A thermal analysis calculates the Conduction of energy across the geometry.

Heat Transfer method of Thermal Analysis

Conduction can be mathematically defined as:

Where

• Q = Heat flow
• k = Thermal conductivity, which is entered as a constant material property
• A = Cross-sectional area (calculated by software)
• = The change in temperature in the direction normal to the Area

Conduction is the basis of what is calculated throughout a model. The true power of a thermal analysis is properly defining how the world that isn't modeled effects a design. The external effects and some internal effects are defined as loads.

Thermal Loads can depict other types of heat transfer

Convection is the transfer of energy between a fluid and a solid (typically the surrounding air). Convection is mathematically defined as:

Where

• Q = Heat flow
• h = Convective heat transfer coefficient (entered manually, and assumed constant)
• A = Surface area of the selected surface (calculated by software)
• Ts = Surface temperature of the selected surface (calculated by software)
• T = Ambient fluid temperature (entered manually, and assumed constant)

To properly account for convection to the world around a model, the convective heat transfer coefficient is key. Many factors can affect the coefficient, from velocity of the surrounding fluid to what the surrounding fluid is. When we consider that computers often use fans for cooling, to increasing the velocity of the fluid is increasing the h value. The higher h value in turn reduces the temperature. The physical properties of the fluid also change the coefficient. To keep the same frame of reference, some computers use liquid cooling instead of air. The h values from a liquid tend to be more efficient (higher) than a gas.

A standard natural convection coefficient to air is in the range of 5-25 W/m^2*K. Many examples can be found online for different fluids or conditions.

Radiation is the transfer of energy between the model and the environment. Radiation is mathematically defined as:

Where

• Q = Heat flow
• = Stefan-Botzmann constant
• = Emissivity of the selected surface (entered manually)
• A = Surface area of the selected surface (calculated by software)
• = Surface temperature of the selected surface raised to the fourth power (calculated by software)
• = Ambient environment temperature raised to the fourth power (T entered manually, the software calculates it to the fourth power)

Using radiation assumes a view factor equal to 1.

Radiation loads only account for energy exchanged with the environment, radiation across the model (part to part, or surface to surface) is not considered. Radiation can become the dominant form of heat transfer in situations with high temperature changes or low flow rates. Notice that the radiation equation has the temperature values raised to the fourth power. As the temperature rises radiation can quickly become the dominant form of heat transfer. As previously mentioned, low velocities such as those in natural convection have low convective heat transfer coefficients. Radiation can become the more dominant form of heat transfer in these scenarios.

Heat Sources

There are three more loads that can add or remove heat to your analysis. These loads use the specific amount of energy instead of using a physics method to calculate the energy.

Internal Heat -

• Allows the specific amount of energy to be put into or removed from a body.

Heat Source -

• Allows specific amount of energy to pass through a surface.

Applied Temperature -

• Locks a surface to or body to a specified temperature. Allowing an infinite amount of energy to be generated or removed to maintain the specified temperature.