April 25, 2016
Thermal Expansion

Posted by: Lee Bedingfield

Thermal expansion is the tendency of a body to experience transformation in volume when the temperature changes.  Basically as an object is heated, the molecular activity increases and the energy stored in the bonds between atoms changes.  With this increase in stored energy, the length of the molecular bonds also increase.  How much a material moves is measured by a materials coefficient of thermal expansion.  Thermal expansion is occurring everyday around you and most people never give it a thought.  Ever see those joints or spans along a bridge?  They are there to account for this phenomenon.  Let’s say a bridge was built and completed right now in Minneapolis without spans.  Things would be fine until one of those nice summer heat waves hit the Midwest and that bridge could buckle and crack.  Shrink fittings are another example where a bushing or other part is made slightly less than the diameter of the shaft.  You have to apply heat to the bushing so it will expand and then slide it over the shaft.  When it cools the bushing will have a nice tight fit.  So why should we even give thermal expansion a second thought?  Well anyone who has worked around HDPE pipe knows that it will shrink and expand quite a bit with temp change.  Any thermoplastic will have a much higher thermal expansion coefficient than say a metal.  You see a thermoplastic is a long chain of repeating subunits or monomers.  Because they line up in a chain the change in molecular bond length affects them greater.  Take the chart below as a reference.  MaxCell® innerduct is a thermoplastic but because it’s a woven mesh fabric the expansion will be minimized.  Under the same conditions, MaxCell innerduct will expand less than 1ft making it a perfect fit for applications with extreme temperature fluctuations.

MaxCell_thermal_expansion.jpg

 

* MaxCell® is a registered trademark of TVC Communications, a division of WESCO distribution, Inc.

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Category: Feature Articles, Cable management

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