With the growing need for more energy, it is always important to design energy-efficient heat exchangers which intern leads to simpler in design, cheaper in cost and higher heat transfer rate. The Double pipe heat exchanger (DPHE) has the benefit of reduced construction and maintenance cost so that its application has been widely supported in industries like food processing, textile, energy, power, oil refineries, and refrigeration. From the earlier year's studies, it has foreseen that a great amount of passive augmented techniques has been introduced to enhance and optimize double pipe heat exchanger. In this review paper, both experimental and numerical works are considered on the aspects of the augmented approach, working conditions, the percentage of heat transfer enhancement, working fluids and observations for a double pipe heat exchanger which is widely discussed. The current study represents the best of a comprehensive review on passive augmented technique as it's been cited regularly. The paper also signifies the amount or percentage of enhancement in Nusselt number and friction factor from previous studies, believing that the review may offer further insights for the researchers on passive augmented techniques. This paper reviews numerical and experimental works of various investigators on these techniques since 1998 such as fins, inserts, swirl generators, turbulators etc. Lastly, the present review article excludes the previous works on twisted tapes as there are a lot of review papers done on it.
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