Adaptation of Current Loop Heat Pipes Design into UAVs 2011-01-2523

The optimization of the available energy within a vehicle is one of the key drivers for all the ongoing projects. This topic is even more critical when the possibility of recharge energy into the vehicle it is quite improbable or even impossible. Hence all the system involved in the energy management shall create synergies.

The Thermal Management is based on two paramount bases. The first one is the location of thermal sources (it can rather been cold sinks or heat sources). The second is the transportation of the energy from one source to a sink. The identification of the sources is based on the vehicle necessities. The definition of the transportation means depend on the vehicle capacities. Traditional system to transport the heat from one place to another are based on fluid displacement. Therefore they need some energy to pump this fluid.

In the last years the use of passive transportation means is being developed in the aerospace industry. One of the methods of free transportation of the heat is based on the Loop Heat Pipe (LHP)

Into a Heat Pipe (HP) the motion of the internal fluid is obtained by capillarity forces due to the heat supply. The LHP is based on the heat pipe technology. The difference is that the liquid and the vapor lines are split.

This paper is based on a development project based on aeronautical environmental. In fact, the platform is an UAV system. The main target of it is the installation of a LHP into a UAV system in order to extract as much heat as possible from the engine exhaust gases in order to anti-ice the wing leading edge and to heat up the fuel to avoid the freezing.

One of the major technological challenges of the project is the adaptation of the current LHP design standard into aeronautical standards, up to now this design takes into account only the spacecraft environment. The interfaces and requirements to install a LHP into an aircraft are quite different. The main differences are in terms of levels and phases of flight. In a spacecraft and/or a satellite the critical phase is the take off and the landing. During those phases systems suffer high level vibration and g-forces but in those scenarios the LHPs are not operative. They will be only operative once the craft is deployed. In the operational state the orbital environment is almost free of gravity and vibration. In an aircraft, the vibration and the g-force may be lower but they are present during the all the operational phases in which the LHP will be working. Other important differences are the maintenance requirement as well as the assembly ones. These requirements get stronger when you have a small UAV that need to be disabled for transportation.

Another innovation point is the controllability of the full system. As there are different cold sources, there should be a control and monitoring system for automatically select where the heat must go.

In order to check the feasibility of all the new features, a rig will be built. Hereunder it is attached a schematic of the laboratory installation to be used during the testing. Mainly it contains the LHP installation to take the heat from an electrical heater -it simulated the heat source- to a leading edge to act as an anti-ice system and to the fuel tank to avoid the freezing of the fuel when necessary. Both elements will be inside a commercial refrigerator to simulate the cold environment that they will suffer when the aircraft operates during stabilizations at high altitudes.

In this rig the behavior of the LHP is to be tested. Different scenarios are simulated such as maintenance, assembly task and the monitoring and control of the different heat sinks.

An additional topic that will be covered after the rig installation and the testing is the certification and qualification process of the system. As the UAV certification topic is not fully covered with the current standards available, a close contact with Spanish airworthiness authority is held to define a valid approach.