Detecting contamination of a cryogenic refrigerant in a cryogenic refrigeration system

Abstract

This invention discloses a sensor, a method, and a refrigeration system for detecting contamination of a cryogenic refrigerant in a cryogenic refrigeration system. The sensor includes: an inlet for coupling to a flow path of a cryogenic refrigerant in the cryogenic refrigeration system; and a thermal conductivity detector in fluid communication with the inlet. The thermal conductivity detector is configured to generate a signal indicating the detected thermal conductivity of a cryogenic refrigerant received from the cryogenic refrigeration system when the sensor is coupled to the cryogenic refrigeration system. The sensor also includes: circuitry configured to convert the thermal conductivity signal into an indication of contamination of the cryogenic refrigerant; and an output terminal configured to output the indication of contamination of the cryogenic refrigerant.

Description

Technical Field

[0001] The scope of this invention relates to the detection of contamination of a cryogenic refrigerant within a cryogenic refrigeration system. Prior Technology

[0002] Cryogenic cooling systems use refrigerants (such as helium). Refrigerant purity is critical because impurities can freeze at low system temperatures, leading to damage or performance degradation. Routine systems regularly monitor the refrigerant to ensure contamination levels remain below acceptable levels. This is accomplished by sampling and using an RGA (Residual Gas Analyzer) to determine contaminants in the sample. An RGA is a complex instrument, typically located in a remote location, and requires significant expertise to operate.

[0003] There is a desire for an analytical technique that allows for routine and inexpensive analysis to be performed in a manner that does not excessively disrupt the normal operation of the system. Summary of the Invention

[0004] One embodiment provides a sensor for detecting contamination of a cryogenic refrigerant in a cryogenic refrigeration system. The sensor includes: an inlet for coupling to a flow path of the cryogenic refrigerant in the cryogenic refrigeration system; a thermal conductivity detector in fluid communication with the inlet, configured to generate a signal indicating the detected thermal conductivity of the cryogenic refrigerant received from the cryogenic refrigeration system when the sensor is coupled to the cryogenic refrigeration system; circuitry configured to convert the thermal conductivity signal into an indication of contamination of the cryogenic refrigerant; and an output configured to output the indication of contamination of the cryogenic refrigerant.

[0005] The inventors of this invention recognized that refrigerants (such as helium) used in cryogenic systems have a high conductivity that, in many cases, is distinctly different from the conductivity of other impurities that can leak into the refrigerant within the system. They also recognized that the ability to identify the presence of impurities or contaminants in the cryogenic refrigerant in the field would allow for more regular testing of the refrigerant and earlier detection of any contaminants. Therefore, embodiments provide a sensor having a thermal conductivity detector for detecting the conductivity of the refrigerant within the cryogenic refrigeration system itself. This allows the testing to be performed regularly and the results to be obtained immediately. In this way, early detection of contamination using a relatively low-cost, easy-to-use sensor is provided. While this sensor may not be as accurate as a conventional RGA analyzer in identifying the nature of the contaminant, the ability to detect the presence of refrigerant contaminants allows for the protection of the cryogenic system, and if a more accurate analysis is deemed helpful, this analysis can be performed. In this way, if a heavier, remote sensing of the refrigerant is used, the results can be accurately targeted at the desired situation, far less frequently than in conventional cases.

[0006] In some embodiments, the sensor has only one port for coupling to the cryogenic refrigerant flow path. This single port serves as an inlet to allow fluid to enter the sensor and also as an outlet when the detection is performed, at which point the refrigerant can exit from the sensor. However, in other embodiments, there is an inlet and an outlet, with the thermal conductivity detector disposed between them, allowing fluid to pass through the sensor so that the refrigerant within the sensor is continuously replenished and represents the refrigerant in the refrigeration system.

[0007] Although the refrigerant can take different forms, in some embodiments, the refrigerant is helium, provided it is configured to operate at low temperatures (typically below 100 K). Helium is frequently used as a refrigerant in cryogenic systems, and embodiments are particularly effective in detecting contaminants in helium because its electrical conductivity in the gaseous state is very high compared to other gases, especially to gaseous impurities that can be found in a contaminated refrigerant. Therefore, any contamination in a helium fluid will result in a significant change in thermal conductivity, and thus can be detected with remarkable accuracy.

[0008] In some embodiments, the sensor further includes control circuitry, the control circuitry including an input for receiving at least one signal indicating a current state of one of the cooling systems, the control circuitry being configured to control the operation of the thermal conductivity detector based on the at least one received signal.

[0009] The sensor is configured to be mounted on the refrigeration system so that it can measure the conductivity of the cryogenic refrigerant in situ and thereby measure the contaminants. It can be controlled by control circuitry that receives signals indicating the current operating state or condition of the refrigeration system; these signals control the sensor to perform the thermal conductivity detection. In this regard, these signals may indicate the current operating state, such as whether it has entered a regeneration state, and / or may indicate a characteristic of the cryogenic refrigerant within the refrigeration system, such as temperature, pressure, or flow rate, which also indirectly indicate the current operating state of the refrigeration system and have an impact on the thermal conductivity measurement.

[0010] In some embodiments, the sensor further includes at least one valve configured to control the flow of the cryogenic refrigerant into and out of the sensor.

[0011] In some embodiments, the sensor may be installed within the refrigeration system within the cryogenic refrigerant flow and may not have a valve associated with the sensor. However, in other embodiments, one or more valves may be associated with the inlet and / or outlet of the sensor, configured to control the flow into and out of the sensor. For example, in the case where the sensor is located in a bypass line, valves may be used to divert the cryogenic refrigerant from its normal flow path, thereby flowing through the bypass line and thus through the sensor when a measurement is performed. When no measurement is performed, the valves may be closed, and the refrigerant may flow through the bypass line. In this respect, the thermal detection measurement may preferably be performed in stagnant flow, and therefore, it is advantageous to control the flow with valves so that the refrigerant indicating the system is trapped but stagnant when a measurement is performed.

[0012] Additionally and / or alternatively, the control circuit may respond to the operation of the refrigeration system, and in particular, control the measurement when the cryogenic refrigerant flow has stopped.

[0013] In other embodiments, such sensors may be within the flowing refrigerant and configured to convert the thermal conductivity measurement into a contamination indication circuit that can receive a signal indicating the flow rate, such that the conversion can take into account the flow effects such as turbulence on the thermal conductivity measurement.

[0014] In some embodiments, the control circuit is configured to control the operation of the at least one valve.

[0015] In the presence of a valve associated with a sensor, the control circuitry of the thermal conductivity detector can then control the operation of one or more valves.

[0016] In some embodiments, the control circuit is configured to activate the thermal conductivity detector to perform a thermal conductivity detection in response to a received signal indicating that the cryogenic refrigeration system is in a regeneration phase.

[0017] As previously mentioned, one problem with contaminants in a cryogenic refrigeration system is that the contaminants freeze at low temperatures, which can lead to damage and / or restrict flow. Therefore, testing for contaminants at temperatures above the cryogenic level is more accurate and effective, where the contaminant will not freeze and will remain within the refrigerant in the sensor. When the cryogenic refrigeration system is used, for example, as a cryogenic vacuum pump, it will then periodically have a regeneration phase when the cryogenic cooler of the cryogenic pump is raised above the cryogenic temperature to release trapped molecules. In this system, performing the contaminant detection measurement during this phase can be advantageous. Therefore, in some embodiments, the control circuit is configured to activate the sensor to perform the thermal conductivity measurement when it is determined that the system is in a regeneration phase and may have reached a specific temperature.

[0018] Another advantage of performing this thermal conductivity measurement during the regeneration phase is that the compressor and the cryogenic pump are not operating during most of the regeneration phase and the flow is stagnant. This means that the measurement does not require correction for flow effects (such as turbulence) and allows for a more accurate or at least simpler measurement.

[0019] In some embodiments, the control circuit is configured to activate the thermal conductivity detector in response to determining that the cryogenic refrigeration system is below 200K, preferably below 100K, and that the contaminant is frozen within the cryogenic refrigeration system, to perform the thermal conductivity detection as a baseline thermal conductivity detection.

[0020] As discussed above, when the refrigeration system is at a low temperature, these contaminants can then be captured. Specifically, when the cryogenic refrigeration system is below 200K, preferably below 100K, many contaminants will freeze in the coldest part of the system, and detecting the thermal conductivity of the cryogenic refrigerant away from the coldest part will provide a baseline indication of a substantially pure refrigerant. Therefore, it is advantageous to perform these thermal conductivity measurements periodically. This is useful in order to accurately compare the difference in thermal conductivity of the cryogenic refrigerant with and without contaminants measured by the same sensor at the same location, and to convert these readings into the amount of contaminants. In the case where the refrigeration system periodically performs a regeneration phase, this baseline detection can then be performed at or near the start of the regeneration phase, where the cryogenic refrigerant is stagnant and not flowing, and the coldest part of the refrigeration system is still at a low temperature. This baseline measurement can be performed for each regeneration cycle, or it can be performed for a subset of cycles, such that after a certain time or number of regeneration cycles, the baseline measurement is repeated and the thermal conductivity measurement used for comparison is updated.

[0021] In some embodiments, the control circuit is configured to respond to a determination that the cooling system is above 220K, preferably above 270K, to control the thermal conductivity detector to activate the thermal conductivity detector to perform the thermal conductivity detection as a contamination thermal conductivity detection.

[0022] To perform an accurate measurement of contaminants present in the cryogenic refrigerant, it is advantageous to perform the measurement when the refrigeration system is determined to be above the cryogenic temperature (e.g., above 220K, preferably above 270K). In cases where the refrigeration system includes a regeneration phase, this higher temperature can then be used to enter the regeneration phase in some manner, and the system can perform a mixing cycle before performing the thermal conductivity measurement. This mixing cycle may include the operation of the compressor and pumps of the refrigeration system for a very short time to mix the refrigerant surrounding the system, such that the contaminants retained in the cooler portion of the system are distributed within the refrigerant. This mixing cycle does not last for a long time because cooling is not required during this cycle. It can last for more than 30 seconds, but typically less than 5 minutes.

[0023] In some embodiments, the circuit is configured to convert the thermal conductivity signal into an indication of contamination of the cryogenic refrigerant based on both the baseline thermal conductivity detection and the contamination thermal conductivity detection.

[0024] The circuit that converts the determined thermal conductivity into an indicator of one of the contaminants can take into account the baseline thermal conductivity detection (if one exists), such that the difference between the two signals can give an accurate indication of one of the contaminants.

[0025] The thermal conductivity detector can take many forms; in some embodiments, the thermal conductivity detector includes a filament thermal conductivity detector.

[0026] Filament thermal conductivity detectors are relatively inexpensive and easy to operate. In some embodiments, there may be two filament thermal conductivity detectors, one filament thermal conductivity detector and another reference filament thermal conductivity detector, the other reference filament thermal conductivity detector being isolated from the refrigeration system and including a refrigerant of a predetermined purity. The circuit is configured to convert the thermal conductivity signal into an indication of contamination of the cryogenic refrigerant based on a comparison of the thermal conductivity detection of the other reference filament thermal conductivity detector and the filament thermal conductivity detector.

[0027] To provide an accurate contamination detection, a filament thermal conductivity detector may require a reference thermal conductivity detector that detects the thermal conductivity of a pure or substantially pure refrigerant, and the difference between that thermal conductivity and the actual thermal conductivity of the refrigerant is used as an indication of contamination.

[0028] In other embodiments, the thermal conductivity detector includes a microelectromechanical system (MEMS) device.

[0029] A MEMS device can be better than a filament detector because it is more accurate and more independent of turbulence and sensor orientation. It also does not require a second device as a reference, but it can perform a baseline measurement at a different time and use the comparison to improve accuracy.

[0030] In some embodiments, the circuit is configured to receive a signal indicating at least one of the temperature and pressure of the refrigerant, and to convert the thermal conductivity signal into a contamination indication based on the at least one temperature and pressure.

[0031] The thermal conductivity measured by the thermal conductivity detector depends on the temperature and pressure of the refrigerant, and therefore, in some embodiments, the circuit can receive signals indicating these values, and these signals can be used to determine contamination. In some embodiments, the sensor itself may include at least one of a temperature and / or pressure sensor, or may have an input for receiving signals from the refrigeration system indicating the temperature and pressure of the refrigerant. In this regard, it may be advantageous if the sensor itself includes a temperature sensor, as this has a significant effect on thermal conductivity, and it is preferable to measure the temperature as close as possible to the location where the thermal conductivity is measured.

[0032] According to one embodiment, another embodiment provides a cryogenic refrigeration system including a cryogenic refrigerant and a sensor for determining contamination of the cryogenic refrigerant.

[0033] In some embodiments, the cryogenic refrigeration system further includes at least one compressor for compressing the cryogenic refrigerant, at least one pump, and a controller for controlling the operation of the cryogenic refrigeration system. The controller is configured to control a mixing cycle by triggering the operation of the compressor and the at least one pump for a predetermined time before transmitting a signal to the sensor to begin detecting the contamination of the cryogenic refrigerant.

[0034] In some embodiments, the at least one pump includes a cryogenic pump.

[0035] As previously mentioned, when determining contamination of a cryogenic refrigerant by detecting thermal conductivity, a mixing cycle may be required to distribute the contaminant within the refrigerant. This can be particularly advantageous when the system is in the process of heating up and stalling, and perhaps during a regeneration phase. Therefore, in some embodiments, a control circuit associated with the refrigeration system may be provided, configured to control a mixing cycle before transmitting a signal to the sensor to initiate a thermal conductivity measurement.

[0036] Another approach provides a method for detecting contamination of a cryogenic refrigerant in a cryogenic refrigeration system, the method comprising: A sensor, including a thermal conductivity detector, is coupled to a cryogenic refrigerant flow path in the cryogenic refrigeration system, such that the cryogenic refrigerant flows into the thermal conductivity detector; The thermal conductivity of the cryogenic refrigerant was measured using this thermal conductivity detector. The measured thermal conductivity is converted into an indication of the amount of contamination in the cryogenic refrigerant; and This indicator outputs the information about the contamination of the cryogenic refrigerant.

[0037] In some embodiments, the refrigeration system includes a cryogenic pump system.

[0038] In some embodiments, the method includes an initial step of determining that the refrigeration system is entering a regeneration phase, and a step of measuring the thermal conductivity is performed during the regeneration phase.

[0039] In some embodiments, the method includes determining that the cryogenic refrigeration system is at a cryogenic temperature, preferably below 100K, and performing a baseline thermal conductivity measurement step.

[0040] In some embodiments, the method includes determining that the refrigeration system is above a cryogenic temperature, preferably above 200K, before performing the step of measuring the thermal conductivity.

[0041] In some embodiments, the step of converting the measured thermal conductivity into an indication of the amount of contamination in the cryogenic refrigerant includes comparing the measured thermal conductivity with the measured baseline thermal conductivity.

[0042] Another specific and preferred embodiment is described in the accompanying independent and supplementary technical solutions. The features of the supplementary technical solutions may be appropriately combined with the features of the independent technical solutions, and may be combined with features other than those expressly specified in the technical solutions.

[0043] When a device feature is described as operable to provide a function, it will be understood that this includes one of the device features that provides or is adapted to provide that function. Simple Explanation of the Diagram

[0044] Embodiments of the present invention will now be further described with reference to the accompanying drawings, wherein:

[0045] Figure 1 shows a cross-section of a sensor according to one embodiment;

[0046] Figure 2 illustrates a sensor according to one embodiment;

[0047] Figure 3 illustrates a MEMS-type TCD according to one embodiment;

[0048] Figure 4 illustrates a cooling system, showing the possible locations of sensors according to an embodiment;

[0049] Figure 5 illustrates a cooling system, showing sensors in a bypass circuit according to one embodiment;

[0050] Figure 6 shows the difference in thermal conductivity measurements between pure helium and helium contaminated with 100 pmm CO2; and

[0051] Figure 7 shows a flowchart illustrating one of the steps in a method according to one embodiment. Implementation

[0052] Before discussing the embodiments in more detail, an overview will first be provided.

[0053] The embodiments provide a method and components for monitoring the purity of a refrigerant, particularly a helium gas stream, using thermal conductivity measurements to determine the presence of gaseous contaminants in a cryogenic refrigeration system (such as a cryogenic pump system). In some cases, this development uses an in-situ method to monitor the purity of the helium gas stream of the refrigerant to determine the presence of contaminants before the gas thermal conductivity measurement adversely affects the system, thereby reducing the need for off-site RGA analysis.

[0054] Various thermodynamic cycles, such as the GM (Gifford McMahon) or Stirling cycles, are used to generate very low temperatures and use helium as the working fluid or refrigerant. One application of this technology is for cryogenic pumps that generate high vacuum; other applications include MRI scanners or high-temperature superconductor cooling. For these systems to operate properly, it is crucial to maintain the helium within the system at a defined purity level. As helium purity decreases, system performance deteriorates, eventually leading to failure and requiring repair and maintenance. This embodiment provides a method for measuring the purity of a refrigerant, such as helium within a refrigeration system of a cryogenic refrigeration system (while it is operating), allowing impurities to be detected before they reach levels that would cause pump failure.

[0055] The detection system uses a thermal conductivity detector (TCD) similar to those used in gas chromatography. A TCD contains a resistor placed in a gas flow path / volume. As a gas flows through the resistor, heat is carried away from the resistor, causing a change in the resistor's temperature (a change in its resistivity). Since different gases have different thermal conductivities, the gas can be detected based on the rate of heat loss (resistivity change) of the resistor.

[0056] The embodiments broadly describe two methods for determining refrigerant purity using TCD. The suitability of one method relative to another depends on a variety of factors, including but not limited to system type, layout, and required detection sensitivity. The term helium or refrigerant environment can mean a stagnant volume or flow of helium or refrigerant gas at any pressure and flow rate. [Using a dual-sensor system—filament] [TCD]

[0057] This method uses two separate TCD sensors, one placed in a high-purity refrigerant environment and the other in a potentially contaminated refrigerant environment. In this example, the refrigerant is helium, and the resistivity of the TCD sensors differs significantly due to the different conductivity of pure and impure helium environments. A Wheatstone Bridge circuit is used to convert the resistance of the two sensors into an output voltage, which can be read by the system to indicate the difference between the two flows. An increased voltage difference between the pure helium system and the measured system indicates increased contamination in the system.

[0058] Except for hydrogen, all gases have lower thermal conductivity than helium. Therefore, helium is commonly used as a reference gas for comparing the thermal conductivity of gases and is also a commonly used refrigerant in cryogenic systems. The standard or reference environment for pure helium is 200 PSIG, and a reference voltage of 5.2 mV is observed under this environment. This voltage is collected over a set time and used for zero-point calibration. When the impure gas passes through the sensing TCD, the reference voltage is then subtracted from the obtained voltage. This allows the user to calculate the voltage change attributable to helium contamination compared to pure helium. An example illustrating this voltage difference is shown in Figure 6. [Using a sensor system—] [MEMS] [type] [TCD]

[0059] The use of a MEMS (Micro-Electro-Mechanical Systems) TCD allows for accurate prediction of contaminant concentrations using a single sensor. MEMS have a signal-to-noise ratio that is significantly higher than their filament counterparts. This, in turn, allows a single MEMS sensor assembly to sense changes in gas purity down to 100 ppm.

[0060] A MEMS solution is more elegant than a filament-based design because a single sensor can be zeroed in a pure gaseous refrigerant. At a constant pressure and temperature, any change in the zero point can be attributed to a change in gas purity. Using a TCD to monitor the purity of a cryogenic helium circuit allows for the detection of contamination before it adversely affects the system. This monitoring can be performed in-situ on a warm system. The TCD can be directly integrated into the refrigerant circuit.

[0061] Figure 1 shows a cross-section of a filament-type thermal conductivity detector (TCD) 5 according to one embodiment. The TCD 5 includes an inlet coupler 10 and an outlet coupler 20 for coupling to a refrigeration system, such as a cryogenic pump. When coupled to the system, refrigerant flows from the inlet 10 through the TCD 5 to the outlet 20. The TCD includes a heated filament 30, the resistance of which depends on its temperature, and consequently, the thermal conductivity of the refrigerant. A channel 25 is provided for receiving a wire that transmits current to the filament 30 and allows for the detection of changes in resistance. Circuitry (not shown) determines the filament resistance and, in some embodiments, compares it to the impedance of a corresponding filament in pure refrigerant, and designs and outputs a measurement of refrigerant contamination based on the difference in values.

[0062] Figure 2 shows a non-cross-sectional view of TCD 5 in Figure 1, which includes an inlet coupling element 10 and an outlet coupling element 20.

[0063] Figure 3 schematically illustrates a MEMS-type TCD 5, which includes an inlet coupler 10 and an outlet coupler 20, as well as an integrated temperature sensor 40 and a pressure transducer 50. The thermal conductivity of the refrigerant gas varies with temperature and pressure, and therefore, some TCDs integrate these sensors, whose values ​​are used to convert the detected thermal conductivity measurements into contamination levels.

[0064] Figure 4 schematically illustrates a refrigeration system and a potential location for the TCD 5 according to one embodiment. The refrigeration system includes a compressor 60 and a plurality of refrigeration units 72. Sensors according to the embodiment can be used in this system to monitor for impurities. These TCD sensors 5 can be placed within the refrigerant lines themselves, and four example locations of the TCD are shown: 5A in the compressor refrigerant supply line, 5B in the compressor refrigerant return line, 5C in the refrigeration unit supply line, or 5D in the refrigeration unit return line.

[0065] The operation of the TCD can be triggered by a control circuit (not shown) to perform measurements at appropriate times. Thermal conductivity measurements can be converted into an indication of refrigerant contamination, which can be used for maintenance decisions to prevent contaminants from rising above dangerous levels. In some embodiments, the TCD can be a filament-type TCD and can be operated in conjunction with a reference filament TCD containing pure refrigerant; the difference in thermal resistance between the reference filament and the other TCDs is used to determine the degree of contamination.

[0066] In other embodiments, the TCD may be a MEMS-type TCD, which can be used to establish a baseline measurement by measuring at a low temperature, where contaminants are trapped in the coldest part of the system and the refrigerant is therefore pure, and compared with measurements taken at a higher temperature, where, in some cases, contaminants are present in the refrigerant after a mixing cycle. The difference in thermal conductivity between the baseline and the higher measurement is used to determine the degree of contamination. These two measurements can be performed during a period when the refrigerant is not flowing, with the baseline measurement performed at the beginning of one of the lower temperature periods and the other measurement performed as the system heats up.

[0067] In some embodiments, measurements from pressure, temperature, and flow sensors that are associated with the TCD itself or are separate components of the refrigeration system can be used to convert thermal conductivity measurements into contamination indications.

[0068] Figure 5 illustrates an alternative system in which the refrigeration unit of Figure 4 is replaced by a cryogenic pump 70. In this embodiment, TCD 5 is located within a bypass line. The flow rate within the bypass line is controlled by valves 75 and 76, which in turn are controlled by control circuitry 80. Control circuitry 80 also controls the operation of TCD 5 and receives signals from TCD 5 indicating conductivity and pressure and temperature measurements from other sensors (not shown). Control circuitry 80 also receives signals from and sends signals to refrigeration system controller 90, which controls the operation of the refrigeration system. Thus, in some embodiments, control circuitry 80 may receive a signal from refrigeration system controller 90 indicating that a regeneration cycle is about to begin, and in response, it may control valve 75 in the bypass line to open and valve 76 to close. Refrigerant then flows into TCD 5, and a baseline thermal conductivity measurement and a pressure and temperature measurement can be performed at the start of the regeneration cycle. Next, control circuit 80 can control valve 76 to open and valve 75 to close, and after a predetermined time or when the refrigerant reaches a predetermined temperature, it can request a mixing cycle from refrigeration controller 90. Refrigeration controller 90 can initiate a mixing cycle by turning on compressor 60 and cryogenic pump 70 for approximately one minute and then turning them off. Next, control circuit 80 can control valve 75 in the bypass circuit to open and valve 76 to close. Then, the hotter mixed refrigerant will flow into TCD 5, and thermal conductivity, pressure, and temperature measurements can be performed. It should be noted that during the regeneration cycle, the compressor and pump are typically not operating, and the refrigerant stagnates; this can be improved by removing flow effects to enhance measurement accuracy. Next, processing circuit 82 within control circuit 80 can determine the amount of refrigerant contamination based on the corresponding thermal conductivity, temperature, and pressure measurements.

[0069] Figure 6 shows the difference in calibration voltage measured by a sensor at different sampling points for pure refrigerant and refrigerant contaminated with 100 ppm CO2. These measurements were performed at different times, with the system flushed between measurements.

[0070] Figure 7 illustrates a flowchart of one of the steps in a method according to one embodiment. Initially, at step S10, the TCD is coupled to a cryogenic refrigerant flow path in a cryogenic refrigeration system. This may involve opening some valves, or it may involve an initial step of installing the TCD into the system. Once coupled, then at step S20, the cryogenic refrigerant flows into the thermal conductivity detector, and at step S30, the thermal conductivity of the cryogenic refrigerant is measured. At step S40, the measured thermal conductivity is converted into an indication of the amount of contamination in the cryogenic refrigerant. This may involve comparing it with a thermal conductivity measurement of uncontaminated refrigerant and / or adjusting the measured temperature, pressure, and potential flow rate of the refrigerant during the thermal conductivity measurement. At step S50, the calculated contamination indication is output directly to a user via a display (not shown) and / or output as a signal to the control circuitry of the refrigeration system.

[0071] Although illustrative embodiments of the invention have been disclosed in detail herein with reference to the accompanying drawings, it should be understood that the invention is not limited to the precise embodiments, and those skilled in the art can make various changes and modifications to it without departing from the scope of the invention as defined by the appended claims and their equivalents.

[0072] 5: Thermal conductivity detector (TCD) 10: Inlet coupling component 20: Export coupling component 25: Channel 30: Filament 40: Integrated Temperature Sensor 50: Pressure transducer 60: Compressor 70: Cryogenic Pump 72: Refrigeration unit 75: Valve 76: Valve 80: Control Circuit 82: Processing Circuit 90: Refrigeration system controller S10: Steps S20: Steps S30: Steps S40: Steps S50: Steps

Claims

1. A sensor for detecting contamination of cryogenic refrigerant in a cryogenic refrigeration system, the sensor comprising: An inlet, which is used to couple to one of the cryogenic refrigerant flow paths in a cryogenic refrigeration system; A thermal conductivity detector in fluid communication with the inlet, configured to generate a detected thermal conductivity signal indicating the cryogenic refrigerant received from the cryogenic refrigeration system when the sensor is coupled to the cryogenic refrigeration system; a circuit configured to convert the thermal conductivity signal into an indication of contamination of the cryogenic refrigerant; an output configured to output the indication of contamination of the cryogenic refrigerant; and a control circuit including an input for receiving at least one signal indicating a current state of the refrigeration system, the control circuit being configured to control the operation of the thermal conductivity detector based on the at least one received signal, and the control circuit being configured to activate the thermal conductivity detector to perform a thermal conductivity detection in response to the at least one received signal indicating that the cryogenic refrigeration system is in a regeneration phase.

2. The sensor of claim 1, the sensor further comprising at least one valve configured to control the flow of the cryogenic refrigerant into and out of the sensor.

3. As in claim 2, the control circuit is configured to control the operation of the at least one valve.

4. For any of the sensors in claims 1 to 3, the control circuit is configured to activate the thermal conductivity detector to perform the thermal conductivity detection in response to determining that the cryogenic refrigeration system is below 200K, preferably below 100K and that the contaminant is frozen within the cryogenic refrigeration system, so as to obtain the thermal conductivity signal as a baseline thermal conductivity detection.

5. For any of the sensors in claim 4, the control circuit is configured to control the thermal conductivity detector to activate the thermal conductivity detector in response to determining that the cooling system is above 220K, preferably above 270K, in order to perform the thermal conductivity detection and obtain the thermal conductivity signal as a contamination thermal conductivity detection.

6. The sensor of claim 5, wherein the circuit is configured to convert the thermal conductivity signal into an indication of contamination of the cryogenic refrigerant based on both the baseline thermal conductivity detection and the contamination thermal conductivity detection.

7. The sensor of any one of claims 1 to 3, wherein the thermal conductivity detector includes a filament thermal conductivity detector.

8. The sensor of claim 7, comprising a further reference filament thermal conductivity detector isolated from the refrigeration system and comprising a refrigerant of a predetermined purity, wherein the circuit is configured to convert the thermal conductivity signal into an indication of contamination of the cryogenic refrigerant based on a comparison of the thermal conductivity detection of the further reference filament thermal conductivity detector and the thermal conductivity detection of the filament thermal conductivity detector.

9. The sensor of any one of claims 1 to 3, wherein the thermal conductivity detector includes a microelectromechanical system (MEMS) device.

10. The sensor of any one of claims 1 to 3, wherein the circuit is configured to receive a signal indicating at least one of the temperature and pressure of the refrigerant, and to convert the thermal conductivity signal into an indication of the contamination of the cryogenic refrigerant based on at least one of the temperature and pressure.

11. A cryogenic refrigeration system comprising a cryogenic refrigerant and a sensor for determining contamination of the cryogenic refrigerant according to any one of claims 1 to 3.

12. The cryogenic refrigeration system of claim 11, further comprising at least one compressor for compressing the cryogenic refrigerant, at least one pump, and a controller for controlling the operation of the cryogenic refrigeration system, the controller being configured to control a mixing cycle for a predetermined time prior to transmitting a signal to the sensor for initiating detection of contamination of the cryogenic refrigerant by triggering the operation of the at least one compressor and the at least one pump.

13. A method for detecting contamination of cryogenic refrigerant in a cryogenic refrigeration system, the method comprising: A sensor, including a thermal conductivity detector, is coupled to a cryogenic refrigerant flow path in a cryogenic refrigeration system, such that the cryogenic refrigerant flows into the thermal conductivity detector; when the cryogenic refrigeration system is in a regeneration phase, the thermal conductivity detector is activated, and the thermal conductivity of the cryogenic refrigerant is measured using the thermal conductivity detector; the measured thermal conductivity is converted into an indication of the amount of contamination in the cryogenic refrigerant; and the indication of the contamination of the cryogenic refrigerant is output.

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