tests. The flow rate was consistently 2.1 L s1,
lower concentrations on the flat ice. For example,
the second test left only 0.6 g of the 100.1 g of par-
independent of ice conditions, the presence of run-
ticles added, yet particle patches were clearly vis-
ners, and the amount of material collected (up to
ible.
a maximum of 212 g preceding a flow measure-
The collector had much more difficulty collect-
ment). Unlike the 30-cm-long model, however, it
ing particles from the extensively roughened ice
was difficult to achieve a uniform slot width along
surface made for the fourth collection efficiency
the 1.2-m-long prototype. For the first two collec-
test. It achieved a collection efficiency of only about
tion efficiency tests, the slot width averaged about
89%. Some of the remaining particles, however,
1 mm, but varied between about 0.5 and 1.5 mm.
were frozen onto the bottoms of the depressions,
This yielded an average gap velocity of about 170
cm s1, much higher than that needed for particle
suggesting that the test technique may have af-
fected the recovery. Nevertheless, we did not know
pickup. Because we were concerned that the nar-
what the SPWW bottom roughness would be like,
row slot sections corresponded to areas of poor
and we wanted to develop a method to retrieve
particle pickup, we attempted to machine the slot
particles easily from rough ice.
to a uniform width of 2 mm. We achieved an aver-
We made several minor modifications to the col-
age slot width of 1.64 mm (Fig. 9), but local varia-
lector during the collection-efficiency tests based
tions ranged from just under 1 mm to 2.8 mm. This
on the observed performance. The first test re-
yielded gap velocities that ranged from 64 to 190
cm/s and averaged 125 cm s1 (assuming a uni-
vealed that the flat-bottomed collector could press
formly distributed total flow of 2.1 L s1), well ex-
particles into very flat ice and be unable to collect
them. We subsequently tested the collector with
ceeding the target minimum of 10 cm/s. This ve-
1.5-mm-diam. Teflon-coated wires wrapped
locity distribution did not appear to affect overall
around the filter arm at the locations of the inter-
collection efficiency (the collector recovered over
nal ribs. We tested these "runners" during the sec-
99% of the particles deployed on combined smooth
ond and third tests and found that the collector
and rough ice during the third test), and we no
did not press the particles into flat ice and it
longer saw any correlation between narrow slot
achieved good collection efficiency. However, the
width and poor particle pickup. We made no fur-
collector could retrieve particles better from deep
ther changes to the slot prior to field deployment.
depressions without these runners. We still
We also conducted particle-collection tests us-
ing the 1.2-m collector in the iced ramp, submerged
brought a quantity of this wire to the SPWW for
in the refrigerated basin. Although these tests were
use if the well-bottom ice appeared to be very
qualitative, visual evidence indicated good collec-
smooth (we did not use it).
tion efficiency where the collector contacted the
We also developed (but again did not use in the
surface. However, the collector left particle patches
SPWW) a method to retrieve particles from rough
on the ramp in areas where it did not conform well
ice. This involved attaching an 8-cm-wide strip of
to the surface shape. We therefore added weight
thin LDPE (the same material used for the check
inside the waterproof housing to allow the collec-
valve) to the underside of the collector arm adja-
tor to conform to more severe surface curvature.
cent to the slot. This external flap would seal itself
The modifications resulting from these tests on
to the ice surface when the pump was on. Flow
the 1.2-m collector were essentially options to im-
could only bypass the flap though deep depres-
prove collection efficiency on very smooth, rough,
sions, effectively cleaning these depressions of
or curved ice and did not affect the basic design.
particles, or by entering the slot from the other side
Thus, we constructed the 2.4-m collector essen-
of the collector, essentially doubling flow veloci-
tially as designed (see Appendix B for a summary
ties. We tested this arrangement in a separate col-
of the collector development tests).
lection efficiency test on very rough ice. It picked
We tested the 2.4-m collector only on the iced,
up particles extremely well, even from 1-cm-deep
submerged ramp. The collector was quite maneu-
depressions, and left the ice visibly clean after a
verable and could sweep across a region with a
single pass. Unfortunately, the shipping deadline
45 upward slope. However, as with the 1.2-m col-
prevented us from conducting a quantitative
lector, we added extra weight near the center of
collection efficiency test, but the visual evidence
the collector to help it conform to the ramp and
from the test conducted suggests that it would
thereby improve its collection efficiency (docu-
have been greater that 99%.
mented visually). The spiked wheels could slip or
We routinely measured flow rates through the
cut through the ice at the steeper ascent angles, so
1.2-m collector during the collection efficiency
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