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Article
Numerical study of the mixed convection flow over a square cylinder

Author: Sajida Lafta Ghashim Jassim ساجدة لفتة
Journal: Iraqi Journal of Chemical and Petroleum Engineering المجلة العراقية للهندسة الكيمياوية وهندسة النفط ISSN: 19974884/E26180707 Year: 2010 Volume: 11 Issue: 1 Pages: 29-45
Publisher: Baghdad University جامعة بغداد

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Abstract

In this work, a numerical study is performed to predict the solution of two – dimensional, steady and laminar mixed convection flow over a square cylinder placed symmetrically in a vertical parallel plate. A finite difference method is employed to solve the governing differential equations, continuity, momentum, and energy equation balances. The solution is obtained for stream function, vorticity and temperature as dependent variables by iterative technique known as successive over relaxation. The flow and temperature patterns are obtained for Reynolds number and Grashof number at (Re= -50,50,100,-100) (positive or negative value refers to aidding or opposing buoyancy , +1 assisting flow, -1 opposing flow) and (102 to 105) , respectively. The results displaced that the recirculation length above the cylinder increases with the increase in Gr number and the average Nu number is the highest at the lower surface of the cylinder, while is the lowest at the top of the cylinder surface. A comparison between the obtained results and the published computational studies has been made and it showed a good agreement.


Article
The Influence of a Heat Source Position Located on the Bottom Wall Inside Square Enclosure on Laminar Natural Convection
تاثير موقع المصدر الحراري المثبت على السطح السفلي لحيز مربع على الحمل الحراري الطباقي

Author: Ihsan Ali Ghani احسان غني
Journal: Journal of Engineering and Sustainable Development مجلة الهندسة والتنمية المستدامة ISSN: 25200917 Year: 2010 Volume: 14 Issue: 3 Pages: 124-141
Publisher: Al-Mustansyriah University الجامعة المستنصرية

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Abstract

Natural convection in two-dimensional square enclosure is studied numerically using a finite difference method. In the present study, top wall is considered adiabatic, two vertical walls are maintained at constant low temperature, the bottom wall is maintained at constant high temperature and the non-heated parts of the bottom wall are considered adiabatic. The aim of this work is to determine the influence of the position of a small heating source located on the bottom wall of a square enclosure (aspect ratio=1) filled with air (Pr=0.71) on the natural convection flow. Three different positions are analyzed ,on the left side (δ=0.1) ,on the center(δ=0.5) and on the right side (δ=0.9). The dimensionless of the heat source length (S) is taken equal to (0.2). The three dimensional differential conservation equations of mass, momentum and energy are solved by a finite difference method for Rayleigh number varying from 103 to 106. Results are presented in the form of streamline and isotherm plots as well as the variation of the Nusselt number at the heat source surface under different conditions. The average Nusselt number and flow behavior are symmetrical for both cases, when heat source located on the left extreme and right extreme of the bottom wall. The average Nusselt number for the extremes (left and right) is higher than the central position for (Ra≤105) because the heat source is adjacent to the cold vertical wall. The average Nusselt number for the central position is higher than the extremes ( left and right) for (Ra>105)because the vortexes rotation of the air in the center of the bottom wall is greater than extremes .The local Nusselt number is very high at the edges of the heat source and reduces towards the center.

اجريت دراسه عدديه لانتقال الحراره بالحمل الحر في حيز مربع باستخدام طريقة الفروقات المحدده .ان الحيز في وضع عمودي وقد تم ابقاء الجداران العموديان للحيز على درجه حراره منخفضه وكذلك تم عزل الجدار العلوي اما بالنسبه للجدار السفلي فقد تم تسخينه جزئيا بواسطة مصدر حراري في درجه حراره عاليه اما الجزء المتبقي من الجدار فقد تم عزله . ان الهدف من البحث هو دراسة تأثير موقع المصدر الحراري في الجدار السفلي على انتقال الحراره بالحمل الحر للحيز المربع المملؤ بالهواء(۰٫۷Pr=) وذلك باعتماد ثلاثة مواقع هي اقصى اليسار(۰٫۱δ=) وفي المنتصف(۰٫۵δ=)واقصى اليمين(۰٫۹δ=). وقد تم حل المعادلات التفاضليه ذات البعدين الخاصه بحفظ الماده والطاقه والزخم بأستخدام طريقة الفروقات المحدده لعدة قيم لرقم رالي بين (۳۱۰-٦۱۰) وقد درست التغيرات في درجة الحراره وحقول السريان مع زيادة رقم رالي للمواقع المذكورة . وقد وجد في الدراسه انه عندما يوضع المصدر الحراري على طرفي الجدار السفلي(اليمين واليسار) فأن معدل رقم نسلت وسلوك الجريان سيكونان متماثلان وذلك لتماثل الشكل الهندسي والظروف الحديه وقد وجد ايضا ان قيم معدل رقم نسلت اعلى في حالة كون المصدر الحراري على الاطراف(اليمين واليسار)مما هو عليه عندما يكون في وسط الجدار لقيم عدد رالي اصغر من او يساوي (۵۱۰)وذلك نتيجة لتأثير الجدران العموديه البارده الملاصقه للمصدر الحراري وكانت قيم معدل رقم نسلت في وسط الجدار اعلى منه


Article
Experimental Study of Heat Transfer Parameters of Impingement Heating System Represented by Conductive Target Plate of Resistive film

Authors: Assim H. Yousif --- Amer M. Al Dabagh --- Salah H. Abid Aun
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2016 Volume: 34 Issue: 8 Part (A) Engineering Pages: 1588-1604
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

The current experimental study focuses on the heat transfer characteristics and pressure losses for impingement systemwhich is used in cooling the liner of gas turbine combustor. Recent experiment method of conductive heat transfer technique with resistive film in the back side target plate is introduced. The present experimental model measured both the heat transfer coefficient for inner target surface and the wall cooling effectiveness for outer target surface. To physically explain the phenomena associated with interaction flow area, a computational fluid dynamic code (Fluent 14) is employed. The continuity, momentum and energy equations arecomputationally solved to analyze the flow field in the jet impingement area. The tests models of the impingement plate are made from round jet holes of inline and staggered arrays arrangement with jet to jet spacing of four-hole diameter. Jet Reynolds numbers of 4200 to 15000 and jet height to diameter ratio of 1.5, 2.0, and 3.0 are maintained. The inline array, as expected enhanced the wall cooling effectiveness over that of the staggered array by10.3%andboth jet spacing and Reynolds number have an evident effect on the discharge coefficient. Empirical correlations are obtained for both arrays arrangement to predict the area-averaged Nusselt number as a function of jet governing parameters.


Article
Thermal Behavior in Dimple Square Duct with Inclined Perforated Baffles

Author: Abeer Hashim Falih
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2016 Volume: 34 Issue: 11 Part (A) Engineering Pages: 2047-2056
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

This research presents a study of heat transfer enhancement and pressure drop in a dimple square duct fitted with∝ =30◦,60◦and 90◦ inclined perforated baffles(baffles open area ratio of 26.17 %). The baffle to duct height ratio (w/a) of 0.3 and the baffle pitch to duct height ratio, PR=1, 2 are introduced in the present work. The tested duct has a constant wall heat flux condition. The experiments are carried out by varying airflow rate in terms of Reynolds number ranging from 1147.8 to 15304. The experimental data of heat transfer and pressure drop of the duct fitted withthe inclined perforated baffles are compared with those of the dimple smooth duct under similar condition. The inclined baffles with PR=1 gives higher heat transfer rate than the one with PR=2 and the smooth ductrespectively ,andthe highest heat transfer and pressure drop is found by using baffle with 30◦.


Article
Effect of Adding Horizontal Rings on the Thermal Behavior of Cylindrical Liquid Enclosure Exposed to High Heat Flux

Authors: Mohammed Hamed Mahmoud --- Ali Jaber Alkhakani
Journal: Thi-Qar University Journal for Engineering Sciences مجلة جامعة ذي قار للعلوم الهندسية ISSN: 20759746 Year: 2015 Volume: 6 Issue: 2 Pages: 35-53
Publisher: Thi-Qar University جامعة ذي قار

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Abstract

Power generation by using concentrated solar thermal energy on liquid enclosures is one of the most promising renewable energy technologies. In this work, a developed liquid enclosure fitted with various number and configurations of horizontal metal rings have been analyzed, fabricated and tested. The influence of adding metal rings arrangement is investigated for its potential to enhance radial heat conduction to the center-line of the enclosure from the side-walls. Experiments were carried out for fluid in both static and dynamic modes of operation inside the enclosure that subjected to high heat flux.A developed two-dimensional CFD model to predict the transient flow and thermal fields within liquid enclosure subjected to heat flux has been developed and tested. The developed numerical model takes into consideration energy transport between the liquid inside enclosure and the solid material of the enclosure. The numerical simulations have been compared with experimental measurement. The computational code has been found in a good level of agreement with the experimental data except for liquid at the peak part of the enclosure.The results indicate that adding metal rings produce significant impact on the transient temperature difference inside enclosure during both static and dynamic modes. The six-ring model is found to be more effective for enhancing radial heat transfer than other three models that have been tested. The in-line arrangement is found to provide better thermal effect as compared to the staggered rings.Two new correlations for natural heat transfer inside liquid enclosures subjected to high heat flux have been formulated (one for no-ring model and the other for six-ring model). The natural Nusselt number is found to be around a constant value for Rayleigh number less than (5 x 108 ).The recommended use of metal rings inside liquid enclosures subjected to heat flux, and the predicted Nusselt number correlation, will add to local knowledge a significant mean to gain more heat in large scale concentrated solar power plants.


Article
The Porosity Effect of Stainless Steel Balls on Forced Convection Pipe Flow
تأثير مسامية كرات الفولاذ المقاوم للصدأ على تدفق الأنبوب الحراري القسري

Authors: Ayser Munner Flayh أيسر منير فليح --- Sajida Lafta Ghashim ساجدة لفته غشيم
Journal: AL-NAHRAIN JOURNAL FOR ENGINEERING SCIENCES مجلة النهرين للعلوم الهندسية ISSN: 25219154 / eISSN 25219162 Year: 2019 Volume: 22 Issue: 2 Pages: 102-108
Publisher: Al-Nahrain University جامعة النهرين

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Abstract

An experimental study has been carried out to investigate the effects of stainless-steel balls on forced convection flow in pipe under uniform heat flux. Water is used as the working fluid and stainless-steel balls as a porous media. The Reynolds number range from (5000 to 9000) based on the diameter of the pipe. The experiments were conducted on three various numbers of stainless-steel balls (N) with various diameters (dp), which give various porosity (0.33, 0.38 and 0.41). These are (N= 2400, dp=1mm), (N=1600, dp=3mm) and (N= 750, dp=5mm). Results show that, heat transfer coefficient increases with the decrease in the porosity due to the reduction in the space between balls. This led to an increase in turbulence and produced eddies. Furthermore, enhancement in heat transfer coefficient reached its maximum value of (45%) for ball diameter with (dp=1mm) and water flow rate (9 L/min). New Correlation equations for the average heat transfer coefficient were obtained for three different diameters of balls (1, 3 and 5 mm).

اجريت دراسة عملية للتحقيق في تاثير كرات الفولاذ المقاوم للصدأ على التدفق الحراري القسري في الأنابيب تحت تدفق فيض حراري منتظم. يستخدم الماء كسائل العمل وكرات الفولاذ المقاوم للصدأ كوسط مسامي. يتراوح عدد رينولدز من (5000 إلى 9000) بناءً على قطر الأنبوب. أجريت التجارب على ثلاثة انواع من الكرات المختلفة في العدد والقطر ( , القطر=1ملم , عدد الكرات= 2400 كرة ( ، (القطر =3 ملم ، عدد الكرات=1600 كرة )، (القطر= 5ملم ، عدد الكرات = 750 كرة) والتي تعطي مسامية مختلفة (0.33 ، 0.38 ، . (0.41 تظهر النتائج أن معامل انتقال الحرارة يزداد مع انخفاض المسامية بسبب انخفاض المسافة بين الكرات وهذا أدى إلى زيادة الاضطراب والدوامات المتولدة. بالاضافة الى ذلك ، فقد تم تحسين معامل انتقال الحرارة إلى أقصى قيمة له بمقدار (45٪) لقطر الكرة ( 1ملم( ومعدل تدفق الماء (9 لتر/ دقيقة.( تم الحصول على معادلات تصحيحية جديدة لمتوسط معامل انتقال الحرارة لثلاثة أقطار مختلفة من الكرات (1 ، 3 ،5 ) ملم .


Article
An Experimental Study on the Effect of Shape and Location of Vortex Generators Ahead of a Heat Exchanger
دراسة عملية عن تأثير شكل وموقع مولدات الدوامات عند مدخل المبادل الحراري

Author: Wisam Abed Kattea وسام عبد كاطع
Journal: Al-Khwarizmi Engineering Journal مجلة الخوارزمي الهندسية ISSN: 18181171 23120789 Year: 2012 Volume: 8 Issue: 2 Pages: 12-29
Publisher: Baghdad University جامعة بغداد

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Abstract

An experimental study is carried out on the effect of vortex generators (Circular and square) on the flow and heat transfer at variable locations at (X = 0.5, 1.5, 2.5 cm) ahead of a heat exchanger with Reynolds number ranging from 62000< Re < 125000 and heat flux from 3000 ≤ q ≤ 8000 W/m2 .In the experimental investigation, an apparatus is set up to measure the velocity and temperatures around the heat exchanger. The results show that there is an effect for using vortex generators on heat transfer. Also, heat transfer depends on the shape and location. The circular is found to be the best shape for enhancing heat transfer at location [Xm=0.5 cm] distance before heat exchanger is the best location for enhancing heat transfer. The square is the best shape for enhancing heat transfer at location [Xm=2.5 cm] distance before heat exchanger is the best location for enhancing heat transfer.The results of flow over heat exchanger with vortex generators are compared with the flow over heat exchanger without vortex generators. Heat transfer around heat exchanger is enhanced (56%, 50%, 36%) at location (X=0.5, 1.5, 2.5cm) respectively by using circular vortex generators without turbulator and heat transfer around heat exchanger is enhanced (39%, 42%, 51%) at location (X=0.5, 1.5, 2.5cm) respectively by using square shape vortex generators without turbulator.

دراسة عملية أجريت لفحص تأثير مولد الدوامات ( الشبكة الدائرية ، الشبكة المربعة ) على الجريان و انتقال الحرارة عند مواقع (X = 0.5, 1.5, 2.5 cm) قبل مبادل حراري ضمن مدى لرقم رينولد 62000< Re < 125000 و فيض حراري 3000 ≤ q ≤ 8000 W/m2.في الدراسة العملية تم نصب و صيانة جهاز مختبري لقياس السرعة و درجة الحرارة حول المبادل الحراري.أظهرت النتائج أن لوجود مولد الدوامات اثر كبير على تحسين انتقال الحرارة ويعتمد هذا على شكل المولد وموقعهِ. الشبكة الدائرية هي الأفضل لعملية نقل الحرارة عند موقع [Xm=0.5 cm] قبل المبادل الحراري. الشبكة المربعة هي الأفضل لعملية نقل الحرارة عند موقع [Xm=2.5 cm]قبل المبادل الحراري. قورنت النتائج العملية في حالة وجود مولد الدوامات مع عدم وجود مولد الدوامات. أظهرت هذه المقارنة تحسن في انتقال الحرارة حول المبادل الحراري بنسب (56%, 50%, 36%)عند مواقع (X=0.5, 1.5, 2.5cm )على التوالي بأسنخدام مولد الدوامات الدائري الشكل نسبةً الى عدم وجود عوائق جريان،وانتقال الحرارة حول المبادل الحراري يتحسن بنسب (39%, 42%, 51%)عند مواقع (X=0.5, 1.5, 2.5cm ) على التوالي بأسنخدام مولد الدوامات المربع الشكل نسبةً الى عدم وجود عوائق جريان.


Article
Compound Heat Transfer Enhancement in Dimpled and Sinusoidal Metal Solar Wall Ducts Fitted with Wired Inserts

Authors: Abeer H. Faleh --- Fouad A. Saleh --- Mohammed H. Mahmoud
Journal: Journal of Engineering مجلة الهندسة ISSN: 17264073 25203339 Year: 2012 Volume: 18 Issue: 5 Pages: 591-610
Publisher: Baghdad University جامعة بغداد

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Abstract

An improved Metal Solar Wall (MSW) with integrated thermal energy storage is presented in this research. The proposed MSW makes use of two, combined, enhanced heat transfer methods. One of the methods is characterized by filling the tested ducts with a commercially available copper Wired Inserts (WI), while the other one uses dimpled or sinusoidal shaped duct walls instead of plane walls. Ducts having square or semi-circular cross sectional areas are tested in this work. A developed numerical model for simulating the transported thermal energy in MSW is solved by finite difference method. The model is described by system of three governing energy equations. An experimental test rig has been built and six new duct configurations have been fabricated and tested. Air is passed through the six ducts with Reynolds numbers from 1825 to 7300. Six, new, correlations for Nusselt number and friction factor are developed to assess the benefits that are gained from using the WI and the dimpled and sine-wave duct walls. It is found that higher heat transfer rates are achieved using the Dimpled, semi–circular duct with Wired Inserts (DCWI). Also, it is found that Nusselt number and the pressure drop in the DCWI are respectively (44.2% -100%) and (101.27% - 172.8%) greater than those of the flat duct with WI. The improvement in Nusselt number for flat duct with WI is found to be (1.4 – 2) times the values for flat duct with no WI. The results demonstrated that DCWI provides enhancements efficiency value that is higher than those obtained from other types of ducts. The developed MSW ducts have added to local knowledge a better understanding of the compound heat transfer enhancement.

في هذاالبحث تم تقديم جدار معدني شمسي (MSW) مطور ذو قابلية خزن حرارية ضمنية. ان الجدار المقترح يستخدم طريقتين لتحسين انتقال الحرارة. الطريقة الاولى تتضمن إملاء قنوات الجريان بحشوات نحاسية من الأسلاك (WI) المتوفرة تجاريا اما الطريقة الثانية فتستخدم مجاري الهواء ذات الجدران المتموجة جيبيا او المقعرة بدلا من المجاري ذات الجدران المستوية. لقد تم اجراء البحث على مجاري ذات مقاطع مربعة و نصف دائرية . تم اجراء الحل للموديل العددي المطور الخاص بمحاكاة الطاقة الحرارية المنقولة باستخدام طريقة الفروقات المحددة. ان هذا الموديل العددي مكون من منظومه من ثلاثة معادلات حاكمه للطاقه. تم في هذا البحث بناء جهاز أختبار عملي وتم تصنيع وأختبار ستة مجاري هواء وإمرار الهواء خلال المجاري ضمن مدى لرقم رينولدز من 1825 الى 7300. من النتائج المستحصلة من هذا البحث تم استحداث ستة معادلات جديدة خاصة برقم ناسلت و معامل الاحتكاك لتخمين الفوائد المكتسبة من الأستعمال المركب لكل منWI و مجاري الهواء ذات الجدران المتموجة جيبيا او المقعرة. لقد وجد ان اعلى معدل لانتقال الحرارة هو للمجرى المدمل ذو المقطع نصف الدائري المحشو (DCWI). النتائج بينت ان نسب رقم ناسلت ومقدار الانخفاض بالضغط للمجرى نوع DCWI هي على التوالي (44.2%-100% ) و (101.27%-172.8% ) اعلى من تلك العائدة الى المجرى المسطح مع WI . وجد ان التحسينات في رقم ناسلت قد بلغت ( 1.4 - 2 ) مرة بالنسبة للمجرى المزود ب WI بالمقارنة مع تلك غير المزودة ب WI.بينت النتائج الخاصة بالبحث الحالي ان الموديل المطور لمقترح DCWI يعطي كفاءة تحسين اعلى من الموديلات الاخرى. النتائج المستخلصة في هذا البحث أضافت للمعرفة المحلية فهم أفضل لتحسين انتقال الحرارة المركب.


Article
A study of Free Convection in A solar Chimney Model

Authors: Sabah Tarik Ahmed --- Miqdam Tariq Chaichan
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2011 Volume: 29 Issue: 14 Pages: 2986-2997
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

A solar chimney is a hot air channel attached to a circular translucentroof opens at the periphery. The roof and the ground below it form an air collector. It enhances natural ventilation by employing air temperature difference between channal inlet and outlet. An experimental work was carried out for a designed and fabricated prototype solar chimney, in Baghdad-Iraq’s autumn weather 2009. The chimney’s tower hight was 4 m and the solar collector diameter was 6 m. A maximum air temperature differance attained was 22ºC at mid day through the solar chimney. The study shows that Iraqi weathers are suitable for this system. Maximum heat transfer coeffecient (h) was 31.83 W/m2K, maximum air volume flow rate achieved was 0.065 m3/s, and maximum air velocity at the chimney outlet acquired was 2.309 m/s. Empirical equation that relates Nusselt and Rayleigh numbers was obtained.


Article
Study and Analysis of Concentric Shell and Double Tube Heat Exchanger Using - Al2O3 Nanofluid
الدراسات والتحاليل للمبادل الحراري ذو القشرة والانابيب المتداخلة المتمركزة باستخدام مائع نانوي كاما اوكسيد الالمنيوم

Authors: Noor Sabih Majeed نور صبيح مجيد --- Basma Abbas Abdulmajeed بسمة عباس عبد المجيد
Journal: Journal of Engineering مجلة الهندسة ISSN: 17264073 25203339 Year: 2017 Volume: 23 Issue: 9 Pages: 50-62
Publisher: Baghdad University جامعة بغداد

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Abstract

Heat exchanger is an important device in the industry for cooling or heating process. To increase the efficiency of heat exchanger, nanofluids are used to enhance the convective heat transfer relative to the base fluid. - Al2O3/water nanofluid is used as cold stream in the shell and double concentric tube heat exchanger counter current to the hot stream basis oil. These nanoparticles were of particle size of 40 nm and it was mixed with a base fluid (water) at volume concentrations of 0.002% and 0.004%. The results showed that each of Nusselt number and overall heat transfer coefficient increased as nanofluid concentrations increased. The pressure drop of nanofluid increased slightly than the base fluid because of the low concentration used.

للمبادل الحراري اهمية في الصناعة سواء في عملية التبريد او التسخين. لزيادة كفاءة المبادل الحراري استخدم المائع النانوي لتحسين انتقال الحرارة بالحمل بالمقارنة مع السائل الاعتيادي. تم استخدام السائل النانوي المتكون من كاما اوكسيد الالمنيوم مع ماء للتبريد في المبادل الحراري ذو الغلاف والانابيب المتداخلة والمتمركزة والذي يجري باتجاه عكسي مع تيارالزيت الساخن. هذه الدقائق النانوية ذات قطر 40 نانو متر, خلطت مع الماء بتراكيز حجمية 0.002 % مع 0.004 %. اظهرت النتائج ان عدد نسلت و معامل الانتقال الحراري الكلي قد ازداد بزيادة تركيز المادة النانوية. ان فرق الضغط للسائل النانوي قد ازداد زيادة طفيفة نتيجة استخدام تركيز واطئ.

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