Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Computational Heat
Transfer
in Engineering Education
Keynote lecture at
International Symposium
CHT

2012
by
Brian Spalding
of CHAM Ltd
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Some preliminary ideas
Which is easier to
understand
?
A
finite
volume
?
Or an
infinitesimal
one
?
Then why do we teach
students about
differential
equations
before
finite

volume
ones
?
We should help it to do
so.
Because finite

volume thinking
has not yet trickled down to
pre

university level.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Upwind

differencing eluded
mathematicians for many years.
The tank

and

tube concept
embodies finite

volume thinking
fluid on the
upstream
side of
the ‘tubes’ flowed
in
to the
‘tank’;
fluid
from
within the tank
flowed
out.
Not for the first time, physical intuition turned out to
be at least as productive as mathematical training.
To ‘tank

and

tubists’ it was
obvious
:
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Intuition suggested that
grids made of cells like
this might reduce
numerical diffusion.
A later tank

and

tube idea:
the X

cell
It was right
Square

cell grids smear
badly in diagonal flow
Doubling the number of
square
cells has much less
effect
In the same flow
X

cells do not
smear at all.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Solving
simultaneous
differential equations was hard.
A 1954 example of
finite

volume success
:
1

D flame propagation
even in graphical
Schmidt

method form!
Temperature profiles on
the right show:
(a) response to the
initial discontinuity;
(b) Temperature

dependent sources
then promote flame
propagation.
Dusinberre’s 1949 book used
finite volumes
for
heat

conduction
; so why not use them for
combustion
too?
Finite

volume
thinking had
solved the
problem
. .
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Heat transfer is taught by way of differential equations
because (a few)
analytical solutions exist
;
A summary of the argument to
be presented
but
only
for seldom

realistic conditions (
uniform
heat

transfer coefficient, temperature

in
dependent properties).
If
the solutions are used for design,
large ‘safety
factors’
must be applied.
Therefore serious designers
would
use
finite

volume

based
computer simulation instead, but only
if
Therefore CHT specialists have a duty: to
promote the
finite

volume
formulation
throughout
education
This has
world

wide
(and bad) economic significance.
they recognised that industry

standard design software
is
still
based on the
unrealistic
presumptions.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Today’s teachers
are
‘computer

savvy’,
using lecture

room
computers, Power

Point, GOOGLE
searches,
etc
Education through simulation
in the lecture

room
But few perform live
simulations
:
they lack tools,
knowledge
and
confidence.
My proposal is that, for
heat

transfer
lecturers,
CHT
can
and should
provide all three
. I shall explain how.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Example:
a file for
flow
&
heat transfer
in
tubes
;
What the CHT community could
provide:
down

loadable
‘Simulation

Scenario
’ files
d
The main window contains the start of an
html file
,
which the lecturer is free to edit .
Above are buttons enabling him/her to do
live
simulations
of flow in tubes.
which a
‘SimScene’

viewer
package reads;
and then shows this
interactions
with which
constitute the lecture.
But the
input data
must first be inspected.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Clicking on the
appropriate bar
and then on the
seventh left

hand
box causes this
menu to appear.
About the TubeFlow package:
data input
via
menu
The
flow formulations
which
can be chosen are shown here.
The lecturer may choose to explain their meanings,
perhaps after first studying the html document.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Heat

transfer text

book
formulae
connect Nusselt,
Reynolds and Prandtl numbers, each containing
thermo

physical property values, treated as
constants
.
Handling temperature

dependent properties
In reality, properties
vary with temperature.
A SimScene

using
lecturer can explore
these effects
in the
class

room;
and
more easily
than
in the laboratory; both
real and fictitious fluids
can be investigated.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Just click on the running man icon; then in a few
seconds the results are available to be displayed.
How the in

classroom
simulations are performed
Nor need the lecturer know how to operate the graphical
display package; for, when the run ends, he will see this:
Clicking on the icon will
activate a macro which creates
images automatically, such as:
contours of temperature
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Some merits of the
down

loadable SimScene system
Graphical displays
make more impact on students’
minds than algebraic derivations.
Moreover students can make
explorations for
themselves
in ‘SimScene homework’ sessions.
and
will have learnt that CHT/CFD
has limitations
too:

Later, as
professional engineers
, they will be readier
to use
finite

volume

based
simulation for design;
viz.
grid

fineness
effects;
computer

size
needs;
and
human error
.
turbulence

model uncertainties;
The lecturer needs only minimal computer skills; and
he/she can deliver ‘
as is
’ or with own
embellishments
.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
The task: Use TubeFlow’s
multi

run
capability
to compute fluid flow and heat transfer
for water,
at 80 degC, in
fully

developed flow
, for
various Reynolds
numbers; and explain the results
Example of a homework
assignment
The student might
obtain this
Not bad. But how
explain the
drooping of the
Nusselt No curve
(bottom

right)
Unravelling puzzles promotes understanding.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Lecturers should
know enough about CHT
to explain
its sources of
uncertainty
:
too

coarse
grids,
turbulence
models,
multi

phase
effects.
Exploring the influence of
uncertain inputs
Then they can enlarge their
students’ knowledge
(and
their own) by saying: ‘Run each turbulence model; then
compare results’.
TubeFlow makes this easy. Here is its multi

run screen:
It will launch 30 runs: 5 models for each of 6 velocities.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Further advantages: some things
need no longer be taught
Text

and hand

books are cluttered with formula which
purport (implausibly and impractically) to be useful in
design. For example:
Likewise, figures like this,
with impossibly low Nusselt
Nos.
They represent someone’s
long

ago hopeful guess; and
they are copied from book to
book without criticism.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
.
More fiction to be binned
Finned

tube bundle Nusselt and Euler Number
formulae according to Rohsenow and Hartnett:
They are neither reliable nor credible because ...
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
(
1
)
The
number
of
dimensionless
parameters
needed
for
finned

tube
bundles
should
be
at
least
12
.
The reasons for binning
(
2
)
The
army
of
experimentalists
needed
systematically
to
explore
this
12

dimensional
space
has
surely
never
been
mobilised
.
Nor
will
it
ever
be
.
(
3
)
Even
if
it
had
been,
it
is
highly
improbable
that
its
findings
would
have
fitted
the
always

preferred
form
:
Nu=a*
Re
b
*
Pr
c
*D
e
*F
g
*H
i
J
k
*L
m
etcetera
wherein
a, b, c, e, g,
i
, k
and
m
are constants, and
D, F,
H, J
and
L
etcetera
are dimensionless parameters.
Only
a SimScene package
devoted to
finned

tube

bundle geometries can work out
the interacting influences of all parameters.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Step 1. Decide
what
parameters
define the scenario,
e.g.
shapes, sizes, materials, thermal conditions
.
How to create a SimScene
package; what’s involved?
Step 2. Decide
what default
values (or lists) shall
appear in the SimScene

viewer’s menu boxes.
Step 3. Decide
what CFD engine
will perform the flow

simulating calculations.
Step 4. Express the above decisions in the CFD
engine’s
Data

Input language
.
Comments: (a) Steps 1 and 2 are the
creative
steps
(b)
Re
Step 3,
any
general

purpose code will serve.
(c) Step 4 requires knowledge of the engine’s language;
but it is
mechanical
in essence.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
1. Knowing only the PHOENICS Input Language (
PIL
), I
used it; but repeat: SimScenes can use
any
CFD engine.
How to create a SimScene
package; some details
2. There does exist a
PIL editor
, with macros, widgets
and other aids. They
may exist
for other engines too.
3. It is Steps 1 and 2 that require
agreement on format
.
Commercial competition should not hinder its making.
4. The current SimScene format can of course be
improved; but refinement
is cheaper than
replacement.
5. For those who make the same choice of engine, I can
provide the Editor,
and how

to

use instructions.
6. My aim is to bring into existence a ‘
critical mass
’ of
SimScenes in a short time. Can that be made
possible
?
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
“I take it those things are to be held
possible
which may
be done by
some person
though not by
every one
;
Regarding
possibility,
Sir Francis Bacon
wrote:
“and which may be done by
many
, though not by any
one;
.
“and which may be done in the
succession of ages
,
though not within the
hour

glass
of any one man’s life;
“and which may be done by
public designation
, though
not by
private endeavour”.
What
public
? Could that be the
CHT community?
Perhaps in
co

operation
with like

minded others?
For, if
‘many’
participate, a plethora of SimScenes might
exist sooner than
‘succession of ages
’ suggests.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Its top page looks
like this:
Another heat

transfer

related
SimScene: HeatEx
If
a
ll SimScenes:
have similar forms,
novelty of
content
stands out better.
Author, date and
institution would be
useful additions.
.
If a CHT

SimScene

Creators’ Club came into existence,
a first task would be to recommend an all

fitting format.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
HeatEx is designed to teach students about shell

and

tube heat exchangers, like this one:
The purpose of HeatEx
Influences of tube and baffle number and positioning are
among those to be simulated.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
As well as the text

book

standard options,:
parallel

,
counter

and
cross

flow, it has
oblique
,
two

baffle
,
leaky
baffle and
four

baffle options.
Available flow configurations
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
It has a menu structure similar to that of TubeFlow.
Data

input facilities
Here the flow configuration is being selected.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
For economical programming and display, it uses
two
grid segments to cover the same space: one for the
shell

and one for the
tube

side
fluid.
Its multiple

grid feature
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
Simulations run in the classroom by the
lecturer
or as
home work by the
students
reveal:
What students can learn from
the HeatEx SimScene
1. That finite

volume

based simulations
fit the text

book
formulae
closely enough
, if the grid is
sufficiently fine.
2. That contours of
temperature in cross

flow exchangers may
look like this
3.That baffles bring
close

to

counterflow
effectiveness
but raise
the
pressure drop.
4.That phase

change effects can be taken account of.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
A few such packages exist; and I hope to create more.
Last words about simulation

scenario packages
But
hundreds
are needed, for the teaching of all
relevant fluid

flow, heat/mass transfer topics; and my
personal ‘
hourglass
’ will certainly not suffice.
I hope therefore to have
conveyed the vision
clearly
enough for some of
you
to share it; and to desire to turn
it into reality.
Finally, I disclose that there is a
sociological
aspect to
my ambition: properly considered, the
‘trickle down
’ of
finite

volume thinking into secondary schools can
widen
the entrance doorway
of the engineering profession.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
The
only
mathematics which is
essential
for understanding CHT is
that of the
storekeeper;
The last slides
‘Infinitesimal’ is
like
‘truly fine
enough’
.
So it no longer makes sense to
bar from studying
engineering
university entrants for whom calculus is
too high
a hurdle
.
Beyond our reach!
and he has
computers
to keep his
books for him.
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
A final speculation
We laugh because
medieval scholars
debated how many
angels could stand on
the head of a pin.
One day we may scorn
mathematicians for their
obsession with the
infinitesimal.
But
finite

volume

based
simulation will survive!
Bath
July 1

6
2012
Advances in
Computational Heat Transfer
and to
all of you
for your attention.
Thank you
To
Alexey
Ginevsky
for conceiving and creating the
SimScene

viewer package and the PIL

editor;
to
Elena
Pankova
for her work on
TubeFlow
and
HeatEx
;
The End
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