Fountain Effect Pump Research Articles

Superfluid liquid helium control for the primordial inflation polarization explorer balloon payload.

The Primordial Inflation Polarization Explorer (PIPER) is a stratospheric balloon payload to measure the polarization of the cosmic microwave background. Twin telescopes mounted within an open-aperture bucket dewar couple the sky to bolometric detector arrays. We reduce detector loading and photon noise by cooling the entire optical chain to 1.7K or colder. A set of fountain-effect pumps sprays superfluid liquid helium onto each optical surface, producing helium flows of 50-100 cm3 s-1 at heights up to 200cm above the liquid level. We describe the fountain-effect pumps and the cryogenic performance of the PIPER payload during two flights in 2017 and 2019.

A sub-Kelvin superfluid pulse tube refrigerator driven by paramagnetic fountain effect pump

A novel sub-Kelvin refrigeration cycle is introduced in this work. The magnetically driven superfluid pulse tube refrigerator (MSPTR) could provide cooling at temperatures below 200mK while rejecting heat at 1.6K and contains no moving mechanical parts. The MSPTR cycle has an advantage over other types of sub-Kelvin cooling in that it can provide distributed cooling. Additionally the MSPTR unlike the dilution refrigerator will be able to function in microgravity without any modification. This work includes a description of the MSPTR cycle and a summary of preliminary design calculations including results used to size components and predict cooling performance.

A closed-cycle dilution refrigerator for space applications

We discuss the development of a gravity-insensitive dilution refrigerator adapted from the open-cycle refrigerator used for the Planck mission. Since the 3He and 4He components are circulated (the 4He by a fountain-effect pump operating at about 2K, the 3He by a compressor at room temperature) rather than ejected into space, the lifetime of a closed-cycle refrigerator is not limited by the quantity of 3He and 4He available. In this work, we concentrate on the design and performance of the cold end (counterflow heat exchanger and mixing chamber) of the refrigerator. We discuss the sizing of the heat exchanger and present cooling power measurements. We detail the working of the fountain pump. We also briefly touch upon some practical issues including the choice of a 3He compressor and the pre-cooling requirements for the dilution refrigerator.

細管内における超流動ヘリウムの一次元流動伝熱解析に関する研究

A modified two-fluid model is applied to the present numerical analysis in order to study the flow and heat transfer of superfluid helium in a micro-channel with a diameter as small as that of a Superleak in a Fountain Effect Pump. Variable properties of superfluid helium and energy dissipations due to two-fluid mutual friction and friction at the channel wall are taken into consideration. The calculation results were in good agreement with experimental results; thus, this simulation code can be used for analyzing flow and heat transfer of superfluid helium in a micro-channel.

極細管における超流動ヘリウムの流動伝熱特性に関する研究

A modified two-fluid model is applied to study flow and heat transfer of superfluid helium in a micro channel with a diameter as small as that of a superleak in a fountain effect pump. Variable properties of superfluid helium and energy dissipations due to the two-fluid mutual friction and the friction at the channel wall are taken into consideration. It is found that the normalfluid component flow is not trivial even in a channel of a diameter of micro meters, and that there exists an optimum diameter which attains the maximum mass flow rate. The flow of superfluid helium through a channel with different temperatures at the ends differs considerably from that of a Newtonian fluid. The strong dependence of the thermodynamic properties on temperature and pressure, as well as the internal-convection mechanism is found to be the causes of the unique flows.

Numerical study of flow and heat transfer of superfluid helium in capillary channels

A modified two-fluid model is adopted to study flow and heat transfer of superfluid helium in a microchannel with a diameter as small as that of a superleak in a fountain effect pump. Variable properties of superfluid helium and energy dissipations due to the two-fluid mutual friction and the friction at the channel wall are fully taken into consideration. It is found that the normal fluid component flow is not trivial even in a channel with diameter of a micrometre, and that there exists an optimum diameter for the maximum mass flow rate. The flow of superfluid helium through a channel with different temperatures at the ends differs considerably from that of a Newtonian fluid. The strong dependence of the thermodynamic properties on temperature and pressure, as well as the internal-convection mechanism are found to be the causes of the unique flows.

閉ループ型ファウンテンポンプ内の伝熱

The heat transfer characteristics of a fountain effect pump in a He II flow loop have been investi gated by experiments and numerical analyses. Temperatures at several points in the loop, pressure difference between both sides of the porous plug and mass flow rate of He II were measured in the experiments. The fountain effect is generated by heat-input at one side of the porous plug. In a closed-loop fountain effect pump, the temperature on the opposite side of the plug also increases even though heat is not input to that side. In this study, we show that a part of the heat-input is transported to the upstream side of the porous plug due to supercompnent flow (zero entropy flow) in the plug. Taking account of the distribution of the heat-input, heat transfer and the pressure drop in the loop and fountain effect at the plug, a model is proposed. From analyses based on the model, the temperature distribution in the loop, pressure difference between both sides of the porous plug and He II mass flow rate can be estimated accurately in the case of laminar flow in the plug.

Performance of fountain effect pumps with different HeII flow loops

Operational characteristics of a fountain effect pump in a HeII flow loop have been experimentally investigated. Relations between a HeII mass flow rate in the loop and a supplied heat to the pump were measured with different dimensions of the porous plug and the tubes which make up the loop. It is confirmed that the supplied heat can be used effectively to drive HeII when appropriate sizes of the plug and the tubes at the inlet and outlet of the pump are chosen. The tube at the inlet of the plug is required to remove most of the supplied heat and to suppress an increase of HeII temperature at the inlet and outlet of the plug. The tube at the outlet of the plug is required to restrict the heat leakage to the downstream of the flow.

Performance of a closed type fountain effect pump

Operational characteristics of He II loop flow driven by a fountain effect pump under steady state condition have been experimentally investigated for different thermal and flow impedances. It is confirmed that an appropriate length of vortex tube, which restricts the heat leak flowing downstream of the pump, is required to utilize the supplied heat and to drive the pump effectively. The He II mass flow rate in the loop does not depend upon the length of the vortex tube provided the vortex tube is longer than the appropriate length in the present experiment. However, the pressure and temperature differences between the outlet and inlet of the pump increase with increase in length of the vortex tube.

Studies on helium flow in experimental loops with different impedances operated with fountain effect pumps

An experimental flow loop with He II flow driven by fountain effect pumps (FEPs) is studied with respect to operation at different flow impedances and with thermal loads applied at different positions. The measured values of temperature, flow rate and pressure drop are compared with calculations resulting from a simplified model which assumes ideal performance of the porous plug and of the heat exchangers and which does not take into account Gorter-Mellink (GM) conduction. The main features of the loop are shown to be well described by this model. Refined calculations with a more complex model, including GM conduction of the He II, are only required for predicting the temperature distribution in some discrete regions of the loop.

Testing methods and performance of IMGC fountain effect pump

A fountain effect pump has been built at the Italian Institute of Metrology (IMGC) with the aim of supplying a closed-loop circuit, intended as a secondary facility for calibration and testing of LHe II flow meters. The pump performance, in terms of pressure-flow rate curves at different values of power input ranging from 3 to 11 W, was obtained using a simple open-loop testing arrangement equipped with an externally operated regulating valve acting as a variable impedance. Construction details of the pump and of the testing loop are given, together with the results. Since the experimental set-up could not ensure adequate stability of bath temperature and level, a more sophisticated testing apparatus is presented, at present in the design phase, which is able to work with saturated or sub-cooled helium and which allows good stability of external parameters to be obtained.

ファウンテンポンプエレメントを通るＨｅ ＩＩ流れの動流特性と実効流路モデルによる定量的評価

The thermomechanical flow of He II through a porous element for a fountain effect pump was experimentally investigated to understand the general flow characteristics and to develop an evaluation formula for the flow rate. Two types of elements, compressed alumina powder elements and SUS fiber elements, were tested in a systematic way. The two flow states, the ideal and superfluid turbulent states, are found to exist according to the magnitude of heat input. It is a general conclusion that the flow rate through the former elements is always far smaller than the prediction from the straight forward application of the Corter-Mellink formula in the superfluid turbulent state. In order to resolve the inconsistency, the effective flow passage model is proposed, in which the tortuosity is introduced to take account of the winding of micro flow pas sages in an element. The model leads to firm understanding of general flow characteristics in both qualitative and quantitative senses, and to deriving the dynaical similarity law for the mass flow rate and the theoretical maximum flow rate. However, the tortuosity experimentally obtained with the alumina elements was considered to be too large, that is to say 4 to 5. On the other hand, those of SUS elements are found to be one or nearly one as expected from the interior structure. It is concluded that the flow rate degradation in the superfluid turbulent state is resulted mostly from the winding effect of passages, and that the model is confirmed to be quite valid.

Thermomechanical flow of He II through a porous element for a fountain effect pump

The thermomechanical flow of He II through a porous element for a fountain effect pump was experimentally investigated to understand the general flow characteristics in both ideal and turbulent flow states. The flow rate increases in proportion to the heat input Q in the ideal superfluid flow state for small Q, but it tends to saturate for further increases of Q in the superfluid turbulent state, and finally reaches a maximum at the He II temperature in the downstream region just below T λ . The flow in the latter state is found to be well formulated in terms of the Gorter-Mellink mutual friction term if it is modified to take account of the interior structure for flow passages in an element. The modified formulation clearly models the existence of the maximum flow rate and a geometrical similarity law for the flow rate. A computer simulation was also successfully attempted to predict the flow characteristics through a fountain effect pump element.

Heat transfer in very narrow channels of low-temperature devices used for fluid management of He II in space

The thermomechanical effect has been utilized in a number of low-temperature devices, including fountain-effect pumps and vapour-liquid phase separators (VLPS). Other applications, such as fluid retention and collection devices, have also been proposed. The present paper gives an overview of the VLPS work performed in the past decade. All the data have been compared under a common frame of reference. The transport process in a VLPS was found to be heat-transfer-controlled. This finding will shed light on the understanding of transport phenomena in other low-temperature devices.

Interaction of He II transfer line and fountain effect pump

The analysis of a He II transfer process consisting of a fountain effect pump coupled to a transfer line is presented. It is shown that the flow rate of the fountain effect pump is largely determined by the hydraulic load, i.e. the transfer line. Based on the isocaloric equation for ideal superfluid flow, pump performance curves are developed. The pressure drop along the transfer line is modelled by using expressions for turbulent flow. Performance of the pump and transfer line are coupled to provide a complete system for analysis. Results are formulated in terms of the hydrodynamic impedance of the system. Examples are studied using the characteristics of the SHOOT transfer line.

Oscillatory He II mass flow behaviour of FEPs in self sutained mode

He II flow driven by Fountain effect pumps(FEPs) operating in self sustained mode in test loops of different impedances have shown oscillatory behaviour for test section heat loads upto 1.2W. The period of oscillation depends on the applied heat load, bath temperature of He II (Tbath) and the impedance of the test loop. The occurrence of oscillations is qualitatively understood due to the existence of an “onset temperature” to generate convection in the loop. The boundary between the stable and oscillatory states have been mapped. A combined normal and self sustained mode of operation of FEP eliminates these oscillations for practical applications.

Oscillatory he II mass flow behaviour of feps in self sutained mode

He II flow driven by Fountain effect pumps(FEPs) operating in self sustained mode in test loops of different impedances have shown oscillatory behaviour for test section heat loads upto 1.2W. The period of oscillation depends on the applied heat load, bath temperature of He II (Tbath) and the impedance of the test loop. The occurrence of oscillations is qualitatively understood due to the existence of an “onset temperature” to generate convection in the loop. The boundary between the stable and oscillatory states have been mapped. A combined normal and self sustained mode of operation of FEP eliminates these oscillations for practical applications.

Iso-chemical potential trajectories in the P − T plane for He II

Trajectories of constant chemical potential in the P− T plane serve as an integral formulation of London's equation. The trajectories are useful for analysis and synthesis of fountain effect pump performance. A family of trajectories is generated from available numerical codes.

Helium II flow through narrow pore filters

Studies of helium II flow through the narrow pore filters of cylindrical shapes, fabricated by compacting under pressure fine powders of aluminium oxide $(0.05 \mu m)$, nickel and chromium $(1 \mu m)$, have been made by measuring the volume flow rates in a two bath arrangement. The "easy" direction mass flow rates are in general agreement with the Gorter Mellink description, but for large temperature gradients where the observed mass flow rates are lower than predicted by the theory and tend to saturation. However if one can treat the cross-sectional area as a fit parameter, our results show that this parameter decreases with increasing chemical potential gradient, very similar to the ease of non-cylindrical geometries. Can then one conclude that irrespective of the geometrical shape of the filter the superfluid flow behaves analogously to the classical flow especially for large pressure differences. The breakthrough studies confirm the occurrence of "choking effect" in the filter made from very fine size aluminium oxide powder. Our studies point to the limitations in using these filters for practical applications such as fountain effect pumps and helium II transfer devices.

Superfluid transport and its applications in space

Various transport modes in superfluid helium are discussed in this paper. They include zero net mass flow (ZNMF) and finite mass flow (FMF) for pure superfluid and normal fluid flow. An attempt is made to characterize these transport modes in a common frame of reference. Two dimensionless numbers are used, namely the dimensionless heat flux number and the dimensionless driving force number. The equations are generalized by the use of a characteristic length so that they can be applied to the transport of He II in any geometry. The theories are then extended to applications in space. In particular, fountain effect pumps (FEPs) and superfluid management at zero g by vapour—liquid phase separators (VLPSs) will be discussed in detail. While transport in a phase separator is close to that of ZNMF, the flow in a FEP belongs to the FMF mode. The transport modes of the above systems using porous media are found to be strongly size dependent. For VLPSs, the heat rejection rate is proportional to the square root of plug permeability, K P. As in the case of FEPs, the volumetric flow rate is inversely proportional to K P. These findings are supported by ZNMF data in capillaries and FMF (gravitational flow) data in millipores, respectively.