On Demand Cooling System for Mine Rebreathers

Details

• Personal Author:
  Srinivas G
• Description:
  In this SBIR project, TDA Research is developing a new, on-demand cooling system for the long duration rebreathers often used for mine rescue operations (i.e. mine rescue reentry rebreathers). Long duration rebreathers are self-contained, closed circuit, pure oxygen backpack sized units used by rescue personnel to reenter an incident area after an accident to rescue stranded personnel and perform other tasks necessary to stabilize the area. Rebreathers conserve air by recirculating exhaled air through a system that chemically scrubs out CO2 and meters in O2 (from a small compressed gas cylinder) to maintain an O2 content of at least 19.5% in the inhaled air. TDA Research set out to develop a long duration rebreather cooling system that can cool 40 degrees C, 100% RH inlet air to a constant 35 degrees C, even with changing air flow rates and heat loads. To achieve this goal, we accomplished these four tasks in the Phase I project: 1. Analyze heat exchangers 2. Build test apparatus 3. Test proof-of-concept cooling system 4. Develop preliminary compact design for Phase II We also fabricated and tested the preliminary Phase II prototype. The proof-of-concept system worked extremely well. It cooled the air in approx. 6 minutes, held a constant outlet air temperature for the full four hour test, and maintained pressure in the 30 psig heat exchanger, which prevented moisture in the air from freezing on the surface. Our test rig included a system for conditioning the inlet air to 40 degrees C, 100% RH, a system for cooling the air using the boiling of R134a and evaporation of water into dry R134a gas, and a system for capturing and recycling the used R134a. We also ran some variable air flow rate experiments, including one with seven different air flow rates (20 L/min to 62 L/min). The proof-of-concept prototype handled all of these test conditions excellently to accommodate a large range of air flow rates, and varied its R134a consumption rate to handle the changing heat loads, while maintaining constant outlet air temperature. While working with the proof-of-concept system, we were able to simplify the TCV, moving from proportional control to binary open/close control. We also simplified the PCV by moving from a pneumatic valve to an electronic solenoid valve. We also increased the water capacity (by >3.4x) of the low pressure heat exchanger by using a robust high capacity PVA chamois. After testing our proof-of-concept system, we designed a preliminary prototype which combined the 30 psig and low pressure heat exchangers into a single unit that was 50% smaller and 76% lighter than our first generation cooling prototype. It also used a smaller and lighter TCV and a smaller, lighter, and fully passive PCV. We used additive manufacturing to print the prototype design out of aluminum and replaced the proof-of-concept cooler with the new prototype in our test rig. We tested the new compact heat exchanger with the same variable air flow rate protocol used for the proof-of-concept prototype system and it performed even better. Both units were able to quickly adjust the R134a flow rate as the air flow rate changed, so as to maintain constant outlet air temperature, and both consumed an almost identical amount of R134a (only 0.14% difference). Additionally, the compact system was able to cool the air even faster than the original proof-of-concept prototype (going from approx. 6 min cooling time to <1 min). With additional design work, we can likely shrink the temperature swings while further reducing the size and weight of the cooling system. [Description provided by NIOSH]
• Subjects:
  Air Movements Occupational Health Oxygen Safety Temperature
• Keywords:
  Air Flow Air Treatment Equipment Cooling Systems Equipment Design Equipment Testing Mine Rescue Oxygen Deficient Atmospheres Rescue Technology Scrubbers Temperature Control
• Series:
  Grant Final Reports
• Publisher:
  National Institute for Occupational Safety and Health
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Final Grant Report
• Place as Subject:
  Colorado ; OSHA Region 8
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Division:
  OEP - Office of Extramural Programs
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  1-28
• NIOSHTIC Number:
  nn:20052569
• Citation:
  Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, R43-OH-011158, 2018 Mar; :1-28
• Contact Point Address:
  Dr. Girish Srinivas, TDA Research, Inc., 12345 W. 52nd Avenue, Wheat Ridge, CO, 80033-1916
• Email:
  gsrinivas@tda.com
• Federal Fiscal Year:
  2018
• Performing Organization:
  TDA Research, Inc., Wheat Ridge, Colorado
• Peer Reviewed:
  False
• Start Date:
  20160915
• Source Full Name:
  National Institute for Occupational Safety and Health
• End Date:
  20170915
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:9b0711311d687acf0faf77f449ddbcc53a0843ed1644493da629d37f2eb927cd229ce2958f3f7c946a0d45f06fcc168b77585ae5befec7d3410273e069ddb1a6
• Download URL:
  https://stacks.cdc.gov/view/cdc/218712/cdc_218712_DS1.pdf
• File Type:
  [PDF - 1.50 MB ]