Wednesday, August 3, 2016

1738: The Bernoulli Principle

The market for a device to create a spray was looming.  Perfume marketers yearned for a device to spray their products onto ladies.

The medical industry yearned for a product to spray medicine into the airways of respiratory patients.  Yet no such product would be possible without knowledge of the Bernoulli Principle.

We are not concerned about the perfume industry here, yet there are two times in the history of aerosol therapy that the perfume market actually helped the medical industry.

The first time was during the mid 19th century, and the second was in the mid 20th century.  The first produced the nebulizer, the second our modern inhaler.

As far as the inhalation of medicines, the medical industry already had one very good method, and that was the inhalation of smoke and steam.  The problem was that there were two different types of medicine: volatile and non-volatile.

Volatile medicines could be ignited and thus inhaled.  Tobacco, for example, is volatile and can be stuffed into a pipe and burned.  Strammonium and Belladonna were volatile, and could be placed on a brick, stone or plate, ignited, and the smoke inhaled.  This knowledge was known since the ancient world.

By the mid 19th century the search was on for a device that would turn a solution into a spray.  It was believed that such a device would break down the solution into atoms, and in this way the solution could be inhaled.  This breakdown was thus referred to as atomization, pulverizing or nebulizing, and the devices created were often referred to as atomizers, pulverizers or nebulizers.

Yet no such machine would have been invented if not for the discovery of the Bernoulli Principle. Daniel Bernoulli observed that when water hits a rock it creates a mist that can be inhaled. He published a book in 1738 where he described that a similar effect could be created by forcing water through a narrow tube.

His concept was based on the fact that the faster water flows through a tube, the less the lateral pressure will be.  A decreased lateral pressure is also referred to as a negative side stream preassure.  If there is a hole in the side of the tube, the negative pressure will force water into the stream.

This same concept was used in creating the first nebulizers, only using air.  Air is forced through a tube, and a hole in the tube is connected to a container with a solution in it that contains the medication.  The fluid is basically sucked in due to the negative sidewall pressure, and turned into a spray or mist. (1, page 61)

This concept is illustrated in figure 1.  In this figure steam is used to create the flow and the negative side stream pressure.  As the steam flows through the tube the negative side stream pressure causes the solution in the cup to be sucked into the stream, and thus a spray is developed.

References:
  1. Clark, William F., Paul J. Mathews, Kenneth A. Wyka, "Foundations in Respiratory Care," 2002, Delmar Thomson Learning

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