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Article
Effect of Fluidized Bed Particle Size on Heat Transfer Coefficient at Different Operating Conditions
تأثير حجم جسيمات الطبقة المميعة على معامل انتقال الحرارة عند ظروف تشغيلية مختلفة

Authors: Ehsan Fadhil Abbas --- Sarah Burhan Izat
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 4 Pages: 24-29
Publisher: Tikrit University جامعة تكريت

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Abstract

The aim of this study is to investigate the effect of gas flow velocity, size of sand particles, and the distance between tubes immersed in a fluidized bed on heat transfer coefficient. Experimental tests were conducted on a bundle of copper tubes of (12.5 mm) diameter and (320 mm) length arranged in a matrix (17×9) and immersed in a fluidized bed inside a plastic container. One of the tubes was used as a hot tube with a capacity of (122 W). (25 kg) of sand with three different diameters of sand particles (0.15, 0.3 and 0.6 mm) was used in these tests at ten speeds for gas flow (from 0.16 m/s to 0.516 m/s). The results showed a significant inverse effect of fluidized bed particles diameter on the heat transfer coefficient. Accordingly, the heat transfer coefficient for (0.15mm) diameter sand was found to be higher than that of (0.3 mm) and (0.6 mm) sand by about (3.124) and (6.868) times respectively, in all tests. The results showed good agreement with results from other studies conducted under the same conditions but with different sandparticle size.

تهدف هذه الدراسة الى التحقق من تأثير كل من سرعة الغاز، حجم جسيمات الرمل والمسافة بين االعمدة المغمورة في الطبقة المميعة على معامل انتقال الحرارة. حيث اجريت اختبارات تجريبية على حزمة من االنابيب نحاسية بقطر )5.12 )ملم وطول )320 )ملم ورتبت على شكل مصفوفة )17×9 )مغمورة في الطبقة المميعة داخل حاوية بالستيكية. استخدمت احدى االنابيب كمصدر للحرارة بسعة )122 )واط. استخدمت ثالثة قياسات لجسيمات الرمل )15.0 ،3.0 و6.0 )ملم وبعشر سرع تراوحت مــــن )16.0 الى 516.0 )م/ ثا. اظهرت النتائج بأن تأثير عكسي كبير لقطر جسيمات الرمل في الطبقة المميعة على معامل انتقال الحرارة. وفقا" لذلك، فان معامل انتقال الحرارة عند الرمل بقطر )15.0 )ملم الذي حصل عليه كانت اعلى عما حصل عليه عند )3.0 )ملم و )6.0 )ملم بحوالي )124.3 )و )868.6) مرة على التوالي في جميع االختبارات. تظهر النتائج بانها توافق بشكل جيد مع نتائج لدراسات اخري اجريت تحت نفس الظروف ولكن مع قياسات الرمل مختلفة.


Article
Experimental and Numerical Study of Heat Transfer Enhancement in a Shell and Tube Heat Exchanger using Helical Coiled Wire Inserts

Authors: Musa Mustafa Weis --- Ehsan Fadhil Abbas --- Ahmed Sami Ridha
Journal: Tikrit Journal of Engineering Sciences مجلة تكريت للعلوم الهندسية ISSN: 1813162X 23127589 Year: 2018 Volume: 25 Issue: 2 Pages: 74-79
Publisher: Tikrit University جامعة تكريت

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Abstract

An experimental work on heat transfer enhancement in a shell and tube heat exchanger by insertion of helical coiled wires into the tube bundle was conducted. Four different pitch sizes were used (4.8, 6.4, 8.0, 9.6) mm. The working fluid for both shell and tube sides of the exchanger was water. Flow arrangement used was parallel and laminar for both sides with a Reynolds number for the tube inside ranging (100-920). Variables were taken into account, including; convection heat transfer coefficient, number of heat transfer units, thermal effectiveness, and pressure drop. CFD analysis was done in order to validate the experimental results. The study results showed an increase in heat transfer coefficient on the tube side by 54% due to the use of 9.6 mm pitched inserts. Highest thermal effectiveness obtained was in the case of 9.6 mm pitch inserts. Pressure drop rose up to 260% due to inserts.

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