heat exchangers
Plate heat exchangers are widely used in industries due to their special characteristics, such as high thermal efficiency, small size, light weight, easy installation, maintenance, and cleaning. The purpose of this study is to consider the effect of depth, angle, and pitch of hemispheric Chevrons on the convective heat transfer coefficient and pressure drop. In the simulation of the heat ex...
[ 10 ] - Analysis of micro-recuperators in small-sized gas turbines –manufacturing potential of Iran
Heat recuperation is often used to improve the overall cycle efficiency of gas turbines. However, generally in small- scale gas turbines, it has a negative effect on turbine inlet temperature, pressure ratio and pressure drops, and thus decreases the overall cycle efficiency. In this paper, a thermodynamic model is performed to evaluate recovered heat as a function of heat exchanger effecti...
[ 11 ] - Investigation of a single-reheat condensing steam power plant based on energy and exergy analysis
Nowadays, energy plays an important role in the economic and community development of country. Consequently, performance analysis of energy systems is one of the effective methods being used to prevent waste of energy resources. Among the different power generation technologies, steam power plants make a significant contribution to power generation in Iran, with a share of 47 % of electrici...
[ 12 ] - Simulation of gas-liquid two phase flow in upriser pipe of gas-lift systems
Gas-lift pumps are devices for lifting liquid phase incorporating the gas phase to be injected in the bottom of liquid column. They are widely used in various industrial applications such as oil extracting in petroleum industries. Gas-liquid flow being the main part of the flow through these systems, flowing in vertical pipes of gas-lift pumps has different regimes namely bubbly, slug, chur...
[ 13 ] - Drag coefficient and strouhal number analysis of cylindrical tube in two phase flow
In many industrial equipment such as boilers and heat exchangers, the cylindrical tubes are exposed to the gas- liquid two phase flow. For any immersed body in flow field vortex shedding is created with a frequency that may be constant or variable, according to conditions such as flow rates, geometry of body, and etc. The failure will happen in the equipment, when this frequency is close to...
[ 14 ] - Visual Observation of Flow Regime Transition in Downward Vertical Gas-Liquid Flow Using Simple Mixer
Different flow patterns of downward gas-liquid two-phaseflow using simple mixer are studied in an experimental manner. An experimental setup is designed and fabricated to allow the visual observation of downward two-phase flow patterns and their transitions. The flow patterns are recorded by a 1200 frames per second high speed video camera. The quality of downward two-phase flow patterns photos...
[ 15 ] - Techno-Economy Study of wind energy in Khvaf in Razavi Khorasan Province in Iran
In this paper, the 10-minutes period measured wind speed data at different heights (10 m, 30 m, and 40 m) are presented for Khvaf, which is one of the major counties with high wind potential in Khorasan provinces in Iran. To the author’s knowledge, there hasn’t been any assessment works in the mentioned site. From the primary evaluation and by determining mean wind speed and also the Weibull fu...
[ 16 ] - Comparative study between dynamic transient and degree-hours methods to estimate heating and cooling loads of building’s wall
In this paper, dynamic transient method and conventional degree-hours method (static) have been compared to estimate heating and cooling loads of building’s wall. All main wall surfaces of various orientations, i.e.South, West, East, North, and horizontal are considered in the climate of Tehran, Iran. In this study, a conventional wall structure, which is comprisedconcrete as main wall material...
[ 17 ] - مطالعه عددی و تجربی رفتار جریان دوفاز همسو در لوله عمودی پایین رو
در مقاله حاضر رفتار و الگوهای جریان دوفازی پائین رو آب – هوا در لوله عمودی به صورت تجربی و عددی مورد بررسی قرار گرفته است. برای بررسی آزمایشگاهی یک دستگاه آزمایش با قابلیت مشاهده و عکس برداری ساخته و راه اندازی شده است. سیالات مورد استفاده آب و هوا بوده و نتایج جریان برای 391 حالت انتخابی با تغییر سرعت ظاهری آب و هوا بدست آمده و پس از پردازش عکسها و بررسی الگوها، نقشه جریان تهیه و ارائه شده است...
[ 18 ] - A method for detecting bubbles in two-phase gas-liquid flow
Detecting bubble in two-phase flow has been a basic issue in two-phase flow systems. A new method for measuring the frequency of bubble formation is presented in this paper. For this purpose, an electronic device was designed and constructed which works based on a change in intensity of laser beam. For this purpose, continues light beam is embedded just above the needle, which is received by a ...
[ 19 ] - Analysis of micro-recuperators in small-sized gas turbines –manufacturing potential of Iran
Heat recuperation is often used to improve the overall cycle efficiency of gas turbines. However, generally in small- scale gas turbines, it has a negative effect on turbine inlet temperature, pressure ratio and pressure drops, and thus decreases the overall cycle efficiency. In this paper, a thermodynamic model is performed to evaluate recovered heat as a function of heat exchanger effectivene...
[ 20 ] - Experimental investigation of bubble growth and detachment in stagnant liquid column using image – based analysis
An experimental study has been carried out to characterize bubble formation, growth, and detachment mechanisms in a stagnant liquid column. Both bubble frequency and bubble detachment size were measured in different gas flow rates, injector diameters and orientations, submergence height, and liquid properties. Experiments were performed for air injection flow rate ranges between 200 mlph and 12...
[ 21 ] - Subcooled two-phase flow boiling in a microchannel heat sink: comparison of conventional numerical models
Subcooled flow boiling in multi-microchannels can be used as an efficient thermal management approach in compact electrical devices. Highly subcooled flow boiling of HFE 7100 is studied in two microchannel heat sinks to choose a proper numerical model for simulating boiling flows in microchannels. Results of five different numerical models, including Volume of Fluid (VOF), Eulerian boiling, Eul...
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