Passivation and Performance of Inorganic Aqueous Solutions in a Grooved, Aluminum Flat Heat Pipe

Abstract

Aluminum heat pipes have traditionally been incompatible with water and water-based fluids because they quickly react with the casing to generate non-condensable hydrogen gas (NCG). The NCGs inhibit the operation of evaporation and condensation based devices, eventually plugging the condenser end of the heat pipe. The heat pipe is then unable to remove heat from the condenser and the device fails. Terdtoon [1] found that these events often happen so rapidly between aluminum and water that measurements cannot even be taken. The present work tested two different, patented inorganic aqueous solutions (IAS) in a flat heat pipe setup. Grooved aluminum plates were used as the heat pipe wick and the tests were run with the heating section raised above the condenser. Compatibility between the working fluid and aluminum heat pipe was established by running the device to dryout and then reducing the heat flux to check for hysteresis. De-ionized water (DI water) was also tested, as a baseline, to establish that it did indeed fail as expected. Operating performance of each mixture was obtained from zero heat input until dryout was reached for multiple angles of inclination. The data show that both IAS mixtures are compatible with aluminum heat pipes and exhibit performance similar to that of a copper and water heat pipe. IAS and aluminum heat pipes could replace existing copper and water devices and deliver similar performance while reducing overall weight by more than three times. An IAS and aluminum heat pipe could also replace existing aluminum and ammonia combinations, currently favored in aerospace applications, to allow for increased performance and a larger operating temperature range while maintaining low device weight.

Effect of design and operating parameters on the thermal performance of aluminum flat grooved heat pipes

“…Porous structure, screen mesh, non-circular micro-channels with sharp-angled corners and axial grooves are some examples of wick structures, which enable the heat pipes to function even against or in the absence of gravity [5]. For the case of grooved wick structures, various groove geometries have been studied in the literature such as fan-shaped [6], circular [7], reentrant [8,9] triangular [9,10], trapezoidal [7][8][9][11][12][13] and rectangular [7][8][9]12,[14][15][16][17][18][19][20][21][22][23][24][25][26][27] cross-sections. Particularly, heat pipes with rectangular grooves can be easily modeled and/or numerically studied due to the simplicity of the groove geometry [28,29].…”

“…unmanned spacecrafts, and low temperature operating conditions due to its lightweight, high electrical and thermal conductivity and ease of machining [35]. Recently, many studies have been carried out to assess the thermal performance of aluminum heat pipes [20,21,25,26,33,36,37]. The effects of filling ratio [27,33] and the groove density [33] on the thermal performance of aluminum heat pipes were investigated for acetone and IPA, and an optimum filling ratio was indicated for each heat pipe studied.…”

“…The possible heat transfer enhancement through the use of acetone-based nanofluids in the heat pipes was investigated for Al 2 O 3 nanoparticles [21] and multi-wall carbon nanotubes [26], and it was shown that replacement of the working fluid with a nanofluid resulted in a better performance. The performance of aluminum heat pipes with inorganic aqueous solutions was compared to that of copper heat pipes with water, and it was concluded that aluminum ones have a potential for replacing conventional copper/water ones [25]. The details of the studies regarding flat heat pipes (both copper and aluminum) with rectangular grooves are summarized in Table 1.…”

Designer fluid performance and inclination angle effects in a flat grooved heat pipe

“…The goal of the modular design was to allow consistent testing of various working fluids and wick structures. Similar designs have been successfully utilized to study grooved and sintered wicks by Wong and Chen [16] and Stubblebine and Catton [17].…”

A new method for evaluating heat pipe fluid compatibility

“…Other oxidizer-containing aqueous fluids containing chromates and even permanganates have been used with aluminum thermosiphons as well [11][12][13] with varying success. Terdtoon et al [14] performed an array of thermosiphon lifetime tests with the goal of studying internal tube corrosion.…”