icepak 常见问题解答.doc

My model is very complicated, what is the best way to build it?

Start simple. First include the most important items such as the cabinet, big power devices, fans,

vents and openings, if any. For first level analysis, ignore small details. For example, you may

smear power sources over blocks or plates, instead of modeling them in detail using small blocks.

Make sure the simple model runs well and the solution makes sense. You can then gradually

include more details into your model. It is absolutely essential that you build your model step by

step!

How can I simplify my model?

aligning nearly-aligned faces of objects

How large should my cabinet be?

In general, the cabinet should be as large as your package enclosure, if you have any. In some

cases, the package is suspended in air or it is inside a very large enclosure (like a wind tunnel). In

such cases, it may be adequate to have a cabinet about 3-5 times as big as the size of the package

in each direction.

How often shall I save?

As with all software products, it is advisable to save as often as possible. This will ensure that

your data is not lost in the event of machine or system failure. In particular, it is important to save

the model before starting the solution process. So, if you need to terminate your solution process

or conductivity of a given block (so that the mesh is the same), you may either save it to a

different name, or, if you wish to use the Restart option, run a second solution under the same

name.

My package is not surrounded by walls on all sides, is it OK to use the cabinet walls or

should I put openings on these walls?

In general, it is not necessary to put openings on all cabinet walls. It is sufficient to put openings

on the walls which are perpedicular to the dominant flow direction(s). However, make sure that

the walls that don't have openings are far enough so that they don't influence the flow distribution

near the package.

Should I include the effect of gravity in my model?

convection problems have maximum velocities of the order of 0.1-0.2 m/s. Compare this with the

velocities you are likely to have in your cabinet due to fans, etc.

Should I include the effect of radiation in my model?

In most forced convection cases (where fluid is pushed through by fans, pumps, etc.), the effect of

radiation is under 2-5% and may be ignored. In some cases, the effect may be of the order of 10%

or even greater and must be included. Examples are:

natural convection cases

sealed systems

Your model probably has too many objects. Even if the number of objects participating in

radiation is small, Icepak still involves the other objects in the calculation. One way of speeding

the calculation is to construct the radiation.ff file from a simpler Icepak model and use this file in

the actual model. To construct the simpler model, make a copy of the actual model and delete

some components that are either not participating in radiation or have minimal effect on radiation.

Then compute the view factor matrix and use the resulting radiation file (radiation.ff) in the actual

model.

How do I decide whether the flow is turbulent or laminar?

Icepak estimates the non-dimensional numbers which will help you determine whether the flow is

turbulent or laminar. For forced convection problems, the number to watch is the Reynolds

Is is easier to import a model from a CAD package or construct the model inside Icepak?

It varies from case to case. In many cases, you can easily and rapidly construct your model in

Icepak. In some cases, however, it may be advantageous to import from CAD packages directly.

This is true in situations where transfering the dimensions (sizes and locations) is time consuming.

What are the CAD package files I can import into Icepak?

You can import an Icepak model from Pro/E directly. You can also import IGES files from any

CAD package and DXF files from AutoCad.

What units should I use?

You can use any system of units or a combination of them (e.g., SI, English system, etc.). You can

define your units in the "Edit unit definitions" under "File/Configure". You can also define units

materials database. The default value of air density can be seen in "Model/Materials". Go to

"Fluid/Gases/Air" and enter the new air density for the elevation under consideration. Make sure

to click "Update" after editing the material properties.

My model is symmetric but my solution is not, what is the reason?

This is most likely due to one or both of the following reasons:

The mesh is not symmetric.

The solution hasn't converged.

I am modeling an interface material, shall I use contact resistance plate or a general heat

What is a typical magnitude of flow velocity due to (pure) natural convection?

It is of the order of 0.1 m/s.

What are the three most essential files of an Icepak model?

They are "job", "model" and "problem". These files contain all the information specified to build

the model, such as the size and location of objects, properties of objects, problem setup data, mesh

specifications, and solver settings. Any Icepak model must have atleast these three files.

What does "pack" and "unpack" mean?

The "Pack" and "Unpack" facility in Icepak allows you to communicate with Icepak support or

with another Icepak user rather easily.

"Pack" means packaging the component files of an Icepak model (job, model and problem) into

one file by tarring and zipping these files. You can send that file to Icepak support or another

Icepak user for examination. In UNIX computers, the packaged file is named as

the directory "jobname", where jobname is the name of the model specified in the packaged job.

How do I print out an Icepak model?

First display the model in the Icepak inteface the way you want the model to appear in the print

(including the size, view, shading, etc.). Then, in the options menu at the far right of the Icepak

main inteface, click "Print" and save the image under one of the file formats allowed, e.g. gif, tiff,

etc. You can then send the saved file to your printer.

Where do I define my units?

You can define units in "File/Configure". Click "Edit unit definitions" and define the units for any

First select "Transient" by going to "File/Problem" and then specify "Start", "End time", "Time

step increment", and "Solution save interval" of your simulation. Then go to "Solution/Setup" and

specifiy the "Iteration/timestep".

What are initial conditions?

These are initial values of velocity and temperature that will be assigned to each cell in the mesh

to serve as the first guess values for the solver. These are just initial guess values and are replaced

by new values after the first iteration is completed. The default initial conditions are sufficient for

most cases.

How do I include the effect of natural convection in my model?

In "File/Problem", toggle the "Gravity vector" and give the gravity value in the appropriate

automatically for it may make many unintended changes.

What is the meaning of "Radiation temperature" on the "Problem/Setup" menu?

"Radiation temperature" is the partial enclosure temperature. When a given surface radiates to

some surfaces, normally all of the radiation does not reach these surfaces. The portion of radiation

that doesn't reach these surfaces is assumed to go to the ambient maintained at a reference

temperature called the "Radiation temperature".

situation?

How do I move, copy or scale a group of objects at the same time?

How do I move a group of objects using the mouse?

How can I change the specifications (material type, power, etc.) of a group of objects in my

model?

What is a part?

How can I scale an object with different scale factors in each of the coordinate directions?

How do I reverse the order of object creation?

different from the original data. What is happening?

What is the difference between "Device" and "Approach" methods in the calculation for pressure

losses in vents and resistances?

I have a few detailed heat sinks in my model and, as a result, the mesh is large. What should I do?

What is a macro?

I have created a heat sink macro and want to send it to my colleague. What is the quickest option?

How do I apply a transient thermal loading (power) to my block?

Can I prescribe several transient power loading segments to my model?

I am only interested in getting the flow distribution and not the temperature. How do I solve for

the flow distribution only?

as conductivity, power, etc.?

The origin of my cabinet is a non-zero number, can I convert it to (0,0,0)?

I am modeling a telecom rack and do not know whether I should use a plate or PCB for my

motherboard?

How can I model small air gaps or interface material between surfaces?

What is the difference between conducting thick plates and contact resistances?

My chassis is not a rectangular prism, how can I construct the cabinet in Icepak?

When should I use hollow blocks?

I have a table of volume flow vs pressure data for my fan, can I load this data directly, instead of

entering it manually?