HAVE YOU EVER WONDERED?

Whither the teakettle whistle

With the winter weather comes the  flu and cold season, which means this device will be getting alot more attention.

Did you know...

Despite decades of brewing tea in a whistling kettle, the source and mechanism of this siren sound of comfort has never been fully described scientifically. Acknowledging the vibrations made by the build-up of steam escaping through two metal spout plates is about as far as the explanation went -- and was good enough for most people.

But not for a team of engineering investigators, who have at last illuminated the mystery. Through a series of experiments, the team has produced a breakthrough in breakfast musings with the world's first accurate model of the whistling mechanism inside the classic stovetop kettle.

They have located the physical source of the teakettle whistle at the spout as steam flows up it, and identified a two-mechanism process of whistle production. Their results show that as the kettle starts to boil, the whistle behaves like a Helmholtz resonator -- the same mechanism that causes an empty bottle to hum when you blow over the neck.

However, above a particular flow speed, the sound is instead produced by small vortices -- regions of swirling flow -- which, at certain frequencies, can produce noise.

The findings are potentially able to explain familiar problems of other wayward whistles, such as the annoying plumbing noises caused by air trapped in pipes or damaged car exhausts.

To interrogate kettle whistles, the team tested a series of simplified kettle whistles in an apparatus by forcing air through them at various speeds.

They then recorded the resulting sounds produced by rushing air, plotted the frequency and amplitude data of the sound, then analyzed it to identify trends in the data. They also used a two-microphone technique to determine frequency inside the spout.

Vortex production starts as steam comes up the kettle's spout and meets a hole at the start of the whistle, which is much narrower than the spout itself. This contracts the flow of steam as it enters the whistle and creates a jet of steam passing through it.

The steam jet is naturally unstable, like the jet of water from a garden hose that starts to break into droplets after it has traveled a certain distance. As a result, by the time it reaches the end of the whistle, the jet of steam is no longer a pure column, but slightly disturbed.

These instabilities cannot escape perfectly from the whistle. As they hit the second whistle wall, they form a small pressure pulse. This pulse causes the steam to form vortices as it exits the whistle, and it is these vortices that produce the siren sound that has conditioned millions of people to anticipate the coming of the tea.

HELP TO NEW AND EXISTING BUILDING TO BECOME ENERGY EFFICIENT

Sensor Suitcase - Brings Energy Efficiency to Small Commercial Buildings

Most buildings in the U.S. don't perform as energy-efficiently as they could simply because energy-using equipment in the building has never been set up to maximize energy performance. Thermostat set points are too low or too high, so rooftop units (RTUs) cool buildings down below recommended temperatures, or keep them too warm (or both).

Or, there is no difference in the set point during hours when the building is unoccupied versus occupied-turning the heat and space conditioning down during unoccupied hours helps lower energy bills substantially. Lights may be left on at night when no one is in the building, or there may be daytime opportunities in spaces that are not continuously occupied.

These are only a few of the problems that energy performance professionals see in the field, problems they can correct through retro-commissioning,the process of assessing the energy performance of an existing building, and then tuning its systems, and implementing no or low-cost energy efficiency improvements. When this is done to a new building, it is called commissioning.

Research published in 2009 by scientists demonstrated that in a large sample of existing buildings, retro-commissioning could save as much as 15 percent of a building's annual energy use, and pay for itself in less than a year, through the resulting utility cost savings.

In large commercial buildings, where the cost-effectiveness of this process is highest, retro-commissioning is beginning to become more common, thanks to growing awareness of its economic benefits to building owners and operators, as well as a thriving industry of building energy performance professionals.

In smaller commercial buildings efficiency efforts, including retro-commissioning have been hampered by several factors.

Small commercial buildings do not typically have budget or business economics that allow investing in enhancements such as comfort and energy improvements. They also don't have in-house staff with the expertise in building systems who can perform retro-commissioning or identify improvement opportunities.

The Sensor Suitcase, is a turn-key hardware and software solution that non-experts can use to generate low or no-cost recommendations automatically on how to improve a building's operating costs, comfort and energy performance.

This project is accomplished by 'embedding' the knowledge and skills of a highly experienced building commissioning practitioner into a scalable hardware and software package that can be easily deployed by a variety of building services personnel to make it easier for building owners and operators reap the benefits and cost savings for building commissioning.

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