8/9/2019 Ex180 Electric Motor Cooling

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Copyright 2002 Fluent Inc. EX180 Page 1of 2

A P P L I C A T I O N B R I E F S F R O M F L U E N T

The task of distributed

power generation is

generally achieved by a

generator set consisting of

an internal combustion

(IC) engine coupled withan electric motor. Cooling

the electric motors is a

challenging task. In

addition to the heat

released from the coils,

the motors receiveadditional heat flux from

the attached IC engine.

The air gap, which is

confined between the

rotor and stationary

components (stator and housing),is generally very small and does

not contribute significantly to the

cooling process. When this is the

case, cooling water is circulated

through the coils in the motor

housing to dissipate the heat.

This example simulates one such

situation and predicts the heat

load distribution on various

components of the electric motor.

The computational results providedetailed insight into the motor

cooling process, and can be used

to guide the design of alternate

strategies for effectively cooling

the motor.

EX180

letter "I". With the

exception of the

stator, all solid motor

components are

simulated as

conducting walls(solid zones),

throughout which the

energy equation is

solved.

The rotor isseparated from the

motor housing and

stator by an air gap

(blue). It contains a

Using FLUENT, a 30 degree

periodic sector of the motor

is analyzed. The calculation

domain (Figure 1) consists

of the engine shaft, rotor,

stator, magnets, motorhousing, and shaft and

housing adapters, which are

used to bolt the motor to the

engine. The stator, not

shown in the figure, lies

inside the rotor and housing,extending from the region

below the magnets to the

region inside the outer

portion of the motor

housing. It has a cross-

section with the shape of the

Electric Motor CoolingThe cooling of an electric motor is studied in this example. The motor consists of rotating and

stationary parts. It heats up because of heat transfer from the engine to which it is mounted and

because of frictional heating in the shaft bearings. Cooling is accomplished by coils mounted in the

housing and to a lesser degree by the air gap between the rotating and stationary components.

Results suggest that additional cooling is required for this particular motor and motor mount design.

Figure 1: The motor geometry

Figure 2:Temperaturecontours on the shaftand motor housing

8/9/2019 Ex180 Electric Motor Cooling

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Copyright 2002 Fluent Inc. EX180 Page 2of 2

pair of magnets (red) that rotates

with the rotor. The motor is boltedto the engine using housing and

shaft adapters. The bolts used to

make the connections, with cross-

sections shown in green, transfer

a significant amount of heat from

the engine to the motor. Gasketsbetween the adapters and engine

mounts are used to minimize this

heat transfer.

Convection heat transfer

boundary conditions are appliedon the exterior surfaces of the

housing. Cooling coils, mounted

in the engine housing, are also

modeled using this boundary

condition. Temperatures arespecified on the adapter surfaces.The faces of the adapter surfaces

that are covered with gaskets are

modeled using the thin wall

thermal resistance boundary

condition. This special boundary

condition allows for a thin layer

of conducting material (the

gasket) between the external

boundary (the engine) and the

fluid or conducting wall zones(the adapters) on the interior of

the domain. The circular bolt-connecting surfaces are

described by constant

temperature boundaryconditions. The stator surfaces

are treated as external

boundaries with a varyingtemperature in the radial

direction.

A rotating zone is used to

simulate the motion of the

rotor, shaft, bearing, and shaftadapter. A hybrid mesh

containing 1.5 milliontetrahedral and hexahedral

cells was created for the

simulation.

Figure 2 shows contours of

temperature on the shaft and

motor housing. The temperature

contours illustrate the heat influx

to these components from the

engine. Contours of temperature

on the rotor are shownin Figure 3. Higher

temperature can be seen

at the lower right corner

(and to a lesser extent,

the lower left corner) ofthe rotor. This is mostly

due to heating from the

shaft adapter, and partly

due to the heat source

that is included to

represent frictionalheating at the site of the

shaft bearings.

Temperature contours on

the magnets are shown

in Figure 4. They

illustrate that the regionsclosest to the engine

Figure 3: Temperature contours on the rotor

(lower right) receive inadequate

cooling compared to those

elsewhere.

In summary, a CFD analysis of an

electric motor mounted onto an ICengine has shown that water coils

are effective in cooling only part

of the motor section - that whichis more distant from the engine.

Regions of the motor components

closest to the engine (magnets,rotor, and housing) showed

consistently higher temperatures

due to direct heat influx through

the adapters and frictional heating

in the bearings. The computationa

results showed that additionalcooling or heat protection would

be necessary in the housingadapters to avoid damage to the

magnets on the engine side. In

addition, higher coolant flow

through the engine side tubewould yield better cooling on the

engine side of the motor.

Courtesy of Lynx Motion

Technology, Inc.(www.lynxmotiontechnology.com)

Figure 4: Temperature contours on the magnets