Velocity interface, condensation

Gieseler et al. utilized tunable diode laser absorption spectroscopy to detect water vapor concentrations, gas velocities and mass flow during freeze-drying of pure water at different pressure and shelf temperature settings and of a 5%w/w mannitol solution. The analyzer was interfaced to the spool that connected the dryer chamber to the condenser. The reported method was advantageous in that primary and secondary drying end-point control based upon mass flow rate was independent of freeze-dryer size and configuration. ... 

Let us introduce a system of coordinates in which the flame is at rest. For the sake of definiteness we shall make the coordinate plane YOZ coincident with the interface between the condensed phase (briefly, c-phase) and the gas, with the c-phase located to the left at x < 0. In a system in which the flame is at rest, the material must move. The velocity of the material u... 

Typical velocity and temperature proGles of the condensate are also given in Mg. 10-21. Note that the velocity of the condensate at the wall is zero because of the "no-slip condition and reaches a maximum at the liquid-vapor interface. The temperature of the condensate is at the interface and decreases gindually to T, at the wall. 

The velocity of the vapor is low (or zejo) so that it exerts no drag on the condensate (no viscous shear on the liquid-vapor interface). 

Examination of Eqs. (35) to (41) does not reveal any parameter that is obviously dependent on flow rate, provided that the applied voltage is maintained constant and vacancy condensation dominates the induction time. Thus, neither the thermodynamics of absorption of X into a surface oxygen vacancy nor the ejection of a cation from the film is expected to depend on flow velocity, nor are the events (e.g., vacancy condensation) that occur at the metal/film interface expected to be sensitive to fluid motion. Thus, the PDM predicts that the breakdown ( pitting ) potential for passive alloys that are of interest to the thermal power industry should not be sensitive to flow rate. The PDM also predicts that the induction time should be insensitive to fluid flow velocity, provided that the induction period is dominated by vacancy condensation at the metal/film interface. 

If vapor velocities are high enough, the vapor shear on the condensate interface initiates turbulence in the condensate film and causes it to flow off the surface more rapidly. These effects increase the... 

The models (photochemical and thermal) can be subdivided into volume and surface models. The processes responsible for ablation in surface models only take place within several monolayers of the surface. As a result, the velocity of the interface between the gaseous and condensed phase depends explicitly on the surface temperature or laser intensity. With volume models, the processes resulting in ablation take place within the bulk of the material. The volume and surface models are ... 

Air at 27°C and 60 percent relative humidity is circulated past 1,5-cm-O.D. tubes through which water is flowing at 60cm/s and 15°C. The air velocity approaching the tubes is 1.5 m/s. (a) Will water condense on the tubes (h) What are the wall temperature and the interface temperature if condensation occurs ... 

Laminar Forced Convection. When the vapor moves in relation to the condensate, a shear stress xg will develop at the liquid-vapor interface. At very high vapor velocities, this shear... 

Within the macroscopic postulates of the theory detonations in condensed phases are generally considered to be quantitatively well defined, while deflagrations are less determinable because of their greater dependence on temporal and spatial factors. For example, in propellant deflagrations, where the reaction rates are strongly dependent on the diffusion of reactants to an interface, propagation velocities may be down to centimeters per second or less, or as high as meters per second. 

After passing through a short (ca,20mm) section of wide-bore capillary (0.5mm I.D.), a portion (0.1%-100%) of the TGA effluent (100-200 ml/min.) is carried into the APCI ion source by a high velocity (ca 2 l.min ) stream of carrier/reagent gas. The amount of TGA effluent allowed into the ion source is accurately (+30 ul/min) controlled by a micrometer dump valve connected in series with a device which measures the pressure on either side of the capillary restriction (this pressure is directly proportional to the flow across the capillary). The relatively high gas velocities as well as the fact that the whole interface assembly is heated (250-350 C) avoids condensation of less volatile materials on the interface walls. 

Under normal conditions a continuous fiow of liquid is formed over the surface and the condensate flows downward under the influence of gravity. Unless the velocity is very high or the liquid film relatively thick, the motion of the condensate is laminar and heat is transferred from the vapor-liquid interface to the surface merely by conduction. The rate of heat flow depends on the rate at which vapor is condensed and the rate at which the condensate is removed. On a vertical surface the film thickness increases continuously from top to bottom. As the surface is inclined from the vertical, the drainage rate decreases and the liquid film becomes thicker. This causes a decrease in the rate of heat transfer. 

Droplets of liquid in the wick are torn from the wick at higher velocities and sent into the vapor resulting in dryout, which is known as entrainment limit. As the vapor and the liquid move in opposite directions, a shear force exists at the vapor-liquid interface. If the vapor velocity is high, a limit can be reached when the liquid is tom from the surface and entrained in the vapor. There is a sudden increase in the fluid circulation, and the liquid return system cannot accommodate the increased flow. There are excess liquid accumulation in the condenser and dryout in the evaporator. The shear force at the liquid-vapor interface is proportional to the dynamic pressure of the moving vapor (p V )/2 and the area (A ) ... 

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