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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.
Temperature distribution on the internal pump assembly
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 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.
Path lines illustrate the flow through the compressor
Temperature distribution on a vertical plane
through the crankshaft axis
The results of the numerical simulation have been validated using an
experimental setup 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%.
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