A mechanistic analysis of sieve tray froth height and entrainment

Journal Article · Fri Sep 01 04:00:00 EDT 1995 · AIChE Journal

DOI:https://doi.org/10.1002/aic.690410907· OSTI ID:118817

Bennett, D L ^[1]; Kao, A S ^[2]; Wong, L W ^[3]

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1. Air Products and Chemicals, Inc., Allentown, PA (United States)
2. Environ, Arlington, VA (United States)
3. Univ. of California, Los Angeles, CA (United States). Dept. of Chemical Engineering

A phenomenologically based model for froth height was developed using the assumption of both vapor- and liquid-continuous-zones within the total froth height. The model demonstrates the importance of liquid and vapor rates and determines that the Weber number (and therefore droplet size and surface tension) has little effect on froth height. A composite air/water database including entrainment data for both the spray and froth regimes is used to develop an entrainment correlation as a function of the ratio of tray spacing to froth height (T{sub s}/h) and the average froth density ({phi} = H{sub L}/h). For conditions resulting in the ratio of liquid inventory to the perforation diameter (h{sub L}/d{sub H}) < 4, the froth height equation requires an empirical correction for froth height, and entrainment depends on {phi}. This results from the predominantly vapor-continuous nature of the froth. For large values of h{sub L}/d{sub H}, the theoretical value for h appears adequate and entrainment is essentially independent of {phi}, since most of the liquid is contained in the liquid-continuous region located far away from the underside of the tray above. In such cases, entrainment is from a light spray on top of the liquid-continuous region, and therefore entrainment depends much less on {phi}. The different dependency of entrainment on {phi} can be used as a method to identify the spray-froth transition. For h{sub L}/d{sub H} < 2, a spraylike condition exists; for h{sub L}/d{sub H} > 2, a frothlike condition exists. The reported dependency of air/water system entrainment on major geometry and operating conditions is described well by the new correlation. Alternate correlations for the non-air/water entrainment data, however, are required. New methods for estimating the impact of entrainment on efficiency are given.

• OSTI ID: 118817
• Journal Information: AIChE Journal, Journal Name: AIChE Journal Journal Issue: 9 Vol. 41; ISSN 0001-1541; ISSN AICEAC
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION
DESIGN
DISTILLATION EQUIPMENT
ENTRAINMENT
FLUID MECHANICS
FOAMS
HEIGHT
MATHEMATICAL MODELS
PERFORMANCE
PROCESS CONTROL