U-PHOS Project: Development of a Large Diameter Pulsating Heat Pipe Experiment on board REXUS 22

U-PHOS Project aims to analyse and characterise the behaviour of a large diameter Pulsating Heat Pipe (PHP) on board REXUS 22 sounding rocket. A PHP is a passive thermal control device consisting of a serpentine capillary tube, evacuated, partially filled with a working fluid and finally sealed. In this configuration, the liquid and vapour phases are randomly distributed in the form of liquid slugs and vapour plugs. The heat is efficiently transported by means of the self-sustained oscillatory fluid motion driven by the phase change phenomena. On ground conditions, a small diameter is required in order to obtain a confined slug flow regime. In milli-gravity conditions, buoyancy forces become less intense and the PHP diameter may be increased still maintaining the slug/plug flow configuration typical of the PHP operation. Consequently, the PHP heat power capability may be increased too. U-PHOS aims at proving that a Large Diameter PHP effectively works in milli-g conditions by characterizing its thermal response during a sounding rocket flight. The actual PHP tube is made of aluminum (3 mm inner diameter, filled with FC-72), heated at the evaporator by a compact electrical resistance, cooled at the condenser by a Phase Change Material (PCM) embedded in a metallic foam. The tube wall temperatures are recorded by means of Fibre Bragg Grating (FBG) sensors; the local fluid pressure is acquired by means of a pressure transducer. The present work intends to report the actual status of the project, focusing in particular on the experiment improvements with respect to the previous campaign

Upgraded Pulsating Heat Pipe Only For Space (U-Phos): Results of the 22nd Rexus Sounding Rocket Campaign

A large tube may still behave, to a certain extent, as a capillary in a micro-gravity environment. This very basic concept is here applied to a two-phase passive heat transfer devices in order to obtain a new family of hybrid wickless heat pipes. Indeed, a Loop Thermosyphon, which usually consists of a large tube, closed end to end in a loop, evacuated and partially filled with a working fluid and intrinsically gravity assisted, may become a capillary tube in space condition and turn its thermo-fluidic behavior into a so called Pulsating Heat Pipe (PHP), or better, a Space Pulsating Heat Pipe (SPHP). Since the objective of the present work is to experimentally demonstrate the feasibility of such a hybrid device, a SPHP has been designed, built, instrumented and tested both on ground and microgravity conditions on the 22nd ESA REXUS Sounding Rocket Campaign. Ground tests demonstrate that the device effectively work as a gravity assisted loop thermosyphon, whether the sounding rocket data clearly reveal a change in the thermal hydraulic behavior very similar to the PHP. Since a microgravity period of approximately 120s is not sufficient to reach a pseudo steady state regime, further investigation on a longer term weightless condition is mandatory

U-PHOS EXPERIMENT: THERMAL RESPONSE OF A LARGE DIAMETER PULSATING HEAT PIPE ON BOARD REXUS 22 ROCKET

A Pulsating Heat Pipe (PHP) is tested on board REXUS 22 sounding rocket in order to obtain data over a relatively long milli-gravity period (120s). The device is made of an aluminum tube bent in a serpentine staggered configuration, closed in a single loop and partially filled with FC-72. Despite the 3mm internal diameter is Greater than the capillary threshold in ground conditions, in milligravity the slug flow pattern is maintained as well as the thermally driven self sustained oscillation of the working fluid. The possibility to build PHPs with big diameters, with increased heat transfer rates and reduced overall Thermal resistances, is an interesting step forward in the fast developing space industry, always craving for greater performances at a reduced weight and cost. The experiment is the natural improvement of the PHOS project, launched on REXUS 18 but only partially successful due to a failure in the de-spin system of the rocket. All the components have been improved, especially the test cell geometry, the data acquisition system -now employing 24 Fiber Bragg Grating optical sensors for a more accurate temperature detection- and the heat sink -now composed by a combination of paraffin wax and metal foams for an enhanced thermal conductivity. The Thermal response of the device is given under a constant heat power supply at the evaporator

U-PHOS Project: Development of a Large Diameter Pulsating Heat Pipe Experiment on board REXUS 22

U-PHOS Project aims at analysing and characterising the behaviour of a large diameter Pulsating Heat Pipe (PHP) on board REXUS 22 sounding rocket. A PHP is a passive thermal control device where the heat is efficiently transported by means of the self-sustained oscillatory fluid motion driven by the phase change phenomena. Since, in milli-gravity conditions, buoyancy forces become less intense, the PHP diameter may be increased still maintaining the slug/plug typical flow pattern. Consequently, the PHP heat power capability may be increased too. U-PHOS aims at proving that a large diameter PHP effectively works in milli-g conditions by characterizing its thermal response during a sounding rocket flight. The actual PHP tube is made of aluminum (3 mm inner diameter, filled with FC-72), heated at the evaporator by a compact electrical resistance, cooled at the condenser by a Phase Change Material (PCM) embedded in a metallic foam. The tube wall temperatures are recorded by means of Fibre Bragg Grating (FBG) sensors; the local fluid pressure is acquired by means of a pressure transducer. The present work intends to report the actual status of the project, focusing in particular on the experiment improvements with respect to the previous campaign

U-PHOS Project: Experimental Results of A Large Diameter Pulsating Heat Pipe on Board Rexus 22

Micro-gravity environments might extent the concept of capillary behavior structure to large diameter tubes. A Loop Termosyphon, in its traditional use, is a two-phase thermal device which usually consists of a large tube, closed end to end in a loop, evacuated and partially filled with a working fluid and intrinsically gravity assisted. With the concept stated here, it may become a capillary tube in space condition and turn its thermo-fluidic behavior into a Pulsating Heat Pipe (PHP), or better, a Space Pulsating Heat Pipe (SPHP). The present work presents the results of the experimental campaign of a SPHP effectuated both on ground and in microgravity conditions. A SPHP has been designed and implemented on board of a sounding rocket launched in the 22nd ESA REXUS Sounding Rocket Campaign. This type of sounding rocket launch guarantees approximately 120s of microgravity environment. The ground tests prior to the launch demonstrated that the device effectively work as a gravity assisted loop thermosyphon, while the experimental data from the microgravity period during the sounding rocket launch reveal a change in the thermal hydraulic behavior similar to the PHP. The micro-g environment provided by the rocket was not sufficient to reach a pseudo steady state regime, therefore, further investigation on a longer term weightless condition is mandatory