Bench Scale Study of the Vacuum Freezing Ejector Absorption Process Page: 48
vii, 257 p. : ill.View a full description of this report.
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The nozzle efficiency was found to be of the
order of 96%. For a convergent divergent
nozzle of large pressure ratio (300 to 3.35
mm Hg abs.) this is a very good efficiency.
3. Diffuser Efficiency
Diffuser efficiency is defined as follows:
Diffuser efficiency = Total press. at diffuser outlet
Total press. at diffuser inlet
The diffuser efficiency varied from 84% to 98.5%.
Diffuser efficiency was greatly affected by the
velocity profile at the inlet of the diffuser. The
more uniform the velocity profile, the higher the
diffuser efficiency. For runs with a uniform
velocity profile, the average efficiency was 95%.
This trend is well established in technical liter-
ature*. Therefore, if care is taken in designing
the mixing cone, a diffuser efficiency of 95% is
obtainable.
4. Effect of Primary Steam Pressure
The effect of primary steam pressure on the mass
ratio of the ejector is shown in figure 2. Fig. 2
is based on data from test series #3. The optim-
ized performance runs were based on test series
#4 and #5 and hence the plotted data is not inter-
changeable without corrections. Fig. 2 shows that
the minimum mass ratio was obtained for a primary
steam pressure of about 300 mm Hg abs. This trend
was expected, since the nozzle was designed for
300 mm Hg abs. At other primary steam pressures
the nozzle was at off design conditions and oper-
ated under or over-expanded, with losses in
efficiency. It may also be pointed out that the
curves in fig. 2 are rather flat near the point
of minimum mass ratio, thereby indicating that
small fluctuations in the primary steam pressure
(+ 10 mm Hg abs.) will have very little effect on
the mass ratio, which is very desirable from pro-
cess control point of view.
5. Primary Steam Temperature
Primary steam is the motive force behind the
ejector. The energy content of the steam is
determined almost entirely by its temperature
(not the pressure). Therefore, if the steam
is superheated to a higher temperature, lesser
*Schlichting, Boundary Layer Theory, 6th Ed.,
McGraw Hill, P. 590-592.-48-
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Koretchko, J. & Hajela, G. Bench Scale Study of the Vacuum Freezing Ejector Absorption Process, report, November 1971; Washington D.C.. (https://digital.library.unt.edu/ark:/67531/metadc11786/m1/57/: accessed April 23, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.