Narrow channels

Figure 2.42 shows boiling curves obtained in an annular channel with length 24 mm and different gap size (Bond numbers). The heat flux q is plotted versus the wall excess temperature AT = 7w — 7s (the natural convection data are not shown). The horizontal arrows indicate the critical heat flux. In these experiments we did not observe any signs of hysteresis. The wall excess temperature was reduced as the Bond number (gap size) decreased. One can see that the bubbles grew in the narrow channel, and the liquid layer between the wall and the base of the bubble was enlarged. It facilitates evaporation and increases latent heat transfer. 

Ali MI, Sadatomi M, Kawaji M (1993) Two-phase flow in narrow channels between two flat plates. Can J Chem Eng 71 657-666... 

Landau LD, Lifshitz EM (1959) Fluid mechanics, 2nd edn. Pergamon, London Landerman CS (1994) Micro-channel flow boiling mechanisms leading to Burnout. J Heat Transfer Electron Syst ASME HTD-292 124-136 Levich VG (1962) Physicochemical hydrodynamics. Prentice HaU, London Morijama K, Inoue A (1992) The thermohydraulic characteristics of two-phase flow in extremely narrow channels (the frictional pressure drop and heat transfer of boiling two-phase flow, analytical model). Heat Transfer Jpn Res 21 838-856... 

Flame Propagation in Narrow Channels and Mechanism of Its Quenching.102... 

To understand the mechanism of flame quenching in narrow channels in detail, one should first examine the data of flames in mixtures of constant composition, but in charmels of different sizes (Figure 6.1.2). The measured propagation velocities in stoichiometric propane/ air mixture are shown in Figure 6.1.2a. For channel widths slightly larger than the quenching distance, the... 

The cooling effect of the channel walls on flame parameters is effective for narrow channels. This influence is illustrated in Figure 6.1.3, in the form of the dead-space curve. When the walls are <4 mm apart, the dead space becomes rapidly wider. This is accompanied by falling laminar burning velocity and probably lowering of the local reaction temperature. For wider charmels, the propagation velocity w is proportional to the effective flame-front area, which can be readily calculated. On analysis of Figures 6.1.2b and 6.1.3, it is evident that the curvature of the flame is a function of... 

The temperature profile inside a narrow channel was determined using resistance probes with a 10 pm Pt-Ir... 

In Chapter 6.1, A. Gutkowski and J. Jarosinski present results of an experimental and numerical study of flame propagation in narrow channels and the mechanism of quenching due to heat losses. This work takes up again classical studies of the quenching distance. The most characteristic features of limit flames are determined experimentally. 

Diffusion in liquids is very slow. Turbulent transport or very narrow channels are necessary for good contact between the phases. The droplets must also be very small to minimize transport hmitations within the drops. An estimation of the time constant for diffusion in a 1-mm drop is (f (10-3)2... 

The surface viscosity varies significantly along the isotherm and across monolayer phase boundaries. Addition of subphase metal ions increases the surface viscosity drastically, as was recently reinvestigated [36]. Recently, microscopy methods have been used to image velocity profiles of different monolayer phases flowing through a narrow channel, such as used in the canal viscometer [37], The two main methods used to study monolayer viscosity are the canal viscometer and the oscillating disc method [8,9]. 

---