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Vol.4 , No. 6, Publication Date: Dec. 23, 2017, Page: 76-81
, liquid helium has a very low boiling point of -269°C (4.2 K) and therefore these cryogens need specialized containers for their storage and transportation. Commercial containers for storing these cryogens are of special construction. To arrest the heat leak, the containers are doubled walled annular space between the inner and outer vessel is evacuated. The heat conduction through the walls is kept a minimum with use of thin walled stainless steel material. To reduce the heat loss due to radiation, the inner tank is wrapped with multiple pairs of reflecting and insulating layers which reflects the heat radiation away. This combination of multi-layer insulation and vacuum is called super-insulation. In practice, the vacuum level of the dewars deteriorates over long period of time and needs to be revived by re-evacuation. The methods, tools, time of evacuation depend on the condition of the dewar. In-house techniques were developed and successfully re-evacuated and revived many dewars at Low Temperature Facility, Tata Institute of Fundamental Research, Mumbai. The paper throws light on the extensive experience explaining the specific techniques and methodology for the reconditioning of vacuum in the cryogenic dewars.&picture=http://www.aascit.org/aascit/decorators/img/journal/896.jpg)
| [1] | Kadayam Venkatraman Srinivasan, Low Temperature Facility, Tata Institute of Fundamental Research, Mumbai, India. |
| [2] | Arvind Hedukar, Low Temperature Facility, Tata Institute of Fundamental Research, Mumbai, India. |
Cryogens like liquid nitrogen and liquid helium are the essential requirement in many areas of scientific research and technology. Liquid nitrogen has a boiling point of -196°C (77 K), liquid helium has a very low boiling point of -269°C (4.2 K) and therefore these cryogens need specialized containers for their storage and transportation. Commercial containers for storing these cryogens are of special construction. To arrest the heat leak, the containers are doubled walled annular space between the inner and outer vessel is evacuated. The heat conduction through the walls is kept a minimum with use of thin walled stainless steel material. To reduce the heat loss due to radiation, the inner tank is wrapped with multiple pairs of reflecting and insulating layers which reflects the heat radiation away. This combination of multi-layer insulation and vacuum is called super-insulation. In practice, the vacuum level of the dewars deteriorates over long period of time and needs to be revived by re-evacuation. The methods, tools, time of evacuation depend on the condition of the dewar. In-house techniques were developed and successfully re-evacuated and revived many dewars at Low Temperature Facility, Tata Institute of Fundamental Research, Mumbai. The paper throws light on the extensive experience explaining the specific techniques and methodology for the reconditioning of vacuum in the cryogenic dewars.
Keywords
Dewar, Evacuation, Vacuum, Evaporation Rate
Reference
| [01] | Technical note on “Procedure for Re-evacuation of Cryogenic Equipment” by Cryofab [Ref: http://www.cryofab.com/manuals/Cryofab_re-evacuation_of_cryogenic_equipment |
| [02] | Technical Note on “Vacuum Levels in Typical Cryogenic Vessels” by M/s Wessington Cryogenics. Ref: http://www.wessingtoncryogenics.com/what-we-do/frequently-asked-questions/vacuum-levels-in-typical-cryogenic-vessels/ |
| [03] | J. Sequeira, Vacuum re-conditioning of cryogenic dewars. Bulletin Indian Vacuum Society 2004, 7 (2), 3-14. |
| [04] | A G Hedukar; K V Srinivasan, Revival Techniques of Cryogenic Dewar, Poster presentation at ACASC-2013, Cappadocia, Turkey. |
| [05] | Paper presented titled “Revival Techniques of Cryogenic Dewars” at the 5th National Conference on Design, Materials & Constructions – NCDMC’16” organized by School of Mechanical & Construction Engineering Department of VEL TECH University, Chennai during April 2016. |
| [06] | Technical note on “Cryogenic Dewar Maintenance” by Tristan Technologies, USA. Ref: http://www.tristantech.com/pdf/dewar_maintenance_v2.pdf. |
| [07] | A G Hedukar; K V Srinivasan., Revival Techniques of Cryogenic Dewar, Oral presentation at IVSNS-2009, CEERI, Pilani during the National Symposium on Vacuum Technology and its Applications to Electronic Devices and Systems. |
| [08] | Installation and Pump out instruction manual by M/s CryoComp, USA. Ref: http://www.cryocomp.com/wp-content/uploads/2016/04/vacuum-valves-v1000-installation-pumpout-datasheet.pdf |
| [09] | FUNDAMENTALS OF CRYOGENIC ENGINEERING - By MAMATA MUKHOPADHYAY. 2010 PHI Learning Pvt. Ltd. |
| [10] | Randall F. Barron, Gregory F. Nellis., Cryogenic Heat Transfer, Second Edition, CRC Press. |
