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Corresponding Author

Daayah, Ahmed

Subject Area

Mechanical Power Engineering

Article Type

Original Study

Abstract

This paper presents an experimental study of laminar forced convection heat transfer for hot water flows 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 is rotated with rotational speeds which varied from 350 to 1580 r.p.m. to give rotational Reynolds number in the range (200 ≤ Rew ≤ 1750). The outer tube of the annulus have a constant diameter of 54.5mm but the diameter of inner tube of the annulus is equal to 21, 26.5 and 33.5 mm so as to give diameter ratios of 0.62, 0.487 and 0.386. Hot water flowed axially through the annular space with velocities that ranged from (0.0042 to 0.52m/s), to give axial Reynolds numbers in the range (130 ≤ Re ≤ 2300), to cover the laminar flow regime. The cold water that flowed through the outer annulus was cooled by a refrigerating circuit. In the present work the effects of radius ratio, axial Reynolds number and rotational Reynolds number on the heat transfer were investigated. The results show that. The rate of heat transfer of the rotational annular tubes is higher than that of the stationary one of the same radius ratio and axial Reynolds numbers. An increase of as much as 200% in the heat transfer is observed for annular tube of radius ratio equal to 0.62, Reynolds number of 1951 rotational Reynolds number of 1744 and rotational speed of 1580 r.p.m respectively, a decreases in heat transfer as much as 36% in the heat transfer is reported for annular tube of radius ratio (B) of 0.386, Reynolds number of 1100, and rotational Reynolds number of 205 and rotational speed of 350 r.p.m respectively. Two correlations were established between Nusselt number and axial Reynolds number. Rotational Reynolds number and radius ratio of the annulus for both stationary and rotational annular tubes.

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