Author

Rajeev Patel

Date of Award

5-1-1988

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemical Engineering

Abstract

The present study was undertaken to experimentally determine the in situ volume fraction of the gas phase when air is bubbled through a stagnant liquid column. The data gathered were used to examine the model proposed by Hasan (1986) for estimating gas void fraction during two-phase flow in vertical and inclined pipes. This model, based on a drift flux approach, relates the in situ velocity of the gas phase to the bubble rise velocity and the mixture velocity.

An experimental set-up consisting of a plexiglass column of 5 inch inside diameter and eighteen feet in height was used to gather data. The column was deviated at 0, 8, 16, 24, and 32 degrees from the vertical. Pipes of 1.87, 2.24, and 3.409 inches were used to create annuli of different dimensions.

Data were gathered for the rise velocities of small and " Taylor" bubbles as well as for void fraction for gas (air) flowing through a stagnant liquid (water) column. These raw data were then converted to superficial gas velocity (Vgg) and void fraction (Eg).

Flow patterns during m u l t i p h a s e flow are loosely grouped into bubbly, slug, churn, and annular types. Due to the relatively low air flow rates available from existing air lines, only bubbly and slug flow patterns were observed.

The void fraction during bubbly and slug flow was given by Eg = Vsg / (CVsg + Vt). The p a r a m e t e r C was f o u n d to be u n a f f e c t e d by p i p e inclination and annuli dimensions. The value of this parameter remained constant at 2.0 for bubbly flow and at 1.2 for slug flow.

The rise velocity of small bubbles, V t , was found to be unaffected by either pipe inclination or annuli dimensions. The overall average bubble rise velocity of 0.84 ft/sec. was in very good agreement with the value calculated by using the Harmathy (1960) correlation.

"Taylor" bubble rise velocity data, however, indicated strong influence of both pipe inclination and annulus dimensions. The data gathered were found to agree well with the following "Taylor" bubble rise velocity correlation proposed by Hasan (1986) VtT = [0.35 + 0.1(Dt/Dc)sin^2(alpha)][gDc(d1-dg)/d1]^2[sqrt(sin(alpha))(1 + cos(alpha))^2]. The above expression successfully accounts for both the pipe inclination and the annulus diameters.

The predictions of the proposed model for flow pattern transition and void fraction were compared with data from several other sources. Good agreement between the data and the predictions of the model were noted.

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