Patent Publication Number: US-2023146746-A1

Title: Thermal conductivity detector

Description:
TECHNICAL FIELD 
     The present invention relates to a thermal conductivity detector which is one of detectors used for detecting components in a gas chromatograph. 
     BACKGROUND OF THE INVENTION 
     A thermal conductivity detector is known as one of the detectors used in a gas chromatograph. A thermal conductivity detector is provided with a filament arranged in a measurement cell through which a gas flows. A thermal conductivity detector quantifies the components in the gas by detecting the heat exchange amount between the filament and the gas. The heat exchange amount between the filament and the gas varies depending on the flow rate of the gas flowing through the measurement cell. Therefore, when the flow rate of the gas flowing through the measurement cell fluctuates, the baseline of the measurement data will also fluctuate, resulting in adverse effects of the analytical result. 
     For the reasons described above, it is important to keep the flow rate of the gas flowing through the measurement cell constant. A variation in the atmospheric pressure is one of factors that cause the change in the flow rate of the gas flowing through the measurement cell. Since the outlet of the measurement cell is open to the atmosphere, the pressure difference between the inlet of the measurement cell and the outlet thereof fluctuates as the atmospheric pressure fluctuates, thereby causing fluctuations of the flow rate of the gas flowing through the measurement cell. Considering the above, the following proposal has been made. That is, a buffer space is provided downstream of the measurement cell, and a constant fluid resistance is provided at the outlet of the buffer space. This prevents atmospheric pressure fluctuations from being transmitted to the outlet of the measurement cell, thereby suppressing pressure fluctuations at the outlet of the measurement cell to stabilize the baseline of the measurement data (see Patent Document 1). 
     PRIOR ART DOCUMENT 
     Patent Document 
     
         
         Patent Document 1: Japanese Unexamined Patent Application Publication No. 2016-080413 
       
    
     SUMMARY OF THE INVENTION 
     Problems to be Solved by the Invention 
     In the case of providing a buffer space downstream of the measurement cell, the larger the volume of the buffer space and the larger the fluid resistance of the outlet of the buffer space, and therefore, the suppression effect of the pressure fluctuations at the outlet of the measurement cell can be enhanced, thereby stabilizing the baseline. On the other hand, in the case of providing a buffer space with a large capacity downstream of the measurement cell, the detector becomes larger in size. To stabilize the baseline while reducing the capacity of the buffer space, it is required to increase the fluid resistance by, for example, reducing the flow path inner diameter of the outlet of the buffer space. However, when the fluid resistance at the outlet of the buffer space is increased, a sample is likely to be clogged at the portion. 
     The present invention has been made in view of the above-described problems and aims to achieve both the stabilization of the baseline and the miniaturization of the detector. 
     Means for Solving the Problems 
     A thermal conductivity detector according to the present invention includes: 
     a cell block provided therein with a measurement cell serving as a space in which a filament for exchanging heat with a gas is arranged, the cell block being provided with a cell inlet for introducing the gas into the measurement cell and a cell outlet for flowing out the gas from the measurement cell; 
     an outlet flow path communicated with the cell outlet of the cell block; 
     a buffer block provided therein with a buffer space, the buffer block having an inlet port for introducing the gas into the buffer space and a discharge port for discharging the gas from the buffer space, the inlet port being fluidly connected to the outlet flow path; and 
     a discharge member retaining a fluid resistance portion for increasing fluid resistance of the discharge port, the discharge member being attached to the buffer block such that the gas discharged from the discharge port passes through the fluid resistance portion, the discharge member being configured to be detachable from the buffer block together with the fluid resistance portion. 
     The subject matter of the present invention is to make it easy to replace a fluid resistance portion when clogging has occurred in the fluid resistance portion for increasing the fluid resistance of the outlet port of the buffer space. Here, examples of the fluid resistance portion include a resistance tube and a filter. In a case where the fluid resistance portion is realized by a resistance tube, it is required to attach a fine resistance tube having an outer diameter of equal to or less than 1 mm depending on the reduction in the buffer space volume to the buffer block. However, such a fine resistance tube cannot be attached to the discharge port of the buffer space in the same connection method as that for a typical pipe. In the present invention, it is configured such that the fluid resistance portion is retained by the discharge member detachably attached to the buffer block, and the fluid resistance portion is detachably attached to the buffer block by detachably attaching the discharge member to the buffer block. 
     Effects of the Invention 
     As described above, in the thermal conductivity detector according to the present invention, it is configured such that the fluid resistance portion is retained by the discharge member detachably attached to the buffer block, and the fluid resistance portion can be detachably attached to the buffer block by detachably attaching the discharge member to the buffer block. Therefore, when clogging has occurred in the fluid resistance portion, the fluid resistance portion can be easily replaced, which in turn can realize both the stabilization of the baseline and the miniaturization of the detector. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a cross-sectional view showing one example of a thermal conductivity detector. 
         FIG.  2    is a cross-sectional view showing a structure of a discharge member of the same example. 
         FIG.  3    is a cross-sectional view schematically showing another example of a thermal conductivity detector. 
         FIG.  4    is a cross-sectional view schematically showing still another example of a thermal conductivity detector. 
     
    
    
     EMBODIMENTS FOR CARRYING OUT THE INVENTION 
     Hereinafter, some embodiments of a thermal conductivity detector according to the present invention will be described with reference to the attached drawings. 
     As shown in  FIG.  1   , the thermal conductivity detector  1  includes a cell block  2 , an outlet pipe  4 , a buffer block  6 , and a discharge member  8 . 
     The cell block  2  is provided therein with a measurement cell  10  in which a filament  12  is arranged. The cell block  2  is provided with a cell inlet  11  for introducing a gas into the measurement cell  10  and a cell outlet  13  for flowing out the gas from the measurement cell  10 . One end of the outlet pipe  4  serving as an outlet flow path is fluidly connected to the cell outlet  13  of the cell block  2 . The filament  12  is for exchanging heat with the gas flowing through the measurement cell  10 . The thermal conductivity detector  1  quantifies the components contained in the gas by reading the signal corresponding to the heat exchange amount between the gas flowing through the measurement cell  10  and the filament  12 . 
     The buffer block  6  is provided therein with a buffer space  14 . The buffer block  6  is further provided with an inlet port  15  for introducing the gas into the buffer space  14  and a discharge port  16  for discharging the gas from the buffer space  14 . The other end of the outlet pipe  4  is fluidly connected to the inlet port  15  of the buffer block  6 . The inner cross-sectional area of the buffer space  14  perpendicular to the inflow direction of the gas from the inlet port  15  is greater than the cross-sectional area of the inner side flow path (i.e., outlet flow path) of the outlet pipe  4  perpendicular to the flow direction. The discharge member  8  is detachably attached to the buffer block  6 . 
     Note that in  FIG.  1   , only one measurement cell  10  is shown inside the cell block  2 . However, two measurement cells  10 , i.e., a measurement cell for a sample gas and a measurement cell for a reference gas, may be provided within the cell block  2 . In a case where two measurement cells  10  are provided in the cell block  2 , these two measurement cells  10  may be fluidly connected to a common buffer space  14 , or two buffer spaces  14  may be provided in the buffer block  6 , and the two measurement cells  10  may be fluidly connected to the respective separate buffer spaces  14 . 
     As shown in  FIG.  2   , the discharge member  8  is provided with a resistance tube  20 , a retaining member  22 , a fixing member  24 , and a seal ring  26 . The resistance tube  20  is, for example, a fine linear tube having an outer diameter of 1 mm or less and an inner diameter of 0.5 mm or less. The resistance tube  20  serves as a fluid resistance portion for increasing the fluid resistance of the discharge port  16 . The retaining member  22  is made of a resin material (for example, silicone rubber) having elasticity. The retaining member  22  retains the outer peripheral surface of the resistance tube  20  with the resistance tube  20  penetrated therethrough. The fixing member  24  is a metal member having a recess for fitting and holding the retaining member  22 . The fixing member  24  is detachably attached to a portion of the buffer block  6  where the discharge port  16  is provided in a state in which the retaining member  22  is retained by the recess. 
     A cylindrical protrusion  18  is provided at a portion of the outer surface of the buffer block  6  where the discharge port  16  is provided. A thread groove is formed on the outer peripheral surface of the protrusion  18 . A thread groove is formed on the inner peripheral surface of the fixing member  24  of the discharge member  8  to be threaded with the thread groove of the outer peripheral surface of the protrusion  18  of the buffer block  6 . By rotating the fixing member  24 , the discharge member  8  can be attached to and detached from the buffer block  6 . 
     The discharge member  8  is attached to the buffer block  6  such that the resistance tube  20  is in fluidic communication between the buffer space  14  and the atmosphere. A seal ring  26  is sandwiched between the tip of the protrusion  18  of the buffer block  6  and the retaining member  22  of the discharge member  8 . The seal ring  26  deforms the resin retaining member  22  at the tip end of the protrusion  18  to enhance the sealing performance, thereby preventing a gas from being discharged from a path other than the resistance tube  20 . 
     With the above-described structure, the fluid resistance of the gas to be discharged from the discharge port  16  increases, reducing the capacitance of the buffer space  14 , which in turn can reduce the size of the buffer block  6 . Since the resistance tube  20  is fine, sample clogging may occur within the resistance tube  20 . However, the detachment/attachment of the discharge member  8  retaining the resistance tube  20  can be easily performed by rotating the fixing member  24 , and therefore, the replacement of the resistance tube  20  can be easily performed. 
     Note that as the fluid resistance portion for increasing the fluid resistance of the discharge port  16 , a filter (a metal crystal filter, a ceramic filter, or the like) may be used instead of the resistance tube  20 . In this case, the filter may be retained by the retaining member  22  or brazed to the fixing member  24  of the discharge member  8 . 
     Further, the attaching/detaching structure of the buffer block  6  with respect to the discharge member  8  is not limited to those utilizing a threaded engagement as long as the buffer block  6  can be detachably attached to the discharge member  8 . Further, the discharge member  8  does not necessarily need to be directly attached to and detached from the buffer block  6 , and may be configured to be detachably attached to the buffer block  6  via a pipe. 
     Further, as shown in  FIG.  3    and  FIG.  4   , a heat retention unit may be provided to prevent the temperature drop of the discharge member  8  to prevent clogging in the fluid resistance portion, such as, e.g., the resistance tube  20 . In the example shown in  FIG.  3   , a heat retention unit is configured by a thermal insulation member  30  surrounding the discharge member  8  to prevent the heat release so that the heat transferred to the discharge member  8  via the metal outlet pipe  4  and the buffer block  6  does not escape. In the example shown in  FIG.  4   , the heat retention unit is constituted by a metal thermally conductive block  32  in contact with the discharge member  8  and a heater  34  for heating the thermally conductive block  32 . 
     The examples described above merely exemplify embodiments of the thermal conductivity detector according to the present invention. Embodiments of the thermal conductivity detector according to the present invention are as follows. 
     According to an embodiment of the present invention, a thermal conductivity detector includes: 
     a cell block provided therein with a measurement cell serving as a space in which a filament for exchanging heat with a gas is arranged, the cell block being provided with a cell inlet for introducing the gas into the measurement cell and a cell outlet for flowing out the gas from the measurement cell; 
     an outlet flow path communicated with the cell outlet of the cell block; 
     a buffer block provided therein with a buffer space, the buffer block having an inlet port for introducing the gas into the buffer space and a discharge port for discharging the gas from the buffer space, the inlet port being fluidly connected to the outlet flow path; and 
     a discharge member retaining a fluid resistance portion for increasing fluid resistance of the discharge port, the discharge member being attached to the buffer block such that the gas discharged from the discharge port passes through the fluid resistance portion, the discharge member being configured to be detachable from the buffer block together with the fluid resistance portion. 
     According to a first aspect of an embodiment of the thermal conductivity detector according to the present invention, the fluid resistance portion is a resistance tube. 
     In the first aspect of the present invention, an outer diameter of the resistance tube is equal to or less than 1 mm. It is difficult to detachably attach a fine resistance tube having an outer diameter of 1 mm or less to a buffer block by a threaded engagement or the like. However, in the embodiment according to the present invention, the resistance tube can be attached to and detached from the buffer block in accordance with the attachment/detachment of the discharge member, and therefore, even in the case of a fine resistance tube, the replacement can be easily performed. 
     Further, in the first aspect of the present invention, the discharge member may include: 
     a retaining member retaining an outer peripheral surface of the resistance tube; and 
     a fixing member configured to be detachably fixed to the buffer block in a state of retaining the retaining member. 
     In the above case, the retaining member may be made of an elastic resin material. With such an aspect, it is possible to prevent the fine resistance tube from being bent. 
     In a second aspect of the embodiment of the thermal conductivity detector according to the present invention, the fluid resistance portion is a filter. 
     In a third aspect of the embodiment of the thermal conductivity detector according to the present invention, the thermal conductivity detector further includes a heat retention unit configured to prevent a temperature drop of the discharge member. With such an aspect, it is possible to suppress clogging of a fluid resistance portion by a sample. 
     In the above-described third aspect of the present invention, the heat retention unit may be provided with a thermally conductive block in contact with the discharge member and a heater for heating the thermally conductive block. 
     DESCRIPTION OF SYMBOLS 
     
         
           1 : Thermal conductivity detector 
           2 : Cell block 
           4 : Outlet pipe 
           6 : Buffer block 
           8 : Discharge member 
           10 : Measurement cell 
           11 : Cell inlet 
           12 : Filament 
           13 : Cell outlet 
           14 : Buffer space 
           15 : Inlet port 
           16 : Discharge port 
           18 : Protrusion 
           20 : Resistance tube (fluid resistance portion) 
           22 : Retaining member 
           24 : Fixing member 
           26 : Seal ring 
           30 : Thermal insulation member 
           32 ; Thermally conductive block