Enhancement of natural and forced convectional heat transfer rate has been the subject of several academic and industrial studies. Air blenders, mechanical agitators, and static mixers have been developed to increase the forced convectional heat transfer rate in compressible and incompressible flows. Stationary devices can be efficiently employed as heat transfer enhancement tool in the natural convection systems with compressible flow. Generally, a stationary heat transfer enhancement insert consists of a number of equal motionless units, placed on the inside of a pipe or channel in order to control flowing fluid streams. These devices have low maintenance and operating costs, low space requirements and no moving parts. A range of designs exist for a wide range of specific applications. The shape of the elements determines the character of the fluid motion and thus determines thermal effectiveness of the heat transfer enhancement insert. There are several key parameters that may be considered in the design procedure of a heat transfer enhancement insert, which lead to significant differences in the performance of various designs. An ideal heat transfer enhancement insert for natural conventional heat transfer of compressible flow applications provides a higher rate of heat transfer and a thermally homogenous fluid with minimized pressure drop and required space. This paper presents the outcomes of the experimental studies by the authors on two industrial stationary inserts and illustrates how a heat transfer enhancement insert can improve the heat transfer in a buoyancy driven compressible flow. Using different measuring tools, the global performance of the inserts are studied in order to choose the most effective design.

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