900 MHz NMR Probe Cryogenic Gas Delivery System

1. N2 gas outlet N2 gas inlet HX dewar LN2 vacuum The Kapton tape around the HX dewar cap, prevents vapor from coming out of the dewar neck. The above graph displays data for 3 different trials. For each trial the temperature was recorded every 5 second. • Cryogenic Fluids have temperatures lower than 123 K (-238°F or -150°C). • A Dewar is a vacuum insulated container that contains a cryogenic fluid. • NMR (Nuclear Magnetic Resonance) analyzes the structure and molecular dynamics of certain atoms when they’re place in a very strong magnetic field such as the 900 MHz magnet at the NHMFL (National High Magnetic Field Laboratory). • The Solenoid Control Valve used in this project uses an electrical signal to control the flow of a fluid by opening or closing the valve in response to sensor readings from the control unit. • NMR spectroscopy allows scientists to assess chemical and structural properties of a sample in non-destructive manner. • Applications of NMR to solid-state samples followed as techniques such as magic angle spinning were developed to increase their inherently poor signal resolution. • NMR spectroscopy is measured from the interactions of applied radio frequency (RF) electromagnetic radiation to the spin polarity of neutrons and protons [Hornak, 1997]. • For modern NMR experiments, a solid or liquid sample is placed inside a probe which locates the sample in the center of the B0 magnetic field created by a superconducting electromagnet. Heat Exchanger Dewar Diagram While running the refill control unit and solenoid valve test we found that the system operated as intended. The control unit triggered the solenoid valve to open and close as needed when a refill was initiated and completed respectively. Refill Controller Box HX LN2 Consumption test 3-way 110 V AC solenoid valve The boil off rate was examined through running a refill test. The system was analyzed under the new system changes (shown in Fig.1 and 2). The table below displays important parameters that were monitored or remained constant during the test. From the HX LN2 consumption test we found that the system has a consumption rate of .1 L/min. We also found that at this rate refills could take place once a day. Time (hh:mm) N2 Flow (scfh) VT T(k) LN2 % N2 pressure (psig) Body N2 Press. (psig) References 11:15 65 88.1 74 13 20 11:44 65 90.5 68 13 20 • Bielecki, D.P. Burum, “Temperature dependence of 207Pb MAS spectra of solid lead • nitrate. An accurate, sensitive thermometer for variable temperature MAS”, • J. Magn. Reson. A 116 (1995) 215–220. • Cengel, Yunus A. and Turner, Robert H. “Fundamentals of Thermal-Fluid Sciences”, • Second Edition, Copyright 2005, The McGraw-Hill Companies • "DSI-Spin and Temperature Control Accessories." 02 Dec. 2008 • Doty Scientific- Leader in High-field MRI and NMR Probe Technology. • http://www.dotynmr.com/acc/acc_spintemp.htm>. • Hornak, Joseph P. "Basics of NMR." RIT CIS - Center for Imaging Science. • 02 Dec 2008 <http://www.cis.rit.edu/htbooks/nmr/>. • Janna, William S. “Design of Fluid Thermal Systems”, Second Edition, • Copyright 1998, PWS Publishing Company • Şen, Özge G. "High Resolution NMR Studies of Phase Transitions in Model H • bonded Solids." Diss. Florida State University, 2007. 12:31 65 91.6 61 13 20 1:06 65 89.0 52 13 20 1:41 65 88.1 42 13 20 3:00 65 87.6 24 13 20 Liquid Nitrogen Supply System Refill Control Unit 900 MHz NMR Probe Cryogenic Gas Delivery System Senior Design Team 2: Academic Year 2008 – 2009 Rebecca Altman, Jason Kitchen, Zachary Stevenson, and Jessica Vanterpool Project Scope Subsystem Testing and Results Conclusion and Recommendations • The design implementations largely meet the project specifications. Experimental testing confirmed a lowest achievable sample temperature of 106 K. The outlet temperature of the HX was close to theoretically predicted values at a given gas flow rate. Our design features an automatic refill controller which includes audible reminders and alarms for standby or cryogen overflow conditions. Testing of the automatic refill controller showed it performed as expected with no need for rework or design modifications. The problem of temperature fluctuation during a refill was solved by insulating the heat exchanger with Mylar and fabricating a sealing ring and vent posts to allow nitrogen boil-off to escape from the HX cryostat in a way which would least cause temperature disturbances. • The unspent portion of our budget leaves ample funds for future refinement of this system if it is deemed advantageous by our sponsors. Now that the system targets 106 K and is capable of automatic refills, future work could be undertaken to further reduce losses, and it could be possible to achieve even lower sample temperatures. However, as noted by one of our sponsors, Mr. Peter Gor’kov, who just attended a conference featuring current state of the art for NMR instrumentation, other research groups have difficulty in reaching temperatures close to 90 K while using liquid nitrogen as a coolant, due to the problem of droplet formation and resultant heater control instability. Refill of Liquid Nitrogen Test The system for cooling samples in nuclear magnetic resonance (NMR) radio frequency (RF) probes used in the 900 MHz magnet to cryogenic temperatures needs to be improved in several aspects. The client has a closed-cycle refrigerator capable of delivering gases to temperatures reaching 193 K. A heat exchanger in a liquid nitrogen bath is currently used in series with this refrigerator to achieve outlet temperatures reaching 123 K. However, this system does not account for the automatic and indefinite refill of liquid nitrogen surrounding the heat exchanger. Also ice formations which build up on tubing adapters on the current system are evidence of poor thermal insulation, and highlight a second area for product improvement. The refill test was used to find out whether or not changing the output pressure (three trials: 22, 10, 6psig) would have an effect on decreasing the temperature fluctuation for the output temperature of the unregulated (without probe heater) HX during refills. A constant temperature allows for a more controlled output probe temperature. Figures 1 and 2 display the new changes of which the test were taken under. Results shows the least amount of temperature fluctuation for the output pressure of 6 psig. However, at 6 psig the flow of into the HX Dewar is very low and slow. If the Dewar were to fill up at 6 psig, the pressure would have to remain constant the entire time to allow constant flow. Background Information Heat Exchanger Coil Testing Using the thermal analysis from the final design, the amount of pre-fabricated cooling coils will remain constant with a calculated 13 outer Hx Coils. Test 1 showed an unpredicted pressure drop due to ice-build up because of the paused experiment. Test 2 and 3 gave the predicted output temperature results with some variation due to the possible small leaks and the impact venting N2 gas could have on the pre-cooling coils. Budget The total amount of money allotted by the sponsor to spend on this project was $4,000. Approximately 56% of the team’s budget was used for subsystem design improvements leaving approximately $1,746 unspent. Liquid Nitrogen Refill Control Unit and Solenoid valve test System Schematic Acknowledgements Sponsors: Dr. William Brey and Peter Gor’kov Advisor: Dr. Steven Van Sciver National High Magnetic Field Laboratory (NHMFL) and the NMR Department: Dr. Riqiang Fu, Andy Powel, and Richard Desilets The FAMU-FSU Department of Mechanical Engineering: Dr. Chiang Shih and Dr. Daudi Waryoba Senior Design Teaching Assistants: Jaron Zadi and Daniel Vertucci Design Decision Matrix Final System Design • The final design for the refill system of the NMR probe includes the following components: • Automated refill controller box • Lockout mode allowing refill to cease incase if emergency • Alarm buzzer for safety • 3-way 110 V AC solenoid valve • De-energized: allows LN2 supply dewar to vent • Energized: Forces LN2 flow from 20 psig N2 • HX coils • 8 inner and outer coils (Converted into 13 outer coils for easier manufacturing) • Output temperature within required range (Theoretical 79 K, Experimental 89 K)