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De Laval nozzles
Posted by: Mike Clark (IP Logged)
Date: January 12, 2003 07:23PM
<HTML>De Laval nozzles
A month or so back David Nergaard suggested using the De Laval nozzle as a means of getting more air into the vaporising burner. I just got round to reading this up and a thought has hit me – we may already have it!
The De Laval nozzle tapers in to a constriction then expands to the output end, gas physics dictating that however much difference in pressure exists between the in and out ends, the gas throughput reaches a peak when the gas velocity through the constriction hits Mach 1. This applies to all constricted nozzle systems. However the interesting bit with the De Laval nozzle is that the proportions of the nozzle can be adjusted to accelerate the gas to higher supersonic speeds as it goes through the expanding output end. Given the right geometry the gas coming out of the nozzle can be made to exit the nozzle at supersonic speeds and not splay out into a wide cone of spray. This of course is what made it right for the De Laval turbine and might possibly help us to entrain more air.
It would be pretty much impossible to machine a De Laval nozzle on my 12 inch lathe but what if we turn the concept inside out? A jet with a flared or coned entry leading to a narrow parallel bore into which is fitted, point first, a tapered needle (ex wifely sewing box) thereby producing the required expanding outlet, annular rather than circular in cross section but does that matter? If the needle was long enough to stick out a little from the nozzle it seems quite likely that fluidics effects would also help the stream of gas to run straight.
Is this what we already have in some of the needle and jet type pilots? A bit of optimisation on the jet and needle might really pay off as the design of the De Laval nozzle has to be tailored to the gas pressure and rate of flow.
Any gas flow experts out there?
Mike</HTML>
A month or so back David Nergaard suggested using the De Laval nozzle as a means of getting more air into the vaporising burner. I just got round to reading this up and a thought has hit me – we may already have it!
The De Laval nozzle tapers in to a constriction then expands to the output end, gas physics dictating that however much difference in pressure exists between the in and out ends, the gas throughput reaches a peak when the gas velocity through the constriction hits Mach 1. This applies to all constricted nozzle systems. However the interesting bit with the De Laval nozzle is that the proportions of the nozzle can be adjusted to accelerate the gas to higher supersonic speeds as it goes through the expanding output end. Given the right geometry the gas coming out of the nozzle can be made to exit the nozzle at supersonic speeds and not splay out into a wide cone of spray. This of course is what made it right for the De Laval turbine and might possibly help us to entrain more air.
It would be pretty much impossible to machine a De Laval nozzle on my 12 inch lathe but what if we turn the concept inside out? A jet with a flared or coned entry leading to a narrow parallel bore into which is fitted, point first, a tapered needle (ex wifely sewing box) thereby producing the required expanding outlet, annular rather than circular in cross section but does that matter? If the needle was long enough to stick out a little from the nozzle it seems quite likely that fluidics effects would also help the stream of gas to run straight.
Is this what we already have in some of the needle and jet type pilots? A bit of optimisation on the jet and needle might really pay off as the design of the De Laval nozzle has to be tailored to the gas pressure and rate of flow.
Any gas flow experts out there?
Mike</HTML>
Re: De Laval nozzles
Posted by: David K Nergaard (IP Logged)
Date: January 15, 2003 11:08AM
<HTML>Using the DeLaval nozzle only helps when using high pressures. I don't think it worth the effort below 100 psi. It will hurt flow velocities at less than 40 psi.
Main burner? Worth a try, especially if you live in the mountains. Pilot light? Forget it!</HTML>
Main burner? Worth a try, especially if you live in the mountains. Pilot light? Forget it!</HTML>
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