for Heat Transfer Analyses
by George Moore, PE, Fluids
& Heat Transfer Manager, J Tarpoff Corp, 513-932-9777 firstname.lastname@example.org
A significant amount of
information is required in order to perform a heat transfer analysis on any
type of component.?By accumulating this information before you start into the
analysis, the calculation itself can be completed in a smooth and efficient
manner.?This will hold true for a simple 1D hand calculation or a complex 3D
finite element model.?The following provides a checklist for accumulating the
types of information you will need to provide the analyst in order to successfully
complete the project.
- Problem Definition:
?/span>The most important information to have before starting the analysis
project is a clear understanding of how the component is used and how the
result will be used.?This will determine the type of analysis that is needed.?
A component that must withstand severe transient thermal gradients which control
stresses at life limiting locations will require a complex transient model.?
The airflow required to maintain the bulk temperature of a component, such
as a motor, below a set value can be accomplished with a steady state hand
- Component Description/Geometry:
?/span>As a minimum, you will need the volumes and surface areas of
the parts in question.?Additional information that may be needed includes
surface finish and contact pressures at mating surfaces.?Also, as the parts
become more complex the component geometry can be used to identify simplifications
that can be made to the model.?For example, a small fillet radius that may
be important to the stress analysis will have no significant impact on the
heat transfer and will complicate the generation of mesh to represent the
- Materials and Properties:?
All materials used in the component must be identified in order to
determine the thermal properties.?The properties normally required are conductivity,
specific heat, mass and surface emissivity.?All
materials must be considered.?A coat of paint or oily dust can significantly
change the emissivity and can provide sufficient
insulation to slow the transient response.
- Flow Systems: ?/span>Most
heat transfer problems involve some type of fluid flow system that can move
heat energy into or out of the component.?This can range from free convection
cooling to complex pumped flow networks with separate heat exchangers.?To
complete the analysis, the heat transfer medium has to be identified (e.g.
air, water, oil) and the flow network must be laid out and flow rates identified
- Heat Sources and Sinks:
?/span>All sources and sinks need to be identified.?The primary sources
are usually easy, but more subtle sources may be present.?Friction, as a
heat source, should always be accounted for when moving parts or viscous flows
are involved. ?/u>In rotating components, pumping and windage can be significant.?Solar heating and radiation
to the night sky should be determined for any component operating outdoors.
- Types of Heat Transfer:
?/span>Four types of heat transfer define the system to be analyzed.?
These are conduction, forced convection, free convection and radiation.?This
step requires information from all of the above steps and is generally the
most challenging part of the analyst抯 job when setting up boundary conditions.
The items given above are
by no means an exhaustive listing of all details that are required by the heat
transfer analyst, but it does cover the types of information required.?Also,
the dividing line between what is provided and what must be determined as part
of the analysis becomes obscure in items 4 ?6.牋 In item 4, the internal flows
generally have to be determined by the analyst.?In Item 5, friction, pumping
and windage are calculated based on the component
geometry, dynamics, and coolant flows.?Item 6, setting up boundary conditions,
is normally completely the job of the analyst.?
By providing as much of
the information covered above as possible, you will create a situation where
you are paying your analyst to do analysis and not to search for information
that should already be available.
About the author:
George Moore, PE has performed
detailed heat transfer analysis on military and commercial jet engines for more
than six years. Prior to that, he spent thirteen years modeling and analyzing
heat transfer and fluid flow loss of coolant scenarios of US Naval nuclear power
plants for the Bechtel Bettis laboratory (formerly operated by Westinghouse