# Compression of candles

1. Dec 11, 2011

### irish_enginee

Hi doing a group project on making tea candles! Silly topic but anyway....

my part is to calculate the pressure needed to make a candle and having trouble with the calculations....

final dimension needs to be a 38mm diameter and 16mm height

using rotary compression to do this.... candle wax comes in and candle comes out...

here is what i have done yet answer seems extreme, any advice would be great !

oh and have attached a word file with sketch and solid works screen capture so hopefully the whole thing makes some sense!!

my workings

assume height of 40mm of wax will drop to give 16mm when compressd

therefore volume of melted wax is

V1=∏r^2 h liquid
=∏(0.019)^2 (0.04)
=0.001134m^2

V2==∏r^2 h compressed
=∏(0.019)^2 (0.016)
=0.00002166m^2

P1V1=P2V2
(101000)(0.001134)=(P2)(0.00002144)
therefore P2=2525kPa

i not really too sure what to think of this value?

not even too sure if i have gone about it in the right way

any help would be great!

oh and can't attach the word file as its too big!

2. Dec 11, 2011

### nvn

irish_enginee: The answers you typed in post 1 do not match the equations you typed above the answers. It appears you did not check your calculations. And volume has units of m^3, not m^2. Try it again, and check your calculations multiple times. By the way ...

1. Always leave a space between a numeric value and its following unit symbol. E.g., 38 mm, not 38mm. See the international standard for writing units (ISO 31-0).

2. For long numbers having five or more digits, the international standard says you can write the digits in groups of three, separated by spaces. E.g., 0.000 045 365 m^3, instead of 0.000045365 m^3.
I was not even aware liquid wax is significantly compressible. Perhaps it contains a lot of air?

3. Dec 11, 2011

### irish_enginee

Hi thanks for reply, sorry for mistakes. Think they are corrected below

I was thinking that liquid wax would contain lots of air too but would compressing it significantly not remove the air? Hence just leaving a solid candle?

"Hi doing a group project on making tea candles! Silly topic but anyway....

my part is to calculate the pressure needed to make a candle and having trouble with the calculations....

final dimension needs to be a 38mm diameter and 16mm height

using rotary compression to do this.... candle wax comes in and candle comes out...

here is what i have done yet answer seems extreme, any advice would be great !

oh and have attached a word file with sketch and solid works screen capture so hopefully the whole thing makes some sense!!

my workings

assume height of 40mm of wax will drop to give 16mm when compressd

therefore volume of melted wax is

V1=∏r^2 h liquid
=∏(0.019)^2 (0.04)
=0.000045364 m^3

V2==∏r^2 h compressed
=∏(0.019)^2 (0.016)
=0.000018145 m^3

P1V1=P2V2
(101000)(0.000045364)=(P2)(0.000018145) aside:101000 taken as atmospheric
therefore P2=252 kPa

i not really too sure what to think of this value?

not even too sure if i have gone about it in the right way

any help would be great!

oh and can't attach the word file as its too big!"

4. Dec 11, 2011

### Travis_King

As an engineer I feel compelled to ask what value is added by calculating this

5. Dec 11, 2011

### irish_enginee

I have attached the general process i hope to use draw in a paint file

Also attached a screen shot of the unfinished process in solid works

Hope its clear

My problem is the candle wax will need to be compressed, yet not too sure how to calculate it

My calculation above is probably totally wrong but a push in the right direction would be great!

6. Dec 11, 2011

### irish_enginee

pictures should now be attached

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7. Dec 11, 2011

### 256bits

From your calculations it appears that you are making an assumption that candle wax is a gas, and for the life of me cannot understand why you would do so. Is the compression prcocess an actual compression, or is it done to ensure that the wax is in the shape of the walls of the container with no air pockets in the finished candle,

Last edited: Dec 11, 2011