Manufacturing & Testing
1 - The Pulsating Heat Pipe & Heat Sink
The teams first port of call when manufacturing the test cell was of course to start with the Pulsating Heat Pipe itself.
Using a jig tailored to the required geometry, the capillary copper pipe was bent and held in place using the heat sinkThe heat sink was designed and manufactured in house, here at the University of Brighton.
Once in place, the PHP was then fitted with a 4 way junction accommodating the two ends of the pipe, a filling port and finally a pressure sensor inlet.
2 - The Chassis
The structural integrity of our test cell chassis is` one of the most important factors to consider when both designing and manufacturing our experiment. Firstly, because it houses all of our components and must be resistant to any shock induced during the hypergarvity phase of the parabolic flights and secondly because the chassis must act as a double containment for the hot fluid (FC-72) inside the pulsating heat pipe.
The team used Maker Beam aluminium extrusions, cut to size to form the skeleton of the test cell. The main advantage of using these extrusions was that the team where able to use the slots in the material to house polycarbonate panels both vertically, comprising the outer shell and horizontally, forming the different compartments of the test cell. In addition to the aluminium extrusions and the polycarbonate panels, aluminium brackets where then manufactured to add extra strength to the assembly.
3 - Sensors & Communications
The team will monitor the performance of the PHP using 15 thermistors. 5 positioned at the evaporator, 5 positioned at the adiabatic section and 5 positioned at the condenser. These thermistors are attached directly to the copper pipe using thermal paste ensuring that the temperature readings are as close as possible to the actual temperature of the fluid inside the pipe. In addition to temperature readings the team will also monitor the internal pressure of the PHP using a pressure transducer as mentioned above.
Monitoring is carried out remotely via Wifi relaying information to a in computer in live time during the parabolic flights. The operator will also be able to control the power delivered to the heaters at the evaporator, via 4 ceramic heating elements. The attitude of the test cell will also be monitored via a series of accelerometers. The Arduino used and the heating elements will be powered by a 12V NiMH Rechargeable Battery Pack which can be replaced easily on the aircraft.
4 - Filling the Pulsating Heat Pipe
Once the pressure sensor is fitted to the PHP, the pipe must be filled with the working fluid. The working fluid chosen here is FC-72 .
This fluid was chosen for three main reasons; it is inert and so will not oxidise the copper tubing once filled, it has viable thermodynamic range that aligns to the operating temperatures/pressures/conditions of the experiment and it also has a capillary diameter at 2g that is higher than the maximum diameter of the chosen copper tubing. The internal volume of the PHP was calculated to be 4.33 ml and, since the targeted filling ratio is 60% , the total volume of fluid required inside the tube is 2.6ml.