الفهرس 
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Abstract
This thesis presents an experimental study of laminar forced convection heat transfer of hot water flowing through annular tube. The test section consisted of two annular spaces, the inner of which for the tested hot water while the outer for the cooling water flow. The inner tube of the annulus was rotated with variable speed of rotation ranging from 350 to 1580 r.p.m, to give a rotational Reynolds number in the range of (19500 ≤ Reω ≤ 100000).The outer tube of the annulus have a constant diameter of 54.5mm and the diameter of inner tube of the annulus is equal to 21, 26.5 and 33.5 mm so, that the diameter ratios are 0.62, 0.487 and 0.386 respectively. Variable numbers of longitudinal ribs of 1, 2, 3 and 4 ribs are used. The length of ribs is kept constant at 500 mm and the height of ribs is equal to14 mm and thickness of 1mm. Hot water velocities ranged from 0.0042m/s to 0.52m/s, to give axial Reynolds numbers in the range of (130 ≤ Re ≤ 2330), to cover the laminar flow regime. The cold water flowing through the outer annulus is cooled by a refrigerating circuit. In the present work the effect of radius ratio, axial Reynolds number and rotational Reynolds number on the heat transfer rate is investigated. The results show that, the rate of heat transfer of the rotational annular tubes is higher than that of the stationary one for same radius ratio and axial Reynolds numbers. Nusselt number increases with Reynolds number and with the number of ribs until it reaches its maximum value for number of ribs equal to 3 and then it decreases with further increase in number of ribs. Three correlations are made to describe the relation between Nusselt number and axial Reynolds number, diameter ratio, rotational Reynolds numbers for stationary, rotating and ribed rotating annuli.