CGT - Test


Test Overview

Test objectives were as follows: 

  • Record thrust data for 3 and 10 seconds
  • Record when frost begins to build up on the nozzle
Test Stand
The test stand was built as simple as possible. A single ball valve controlled CO2 flow to the thruster, with high pressure gas coming directly from the CO2 bottle (blow down system). The thrust sat strapped to a wooden block, which was then attached to a drawer slide. This block had a screw that would push on a load cell mounted to a metal bracket. This load cell would record the thrust produced by the nozzle. 



Data was collected from the load cell by filtering and amplifying it with an HX711 circuit board and then logging data through an Arduino serial output. This data was recorded using an open source software called CoolTerm.



Control box (pink box) contained the Arduino and load cell circuit. Control box was also wired to an emergency stop (cardboard box with #10 on it). 



Test Data Observations 


One larger problem became evident during test: the thruster was only meeting half of its designed thrust. Designed to produce at least 20lbs with an injection pressure of 850psi, the thruster was underperforming drastically. While there were temperature deviations between tests, these temperatures never varied more than 5 degrees. Additionally, no obstructions existed within the fluid lines. 

The most likely causes for the underperformance is the following:

1. Choked flow upstream 
The high pressures of the system and cost constraints restricted me to the use of 1/4" tube and flex hose. Unfortunately, the ID of the -04AN fitting on the nozzle was slightly smaller than that of the nozzle's throat. The ID of the flex hose leading the the thruster was also smaller than the throat. 

2. Losses in the flex hose
The flex hose had multiple loops to allow the thruster to move on the drawer slide, it's possible that these bends could have kinked the hose and caused a significant pressure drop before reaching the nozzle. 

3. Insufficient pressure/mass flow rate
This is the most likely explanation. It's possible that the bottle pressure read by my regulator was incorrect or my regulator restricted flow enough in my lines to prevent high thrust levels from being achieved. 





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