WMOD00479

• Title: Design and Field Testing of a Remote Ground-Based Liquid Propane Dispenser
• Weather Modification - Doc Type: Report

from either tank so that a tank can be emptied before
the next tank is used. All plumbing uses 6.33-mm (1/4-
in) copper tubing. In line from the solenoids is a turb~ne
flow trar.sd~cer (man'-lfactured by HOW-SCa.ll (Model
20lB)). This operates on the principle that the rotational
velocity of the liquid is directly proportional to flow rate.
A neutrally buoyant ro~or spins between V-jewel
bearings. Rotor movement is sensed when notches in the
rotor interrupt an infrared light beam between an LED
and pamotransistoi". The output of the meter is linear
over a range of 2.27 to 22.7 Llhr (0.6 to 60 gal/hr).
From the flowmeter, iiquid is delivered to three separate
soler:oids that control three indeper:dent nozzles. Thee
nozzles are installed to provide recund:m.cy 1:1 case a
nozzle clogs or malfunctiop.s. In line with the flowmeter
is a press;;re gauge and pressure relief valve. TIe
pressure gauge has no analog output and is used for
manual reading oaly. Seeding rates are directly
proportional to internal tank pressure so that during
initial testing it was ii11ponant to monitor tank pressure.

From the solenoids, 0.9-meter-iong copper tubing
is run inside 7.6-cm-square reinforced steel tubing to t~e
top of the dispenser where three standard off-thc-shelf
brass nozzles (\Vhirljet Ij4-SS-.5-.5w, orifice size 0.8n:m
(1/32 in) are mounted. These brass nozzles provide both
a wide angle spray pattern and low flow capability. They
are rated at 34 Llhr for propane (specific gravity 0.5) at
350 kPa. Small thermocouples with a measurement
range from -173 to 737 cC for a 0- to 5-V output are
mounted in the spray pattern within 5 cm of the nozzles.
These temperature data provide verification that liquid
propane is vaporizing from the nozzle. A small sheet
metal wind screen is attached to the top of the dispenser
to protect the nozzles from rime ice. A small whip radio
antenna is also ffiour..ted at the top of the dispenser.

The third module consists of a battery box
containing a 12- V deep-cycle battery. The battery is
recharged by two 45- W solar panels mounted above L'1e
electronics module. A voltage regulator is used to
protect the radio and microprocessor from excessively
high voltages produced by the solar panels on cloudless
days.

A prototype dispenser of this design was installed
near Summit Lake, California at an elevation of 2146 m
on ~larch 8, 1989 (Fig.2). Initial problems in establishing
radio communications to the dispenser via a repeater on
Bed.."Wourth Peak delayed ip.stallatioil until late ",inter.
Due to half-duplex radio communication, proper time
delays were required for transmitting and receiving
through the repeater between the Sacramento-based PC
used to controi operations and the microprocessor at the
dispenser. A simple schematic of the communications
path is shown in Fig. 3.

T es~ing of the dispenser consisted of sending
commands via radio to open a tank solenoid and a
nozzle solenoid. Confirmation of liquid release was
determined when the nozzle temperature dropped
below -30 cc. About 30 hr of seeding were conducted
during March.

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Figure 2 Prototype propane dispenser installed near
Summit Lake in March of 1989. The two propane tanks
are buried in the snow in the foreground of the picture.

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Figure 3 Communications path used to transIrJt and
receive c.ontrol and verification information to and from
remote dispenser.

Several problems were discovered during this
limited test period. It was observed that, during propane
release, the measured flow rates barely increased above
zero. It was determined after deinstallation that the
flowmeter had been severely damaged prior to
installation at Summit Lake. Compressed air was used to
purge the plumbing of debris before field installation.
This produced flow rates of 600 to 700 Lfhr; when in
fact, the meter was only rated for 225 L/nr. Many of the
blades were broken off the smail turbine resulting in the
meter severely underestimating the flow rates.

Seeding rates were determilied to be much higher
than anticipated based on preliminary field testing.
When the tanks were buried in snow, they maintained
higher internal pressure than expected (propane vapor
pressure is directly proportional to lank temperature).
This caused seeding rates to be about a factor of 5