Heat exchanger tubes used in large refrigeration systems are generally enhanced

both inside and outside. Because it is difficult to attach temperature sensors for wall temperature measurements

specific test methods are required for the performance evaluation of such double-sided enhanced tubes. These include the Wilson plot method (WPM)

modified Gnielinski formula (MGF)

and Wilson–Gnielinski formula (W-GF)

which have their own applications and limitations. In this study

a new and user-friendly test method––the undetermined exponent method (UEM)––was developed for double-sided enhanced tubes. The internal and external heat transfer coefficients can be separated effectively and efficiently by obtaining the undetermined parameters in the correlation through linear fitting and optimization. Experiments under two different conditions on a double-sided enhanced tube with R134a evaporating outside and water flowing inside were conducted

and a comparative study of the WPM

MGF

W-GF

and UEM test methods was performed. The internal and external enhanced factors obtained by the four methods were 2.88–3.23 and 3.15–3.54

respectively

and the difference in the internal and external heat transfer coefficients was within 15% and 11%

respectively. These four methods can be applied under different conditions

yet the proposed UEM is a more efficient and accurate test method with fewer restrictions and more convenience.