Patent Grant
9216309
U.S. Pat. No. 6,116,049
None
None
None
The adiabatic expansion nozzle (U.S. Pat. No. 6,116,049 issued Sep. 12, 2000 to DOT, inventor Robert Filipczak) demonstrated superior firefighting ability. Later designs, submitted after the patent was issued found that a replacement nozzle could be made for the ordinary discharge horn on a hand-held, 5-pound carbon dioxide fire extinguisher. Off-the-shelf fire extinguishers made by several companies were retrofitted with a suitably sized adiabatic expansion nozzle, by unscrewing the ⅛ NPT thread on the existing discharge horn and screwing in the adiabatic expansion nozzle. The nozzle worked well but was not very robust. Solder joints failed in some versions of the nozzle and residual dry ice developed inside and could lead to clogging. While the US Government tried to license the idea to private companies, none were willing to take on what was, in essence, a research project or go through the licensing procedure. The fluorocarbon (HFC-23) version worked in the FAA hidden fire scenario, but was not considered a viable replacement agent because high levels of hydrofluoric acid were produced, dangerous to anyone not wearing a self-contained breathing apparatus (SCUBA). Some of the FAA research efforts are contained in an internal publication, “Development and Performance of an Adiabatic Expansion Nozzle for Improved Fire Extinguishers” DOT/FAA/AR-TN01/60. The project has been dormant since the retirement of the inventor from DOT in 2006. All subsequent research, design, and reduction to practice has not involved DOT support or moneys.
The previous design in U.S. Pat. No. 6,116,049 demonstrated the ability to produce dry ice but was not properly sized nor optimized for hand-held fire extinguisher use. The new design minimizes previously encountered problems and has been made robust and practical. Other potential uses and firefighting applications are discussed.
Accordingly, it is the object of this invention is to calculate and execute the designs of adiabatic expansion nozzles to fight a wide array of home, automobile, commercial and military fire scenarios. This is the specific design for the Underwriter's Laboratory 5-B rated, hand-held 5-pound carbon dioxide fire extinguisher, but other applications for the device are also explained. Calculations are presented to describe appropriate tubing diameters and tube offsets for this specific application.
It is a further object to design and produce adiabatic expansion nozzles in various sizes depending on the size of a potential fire The nozzle can be scaled to almost any size, determined only by the flow rate and size of the carbon dioxide containment vessel.
It is a further object to use an adiabatic expansion nozzle for fixed fire systems. Current carbon dioxide systems call for total flood of spaces, which is very hazardous to occupants. Deposition of dry ice stratifies the carbon dioxide, collecting and settling to the floor, minimizing personnel hazards.
It is a further object to use an adiabatic expansion nozzle to inert large capacity fuel tanks and create an internal fire fighting capability for suitably outfitted tanks.
It is a further object to provide a cryogenic cooling device with low output velocity and uniform temperature discharge.
As shown in
Adiabatic is a term from thermodynamics that means “without the addition or subtraction of heat.” At room temperature, CO2 exists as a liquid with a vapor pressure of 830 PSI (pound of pressure per square inch). At room pressure (760 mm Hg), CO2 exists as a gas or as a solid at −79 C. Solid CO2 is also known as “dry ice” and is used to transport frozen foods and other items. The CO2 does not melt, or turn into liquid, but rather sublimes directly to the gas phase: hence the term “dry” ice.
For an adiabatic system, think of that tank of liquid CO2 as being in a thermos bottle. No heat is being added or subtracted: if the contents are cold or hot they will remain cold or hot Now, think of that bottle as not having a lid, but an airtight piston holding the pressure of the liquid. If the piston is raised, increasing the volume of the bottle, two things happen. The liquid boils as the volume increases, and the remaining liquid get colder from subtracting the heat of vaporization from the liquid turning to gas. If the piston is lifted until the bottle is at room pressure, the contents of the bottle are now gaseous and solid CO2, with no liquid remaining. If weights are applied to the piston until the pressure is again 830 PSI, the gas will increase in temperature, the dry ice will melt, and at the end of the cycle the CO2 will be liquid at room temperature. Remove work, the volume expands and the temperature drops ΔW=−ΔQ. Add work (subtract it from the environment), the volume shrinks and the temperature increases.
The adiabatic nozzle simulates this, in that liquid CO2 is allowed to expand in a very small volume while the flow is reversing direction. The discharge from the nozzle is a low-pressure dry ice snow. True adiabatic process are reversible, however. Here the CO2 cannot be put back in the bottle as liquid. As shown in the Technical Note, theoretical conversion efficiency from liquid to solid is 31% but this would be with a near zero discharge pressure.
The problem in the initial nozzle design is twofold. The distances between end caps 22 and 34 and between end caps 18 and 26 are not specified. This leads to accumulation of dry ice inside the nozzle and can cause clogging. Also, the tubing diameters were selected based on what was easily available, not what might work best. The prototype in the issued patent proved that dry ice snow could be formed continuously, but there was no real attempt at optimizing a hand-held fire extinguisher.
Experiments showed that turbulence in not desirable. Coiling the inlet tube T1 reduced conversion efficiency. Solid CO2 would build up in any dead areas that allow flow stagnation near the end caps. Any areas where flow would constrict, rather than expand, reduced efficiency. The new design eliminates or reduces these problems.
Liquid CO2 reaches the nozzle and flow through the nozzle is controlled by the diameter of the inlet tube T1. The area expansions for the design are 10× from T1 into T2 with subsequent expansion to be 2×, for the hand-held extinguisher.
If the nozzle is used as a stationary system, for example in a galley situation or above machine equipment, throw distance is not i important so the expansion ratios can be increased to convert more of the liquid into dry ice. Fuel storage tanks can be suppressed from inside the tank. Dry ice floats on fuel or solvents, breaking the fuel air boundary, and extinguishing a fire.
A 5-pound (Underwriter's Lab 5-B rated) carbon dioxide extinguisher has a minimum discharge time of 8 seconds. 3/16 in. 0.016 wall brass tubing was found to have the required flow rate. The needed tubing diameters can be calculated based on the outside diameter (OD), the tubing wall thickness, and the desired degree of expansion. Using expansion factors of approximately 10×, 2×, 2×, 2×, and 2× the dimensions are calculated. Telescoping brass tubing is commonly available through hobby shops from 1/16-in to ¾-in 1/32-in. increments, with approximately/64 (0.016-in.) wall thickness.
The area of a circle is A=πr2, where A is the area and r, the radius of the circle. The circumference of a circle is L=2πr, where r is the radius. The area of a cylinder is A=Lh where L is the circumference multiplied by height, h.
If the inlet is 3/16-in tubing, the inside diameter is 5/32-in and the area A=π( 15/64)2 A=0.0192 in2 To have a 10× expansion the area, the second tube is 0.192=π(r2) and r=0.247. The inside diameter of the tube is 0.494 in. so 17/32 tubing is used for the first expansion.
To have the annular space between the second and third tubes equal to twice the area of the second tube, where r is the respective radii of T2 and T3:
A3=2A2=2(0.192)=0.384 in2
π(r2T3)−π(r2T2)=0.384
π(r2T3)=0.384+0.192=0.576
r2T3=0.576
rT3=0.428 or the tube diameter for T3=0.865 in. is rounded off to ⅞ in.
A4, A5, and A6 are calculated in the same manner. The remaining tubes are determined to be 1⅜ in., and 2 in. The ID of the discharge horn into which the nozzle is situated should be 2¾ in. This maintains the same carbon dioxide discharge rate as existing 5-B rated fire extinguisher and the same discharge horn dimensions.
Since the area of the cylinder between tubes at flow reversal is equal to the area of the inner tube, π r2=2πrh h=½ r. Because the annual space between tube is twice the area of the inside tube the distance from the end cap to the tube can be equal to the radius of the inner tube, which allows the 2× expansion at the point of flow reversal. The distance between T2 and the end cap on T3=¼ in. Less than that distance would lead to contraction, instead of expansion. More than that invites deposition of solid on the end cap.
Also of importance is to remove the eddy at flow reversal that occurs in the original design at the squared ends of the cylindrical shape, or dry ice will build up. Since the distance between tube and end cap is equal to radius, the rounding should be a dimension between the diameter, 2r, and r the radius of the outer tube.
The tubing sizes calculated for this application which are commercially available were: T1= 5/16″- 1/64″ wall, T2= 17/32″- 1/64″ wall, T3=⅞″-0.025″ wall, T4=1⅜″-0.025″ wall, T5=2″-0.025″-wall and T6 the inside diameter (ID) of the discharge horn to be 2¾″.
The radius of the curve of the end caps was selected to be a uniform ⅜-in. to minimize tooling cost for the end cap stampings. Height, H, is measured from the inner tube to the curved portion of the end cap, E. ⅜-in. is larger than all of the annular distances between tubes, and H is measured to the intersection point with the inner tube and curved portion of the end cap. The radius of curvature of the end cap should be ne less that the distance between tubes.
The discharge horn 10 is represented as a round tube, curved at the end where it meets inlet tube 12. Depending on the application, the outlet could focus in, expand out, or use vanes as in the original patent (U.S. Pat. No. 6,116,049) to direct solid flow but not inhibit expansion. Depending on the application, the outlet can be square or rectangular to accommodate specific areas protected by fixed systems. The discharge horn represented in
| Number | Name | Date | Kind |
|---|---|---|---|
| 6116049 | Filipczak | Sep 2000 | A |
