Heat transfer enhancement plays an important role in improving energy efficiency and developing high performance thermal systems. Phase-change heat transfer processes take place in thermal systems; typically heat transfer enhanced tubes are used in these systems and they are designed to increase heat transfer coefficients in evaporation and condensation. Enhanced heat transfer tubes are widely used in refrigeration and air-conditioning applications in order to reduce cost and create a smaller footprint of the application.

Microfins, roughness and dimples are often incorporated into the inner surface of tubes in order to enhance heat transfer performance. Under many conditions, enhanced surface tubes can recover more energy and provide the opportunity to advance the design of many heat transfer products.

Convective condensation heat transfer and pressure loss characteristics were investigated for R410A on the outside of: (i) a smooth tube (outer diameter 12.7 mm); (ii) an external herringbone tube (fin root diameter 12.7 mm); and (iii) the 1EHT tube (outer diameter 12.7 mm) for very low mass fluxes. Data was obtained for values of mass flux ranging from 8 to 50 kg/(m2 s); at a saturation temperature of 318 K; with an inlet quality of 0.8 (±0.05) and an outlet quality of 0.1 (±0.05). In a comparison of heat transfer at a low mass flux, both the 1EHT tube and the herringbone tube did not perform as well as the smooth tube. And it’s difficult to analyze the reason for this strange phenomenon.

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