Performance Enhancement of Double Pipe Heat Exchangers by Enforced Turbulence on Single Surface

Results are presented from Theoretical analysis for pressure drop and heat transfer in annular flow having repeated turbulators. The annular flow represents the outer part of counter flow in a double-pipe heat exchanger. The modeling enables estimation of the friction factor, Nusselt number and Stanton number. The mathematical modeling is based on the law of the wall similarity to correlate both friction factor and heat transfer coefficient. The regime of hot water inside the inner pipe is investigated within a Reynolds number range from 10000 to 72000. The annular cold flow is ranging 26000 to 200000 Reynolds number. Four different types of promoter installations were tested. The results are verified by comparing with experiments. They are in good agreement. The results have shown enhancement in the heat transfer coefficient combined with increase in the friction factor. The performance index has shown highest enhancement of about 1.8 at pitch to diameter ratio equal 10 and promoter height to hydraulic diameter equal 0.0595 when the promoters are attached to inner surface of the outer pipe.

Key words: Heat exchangers, heat transfer enhancement, ribbing, friction, Counter flow.