Augmentation in heat transfer is very useful for various engineering and scientific applications due to the call for energy and cost saving. The heat transfer and pressure drop characteristics in annuli of double pipe heat exchanger using helical and plain surface ring turbulators are studied through experimental investigation. The effect of helical surface ring turbulators and plain surface ring turbulators are studied for varied range of pitch ratio (4.0–6.4), Reynolds Number (3,000–10,500) and two different diameter ratios (0.475 and 0.54). Water (hot fluid) flows in the inner tube and air (cold fluid) flows through the annulus. The tests are conducted for air with uniform wall temperature condition. The heat exchanger with least pitch and least diameter ratio is found to exhibit the highest Nusselt number and pressure drop. Results indicate that maximum enhancement is obtained for smallest diameter ratio 0.475 and pitch ratio 4.0 at lowest Reynolds Number. Also, thermal performance factor is always greater than unity for the DPHE using helical surface turbulators. Correlations have been developed for enhancement in Nusselt number and friction factor; show the good agreement with experimental test data within test range.

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