Ice accretion measurements were made on solid rods, flat plates, and
wires. We used rods of three diameters (19.1 mm (0.75 inch), 25.4 mm
(1 inch), and 31.8 mm (1.25 inch)), composed of three materials (wood,
dark gray polyvinyl chloride (PVC), and aluminum), and mounted at
three inclinations (0° (i.e., horizontal), 30°, and 60°). Each rod was
60 cm long and attached to one side of a post (i.e., one rod per side,
four rods per post). The posts were 9 × 9 cm and installed at a height
of 1.2 m above the ground.
Plates (10 × 30 × 0.6 cm) were constructed of three different
materials (plywood, aluminum, and PVC) and glued with construction
adhesive to a 1.3-cm-thick marine-grade plywood base. The PVC plates
were two different colors (white and dark gray), but otherwise
identical. Each of the four different types of plates (wood, white
PVC, gray PVC, aluminum) was mounted horizontally with a shelf bracket
on posts that were identical to those used for rods (4 plates per
post).
Ice accretion on wires was determined with two types of electrical
transmission lines: 1) a bare neutral wire that consisted of 8-mm
diameter stranded aluminum conductor steel-reinforced cable (six
2.7-mm aluminum wires wrapped around one 2.7-mm steel wire); and 2) an
insulated phase wire that consisted of 9.7-mm diameter stranded all
aluminum conductor cable (seven 2.5-mm aluminum wires) covered with a
1.1-mm-thick layer of black cross-linked polyethylene.
One-meter lengths of each wire type were suspended horizontally 1 m
above the ground between posts with mounted rods or plates. The 1-m
wires were centered between posts and attached with U-bolts to two
0.5-m lengths of smaller wire on both ends to make up the 2 m span.
Twelve posts were arranged in a grid (3 posts x 4 posts with 2 m
spacing between posts) in each of two adjacent blocks (24 posts
total). Twenty of the posts were used for ice measurements on rods and
four posts were used for ice measurements on plates. Posts were
randomly selected to have either rods or plates and each side of the
posts were randomly assigned a specific type of rod or plate. Wires
were randomly assigned to pairs of adjacent posts. There were two to
four replicates of each unique rod combination (i.e., diameter,
inclination, and material), four replicates of each plate material,
and three replicates of both wire types.
The study was conducted in an open field in front of the Robert S.
Pierce Ecosystem Laboratory at the Hubbard Brook Experimental Forest
(43°56'36"N, 71°41'58"W). We simulated a glaze ice event by
spraying water over the ice collectors during sub-freezing conditions.
Water was pumped from a nearby pond through a 3.8-cm diameter
high-pressure firefighting hose and sprayed at a rate of 300 L min-1
with a variable stream nozzle. A supply pump was placed next to the
pond and a secondary pump was secured to the bed of a utility task
vehicle (UTV). The hose was connected to the pumps and stabilized with
a monitor mounted on the UTV. The UTV was driven slowly back-and-forth
alongside the icing study area while water was sprayed evenly over the
collectors so that the water droplets fell from above and froze on
contact. Two target ice amounts were selected: 6.4 mm (0.25 inch) and
12.7 mm (0.5 inch) of radial ice accretion.
The ice storm simulation occurred on 19 February 2019 and the
collectors were sprayed and measured at night (6:30 to 11:30 p.m.)
when air temperatures were below freezing. Ice thickness measurements
were made using digital calipers (Vinca DCLA-0605, Clockwise Tools,
Inc.) with a manufacturer-specified accuracy of ±0.02 mm. Once the
target level of ice had roughly been achieved, we started making the
measurements. One hour and 20 minutes of spraying was required to
reach the lower target level of ice (6.4 mm), at which time we made a
round of measurements. We then immediately resumed spraying and
continued for another 1 hour and 15 minutes until reaching the higher
target level of ice (12.7 mm), at which time we made two back-to-back
rounds of measurements to assess reproducibility.
Ice accretion on rods and wires was measured both vertically (measured
from top to bottom of rod or wire) and horizontally (measured from
side to side of rod or wire) at three locations along each rod or
wire: the center location and halfway between the center and the two
different ends of the rod or wire (six measurements per rod or wire).
Ice measurements on plates were made at the midpoint of each side,
excluding the side that abutted the post (3 measurements per plate).
Any ice that formed underneath the plates was scraped off prior to
making measurements so that only ice that accumulated on top of the
plates was measured.
Measurements were made before any ice was applied, and immediately
after both levels of icing. In total, 2,256 caliper measurements were
made in this study: four rounds of measurements (one round without
ice, one round for the lower level of ice, two rounds for the higher
level of ice); 480 measurements for rods per round (20 posts, four
rods per post, six measurements per rod); 48 measurements for plates
per round (four posts, four plates per post, three measurements per
plate); and 36 measurements for wires per round (six wires, six
measurements per wire).
