## 4 Experimental Results and Discussion
### Condensation Heat Transfer Coefficient Results and Discussion
Moreover, the saturation temperature changes the thermophysical properties of refrigerant, as shown in Table 2.  
Figures 13 and 14 show the effect of tube diameter on condensation heat transfer coefficient. Experimental data were collected for R134a with different test tube diameters. Figure 13 shows heat transfer coefficient of R134a in one smooth (\(d_{i}=2.14\) mm) and two microfin (\(d_{e}=2.17\) and 3.18 mm) tubes at mass flux and saturation temperature of 50 kg m\({}^{-2}\)s\({}^{-1}\) and 20 \({}^{\circ}\)C, respectively. In Figures 13 and 14, the decrease of tube diameter can help to increase the heat transfer coefficient and comparing the results for the two microfin tubes shows that the heat transfer coefficient of \(d_{e}=3.18\) mm tube was about 1.1-1.6 times lower than \(d_{e}=2.17\) mm tube. Actually, when the tube diameter decreased, the effect of shear stress and surface tension enhanced, resulting in the easy occurrence of annular flow regime. Similar experimental trends were also observed by [PERSON] et al. [24] and [PERSON] [31], as shown in Figure 14.  
Figure 11: Effect of mass flux and vapor quality on condensation heat transfer coefficient at: (**a**) \(G=300\) kg m\({}^{-2}\)s\({}^{-1}\); (**b**) \(G=100\) kg m\({}^{-2}\)s\({}^{-1}\); and (**c**) \(G=50\) kg m\({}^{-2}\)s\({}^{-1}\). Figure 12: Effect of saturation temperature on condensation heat transfer coefficient: (**a**) smooth tube; and (**b**) microfin tube. Figure 13: Effect of tube diameter on condensation heat transfer coefficient. Comparison with the Condensation Heat Transfer Correlations  
To validate the experimental procedure, the experimental condensation heat transfer data of the microfin and smooth tube were compared with the four typical condensation heat transfer correlations proposed by [PERSON] et al. [32], [PERSON] [33], [PERSON] [1] and [PERSON] [34], as shown in Figure 15. The compared condensation heat transfer correlations are listed in Table 5. The average deviation (AD) and mean deviation (MD) are listed in Table 6 and calculated by Equations (13) and (14), respectively. Figure 10:0  
Figure 10:1 \begin{table}
\begin{tabular}{c c c} \hline \hline
**Author(s)** & **Correlation** & **Experimental Condition** \\ \hline [PERSON] et al. [32] & \(h_{tp}=\frac{Nuk}{d_{s}}\), \(Nu=\sqrt{Nu_{FC}^{2}+Nu_{CC}^{2}}\) & \(d=8\) mm, smooth tube. \\ \(Nu_{FC}=0.0152R_{l}^{0.77}\big{(}1+0.6P_{l}^{0.8}\big{)}\frac{\phi_{L}}{X_{m}}\) & Fluid: R134a, R22, R123 \\  & \(Nu_{CC}=0.725R(\xi)\big{(}\frac{Ga_{l}P_{l}}{Ph}\big{)}^{0.25}\) & G: 90–400 kg m\({}^{-2}\)s\({}^{-1}\). \\ \hline [PERSON] and [PERSON] [33] & \(h_{tp}=0.023R_{l}^{0.8}P_{l}^{0.4}\big{(}1+\frac{2.22}{\lambda_{H}^{2}}\big{)} \frac{\phi_{L}}{d_{s}}\) & \(d=3.14\)–7.04 mm, smooth tube. \\  & & Fluid: R134a, R12, R22, mixture (R32/ R125), G: 25–800 kg m\({}^{-2}\)s\({}^{-1}\). \\ \hline [PERSON] and [PERSON] [1] & \(h_{tp}=\frac{Nuk}{d_{s}}\), \(Nu=\sqrt{(Nu_{FC}^{2}+Nu_{NC}^{2}}\) & \(d_{o}=7.52\) mm, microfin tube. \\ \(Nu_{FC}=2.12\sqrt{f_{v}}\big{(}\frac{\phi_{L}}{P_{l}}\big{)}^{0.1}\big{(}\frac {x}{\tau-z}\big{)}\phi_{v}R_{l}^{0.5}P_{l}^{0.5}\) & Fluid: R134a, R123, R22 \\  & \(Nu_{NC}=1.98\frac{H(\xi)}{H_{u}^{2}G^{0.81}}\big{(}\frac{Ga_{l}P_{l}}{Ph_{l}} \big{)}^{0.25}\) & \(G:\) 200–500 kg m\({}^{-2}\)s\({}^{-1}\). \\ \hline Kedzierski and Goncalves [34] & \(h_{tp}=\frac{Nuk}{d_{s}}\) & \(d=3.14\)–7.04 mm, microfin tube. \\  & & Fluid: R134a, R124, R32, R410A, \\  & & mixture (R32/ R125) \\  & & G: 57–555 kg m\({}^{-2}\)s\({}^{-1}\). \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Condensation heat transfer correlations. Figure 14: Average condensation heat transfer coefficient of different tube, inner diameter of 8 mm [24], 5.35 mm [31], 3.36 mm [31] and 1.17 mm [31] at mass flux 400 kg m\({}^{-2}\)s\({}^{-1}\).