070224_001 -
Air and water mixing static fire test
Aim
This experiment was carried out in order to measure the internal
air temperature and the skin temperature of a rocket. We wanted
to determine to what degree the temperature increase due to air
compression would affect the strength of the PET bottles.
Experiment Setup
The 8L
Polaron
III rocket was set up on the
launcher and tied down for this experiment. A thermocouple
connected to a multimeter with a temperature function was used
to read the temperatures. The thermocouple offers a fast
response to changing temperatures.
No water was used in these experiments.
When measuring the skin temperature we
just placed the sensor onto the bottle, but
probably should have been shielded from the
environment.
Firing the rocket by hand.
The cool fog inside the rocket after a test
firing.
Measuring the inside and outside
temperatures of the rocket. The thin wire is the
thermocouple.
Results
The
ambient temperature was 22 degrees C.
Static Fire Test #3
The rocket was filled to 50 psi and the
external skin temperature was measured during
filling to be 25 degrees C.
+3 above
ambient.
When the air was let out, the
thermocouple was placed inside the rocket and the air
temperature was measured at 16 degrees C. -6
below ambient.
The rocket was filled to 100 psi and the
outside skin temperature was measured during
filling to be 27 degrees C. Which is
+5C above
ambient.
When the air was let out, the
thermocouple was placed inside and the air
temperature was measured at 8 degrees C.
Which is -14C
below ambient.
Conclusions / Analysis
The temperature measurements indicated
that there is unlikely to be much effect
on the PET bottle material with the
pressures we regularly use unless
combined with other sources of heat.
Things to consider
If the bubbles are produced in an
efficient manner it may be possible to use
that to an advantage with an expanding
nozzle.
Antigravity
Research used detergent
to create foam inside the rocket with an
expanding nozzle to make the rocket more
efficient. When perfected a technique based
on the static fire test #1 may be used to
generate the same effect without the
viscosity penalty of using detergent.
If the temperature of the air inside the
rocket drops below freezing at higher launch
pressures, it may be likely that the during
the air pulse tiny water droplets exiting
could be freezing and exiting as ice or
snow?
