Method for Cooling a Detector

Abstract

A detector, in particular an IR detector in the seeker head of a guided missile, is cooled with expanding gas generated by depressurizing a pressurized fluid. A mixture which forms a positive azeotrope, including argon or nitrogen as a main component and at least one alkane as a secondary component, is expanded as the fluid. The composition is preferably in the region of a eutectic mixture in order to avoid a component freezing adjacent to the expansion nozzle. This makes it possible to considerably extend the life of the cooler in comparison to that when using pure cooling gases such as nitrogen or argon, and to cool the detector down more quickly, subject to the same constraints.

1 . A method of cooling a detector, the method which comprises:
 providing a pressurized fluid, the pressurized fluid being a mixture of argon or nitrogen as a main component and at least one alkane as a secondary component, the mixture forming a positive azeotrope; and   expanding the pressurized fluid and using an expanding gas to cool the detector.   
   
   
       2 . The method according to  claim 1 , which comprises cooling an IR detector in a seeker head of a guided missile. 
   
   
       3 . The method according to  claim 1 , wherein a boiling point of the azeotrope is below 100 K. 
   
   
       4 . The method according to  claim 3 , wherein the boiling point of the azeotrope lies below 90 K. 
   
   
       5 . The method according to  claim 1 , which comprises expanding a mixture with an azeotrope having a composition in a vicinity of a eutectic composition thereof. 
   
   
       6 . The method according to  claim 1 , which comprises choosing the components of the mixture to be completely soluble in one another in a condensed liquid phase, with at least one liquid component being soluble in another liquid component. 
   
   
       7 . The method according to  claim 5 , wherein the eutectic composition of the mixture has a melting point below 90 K. 
   
   
       8 . The method according to  claim 1 , which comprises providing the pressurized fluid at a pressure of more than 100 bar. 
   
   
       9 . The method according to  claim 1 , which comprises providing the pressurized fluid at a pressure of more than 300 bar. 
   
   
       10 . The method according to  claim 1 , which comprises providing the pressurized fluid at a pressure of above 800 bar. 
   
   
       11 . The method according to  claim 8 , which comprises choosing an initial pressure of the mixture such that partial pressures of individual gases are in a pressure range of a respective optimum integral Joule-Thomson coefficient of each individual gas corresponding to a molar composition in the mixture. 
   
   
       12 . The method according to  claim 8 , which comprises providing a mixture of 30-70% by volume of nitrogen and 20-80% by volume of methane. 
   
   
       13 . The method according to  claim 1 , which comprises providing a mixture comprising 20-70% by volume of nitrogen, 20-40% by volume of methane, and 10-40% by volume of ethane. 
   
   
       14 . The method according to  claim 13 , wherein the mixture comprises 30-70% by volume of nitrogen, 15-35% by volume of ethane, and 15-35% by volume of propane. 
   
   
       15 . The method according to  claim 1 , wherein the mixture comprises 20-70% by volume of nitrogen, 10-30% by volume of methane, 10-25% by volume of ethane, and 10-25% by volume of propane. 
   
   
       16 . The method according to  claim 1 , wherein the mixture comprises 45-60% by volume of argon and 35-50% by volume of methane. 
   
   
       17 . The method according to  claim 1 , which comprises temperature-stabilizing the pressurized fluid. 
   
   
       18 . The method according to  claim 17 , which comprises stabilizing the fluid at a temperature above room temperature. 
   
   
       19 . The method according to  claim 17 , which comprises expanding the fluid from a pressurized bottle, and stabilizing the temperature of the fluid by way of a heating element acting on the pressurized bottle. 
   
   
       20 . The method according to  claim 1 , which comprises admixing between 5 and 15% by volume of heptafluoropropane to the fluid as a further component. 
   
   
       21 . The method according to  claim 1 , which comprises admixing between 3 and 20% by volume of tetrafluoromethane to the fluid as a further component. 
   
   
       22 . The method according to  claim 1 , which comprises conducting the expanded gas to flow in counterflow to the pressurized fluid prior to expansion, to thereby cool the pressurized fluid. 
   
   
       23 . The method according to  claim 1 , which comprises expanding a further pressurized fluid to form a further expanding gas, and cooling the pressurized fluid with the further expanding gas prior to expanding the pressurized fluid. 
   
   
       24 . The method according to  claim 23 , which comprises conducting the further expanded gas of the further pressurized fluid flows in counterflow to the pressurized fluid for cooling the pressurized fluid. 
   
   
       25 . The method according to  claim 23 , which comprises conducting the further expanded gas in counterflow to the further pressurized fluid, to cool the further pressurized fluid prior to expanding the further pressurized fluid. 
   
   
       26 . The method according to  claim 23 , which comprises spraying the expanding gas of the fluid against the detector. 
   
   
       27 . The method according to  claim 23 , wherein the further pressurized fluid is tetrafluoromethane. 
   
   
       28 . The method according to  claim 23 , which comprises using a common fluid for the pressurized fluid and the further pressurized fluid.