Microgravity Influence on Bubble Growth and Detachment

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Mar 18, 2010 - Pool boiling was studied in hypergravity at 1.7 ±. 0.5 g and in microgravity at 0.01 ± 0.025 g. The fluid used in the study is FC-72 with a ...
Microgravity Sci. Technol. (2010) 22:377–385 DOI 10.1007/s12217-010-9186-9

ORIGINAL ARTICLE

Convective Boiling Between 2D Plates: Microgravity Influence on Bubble Growth and Detachment Damien Serret · David Brutin · Ouamar Rahli · Lounès Tadrist

Received: 14 January 2010 / Accepted: 1 March 2010 / Published online: 18 March 2010 © Springer Science+Business Media B.V. 2010

Abstract The experiment detailed in this paper presents results obtained on the nucleation, growth and detachment of HFE-7100 confined vapour bubbles. Bubbles are created on an artificial nucleation site between two-dimensional plates under terrestrial and microgravity conditions. The experiments are performed by varying the shear flow by changing the convective mass flow rate, and varying the bubble nucleation rate by changing the heat flux supplied. The experiments are performed under normal (1 g) and reduced gravity (μg). The distance between the plates is equal to 1 mm. The results of these experiments are related to the detachment diameters of bubbles on the single artificial nucleation site and to the associated effects on the heat transfer by the confinement influence. The experimental device allows the observation of the flow using both visible video camera and infrared video camera. Here, we present the results obtained concerning the influence of gravity on the bubble detachment diameter and the images of 2D bubbles obtained in microgravity by means of an infrared camera. The following parameters: nucleation site surface temperature, bubble detachment diameter and bubble nucleation frequency evidence modifications due to microgravity. Keywords Nucleation site · Convective boiling · Infrared measurement · Visualization · Reduced gravity

D. Serret · D. Brutin (B) · O. Rahli · L. Tadrist Laboratoire IUSTI, Ecole Polytechnique Universitaire de Marseille, Technopôle de Château-Gombert, 5 rue Enrico Fermi, 13453 Marseille, France e-mail: [email protected]

Introduction Today, convective boiling is still an important subject in the field of phase change due to its wide range of application. Many studies have analysed different regimes between the entrance and the outlet of a channel where convective boiling occurs: sub-cooled nucleate boiling, bubbly flow, slug flow. We recently studied convective boiling at macroscopic scale (Luciani et al. 2009); the objective in this paper is to focus on the sub-cooled nucleate boiling flow in a 2D cell to investigate only a single bubble nucleation process. The originality of this work is to investigate this regime in a HeleShaw cell. This kind of experimental configuration has already been used for various experimental studies such as the Marangoni effect (Arlabosse 1997), Kelvin Helmholtz instability (Mainhagu et al. 2007), and the mix of two miscible liquids (Meignin et al. 2003). Furthermore, the geometry of the cell avoids any optical aberration due to a high thermal gradient in the thermal boundary close to the wall. Indeed, the phenomenon mentioned by Kenning et al. (2004) and Barthès (2006) induces a wrong position for all observed interfaces. This geometry avoids any problem due to three-dimensional effects (the created bubble is maintained in the same plane during the whole of its growing and detachment phases). This configuration also allows us to use an infrared camera on one side of the cell and the other side is fitted with a visible camera; the study of a single nucleation site in a 2D cell has never previously been performed with the two cameras. A literature review on boiling (pool and convective) evidences the new field of investigation open to analyse and understand the nucleation in microgravity (see Table 1).

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Table 1 Studies dealing with boiling in microgravity performed since 2000 Author,

Year

Fluid

Microgravity access

Experimental technique used

Verthier et al. (2009) Celata et al. (2009) Zhao et al. (2009) Kawanami et al. (2007) Sodtke et al. (2006) Zhang et al. (2005) Henry and Kim (2004) Di Marco et al. (2003) Straub (2000)

2009 2009 2009 2007 2006 2005 2004 2003 2000

FC-72 FC-72 R113 LN2 FC-72 FC-72 FC-72 FC-72 R11

Parabolic flights (CNES) Parabolic flights (ESA) Scientific satellite Parabolic flights (NASA) Parabolic flights (ESA) Parabolic flights (NASA) Parabolic flights (NASA) Drop tower (JAXA) NASA SpaceLab IML-2

‘Quenching’ in glass capillary tubes ‘Quenching’ in glass capillary tubes Pool boiling on Platinum wire Transparent resistive deposit on a cylinder Utilization of liquid crystals Flow in a channel heating by resistive deposit Network of Platinum resistances Utilization of an electrical field Circular heater of 160 μm in diameter

In 2000, Straub (2000) analysed in a research paper experimental results obtained in 1994 during a ‘SpaceLab IML-2’mission flight. The objective of the experiment was to perform pool boiling in microgravity using hemispheric resistance of 0.26 mm in diameter. The resistances are also used to perform measurements. The author analysed R11 subcooling influence on the heat transfer coefficient by conducting experiments on Earth after the mission. However, for subcooling between 10 to 30◦ C, the heat transfer are reduced in microgravity up to −50% at 30◦ C of subcooling. For subcooling values below 10◦ C, the heat transfer coefficient becomes its classical value under terrestrial gravity. The author remarked that the heat flux density reached during microgravity and normal gravity is about 900 kW m−2 . These heat flux densities are about two times higher compared to those observed with boiling on a plate. Finally, the author concluded that based on the experiments performed in microgravity, the gravity level strongly influence the heat and mass transfer mainly in the transition area between nucleate and film boiling. In 2003, Di Marco et al. (2003) studied the influence of the electrical field and the gravity field on the detachment and motion of Nitrogen bubbles injected in FC-72 at ambient pressure and temperature through a 0.1 mm-diameter hole made in a horizontal tube. This configuration was chosen to separate the mechanical effects on the bubbles from the mass and thermal effects caused by boiling. An electrical field is generated around the tube by imposing a constant potential between 0 to 18 kV using a circular cage at the tube outside. The experiments were performed in the JAMIC drop tower at Hokkaido, Japan. The authors access the bubbles diameter, the frequency and nucleation velocity using a treatment performed on the images recorded using a high speed video camera. The results evidenced that without an electrical field, there is no detachment at a low mass flow rate. However, for a high mass flow rate, the flow is sufficient to cause bubble

detachment even without gravity. When an electrical field is applied, the detachment is quicker for bubbles with larger diameters compared to the situation with gravity. In 2004, Henry and Kim (2004) investigated the influence of the heating element on pool boiling. They used a heater-array made of 96 heaters of 0.27 × 0.27 mm, each micro-heater was independent. The area of one micro-heater was 0.073 mm2 . This configuration has enabled the authors to study different heating configurations : – – –

9 (3 × 3) micro-heaters with a total area of 0.81 mm by 0.81 mm = 0.66 mm2 , 36 (6 × 6) micro-heaters with a total area of 1.62 mm by 1.62 mm = 2.62 mm2 , 96 (10 × 10 − 4) micro-heaters with a total area of 2.7 mm by 2.7 mm = 7.00 mm2 .

The last configuration with 96 micro-heaters provided a heating area about four times wider than the ‘36’ configuration and about ten times wider than the ‘9’. Pool boiling was studied in hypergravity at 1.7 ± 0.5 g and in microgravity at 0.01 ± 0.025 g. The fluid used in the study is FC-72 with a saturation temperature of 56.7◦ C under 1 bar. The heating system was regulated in temperature. The system thus enables access to the heating power used, and hence to the heat flux density used for boiling. Consequently, it was possible to deduce the heat transfer coefficient. For a small heating area with ‘9’ micro-heaters, bubbles are formed in hypergravity or microgravity almost identically for the same conditions: with a sub-cooling of 34◦ C. However, for the ‘36’ and ‘96’ micro-heaters configuration, boiling is completely different. In hypergravity, isolated bubbles are formed where as in microgravity a single vapour bubble is formed. This phenomenon is related to the fluid capillary length which is 0.82 mm with a terrestrial gravity. Bubbles generated are typically very close to the capillary length. In the study, the authors

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also evidence the influence of heater size, sub-cooling and gravity level on heat transfer. In 2006, Sodtke et al. (2006) performed a study at the nucleation site size using liquid crystals. The authors focused on the foot of the bubble where the heat transfer is the greatest. The theoretical wall temperature on the fluid side is obtained using a thin layer model of the heating wall based on nucleate boiling. The comparison with the experiment is performed using a heating thin metallic film. The temperature measurement is performed using a high resolution camera to record the reactive liquid crystals to the temperature. Using this technique, the authors obtained during a parabolic flight campaign a good agreement between the experiment and the model. In 2007, Kawanami et al. (2007) studied liquid nitrogen convective boiling in microgravity during parabolic flight campaigns performed on board the KC-135. Liquid nitrogen was used since its physical properties are very close to liquid hydrogen and liquid oxygen. A gold transparent deposit of 10 nm was used to induce boiling in a Pyrex tube of 7 mm inner diameter. The objective of the study was to observe the cryogenic fluid behaviour under reduced gravity conditions. The existence of a cryogenic fluid close to saturation conditions in microgravity is a problem of great interest for space research; more especially, for the re-ignition of rockets under microgravity conditions. The fluid behaviour in the pipes, the flow separation brings a new field of research to this area. Very recently, Celata et al. (2009) performed quenching experiments in tubes under microgravity. The experiment objective is to obtain quantitative data and flow observation on the re-wetting under microgravity conditions to enable comparison with results obtained under normal gravity. The authors used Pyrex tube of 6 mm in diameter. The fluid used is FC-72. The temperature measurements were obtained at the external wall of the tube, inlet and outlet fluid temperature measurements were available such as pressure measurements and mass flow rate. The results obtained by the authors evidence the strong reduction in the quenching velocity in microgravity in comparison to normal gravity. However, the authors note that the wall temperature dynamics do not seem to be influenced by the gravity level. These results have to be confirmed with temperature measurements from the inside of the tube, since the Pyrex conductivity is very low and thus induces strong heat fluxes and temperature gradients. The Pyrex thermal diffusivity should be taken into account during these checks. The flow structures observed were annular flows with a inside core of liquid

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and vapour close to the wall followed by a classical convective boiling regime. The objective of this study with this particular experimental set-up is mainly to quantify the microgravity influence on boiling. The wall effects due to the confinement exist with or without gravity. We expect to observe changes in boiling nucleation parameters (nucleation frequency, nucleation duration and nucleation site temperature) in microgravity compared to normal gravity to enable us to achieve a better understanding of the nucleation phenomenon in microgravity. The difficulty for this understanding is the wall confinement effect on the bubble.

Experimental Set-up The Loop The fluid loop located in the confinement box works as follows: the fluid stored in 10-ml syringes is injected by a syringe pump (Fig. 1). The fluid is initially preheated in order to reach a temperature close to saturation (54.4◦ C), typically about 5◦ C below saturation: 50◦ C. Once preheated the fluid arrives in the test cell described hereafter.In the cell, a few watts suffice to initiate boiling since the fluid is already almost saturated. A single bubble is created from a single triangular nucleation site mechanically created with a drill (50 μm in diameter) and is studied. The fluid flow is recorded using visible and infra-red cameras. The liquid and thus the bubble created, will leave the cell and proceed to the condensor where the gas will become a liquid. This permanent flow is carried out at very low speeds (highest Reynolds number is 40) in order to allow for the dissipation of the heat produced by heating a 0.1mm thick Inconel film. The storage tank attenuates the variations of level during de-gasification on Earth before the flights. There is no work under pressure in this study as the overpressure necessary to create and evacuate a bubble is approximately one Pascal. The experiments were carried out according to the following procedure: for a given mass flow rate (constant liquid velocity at the entry of the cell) and a fixed power of heating, the parameters of the experiment were acquired permanently at 50 Hz. Along with the pressure and temperature measurements, the visible and infrared video acquisitions of the flow were carried out from 30 s before the parabola until 30 s after the parabola. In the boiling mode, the fluid generated successive bubbles from the nucleation site whose size varied according to the degree of containment. With

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Microgravity Sci. Technol. (2010) 22:377–385 Fresh air

Fresh air

Fresh air

Fresh air

Peltier + heat sink

Manual insulating valve

Peltier + heat sink

Aluminum

Heat Sink

Polycarbonate

Condensor 1

Degasing automatic valve

HVAC

Condensor 2 Internal air

Internal air

P Manual valve

Studied bbble

Heating film

Liquide level

2D flow

Liquid trap Connecting valve to the box

Heat exchanger

Peltier + heat sink

Heat exchanger

Peltier + heat sink

Internal air

One-way valve

Expansion latex membrane

Porous media

Test cell

Internal air

Working pressure valve

Pressure transducer

Two-way syringe-pump Confinement box

Fig. 1 Confinement box and its equipment to boil the flow in the 2D cell

the device arranged in this way, it was possible to control the heating and fluid parameters (fluid inlet temperature and the heat flux supplied to the fluid). The test cells were rectangular with various dimensions. For this paper, one cell dimension is presented. The cells were made of polycarbonate with a side face in ZnSe. The latter face was transparent with visible and infra-red radiation between 8 and 12 μm, which is the wavelength of the infra-red camera as used in these experiments (FLIR A40M). The infra-red movies are performed at 25 images/s with an integration time of 40 ms. The ZnSe plate used was treated on one side to obtain a total transitivity of 85%. Heating was ensured by an electrically-powered 100-μm Inconel film (Figs. 2 and 3). A 50-μmm triangular nucleation site was created on the Inconel plate. Instrumentation was based on temperature acquisitions. A K-type thermocouple was positioned in the cell and allowed the measurement of wall temperature below the nucleation site. Visualization was carried out through the polycarbonate side face with a video camera AVT Pike (50 frames/s). The experiments were repeated for each channel entry flow.

For two parabolas, we imposed a wall heat flux and a flow of fluid, which enabled us to know the growth dynamics of confined bubbles for three levels of gravity (μg, 1 and 1.8 g).

Fig. 2 3D view of the test cell with the bubble in yellow

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the pressure fall too much. This rebalancing was thus done in stages using a vase plug. If the membrane had suddenly broken, the supporting role of the vase plug was to avoid an escape towards double containment. The vase plug then served as a liquid trap and allowed the visualization of the liquid HFE-7100. The Fluid

Fig. 3 Cross-section view of the test cell: visible observation from the left and infra-red from the right

The experiments were carried out at cabin pressure (835 mbar). For this purpose we added a surge tank containing a latex membrane in order to follow the changes in cabin pressure. Nevertheless, locally the pressure can increase to a maximum of 100 Pa. This means that the pressure before the cell entrance can reach 835 + 1 = 836 mbar. After the test cell we measured the absolute pressure of the loop in the buffer tank, which must be equal to the cabin pressure in order to have stable and reproducible operating conditions. We degazed by remotely actuating an electromagnetic valve if the pressure exceeded 845 mbar. It was possible to work at constant ambient pressure. In conjunction, the set point of an automatic valve was fixed at 850 mbar. An additional numerical pressure gauge was installed outside the enclosure on the vent-line in order to monitor the vent-line pressure (400 mbar). The total volume of the loop (pipes included) was about 120 ml, with approximately 100 ml of liquid HFE-7100 (four syringes containing 10 ml, a buffer volume of 40 ml and the pipes) and 20 ml of gas (HFE-7100 vapor mainly in the surge tank). The volume of the flexible membrane was approximately 200 ml in order to absorb possible variations of pressure. The containment was isolated thermally by means of a 5-mm-thick neoprene plate. The role of the electromagnetic valves at the exit of the surge tank was to allow a rebalancing of the pressure of the loop with cabin pressure if degasification made

HFE-7100 has been investigated using a spectrophotometer. HFE-7100 has been used due to its semitransparency properties in the infra-red wavelength. Absorptivity measurements have been performed using a FTIR NICOLET Nexus 560 spectrophotometer to access the absorptivity in between 2.5 to 14 μm. For the purpose of this study, we analyse and extract only the data in the range of 7.5 to 13 μm which corresponds to our infra-red camera wavelength band (FLIR A40). The experimental cell is composed of CaF2 crystal which are used for their almost total transparency properties in the range of the spectrophotometer. Teflon spacers are used to obtain the adequate optical fluid thickness. 3 spacers thickness are available : 0.1, 0.2 and 0.5 mm, they can be added. The optical fluid thickness is deduced based on 9 independent measurements of the spacers set using a Mitutoyo CD-15CPX calliper which have a uncertainty of ± 0.02 mm, a resolution of 0.01 mm and a repeatability of 0.01 mm; so a total uncertainty of 0.04 mm. The error bar provided on abscissa are the sum of the total uncertainty of the nine measurements. The absorptivity measurements are performed three times, each time the test cell is empty without liquid for the background measurement,

Fig. 4 Spectral transmittivity of HFE-7100 degassed and non degassed

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Microgravity Sci. Technol. (2010) 22:377–385 Thermocouple

Electrode

then the test cell is filled with liquid. These three independent measurements enable the ordinate error bar, which is the discrepancy, to be provided. In Fig. 4, we provided two spectrometers obtained with both degassed and non-degassed HFE-7100. The noticeable peaks are related to CO2 presence in the non-degassed HFE-7100. The global emissivity of the non degassed fluid is 0.701 ± 0.006 while the global emissivity of the degassed fluid is 0.695 ± 0.002 (Fig. 5). Consequently the difference between both values is 0.80% ± 1.10%. The difference between both the emissivities is small enough compared to the accuracy, to be neglected. However, the fluids used for the parabolic flight experiments were degassed.

Electrode

Data Analysis

Fig. 6 Visible images of 2D bubble growth and detachment in microgravity

1g Vapour bubble

Liquid injection at 2°C below saturation

level: 1.8 g), then the injection at 47◦ (gravity level: ± 0.05 g) and finally after 22 s of microgravity the pullout resource to return to 1 g. For our experiments, only the normal gravity and microgravity periods were studied. Gravity Influence on Bubble Nucleation In Fig. 7 we present, for a given heat flux of 1.3 W/cm2 and a 1-mm-thick confinement, the variation of the bubble detachment diameter measured for several bub¯ at bles as a function of the mean liquid velocity (U) the cell entrance, which is directly related to the shear

Detatchement diameter (mm)

During a flight, experiments were performed with a constant heat flux supplied to the heating film. The first experiments were carried out with a high mass flow rate; then the mass flow rate was reduced in order to increase the bubble generation frequency and/or to modify the detachment parameters (Fig. 6). Due to the short period of time in between two parabolas (120 s), the mass flow rate decrease was small to permit a new stationary state in less than 60 s. Each experiment was performed twice for the same heat flux and the same mass flow rate to make sure of its reproducibility. A campaign is composed of three days of flights. During each day’s flight 31 parabolas are performed. Parabolas consist of three parts: first a pull-up resource to increase the slope of the plane from 0◦ to 47◦ (gravity

Artificial nucleation site

Flow velocity (mm/s)

Fig. 5 Global emissivity of HFE-7100 function of the fluid optical thickness

Fig. 7 Influence of gravity on the detachment diameter variation as a function of the mean shear flow velocity determined, based on the visible images

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383 57.5°C

flow for a 2D plane (τ ) by Eq. 1 where h is the channel height. τ=

4 μU¯ z h2

56

(1)

In normal gravity the detachment diameter is roughly constant even with a shear flow two times greater (2 to 6 mm/s). The detachment diameter measures 0.5 mm for this 2D situation, which is consistent with the capillary length of HFE-7100. Thus the mean bubble detachment diameter on a horizontal plate in a 3D pool boiling situation given by Eq. 2 is 0.17 mm based on Fritz (1935).   12 σ Db = 0.0208θ (2) g( L − V ) Our situation of boiling below a surface allows the bubble to grow and thus to detach for a larger diameter. In microgravity, the detachment diameter decreases with increasing liquid inlet velocities and therefore with increasing shear flows. This tendency to decrease can be explained by the modified shape of the bubbles in microgravity and by the slip observed. In normal gravity the bubbles stick to the heating plate whereas in microgravity, without gravitational forces, they are circular in the 2D cell and quickly detach themselves from the nucleation site due to the shear flow. In normal gravity, the bubble grows from its nucleation site and the fluid flow coming from the left side circumvents the growing bubble as we evidence in the next section dealing with the infra-red videos. In microgravity the bubble is detached quickly which enables a new bubble to grow (Figs. 8 and 9).

54

52

50 49.8°C

Fig. 9 Infra-red and visible images of a single bubble stuck on the heating plate [Qm = 5.7 kg.m−2 .s−1 et Qw = 1.3 W cm−2 ]

temperature of the nucleation site and to highlight the frequency of detachment of the bubbles based on the signal of the temperature. The analysis of the infra-red video enables us to determine the temperature variation (increase then reduction) at the level of the nucleation site when the microgravity appears. Slip of the vapour bubbles along the heated film causes temperature fluctuations of approximately 0.5◦ C. Figure 10 highlights the periodic fluctuations for the nucleation site temperature in terrestrial gravity with peaks which correspond to the onset of bubble growth, with a vapour first small bubble; this growth requires a lot of energy which is partly obtained as the sensible heat of materials and the fluid in the vicinity. The average temperature of the site is of 57.5◦ C. The bubble growth time observed is also

58,1

Bubble Infra-red Motion

Terrestrial gravity

Reduced gravity

1 mm

Begining of nucleation 57,9

Nucleation site temperature (°C)

The resolution of the infra-red videos carried out, enables us to confirm the presence of the bubble and its level of thermal disturbance on the flow, nevertheless a higher resolution is necessary if one wants to analyse the transfers to the level of the base of the bubble. It is however possible to follow the change at the

57,7

57,5

57,3 Latency time between two bubbles

1 mm

Bubble detachment

1g

57,1 0

0,5

1

1,5

2

2,5

3

3,5

Time (s)

Flow

Fig. 8 Bubble shapes in the 2D cell

Flow

Fig. 10 Nucleation site temperature evolution under terrestrial gravity (uncertainty on the temperature is ± 0.15◦ C) [Qm = 5.7 kg.m−2 .s−1 , Qw = 1.3 W cm−2 ]

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obtained with an average growth time until the 300 ms detachment for one total duration of the cycle of about a second. Figure 11 highlights the temperature of the same nucleation site in microgravity for the same experimental conditions, the average temperature of the nucleation site is slightly lower at 55.6◦ C. The bubble growth time observed is shorter with a 210 ms average for a growth cycle of approximately 850 ms. The temperature fluctuation amplitude at the nucleation site during microgravity is approximately 2.0◦ C (against 0.5◦ C under normal gravity) when a bubble grows in microgravity then detaches. The heat flux is provided to the heating film is constant, a fall in the temperature at the nucleation site thus means an increase in the coefficient of exchange at the time of the bubble growth. A sudden and strong increase in the nucleation site temperature is thus associated with the absence of a bubble during the transitional period. The activated nucleation site delivers a new vapour bubble since vapour is present within the nucleation site. The transition to microgravity results in a decrease in the average nucleation site temperature; the nucleation causes more notable fluctuations in the nucleation site temperature which is in agreement with the frequency of bubble detachment which increases in microgravity compared to the same situation in terrestrial gravity. From this work, we obtained results on the growth of single bubbles and their detachment under normal gravity and microgravity conditions. The technique of visualization used is based on simultaneous visualization with both visible camera and an infra-red camera inside a 2D cell which has one face transparent to

57,6

Nucleation site temperature (°C)

57,1

Begining of nucleation

56,6

56,1

the infra-red radiation. This enables us to visualize the size and the shape of the bubbles at the time of their growth and their detachment from the artificial nucleation site. The convective flow created in order to shear the bubbles confirms an early detachment of the bubbles in microgravity compared with the same situation under terrestrial gravity. This detachment diameter in microgravity strongly decreases with increasing flow velocities. The visualization highlight the influence of the flattened shape of the bubbles under terrestrial gravity. The bubbles are pressed on the heating film and generate small nucleation site temperature fluctuations compared to the same situation in microgravity. Without gravity, as soon as the bubbles are created, the bubbles depart from the nucleation site with a higher heat removal rate. The nucleation site temperature fluctuations amplitude is consequently higher in microgravity, but with a shorter nucleation time. This mechanism in microgravity of greater nucleation site temperature variation and greater nucleation frequency induces a lower nucleation average temperature; thus a better local heat transfer coefficient.

Conclusions and On-going-work We have presented here the first results obtained on bubble growth and detachment under normal gravity and reduced gravity conditions in a 2D Hele-Shaw cell. The observation technique we have developed is based on the simultaneous visible and infra-red visualisation of a 2D cell. It enables us to visualize the size and shape of the bubbles during all stages of nucleation, growth and detachment. The convective flow created in the 2D cell evidences a constant detachment diameter under normal gravity conditions, whereas in microgravity the bubble detachment diameter decreases sharply. The visualization indicates that in normal gravity bubbles are stuck to the heating film, whereas in microgravity they slip on the heating film very quickly after their initial growth from the nucleation site.

55,6

Acknowledgements We would like to thank the European Space Agency for their financial assistance and the campaign carried out at Bordeaux, Mérignac, France. We would also like to thank Novespace for their assistance during the campaign.

55,1

54,6

Latency time between two bubbles

54,1

Bubble detachment

References

53,6 0

1

2

3 4 Time (s)

5

6

7

Fig. 11 Nucleation site temperature evolution under reduced gravity (uncertainty on the temperature is ± 0.15◦ C) [Qm = 5.7 kg.m−2 .s−1 and Qw = 1.3 W cm−2 ]

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