Wind Turbine

appliances
Thermal
Mapping of
a Hermetic
Compressor
Temperature distribution on the internal
pump assembly
by Rahul Chikurde and S. Manivasagam, Kirloskar Copeland Ltd., Karad, India
The complex fluid flow and heat transfer
phenomena in hermetic compressors are
very difficult to analyze theoretically. Because
there is insufficient understanding of the physics
involved, assumptions are often made in order
to solve these problems analytically, and these
assumptions can have a negative impact on
the quality of the results. To cope with today’s
high-energy efficiency standards, there is a need
to overcome these limitations, so that the flow
and heat transfer inside the compressor can
be better understood.
At Kirloskar Copeland in Karad, India, CFD
has been used to perform a more rigorous analysis
of the entire compressor domain, including
the suction and discharge gas paths. The
ability of the FLUENT code to deal with conjugate
heat transfer (conduction and convection)
in a turbulent flow encouraged engineers to
perform a flow and thermal analysis for the
entire compressor. The effort has helped predict
such important characteristics as motor
winding temperature, and velocity and pressure
fields across the domain. The powerful
visualization tools have made it easy to see the
overall flow patterns along the gas flow paths.
The thermal performance of the compressor
plays an important role in the optimal working
of the appliance in which it is fitted. Hence,
it is necessary to carefully simulate the heat
transfer inside the compressor, since it governs
the energy efficiency of the whole system.
The most important contributors to the
thermal performance are the suction gas superheating,
which is mainly due to heat sources
20 Fluent NEWS spring 2002
related to the copper and iron (or core) losses
and the heat of compression, and volumetric
and energy losses occurring in the suction and
discharge gas paths. Other heat sources inside
the compressor are due to rotor and frictional
losses. Each of these effects is represented by
a volumetric heat source in the FLUENT model.
To date, the CFD analysis has provided predictions
for the temperatures on numerous
components inside the compressor. This information
has been used to help design more
efficient motors (with better cooling) and select
the appropriate Internal Overload Protector
(OLP), which protects the motor from overheating
under adverse conditions.
The results of the numerical simulation have
been validated using an experimental set-up
that uses conventional thermocouples to perform
thermal mapping of the compressor. The
numerical solution has been found to agree
well with the experimental results. Because
the simulation resembles the actual testing of
the compressor on the calorimeter test rig under
specified conditions, the compressor behavior
can be visualized and thoroughly understood
well before the prototypes are built and
tested. If need be, the compressor design can
be altered to obtain the target performance.
The success of the validation work has given
Kirloskar Copeland engineers the necessary confidence
to use CFD during the product development
stage for new equipment, thereby
reducing the number of prototypes for trial
and error, and the total design cycle time by
almost 30%. ■
Path lines illustrate the flow through
the compressor
Temperature distribution on a vertical plane
through the crankshaft axis