Heat transfer and pressure drop characteristics of refrigerant R410A inside three horizontal enhanced tubes (EHT) and one smooth tube were investigated experimentally. All stainless steel two-side enhanced tubes were fabricated using a multiple high-pressured extruding process. These three-dimensional two-layer surface structures are composed of staggered dimpled protrusions or boat-shaped cavities and petal-shaped background patterns in a grid-like arrangement. According to the single-phase heat balance analysis

the proportion of heat loss in total heat is no more than 5% for the entire test range. Changing the water flow rate in the case where the refrigerant mass flow rate was maintained at a fixed value

the water-side heat transfer coefficients for each tube tested were obtained by the Wilson plot method. On basis of the thermal resistance model

it was found that 1EHT-1 exhibits the best single-phase heat transfer performance

followed by the 3EHT and 1EHT-2. A large difference between the experimental results of these evaporation and condensation tests was observed in the three enhanced tubes. It can be attributed to the effect of low thermal conductivity of stainless steel on the temperature distribution in the region of protrusions/cavities.