TAILIEUCHUNG - Two Phase Flow Phase Change and Numerical Modeling Part 13

Tham khảo tài liệu 'two phase flow phase change and numerical modeling part 13', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 350 Two Phase Flow Phase Change and Numerical Modeling for the ethanol case. At large capillary numbers all data are larger than the Taylor s law. Inertial force is often neglected in micro two phase flows but it is clear that the inertial force should be considered from this Reynolds number range. In Fig. 8 b dimensionless initial liquid film thickness in mm inner diameter tube shows different trend at Ca showing some scattering. Reynolds number of ethanol in mm inner diameter tube becomes Re 2000 at Ca . Thus this different trend is considered to be the effect of flow transition from laminar to turbulent. Figure 8 c shows initial liquid film thickness for water. At Re 2000 initial liquid film thickness does not increase but remains nearly constant with some scattering. This tendency is found again when Reynolds number exceeds approximately Re 2000. The deviation from Taylor s law starts from the lower capillary number than FC-40 and ethanol. Dimensionless initial liquid film thickness of water shows much larger values than that of ethanol and Taylor s law. In the case of mm inner diameter tube dimensionless initial liquid film thickness is nearly 2 times larger than the Taylor s law at Ca . It is clearly seen that inertial force has a strong effect on liquid film thickness even in the Reynolds number range of Re 2000. Scaling analysis for circular tubes Bretherton 1961 proposed a theoretical correlation for the liquid film thickness with lubrication equations as follows f Dh 2 l Ơ 12 Aussillous and Quere 2000 modified Bretherton s analysis and replaced the bubble nose curvature K 1 Dh 2 with K l Dh 2 -ổo . In their analysis the momentum balance and the curvature matching between the bubble nose and the transition region are expressed as follows pU2 1 í Ơ 2 l Dh 2 -ố0 0 . Ơ Dh 2 -d0- 13 14 where Ả is the length of the transition region as shown in Fig. 9. Eliminating Ả from Eqs. 13 and 14 they obtained following relation for .

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