An assessment of refrigerant heat transfer, pressure drop, and void fraction effects in microfin tubes

Microfin tubing can significantly increase heat transfer in refrigeration evaporators and condensers. The effectiveness of microfins is dependent on fluid properties, flow field configuration, heat flux direction (evaporation and condensation), and tube geometry. This review focuses on the performance of microfin tubes in refrigeration systems and details information known about microfin tube performance as well as information that is not yet investigated. Generally, microfins enhance heat transfer by an amount that is similar or greater than the amount of surface area added to the internal wall surface. Pressure drop does not tend to increase significantly; however, the range of reported pressure drop effects is broad. Oil generally degrades heat transfer and increases pressure drop; however, the oil concentration and viscosity are important factors.