Geyser Effect Research Articles

Fabrication and thermal performance of a novel roll-bond flat thermosyphon

In this work, a novel wickless heat pipe fabricated using the roll-bond process and called the roll-bond flat thermosyphon was proposed for electronic component cooling due to its slim and large-size configuration, low-cost, and mass-production capable. The thermal performance of roll-bond flat thermosyphon was investigated through the tests in terms of 3 typical structures (stagger, cross and align) and 4 filling ratios (5%, 10%, 20%, and 40%) under the increasing heat power, and evaluated with the effective thermal conductivity and the maximum heat transfer capacity. The phenomena of boiling regime evolution, geyser effect, liquid entrainment and dry-out, can be found through the temperature responses in the cases of progressive filling ratios and heating powers. The cross-structured sample was found to behave the worst among the three structures due to its blocked up-flowing inflated circuits. The highest effectivity thermal conductivity of 22404 (W/K·m) was found in the 5%-align sample, however, accompanied with early dry-out. The heat transfer capability is positive correlated to the filling ratio, and maximum heat transfer capacity of 100 W (heat flux of 14.9 (kW/m2)) was recorded in the stagger-40% sample. The 20%-stagger sample is recommended as the optimum design, due to its more stable and relative high thermal conductivity, which is peaked to 16019 (W/K·m), and averaged at 12616 (W/K·m) in the range of 0–90 W.

Toy geyser experiment: periodicity, operating conditions and coupling

A natural geyser can be reproduced by a toy experiment composed of a water pool located above a water reservoir, the two being connected by a long and narrow tube. When the bottom reservoir is heated, the system may experience periodic eruptions of hot water and steam at the top similarly to the geyser effect occurring in nature. The eruption frequency of a toy geyser is inspected experimentally as a function of the heating power and the height of the setup. We propose a thermodynamic model of this system that predicts the time between eruptions. A phase diagram that takes into account the thermal energy provided to the geyser and the geometry was constructed for the toy geyser. The conditions to obtain the geyser effect have been determined. The study of the toy geyser is then extended to the case of two reservoirs connected to the same tube. Such a coupled system adopts a complex time evolution that reflects the dynamics of natural geysers. We analyze the behavior of a toy geyser with two reservoirs by way of statistical tools and develop a theoretical model in order to rationalize our observations.

Experimental investigation of the influence of the geyser boiling phenomenon on the thermal performance of a two-phase closed thermosyphon

Heat pipes' thermal performance can be greatly affected by the occurrence of geyser boiling, a phase-changing phenomenon. Thus, it is important to investigate the effect of such a phenomenon on the thermal characteristics of the heat pipe. In the current work, extensive experimental investigations have been carried out to consider the influence of geyser boiling on the thermal performance of a two-phase closed thermosyphon (TPCT), in terms of temperature distribution and thermal resistance. This study has been conducted for different water fill ratios as a working fluid (25%, 65%, 100%) and at various orientations (90, 60, 30, 10°) with a wide range of heat loads (20–400 W). The study reveals that the temperature distributes uniformly on the thermosyphon wall after the geyser effect occurrence. In addition, after the geyser boiling, a considerable decrease in the evaporator wall temperature is obtained; especially at a fill ratio of 100% and tilt angles of 90 and 30°, regardless of the increase in the heat loads. Consequently, for example, at the vertical orientation and a heat load of 20 W, the thermal resistance of the TPCT for the fill ratio of 100% decreases from about 200% higher than that for a fill ratio of 25% to become the lowest thermal resistance at a heat input of 50 W. Also, the results show that the heat transfer limit of the thermosyphon heat pipe can be noticeably increased after the occurrence of the geyser boiling. This study highlights the effects of the geyser boiling on the thermal performance of heat pipes.

Effect of inclination angle and fill ratio on geyser boiling phenomena in a two-phase closed thermosiphon – Experimental investigation

Geyser boiling is a complex phenomenon which may occur in heat pipes causing high temperature and pressure oscillation leading to noticeable vibration. Therefore, understanding of such process is essential to improve heat pipes thermal performance and avoid damage. In this experimental study, a comprehensive investigation of several parameters on the characteristics of the geyser boiling has been conducted during the operation of two-phase closed thermosiphon (TPCT) using water as the working fluid. The effect of different inclination angles (90, 60, 30 and 10°) at various fill ratios defined as volume of liquid in the evaporator to the volume of the evaporator (25%, 65% and 100%) on the geyser boiling has been investigated at a broad range of heat load and for various mass flow rates and inlet temperatures of the cooling water. These important parameters have been examined to report the occurrence and period of the geyser effect at each heat input. The results showed that the orientation and the liquid charge have a significant impact on the occurrence and period of the geyser boiling at low and high heat inputs. For example, at a fill ratio of 100%, the geyser boiling occurs at a lower heat input compared with that for fill ratios 25%, 65% at all inclination angles, while it happens at a higher heat load at a low inclination 10° compared with other angles at all fill ratios. In addition, at high input energies, it almost disappears at orientations of 90 and 60° for all liquid charges. Also, comparing with fill ratios of 25% and 65%, a shorter period is observed for a fill ratio of 100% at angles of 90, 30 and 10°, whereas it is longer at 60° and low heat inputs. This work highlights the effects of the operating conditions on geyser boiling in heat pipes.

Weakly entrained transport tuned by interface noises wave

We conducted a detailed derivation of the possible entrainment in a cylinder filled with 4He and 3He which is induced by a small-amplitude surface elastic wave propagating along the flexible interface by considering the nonlinear coupling between the interface and the microscopic (slip) effect of dynamic vacancies as well as He-3 impurities. We numerically obtain possible critical bounds for frozen or zero-flux states corresponding to specific rarefaction measure and wave number which might be relevant to the rather small critical velocity or disappearance of geyser effect and frictionless transport of flowing helium crystal reported before. Our numerical results demonstrate that the complicated boundary or interface induced transport can produce a net effect resembling the transition-state as well as reaction kinetics.

The geyser effect in the vacuum expansion of solid 3He0.544He0.46 and the determination of the Poisson ratio

Periodic bursts, also called the geyser effect, previously observed in the vacuum expansion of pure and <1% 3He-doped solid 4He, are shown to occur also in solid 3He–4He alloys. Results are reported for 3He0.544He0.46 for the temperature range of 1.73–2.13 K and pressures up to 92 bar, and then compared with the results for pure solid 4He. The geyser period is found to increase with pressure much faster in the mixed solid than in pure solid 4He. A direct measurement of the internal pressure exerted on the lateral walls of the source chamber provides the first information on the Poisson ratio of polycrystalline pure and mixed solids.

The Geyser effect in the expansion of solid helium into vacuum

The mechanism behind the intensity oscillations accompanying the flow of solid helium through a micron-sized orifice into vacuum, called the geyser effect, is investigated by measuring the pressure pulses at various locations in the entire flow system. The new results reveal that the source chamber pressure pulses have the same shape as the external detector pulses monitored in the previous experiments [G. Benedek et al., Phys. Rev. Lett. 95, 095301 (2005)]. New experiments in which the external gas reservoir is isolated from the pressure regulator provide direct information on the mechanism of the collapse leading to the geyser pulses. Thus each geyser pulse is triggered by the breakdown of a plug located upstream of the source chamber. The flow of liquid through the orifice determines the shape of the subsequent geyser pulse.

Sonochemical and photosonochemical degradation of 4-chlorophenol in aqueous media

The degradation of 4-chlorophenol (4-CP) in aqueous media by 516 kHz ultrasonic irradiation was investigated in order to clarify the degradation mechanism. The degradation of concentrated 4-CP solution by means of ultrasound, UV irradiation and their combined application was also studied. The obtained results indicate that OH radical are the primary reactive species responsible for 4-CP ultrasonic degradation. Very little 4-CP degradation occurs if the sonolysis is carried out in the presence of the OH radical scavenger tert-butyl alcohol, also indicating that little or no pyrolysis of the compound occurs. The dominant degradation mechanism is the reaction of substrate with OH radicals at the gas bubble–liquid interface rather than high temperature direct pyrolysis in ultrasonic cavities. This mechanism can explain the lower degradation rate of the ionic form of 4-CP that is partly due to the rapid dissociation of OH radicals in alkaline solutions. The sonochemical destruction of concentrated 4-CP aqueous solution is obtained with low rate. Coupling photolysis with ultrasound irradiation results in increased efficiency compared to the individual processes operating at common conditions. Interestingly, the photosonochemical decomposition rate constant is greater than the additive rate constants of the two processes. This may be the result of three different oxidative processes direct photochemical action, high frequency sonochemistry and reaction with ozone produced by UV irradiation of air, dissolved in liquid phase because of the geyser effect of ultrasound streaming. Additionally, the photodecomposition, at 254 nm, of hydrogen peroxide produced by ultrasound generating OH radical can partly explain the destruction enhancement.

Instability of Heat Pipe Performance at Large Axial Accelerations

To investigate the feasibility of using heat pipes in airborne systems, heat pipe performance at large axial accelerations in the range of 3–12g was studied experimentally. The heat input chosen corresponded to the optimal heat pipe performance without acceleration. When applied against the direction of the liquid flow (unfavorable orientation) the accelerations were large enough to exceed the capillary limit, as was seen from the strong increase in the evaporator temperature. The influence of accelerations in the direction of the liquid flow (favorable orientation) was found to be more complicated. While at the acceleration of 3g the heat pipe performance improved, at higher accelerations instability developed with resulting large-amplitude oscillations of the evaporator temperature. The instability found in these experiments is thought to be related to the geyser effect observed in thermosyphons.

Ébullition en milieu poreux: analyse expérimentale de la stabilité du front zone liquide-zone diphasique

We are interested in the problem of boiling in a porous column made up of glass beads saturated with water. The temperature of the plate at the bottom of the column is fixed at a value higher than the boiling point of water. The temperature at the top of the column is imposed at a value allowing a liquid zone to be present (by re-condensation), whereas the pressure is kept at the atmospheric value. We report in this paper different tests for which we have modified the size of the beads in order to obtain stable and unstable situations. In the last case, instabilities appear in the form of periodic oscillations of the temperature field and are accompanied by outlet then inlet of water through the permeable upper surface (‘Geyser effect’). After having mentioned the 1D treatment of stable situations, we examine unstable ones for which the convection in the liquid zone plays a disturbing effect. A simplified linear stability analysis taking into account the increase of effective conductivity of the liquid zone with free convection is carried out with a view to obtaining a new stability criterion.

Means of protecting cryogenic systems from the geyser effect

New means of protection, which permit a low fluid boil in the pipeline without proceeding into an avalanchelike process, have been developed on the basis of theoretical and experimental investigations of the geyser effect in cryogenic systems with an end thermal influx from a regulating fitting. An equation is presented for computing the time allowed for the low fluid boil. Pressure increase in the overhead reservoir is discussed and a cryogenic reservoir with concentric pipeline equipped with a hood for vapor elimination is illustrated. Vapor removal from a vertical pipeline is examined. A structural method of protecting cryogenic systems from the geyser effect is discussed; the value of this method consists in its high reliability.

The geyser effect in a two-phase thermosyphon

An interesting phenomenon, which was observed during experimental research work carried out on a two-phase thermosyphon with water as the working fluid, is described. The phenomenon is a pulsed boiling at low pressure and was called the “Geyser Effect”. The heat transfer coefficient at the thermosyphon evaporator has been measured and a functional law, which links this coefficient with the pressure and the specific thermal flux, is proposed; a correlation of the type Nu * = C Re * aPr b is also shown to represent satisfactorily the experimental data.