Electronics Cooling Series: Specific Heat Capacity
David W. Sundin, Ph.D.
One of the most important characteristics of an efficient heat transfer medium is a high “heat capacity”, which is also referred to as “specific heat” (1). Sometimes, the phrases are used together, as “Specific Heat Capacity”. What, exactly, is the heat capacity of a material, and how does it affect the efficiency of cooling of a circuit board or in a data center?
When a material is heated, there are three factors that dictate the final temperature: the mass of the material being heated, the makeup of the material and the amount of heat applied. Even with the same amount of heat applied, different materials will end up at different temperatures. Specific Heat Capacity quantifies this different behavior. Specific Heat Capacity is the amount of energy that must be applied to a given material to raise its temperature one degree.
Here’s an example: Air has a low heat capacity (1.003 J/g-K). Water has a high heat capacity (4.18 J/g-K). If you apply heat to the same mass of each material, they will end up at have very different temperatures. The air will get hot very quickly, while the water requires much more heat input to get hot.
This ability to absorb heat means that even low flowrates of water can move a significant amount of energy. If a different fluid were chosen that has a lower heat capacity, the system would have to be scaled up: higher flowrates, greater radiator surface area, etc.
Here’s a chart of heat capacities of popular heat transfer materials:
|Air||Water||Synthetic or Petroleum Oil|
|Heat Capacity, W/m-K||1.003||4.18||2.56|
You can see that air and water frame the spectrum, with oils being in the middle.
Heat capacity is only one of the components of heat transfer. A fluid’s viscosity and flow patterns are also extremely important. Also, when choosing a heat transfer medium, external factors must be taken into account. Contact a suitable expert or supplier of heat transfer fluids for additional assistance and information.
David Sundin can be reached at:
U.S Telefone: 903-231-3141
(1) Specific Heat is a way to express heat capacity as a dimensionless number by comparing a heat capacity value with that of water, which for our purposes is 1.
(2) Heat Capacity of a material varies slightly as a function of temperature.