Explanation of Specific Heat and Internal Energy in Engineering

In thermodynamics, heat transfer, and fluid mechanics a very good understanding of specific heats for liquids, gases, and solids. These are the fundamental information before starting these engineering disciplines. Here, we explain them. 

First of all, you need to understand what the ‘ideal gas’ means. An ideal gas is the state of gas in which molecular actions are neglected. Gases approximate to ideal gas phase with the increasing temperature and decreasing pressure. 

An ideal gas is an assumption in engineering calculations. If you are assuming a gas as an ideal gas, you can use the equation below; 

Here, ‘P’ is the absolute pressure, ‘T’ is the absolute temperature, ‘R’ is the gas constant and ‘ρ’ is the density. 

What Is the ‘Specific Heat’? 

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Specific heat is the required heat to increase the unit mass’s temperature by one degree. It can be in Kelvin or Celsius. Specific heat is defined in both constant volume and constant pressure. So there are two specific heat values; specific heat in constant pressure(Cp) and specific heat in constant volume(Cv). 

Specific heat in constant pressure is higher than the specific heat in a constant volume. Because of the constant pressure process, the system must expand and there will be additional energy required to increase the volume of the system. This difference is given as ‘R’. 

So, if you add ‘R’ to the specific heat in constant volume, you will have the specific heat in constant pressure value. 

Specific Heats of Incompressible Substances

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The meaning of incompressible substance is that if the pressure and volume of the substance do not change in a process, this substance is called incompressible. So, for the incompressible substances, the specific heat does not change with constant temperature or constant pressure. This is only called specific heat(C). 

Solids have only one specific heat and gasses have generally two. 

Calculation of Internal Energies of Substances

Specific heats are generally used for finding the internal energy change of substances. If you want to find the internal energy change of a mass of a substance between two temperatures, you need to use the average value of the specific heat in this temperature range. Because specific heat value changes with the temperature. 

These formulas are used to find the internal energy changes of substances. The ‘m’ is the amount of mass. 


The general expression of specific heats, internal energy calculations, incompressible substances, and ideal gases can be summarized like above. 

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