Dimensional analysis and empirical correlations for heat transfer and pressure drop in condensation and evaporation processes of flow inside micropipes: case study with carbon dioxide (CO2)

in this paper, the experimental results of the convection heat transfer coefficient and pressure drop values during condensation and evaporation of co2 were obtained at different operating conditions for flow inside micropipes. reynolds number (red) ranged between 2000 and 15000. the dimensional analysis technique was utilized to develop correlations for nusselt numbers and pressure drops. a comparison between experimental and correlated results was carried out. the results showed that for the condensation process, the bias errors were 5.25% and 0.4% for pressure drops and nusselt number respectively. consequently, average standard deviation (asd) values reached 17.94% and 4.62% for both respectively. on the other hand, for the evaporation process, the nusselt number error was 3.8% with an asd of 4.14%. the correlations presented in the present work can be used in calculating pressure drops and heat transfer coefficients for phase change flows in mini and micro tubes. it helps to enhance design calculations of heat exchangers, condensers and evaporators