Entrainment Limit

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 )  

Substituting in the entrainment limit, we get the heat transport limit  

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Rossiter (1986) demonstrated the procedure for the production process of crystalline common salt from brine. It was found that the optimal median size is determined by the entrainment limit in the crystallizer. The crystallizer had to be operated at maximum allowable temperature and the slurry density measured for quality constraints. It was also suggested that cost discontinuities should be imposed based on temperatures of the available heat sources, possible materials of construction and other intrinsic properties of the system. 

Entrainment limit, heat pipe, 13 230 Entrainment rate, calculating, 11 814-816 Entrance span areas, in thermal design, 13 258... 

Figure 8. Regions of different behavior of the externally driven limit cycle of Model 2 (see Figures 5-7) (I) free oscillation (limit cycle with (II) quasi-peri-odic oscillation (III) entrainment (limit cycle with X) (IV) unstable region — onset of traveling waves.

Ermentrout, G. B., and Rinzel, J. (1984) Beyond a pacemaker s entrainment limit phase walk-through. Am. J. Physiol. 246, R102. 

Geometric variables for design are few perforation type and size, open area, and tray spacing. The perforations are usually round and in the range of 12.7- to 25.4-mm diameter. Open areas run from 15 to 25%. Vapor flow capacity (entrainment limitation) is correlated in a fashion similar to that for crossflow trays, as shown in Figure 12.41, from reference 47. The hgure is based on FRI data taken in a 1.2-m diameter column. 

Entrainment Limitation. As a result of the high vapor velocities, liquid droplets may be picked up or entrained in the vapor flow and cause excess liquid accumulation in the condenser and hence dryout of the evaporator wick [14]. This phenomenon requires that, for proper operation, the onset of entrainment in countercurrent two-phase flow be avoided. The most commonly quoted criterion to determine this onset is that the Weber number We, defined as the ratio of the viscous shear force to the force resulting from the liquid surface tension,... 

G. P. Peterson and B. Bage, Entrainment Limitations in Thermosyphons and Heat Pipes, ASME J. Energy Resources Technology (113/3) 147-154,1991. 

Maximum temperature of feed in evaporative crystallizer Minimum operating temperature in evaporative crystallizer Maximum evaporation rate based on heat transfer area or liquid droplet entrainment limitation Maximum residence time at design capacity... 

Fractional entrainment limit, limit on heat flux on the reboiler and limits on the utility flowrates ... 

Gas entrainment. Gas entrainment tests were conducted in order to develop a method to evaluate the gas entrainment limits in an actual plant and to check that no gas is entrained, particularly in the IHX vessel. Tests were conducted using four models of 1/10, 1/6, 1/3 and 1/1.6 scales as gas entrainment might depend on the scale of the model. It was found that reducing the flow speed at the free liquid surface will prevent gas entrainment due to broken or superimposed waves. A survey shows that gas entrainment can be suppressed by the introduction of measures such as a horizontal perforated plate or a perforated cylinder near the inlet nozzle. 

Taken on its own, the TAC versus L curve passes through a shallow minimum at a value of L of about 250 pm. This figure is substantially below the lower bound imposed by the feasible zone determined by the entrainment limit, however, which ranges from about 420 to 650 pm. Thus the notional optimum value of L at 250 pm cannot be achieved in practice at the temperatures within the range considered, although there is clearly an economic incentive to do so. 

A Viscous limit B Sonic limit C Capillary limit D Entrainment limit E Boiling limit (low T fluids)... 

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