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Inherently Safe Looped Thermosyphon Cooling System for Aircraft Applications using Dielectric Fluid H-Galden

TL;DR: In this paper, an inherently safe liquid cooling system for modern civil aircraft is presented, which uses a dielectric working fluid for the natural circulation in a looped thermosyphon operating in both one and two-phase mode.
Abstract: This paper presents experimental results of an inherently safe liquid cooling system. A test rig is operated at Hamburg University of Technology in order to prove the concept and gather first data for electronics cooling in modern civil aircraft. The cooling system uses a dielectric working fluid for the natural circulation in a looped thermosyphon operating in both oneand two-phase mode. First the mass flow of this natural circulation system is investigated comparing the measurement data to calculations. After that the cooling performance of the system is evaluated by taking a closer look at the heat loads and corresponding temperatures. Finally heat transfer coefficients in the cold plate are calculated. The results are discussed with respect to the following parameters, which are varied in the test series conducted: heat load, the heat sink temperature and the system orientation. 1. INHERENTLY SAFE COOLING SYSTEMS The power densities of electronic components are increasing continuously, thus conventional air cooling systems are replaced with liquid cooling to remove the waste heat (Dietl et al., 2008). Liquid cooling systems can transfer much higher waste heat flux densities. State-of-the-art liquid cooling systems use a closed cooling loop basically consisting of a cold plate and a cooler connected with pipes. The liquid is circulated by a pump. In the cold plate the waste heat from the electronic components is transferred to the working fluid. This hot liquid is pumped to the cooler, where the waste heat is discharged in most cases to sink the ambient air acting as the final heat. 1.1 Objective in Aircraft Applications Crucial flight systems (e.g. avionics) need highly reliable cooling systems. In common civil aircraft these systems are air cooled using forced convection. The electronics are air-ventilated by fans. Nevertheless the cooling systems are designed to ensure a minimum cooling performance without fans for some time to allow a safe landing at the nearest airport. With increasing power densities of microprocessors and power electronics the waste heat flux densities increase and air cooling has to be replaced by liquid cooling systems like described above. The reliability is a critical issue for these active liquid cooling systems compared to the conventional air cooling. With a failure in a coolant pump, which can have many reasons, the liquid stops circulating and the electronics get overheated very quickly. Thus, analogically to air cooling, it is the aim of an inherently safe liquid cooling system to ensure a minimum cooling performance without a coolant pump. In this passive configuration the circulation of the working fluid has to be actuated by buoyancy forces, which result from density differences. In one-phase operation this is a critical issue, as the density does not vary much for most liquids. A significant change in density is achieved by evaporating the working fluid. Therefore two-phase operation is highly attractive for inherently safe liquid cooling and will be the main focus of this paper.

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Journal ArticleDOI
TL;DR: In this article, a novel design for a heat exchanger was experimentally evaluated in an Embraer test aircraft on the ground and in-flight conditions, which consisted of two condensers, linked to one shared evaporator by two parallel loop thermosyphons.

52 citations

Journal ArticleDOI
TL;DR: In this article, a novel design for a heat exchanger system, for which a patent application has been filed, was experimentally evaluated in the laboratory under variable thermal conditions characteristic of an aircraft in operation.

28 citations

Journal ArticleDOI
TL;DR: In this paper, a passive cooling system based on heat pipe technology was tested in-flight in an Embraer test aircraft, and the couplings between HES evaporator and IHTE condensers were designed to assure practical fitting and low contact resistance.

13 citations

01 Jan 2017
TL;DR: In this article, a heat exchanger system (HES) was experimentally evaluated on ground and in-flight conditions aiming the passive cooling of avionics systems, which consists of two condensers, linked to one shared evaporator by two parallel loop-thermosyphons.
Abstract: A novel design for a heat exchanger system (HES) was experimentally evaluated on ground and in-flight conditions aiming the passive cooling of avionics systems. The heat exchanger prototype consists of two condensers, linked to one shared evaporator by two parallel loop-thermosyphons. The air stream on the external side of the fuselage and the air conditioning system served as heat sinks. A heat pipe and four thermosyphons were employed as intermediary heat transfer elements (IHTEs) between heat sources and the HES evaporator. The IHTE design parameters such as filling ratio, inclination angle, aspect ratio and coupling geometries (contact between condenser of IHTE and evaporator of HES) were evaluated. Water was applied as the working fluid. The HES and IHTEs prototypes were qualified for flight after thermal assessments in laboratory and constrained acceptance tests. The tests were conducted at flight Mach numbers up to 0.78 and at altitudes of up to 12 km, corresponding to air static temperatures of -56 oC. Under cruise flight conditions, the HES is able to dissipate 900 W maintaining vapor temperatures below typical working values for avionics; e.g. 70 to 100 oC. Efficient performance of thermosyphon was also shown in freezing conditions of the working fluid. Geyser boiling phenomenon eventually yields intense vibrations at the HES evaporator. Thermal changes in the heat sinks hardly affect IHTEs. Heat pipe and thermosyphons with 0.7 m length can dissipate 120 W and 500 W, respectively. Forced convection can be an alternative where heat conduction between avionics and IHTE evaporators is not possible. Conical and cylindrical IHTEs condensers were demonstrated as possible fitting geometries for thermal couplings.

4 citations