tailieunhanh - Heat Transfer Handbook part 76

Heat Transfer Handbook part 76. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | CONDENSATION IN SMOOTH TUBES 745 Figure Taitel-Dukler 1976 jrid i iUons on G-x coordinates for R-134a at 35 C in a tube. From Dobson and Chato 998. regions of wavy wavy-annular then annular flow. The quality range over which the wavy and wavy-annular flow regimes occurred decreased as mass flux was increased. The predictions of the Taitel-Dukler map are translated onto mass flux-quality G-x coordinates in Fig. . At low mass fluxes stratified flow is predicted across the entire range of quality. At slightly higher mass fluxes wavy flow is predicted across most of the quality range with a small amount of stratified flow at low quality. At mass fluxes above 140 kg s m2 slug flow is predicted for qualities below and annular flow is predieted for ali h ighcr quelities. It lo elooe to tboo noundary that the observed flow regimes deviated most significantly from the Taitel-Dukler predictions. The length of the slug flow region was underpredicted and this was consistently followed by some wavy orwavy-annularflow that was not per dicted by the Taitel-Duklermap. The apparent discrepancy between the observed and predicted flow regimes at mass fluxes slightly above the annularboundayr of the Taitel-Duklermap is due largely to differences in terminology. In an early experimental verification of the Taitel-Dukler map Barnea et al. 1980 used the term wavy-annular flow to refer to a hybrid pattern observed at the lowest gas rates where the slug-to-annular transition occurred. A similar regime has been termed proto-slug flow by Nicholson et al. 1978 and pseudo-slug flow by Lin and Hanratty 1989 . Because this pattern occurs after the wavy flow has become unstable it is properly labeled as intermittent or annular flow in Taitel-Dukler terminology. From a heat transfer standpoint however the instability of the wavy flow near this boundary is less important than the significant stratification due to gravity. At higher mass fluxes the range of quality 746 .