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Article
Optimization of Microchannel Geometries to Enhance Convection Cooling of Parallel Plate Duct Flow
تحسین انتقال الحرارة بالحمل القسري لتبرید القنوات الصغیرة باستخدام اشكال جدیدة

Author: Faris A. Badawy
Journal: Engineering and Technology Journal مجلة الهندسة والتكنولوجيا ISSN: 16816900 24120758 Year: 2014 Volume: 32 Issue: 1 Part (A) Engineering Pages: 46-62
Publisher: University of Technology الجامعة التكنولوجية

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Abstract

Forced convection heat transfer from arrays of microchannels was considered for fixed volume and fixed pressure drop constraints. Order of magnitude relationships were developed for the optimal dimension of a number of fundamental duct shapes including the parallel plate channel with rectangular,square, rhombus, isosceles right triangle, circular duct and elliptic duct. Using the exact analysis method to produce an approximate expression for the optimal duct shape was developed for all ducts considered. Where approximate analytical results show that the optimal shape is the parallel plate channel duct array but withaddition a triangular or rectangular duct to the parallel plate, where the rectangular model give a percent of (52%) increasing in the heat dissipation higher than the circular at an aspect ratio about (b/a=0.4), while give a percent of increase about (87%) in the same aspect ratio compared with rhombus duct model in heat dissipation due to their ability to provide the most efficient arrays in a fixed volume. Comparison of the approximate results with exact results from theliterature show excellent agreement for the optimal duct dimensions.


Article
Effect of the Axial Heat Conduction in Parallel Flow Rectangular Microchannel Heat Exchanger

Author: Hayder Mohammed Hasan
Journal: University of Thi-Qar Journal for Engineering Sciences مجلة جامعة ذي قار للعلوم الهندسية ISSN: 26645564/26645572 Year: 2013 Volume: 4 Issue: 1 Pages: 113-137
Publisher: Thi-Qar University جامعة ذي قار

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Abstract

The axial heat conduction in parallel flow microchannel heat exchanger with rectangular ducts was numerically investigated, for laminar, 3-D, incompressible, and steady state flow of water. The governing equations, continuity, Navier-Stokes equations (momentum equations), and the energy equations for the hot and cold fluids were solved by using SIMPLE algorithm with finite volume method and FORTRAN code to obtain the temperature distribution for the two fluids and the separating wall between them. The results play an important role of the axial heat conduction on the effectiveness in parallel flow microchannel heat exchanger and the factors affecting the axial heat conduction are; Reynolds number Re, thermal conductivity ratio , aspect ratio α and channel volume. Increasing of Re, , α and channel volume each separately leads to increase the axial heat conduction and vice versa.

عدديا تمت دراسة تأثير التوصيل الحراري المحوري في مبادل حراري مايكروي ذي قنوات مستطيلة الشكل لجريان متوازي طباقي ثلاثي الأبعاد للماء وفي حالة الاستقرار ولا انضغاطي. تم حل المعادلات الحاكمة للجريان وهي معادلة الاستمرارية continuity) (equation ومعادلات الزخم (momentum equations) و معادلة الطاقة ((energy equations باستخدام طريقة ((SIMPLE method وقد تم تحويل المعادلات الحاكمة إلى الشكل العددي باستخدام طريقة الحجوم المحددة (finite-volume method) وباستخدام لغة فورتران (FORTRAN). بهذه الطريقة تم إيجاد التوزيع لدرجتي حرارة المائعين والجدار الذي يفصل بينهما. من خلال ملاحظة النتائج المستحصلة من الحل العددي, تبين بأن هنالك تأثير مهم للتوصيل الحراري المحوري على الفعالية في المبادل المايكروي كما إن هنالك مجموعة من العوامل التي تؤثر عليه وهي, عدد رينولدز(Reynolds number Re) ونسبة الموصلية الحرارية (thermal conductivity ratio Kr ) والنسبة الباعية (aspect ratio α) وحجم القنوات. عند زيادة Re و Krوα وحجم القنوات كل على حدة يزداد التوصيل الحراري المحوري, والعكس صحيح.


Article
NUMERICAL STUDY OF PRESSURE DROP AND FLUID FRICTION IN LAMINAR FLOW RECTANGULAR MICROCHANNELS
دراسة عددية لهبوط الضغط واحتكاك المائع في جريان طباقي لقنوات مايكروية مربعة الشكل

Author: Hayder Mohammed Hasan حيدر محمد حسن
Journal: Basrah Journal for Engineering Science مجلة البصرة للعلوم الهندسية ISSN: Print: 18146120; Online: 23118385 Year: 2014 Volume: 14 Issue: 1 Pages: 108-121
Publisher: Basrah University جامعة البصرة

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Abstract

An incompressible three dimensional continuity and Navier-Stokes (momentumequations) equations are numerically solved to obtain the pressure drop and fluid friction inlaminar steady state micro-channel flow of water. The governing equations are solved byusing SIMPLE algorithm with finite volume method and FORTRAN code to obtain pressurefield in rectangular micro-channel and then from the pressure field both friction factor f andfriction constant Cf are obtained.The results showed that the factors affecting the pressure drop, friction factor f andfriction constant Cf are; channel length L, Reynolds number Re, aspect ratio α, channelvolume chV and hydraulic diameter hD . Increasing of channel length L leads to increaseeach pressure drop, f and Cf. On other hand, increasing of Re leads to increase pressure dropand decrease the f, while the Cf increase with low value of Re (Re less than 50) and thennearby with approximately constant value. Moreover, increasing of α, chV and hD eachseparately leads to decrease pressure drop and increase both f and Cf.


Article
NUMERICAL INVESTIGATION OF MICROCHANNEL HEAT SINK WITH MEPCM SUSPENSION WITH DIFFERENT TYPES OF PCM

Authors: Hind Lafta TBENA --- Mushtaq Ismael HASAN
Journal: Al-Qadisiyah Journal for Engineering Sciences مجلة القادسية للعلوم الهندسية ISSN: 19984456 Year: 2018 Volume: 11 Issue: 1 Pages: 115-133
Publisher: Al-Qadisiyah University جامعة القادسية

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Abstract

The aim of this paper is to study the microencapsulated phase change materials (MEPCM) suspension as a coolant instead of pure fluid in the micro channel heat sink (MCHS) with different core and wall materials as well as different base fluids. The MEPCM suspension using in this study consist of microcapsules constructed from n-octadecane, RT44 as a phase change materials (PCM) and shell materials are poly-methylmthacrylate (PMMA), poly-alpha olefin (PAO), these capsules are suspended in (pure water, ethylene glycol and pure oil) in a concentration of (0–20)% and have been used as a cooling mediums at different ambient temperatures. Constant heat flux is applied at base of heat sink. The results obtain show that, using MEPCM suspensions as a coolant in micro heat sink instead of conventional cooling with pure fluid lead to enhance the cooling performance of micro heat sink is be 20.91% with (RT44+PMMA) pure oil, 16.91% with (RT44+PMMA) for ethyleneglycol and 12.91% with (RT44+PMMA) for pure water at concentration 2% and


Article
Experimental and Numerical Study to Enhance of Heat Transfer Coefficientin Air Flow Using Microchannel

Authors: Jalal M. Jalil --- Ghada A. Aziz
Journal: Journal of University of Babylon مجلة جامعة بابل ISSN: 19920652 23128135 Year: 2018 Volume: 26 Issue: 7 Pages: 112-123
Publisher: Babylon University جامعة بابل

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Abstract

Experimental and numerical study of fluid flow and heat transfer in microchannel airflowis investigated. The study covers changing the cooling of micro-channel for the velocities and heater powers. The dimensions of the microchannel were, length = 0.1m, width = 0.001m, height = 0.0005 m. The experimental and numerical results were compared with the previous paper for velocities up to 20 m/s and heater powers up to 5 W and the comparison was acceptable. In this paper, the results were extended numerically for velocities up to 60 m/s. The numerical solution used finite volume (SIMPLE algorithm) to solve Navier Stokes equations (continuity, momentum and energy). The results show that the heat transfer coefficient increases up to 220 W/m2oC for velocity 60 m/s.

تم في هذا البحث دراسة جريان المائع(الهواء) وانتقال الحرارة في القنواةالصغرى.شملت الدراسة تغير السرع وطاقة الهيتر.حيث ان ابعاد القناة الصغرى كانت الطول 0.1, العرض 0.001, الارتفاع 0.0005( m). تم مقارنة النتائج العملية والنظرية في بحث سابق لغاية سرعة 20 m/s وطاقة الهيترالذي ثبتت ابعاده بما يتناسب مع ابعاد القناة الصغرى لغاية 5 W وكانت المقارنة مقبولة. في هذا البحث، تم تمديد النتائج عدديا للوصول الى السرعة60(m/s). استخدم في الحل العددي طريقة الحجوم المحددة لحل معادلاتstokes­Navier (حفظ الكتلة والزخم والطاقة). اظهرت النتائج ان معامل انتقال الحرارة ازداد الى قيمة 225(C° ²W/m) للسرعة.60 (m/s).

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