Written by Sarah Paulin
Nikola Tesla, the inventor of the Tesla Turbine, determined that there were three key points to achieving maximum efficiency with the turbine:
- Inlet Nozzle
- Disk Geometry
- Outlet Nozzle
The Inlet Nozzle:
The inlet nozzle is thought to be the most important
component with a complex shape that is needed to achieve maximum conversion of gas pressure to shaft horsepower. The two functions of an inlet nozzle include: conversion of gas pressure into gas kinetic energy; and directing that gas kinetic energy through parallel
streams and into the rotor, or turbine disk pack.
There are a variety of nozzle designs. The traditional convergent-divergent nozzle is seen in Figure 1.
The shape of the nozzle is most important for maintaining efficiency when converting gas pressure (the potential energy) into gas kinetic energy. Gas or steam enter through the nozzle at point A, which allows for an increase in velocity at point d (vena contracta). A rapid expansion of gas occurs due to the increase in volume beyond point d, which increases the velocity once again while simultaneously cooling the gas. Once past the divergent portion of the nozzle, a parallel section is needed on the end in order to straighten the flow.
The objective of a properly designed nozzle is to efficiently convert a stagnant, pressurized air mass into a high velocity gas. This increase in velocity will propel several times the speed of sound, reaching up to four thousand feet per second. The trans-sonic region is focused at the smallest diameter of the nozzle, d. In the divergent region, the gas becomes supersonic.
When constructing and designing an efficient convergent-divergent nozzle, it is most effective to begin with the exit point. The diameter of the parallel tube must be equal or slightly less to the width of the disk pack. This is to ensure that the gas is not released around the end plates. Note: disk packs that are wider require elongation rather than a round shape.
For example, a disk pack that is .5 inches between the end plates should be accompanied by a parallel nozzle region of 0.5 inches in diameter. Working backwards, the divergent angle should be 10 degrees with a divergent length being as long as possible.
The diameter of d is based on: the working pressure of A; the flow rate of the turbine horsepower; and maintaining the highest level of velocity.
It is important to try and keep the diameter of d as tight as possible while still ensuring high gas velocity in order to maximize the turbine's horsepower potential. Using the figures above, a diameter of 0.125 inches to 0.25 inches would be needed. The final calculation is of radius R. R=3/2d.
Figure 2 shows a nozzle design that is similar in principle to the traditional convergent-divergent nozzle, but is easier to construct. It is comprised of a straight tube which is centered with a shaped insert. This insert is to follow the same calculations as the traditional nozzle and secured in the center of the tube.
Disk Geometry:
Disk geometry is capable of providing maximum efficiency when the correct materials, spacing and
position is composed together. A high strength stainless steel (361 or 461) with bright polish is needed to begin. The disks should be spaced between 0.032 inches and 0.123 inches. The narrow spacing allows for increased torque, but lower horsepower. A star shape disk should be placed in the center with 0.5 inch round washers in the middle and outer positions. With a ten inch turbine, six washers would be used at the midpoint and twelve on the outer periphery. At the center of the engine, the exit nozzle is used to control back-pressure, horsepower, and maintain overall efficiency. Generally, the bigger the exhaust opening, the more horsepower and torque will be generated, however efficiency will decrease.
Outlet Nozzle:
The outlet nozzle, or exhaust port, will vary depending on three variables: torque; horsepower; and efficiency. Similarly to the inlet nozzle, the larger the port, the more horsepower and torque, however this lowers the efficiency of the turbine. For the most efficiency, a proportional exhaust system is needed.
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Related Articles:
Three Keys to Tesla Turbine EfficiencyPhoenix Navigation
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1944: Camano Class Light Cargo Ship was laid down for the US Army as FS-289 at Wheeler Shipbuilding in Whitestone, NY.
1945: Delivered to US Army.
1950: Acquired by the US Navy on July 1, 1950 and placed in service as USNS New Bedford (T-AKL-17).
1954: The movie, Mister Roberts, was made on the USNS New Bedford (T-AKL-17).
1955 - 1963: Used as a cargo supply ship for the Texas Towers, a network of advanced radar stations located off the Eastern Seaboard. In 1957, Capt. Sixto Mangual was commander of the AKL-17 and in 1961 it was rechristened the USNS New Bedford. The New Bedford, sailing out of State Pier, was keeping vigil when Texas Tower No. 4 callapsed off the New Jersey coast during a January 1961 nor'easter.
1963: Reclassified as Miscellaneous Unclassified (IX-308).
1971: The New Bedford (IX-308) served as a Torpedo Test Firing Vessel in the Puget Sound area.
1994: Ceremony in New Bedford.
1995: The ship was struck from the Naval Register on April 4.
2004: The Sea Bird's current disposition is a tuna long liner (fishing boat) out of San Diego, CA.
2006: Design of the Tesla Turbine began on June 11, 2006. The Sea Bird was sold by Defense Reutilization and Marketing Service for commercial service.
2007: The Sea Bird was drydocked for renovations.
2008: The Sea Bird setting sail to Sea-Tac in Seattle, WA.
2009 - 2010: The Sea Bird is currently docked at Seattle Sea-Tac.
