Effect of the application of an electric field on the performance of a two-phase loop device: Preliminary results

In the last decade, the continuous development of electronics has pointed out the need for a change in mind with regard to thermal management. In the present scenario, Pulsating Heat Pipes (PHPs) are novel promising two-phase passive heat transport devices that seem to meet all present and future thermal requirements. Nevertheless, PHPs governing phenomena are quite unique and not completely understood. In particular, single closed loop PHPs manifest several drawbacks, mostly related to the reduction of device thermal performance and reliability, i.e. the occurrence of multiple operational quasi-steady states. The present research work proposes the application of an electric field as a technique to promote the circulation of the working fluid in a preferential direction and stabilize the device operation. The tested single closed loop PHP is made of a copper tube with an inner tube diameter equal to 2.00 mm and filled with pure ethanol (60% filling ratio). The electric field is generated by a couple of wire-shaped electrodes powered with DC voltage up to 20 kV and laid parallel to the longitudinal axis of the glass tube constituting the adiabatic section. Although the electric field intensity in the working fluid region is weakened both by the polarization phenomenon of the working fluid and by the interposition of the glass tube, the experimental results highlight the influence of the electric field on the device thermal performance and encourage the continuation of the research in this direction

Pulsating Heat pipe only for Space (PHOS): Results of the REXUS 18 sounding rocket campaign

Two Closed Loop Pulsating Heat Pipes (CLPHPs) are tested on board REXUS 18 sounding rocket in order to obtain data over a relatively long microgravity period (approximately 90 s). The CLPHPs are partially filled with FC-72 and have, respectively, an inner tube diameter larger (3 mm) and slightly smaller (1.6 mm) than the critical diameter evaluated in static Earth gravity conditions. On ground, the small diameter CLPHP effectively works as a Pulsating Heat Pipe (PHP): the characteristic slug and plug flow pattern forms inside the tube and the heat exchange is triggered by thermally driven self-sustained oscillations of the working fluid. On the other hand, the large diameter CLPHP works as a two- phase thermosyphon in vertical position and doesn't work in horizontal position: in this particular condition, the working fluid stratifies within the device as the surface tension force is no longer able to balance buoyancy. Then, the idea to test the CLPHPs in reduced gravity conditions: as the gravity reduces the buoyancy forces becomes less intense and it is possible to recreate the typical PHP flow pattern also for larger inner tube diameters. This allows to increase the heat transfer rate and, consequently, to decrease the overall thermal resistance. Even though it was not possible to experience low gravity conditions due to a failure in the yoyo de-spin system, the thermal response to the peculiar acceleration field (hyper-gravity) experienced on board are thoroughly described

Effect of Dead Volumes on Single Closed Loop Pulsating Heat Pipes,

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Large Diameter Pulsating Heat Pipes On Board The Esa Rexus 18 Sounding Rocket

The Pulsating Heat Pipe (PHP) is a promising two-phase passive heat transfer device for the thermal management in space applications. A recent parabolic flight experiment has already shown that a capillary tube PHP has the same thermal performance either on low gravity environment or on ground with the evaporator and condenser placed horizontally with respect to the gravity vector. An increase of the inner tube diameter theoretically may lead to an increase of the thermal performance but it is only achievable in the presence of low gravity conditions. In order to verify such concept, two large diameter PHPs have been tested on board REXUS 18 rocket. The tested PHPs consist of two closed loops made of aluminium tubes with fourteen curves arranged on two planes. Both are filled with the refrigerant FC-72 and have an inner tube diameter larger than the critical diameter (3 mm) and around the critical diameter (1.6 mm), respectively. The heat input is supplied by two heating cables wrapped around the tube and placed asymmetrically with respect to the curves, so as to promote the fluid circulation in a preferential direction. The heat is transferred through the devices and, at the end, released in a phase change material via latent heat of fusion without any appreciable temperature buildup for the entire duration of each experimental run. In the occurrence of the milli-gravity conditions experienced on board the rocket, surface tension prevails over buoyancy and the flow pattern inside the devices switches to the slug and plug PHPs typical operational regime. The temperature and pressure trends reveal such a regime transition and provide further information on the usability of large diameter PHPs in microgravity environments

Thermal Response of a Pulsating Heat Pipe on Board the Rexus 18 Sounding Rocket: PHOS Experiment Chronicles

This work presents the experimental results of two Pulsating Heat Pipes (PHP) with different internal tube diameter tested on board the REXUS 18 sounding rocket. As shown in Figure 1, both the test cell (experiment box containing the two PHPs) and the electronic hardware (battery pack, power management and data handling) are designed, developed and implemented by the team. The PHPs are both filled with FC-72, thus, being the critical diameter around 1.7mm at ambient temperature and on Earth gravity conditions, one PHP (1.6 mm I.D.) is around the critical diameter while the other one (3 mm I.D.) is larger. The acronym PHOS, Pulsating Heat pipe only for Space, indeed resume the concept of a two phase closed loop that is working as a PHP only in microgravity: surface tension prevails over buoyancy and the flow pattern should switch to the slug and plug PHPs typical operational regime also when the diameter is above the critical. The temperature and pressure trends are expected to reveal such a regime transition and provide further information for future space applications. The tested PHPs consist of a closed end-to-end aluminium tube with fourteen curves arranged on two planes constituting the evaporator or hot section. A heating cable wrapped around the tube in the evaporator section supplies the desired heat flux, while a phase change material allows dissipating the heat in the condenser section. A set of thirty thermocouples for each PHP is located in different tube positions and the local fluid pressure is recorded by means of a mini pressure transducer in the condenser section. Ground and flight results are compared in terms of temperature and pressure temporal trends