Kongkaitpaiboon V.   Ruengpayungsak K.   Wongcharee K.   Thianpong C.   Eiamsa-ard S.  

Fluid flow and heat transfer characteristics in round tubes fitted with circular-ring turbula-tor

Reporter: Eiamsa-ard S.

Heat transfer augmentation (HTA) techniques are frequently used in a heat exchanger system in order to augment heat transfer and increase the thermal performance of the system. Heat transfer augmentation can be classified broadly into two main techniques: active and passive methods. In the active methods, heat transfer is improved by supplying extra energy to the fluid or the equipment.  On the other hand, the passive enhancement can be attained with-out any external energy. In general, the passive method involves the modifications of flow sur-faces (such as rough surfaces, treated surfaces and extended surfaces) as well as incorporations of inserts (such as turbulators and swirl generators).

The present paper reports heat transfer and friction factor characteristics in the tubes with circular-ring turbulator (CRT) inserts.  Each circular-ring (CRT) was placed on the inner surface of a tube heat exchanger at three spacing ratio defined as a ratio of baffle interval to outer diameter of baffle (SR = s/Dob = 1.0, 2.0 and 3.0). The experiments were conducted under uni-form heat flux condition for Reynolds number between 5000 and 15,000 (based on the inner diameter, D), air as the working fluid. The plain tube was also tested for assessment. The ob-tained results demonstrate that the presence of the CRT inserts leads to the increases of both Nusselt number and friction as compared to those of the plain tube. The improvement of Nusselt number is directly related to the superior destruction of the boundary layer which is responsible by the secondary flow around the CRT and hence, the strong turbulence/reverse flow.

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