GAS BUBBLE REMOVAL FROM CAVITY COOLING LIQUID

Abstract: Method of cooling cavities in which the heat producing means are submerged in liquid coolant in which gas bubbles form which comprises applying a reduced pressure in the cavity (1) through a flow line (9) to a low pressure area (12) beyond the cavity in relation to the fluid flow.

Description: GAS BUBBLE REMOVAL FROM CAVITY COOLING LIQUID This invention relates to a method of cooling cavities, particularly laser cavities, and in parti¬ cular, though not exclusively, it relates to portable laser systems. 5 , Efficiencies of the Neodymium YAG lasers commonly used, for instance as laser target designators, are generally low such as 1 to 1.57 0 leaving a large amount of electrical energy supplied to the lamp to be removed as heat. For this purpose the laser 10. cavity is filled with a cooling fluid, which in the case of portable lasers especially may be high purity water, circulated by an electrically driven pump. One of the problems with maintaining good coolant 15 , circulation is that gases are inevitably dissolved in the coolant and come out of solution preferentially in the cavity where the temperatures are highest and these gases collect, in region at the top of the cavity in which the laser rod and its pumping lamp 20. operate. With increasing volume of gas this results successively in uneven illumination of the laser rod, distortion and loss of efficiency due to uneven rod cooling, and finally damage to the rod and cavity 5 , wall coatings due to excessive temperatures. To avoid difficulties due to gas bubbles entrained in a liquid used for cooling, it has been proposed heretofore, see the Specification of United States Patent No. 4,197,512 Luc Breuac, assigned to Society Anonyme dite: Compagnie Industrielle des Lasers, in which the domes of a laser cavity have membranes which are impermeable to the cooling liquid but permeable to the gas so that the gas can be forced 5. from the system because of the pressure in the system. It is possible that the flushing of gas from a cavity can be achieved by high speed pump operation but this is not generally practical and in portable battery power equipped laser devices this is not 10. an appropriate solution. The object of the present invention is to provide a method of removing gas bubbles from the cooling fluid in laser installations, the invention being not necessarily limited however to portable or battery 15. powered equipment or to lasers but applies where a cavity has a flow of cooling liquid through it which flows over the heat producing components. The object of the invention is achieved by utilizing ducts in the housing system of the heat 20. producing members which open to gas collecting regions, at least at one portion of the cavity, to allow gases to be withdrawn from these regions, the duct leading to an area where a reduced pressure exists in relation to the pressure of the coolant in the housing. This 25. may be achieved by using a junction or a venturi at or adjacent the cooling fluid outlet from the housing. By means of such an arrangement flow is induced in the duct by the flow of the coolant and this 30. flow draws the bubbles out of the cavity and it is found in practice that the cavity remains free of air bubbles so long as coolant flow is continued without having to pump excessive amounts of coolant through the system. The fact that the cavity remains completely 5. filled with coolant due to this gas draw-off system ensures that the heat producing members operate without damage and other problems referred to earlier herein. The invention thus relates to a method of cooling 10. cavities in which the heat producing means in the cavity are submerged in a liquid coolant caused to flow through the cavity and in which the liquid coolant enters the cavity at a first region and leaves same at a second region, characterised by applying 15. a reduced pressure, relative to the pressure in the said cavity, to duct means communicating with the cavity at least at an elevated zone of the cavity where gas bubbles tend to collect, generating a reduced pressure in the duct means, and drawing 20. the gas bubbles, together with liquid coolant, through the duct means and discharging at least the liquid coolant back to the coolant supply at a point beyond the cavity where a lower pressure exists than in the cavity. 25. The means comprise inlet means to the cavity, for the liquid coolant, outlet means from the cavity, for the liquid coolant, a duct from the area of the cavity where gas bubbles tend to collect to a part of the liquid coolant circuit beyond the 30. cavity where a lower pressure exists than in the cavity, whereby the reduced pressure draws the bubbles, together with some liquid coolant from the cavity ^NATl and discharges same into the liquid coolant circuit beyond the cavity. In order however that the invention will be more fully appreciated an embodiment thereof is 5. described herein with reference to the accompanying drawings in which: FIG. 1 is a schematic view of a system using the invention, and FIG. 2 is central longitudinal sectional view 10. of a laser assembly using a venturi to achieve the reduced pressure to draw the gas bubbles from the upper part of the cavity in the housing. Referring first to FIG. 1, the cavity 1 of the housing 2 has in it the heat generating means 15. such as a laser rod 3 and optical pump 4. To dissipate the heat, liquid coolant from a tank 5 is caused by the pump 6 to flow through the line 7 into and through the cavity 1 back to the tank 5 through the line 8, but a lower pressure 20. area of the system is connected by the flow line 9 to the upper part 10 of the cavity 1 which is the area in which the gas bubbles collect. The lower pressure area 12 may be achieved by using a venturi in the line 8 leading from the 25. cavity 1 back to the tank 5, the gas being drawn from the cavity through the extraction apertures 13 and duct 14 to the flow line 9 and thus to the venturi and is then carried to the tank 5 through the line 8. OH* &RNA Instead of using a venturi it is possible to connect the flow line 9 to the line 8 with a simple junction. Instead of connecting to line 8 it is possible 5. to connect the flow line directly to the tank 5 as indicated by the line 15 shown by chain lines. In a battery powered laser installation it is convenient to use the arrangement shown in FIG. 2, in which similar reference numerals are used. 10. In this form the laser rod 3 and the optical pump 4 are mounted in the cavity 1 formed within the housing 2, and both the optical pump 4 and the laser rod 3 are sealed into the cavity by 0-rings 17. The cavity 1 is supplied with the coolant, 15. which is preferably high purity water, through an inlet 20 and flows thence through the cavity 1 and leaves the cavity 1 through an outlet 21 which has the low pressure area 12, in the form of a venturi, formed in it to give an area of reduced pressure 20. at the immediate outlet from the housing 2. Forming part of the housing 2 is the duct 14 which opens into the cavity 1 through the two extraction apertures 13 and if required may also have further openings into the cavity 1, and this duct 14 communi- 25. cates with the flow line 9 which opens into the outlet 21 through the low pressure area 12, that is it opens at the area where the flow of coolant causes a reduced pressure so that the pressure within the cavity 1 is higher than the pressure in the 30. flow line 9, the action of this being, as the coolant Oh' . WIP * *R« NA flows through the chamber, to draw any gas bubbles trapped in it, which normally remain relatively static in the upper part of the cavity 1, back into the coolant supply externally of the cavity 1. 5. From the invention it will be seen that because of the low pressure zone in the upper part of the cavity, effective scavenging with moderate flow rates of the coolant results even if the cavity is tilted, thus reducing coolant pumping power require- 10. ments as required for instance with battery operation. In the drawings the full line arrows show coolant flow direction, while the dotted line arrows show the path of the gas bubbles.

Claims: THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. The method of cooling cavities in which the heat producing means in the cavity are submerged in a liquid coolant caused to flow through the cavity and in which the liquid coolant enters the cavity 5. at a first zone and leaves same at a second zone, characterised by: (a) applying a reduced pressure, relative to the pressure in the said cavity, to duct means communicating with the cavity 10. at least at an upper part of the said cavity where gas bubbles tend to collect, (b) generating a reduced pressure in the said duct means, and (c) drawing the gas bubbles, together with 15. liquid coolant, through the said duct' means and discharging the same back to the said coolant circuit at a point beyond the said cavity where a lower pressure exists than in the said cavity. 2. The method of claim 1 further characterised by passing the said liquid coolant through a venturi beyond the said cavity whereby to produce the said lower pressure than that existing in the said cavity. 3. Means for cooling cavities in which heat-producing means are submerged in a liquid coolant flowing through a cavity and in which the said cavity has a region in which gas bubbles collect, the structure 5. being characterised by: (a) inlet means to the said cavity, for the said liquid coolant, (b) outlet means from the said cavity, for the said liquid coolant 10. (c) a duct from the said gas collecting region of the said cavity to a part of the liquid coolant circuit beyond the said cavity where a lower pressure exists than in the said cavity, whereby said reduced pressure 15. draws the said bubbles, together with some liquid coolant from the said cavity, and discharges same into the said liquid coolant circuit beyond the said cavity. 4. Means for cooling cavities according to claim 3 further characterised by a junction in the said liquid coolant circuit arranged to generate the said lower pressure to withdraw the said bubbles with some 5. liquid coolant from the said cavity. 5. Means for cooling cavities according to claim 4 wherein the said junction is a venturi positioned at the said outlet means to be actuated by the liquid coolant flow through the said outlet means. 6. Means for cooling cavities according to claim 3 applied to laser cavities having a laser rod and optical pumping means for the said laser rod and having means to circulate the liquid coolant through 5. the said cavity, characterised by a housing defining the said cavity, liquid coolant inlet means to the said housing, liquid coolant outlet means from the said housing spaced from the said inlet means, means to form a low pressure zone at or adjacent the said outlet 10. means, and at least an extraction aperture in the upper part of the said housing communicating with a duct connected by a flow line with the said low pressure zone whereby the said low pressure zone draws gas bubbles and some liquid coolant from the said cavity and injects it 15. into the liquid coolant beyond the said cavity through the said outlet means. 7. Means according to claim 6 characterised in that the said low pressure zone at or adjacent the said outlet is a junction. 8. Means according to claim 7 characterised in that the said low pressure zone at or adjacent the said outlet is a venturi. 9. Means for cooling cavities according to claim 3 applied to laser cavities having a laser rod and optical pumping means for the said laser rod and having means to circulate the liquid coolant through 5. the said cavity, characterised by a housing defining the said cavity, said liquid coolant inlet means being disposed at one end portion of the said housing, said liquid coolant outlet means being disposed at the other end portion of said housing, a tank to contain the 10. liquid coolant, pump means to circulate the said liquid coolant through the said cavity and return same to the said tank, at least one extraction aperture in the said housing communicating with a flow line connected to said tank independently of the circuit through which the said 15. liquid coolant is pumped whereby the said gas bubbles and some liquid coolant are discharged from the said cavity to the said tank. 10. Means for cooling cavities constructed and operating substantially as described and illustrated with reference to the accompanying drawings.

Inventors: O'CONNOR GRAHAM GEOFFREY, TAYLOR DONALD, O'CONNOR, GRAHAM, GEOFFREY, TAYLOR, DONALD
Applicants: COMMW OF AUSTRALIA, THE COMMONWEALTH OF AUSTRALIA CARE OF THE SECRETAR
Application year: 1984
Main classification: G12B15
IPC codes: G12B15, H01S3