The effect of cooling temperature on heat pipe performance has generally received little consideration. In this paper, we studied the performance of a Constrained Vapor Bubble (CVB) heat pipe using a liquid mix- ture of 94 vol%-pentane and 6 vol%-isohexane at different cooling temperatures in the microgravity envi- ronment of the International Space Station (ISS). Using a one-dimensional (1-D) heat transfer model developed in our laboratory, the heat transfer coefficient of the evaporator section was calculated and shown to decrease with increasing cooler temperature. Interestingly, the decreasing trend was not the same across the cooler settings studied in the paper. This trend corresponded with the change in the tem- perature profile along the cuvette. When the cooling temperature went from 0 to 20 C, the temperature of the cuvette decreased monotonically from the heater end to the cooler end and the heat transfer coef- ficient decreased slowly from 456 to 401 (W m 2 K 1) (at a rate of 2.75 W m 2 K 2). However, when the cooling temperature increased from 25 to 35 C, a minimum point formed in the temperature profile, and the heat transfer coefficient dramatically decreased from 355 to 236 (W m 2 K 1) (at a rate of 11.9 W m 2 K 2). A similar change in decreasing trend was observed in the pressure gradient and liquid velocity profile. The reduced heat pipe performance at high cooling temperatures was consistent with the reduced evaporation which was indicated by the decreasing internal heat transfer and the increasing liq- uid film thickness along the cuvette as seen in the surveillance images. The result obtained is important for future heat pipe design because we now have a better understanding of the working temperature ranges of these devices.
To understand the boiling crisis mechanism, one can take advantage of the slowing down of boiling at high pressures, in the close vicinity of the liquid-vapor critical point of the given fluid. To preserve conventional bub- ble geometry, such experiments need to be carried out in low gravity. We report here two kinds of saturated boiling experiments. First we discuss the spatial experiments with SF6 at 46 ◦ C. Next we address two ground-based experi- ments under magnetic gravity compensation with H2 at 33 K. We compare both kinds of experiments and show their complementarity. The dry spots under vapor bubbles are visualized by using transparent heaters made with metal oxide films. We evidence two regimes of the dry spots growth: the regime of circular dry spots and the regime of chain coalescence of dry spots that immediately pre- cedes the heater dryout. A recent H2 experiment is shown to bridge the gap between the near-critical and low pressure boiling experiments.
DECLIC is a multi-user facility to investigate critical fluids behaviour and directional solidification of transparent alloys, developed in the frame of a joint NASA/CNES research program. The instrument is a miniaturized thermo optical laboratory in which one can plug inserts containing the materials to be studied.
In August 2011, an approach was made to Moët Hennessy USA by a scienti c research company called NanoRacks, LLC based in Houston,Texas, USA. NanoRacks designs and implements research programmes aboard the International Space Station via a Space Act Agreement with NASA, in conditions of micro-gravity, compared to the conditions on Earth. Given its very particular taste pro le, the Ardbeg Islay Single Malt Scotch Whisky was already well known to the scientists of NanoRacks, and they had developed an idea, involving some form of experiment, or examination, of the effect of micro-gravity on the behaviour of terpenes, the building blocks of avour for whisky spirits as well as for many other foods and wines, as research into terpenes in micro-gravity was limited.We were therefore offered an opportunity to participate in this experiment, including contributing to the design of it, however, our timescale for participation was extremely tight. We collected a quantity of Ardbeg distillate (the liquid resulting from distillation which is normally lled into oak barrels for maturation), along with oak wood shavings from the inside of a charred American White Oak ex-Bourbon barrel, which was due to be despatched from the cooperage to Ardbeg Distillery on the Island of Islay for lling with new Ardbeg distillate.These materials were carefully packaged and sent to the NanoRacks scientists in Houston, where they were packaged into their small sample testing system, known as MixStixTM, which in turn were sent to Kazakhstan to be loaded on to the Soyuz booster rocket destined for the International Space Station. A number of the MixStixTM were also sent to us to use as controls. Three days after launch, the MixStixTM were passed over to astronauts aboard the International Space Station.After an initial period of acclimatisation to the conditions aboard the ISS, in January 2012, the experiment was initiated, as the astronauts broke the glass separating walls in the individual MixStixTM, thus allowing the distillate and the oak wood shavings to come into contact with each other. At the same time on Ear th, we initiated the control experiment by breaking the separating wall in my MixStixTM on Islay (which had been sent back to me at Ardbeg Distillery from NanoRack’s laboratories in Houston, USA). The MixStixTM vials remained on the International Space Station until September 2014, nally returning to the Baikonur Cosmodrome in Kazakhstan on 12th September 2014.The vials were in conditions of micro-gravity, with the distillate and oak wood in contact, for a total of 971 days, orbiting the Earth 15 times a day during this period.The MixStixTM vials were delivered back to Ardbeg in November 2014, after which the distillate from both the micro-gravity and Earth control samples was carefully extracted.A range of comparative analyses were then carried out,to determine if there were any differences between the two sets of samples.
Capillary Channel Flow (CCF) EU2–02 on the International Space Station (ISS): An Experimental Investigation of Passive Bubble Separations in an Open Capillary Channel
It would be signi cantly easier to design uid systems for spacecraft if the uid phases behaved similarly to those on earth. In this research an open 15:8 wedge- sectioned channel is employed to separate bubbles from a two-phase ow in a micro- gravity environment. The bubbles appear to rise in the channel and coalesce with the free surface in much the same way as would bubbles in a terrestrial environ- ment, only the combined e ects of surface tension, wetting, and conduit geometry replace the role of buoyancy. The host liquid is drawn along the channel by a pump and noncondensible gas bubbles are injected into it near the channel vertex at the channel inlet. Control parameters include bubble volume, bubble frequency, liq- uid volumetric ow rate, and channel length. The asymmetrically con ned bubbles are driven in the cross- ow direction by capillary forces until they at least become inscribed within the section or until they come in contact with the free surface, whereupon they usually coalesce and leave the ow. The merging of bubbles en- hances, but does not guarantee, the latter. The experiments are performed aboard the International Space Station as a subset of the Capillary Channel Flow experi- ments. The ight hardware is commanded remotely and continuously from ground stations during the tests and an extensive array of experiments is conducted identi- fying numerous bubble ow regimes and regime transitions depending on the ratio and magnitude of the gas and liquid volumetric ow rates. The breadth of the pub- licly available experiments is conveyed herein primarily by narrative and by regime maps, where transitions are approximated by simple expressions immediately useful for the purposes of design and deeper analysis.
A series of fluid physics microgravity experiments with an enough long run time were performed in the ‘‘KIBO,’’ the Japanese Experiment Module aboard the International Space Station, to examine the transition to chaos of the thermocapillary convection in a half zone liquid bridge of silicone oil with a Prandtl number of 112. The temperature difference between the coaxial disks induced the thermocapillary-driven flow, and we experimentally demonstrated that the flow fields underwent a tran- sition from steady flow to oscillatory flow, and finally to chaotic flow with increasing temperature differ- ence. We obtained the surface temperature time series at the middle of the liquid bridge to quantitatively evaluate the transition process of the flow fields. By Fourier analysis, we further confirmed that the flow fields changed from a periodic, to a quasi-periodic, and finally to a chaotic state. The increasing nonlin- earity with the development of the flow fields was confirmed by time-series chaos analysis. The deter- mined Lyapunov exponent and the translation error indicated that the flow fields made transition to the chaotic field with the increasing temperature difference.
Contribution to the benchmark for ternary mixtures: Measurement of the Soret, diffusion and thermodiffusion coefficients in the ternary mixture THN/IBB/nC12 with 0.8/0.1/0.1 mass fractions in ground and orbital laboratories
We have determined the Soret (ST), diffusion (D, and thermodiffusion (DT) coefficients in a ternary mixture of tetralin-isobutylbenzene-n-dodecane with a composition of 0.80/0.10/0.10 by mass fraction at a temperature of 298K. The Soret coefficients were measured in the microgravity experiment DCMIX1 and on the ground by optical digital interferometry (ODI) using two lasers with different wavelengths. The values of the Soret coefficients were determined from the stationary separation of the components using two- and six-parameter fits. The diffusion coefficients were independently measured using the Taylor Dispersion Technique in the ground laboratory, and the thermodiffusion coefficients were derived from known ST and matrix D. The processing of the data from the DCMIX experiment conducted on the International Space Station is discussed in detail. The multi-user design of the on-board instrument causes perturbations in the component separation. Several recommendations are suggested for improving the quality of the microgravity results. For example, we demonstrated that the tomography reconstruction of the 3-D concentration field allows to restore the underestimated component separation resulting from the spatial non-linearity of the temperature field. Furthermore, to avoid errors in component separation due to mass exchange between the working liquid volume and the expansion volume at the top of the cell, we suggest considering the evolution of the separation only in the lower half of the cell. The results of this study displayed reasonable quantitative agreement between the microgravity and ground experiments.
Temperature dependence of Soret and diffusion coefficients for toluene-cyclohexane mixture measured in convection-free environment
We report on the measurement of diffusion (D), Soret (S(T)), and thermodiffusion (D(T)) coefficients in toluene-cyclohexane mixture with mass fraction of toluene 0.40 onboard of the International Space Station. The coefficients were measured in the range of the mean temperatures between 20 degrees C and 34 degrees C. The Soret coefficient is negative within the investigated temperature range and its absolute value |S(T)| decreases with increasing temperature. The diffusion coefficient for this system increases with temperature rising. For comparison, the temperature dependence of diffusion coefficient was measured in ground laboratory using counter-flow cell technique and revealed a good agreement with microgravity results. A non-direct comparison of the measured onboard Soret coefficients with different systems indicated a similar trend for the temperature dependent behavior. Unexpected experimental finding is that for this system the thermodiffusion coefficient D(T) does not depend on temperature.
Complex (Dusty) Plasma Research under Microgravity Conditions: PK-3 Plus Laboratory on the International Space Station
Complex (dusty) plasma research under microgravity conditions complements the research in the laboratory. Due to reduction of the main force on microparticles in the lab — gravity — it is possible to form complex plasmas in the bulk region of plasmas in homogeneous large 3D systems and to investigate other phenomena than those accessible on Earth in detail. Therefore, PK-3 Plus was operated as a long-term microgravity facility from 2006 to 2013 on the International Space Station ISS. It was perfectly suited for the formation of large stable liquid and crystalline systems and provided interesting insights into processes like crystallisation and melting, laning and phase separation in binary mixtures, electrorheological effects due to ac electric fields and projectile interaction with a strongly coupled complex plasma cloud.
Growth of InxGa1−xSb alloy semiconductor at the International Space Station (ISS) and comparison with terrestrial experiments
BACKGROUND: InxGa1 − xSb is an important material that has tunable properties in the infrared (IR) region and is suitable for IR-device applications. Since the quality of crystals relies on growth conditions, the growth process of alloy semiconductors can be examined better under microgravity (μG) conditions where convection is suppressed.;AIMS: To investigate the dissolution and growth process of InxGa1 − xSb alloy semiconductors via a sandwiched structure of GaSb (seed)/InSb/GaSb(feed) under normal and μG conditions.;METHODS: InxGa1 − xSb crystals were grown at the International Space Station (ISS) under μG conditions, and a similar experiment was conducted under terrestrial conditions (1G) using the vertical gradient freezing (VGF) method. The grown crystals were cut along the growth direction and its growth properties were studied. The indium composition and growth rate of grown crystals were calculated.;RESULTS: The shape of the growth interface was nearly flat under μG, whereas under 1G, it was highly concave with the initial seed interface being nearly flat and having facets at the peripheries. The quality of the μG crystals was better than that of the 1G samples, as the etch pit density was low in the μG sample. The growth rate was higher under μG compared with 1G. Moreover, the growth started at the peripheries under 1G, whereas it started throughout the seed interface under μG.;CONCLUSIONS: Kinetics played a dominant role under 1G. The suppressed convection under μG affected the dissolution and growth process of the InxGa1 − xSb alloy semiconductor.