US 3750414 A
A cryogenic device incorporates a liquid storage vessel from near the bottom of which a transfer passage leads to a closed cryogenic chamber having an exhaust passage closable by a liquid level sensitive device in the closed chamber. A heat sink is in heat-exchanging relation with the transfer passage. A by-pass pipe in which a shut-off valve is intercalated connects the upper part of the liquid storage vessel to the transfer passage.
Claims available in
Description (OCR text may contain errors)
United States Patent [1 1 [111 3,750,414 Heftman [4 1 Aug. 7, 1973 1 CRYOGENIC DEVICE FOR COOLING 3,418,822 12/1968 Massey 62/52 OBJECTS 3,126,711 3/1964 Miller 62/52  Inventor: George Hettman, Hatch End,
England  Assignee: The Rank Organization Limited,
London, England  Filed: Sept. 16, 1971 [2!] Appl. No.: 181,111
 Foreign Application Priority Data Sept. 16, 1970 Great Britain 44,106/70  US. Cl. 62/55, 62/514  Int. Cl. Fl7c 7/02  Field of Search 62/514, 50, 52, 54, 62/55  References Cited UNITED STATES PATENTS 3,440,829 4/1969 Davis-White 62/55 FOREIGN PATENTS OR APPLICATIONS 929,795 1/1960 Great Britain 62/52 Primary Examiner-Meyer Perlin Assistant Examiner-Paul Devinsky Attorney-Holcombe, Wetherill & Brisebois  ABSTRACT A cryogenic device incorporates a liquid storage vessel from near the bottom of which a transfer passage leads to a closed cryogenic chamber having an exhaust passage closable by a liquid level sensitive device in the closed chamber. A heat sink is in heat-exchanging relation with the transfer passage. A by-pass pipe in which a shut-off valve is intercalated connects the upper part of the liquid storage vessel to the transfer passage.
3 Claims, 2 Drawing Figures PATENTEUAUB H973 SHEET 1 BF 2 PAIENTEWn H975 SHEEI 2 BF 2 1 CRYOGENIC DEVICE FOR COOLING OBJECTS This invention relates to cryogenic devices and particularly to devices for cooling instruments which perform best at very low temperatures. As an example it may be remarked that infrared detectors for certain purposes require to be cooled to the temperature of liquid notrogen.
Such a known device referred to as a Liedenfrost system and illustrated diagrammatically in FIG. 1 of the accompanying drawings incorporates a closed liquid gas storage vessel 1, a closed cryogenic chamber 2 arranged to contain an article 3 to be cooled, a transfer passage 4 leading from near the bottom of the storage vessel 1 into the cryogenic chamber 2, a liquid level sensitive devices in the cryogenic chamber 2 constituted by a float valve 5 operative to close an exhaust passage 6 at a given level of liquid in the chamber, and a heat sink 7 in heat-exchanging relationship with the transfer passage 4. 8 denotes a quantity of a cryogenic liquid in the vessel 1. Usually the storage vessel 1 is fitted with a pressure relief valve 9 set to open automatically at a predetermined pressure.
In operation of the Liedenfrost system as described and illustrated a quantity of a cryogenic liquid, for example liquid nitrogen, is put into the storage vessel. The liquid absorbs heat from the surroundings and begins to boil so that the space in the vessel above the liquid becomes filled with gas. The gas pressure in the vessel l rises until it reaches the pressure at which the relief valve 9 is set to open whereupon the pressure in the vessel 1 remains constant. The pressure on the surface of the liquid 8 forces liquid to rise of the transfer passage 4 and to enter the heat sink 7. Here some of the liquid in the passage 4 boils. With a properly chosen setting of the relief valve 9, the correct setting being determined mainly by the dimensions of the storage vessel 1 and the transfer pipe 4 and the ambient temperature, gas produced in the transfer passage 4 at the heat sink 7 by boiling of liquid in the transfer passage 4 carries with it droplets of liquid into the cryogenic chamber 2 where the droplets combine to produce a liquid content in the cryogenic chamber 2. The liquid level in the chamber 2 rises until the float valve 5 operates to'close the exhaust passage 6 whereupon the pressure rises in the chamber 2 until it becomes high enough to stop the further movement of liquid through the transfer passage 4. A drop in liquid level in the chamber 2 causes the float valve 5 to open the exhaust passage 6 whereupon the pressure in the chamber 2 is released. The pressure in the vessel 1 thereupon forces more liquid into the chamber 2. By this mechanism the liquid in the chamber 2 is maintained at the desired level while there is liquid in the vessel 1.
The described Liedenfrost system suffers from the disadvantage that water gradually accumulates in the chamber 2 and in sufficient quantity can impair the efficiency and effectiveness of operation of the system and even cause the chamber 2 to break by freezing therein. The water is deposited by liquid gas coming over from the vessel 1. The water becomes mixed with the stored liquid principally by condensing therein from the atmosphere while the storage vessel 1 is being filled. Although there may not be a great deal of water present in each filling of the vessel 1 all the water in successive fillings of the vessel 1 is transferred-to the chamber 2 and accumulates there.
It is an object of the present invention to provide an improved device which is arranged to operate on the Liedenfrost principle but which is free from the trouble of water accumulation in the cryogenic vessel.
According to the invention a cryogenic device of the type described incorporates a by-pass passage one end of which terminates in the upper part of the vessel at a point above the normal level of liquid in the vessel and the other end of which terminates at the transfer passage, and a shut-off valve intercalated in the by-pass passage.
Conveniently the vessel is closed by a lid incorporating a plug through which the transfer passage passes, the plug being fitted with heat-absorbing tins and functioning as the heat sink. The plug may incorporate the pressure relief valve, the by-pass passage and the shutoff valve.
Alternatively the by-pass passage may be consitituted by an extenral pipe in which the shut-off valve is fitted.
A practical embodiment of the invention is illustrated in FIG. 2 of the accompanying drawings in which the parts already illustrated in FIG. I are indicated by the same reference numerals.
In FIG. 2, 10 denotes a by-pass passage connected at one end into the upper part of the vessel by way of the heat sink 7 and at the other end into the transfer passage 4. 11 denotes a shut-off valve intercalated in the by-pass passage 10.
In normal operation of the device according to the invention the shut-off valve 11 is closed and cryogenic liquid is transferred from the vessel 1 to the chamber 2 at the required rate in the manner described in connection with the known device of FIG. I. At the end of each period of use the device is put outof action by opening the valve 11. This has the effect of equalizing the pressure in the vessel 1 and the transfer passage 4 and liquid is then no longer tranferred from the vessel 1 to the chamber 2. The liquid level in the chamber 2 soon drops and the float valve 5 opens the exhaust passage 6. Because the valve 11 is now open gas from the upper part of the vessel ll now flows into the chamber 2 and out through the exhaust passage 6. This gas is completely dry because any water present in the vessel 1 is in condensed form in the liquid because of the low temperature of the liquid. The dry gas flowing through the chamber 2 evaporates any water therein and carries the water vapour away-with it as it escapes through the exhaust pipe 6. The water content of the chamber 2 is thus reduced or completely removed by the time the device is next brought into service by closing the valve ll.
Preferably enough liquid is put into the vessel 1 to last a period of 24 hours which includes the normal periot! in service with the remainder of the 24 hours being the drying period during which gas from the vessel 1 flows through the chamber 2.
What is claimed is:
1. In a cryogenic device comprising a closed gas storage vessel for holding a supply of liquefied gas beneath a layer of gas in the gaseous state, a closed cryogenic chamber, a transfer passage leading into said cryogenic chamber from a point near the bottom of said storage vessel covered by said liquefied gas during normal operation of said device, an exhaust passage leading from the cryogenic chamber, a liquid level sensitive device in the cryogenic chamber operative to close the exhaust passage when a predetermined liquid level in said through which the transfer passage passes, the plug being arranged to function as the heat sink and incorporating a pressure relief valve, and the by-pass passage with the shut-off valve.
3. A device as claimed in claim 1 in which the by-pass passage is constituted by an external pipe in which the shut-off valve is fitted.
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