Abstract:
A LN 2  maintenance system is provided. The maintenance system includes an input sensor and a solenoid. The input sensor is adapted to monitor the temperature of the medium in an input tube to a device using the LN 2 . The solenoid is adapted bleed off the medium based on the monitored temperatures.

Description:
BACKGROUND  
       [0001]     Liquid nitrogen (LN 2 ) is used for many applications in industry because of its thermal characteristics. In large systems, the LN 2  is usually sourced from a large reservoir located far away from the device that uses the LN 2 . One problem with this delivery method is that the LN 2  can begin to boil off in the delivery lines. Even with vacuum jacket lines, if the line is not used often, the LN 2  will begin to boil off in the line and turn to gas nitrogen (GN 2 ). Moreover, the last few feet of lines carrying the LN 2  into the device are typically plumbed with copper tube that is at room temperature. At room temperature LN 2  will boil off into GN 2  in a relatively rapid fashion.  
         [0002]     Because of this boiling off of the LN 2 , when a device requests a flow of LN 2  all the GN 2  in the supply lines must first be vented off before the flow of LN 2  can be delivered. In systems that use LN 2  for process control, such as fluids carts or chambers, the delay caused by the required venting of the GN 2  can cause major temperature oscillations resulting in unacceptable performance. In addition, waiting for the LN 2  to arrive can add up to twenty minutes per cycle resulting in added cycle time and more cost.  
         [0003]     For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a an efficient and effective system and method of removing or preventing GN 2  in an LN 2  delivery system.  
       SUMMARY OF INVENTION  
       [0004]     The above-mentioned problems of current systems are addressed by embodiments of the present invention and will be understood by reading and studying the following specification.  
         [0005]     In one embodiment, an LN 2 maintenance system is provided. The maintenance system includes an input sensor and a solenoid. The input sensor is adapted to monitor the temperature of the medium in an input tube to a device using the LN 2 . The solenoid is adapted bleed off the medium based on the monitored temperatures.  
         [0006]     In another embodiment, a liquid nitrogen (LN 2 ) system is provided. The system comprises an input tube, an input sensor, and a solenoid. The input tube is used to provide a flow of LN 2  to a device. The input sensor is adapted to measure the temperature in the input tube. The solenoid is adapted to selectively bleed off a medium in the input tube during idle periods of the device based on the measured temperatures.  
         [0007]     In yet another embodiment, a method of maintaining a supply of a medium in a first state is provided. The method includes measuring the temperature of the medium in an input tube. Comparing the measured temperature with a reference temperature and when the measured temperature is above the reference temperature, bleeding off the medium in the input tube.  
         [0008]     In still another embodiment, a liquid nitrogen (LN2) maintenance system is provided. The system includes a means to automatically bleed off gas nitrogen (GN2) in an input tube during idle periods of a device using the LN 2  so that LN2 is available relatively instantaneously upon activation of the process control chamber. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]     The present invention can be more easily understood and further advantages and uses thereof more readily apparent, when considered in view of the description of the preferred embodiments and the following figures in which:  
         [0010]      FIG. 1  is an illustration of a LN 2  system of the present invention; and  
         [0011]      FIG. 2  is a flow chart illustrating one method of an embodiment of the present invention. 
     
    
       [0012]     In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the present invention. Reference characters denote like elements throughout Figures and text.  
       DETAILED DESCRIPTION  
       [0013]     In the following detailed description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the inventions may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that logical, mechanical and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the claims and equivalents thereof.  
         [0014]     Embodiments of the present invention provide an efficient and effective method of providing LN 2  to system. In particular, in embodiments of the present invention, a small amount of LN 2  and/or GN 2  is automatically bled off during idle periods so that GN 2  does not have time to build up in an input tube. By doing this, LN 2  is available immediately when requested in the chamber.  
         [0015]     Referring to  FIG. 1 , an illustration of a LN 2  system  100  of one embodiment of the present invention is provided. As illustrated,  FIG. 1  includes a chamber  104  for process control. An input tube  102  is used to plumb LN 2  into the chamber  104 . In one embodiment, the input tube is a copper tube having an input  112  to receive a flow of LN 2  from vacuum jacket lines (not shown) and an output  114  to output the flow of LN 2  to the chamber  104 . The LN 2  system includes a LN 2  maintenance system. The maintenance system includes a control input sensor  108 , a controller  106  and a solenoid  110 . The control input sensor  108  is in contact with input tube  102 . The control input sensor  108  measures the temperature of the medium (gas or liquid) in the input tube  102 . The control input sensor  108  is in communication with the controller  106 . The controller  106  is coupled to the solenoid  110 . The solenoid  110  selectively bleeds GN 2  from the input tube  102  under the control of the controller  106  when the system is idle. In particular, the controller  106  activates the solenoid  110  to bleed of the medium (LN 2  or GN 2 ) in the input tube  102  when the input sensor  108  senses a temperature that indicates a gas is in the input tube  102 . In one embodiment, the medium is bleed off through and exhaust tube  116 . In another embodiment, the medium is simply bled off into the chamber  104 . The heaters in the chamber  104  can easily overcome the effects of the medium during its hot dwell. This embodiment allows for fewer moving parts and allows the system to be retrofitted to existing systems. Moreover, in an embodiment in which the medium is bled off into the chamber, the medium can be used to cool the chamber off by bleeding off small amounts of the medium.  
         [0016]     The LN 2  system described above in relation to a chamber  104  is made by way of example and not be limitation. Many different types of devices that use LN 2  can utilize embodiments of the LN 2  maintenance system of the present invention. Another example is a fluid chiller where the LN 2  conditions a fluid that is circulated in a closed loop.  
         [0017]     Referring to  FIG. 2 , a flow chart  200  illustrating one method of the present invention is provided. As illustrated in  FIG. 2 , the process starts by monitoring the temperature of the medium in the input tube ( 202 ). In embodiments of the present invention this is done with an input sensor  108  that is coupled to measure the temperature of the medium in the input tube  102 . In one embodiment, the input sensor  108  is simply in thermal communication with a portion of the input tube  108 . In another embodiment, the input sensor  108  is in direct thermal contact with the medium in the input tube  108 .  
         [0018]     Temperatures sensed by the input sensor  108  are compared by the controller  106  to a stored reference temperature ( 204 ). In embodiments of the present invention, the reference temperature is selected to ensure gas will not build up in the input tube  102 . In one embodiment, the reference temperature is the temperature in which a liquid changes to a gas. In another embodiment, the reference temperature is a temperature near the temperature in which the liquid changes to a gas. If a sensed temperature is below the reference temperature ( 204 ), the input sensor  108  continues to monitor the medium ( 202 ). If a sensed temperature is above the reference temperature ( 204 ), the solenoid  110  is activated to bleed off the medium ( 206 ). As illustrated in  FIG. 2 , the process continues by monitoring the temperature of the medium ( 202 ).  
         [0019]     When the system  100  is using the LN 2  for process control, the solenoid  110  will not bleed any LN 2  because the temperature of the medium (which will be LN 2 ) will be below the reference temperature. Hence, the present invention will only bled off small amounts of LN 2  during periods of idle time. Moreover, embodiments of the present invention control the temperature at the inlet to the system. When the supply line is completely full of GN 2 , the embodiments of the present invention will bleed the GN 2  at full power. Once the LN 2  arrives at the inlet (input tube  102 ), the embodiments will only bleed the LN 2  at a rate necessary to maintain it at the input tube  102 . Accordingly, embodiments of the present invention provide an efficient and effective bleeding system that is free from operator input. In addition in systems sourced by long LN 2  feed lines, the present invention is critical for performance.  
         [0020]     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present invention. For example, other systems requiring a medium of a first state could use the above embodiments. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.