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.

Micro channel --- Forced Convection --- Optimal Geometry

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.

laminar flow --- rectangular micro-channel --- numerical solution --- pressure drop --- friction factor and friction constant

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).

Rectangular channel --- Micro-channel --- CFD --- 3D Simulation --- Heat transfer coefficient. --- قناة مستطيلة، قناة الصغرى،CFD، محاكاة 3D، معامل نقل الحرارة.