Effect Of Rotation on the Flow Resistance and Heat Transfer in Circular Tubes Rotating About a Parallel Axis

Abstract

Many engineering installations and equipment include rotating elements, which work under severe operating conditions and different temperature levels, such as turbines, generators, engines, rotating heat exchangers, etc. The severe operating conditions along with the high temperatures extremely affect the crystal structure and increase rate of mechanical wear, and therefore reduce their lifetime. For these reasons, many studies have been done to achieve a good cooling process for such rotating elements. For example, rotating heat exchangers and cooling of turbine blades (gas or steam turbines) which may operate at temperatures up to 1800 °C. The rate of cooling process is significantly affected by the rotation speed. Therefore, many researchers have to study the effects of rotation on the heat transfer process e.g. do great efforts. A survey of literature is made to clear all studies made in this subject during the last few decades. It shows that there is a lack of experimental studies that investigate the effect of rotating on flow characteristics and heat transfer in a tube rotating around a parallel axis and the effect of the various parameters of this construction. The present study focuses on this point. A test rig is designed to study the effect of the following parameters on both flow and heat transfer characteristics; • The distance between the tube and the axis of rotation. • Variation ofthe rotational speed oftube.

The test rig includes a mechanism for power supply fixed on the rotating tube and also for the thermocouples led out from the rotating tube to the measuring device. Water is used as a heat transfer fluid and sealing between the rotating tube and the fixed ends of the test rig is provided. The results show a considerable increase in both the heat transfer and friction coefficients with the increase of the rotational speed, and the distance between the tube and its axis of rotation (radius of rotation).