Pumping unit for delivery of liquid medium from a vessel

The invention relates to a pumping unit and, in particular, to a high pressure pump, for example for delivery of a liquid medium such as liquid cryogen from a vessel with sufficiently high pressure, while maintaining low pressure in the vessel itself.

There are some US patents describing pumping systems, which operate on the basis of a geyser principle.

U.S. Pat. No. 4,552,208 describes an apparatus and method for circulating a heat transfer liquid from a heat collector to a heat exchanger which is located at a level below that of the heat collector by at least partially vaporizing the heat transfer liquid in the steeply sloped collector and the vapor/liquid rises in a series of “slugs” to a condenser located adjacent the top end thereof. The vapor is condensed and the hot liquid is forced downwardly to the heat exchanger by the pressure of the rising slugs of vapor and liquid. After giving up useful heat in the heat exchanger the now cooled liquid is recirculated to the condenser and thence to the collector.

U.S. Pat. No. 4,611,654 teaches a passive heat transfer system wherein the vapor generated by the boiling of a working fluid is harnessed to transport the working fluid from a heat source to a heat sink below the heat source. A passive circulation unit is installed in a heat transfer system between the outlet port of a heat collector and a collector drain duct that leads to a heat sink that is positioned below the heat collector. In preferred embodiments, a collector feed duct permits fluid to return to the heat collector from the heat sink and a check valve prevents flow in the opposite direction. The passive circulation unit includes an upper chamber and a lower chamber disposed in vertical array, with the lower end of the lower chamber being positioned above the heat collector outlet port. In the simplest embodiment, the two chambers are connected by a vent duct that leads from the bottom region of the lower chamber to the top region of the upper chamber. The collector drain duct connects to an opening in the lower end of the upper chamber. In a second disclosed embodiment, the passive circulation unit is fitted with a valve that intermittently interrupts the flow of working vapor through the lower chamber and thereby causes working fluid to be displaced into the vent duct and expelled therefrom into the upper chamber in a cyclical manner.

U.S. Pat. No. 4,676,225 describes a geyser pump and a geyser pumped heat transfer system having a multitude of heat absorbing tubes from which heated liquid is pumped into a vapor/liquid separator by geyser action enhanced by positive vapor bubble generation apparatus and flow control methods. A vapor condenser in communication with the separator recovers heat contained in the vapor bubbles and maintains low separator pressure. Pumping starts and stops in response to temperature differences and the pumping rate is proportional to the heating rate. For bubble generation a small volume of the working fluid is isolated in good thermal contact with the absorbing tube and an aperture is formed in communication between the isolated volume and the main volume of working fluid. The small volume of working fluid can be enclosed by inserting into the geyser pump tube a device in the form of a flanged cylinder or a U-shaped tube. Vapor forms readily in the isolated volume and a vapor.+−.liquid interface at the aperture minimizes superheating in the liquid. A directional flow constriction in the absorbing tube which may be in the form of a check valve improves pumping rates and minimizes oscillations which may be produced by the pulsed flow inherent in a geyser pump system. A flow restriction which may be in the form of an orifice or reduced tube diameter moderates peak flow rates by locally and transiently increasing static pressure in expanding bubbles.

U.S. Pat. No. 6,042,342 describes a fluid displacement system having a pressure vessel, an expansion vessel, first and second tubes in fluid communication with the two vessels, and an energy source. Fluid contained within the system is transferred from one vessel to the other by activating the energy source, which in turn generates pressure in the pressure vessel. The generated pressure in the pressure vessel, in turn, displaces the fluid in the expansion vessel.

Each of the above patents teach a proposed solution which is not useful for cryogenic devices, but instead is only useful for the taught application.

None of the above background art references teaches or describes a high pressure pump of the geyser type that is at least partially inserted into a vessel that is capable of delivering a liquid or liquid-gaseous medium at high pressure while maintaining low pressure in the vessel itself. A pumping unit according to the present invention overcomes these drawbacks by providing such a pump that delivers a liquid medium (and/or a liquid-gaseous medium) from a low pressure vessel such that the delivered medium has sufficiently high pressure, by providing the liquid medium in the form of separated pulses. The pump preferably features a conduit embedded into the vessel, such that the proximal end of this conduit is situated in the vicinity to the bottom of the vessel.

By “high pressure” it is meant at least about 1.5 atmospheres, preferably at least about 2 atmospheres and more preferably at least about 10 atmospheres.

The lower section of the conduit is preferably provided with at least a first check valve, which, preferably, is normally open. In addition, the lower (boiling) section of the conduit is preferably provided with an electrical heating element, more preferably of low thermal inertia, and a layer of an outer thermal insulation to reduce heating of the surrounding liquid medium by the electrical heating element. The electrical heating element can be a resistive heating element, or a heating inductive element. The electrical heating element receives pulses of DC or AC, for example preferably from an outer power-control unit.

There is preferably a condensation section of the conduit; this section is situated in immediate vicinity of the aforementioned boiling section and, preferably, in the immediate vicinity of the bottom of the vessel; therefore, this condensation section in the operation state of the pumping means is immersed into the liquid medium in the vessel.

It should be noted that the duration of the electrical heating pulses is preferably significantly less than the time required for vapor that is generated by these pulses to rise to the upper section of the central feeding conduit. Instead, preferably the gas is formed but then cools in the upper section of the central feeding conduit, returning to a liquid state before exiting the conduit. The upper section of the conduit is provided with a second check valve of open or closed types.

As described in greater detail below, an exemplary, non-limiting embodiment of a pump according to the present invention may be provided wherein the vessel is a Dewar flask and the liquid or liquid-gaseous medium is a liquid cryogen. In this case, the pump is called a siphon.

The pumping unit of the present invention comprises a central feeding conduit, which is preferably largely positioned within the Dewar flask such that at least about 50% and more preferably at least about 60%, and most preferably at least about 75% of the central feeding conduit is positioned within the Dewar flask. Its lower section is situated in the Dewar flask and the upper section is located outside the Dewar flask; a sealing unit, preferably in the form of a annular rubber ring, allows installation of the pumping unit in the Dewar flask neck. A section of a tubular piece surrounding the central feeding conduit is joined sealingly with the annular rubber ring. The tubular piece acts as a jacket and will be named in the following text “jacket”.

According to preferred embodiments of the present invention, the central feeding conduit is preferably fabricated from a metal including but not limited to brass, stainless steel etc.

The upper edge of the external conduit or jacket is sealed with the outer section of the central feeding conduit.

Two check valves are installed on the central feeding conduit: a lower check valve and an upper one. The upper check valve can be positioned in the upper or middle internal spaces of the Dewar flask or outside the Dewar flask. The lower check valve is positioned near the lower end of the central feeding conduit.

The upper check valve may optionally be either of the type that is normally closed or normally open, and the lower check valve may optionally be of the normally closed type or of the normally open type. When the first or lower check valve is open, cryogen enters into the central feeding conduit via this first check valve under hydrostatic pressure of the cryogen in the Dewar flask.

Preferably an electrical heating element is positioned on the central feeding conduit in the immediate vicinity of the lower check valve and somewhat above it. This electrical heating element is preferably of low thermal inertia.

The electrical heating element may optionally be of the resistive and/or electromagnetic inductor types. In the second case, the section of the central feeding conduit, which is surrounded by the electromagnetic inductor, preferably contains elements from ferromagnetic material. In such a way, in the second case, the electrical heating element consists of the inductor and the ferromagnetic tubular section of the central feeding conduit surrounded by the inductor.