## 4 Experimental Results and Discussion
### Frictional Pressure Drop Results and Discussion
\[AD\ =\ \frac{1}{n}\sum_{i=1}^{n}\left(\frac{\Delta P_{F,Pre}-\Delta P_{F,Exp}}{ \Delta P_{F,Exp}}\right)\times 100 \tag{11}\]  
\[MD\ =\ \frac{1}{n}\sum_{i=1}^{n}\left|\frac{\Delta P_{F,Pre}-\Delta P_{F,Exp}}{ \Delta P_{F,Exp}}\right|\times 100 \tag{12}\]  
Figure 6: Effect of saturation temperature on frictional pressure drop. Figure 7: Effect of tube diameter on frictional pressure drop. \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. [2] & \(-26.29\) & \(26.33\) & \(-32.83\) & \(44.79\) & \(-30.88\) & \(35.24\) \\ Muller and Heck [18] & \(11.64\) & \(22.93\) & \(7.50\) & \(40.88\) & \(7.05\) & \(30.03\) \\ [PERSON] et al. [19] & \(5.98\) & \(27.33\) & \(-7.76\) & \(36.80\) & \(0.48\) & \(31.06\) \\ [PERSON] et al. [20] & \(-26.72\) & \(33.29\) & \(-41.95\) & \(46.75\) & \(-34.11\) & \(40.89\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Deviations of frictional pressure drop. AD: average deviation; MD: mean deviation. \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Author(s)**} & \multicolumn{2}{c}{**Correlation**} & \multicolumn{2}{c}{**Experimental Condition**} \\ \hline [PERSON] et al. [2] & \(\left(\frac{\Delta P}{\Delta z}\right)_{F}=\phi_{\rm p}^{2}\left(\frac{\Delta P}{ \Delta z}\right)_{\rm v}\), \(\left(\frac{\Delta P}{\Delta z}\right)_{\rm v}=\frac{0.092G^{2}\pi^{2}}{d_{\rm e }p_{\rm e}(Gad_{\rm e}\mu_{\rm e})^{2}}\) & \(d_{\rm o}\) = 7 mm, smooth, helical and herringbone microfin tube. \\  & \(\phi_{\rm v}=1.1+1.3X_{t}^{0.35}\left[\frac{G}{\{gd_{\rm e}\mu_{\rm e}(\mu_{ \rm e}-\mu_{\rm e})^{1.35}\}}\right]^{0.35}\) & Fluid: R410A, R22 \\  & \(G\): 100-400 kg m\({}^{-2}\)s\({}^{-1}\). \\ \hline Muller and Heck [25] & \(\left(\frac{\Delta P}{\Delta z}\right)_{F}=E(1-x)^{1/3}+\left(\frac{\Delta P}{ \Delta z}\right)_{\rm v}x^{3}\) & \(d\) = 4-392 mm \\  & \(E=\left(\frac{\Delta P}{\Delta z}\right)_{\rm lo}+2\left[\left(\frac{\Delta P}{ \Delta z}\right)_{\rm v0}-\left(\frac{\Delta P}{\Delta z}\right)_{\rm lo}\right]x\) & Fluid: air–water, air-oil, hydrocarbon, R11, R12, R22 \\  & \(G\): 50-2490 kg m\({}^{-2}\)s\({}^{-1}\). \\ \hline [PERSON] et al. [26] & \(\left(\frac{\Delta P}{\Delta z}\right)_{F}=\phi_{\rm v}^{2}\left(\frac{\Delta P }{\Delta z}\right)_{\rm v}\) & \(d_{\rm i}\) = 8.4 mm, smooth tube. \\  & \(\phi_{\rm v}=1+0.5\left[\frac{G}{\{gd_{\rm e}\mu_{\rm e}(\mu_{\rm e}-\mu_{\rm e })^{1.35}\}}\right]^{0.75}\) & \(d_{\rm i}\) = 8.4 mm, smooth tube. \\  & \(\phi_{\rm v}=1+0.5\left[\frac{G}{\{gd_{\rm e}\mu_{\rm e}(\mu_{\rm e}-\mu_{\rm e })^{1.35}\}}\right]^{0.75}\) & \(\chi_{tt}^{0.35}\) & \(G\): 99.8–402 kg m\({}^{-2}\)s\({}^{-1}\). \\ \hline [PERSON] et al. [27] & \(\left(\frac{\Delta P}{\Delta z}\right)_{\rm v}=\phi_{\rm l}^{2}\left(\frac{ \Delta P}{\Delta z}\right)_{\rm lo}\), \(\left(\frac{\Delta P}{\Delta z}\right)_{\rm lo}\), \(\left(\frac{\Delta P}{\Delta z}\right)_{\rm lo}=\frac{2f_{\rm e}[G(1-x)]^{2}}{d_{ \rm e}p_{\rm l}}\) & \(d_{\rm o}\) = 9.51–9.55 mm, \\  & \(\phi_{\rm l}^{2}=1.376+\frac{7f_{\rm e}[\Delta P}{\Delta z}]^{0.75}\) & \(d_{\rm i}\) = 9.51–9.55 mm, \\  & \(f_{lo}=1.376+\frac{7f_{\rm e}[\Delta P}{\Delta z}]^{0.75}\) & \(\chi_{rr}^{0.35}\) & \(d_{\rm o}\) = 9.51–9.55 mm, \\  & \(f_{lo}=0.046k\mu_{\rm l}^{-0.2}\left(\frac{d_{\rm i}}{d_{\rm i}}\right)\left(1- \frac{\sigma m}{\pi d_{\rm lo}^{2}\cos\beta}\right)^{0.5}\) & \((\sec\beta)^{0.75}\) & Fluid: R22, R407C, R134a \\  & & \(G\): 400–800 kg m\({}^{-2}\)s\({}^{-1}\). \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Pressure drop correlations. Figure 8: _Cont._