Cryogenic Cooling Mathew C Wright October 2016 Cryogenic
Cryogenic Cooling Mathew C. Wright October 2016
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Cryogenic Cooldowns Types of Cryogenic Cool Downs: 1. 2. 3. 4. 5. 6. Using LN 2 to cool down Cold Boxes Using 4 K helium to cool down cryo modules Using LN 2 HX to cool helium to cool magnets Mixing 300 K helium with 4 K helium Using Turbines to cool down cold boxes before LN 2 Directly injecting LN 2 into helium dewars then finishing the cool down with 4 K helium
Cryogenic Cooldowns Things to be concerned about: • Thermo-mechanical stresses of the components – Especially heat exchangers • Oil or contamination migration • Capacity Limitations of the Equipment – Refrigeration – Helium Recovery / Purification – Gas Management
Cryogenic Cooldowns Basic Rule: Cooling provided by the supply stream must be greater than that absorbed by return stream – rest of the cooling is used to cool down the equipment (HX etc. ). This imbalance across the two streams is created by the bypass flow.
Cryogenic Cooldowns Concerns: To reduce thermo-mechanical stresses of the components • Normally Delta T less than 50 K − • Thermal strain (i. e. contraction rate) is directly proportional to ∆T. More strain = More Stress! Cool down rate is less than 1 K/min
Cryogenic Cooldowns Concerns To reduce Thermo-mechanical stresses of the components • Delta T less than 50 K Here, ∆T is the temperature difference between the streams at warm end or at the cold end.
Cryogenic Cooldowns Concerns To reduce Thermo-mechanical stresses of the components • Flow through all HX passes should be low, causing the Cooldown to be extremely slow
Cryogenic Cooldowns Concerns Contamination migration • • Loads / Cryogenic Vessels: Always assumed Dirty. Entire cool down flow is taken to recovery system (via. Vaporizer). This also creates flow imbalance across HX. Cold Box Adsorbed Beds: Isolated/Bypassed until the process flow reaches the temperature they are meant to operate (i. e. 80 K/20 K). If possible they should be cooled separately (using same method as 1).
Cryogenic Cooldowns Basic Rules Oil or contamination migration – Start Cool Downs of all Cold boxes w/ LN 2 • • Check outlet vent to ensure the LN 2 supply valve is only cracked open – Use a bag over the vent pipe and crack open the valve until the bag starts to slowly inflate Cold box 80 K carbon beds are 100 K or less before starting turbines to reduce the chance of contamination getting down stream when turbines are started
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Cryogenic Cooldowns CHL 1 Direct LN 2 injection
Cryogenic Cooldowns CHL 1 Direct LN 2 injection
Cryogenic Cooldowns Jlab Style Cryo Module Cool Down Direct 4 K injection
Cryogenic Cooldowns Jlab Style Cryo Module Cool Down
Cryogenic Cooldowns Both LINAC’s can be supported by either CHL 1 and CHL 2 without having to warm-up any cryo modules Modules typically have to be warmed up for maintenance on the module
Solenoid in Hall D § § § Bore 4 m long 2 m diameter Field at the axis ~ 2 T at 1350 A Full energy ~ 23 MJ at 1350 A 4 coils in 4 separate He baths Built at SLAC in 1970’s, refurbished at IUCF and Jlab § Total helium reservoirs 3500 liters
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Cryogenic Cooldowns Hall D: Employing cool-down heat exchangers
Cryogenic Cooldowns Employing cool-down heat exchangers
Cryogenic Cooldowns Hall D: Employing cool-down heat exchangers
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Cryogenic Cooldowns Hall A: Employing cool-down heat exchangers
Cryogenic Cooldowns Other Cool Down Methods A. Mixing 300 K w/ 4 K helium 1) 2) Uses 4 K capacity when LN 2 could be used Flow may need to be limited based on a) Size of the Recovery system b) Size of the Refrigerator B. Warm (300 K) start-up of turbines 1) Concern is that the 80 K carbon beds are not cold and that contamination will migrate to the turbines C. Cool Down with LN 2 directly into the process A. Rumors of people using LN 2 directly injected into a helium dewar to cool down, then pump out the N 2, and continue cooling with helium A. Concerned amount contamination B. If there are valves back to the helium system, concerned those valves leak and that the helium system has to be shut down to clean it up.
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