The Secret Competitive Advantage for Military, Law Enforcement and Safety Professionals: Thermal Conductivity of IcePlate®

But - how does wearing the IcePlate® keep you warm and what is the science behind this conductive heating effect?

Thermal conduction is the transfer of heat between two bodies that are in direct contact.  On a microscopic level, this transfer occurs between the collision of particles and electrons within the bodies themselves [1].  When a warmer molecule collides with a cooler molecule, energy is transferred from the former to the latter.  In the case of the IcePlate®, the two bodies (the IcePlate® itself and the human body that is has contact with) are stationary relative to each other.  The speed at which the transfer of heat can occur is related to the difference in temperature between the two bodies (in this case the IcePlate® is filled with water warmer than the internal human body temperature of 98.6 degrees F) [1].  As you can imagine, if the two bodies were the same temperature, the rate of heat transfer would be zero.      

Different Materials, Different Conductive Properties

The answer has to do with thermal conductivity.  Different materials conduct heat at different rates.  Metal is a great conductor of heat, which means that it will transfer heat from your 98.6 degree F hand very quickly, making your hand feel cold.  Wood, alternately, is a poor conductor of heat, and in this case, will feel more room temperature to the touch [2]. 

Thermal Conduction Equation (I love equations!)

Let's talk a little bit about the equation used to calculate Thermal Conduction.  

Q/t = [kA(T2-T1)]/d

If looking at that equation gives you anxiety, don't worry we are going to break it down.  What do those letters and characters even mean?!

Q: Energy (in this case heat energy) measured in Joules

t: Time in seconds

(Watts are actually Joules per unit second.  So, Q/t = Watts.  That is what we will be solving for.)

k: Thermal Conductivity Constant.  This constant is material specific.  Each type of material has its own constant.  Change the material, change the constant.  Tin has a Thermal Conductivity Constant of 68.2 and the Constant for wood can range from 0.16 to 0.25 W/mK [3].

A: Cross sectional area.  The amount of heat transferred increases proportionally with surface area.  Imagine that an IcePlate® (at 10" x 12") will transfer more heat than a small hand warmer of the same temperature and material.

T2: Temperature of the warmer object in Kelvin.

T1: Temperature of the colder object in Kelvin.

d: The thickness of the material through which heat transfers.  The thicker the object, the slower the rate.  (This is particularly interesting when you compare the thin design of the IcePlate® with bulkier hydration systems.)

IcePlate® Heating Capability (in Watts)

k: The IcePlate® is made from a High Density Polyethylene (HDPE) with a thermal conductivity constant of roughly 0.50 W/(mK). [4]

A: The IcePlate® is the same size as a medium SAPI plate (10" x 12").  We need to convert our inches measurement into meters to keep our units consistent.  10 inches = 0.254 meters; 12 inches = 0.3048 meters.  A = 0.254 meters x 0.3048 meters = 0.07742 meters squared.

T2: Let's assume here that the temperature of the IcePlate® is 160 degrees F (the temperature of water coming out of a Bunn coffee machine that I was using the other day).  We need to convert this to Kelvin units (the primary temperature measurement in the physical sciences).  160 degrees F = 344.26 K.

T1:  Let's assume you don't have a crazy fever and that you have a normal body temperature of 98.6 degrees F.  98.6 degrees F = 310.15 K.

d: The IcePlate® has a width of 1 inch.  1 inch  = 0.0254 meters.

We have our numbers, so let's put them into our equation.

Watts = [0.50 * 0.07742 meters squared * (344.26 K - 310.15 K)]/0.0254 meters

52 Watts of Heating Power

Pretty cool, huh?

Note: This study is actually the Wattage if you were wearing the IcePlate® against your bare skin (which we do not recommend).  When you wear a base layer or a Safety Vest, you are adding insulation, which changes the rate of heat transfer.

Stay Warm (with IcePlate®) and Live Your Life (Efficiently)