## 5 Conclusions  
Experiments were carried out to investigate the adiabatic pressure drop and condensation heat transfer coefficient of R134a in a horizontal smooth and microfin tube with outer diameter of 2.5 mm. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Correlation**} & \multicolumn{2}{c}{**Smooth Tube**} & \multicolumn{2}{c}{**Microfin Tube**} & \multicolumn{2}{c}{**All Data**} \\ \cline{2-7}  & **AD (\%)** & **MD (\%)** & **AD (\%)** & **MD (\%)** & **AD (\%)** & **MD (\%)** \\ \hline [PERSON] et al. [32] & \(2.15\) & \(31.10\) & \(-40.74\) & \(98.14\) & \(-24.48\) & \(73.56\) \\ [PERSON] and [PERSON] [33] & \(-15.36\) & \(20.69\) & \(-60.16\) & \(60.16\) & \(-43.36\) & \(45.36\) \\ [PERSON] and [PERSON] [1] & \(99.57\) & \(99.68\) & \(-12.47\) & \(35.87\) & \(27.97\) & \(59.19\) \\ [PERSON] and [PERSON] [34] & \(75.48\) & \(77.62\) & \(-34.42\) & \(40.10\) & \(6.06\) & \(53.92\) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Deviations of condensation heat transfer coefficient. Figure 15: Comparison between the experimental and predicted condensation heat transfer coefficients using correlations: (**a**) [PERSON] et al. [32]; (**b**) [PERSON] and [PERSON] [33]; (**c**) [PERSON] and [PERSON] [1]; and (**d**) [PERSON] and [PERSON] [34]. The experimental results for pressure drop, flow pattern and heat transfer were analyzed and compared with correlations. Some conclusions about this study are as follows. The frictional pressure drop as well as condensation heat transfer coefficient increased with mass flux and vapor quality. The increase rate of pressure drop was higher in microfin tube compared to the smooth tube with the same experimental condition. The frictional pressure drop was higher in microfin tube for all mass fluxes and was about 1.5 times greater than that of smooth tube at mass flux 50 kg m\({}^{-2}\)s\({}^{-1}\). Pressure drop penalty factor range was 1.01-2.11. Condensation flow patterns were predicted by two widely used flow pattern maps and annular, semi-annular, wavy, and slug and plug flow patterns were observed inside the tube. With the increase of mass flux, the zone of annular flow regime increased in the flow pattern map. Heat transfer coefficient was higher in microfin tube for all mass fluxes and was about 2-5 times greater than that of smooth tube at mass flux of 100 kg m\({}^{-2}\)s\({}^{-1}\). Decrease of tube diameter could increase heat transfer coefficient. Four well-known pressure drop and condensation heat transfer correlations were used to predict the present experimental data. The pressure drop prediction correlations in ascending mean deviation order are: [PERSON] and [PERSON], [PERSON] et al., [PERSON] et al., and [PERSON] et al. The heat transfer prediction correlations in ascending mean deviation order are: [PERSON], [PERSON], [PERSON] and [PERSON], and [PERSON] et al. Investigation, M.K.B., and K.N. ; Formal analysis, Data curation and Writing--original draft, M.K.B. ; Supervision, K.K. and A.M.; and Project administration, A.M. This research was funded by the Japan Copper Development Association. The authors would like to thank the Japan Copper Development Association for their financial support. The authors declare no conflict of interest.