Correlation of two-phase friction for refrigerants in small-diameter tubes

Natural Circulation in Single and Two Phase Thermosyphon Loop with Conventional Tubes and Minichannels

“…The Stomma correlation (Stomma, 1979) for void fraction, the Friedel correlation (Friedel, 1979) for the friction pressure drop of two-phase flow in adiabatic region, the Müller-Steinhagen & Heck correlation (Müller-Steinhagen & Heck, 1986) for the friction pressure drop of two-phase flow in diabatic region and the Mikielewicz correlation (Mikielewicz et al, 2007) for the flow boiling heat transfer coefficient in conventional channels can be used to evaluate the thermosyphon loop. In order to evaluate the thermosyphon loop with minichannels the following correlations such as the El-Hajal correlation (El-Hajal et al, 2003) for void fraction, the Zhang-Webb correlation (Zhang & Webb, 2001) for the friction pressure drop of two-phase flow in adiabatic region, the Tran correlation (Tran et al, 2000) for the friction pressure drop of twophase flow in diabatic region and the Mikielewicz correlation (Mikielewicz et al, 2007) for the heat transfer coefficient in evaporator, the Mikielewicz correlation for condensation heat transfer coefficient in minichannels, can be used in calculations. The distribution of the mass flux against the heat flux approaches a maximum and then slowly decreases for minichannels, and two flow regimes can be clearly identified: GDRgravity dominant regime and FDR -friction dominant regime as shown in Fig.…”

“…In case of a thermosyphon loop with minichannels, it is necessary to apply some other correlations for void fraction and the local two-phase friction coefficient in the two-phase region, and local heat transfer coefficient for flow boiling and condensation. The following correlations have been used in calculations of the thermosyphon loop with minichannels: the El-Hajal correlation for void fraction (El-Hajal et al, 2003), the Zhang-Webb correlation for the friction pressure drop of two-phase flow in adiabatic region (Zhang & Webb, 2001), the Tran correlation for the friction pressure drop of two-phase flow in diabatic region (Tran et al 2000), the Mikielewicz (Mikielewicz et al, 2007) and the Saitoh (Saitoh et al, 2007) correlations for the flow boiling heat transfer coefficient for minichannels, the Mikielewicz and the Tang (Tang et al, 2000) correlations for condensation heat transfer coefficient for minichannels. After integrating momentum equation (2) …”

“…where The local two-phase friction coefficient in two-phase adiabatic region was calculated using the Zhang & Webb formula (Zhang & Webb, 2001): ; dz dp dl dp 64 . 1 (20) and the local two-phase friction coefficient in two-phase diabatic regions was calculated using the Tran formula (Tran et al, 2000):…”

Pressure drop during condensation of refrigerants in pipe minichannels

“…This problem is important as the correlations recommended for calculations and which describe flow resistances concern conventional channels in particular. It is proven in many publications that one cannot unanimously use those correlations which have been verified for conventional channels in relation to channels with small diameters, especially for those refrigerants which undergo phase changes (boiling or condensation) [6,17].…”

Modeling of Pressure Drop During Refrigerant Condensation in Pipe Minichannels

“…In fact, modifications of these correlations describing the friction pressure drop and the results based on these methods embasked in two directions, i.e., to better define the constant C in the Lockhart-Martinelli equation or determination, usually through the experimental investigations of the real extent of a two-phase correction coefficient Φ 2 l of resistance. With respect to the minichannels, the correlations due to Mikielewicz et al [16], Mishima and Hibiki [17], Tran et al [24], Lee and Lee, [12], Zhang and Webb [27] or Zhang et al [26] should be acknowledged. Also deserving acknowledgement of confidence are the correlations of Cavallini and Garimella, which have been documented on a theoretical basis as well as tested experimentally.…”