Saturday, April 25, 2009, 06:22 PM
The goal behind sensing the fluid level in the liquid oxygen tank is to reduce the time required to fill the liquid oxygen tank and to reduce the quantity of LOX wasted for a given test (i.e. just load the quantity of LOX needed for that test firing).
Today the computer and propulsion teams started the day by performing some fluid level experiments with external temperature sensors. A simulated “tank” was created using 2” cast iron piping, sealed at one end. The tank was insulated using several layers of pipe wrap, and a few thermocouples were mounted to the exterior of the tank, under the insulation. The test fluid was alcohol, chilled to -100 deg F using dry ice. When the tank was filled with cryogenic alcohol to various levels, the thermocouples quickly responded – those next to fluid indicated very cold temperatures, whereas those next to an empty part of the tank indicated a much warmer temperature. Using this temperature difference, the level of alcohol in the tank could be readily determined, even if the tank was fully chilled and then part of the fluid was poured out (though not as fast, in this case).
The team was concerned, though, that the significant thermal sink of the liquid oxygen might make the results more difficult to determine in the actual application. So, small patch heaters were made using the nichrome wire from a home heating pad. The heaters ringed each thermocouple and when activated, the sensors next to fluid responded much differently than those next to an empty tank: the temperature indication of the sensors next to fluid did not rise as high as those next to gas, and when the heater power was turned off, the temperature of the sensors next to fluid decayed much faster than those next to gas.
Based on the success of this test and the simplicity of the sensors and heaters, this method was chosen for the LOX tank.
By the end of the day, a strip of foam insulation on the LOX tank was removed and the surface was prepped for the lox level sensing system.
After the students left for the day, the LOX tank was taken to a safe area and six thermocouples were welded to the body of the LOX tank at the 5, 20, 25, 30, 50, and 75% full locations.
| permalink
Saturday, April 11, 2009, 05:02 PM
Today was a very productive day for the plumbing team, with a major focus on the LOX system. Our main accomplishments were adding a dedicated nitrogen purge to the downstream side of the main lox valve (to reduce ice formation), swapping the LOX drain and vent valves (to increase the vent flowrate thereby reducing the time required to fill the LOX tank), and adding a larger vent line to the LOX tank (to increase the vent flowrate). By the end of the day, the new lines were cleaned, installed, and insulated.
The computer team spent most of the day working on sensors and making improvements to the test stand software. Based on the remaining time before the May test firing, unfortunately, it looks like we will not be able to complete a new motor controller for this test firing.
At the end of the day, the computer and propulsion teams brainstormed methods for sensing the level of liquid oxygen in the LOX tank without making major modifications to the tank itself. The three most popular methods were an acoustic “tapping” method, a linear capacitance sensor (internal or external), and external temperature sensors. More work on this next week.
| permalink
Saturday, March 28, 2009, 05:10 PM
After a couple of volunteer planning sessions, the first student work day was today. We spent the first part of the meeting reviewing the successes and failures of our last test firing and discussed goals and schedule. The latter half of the meeting was spent cleaning, reassembling, and testing the test stand, plumbing, and computer system. All of the components appear to work fine after long-term storage (all that could be tested in our shop at Boeing).
At the end of the meeting, we identified potential solutions to some of the lingering trouble spots with the rocket motor system (such as the ignitor, main lox valve, a couple of computer issues, and the duration of LOX loading).
| permalink
Back Next
