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Thermal Analysis Induction motor heat sink

Question asked by Jason Sanders on Aug 14, 2017

I am attaching an example setup of my analysis I want to perform.


The only real difference is the blower housing is a double inlet.  I want to perform a heat transfer analysis on the motor controls to determine the temperature in two of the components.  The two components i'm interested in are located in the can on the end of the motor (similar to the grey can in the picture on the right side of the motor).  Only one component is in contact with the heat sink.  The other component I am interested in, will solely be cooled by the internal fan circulating air.  there are vents in the motor shell that will allow air to circulate.  I want to add a heat sink that the hottest component will be attached so it is exposed to the air that will aid in cooling (not shown in the picture).  I can't move the component to be in contact with the heat sink, the board design is set and I can't convince anyone to alter it, so I want to try to show them the current situation, and then a proposed model with both components in contact with the heat sink.  The can, where the circuit board and electronics are located, will be made of plastic (this is a management decision and I can't change it) with a cutout section for the heat sink.  The heat sink will be made of aluminum.  There are thermal pads between the electrical components and the  heat sink.  I have used the Thermal resistance feature to model the thermal pads we will use, and the thermal pad we are going to use is one of the materials listed in Solidworks.  I have used a surface heat source on each electrical component that is in contact with the heat sink since that is the only direction the heat will flow.


There is also an internal fan inside the motor that is providing a minimal amount of airflow inside the motor.  i'm trying to convince people to redesign this, so I'm trying to include that in my analysis as well.


I have applied heat generated from the stator and rotor as well as the bearings inside the motor.


I have run this analysis a few ways but get way higher temperatures than I would expect.  I have run it as an external and internal analysis.


I ran an initial analysis just to determine airflow velocity over the surface of the model where I put the heat sink.  The ambient temperature the motor will be residing is 55C.  The two components inside the control can are at 12 W and 7W.  I determined the Prandtl number and then calculated the Nusselt, Reynolds and Grashof numbers to determine a heat transfer coefficient.   I have a good confidence in my heat transfer coefficient; however, I am having difficulties in setting up the heat transfer analysis for the electrical components.  This will be a steady state analysis.  Once I got the heat transfer coefficient I was going to suppress the blower, fan, and housing just leaving the motor and use the heat transfer coefficient.


I can go into all the various steps I've gone through but honestly this would get convoluted and confusing.  Could someone give me a procedure for approaching this? 


1.   Do I run it as an external or internal?


2.  Should I use the heat transfer coefficient on the exterior surface of the motor or just model the exterior flow from the blower going over the motor and the internal airflow inside the motor along with the thermal inputs from the electronics, stator, rotor, and bearings?


3.  Am I modeling my electrical components correctly by applying surface heat generation between the electrical components and the heat sink; along with the thermal resistance on the surface between electrical components and heat sink?


I may be over looking alot of information that may be needed to get an accurate picture, so I will try to provide any further information.  But mainly I am wondering how would someone approach this?


Thanks in advance!