UNIFIED ENGINEERING                        Fall 2005                                                    Ian A. Waitz

Problem T1. (Unified Thermodynamics)

Below is a schematic of a water rocket that you will be evaluating later in the semester. The baseline system uses a standard 2-liter soda bottle for the rocket structure and fuel storage. The bottle is partially filled with water and mounted on a rocket launch mechanism. A metal restraining pin is inserted over the lip of the bottle-neck to keep the bottle on the launcher until it is ready for launch. Air is then pumped through the rod to pressurize the bottle; a small rubber o-ring on the launch rod provides an airtight seal at the mouth of the bottle.

The launch is initiated when the retaining pin is removed. The rocket launch consists of three stages. The first stage is the period between the start of the launch and when the rocket nozzle (bottle mouth) just reaches the top of the launch rod. During the second stage the compressed air forces the water out of the bottle at high speed as the bottle rises into the sky. The third stage is a ballistic stage, in which the rocket continues upward under only the influence of gravity and drag, reaching some maximum altitude before falling back to the ground.

Consider the full system to be a bicycle pump, the person who pressurizes the rocket with the pump, and the water rocket itself. Describe the conversions of energy (internal, potential, kinetic and chemical) and exchanges of heat and work for this system starting with the pressurizing of the bottle, through the launch, and ending with the bottle back on the ground. Note at which points in the process heat is transferred to or from the surroundings. (LO#1, LO#2, LO#3)

Water Bottle Rocket and Launching Mechanism