Mechanical PE Exam Topic Concepts

Specific Heat Capacity

Get the Specifics of Specific Heat Capacity

Today’s concept discussion is on specific heat capacity.  Basically, different fluids will ‘heat up’ differently (more specifically they store heat differently).  In Thermodynamics you need a way to take the fluid’s properties for storing heat into account.  That’s where specific heat comes in.

Before we discuss specific heat capacity we need to define heat capacity.  Heat capacity, as shown in the formula below, is the heat added divided by the change in temperature.  In other words, it is a measure of how the temperature changes for a given amount of heat added.  Obviously, the temperature change of the fluid will also depend on the amount of fluid.  Therefore, the specific heat (lower case c) is the heat capacity per unit mass.

specific heat capacity formulas

Specific Heat Capacity of Gases

For gases we need to define two separate specific heat values.  The temperature change will depend on whether the volume is held constant or if gas is able to expand.  We use a subscript v to define specific heat capacity at a constant volume.  A subscript p is used to define the specific heat capacity at a constant pressure.  The specific heat ratio is defined as the ratio of the constant pressure specific heat to the constant volume specific heat.

How do we use Specific Heat Capacity in Thermodynamics?

There are several types of problems in Thermodynamics that use specific heats.  It can be used to determine final equilibrium temperatures.  It is used to determine the change in internal energy of a gas when heat is added or subtracted.  For the PE exam you want to have a table of specific heat values for common gases.

What do you think?

I hope this short blog helped define specific heat capacity.  It is commonly used in Thermodynamics, so it is important to understand its use.  Let me know if you have thoughts or questions about this topic.  Also, head over to www.MechanicalPEAcademy.com/Facebook to like my Facebook page.  It has updates and additional content.

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