Experimental study of a closed loop flat plate pulsating heat pipe under a varying gravity force

Abstract

This paper reports on an experimental study of a closed loop Flat Plate Pulsating Heat Pipe (FPPHP) tested on ground and on board of an aircraft during the 60th ESA parabolic flight campaign, during which hyper- and microgravity conditions were reproduced. The tested FPPHP consists of two brazed copper plates, into one of which a continuous rectangular channel (1.6 x 1.7 mm(2)) with 12 bends in the evaporator is machined. The channel is filled with FC-72 as working fluid with a volumetric filling ratio of 50%. Tests have been conducted with the FPPHP positioned both horizontally and vertically (bottomheated). The FPPHP presents an innovative design, involving the milling of grooves between the channels. Experimental results on the ground show that the thermal device can transfer more than 180 W in both inclinations, and that the horizontal operation is characterized by repeated stop-and-start phases and lower thermal performance. The FPPHP can operate under microgravity conditions and with a transient gravity force, with global thermal resistance reaching 50% and 25% of that of the empty plate (or around 66% and 35% of a full copper spreader of same overall dimensions), in horizontal and vertical orientation respectively. The temperature homogeneity remains within 10 K in the evaporator section and 3 K in the condenser section with thermal power transfer up to 180 W. Minimum thermal resistance of 0.12 K W-1 was recorded, with its value rising as heating grew more powerful. A parabolic flight test demonstrated that the FPPHP in vertical inclination is rapidly influenced by variation of gravity field, even if, due to the novel geometry, it continues to operate under microgravity. In horizontal inclination, on the other hand, there was no observable parameter change during gravity field variations

Hybrid Pulsating Heat Pipe for space applications with non-uniform heating patterns: Ground and microgravity experiments

“…Such passive thermal device is actually a hybrid system, since it works as a Multi-Evaporator Loop Thermosyphon (MELT) on ground [24] and as a capillary PHP in microgravity conditions. Other successful attempts were also performed by Ayel et al [25,26] in hyper/micro gravity conditions by means of parabolic flights. Their Flat Plate Pulsating Heat Pipe was filled up with FC-72, and the hydraulic diameter was 2 mm, which is higher than the capillary static and dynamic thresholds (Table 2).…”

A novel pyroelectric generator utilising naturally driven temperature fluctuations from oscillating heat pipes for waste heat recovery and thermal energy harvesting

“…16 Tubes fabricated from copper lead to high heat transport rates with minimal temperature gradients due to the high thermal conductivity of the material. 17 In this work, we therefore employed a 24 channel flat plate OHP design (1.6 Â 2.0) mm 2 (Equation (1)) and (Equation (2)) with 12 U-turns machined into a 2 mm thick copper base plate (20 Â 12) cm 2 ( Figure 4).…”

Visualization of Flow Patterns in Closed Loop Flat Plate Pulsating Heat Pipe Acting as Hybrid Thermosyphons under Various Gravity Levels

“…The critical limit of the internal diameter capable to maintain the characteristic slug/plug regime in microgravity conditions is still unknown. In addition for pulsating heat pipes tested under microgravity conditions, an intermittent thermofluid behavior has been observed by [13], as well as temperature fluctuations [12], whose origin ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 5 could be assigned to stop-and-start flow motions occurring inside the PHP during those phases.…”

“…This point will be further discussed in the next section for the present FPPHP. However, if it has been demonstrated that capillary pulsating heat pipes can operate under microgravity conditions [8][9][10][11][12], and more recent studies from Mangini et al [13,14] showed that the flow pattern ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 4 switched from stratified flow under normal or hyper gravity conditions to slug flow under microgravity conditions, for uniform heating patterns [13] as well as non-uniform heating patterns [14]. They tested a 3 mm internal diameter tubular PHP (well above the critical diameter value fixed at around 1.66 mm for the tested fluid, FC72, at 20°C) with a transparent tube portion on the upper part of the bench above the condenser zone.…”