Anthony Kelley, Lead Flow Research Engineer, Marshall Space Flight Center, Huntsville, AL
- Saturday, 18 November 2006
As petroleum prices spiral higher, new technologies are being developed to help keep prices down. The balanced flow meter, technology originally developed by NASA for the space shuttle, promises to ease pain at the pump by being more precise and consuming less power than current metering devices. Leading the project is NASA engineer Anthony Kelly.
NASA Tech Briefs: What is the balanced flow meter, and how does it work?
Anthony Kelley: The balanced flow meter is a replacement for standard orifice plates. It’s a thin plate that goes into a flow stream of any shape, usually a round channel, normally a pipe, and instead of a single hole in the middle, it has multiple holes that are drilled and spaced per special sets of equations to balance energy across the face of the plate. And what this results in is very rapid return to fully-developed flow downstream of the plate. The fluid flows through the plate, and as it flows through, it creates a pressure differential across the plate; it’s called a differential head flow meter. So, that pressure difference across correlates to flow rate in the plate, through the plate, through the pipe. And that lets you calculate flow in systems, and the trick to this thing is that it is extremely accurate and gets you back to fully-developed flow very rapidly.
NTB: Why was it developed?
Kelley: We started off looking for something that would be a flow meter compatible in LOx (liquid oxygen). Liquid oxygen is a pretty severe fluid to operate in; if you have moving parts or any kind of part-friction, you can start a fire that consumes everything. Even metal will burn in the presence of LOx. And so we were looking for some kind of flow meter for rocket engine systems that would be LOx safe, LOx compatible. And this thing has no moving parts; it’s very compatible with LOx.
And that fills a need that is kind of unique. We have in the past put turbines in place of a LOx flow meter, and we had one fail and wiped out a test stand. I mean, literally torched it. You have to be very aware of that, and as a result, we typically don’t fly with LOx flow meters. This device is meant to go in there and be a replacement and be able to actually be used in flight applications.
NTB: How is it superior to a single orifice flow meter?
Kelley: To compare and contrast, they both cost about the same amount to make. They both fit the same profile — like in industrial applications, they’ll build welded-pipe systems to accommodate a quarter-inch or half-inch plate. We can be a direct, drop-in replacement to an orifice meter.
Single-hole orifice meters are used world-wide, and they are the number-one, most common flow meter technology ever purchased. I mean, there are billions of these things used around the world. So this is a direct replacement for all of those devices, and when you drop it in into the same pipe system, with the same instrumentation, you usually get about a ten-times improvement in accuracy. You get what is called a “permanent pressure loss” — any time you restrict the fluid, you loose fluid energy, and you never recover that. If you have a 100 PSI upstream and you go through a restrictive orifice or a plate like it, you may have 90 PSI downstream. Well, a standard orifice will have 70 PSI downstream. Our plate will have you almost back up to 100 PSI downstream. It’ll have like 95. That’s permanent pressure loss, and it does not have near the loss.
It also does not need to have straight pipe runs. With the single-hole orifice, if you put it downstream of an elbow or pipe bends or things like that, you get non-uniform flow distribution. That changes the accuracy of the meter and can mess things up and make it inaccurate. With the balanced flow meter, you don’t have that problem, because it actually conditions flow at the same time it is metering flow. And with just a very small Delta-P across the plate, it doesn’t care if you’re right downstream of double elbows or anything like that. We’ve actually tested it in those configurations, with no degradations in accuracy.