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Article
The Optimal Spacing between Finned Tubes Cooled by Free Convection Using Constructal Theory

Authors: Ahmed Waheed Mustafa --- Mays Munir Ismael
Journal: AL-NAHRAIN JOURNAL FOR ENGINEERING SCIENCES مجلة النهرين للعلوم الهندسية ISSN: 25219154 / eISSN 25219162 Year: 2017 Volume: 20 Issue: 4 Pages: 815-822
Publisher: Al-Nahrain University جامعة النهرين

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Abstract

The optimal spacing between finned tubes cooled by free convection is studied numerically. A row of isothermal finned tubes are installed in a fixed volume and the spacing between them is selected according to the constructal theory (Bejan's theory). In this theory the spacing between the tubes is chosen such that the heat transfer density is maximized. A finite volume method is employed to solve the governing equations; SIMPLE algorithm with collocated grid is utilized for coupling between velocity and pressure. The range of Rayleigh number is (103 ≤ Ra ≤ 105), the range of the tube position is (0.25 ≤  ≤ 0.75), and the working fluid is air (Pr =0.71). The results show that the optimal spacing decreases as Rayleigh number increases for all tube positions, and the maximum density of heat transfer increases as the Raleigh number increases for all tube positions and for Ra=105 the highest value of heat transfer density occurs at tube position ( =0.75) while the lowest value occurs at tube position ( =0.25). The results also show that the optimal spacing remains constant with change of the tube position at constant Rayleigh number.

البعد الامثل بين انابيب مزعنفة مبردة بالحمل الحر درس عدديا. صف من الانابيب المزعنفة ثابتة درجة الحرارة نصبت في حجم محدد والبعد بينهم اختير بموجب نظرية التشييد (نظرية بيجان). في هذة النظرية البعد اختير بحيث تكون كثافة انتقال الحرارة اقصى ما يمكن. طريقة الحجم المحدد استخدمت لحل المعادلات الحاكمة, خوارزمية SIMPLE مع شبكة متحدة الموقع استخدمت للربط بين السرعة والضغط. مدى رقم رايلي (103 ≤ Ra ≤ 105) , مدى موقع الانبوب(0.25 ≤  ≤ 0.75) ومائع التشغيل هو الهواء (Pr=0.7). بينت النتائج ان البعد الامثل يقل مع زيادة رقم رايلي لكل مواقع الانبوب وعند Ra=105القيمة العليا لكثافة انتقال الحرارة العظمى تحدث عند موقع الانبوب (=0.75) , وقيمتها السفلى تحدث عند موقع الانبوب (=0.25).بينت النتائج ايضا ان البعد الامثل يبقى ثابت مع تغير موقع الانبوب عند رقم رايلي ثابت.


Article
Evaluation of the Performance of Steel in Reinforced Concrete by Electrochemical Methods

Authors: Dhia C. Ali --- Nawal J. Hammadi --- Enas M. Manea
Journal: Basrah Journal for Engineering Science مجلة البصرة للعلوم الهندسية ISSN: Print: 18146120; Online: 23118385 Year: 2014 Volume: 14 Issue: 2 Pages: 67-76
Publisher: Basrah University جامعة البصرة

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Abstract

The effect of different dosages of the high range water reducing admixture–additive- (HRWRA), the commercially polymeric material (Plastocrete-N), on the corrosion resistance of embedded steel in concrete exposed to chloride solution in the absence and presence of sulfate ions was studied. In the present study, four levels of polymeric material (Plastocrete-N) (0.125%, 0.250%, 0.375%, and 0.500% by weight of cement) were used to prepare HRWRA treated concrete. The concrete specimens exposed to chloride and chloride–sulfate solutions at concentrations of (3.5% NaCl and 5% Na2SO4), at ambient temperature. The electrochemical behavior of steel in both reference and HRWRA concretes was studied under the effect of corrosive environments using corrosion measurement systems such as: a) half – cell potentials measurement system and b) accelerated corrosion test system. The results showed that a longer time of corrosion initiation (180 day) observed with 0.500% HRWRA containing concrete compared to other different HRWRA percentage including the reference concrete. It was concluded that the use of 0.500% HRWRA provided superior protection to steel reinforcement in concrete that subjected to corrosive environments. Furthermore, the steel with 0.500% HRWRA was subjected to corrosion test by mass loss, it is evident that a reduction in mass loss by about 90.2% and 85.2% in both solutions, respectively.


Article
Numerical Investigation for Enhancement of Heat Transfer in Internally Finned Tubes Using ANSYS CFX Program

Authors: Ali Shakir --- Ammar O --- Nofil Baqer
Journal: Basrah Journal for Engineering Science مجلة البصرة للعلوم الهندسية ISSN: Print: 18146120; Online: 23118385 Year: 2015 Volume: 15 Issue: 1 Pages: 32-42
Publisher: Basrah University جامعة البصرة

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Abstract

In this study, a numerical investigation has been carried out for single phase flow behavior for thirty six internally finned tubes to demonstrate the effect of axial pitch to fin height ratio (p/e) for 0.8≤p/e≤6.345, helix angle of internal fins (β) for 30°≤β≤70°, apex angle of internal fins (α) for 0°≤α≤53.13°, internal fin height (e) for 0.6mm≤e≤1.0mm, internal tube diameter (di) with 14 mm and Reynolds number (Re) of single phase flow for 10000≤Re≤50000 on enhancement of forced convection heat transfer and reduction of friction factor by using ANSYS CFX program. It solves the three-dimensional Navier-Stokes equations for steady state turbulent with SST model and enhance wall treatment. The numerical analysis provided at fully developed velocity and temperature. Numerical results showed that the smallest axial pitch to fin height ratio (p/e) =0.8 and with apex angle α=10 degree provided enhancement of heat transfer of 2.8 to 3.55 times higher than of smooth tube. Finally, present numerical results are seen to be in good agreement with literature experimental correlations.


Article
Numerical investigation for enhancement of heat transfer in internally finned tubes using ANSYS CFX program

Authors: Ali Shakir --- Ammar Ali --- Nawfel Mohammed
Journal: Basrah Journal for Engineering Science مجلة البصرة للعلوم الهندسية ISSN: Print: 18146120; Online: 23118385 Year: 2016 Volume: 16 Issue: 2 Pages: 89-99
Publisher: Basrah University جامعة البصرة

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Abstract

In this study, a numerical investigation has been carriedout for single phase flow behavior for thirty six internally finnedtubes to demonstrate the effect of axial pitch to fin height ratio(p/e) for 0.8≤p/e≤6.345, helix angle of internal fins (β) for30°≤β≤70°, apex angle of internal fins (α) for 0°≤α≤53.13°, internalfin height (e) for 0.6mm≤e≤1.0mm, internal tube diameter (di)with 14 mm and Reynolds number (Re) of single-phase flow for10000≤Re≤50000 on enhancement of forced convection heattransfer and reduction of friction factor by using ANSYS CFXprogram. It solves the three-dimensional Navier-Stokes equationsfor steady state turbulent with SST model and enhance walltreatment. The numerical analysis provided at fully developedvelocity and temperature. Numerical results showed that thesmallest axial pitch to fin height ratio (p/e) =0.8 and with apexangle α=10 degree provided enhancement of heat transfer of 2.8 to3.55 times higher than of smooth tube. Finally, present numericalresults are seen to be in good agreement with literatureexperimental correlations

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