hw4 transient1dslab 01-2czx5uu

8/17/2019 HW4 Transient1DSlab 01-2czx5uu

1/19

Homework 4 additional material

For this assignment, you will use the computational software COMSOL 4.x (andor !", a#aila$le in

%cademic Computing Center &ngineering Li$rary (%CC&L" at the Carpenter 'all. ooms ha#ing

access to COMSOL are the )lue oom and the Sunset *rill on the *round Floor and the *reenoom, Orange oom and ed oom on the +nd oor.

-ou can nd when the facilities are open at www.accel.cornell.edu

/ote0 if you are using COMSOL !, you can easily use this manual. 1ust the shape of some icons

might $e di2erent.

http://www.accel.cornell.edu/http://www.accel.cornell.edu/


2/19

Title

3nderstanding the &2ect of )oundary Conditions 3sing ransient 'eat ransfer in a Sla$

Background:

%s you 5now, $oundary conditions and other parameters change the solutions. 6t helps to learn

the e2ects of $oundary conditions and other parameters if we can change the parameters7uic5ly and get a new solution (without ha#ing to spend a lot of time in the solution process".

herefore, we ha#e implemented a simple pro$lem in a computational software (one that you do

not need to sol#e" where you simply change a few parameters and see their e2ects on the

results.

What you need to do:

-ou will simply open the le pro#ided, change a few things and clic5 sol#e to see di2erent results.

Most of the time will $e spent on interpreting the results8this is the goal of this exercise. 6n this

exercise, we are not trying to ha#e you learn the software.

What to turn in:

See the following two pages.

We gave you the results:

Since our goal is to understand the solution rather than to learn the software, the results you

should expect are also pro#ided in this document9 :hile it may $e possi$le to answer the

7uestions without actually running the software, it is not recommended as it will $e more di;cult

and you are li5ely to ma5e mista5es.

You are most welcome to try other conditions (do not turn in these

materials). Our net homework will !e di"erent and will allow you

to solve a more interesting #ro!lem$that is not the goal here.

%oals


3/19

What to turn in (&u!mit this and the 'ollowing #age only hand

written ok)

Boundary ondition * Boundary condition +:hy is the

temperature

#ariation along

the sla$

thic5ness

somewhat

linear at late

times $ut not at

early times?

&xplainwhether the

temperature

prole will 5eep

changing

fore#er.

6s the time rate

of temperature

change at anylocation inside

the sla$ the

same at early

#s. late times?

:hy?

6s the

temperature

gradient at any

location insidethe sla$ the

same at early

#s. late times?

:hy?

6s the

>


4/19

temperature

gradient @ero at

late times?

:hy?

=o the surface

temperatures

of the right and

left sides of the

sla$ remain

constant

throughout the

time? :hy?

Boundary condition , (note change o' !oundary condition)6s the

magnitude of

the ux the

same

throughout the

sla$ thic5ness?

&xplain why or

why not?:hich regions

in the sla$ does

the assumption

of


5/19

+

Sla$

-ro!lem escri#tion he pro$lem here is a += sla$ su$Bect to di2erent $oundary conditions. he goal is to analy@e the

transient heat transfer through the sla$. he sla$ is < cm wide and DC. hermal conducti#ity of the sla$ is A.!AA 15g.E.

Boundary onditions:e will examine three di2erent $oundary conditions0

Ta!le *: Three !oundary conditions to !e used

Boundary conditions&et &ide * &ide + &ide , &ide 4

< >DC 6nsulated 6nsulatedh H


6/19

you should not use #ersions >". 6f $y dou$le clic5ing it opens #ersion >.x, close it and open

COMSOL 4.> (or !" and open the downloaded le within the #ersion 4.> (or !".


7/19

,

+

*

&te# *.*: eci'ying the 0aterial -ro#erties o sol#e the energy e7uation numerically (as opposed to analytically", we need to pro#ide

material properties li5e thermal conducti#ity, density and specic heat.

o specify material properties (these steps are shown on screenshot in color"0


8/19

&te# *.+: &etting u# Boundary ondition * (see Ta!le *):e now specify these $oundary conditions to the pro$lem. he default $oundary condition for

this sol#er is thermal insulation so we do not need to change the $oundary condition on sides +

and >.

Tem#erature. %s you may notice, the side < of sla$ is selected in Boundary &election

(gure in next page".

J


9/19

*

+

4. 6n the &ettings window, locate the Tem#erature section and type +>. in

Tem#erature edit eld (gure in next page".


10/19

4

,


11/19

*

+

,

4

&te# *.,: &olving o sol#e a transient pro$lem, we need to assign the times in which we li5e to ha#e the results.

For this module, we as5 the software to sa#e the results e#ery


12/19

*

+

,

4

78

9

;

&te# *.4:


13/19

* -lot %rou# windowN

1egend.. 6n the 0odel Builder

window, clic5 on


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*

&te# +.*: &etting u# Boundary onditions + (see Ta!le *):e are done with the rst set of $oundary conditions. o 5eep the results for further analyses,

you may sa#e this le and use the original module le again for e#ery new set of $oundary

conditions.

%s the default $oundary condition is thermal insulation, we Bust need to disa$le the constant

temperature $oundary condition on the left side of sla$ and it would automatically turn toinsulation $oundary condition.


15/19


16/19

You should !e seeing the 'ollowing results

Figure ! Figure

Figure Figure J


17/19

,

4

&te# ,.*: &etting u# Boundary ondition , (see Ta!le *)6n the third set of $oundary conditions, the temperature on all sides of the sla$ is 5ept constant

at


18/19

*

+

&te# ,.+: &olving)ecause a new set of $oundary conditions are introduced, we need to run the COMSOL again to

ha#e the compati$le results. he sol#ing step can $e done exactly li5e step for the rst set of

$oundary conditions.

&te# ,.,:


19/19

You should !e seeing the 'ollowing results

gure

gure

hw4 transient1dslab 01-2czx5uu

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